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2021 Volume 37 Issue 10
2021, 37(10): 190506
doi: 10.3866/PKU.WHXB201905067
Abstract:
Cancer remains a major global cause of morbidity and mortality. Diagnosis at an early stage can significantly improve the survival of cancer patients. Cancers of different origins often have vastly different genotypes and phenotypes. Therefore, it is challenging to establish a universal strategy for cancer detection. Universal cancer detection can be potentially achieved by using pH-responsive probes. An acidic microenvironment is mainly caused by lactic acid accumulation in rapidly growing tumor cells. Based on the difference in pH between tumor and normal tissues, fluorescent materials that respond to a pH of around 6.8 are ideal for tumor detection. Carbon quantum dots (CQDs) have attracted much attention in bioimaging owing to their outstanding characteristics such as stable photoluminescence, low cytotoxicity, excellent biocompatibility, and resistance to photobleaching. In this study, red fluorescent CQDs (R-CQDs) were synthesized by the solvothermal treatment of 4-(dimethylamino) phenol in the presence of potassium periodate. The UV-Vis spectrum of the R-CQDs showed a characteristic absorption peak at 545 nm. The photoluminescence spectrum revealed an emission peak at 640 nm. The brightness of this photoluminescence peak was quantified to be 12.8% in terms of the absolute quantum yield (QY). Transmission electron microscopy (TEM) images showed that the R-CQDs have uniform sizes with an average diameter of 4 nm and a lattice spacing of 0.21 nm. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed that the R-CQDs have a large number of carboxyl groups. The Raman spectrum of the R-CQDs showed the characteristic D band at 1340 cm-1 and G band at 1585 cm-1. The X-ray powder diffraction (XRD) pattern showed a broad (002) peak centered at around 23°. The R-CQDs were responsive to highly acidic or alkaline conditions. The incorporation of a block copolymer (MeO-PEG-PDPA), prepared by atom transfer radical polymerization (ATRP), on the R-CQDs produced pH-responsive fluorescent CQDs (pRF-R-CQDs). Photoluminescence (PL) spectra showed that the pRF-R-CQDs were responsive at pH 6.8. At pH > 6.8, the fluorescence of the pRF-R-CQDs would be quenched because of deprotonation of the amine groups. In contrast, protonation of the amine groups would lead to a dramatic increase in fluorescence emission. TEM images showed that the pRF-R-CQDs self-assemble and disassemble at pH 6.8 because of their pH-responsive properties. Compared with most existing fluorescent materials, the pRF-R-CQDs can effectively resist photobleaching and autofluorescence. Moreover, these pRF-R-CQDs have minimal toxicity and can distinguish tumors from normal tissues. Therefore, pRF-R-CQDs have great potential for use as a universal material in tumor microenvironment diagnosis.![]()
Cancer remains a major global cause of morbidity and mortality. Diagnosis at an early stage can significantly improve the survival of cancer patients. Cancers of different origins often have vastly different genotypes and phenotypes. Therefore, it is challenging to establish a universal strategy for cancer detection. Universal cancer detection can be potentially achieved by using pH-responsive probes. An acidic microenvironment is mainly caused by lactic acid accumulation in rapidly growing tumor cells. Based on the difference in pH between tumor and normal tissues, fluorescent materials that respond to a pH of around 6.8 are ideal for tumor detection. Carbon quantum dots (CQDs) have attracted much attention in bioimaging owing to their outstanding characteristics such as stable photoluminescence, low cytotoxicity, excellent biocompatibility, and resistance to photobleaching. In this study, red fluorescent CQDs (R-CQDs) were synthesized by the solvothermal treatment of 4-(dimethylamino) phenol in the presence of potassium periodate. The UV-Vis spectrum of the R-CQDs showed a characteristic absorption peak at 545 nm. The photoluminescence spectrum revealed an emission peak at 640 nm. The brightness of this photoluminescence peak was quantified to be 12.8% in terms of the absolute quantum yield (QY). Transmission electron microscopy (TEM) images showed that the R-CQDs have uniform sizes with an average diameter of 4 nm and a lattice spacing of 0.21 nm. Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed that the R-CQDs have a large number of carboxyl groups. The Raman spectrum of the R-CQDs showed the characteristic D band at 1340 cm-1 and G band at 1585 cm-1. The X-ray powder diffraction (XRD) pattern showed a broad (002) peak centered at around 23°. The R-CQDs were responsive to highly acidic or alkaline conditions. The incorporation of a block copolymer (MeO-PEG-PDPA), prepared by atom transfer radical polymerization (ATRP), on the R-CQDs produced pH-responsive fluorescent CQDs (pRF-R-CQDs). Photoluminescence (PL) spectra showed that the pRF-R-CQDs were responsive at pH 6.8. At pH > 6.8, the fluorescence of the pRF-R-CQDs would be quenched because of deprotonation of the amine groups. In contrast, protonation of the amine groups would lead to a dramatic increase in fluorescence emission. TEM images showed that the pRF-R-CQDs self-assemble and disassemble at pH 6.8 because of their pH-responsive properties. Compared with most existing fluorescent materials, the pRF-R-CQDs can effectively resist photobleaching and autofluorescence. Moreover, these pRF-R-CQDs have minimal toxicity and can distinguish tumors from normal tissues. Therefore, pRF-R-CQDs have great potential for use as a universal material in tumor microenvironment diagnosis.
2021, 37(10): 190707
doi: 10.3866/PKU.WHXB201907077
Abstract:
Fullerene molecules have nano-scale cavities in which various metal or metal clusters of different sizes can be embedded to form metallofullerenes with unique core-shell structures. The physical and chemical properties of metallofullerenes can be modified through the interaction between the encapsulated metals and the fullerene cages. As such, the investigation of metallofullerenes with novel structures has been a principal research focus in the field of fullerenes. In this study, we investigated the size matching effect between encapsulated clusters and fullerene cages for the endohedral metal carbonitride clusterfullerenes in order to discover new metallofullerenes. The stability and electronic structure of the metallofullerenes formed by encapsulating M3NC clusters (M = Y, La, Gd) into D2(186)-C96 and D2(35)-C88 fullerenes were studied using quantum chemical calculations. It was found that the fullerene cages formed stable structures by accepting six electrons transferred from the encapsulated clusters. The change in configuration of the encapsulated clusters was clarified by a comparison with the corresponding M3N@C2n metal nitride clusterfullerenes; the size matching effect between M3NC cluster and fullerene cage was elucidated on the basis of the calculated results and previous studies on Sc3NC@Ih(7)-C80. For the D2(186)-C96 fullerene, the Gd3NC cluster was found to have smaller changes in the configuration as compared with the La3NC cluster, proving that Gd3NC is more suitable than La3NC for encapsulation in the D2(186)-C96 fullerene cage. In addition, it was determined that the La3NC cluster requires a large structural change to maintain its planar configuration. For the D2(35)-C88 fullerene cage, the Y3NC cluster is more suitable than Gd3NC for encapsulation owing to the smaller size of the Y3NC cluster. The spatial distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of Gd3NC@D2(186)-C96 were found to be similar to those of Gd3N@D2(186)-C96. However, a unique endohedral cluster-based occupied molecular orbital was found for Gd3NC@D2(186)-C96. This orbital is derived from the interaction between the NC unit and the Gd atoms. The spatial distribution of the HOMO of Y3NC@D2(35)-C88 is similar to that of Y3N@D2(35)-C88, while the LUMO of Y3NC@D2(35)-C88 has a much larger contribution from the endohedral cluster as compared to Y3N@D2(35)-C88. Thus, the addition of a carbon atom in the cluster has a remarkable impact on the electronic structure of the metallofullerenes. With respect to structural characteristics, we found that the three fullerene cages, D2(186)-C96, D2(35)-C88, and Ih(7)-C80, have a uniform distribution of five-membered carbon atom rings; these fullerenes can be greatly stabilized in the form of C2n6- anions. However, the formation mechanism of fullerenes and metallofullerenes, at present, is poorly understood. Based on the structural analysis, we propose a direct mechanism for the formation of fullerenes without the Stone-Wales isomerization, i.e., the rearrangement of five-membered rings through the addition of carbon atoms and the transformation into larger carbon cages while maintaining stable structural units. ![]()
Fullerene molecules have nano-scale cavities in which various metal or metal clusters of different sizes can be embedded to form metallofullerenes with unique core-shell structures. The physical and chemical properties of metallofullerenes can be modified through the interaction between the encapsulated metals and the fullerene cages. As such, the investigation of metallofullerenes with novel structures has been a principal research focus in the field of fullerenes. In this study, we investigated the size matching effect between encapsulated clusters and fullerene cages for the endohedral metal carbonitride clusterfullerenes in order to discover new metallofullerenes. The stability and electronic structure of the metallofullerenes formed by encapsulating M3NC clusters (M = Y, La, Gd) into D2(186)-C96 and D2(35)-C88 fullerenes were studied using quantum chemical calculations. It was found that the fullerene cages formed stable structures by accepting six electrons transferred from the encapsulated clusters. The change in configuration of the encapsulated clusters was clarified by a comparison with the corresponding M3N@C2n metal nitride clusterfullerenes; the size matching effect between M3NC cluster and fullerene cage was elucidated on the basis of the calculated results and previous studies on Sc3NC@Ih(7)-C80. For the D2(186)-C96 fullerene, the Gd3NC cluster was found to have smaller changes in the configuration as compared with the La3NC cluster, proving that Gd3NC is more suitable than La3NC for encapsulation in the D2(186)-C96 fullerene cage. In addition, it was determined that the La3NC cluster requires a large structural change to maintain its planar configuration. For the D2(35)-C88 fullerene cage, the Y3NC cluster is more suitable than Gd3NC for encapsulation owing to the smaller size of the Y3NC cluster. The spatial distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of Gd3NC@D2(186)-C96 were found to be similar to those of Gd3N@D2(186)-C96. However, a unique endohedral cluster-based occupied molecular orbital was found for Gd3NC@D2(186)-C96. This orbital is derived from the interaction between the NC unit and the Gd atoms. The spatial distribution of the HOMO of Y3NC@D2(35)-C88 is similar to that of Y3N@D2(35)-C88, while the LUMO of Y3NC@D2(35)-C88 has a much larger contribution from the endohedral cluster as compared to Y3N@D2(35)-C88. Thus, the addition of a carbon atom in the cluster has a remarkable impact on the electronic structure of the metallofullerenes. With respect to structural characteristics, we found that the three fullerene cages, D2(186)-C96, D2(35)-C88, and Ih(7)-C80, have a uniform distribution of five-membered carbon atom rings; these fullerenes can be greatly stabilized in the form of C2n6- anions. However, the formation mechanism of fullerenes and metallofullerenes, at present, is poorly understood. Based on the structural analysis, we propose a direct mechanism for the formation of fullerenes without the Stone-Wales isomerization, i.e., the rearrangement of five-membered rings through the addition of carbon atoms and the transformation into larger carbon cages while maintaining stable structural units.
2021, 37(10): 191103
doi: 10.3866/PKU.WHXB201911039
Abstract:
Synthetic matrices provide powerful tools for dissecting molecular interactions involved in the organization of the extracellular matrix (ECM), establishment of cell axis polarity, and suppression of neoplasticity in pre-cancerous endothelial cells. Collagen is the most abundant protein in extracellular matrix. A de novo approach is essential for the synthesis of collagen matrices which can have a broad impact on the understanding of matrix biology and our capacity to construct safe and medically useful biomaterials. Conventionally, the ECM has been studied by an analytical "top-down" approach, where the individual components of the matrix are first isolated and then characterized to explore their biochemical and functional properties. Since native collagen is difficult to modify and can engender pathogenic and immunological side effects, its application on tissue regeneration is limited. Therefore, we attempted to synthesize artificial collagen directly through small organic molecule recognition. The collagen-like peptides possess various benefits such as being clean, programmable, and easy to modify; therefore, in recent years, they have been used as ideal substrates for the synthesis of collagen nanomaterials. The self-assembly of collagen-like peptides is mainly driven by various non-covalent interactions such as electrostatic attraction, π-π stacking, and metal coordination. This renders a difficulty in the rational design of uniform nanostructures from short synthesized peptides and demands a novel strategy. To date, small organic molecules have been rarely used for the self-assembly of collagen-like peptides. In the present study, we attempted to use the small organic molecules for the combined supramolecular self-assembly of collagen-like peptides. Initially, the collagen-like peptides, (POG)6 and (POG)8, synthesized by the solid-phase synthesis technique, were both modified chemically using 4, 4'-methylene bis(phenyl isocyanate) to obtain the collagen-like hybrid peptides, AP6 and AP8, respectively. Phenyl isocyanate contributes to the formation of potential weak forces, such as hydrogen bonds and π-π stacking at the N-terminal regions of the collagen-like hybrid peptides. The purity and molecular weight of the collagen-like hybrid peptides were analyzed using analytical high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF), respectively. The stability of AP6 and AP8 triple helices was analyzed by circular dichroism (CD) spectroscopy. The small organic molecule 4, 4'-methylene bis(phenyl isocyanate) promoted the unfolding of (POG)6 and increased the melting temperature (Tm) of (POG)8 from 37.7 to 58.8 ℃to form a triple helix. The hydrodynamic radii of collagen-like hybrid peptides were measured by dynamic light scattering (DLS). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to analyze the morphology of the aggregation states. AFM results showed that the collagen-like hybrid peptides, AP6 and AP8, formed nanofibers spontaneously. Consistent with the AFM results, TEM showed that the AP6 and AP8 collagen-like hybrid peptides also formed nanofiber structures. The formation of stable complexes was attributed to the presence of multiple weak interactions such as hydrogen bonding, π-π stacking, and hydrophobic interactions. In the present study, we demonstrated that the chemical modification of collagen-like polypeptides at the N-terminus via the small organic molecule, 4, 4'-methylene bis(phenyl isocyanate), promoted the intramolecular and intermolecular assembly of collagen-like peptides. A simple and effective strategy has been developed in this study to promote the self-assembly of collagen-like peptides. ![]()
Synthetic matrices provide powerful tools for dissecting molecular interactions involved in the organization of the extracellular matrix (ECM), establishment of cell axis polarity, and suppression of neoplasticity in pre-cancerous endothelial cells. Collagen is the most abundant protein in extracellular matrix. A de novo approach is essential for the synthesis of collagen matrices which can have a broad impact on the understanding of matrix biology and our capacity to construct safe and medically useful biomaterials. Conventionally, the ECM has been studied by an analytical "top-down" approach, where the individual components of the matrix are first isolated and then characterized to explore their biochemical and functional properties. Since native collagen is difficult to modify and can engender pathogenic and immunological side effects, its application on tissue regeneration is limited. Therefore, we attempted to synthesize artificial collagen directly through small organic molecule recognition. The collagen-like peptides possess various benefits such as being clean, programmable, and easy to modify; therefore, in recent years, they have been used as ideal substrates for the synthesis of collagen nanomaterials. The self-assembly of collagen-like peptides is mainly driven by various non-covalent interactions such as electrostatic attraction, π-π stacking, and metal coordination. This renders a difficulty in the rational design of uniform nanostructures from short synthesized peptides and demands a novel strategy. To date, small organic molecules have been rarely used for the self-assembly of collagen-like peptides. In the present study, we attempted to use the small organic molecules for the combined supramolecular self-assembly of collagen-like peptides. Initially, the collagen-like peptides, (POG)6 and (POG)8, synthesized by the solid-phase synthesis technique, were both modified chemically using 4, 4'-methylene bis(phenyl isocyanate) to obtain the collagen-like hybrid peptides, AP6 and AP8, respectively. Phenyl isocyanate contributes to the formation of potential weak forces, such as hydrogen bonds and π-π stacking at the N-terminal regions of the collagen-like hybrid peptides. The purity and molecular weight of the collagen-like hybrid peptides were analyzed using analytical high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time of flight (MALDI-TOF), respectively. The stability of AP6 and AP8 triple helices was analyzed by circular dichroism (CD) spectroscopy. The small organic molecule 4, 4'-methylene bis(phenyl isocyanate) promoted the unfolding of (POG)6 and increased the melting temperature (Tm) of (POG)8 from 37.7 to 58.8 ℃to form a triple helix. The hydrodynamic radii of collagen-like hybrid peptides were measured by dynamic light scattering (DLS). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were used to analyze the morphology of the aggregation states. AFM results showed that the collagen-like hybrid peptides, AP6 and AP8, formed nanofibers spontaneously. Consistent with the AFM results, TEM showed that the AP6 and AP8 collagen-like hybrid peptides also formed nanofiber structures. The formation of stable complexes was attributed to the presence of multiple weak interactions such as hydrogen bonding, π-π stacking, and hydrophobic interactions. In the present study, we demonstrated that the chemical modification of collagen-like polypeptides at the N-terminus via the small organic molecule, 4, 4'-methylene bis(phenyl isocyanate), promoted the intramolecular and intermolecular assembly of collagen-like peptides. A simple and effective strategy has been developed in this study to promote the self-assembly of collagen-like peptides.
2021, 37(10): 200102
doi: 10.3866/PKU.WHXB202001024
Abstract:
Graphene has become a research focus in recent years owing to its excellent characteristics, and glass is a commonly used material with high transparency and low cost. Graphene glass combines the excellent properties of both graphene and glass; graphene glass has not only high thermal conductivity, high electrical conductivity, and good surface hydrophobicity but also exhibits superior electrothermal conversion and wide-spectrum high-light-transmittance characteristics. Therefore, the study of graphene glass films is of theoretical value and practical significance. In this study, a high-purity glass-based (JGS1 quartz glass) multilayer graphene film was developed based on an atmospheric-pressure chemical vapor deposition (APCVD) method, and its electrical characteristics, light transmittance, and electrical heating characteristics were experimentally investigated in detail. The results show that graphene glass with different surface resistance values obtained through direct growth on a high-purity quartz glass substrate using the APCVD method, not only has excellent uniformity and quality, but also has considerably flat and high transmittance across the entire visible light region and exhibits excellent heating performance and fast response time. For graphene glass with a surface resistance of 1500 Ω·sq-1, the light transmittance can reach 74%, and the saturation temperature can rise to 185 ℃ by applying a bias voltage of 40 V. In addition, when the resistance value of the graphene glass is 420 Ω·sq-1, the graphene glass reaches a high saturation temperature of 325 ℃ in 40 s, and the corresponding heating rate can exceed 18 ℃·s-1, achieving a significantly higher heating rate than other heating films at the same voltage. Compared with the polyethylene-terephthalate- (PET-) based and silicon-based graphene films obtained by the transfer, graphene glass has a higher saturation temperature, shorter thermal response time, and faster heating rate. Furthermore, graphene glass exhibits better heating cycle stability and longer-term heating stability at a constant voltage. In addition, an experiment using the graphene glass to thermally tune the wavelength of a vertical-cavity surface-emitting laser was conducted and gave good results. The position of the laser peak controlled by the graphene glass was red-shifted by 1.78 nm by applying a voltage of 20 V, and the wavelength tuning efficiency reached 0.059 nm·℃-1. Compared with PET-based and silicon-based graphene films, the actual electrical heating capacity of graphene glass increased by 195%. These experimental findings demonstrate that graphene glass transparent films with excellent electric heating characteristics can be used in various transparent electric heating fields and have relatively wide application prospects.![]()
Graphene has become a research focus in recent years owing to its excellent characteristics, and glass is a commonly used material with high transparency and low cost. Graphene glass combines the excellent properties of both graphene and glass; graphene glass has not only high thermal conductivity, high electrical conductivity, and good surface hydrophobicity but also exhibits superior electrothermal conversion and wide-spectrum high-light-transmittance characteristics. Therefore, the study of graphene glass films is of theoretical value and practical significance. In this study, a high-purity glass-based (JGS1 quartz glass) multilayer graphene film was developed based on an atmospheric-pressure chemical vapor deposition (APCVD) method, and its electrical characteristics, light transmittance, and electrical heating characteristics were experimentally investigated in detail. The results show that graphene glass with different surface resistance values obtained through direct growth on a high-purity quartz glass substrate using the APCVD method, not only has excellent uniformity and quality, but also has considerably flat and high transmittance across the entire visible light region and exhibits excellent heating performance and fast response time. For graphene glass with a surface resistance of 1500 Ω·sq-1, the light transmittance can reach 74%, and the saturation temperature can rise to 185 ℃ by applying a bias voltage of 40 V. In addition, when the resistance value of the graphene glass is 420 Ω·sq-1, the graphene glass reaches a high saturation temperature of 325 ℃ in 40 s, and the corresponding heating rate can exceed 18 ℃·s-1, achieving a significantly higher heating rate than other heating films at the same voltage. Compared with the polyethylene-terephthalate- (PET-) based and silicon-based graphene films obtained by the transfer, graphene glass has a higher saturation temperature, shorter thermal response time, and faster heating rate. Furthermore, graphene glass exhibits better heating cycle stability and longer-term heating stability at a constant voltage. In addition, an experiment using the graphene glass to thermally tune the wavelength of a vertical-cavity surface-emitting laser was conducted and gave good results. The position of the laser peak controlled by the graphene glass was red-shifted by 1.78 nm by applying a voltage of 20 V, and the wavelength tuning efficiency reached 0.059 nm·℃-1. Compared with PET-based and silicon-based graphene films, the actual electrical heating capacity of graphene glass increased by 195%. These experimental findings demonstrate that graphene glass transparent films with excellent electric heating characteristics can be used in various transparent electric heating fields and have relatively wide application prospects.
2021, 37(10): 200104
doi: 10.3866/PKU.WHXB202001046
Abstract:
X-rays are widely used in many fields, including medical imaging, chemical structure analysis, and nondestructive examinations. However, long-term X-ray exposure is harmful to human health. Hence, radiation protection materials, especially wearable materials with outstanding performances, are in need of development. Lead (Pb) plates are commonly used as traditional radiation protection materials but have the disadvantages of heavy mass, toxicity, and poor wearability. Cement and alloy also are used to shield the X-ray, whereas application is limited by its heavy mass. In recent years, the wearable polymer based radiation protection was developed but has the defect which is low interfacial compatibility, resulting in poor shielding properties of the material. The K or L absorption edge of an element plays a major role in the attenuation of X-ray photon energy, and has a significant attenuation effect on X-ray photons with similar energy. As an alternative, it has been reported that the K absorption edge of rare earth (RE) elements is located in the range of 40–80 keV, which corresponds to the energy range of X-rays and medical X-ray energy range. Additionally, natural leather (NL) is an abundant natural biomass that is composed of multi-layered collagen fibers and contains amino (―NH2), carboxyl (―COOH), and hydroxyl (―OH) groups. We believe that RE nanoparticles can be uniformly immobilized and stabilized by NL. In this study, we developed a novel strategy to prepare X-ray radiation protective materials by combining RE nanoparticles with NL. NL-based protective materials have the advantages of being lightweight and wearable while providing excellent protection. NL-based RE oxide nanoparticle composites (RE-NL) were successfully prepared by a "retanning" method and verified by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). X-ray protection tests showed that La-NL had the best shielding performance compared to the other tested RE oxide-loaded NLs owing to the small difference between the K-edge energy of La and the incident energy. Moreover, La7.80-NL (La2O3 content of 7.80 mmol·cm-3, 0.7 mm) showed better protection performance than a Pb plate with a high-Z elemental content (54.7 mmol·cm-3, 0.25 mm) at 40–80 keV, confirming that the uniform distribution of RE oxides in NL provides enhanced X-ray shielding performance. The RE-NL also displayed a much better tensile strength, tear strength, and softness compared with polymer-based RE oxide composites. Meanwhile, it has the foldability and character of tailor. Therefore, the reported NL-based RE protective materials show promising potential for various scenarios requiring radiation protection. ![]()
X-rays are widely used in many fields, including medical imaging, chemical structure analysis, and nondestructive examinations. However, long-term X-ray exposure is harmful to human health. Hence, radiation protection materials, especially wearable materials with outstanding performances, are in need of development. Lead (Pb) plates are commonly used as traditional radiation protection materials but have the disadvantages of heavy mass, toxicity, and poor wearability. Cement and alloy also are used to shield the X-ray, whereas application is limited by its heavy mass. In recent years, the wearable polymer based radiation protection was developed but has the defect which is low interfacial compatibility, resulting in poor shielding properties of the material. The K or L absorption edge of an element plays a major role in the attenuation of X-ray photon energy, and has a significant attenuation effect on X-ray photons with similar energy. As an alternative, it has been reported that the K absorption edge of rare earth (RE) elements is located in the range of 40–80 keV, which corresponds to the energy range of X-rays and medical X-ray energy range. Additionally, natural leather (NL) is an abundant natural biomass that is composed of multi-layered collagen fibers and contains amino (―NH2), carboxyl (―COOH), and hydroxyl (―OH) groups. We believe that RE nanoparticles can be uniformly immobilized and stabilized by NL. In this study, we developed a novel strategy to prepare X-ray radiation protective materials by combining RE nanoparticles with NL. NL-based protective materials have the advantages of being lightweight and wearable while providing excellent protection. NL-based RE oxide nanoparticle composites (RE-NL) were successfully prepared by a "retanning" method and verified by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). X-ray protection tests showed that La-NL had the best shielding performance compared to the other tested RE oxide-loaded NLs owing to the small difference between the K-edge energy of La and the incident energy. Moreover, La7.80-NL (La2O3 content of 7.80 mmol·cm-3, 0.7 mm) showed better protection performance than a Pb plate with a high-Z elemental content (54.7 mmol·cm-3, 0.25 mm) at 40–80 keV, confirming that the uniform distribution of RE oxides in NL provides enhanced X-ray shielding performance. The RE-NL also displayed a much better tensile strength, tear strength, and softness compared with polymer-based RE oxide composites. Meanwhile, it has the foldability and character of tailor. Therefore, the reported NL-based RE protective materials show promising potential for various scenarios requiring radiation protection.
2021, 37(10): 200300
doi: 10.3866/PKU.WHXB202003005
Abstract:
Direct alcohol fuel cells (DAFCs) have attracted considerable research interest because of their potential application as alternative power sources for automotive systems and portable electronics. Pd-based catalysts represent one of the most popular catalysts for DAFCs due to their excellent electrocatalytic activities in alkaline electrolytes. Thus, it is of great importance to understand the structure-activity relationship of Pd electrocatalysts for alcohol electrocatalysis. Recently, size- and shape- controlled Pd nanocrystals have been successfully synthesized and subsequently used to study the size and shape effects of Pd electrocatalysts on alcohol electrocatalysis, in which the Pd (100) facet exhibited higher electrocatalytic oxidation activity for small alcohol molecules than the Pd (111) and (110) facets. Although it is well known that capping ligands, which are widely used in wet chemistry for the size- and shape-controlled synthesis of metal nanocrystals, likely chemisorb onto the surfaces of the resulting metal nanocrystals and influence their surface structure and surface-mediated properties, such as catalysis, this issue was not considered in previous studies of Pd nanocrystal electrocatalysts for electrocatalytic oxidation of small alcohol molecules. In this study, we prepared polyvinylpyrrolidone (PVP)-capped Pd nanocrystals with different morphologies and sizes and comparatively studied their electrocatalytic activities for methanol and ethanol oxidation in alkaline solutions. The chemisorbed PVP molecules transferred charge to the Pd nanocrystals, and the finer Pd nanocrystals had a higher coverage of chemisorbed PVP, and thus exposed fewer accessible surface sites, experienced more extensive PVP-to-Pd charge transfer, and were more negatively charged. The intrinsic electrocatalytic activity, represented by the electrochemical surface area (ECSA)-normalized electrocatalytic activity, of Pd nanocubes with exposed (100) facets increases with the particle size, indicating that the more negatively-charged Pd surface is less electrocatalytically active. The Pd nanocubes with average sizes between 12 and 19 nm are intrinsically more electrocatalytically active than commercial Pd black electrocatalysts, while the activity of Pd nanocubes with an averages size of 8 nm is less. This suggests that the enhancement effect of the exposed (100) facets surpasses the deteriorative effect of the negatively charged Pd surface for the Pd nanocubes with average sizes between 12 and 19 nm, whereas the deteriorative effect of the negatively charged Pd surface surpasses the enhancement effect of the exposed (100) facets for the Pd nanocubes with average sizes of 8 nm due to the extensive PVP-to-Pd charge transfer. Moreover, the Pd nanocubes with average sizes of 8 nm exhibit similar intrinsic electrocatalytic activity to the Pd nanooctahedra with (111) facets exposed and average sizes of 7 nm, indicating that the electronic structure of Pd electrocatalysts plays a more important role in influencing the electrocatalytic activity than the exposed facet. Since the chemisorbed PVP molecules block the surface sites on Pd nanocrystals that are accessible to the reactants, all Pd nanocrystals exhibit lower mass-normalized electrocatalytic activity than the Pd black electrocatalysts, and the mass-normalized electrocatalytic activity increases with the ECSA. These results clearly demonstrate that the size- and shape-dependent electrocatalytic activity of Pd nanocrystals capped with PVP for methanol and ethanol oxidation should be attributed to both the exposed facets of the Pd nanocrystals and the size-dependent electronic structures of the Pd nanocrystals resulting from the size-dependent PVP coverage and PVP-to-Pd charge transfer. Therefore, capping ligands on capped metal nanocrystals inevitably influence their surface structures and surface-mediated properties, which must be considered for a comprehensive understanding of the structure-activity relationship of capped metal nanocrystals. ![]()
Direct alcohol fuel cells (DAFCs) have attracted considerable research interest because of their potential application as alternative power sources for automotive systems and portable electronics. Pd-based catalysts represent one of the most popular catalysts for DAFCs due to their excellent electrocatalytic activities in alkaline electrolytes. Thus, it is of great importance to understand the structure-activity relationship of Pd electrocatalysts for alcohol electrocatalysis. Recently, size- and shape- controlled Pd nanocrystals have been successfully synthesized and subsequently used to study the size and shape effects of Pd electrocatalysts on alcohol electrocatalysis, in which the Pd (100) facet exhibited higher electrocatalytic oxidation activity for small alcohol molecules than the Pd (111) and (110) facets. Although it is well known that capping ligands, which are widely used in wet chemistry for the size- and shape-controlled synthesis of metal nanocrystals, likely chemisorb onto the surfaces of the resulting metal nanocrystals and influence their surface structure and surface-mediated properties, such as catalysis, this issue was not considered in previous studies of Pd nanocrystal electrocatalysts for electrocatalytic oxidation of small alcohol molecules. In this study, we prepared polyvinylpyrrolidone (PVP)-capped Pd nanocrystals with different morphologies and sizes and comparatively studied their electrocatalytic activities for methanol and ethanol oxidation in alkaline solutions. The chemisorbed PVP molecules transferred charge to the Pd nanocrystals, and the finer Pd nanocrystals had a higher coverage of chemisorbed PVP, and thus exposed fewer accessible surface sites, experienced more extensive PVP-to-Pd charge transfer, and were more negatively charged. The intrinsic electrocatalytic activity, represented by the electrochemical surface area (ECSA)-normalized electrocatalytic activity, of Pd nanocubes with exposed (100) facets increases with the particle size, indicating that the more negatively-charged Pd surface is less electrocatalytically active. The Pd nanocubes with average sizes between 12 and 19 nm are intrinsically more electrocatalytically active than commercial Pd black electrocatalysts, while the activity of Pd nanocubes with an averages size of 8 nm is less. This suggests that the enhancement effect of the exposed (100) facets surpasses the deteriorative effect of the negatively charged Pd surface for the Pd nanocubes with average sizes between 12 and 19 nm, whereas the deteriorative effect of the negatively charged Pd surface surpasses the enhancement effect of the exposed (100) facets for the Pd nanocubes with average sizes of 8 nm due to the extensive PVP-to-Pd charge transfer. Moreover, the Pd nanocubes with average sizes of 8 nm exhibit similar intrinsic electrocatalytic activity to the Pd nanooctahedra with (111) facets exposed and average sizes of 7 nm, indicating that the electronic structure of Pd electrocatalysts plays a more important role in influencing the electrocatalytic activity than the exposed facet. Since the chemisorbed PVP molecules block the surface sites on Pd nanocrystals that are accessible to the reactants, all Pd nanocrystals exhibit lower mass-normalized electrocatalytic activity than the Pd black electrocatalysts, and the mass-normalized electrocatalytic activity increases with the ECSA. These results clearly demonstrate that the size- and shape-dependent electrocatalytic activity of Pd nanocrystals capped with PVP for methanol and ethanol oxidation should be attributed to both the exposed facets of the Pd nanocrystals and the size-dependent electronic structures of the Pd nanocrystals resulting from the size-dependent PVP coverage and PVP-to-Pd charge transfer. Therefore, capping ligands on capped metal nanocrystals inevitably influence their surface structures and surface-mediated properties, which must be considered for a comprehensive understanding of the structure-activity relationship of capped metal nanocrystals.
2021, 37(10): 200303
doi: 10.3866/PKU.WHXB202003037
Abstract:
Recently, the application of ReaxFF based reactive molecular dynamics simulation (ReaxFF MD) in complex processes of pyrolysis, oxidation and catalysis has attracted considerable attention. The analysis of the simulation results of these processes is challenging owing to the complex chemical reactions involved, coupled with their dynamic physical properties. VARxMD is a leading tool for the chemical reaction analysis and visualization of ReaxFF MD simulations, which allows the automated analysis of reaction sites to get overall reaction lists, evolution trends of reactants and products, and reaction networks of specified reactants and products. The visualization of the reaction details and dynamic evolution profiles are readily available for each reactant and product. Additionally, the detailed reaction sites of bond breaking and formation are available in 2D chemical structure diagrams and 3D structure views; for specified reactions, they are categorized on the basis of the chemical structures of the bonding sites or function groups in the reacting species. However, the current VARxMD code mainly focuses on global chemical reaction information in the simulation system of the ReaxFF MD, and is incapable of locally tracking the chemical reaction and physical properties in a 3D picked zone. This work extends the VARxMD from global analysis to a focused 3D zone picked interactively from the 3D visualization modules of VARxMD, as well as physical property analysis to complement reaction analysis. The analysis of reactions and physical properties can be implemented in three steps: picking and drawing a 3D zone, identifying molecules in the picked zone, and analyzing the reactions and physical properties of the picked molecules. A 3D zone can be picked by specifying the geometric parameters or drawing on a screen using a mouse. The picking of a cuboid or sphere was implemented using the VTK 3D view libraries by specifying geometric parameters. The interactive 3D zone picking was implemented using a combination of observer and command patterns in the VTK visualization paradigm. The chemical reaction tracking and dynamic radial distribution function (RDF) of the 3D picked zone was efficiently implemented by inheriting data obtained from the global analysis of VARxMD. The reaction tracking between coal particles in coal pyrolysis simulation and dynamic structure characterization of carbon rich cluster formation in the thermal decomposition of an energetic material are presented as application examples. The obtained detailed reactions between the coal particles and comparison of the reaction between the locally and globally picked areas in the cuboid are helpful in understanding the role of micro pores in coal particles. The carbon to carbon RDF analysis and comparison of the spherical region picked for the layered molecular clusters in the pyrolysis system of the TNT crystal model with the standard RDF of the 5-layer graphene demonstrate the extended VARxMD as a chemical structure characteristic tool for detecting the dynamic formation profile of carbon rich clusters in the pyrolysis of TNT. The extended capability of VARxMD for a 3D picked zone of a ReaxFF MD simulation system can be useful for interfacial reaction analysis in a catalysis system, hot spot formation analysis in the detonation of energetic material systems, and particularly the pyrolysis or oxidation processes of coal, biomass, polymers, hydrocarbon fuels, and energetic materials. ![]()
Recently, the application of ReaxFF based reactive molecular dynamics simulation (ReaxFF MD) in complex processes of pyrolysis, oxidation and catalysis has attracted considerable attention. The analysis of the simulation results of these processes is challenging owing to the complex chemical reactions involved, coupled with their dynamic physical properties. VARxMD is a leading tool for the chemical reaction analysis and visualization of ReaxFF MD simulations, which allows the automated analysis of reaction sites to get overall reaction lists, evolution trends of reactants and products, and reaction networks of specified reactants and products. The visualization of the reaction details and dynamic evolution profiles are readily available for each reactant and product. Additionally, the detailed reaction sites of bond breaking and formation are available in 2D chemical structure diagrams and 3D structure views; for specified reactions, they are categorized on the basis of the chemical structures of the bonding sites or function groups in the reacting species. However, the current VARxMD code mainly focuses on global chemical reaction information in the simulation system of the ReaxFF MD, and is incapable of locally tracking the chemical reaction and physical properties in a 3D picked zone. This work extends the VARxMD from global analysis to a focused 3D zone picked interactively from the 3D visualization modules of VARxMD, as well as physical property analysis to complement reaction analysis. The analysis of reactions and physical properties can be implemented in three steps: picking and drawing a 3D zone, identifying molecules in the picked zone, and analyzing the reactions and physical properties of the picked molecules. A 3D zone can be picked by specifying the geometric parameters or drawing on a screen using a mouse. The picking of a cuboid or sphere was implemented using the VTK 3D view libraries by specifying geometric parameters. The interactive 3D zone picking was implemented using a combination of observer and command patterns in the VTK visualization paradigm. The chemical reaction tracking and dynamic radial distribution function (RDF) of the 3D picked zone was efficiently implemented by inheriting data obtained from the global analysis of VARxMD. The reaction tracking between coal particles in coal pyrolysis simulation and dynamic structure characterization of carbon rich cluster formation in the thermal decomposition of an energetic material are presented as application examples. The obtained detailed reactions between the coal particles and comparison of the reaction between the locally and globally picked areas in the cuboid are helpful in understanding the role of micro pores in coal particles. The carbon to carbon RDF analysis and comparison of the spherical region picked for the layered molecular clusters in the pyrolysis system of the TNT crystal model with the standard RDF of the 5-layer graphene demonstrate the extended VARxMD as a chemical structure characteristic tool for detecting the dynamic formation profile of carbon rich clusters in the pyrolysis of TNT. The extended capability of VARxMD for a 3D picked zone of a ReaxFF MD simulation system can be useful for interfacial reaction analysis in a catalysis system, hot spot formation analysis in the detonation of energetic material systems, and particularly the pyrolysis or oxidation processes of coal, biomass, polymers, hydrocarbon fuels, and energetic materials.
2021, 37(10): 200500
doi: 10.3866/PKU.WHXB202005004
Abstract:
Carbon dots (C dots) are relatively novel carbon nanomaterials that have attracted significant interest due to their unique photoluminescence, good biocompatibility, and stability. The preparation methods of C dots was usually summarized into "top-down" and "bottom-up", and mixed acid reflux is a top-down strategy that can be used to synthesize C dots, during which neutralization is a necessary step that can significantly influence the properties and potential applications of the final product. Previously, this research area mainly focused on tuning the properties of C dots by changing the starting materials and/or varying the reaction conditions; the influence of the reagents used during neutralization has been largely ignored. As the previously reported C dots prepared by mixed acid reflux were obtained from different starting materials under varied conditions, a meaningful comparison is difficult. Herein, yellow-emitting C dots were prepared by mixed acid-refluxing a carbon-rich material derived from fullerene carbon soot. For the same batch of as-prepared C dots, the influences of four reagents, i.e., NaOH, Na2CO3, K2CO3, and NH3·H2O, during neutralization on the structures and photoluminescence of the resulting C dots were investigated in detail. The results of thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy clearly showed that the reagent used during neutralization can affect the degree of dissociation of the acidic functional groups on the C dots. This is further supported by examination of the C dot/surfactant mixtures where subtle changes in the phase behavior were observed. Structural changes of the C dots cause variations in their surface states, ultimately altering the optical characteristics, including UV-vis absorption and fluorescence. Among the treated C dots, the sample prepared with Na2CO3 showed the strongest emission under the same excitation wavelength, while that prepared with NH3·H2O exhibited a distinct red shift (~8 nm) in the emission curve. The results presented herein provide clear evidence that neutralization reagent selection is important for optimizing the properties of the resulting C dots obtained by mixed acid reflux. In addition, the photoluminescence of the C dots can be influenced by their counterions, providing a novel method for tuning the properties of C dots while explaining their behavior in saline solutions. In short, the basicity of the neutralizing reagent and the type of counterions affect the structure of the C dots surface, which brings different performances. This work reminds researchers that it is necessary to use the type of neutralizing reagent as an experimental condition when preparing C dots in the future.![]()
Carbon dots (C dots) are relatively novel carbon nanomaterials that have attracted significant interest due to their unique photoluminescence, good biocompatibility, and stability. The preparation methods of C dots was usually summarized into "top-down" and "bottom-up", and mixed acid reflux is a top-down strategy that can be used to synthesize C dots, during which neutralization is a necessary step that can significantly influence the properties and potential applications of the final product. Previously, this research area mainly focused on tuning the properties of C dots by changing the starting materials and/or varying the reaction conditions; the influence of the reagents used during neutralization has been largely ignored. As the previously reported C dots prepared by mixed acid reflux were obtained from different starting materials under varied conditions, a meaningful comparison is difficult. Herein, yellow-emitting C dots were prepared by mixed acid-refluxing a carbon-rich material derived from fullerene carbon soot. For the same batch of as-prepared C dots, the influences of four reagents, i.e., NaOH, Na2CO3, K2CO3, and NH3·H2O, during neutralization on the structures and photoluminescence of the resulting C dots were investigated in detail. The results of thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy clearly showed that the reagent used during neutralization can affect the degree of dissociation of the acidic functional groups on the C dots. This is further supported by examination of the C dot/surfactant mixtures where subtle changes in the phase behavior were observed. Structural changes of the C dots cause variations in their surface states, ultimately altering the optical characteristics, including UV-vis absorption and fluorescence. Among the treated C dots, the sample prepared with Na2CO3 showed the strongest emission under the same excitation wavelength, while that prepared with NH3·H2O exhibited a distinct red shift (~8 nm) in the emission curve. The results presented herein provide clear evidence that neutralization reagent selection is important for optimizing the properties of the resulting C dots obtained by mixed acid reflux. In addition, the photoluminescence of the C dots can be influenced by their counterions, providing a novel method for tuning the properties of C dots while explaining their behavior in saline solutions. In short, the basicity of the neutralizing reagent and the type of counterions affect the structure of the C dots surface, which brings different performances. This work reminds researchers that it is necessary to use the type of neutralizing reagent as an experimental condition when preparing C dots in the future.
2021, 37(10): 190508
doi: 10.3866/PKU.WHXB201905084
Abstract:
Dye-sensitized solar cells (DSSCs) are the most promising alternatives to traditional fossil energy because of their advantages of low production cost, facile structure, relatively low environmental impact, relatively high photoelectronic absorption efficiency, and overall high efficiency. In addition, several studies on sensitizers as vital components have been conducted over the last three decades. Compared to metal dyes, metal-free organic dyes have been considered as promising candidates because of their simple fabrication, multiple structures, high molar absorption coefficients, easily tunable properties, and environmental friendliness. In this study, we systematically investigated the optoelectronic properties of six metal-free organic donor-acceptor dyes (RD1–6) derived from the known dye R6 by using the density functional theory (DFT) and time-dependent DFT methods. Cell performance parameters were discussed, including the geometrical and electronic structures, absorption spectrum, adsorption energy, light harvesting efficiency (LHE) curve, predictive short circuit current density (JscPred.), predictive open circuit voltage (VocPred.), and theoretical power conversion efficiency (PCE). Results revealed that all the designed dyes exhibited high theoretical PCE. In particular, dyes RD1, 2, and 4–6 showed greater conjugations, and dyes RD1–3 had smaller energy gaps than those of the reference dye. In addition, dyes RD1–3, 5, and 6 exhibited better light harvesting capacities that covered the entire visible region and extended to the near-infrared region with obviously red-shift maximum absorption wavelengths (λmax), wider LHE curves, and higher JscPred. as compared to the reference dye. It was critical that dyes RD1 and 2 not only have greater conjugations and narrow band gaps but also good light harvesting capacities with more than 56-nm red-shift maximum absorption wavelengths and broadened LHE curves than those of the reference dye. Notably, mainly because of an average increment of 12.0% of JscPred., a remarkable increment of the theoretical power conversion efficiency was observed from 12.6% for dye R6 to 14.1% for dyes RD1 and 2. Thus, dyes RD1 and 2 exhibited superior cell performances and could be promising sensitizer candidates for highly efficient DSSCs. These results could be used to guide effective synthetic efforts in the discovery of efficient metal-free organic dye sensitizers in DSSCs. ![]()
Dye-sensitized solar cells (DSSCs) are the most promising alternatives to traditional fossil energy because of their advantages of low production cost, facile structure, relatively low environmental impact, relatively high photoelectronic absorption efficiency, and overall high efficiency. In addition, several studies on sensitizers as vital components have been conducted over the last three decades. Compared to metal dyes, metal-free organic dyes have been considered as promising candidates because of their simple fabrication, multiple structures, high molar absorption coefficients, easily tunable properties, and environmental friendliness. In this study, we systematically investigated the optoelectronic properties of six metal-free organic donor-acceptor dyes (RD1–6) derived from the known dye R6 by using the density functional theory (DFT) and time-dependent DFT methods. Cell performance parameters were discussed, including the geometrical and electronic structures, absorption spectrum, adsorption energy, light harvesting efficiency (LHE) curve, predictive short circuit current density (JscPred.), predictive open circuit voltage (VocPred.), and theoretical power conversion efficiency (PCE). Results revealed that all the designed dyes exhibited high theoretical PCE. In particular, dyes RD1, 2, and 4–6 showed greater conjugations, and dyes RD1–3 had smaller energy gaps than those of the reference dye. In addition, dyes RD1–3, 5, and 6 exhibited better light harvesting capacities that covered the entire visible region and extended to the near-infrared region with obviously red-shift maximum absorption wavelengths (λmax), wider LHE curves, and higher JscPred. as compared to the reference dye. It was critical that dyes RD1 and 2 not only have greater conjugations and narrow band gaps but also good light harvesting capacities with more than 56-nm red-shift maximum absorption wavelengths and broadened LHE curves than those of the reference dye. Notably, mainly because of an average increment of 12.0% of JscPred., a remarkable increment of the theoretical power conversion efficiency was observed from 12.6% for dye R6 to 14.1% for dyes RD1 and 2. Thus, dyes RD1 and 2 exhibited superior cell performances and could be promising sensitizer candidates for highly efficient DSSCs. These results could be used to guide effective synthetic efforts in the discovery of efficient metal-free organic dye sensitizers in DSSCs.
2021, 37(10): 190602
doi: 10.3866/PKU.WHXB201906027
Abstract:
In single-molecule junctions, anchoring groups that connect the central molecule to the electrodes have profound effects on the mechanical and electrical properties of devices. The mechanical strength of the anchoring groups affects the device stability, while their electronic coupling strength influences the junction conductance and the conduction polarity. To design and fabricate high-performance single-molecule devices with graphene electrodes, it is highly desirable to explore robust anchoring groups that bond the central molecule to the graphene electrodes. Condensation of ortho-phenylenediamine terminated molecules with ortho-quinone moieties at the edges of graphene generates graphene-conjugated pyrazine units that can be employed as anchoring groups for the construction of molecular junctions with graphene electrodes. In this study, we investigated the fabrication and electrical characterization of single-molecule field-effect transistors (FETs) with graphene as the electrodes, pyrazine as the anchoring groups, and a heavily doped silicon substrate as the back-gate electrode. Graphene nano-gaps were fabricated by a high-speed feedback-controlled electro-burning method, and their edges were fully oxidized; thus, there were many ortho-quinone moieties at the edges. After the deposition of phenazine molecules with ortho-phenylenediamine terminals at both ends, a large current increase was observed, indicating that molecular junctions were formed with covalent pyrazine anchoring groups. The yield of the single-molecule devices was as high as 26%, demonstrating the feasibility of pyrazine as an effective anchoring group for graphene electrodes. Our electrical measurements show that the ten fabricated devices exhibited a distinct gating effect when a back-gate voltage was applied. However, the gate dependence of the conductance varied considerably from device to device, and three types of different gate modulation behaviors, including p-type, ambipolar, and n-type conduction, were observed. Our observations can be understood using a modified single-level model that takes into account the linear dispersion of graphene near the Dirac point; the unique band structure of graphene and the coupling strength of pyrazine with the graphene electrode both crucially affect the conduction polarity of single-molecule FETs. When the coupling strength of pyrazine with the graphene electrode is weak, the highest occupied molecular orbital (HOMO) of the central molecule dominates charge transport. Depending on the gating efficiencies of the HOMO level and the graphene states, devices can exhibit p-type or ambipolar conduction. In contrast, when the coupling is strong, the redistribution of electrons around the central molecule and the graphene electrodes leads to a realignment of the molecular levels, resulting in the lowest unoccupied molecular orbital (LUMO)-dominated n-type conduction. The high yield and versatility of the pyrazine anchoring groups are beneficial for the construction of single-molecule devices with graphene electrodes. ![]()
In single-molecule junctions, anchoring groups that connect the central molecule to the electrodes have profound effects on the mechanical and electrical properties of devices. The mechanical strength of the anchoring groups affects the device stability, while their electronic coupling strength influences the junction conductance and the conduction polarity. To design and fabricate high-performance single-molecule devices with graphene electrodes, it is highly desirable to explore robust anchoring groups that bond the central molecule to the graphene electrodes. Condensation of ortho-phenylenediamine terminated molecules with ortho-quinone moieties at the edges of graphene generates graphene-conjugated pyrazine units that can be employed as anchoring groups for the construction of molecular junctions with graphene electrodes. In this study, we investigated the fabrication and electrical characterization of single-molecule field-effect transistors (FETs) with graphene as the electrodes, pyrazine as the anchoring groups, and a heavily doped silicon substrate as the back-gate electrode. Graphene nano-gaps were fabricated by a high-speed feedback-controlled electro-burning method, and their edges were fully oxidized; thus, there were many ortho-quinone moieties at the edges. After the deposition of phenazine molecules with ortho-phenylenediamine terminals at both ends, a large current increase was observed, indicating that molecular junctions were formed with covalent pyrazine anchoring groups. The yield of the single-molecule devices was as high as 26%, demonstrating the feasibility of pyrazine as an effective anchoring group for graphene electrodes. Our electrical measurements show that the ten fabricated devices exhibited a distinct gating effect when a back-gate voltage was applied. However, the gate dependence of the conductance varied considerably from device to device, and three types of different gate modulation behaviors, including p-type, ambipolar, and n-type conduction, were observed. Our observations can be understood using a modified single-level model that takes into account the linear dispersion of graphene near the Dirac point; the unique band structure of graphene and the coupling strength of pyrazine with the graphene electrode both crucially affect the conduction polarity of single-molecule FETs. When the coupling strength of pyrazine with the graphene electrode is weak, the highest occupied molecular orbital (HOMO) of the central molecule dominates charge transport. Depending on the gating efficiencies of the HOMO level and the graphene states, devices can exhibit p-type or ambipolar conduction. In contrast, when the coupling is strong, the redistribution of electrons around the central molecule and the graphene electrodes leads to a realignment of the molecular levels, resulting in the lowest unoccupied molecular orbital (LUMO)-dominated n-type conduction. The high yield and versatility of the pyrazine anchoring groups are beneficial for the construction of single-molecule devices with graphene electrodes.
2021, 37(10): 191005
doi: 10.3866/PKU.WHXB201910059
Abstract:
Bacterial infection is a major threat to human health, and can cause several diseases including gastroenteritis, influenza, tetanus, and tuberculosis. As conventional antibiotic treatment may cause various undesirable effects such as stomach disorder and bacterial resistance, it is necessary to improve the antibacterial efficiency of antibiotics. Here, we synthesized a peptide-based copolymer, poly(ε-caprolactone)-block-poly(glutamic acid)-block-poly(lysine-stat-phenylalanine)[PCL34-b-PGA30-b-P(Lys16-stat-Phe12)] by ring-opening polymerization (ROP) of ε-caprolactone and amino acid N-carboxyanhydride (NCA). Successful synthesis of the copolymer was verified by proton nuclear magnetic resonance and size exclusion chromatography. This copolymer can self-assemble into negatively charged micelles (-26.7 mV) under alkaline conditions by solvent switch method. The micelle structure was confirmed by transmission electron microscopy and dynamic light scattering, and revealed to have a diameter of ~42 nm. Antibiotics were loaded into micelles during the self-assembly process, and cell viability assay was conducted to evaluate its cytotoxicity with and without tobramycin. No obvious cytotoxicity was observed for both micelles when the concentration was lower than 300 μg·mL-1. The antibiotic-loaded micelles demonstrated very low minimum inhibitory concentrations (MICs) against both Gram-negative Escherichia coli (E. coli) (7.8 μg·mL-1) and Gram-positive Staphylococcus aureus (S. aureus) (18.2 μg·mL-1), while the MICs of free tobramycin were 3.9 and 1.0 μg·mL-1, respectively. The drug-loading content and efficiency of the micelles were 5.2% and 24.3%, respectively. Therefore, the MICs of the loaded tobramycin against E. coli and S. aureus were 0.4 and 0.9 μg·mL-1, respectively, suggesting that the micelle could enhance the antibacterial activity of antibiotics. Tobramycin-loaded micelles demonstrated a sustained release characteristic, with 85% of the antibiotics released after 8 h. In bacteria-induced acidic microenvironment, the coil conformation of PGA blocks transforms and PGA blocks shrink toward the micelle core. Concomitantly, the carboxyl side chains are protonated in an acidic environment, increasing the hydrophobicity of this micelle. Antibiotics will be captured when reaching the outer core to slow down the releasing process. Furthermore, the poly(lysine-stat-phenylalanine) [P(Lys-stat-Phe)] coronas with broad spectrum intrinsic antibacterial activity can penetrate the bacterial cell membrane, leading to leakage of the cellular contents of the bacteria and ultimately their death. Due to the sustained release property of micelle and the intrinsic activity of the antibacterial peptide segments, this micelle can greatly enhance the antibacterial activity of antibiotics. Overall, this antibiotic-loaded micelle provides a novel approach for significantly reducing the antibiotics dosage and avoiding the associated health risks. ![]()
Bacterial infection is a major threat to human health, and can cause several diseases including gastroenteritis, influenza, tetanus, and tuberculosis. As conventional antibiotic treatment may cause various undesirable effects such as stomach disorder and bacterial resistance, it is necessary to improve the antibacterial efficiency of antibiotics. Here, we synthesized a peptide-based copolymer, poly(ε-caprolactone)-block-poly(glutamic acid)-block-poly(lysine-stat-phenylalanine)[PCL34-b-PGA30-b-P(Lys16-stat-Phe12)] by ring-opening polymerization (ROP) of ε-caprolactone and amino acid N-carboxyanhydride (NCA). Successful synthesis of the copolymer was verified by proton nuclear magnetic resonance and size exclusion chromatography. This copolymer can self-assemble into negatively charged micelles (-26.7 mV) under alkaline conditions by solvent switch method. The micelle structure was confirmed by transmission electron microscopy and dynamic light scattering, and revealed to have a diameter of ~42 nm. Antibiotics were loaded into micelles during the self-assembly process, and cell viability assay was conducted to evaluate its cytotoxicity with and without tobramycin. No obvious cytotoxicity was observed for both micelles when the concentration was lower than 300 μg·mL-1. The antibiotic-loaded micelles demonstrated very low minimum inhibitory concentrations (MICs) against both Gram-negative Escherichia coli (E. coli) (7.8 μg·mL-1) and Gram-positive Staphylococcus aureus (S. aureus) (18.2 μg·mL-1), while the MICs of free tobramycin were 3.9 and 1.0 μg·mL-1, respectively. The drug-loading content and efficiency of the micelles were 5.2% and 24.3%, respectively. Therefore, the MICs of the loaded tobramycin against E. coli and S. aureus were 0.4 and 0.9 μg·mL-1, respectively, suggesting that the micelle could enhance the antibacterial activity of antibiotics. Tobramycin-loaded micelles demonstrated a sustained release characteristic, with 85% of the antibiotics released after 8 h. In bacteria-induced acidic microenvironment, the coil conformation of PGA blocks transforms and PGA blocks shrink toward the micelle core. Concomitantly, the carboxyl side chains are protonated in an acidic environment, increasing the hydrophobicity of this micelle. Antibiotics will be captured when reaching the outer core to slow down the releasing process. Furthermore, the poly(lysine-stat-phenylalanine) [P(Lys-stat-Phe)] coronas with broad spectrum intrinsic antibacterial activity can penetrate the bacterial cell membrane, leading to leakage of the cellular contents of the bacteria and ultimately their death. Due to the sustained release property of micelle and the intrinsic activity of the antibacterial peptide segments, this micelle can greatly enhance the antibacterial activity of antibiotics. Overall, this antibiotic-loaded micelle provides a novel approach for significantly reducing the antibiotics dosage and avoiding the associated health risks.
2021, 37(10): 191100
doi: 10.3866/PKU.WHXB201911009
Abstract:
The preparation of high-efficiency and low-cost adsorbents for the defluoridation of drinking water remains a huge challenge. In this study, single-layer and multi-layer boehmite were first synthesized via an organic-free method, and active alumina used for fluoride removal from water was obtained from the boehmite. The advantage of a single layer is that more aluminum is exposed to the surface, which can provide more adsorption sites for fluoride. The active alumina adsorbent derived from single-layer boehmite exhibits a high specific surface area and excellent adsorption capacity. The high surface area ensures a high adsorption capacity, and the organic-free synthesis method lowers the preparation cost. The as-prepared adsorbent was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption analysis. The single-layer structure of boehmite was determined from the simulated XRD diffraction pattern of single-layer boehmite. The disappearance of the (020) diffraction peak of boehmite illustrates that the dimensions in the b direction are extremely small, and according to the XRD simulation results, the single-layer structure of boehmite could be determined. Single-layer boehmite with a surface area of 789.4 m2·g-1 was formed first. The active alumina obtained from the boehmite had a surface area of 678.4 m2·g-1, and the pore volume was 3.20 cm3·g-1. The fluoride adsorption of the active alumina was systematically studied as a function of the adsorbent dosage, contact time, concentration, co-existing anions, and pH. The fluoride adsorption capacity of the active alumina obtained from the single-layer boehmite reached up to 67.6 mg·g-1, which is higher than those of most alumina adsorbents reported in the literature. The adsorption capacities of the active alumina are related to the specific surface area and the number of hydroxyl groups on the surface. Dosages of 0.6, 1.0, and 2.6 g·L-1 of active alumina were able to lower the 10, 20, and 50 mg·L-1 fluoride solutions, respectively, below the maximum permissible limit of fluoride in drinking water in China (1.0 mg·L-1), suggesting that the active alumina synthesized in this work is a promising adsorbent for defluoridation of drinking water. In addition, the fluoride adsorption is applicable in a wide pH range from 4 to 9 and is mainly interfered by SO42- and PO43-. Further investigation suggested that the fluoride adsorption of the active alumina follows the pseudo second-order model and Langmuir isotherm model ![]()
The preparation of high-efficiency and low-cost adsorbents for the defluoridation of drinking water remains a huge challenge. In this study, single-layer and multi-layer boehmite were first synthesized via an organic-free method, and active alumina used for fluoride removal from water was obtained from the boehmite. The advantage of a single layer is that more aluminum is exposed to the surface, which can provide more adsorption sites for fluoride. The active alumina adsorbent derived from single-layer boehmite exhibits a high specific surface area and excellent adsorption capacity. The high surface area ensures a high adsorption capacity, and the organic-free synthesis method lowers the preparation cost. The as-prepared adsorbent was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FTIR) and nitrogen adsorption-desorption analysis. The single-layer structure of boehmite was determined from the simulated XRD diffraction pattern of single-layer boehmite. The disappearance of the (020) diffraction peak of boehmite illustrates that the dimensions in the b direction are extremely small, and according to the XRD simulation results, the single-layer structure of boehmite could be determined. Single-layer boehmite with a surface area of 789.4 m2·g-1 was formed first. The active alumina obtained from the boehmite had a surface area of 678.4 m2·g-1, and the pore volume was 3.20 cm3·g-1. The fluoride adsorption of the active alumina was systematically studied as a function of the adsorbent dosage, contact time, concentration, co-existing anions, and pH. The fluoride adsorption capacity of the active alumina obtained from the single-layer boehmite reached up to 67.6 mg·g-1, which is higher than those of most alumina adsorbents reported in the literature. The adsorption capacities of the active alumina are related to the specific surface area and the number of hydroxyl groups on the surface. Dosages of 0.6, 1.0, and 2.6 g·L-1 of active alumina were able to lower the 10, 20, and 50 mg·L-1 fluoride solutions, respectively, below the maximum permissible limit of fluoride in drinking water in China (1.0 mg·L-1), suggesting that the active alumina synthesized in this work is a promising adsorbent for defluoridation of drinking water. In addition, the fluoride adsorption is applicable in a wide pH range from 4 to 9 and is mainly interfered by SO42- and PO43-. Further investigation suggested that the fluoride adsorption of the active alumina follows the pseudo second-order model and Langmuir isotherm model
2021, 37(10): 191105
doi: 10.3866/PKU.WHXB201911053
Abstract:
Ethanol has great application prospects given it is an important essential chemical and a substitute for traditional energy sources. Currently, ethanol production is achieved through grain fermentation and petroleum-based ethylene hydration. However, the inefficient fermentation processes and increasingly depleted crude oil resources hinder the large-scale production of ethanol. Therefore, the development of alternative technologies for ethanol production has become an important issue. The direct production of ethanol from syngas (CO + H2) is considered to be a new strategy to acquire high value-added products and achieve clean utilization of carbonaceous resources such as coal, natural gas, and biomass. Supported Rh-based catalysts have been extensively studied as the most promising and effective systems for the direct production of ethanol from syngas. The use of promoters and supports is generally effective in increasing the activity and ethanol selectivity of supported Rh-based catalysts. Fe is widely used in the research on Rh-based catalysts, as it is one of the most effective promoters for enhancing ethanol selectivity. In this work, with the aim of exploring the role of the support, we used the incipient wetness impregnation method to prepare Fe-promoted Rh-based catalysts supported by CeO2, ZrO2, and TiO2 for the synthesis of ethanol from syngas. CO conversion of CO on the RhFe/TiO2 catalyst was as high as 18.2% under the reaction conditions of 250 ℃ and 2 MPa, and the selectivity to ethanol in the alcohol distribution was 74.7%, which was much higher than that observed with RhFe/CeO2 and RhFe/ZrO2 under the same conditions. The characterization results showed that the specific surface of the catalyst followed the order RhFe/CeO2 < RhFe/ZrO2 < RhFe/TiO2; the dispersion of Rh increased sequentially, and the particle size decreased in the same order. A larger specific surface area may favor the dispersion of the Rh species, and the highly dispersed Rh species would imply a greater number of active sites on the surface of the support. The results of H2-temperature-programmed reduction indicated possible interactions between Rh and the support as well as between Rh and Fe, and partial reduction of TiO2 under the experimental reduction conditions; however, the other supports did not undergo reduction. The results of X-ray photoelectron spectroscopy indicated that the RhFe/TiO2 catalyst had the largest amount of Rh0 as well as Rh+ species. Thus, this catalyst has more (Rhx0-Rhy+)-O-Feδ+ active sites for the synthesis of ethanol, which greatly increases the ethanol selectivity. CO-temperature programmed desorption was used to confirm the CO adsorption capacity of different catalysts. The results showed that TiO2 enhances the adsorption of CO due to the presence of more O vacancies and Ti3+ ions, which is beneficial to the improvement of the catalyst activity. ![]()
Ethanol has great application prospects given it is an important essential chemical and a substitute for traditional energy sources. Currently, ethanol production is achieved through grain fermentation and petroleum-based ethylene hydration. However, the inefficient fermentation processes and increasingly depleted crude oil resources hinder the large-scale production of ethanol. Therefore, the development of alternative technologies for ethanol production has become an important issue. The direct production of ethanol from syngas (CO + H2) is considered to be a new strategy to acquire high value-added products and achieve clean utilization of carbonaceous resources such as coal, natural gas, and biomass. Supported Rh-based catalysts have been extensively studied as the most promising and effective systems for the direct production of ethanol from syngas. The use of promoters and supports is generally effective in increasing the activity and ethanol selectivity of supported Rh-based catalysts. Fe is widely used in the research on Rh-based catalysts, as it is one of the most effective promoters for enhancing ethanol selectivity. In this work, with the aim of exploring the role of the support, we used the incipient wetness impregnation method to prepare Fe-promoted Rh-based catalysts supported by CeO2, ZrO2, and TiO2 for the synthesis of ethanol from syngas. CO conversion of CO on the RhFe/TiO2 catalyst was as high as 18.2% under the reaction conditions of 250 ℃ and 2 MPa, and the selectivity to ethanol in the alcohol distribution was 74.7%, which was much higher than that observed with RhFe/CeO2 and RhFe/ZrO2 under the same conditions. The characterization results showed that the specific surface of the catalyst followed the order RhFe/CeO2 < RhFe/ZrO2 < RhFe/TiO2; the dispersion of Rh increased sequentially, and the particle size decreased in the same order. A larger specific surface area may favor the dispersion of the Rh species, and the highly dispersed Rh species would imply a greater number of active sites on the surface of the support. The results of H2-temperature-programmed reduction indicated possible interactions between Rh and the support as well as between Rh and Fe, and partial reduction of TiO2 under the experimental reduction conditions; however, the other supports did not undergo reduction. The results of X-ray photoelectron spectroscopy indicated that the RhFe/TiO2 catalyst had the largest amount of Rh0 as well as Rh+ species. Thus, this catalyst has more (Rhx0-Rhy+)-O-Feδ+ active sites for the synthesis of ethanol, which greatly increases the ethanol selectivity. CO-temperature programmed desorption was used to confirm the CO adsorption capacity of different catalysts. The results showed that TiO2 enhances the adsorption of CO due to the presence of more O vacancies and Ti3+ ions, which is beneficial to the improvement of the catalyst activity.
2021, 37(10): 191203
doi: 10.3866/PKU.WHXB201912033
Abstract:
Developing novel and efficient catalysts is a significant way to break the bottleneck of low separation and transfer efficiency of charge carriers in pristine photocatalysts. Here, two fresh photocatalysts, g-C3N4@Ni3Se4 and g-C3N4@CoSe2 hybrids, are first synthesized by anchoring Ni3Se4 and CoSe2 nanoparticles on the surface of well-dispersed g-C3N4 nanosheets. The resulting materials show excellent performance for photocatalytic in situ hydrogen generation. Pristine g-C3N4 has poor photocatalytic hydrogen evolution activity (about 1.9 μmol·h-1) because of the rapid recombination of electron-hole pairs. However, the hydrogen generation activity is well improved after growing Ni3Se4 and CoSe2 on the surface of g-C3N4, owing to the unique effect of these selenides in accelerating the separation and migration of charge carriers. The hydrogen production activities of G-C3N4@Ni3Se4 and g-C3N4@CoSe2 are about 16.4 μmol·h-1 and 25.6 μmol·h-1, which are 8-fold and 13-fold that of pristine g-C3N4, respectively. In detail, coupling Ni3Se4 and CoSe2 with g-C3N4 greatly improves the light absorbance density and extends the light response region. The photoluminescence intensity of the photoexcited Eosin Y dye in the presence of g-C3N4@Ni3Se4 and g-C3N4@CoSe2 is weaker than that in the presence of pure g-C3N4. On the other hand, the upper limit of the electron-transfer rate constants in the presence of g-C3N4@Ni3Se4 and g-C3N4@CoSe2 is greater than that in the presence of pure g-C3N4. Among the g-C3N4@Ni3Se4@FTO, g-C3N4@CoSe2@FTO, and g-C3N4@FTO electrodes, the g-C3N4@FTO electrode has the lowest photocurrent density and the highest electrochemical impedance, implying that the introduction of CoSe2 and Ni3Se4 onto the surface of g-C3N4 enhances the separation and transfer efficiency of photogenerated charge carriers. In other words, the formation of two star metals selenide based on g-C3N4 can efficiently inhibit the recombination of photogenerated charge carriers and accelerate photocatalytic water splitting to generate H2. Meanwhile, the right shift of the absorption band edge effectively reduces the transition threshold of the photoexcited electrons from the valence band to the conduction band. In addition, the more negative zeta potential for the g-C3N4@Ni3Se4 and g-C3N4@CoSe2 catalysts as compared with that for pure g-C3N4 leads to a notable enhancement in the adsorption of protons by the sample surface. Moreover, the results of density functional theory calculations indicate that the hydrogen adsorption energy of the N sites in g-C3N4 is -0.22 eV; further, the hydrogen atoms are preferentially adsorbed at the bridge site of two selenium atoms to form a Se―H―Se bond, and the adsorption energy is 1.53 eV. In-depth characterization has been carried out by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, transient photocurrent measurements, and Fourier transform infrared spectroscopy; the results of these experiments are in good agreement with one another. ![]()
Developing novel and efficient catalysts is a significant way to break the bottleneck of low separation and transfer efficiency of charge carriers in pristine photocatalysts. Here, two fresh photocatalysts, g-C3N4@Ni3Se4 and g-C3N4@CoSe2 hybrids, are first synthesized by anchoring Ni3Se4 and CoSe2 nanoparticles on the surface of well-dispersed g-C3N4 nanosheets. The resulting materials show excellent performance for photocatalytic in situ hydrogen generation. Pristine g-C3N4 has poor photocatalytic hydrogen evolution activity (about 1.9 μmol·h-1) because of the rapid recombination of electron-hole pairs. However, the hydrogen generation activity is well improved after growing Ni3Se4 and CoSe2 on the surface of g-C3N4, owing to the unique effect of these selenides in accelerating the separation and migration of charge carriers. The hydrogen production activities of G-C3N4@Ni3Se4 and g-C3N4@CoSe2 are about 16.4 μmol·h-1 and 25.6 μmol·h-1, which are 8-fold and 13-fold that of pristine g-C3N4, respectively. In detail, coupling Ni3Se4 and CoSe2 with g-C3N4 greatly improves the light absorbance density and extends the light response region. The photoluminescence intensity of the photoexcited Eosin Y dye in the presence of g-C3N4@Ni3Se4 and g-C3N4@CoSe2 is weaker than that in the presence of pure g-C3N4. On the other hand, the upper limit of the electron-transfer rate constants in the presence of g-C3N4@Ni3Se4 and g-C3N4@CoSe2 is greater than that in the presence of pure g-C3N4. Among the g-C3N4@Ni3Se4@FTO, g-C3N4@CoSe2@FTO, and g-C3N4@FTO electrodes, the g-C3N4@FTO electrode has the lowest photocurrent density and the highest electrochemical impedance, implying that the introduction of CoSe2 and Ni3Se4 onto the surface of g-C3N4 enhances the separation and transfer efficiency of photogenerated charge carriers. In other words, the formation of two star metals selenide based on g-C3N4 can efficiently inhibit the recombination of photogenerated charge carriers and accelerate photocatalytic water splitting to generate H2. Meanwhile, the right shift of the absorption band edge effectively reduces the transition threshold of the photoexcited electrons from the valence band to the conduction band. In addition, the more negative zeta potential for the g-C3N4@Ni3Se4 and g-C3N4@CoSe2 catalysts as compared with that for pure g-C3N4 leads to a notable enhancement in the adsorption of protons by the sample surface. Moreover, the results of density functional theory calculations indicate that the hydrogen adsorption energy of the N sites in g-C3N4 is -0.22 eV; further, the hydrogen atoms are preferentially adsorbed at the bridge site of two selenium atoms to form a Se―H―Se bond, and the adsorption energy is 1.53 eV. In-depth characterization has been carried out by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, transient photocurrent measurements, and Fourier transform infrared spectroscopy; the results of these experiments are in good agreement with one another.
2021, 37(10): 191205
doi: 10.3866/PKU.WHXB201912053
Abstract:
The stability of nanocarriers in physiological environments is of importance for biomedical applications. Among the existing crosslinking approaches for enhancing the structural integrity and stability, photocrosslinking has been considered to be an ideal crosslinking chemistry, as it is non-toxic and cost-effective, and does not require an additional crosslinker or generate by-products. Meanwhile, most current temperature-responsive nanocarriers are designed and synthesized for drug release by increasing temperature. However, heating may induce cell damage during triggered drug release. Therefore, lowering temperature-triggered nanocarriers need to be developed for drug delivery and safe drug release during therapeutic hypothermia. In this study, we prepared an amphiphilic block copolymer, poly(ethylene oxide)-block-poly[N-isopropyl acrylamide-stat-7-(2-methacryloyloxyethoxy)-4-methylcoumarin]-block-poly(acrylic acid) [PEO43-b-P(NIPAM71-stat-CMA8)-b-PAA13], by reversible addition fragmentation chain transfer (RAFT) polymerization. Successful synthesis of the polymer was verified by proton nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The copolymers self-assembled into vesicles in aqueous solution, with the P(NIPAM-stat-CMA) block forming an inhomogeneous membrane and the PEO chains and PAA chains forming mixed coronas. The cavity of this vesicle could be utilized to load hydrophilic drugs. The CMA groups could undergo photocrosslinking and enhance the stability of vesicles in biological applications, and the PNIPAM moiety endowed the vesicle with temperature-responsive properties. Upon decreasing the temperature, the vesicles swelled and released the loaded drugs. The size distribution and morphology of the vesicles were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) experiments. After staining with phosphotungstic acid, the hollow morphology of the vesicles with a phase-separated inhomogeneous membrane was observed by TEM and SEM. The DLS results showed that the hydrodynamic diameter of the vesicles was 208 nm and the polydispersity was 0.075. The size of the vesicles observed by TEM was between 180 and 200 nm, which was in accordance with that measured by DLS. To verify the drug loading capacity and controlled release ability of the vesicle, a water-soluble antibiotic was encapsulated in the vesicles. The experimental results showed that the drug loading content was 10.4% relative to the vesicles and the drug loading efficiency was approximately 32.7%. For vesicles containing the same amount of antibiotics, the release rate at 25 ℃ was 35% higher than that at 37 ℃ after 12 h in aqueous solution. Overall, this photocrosslinked vesicle with temperature-responsive properties facilitates lowering temperature-triggered drug release during therapeutic hypothermia. ![]()
The stability of nanocarriers in physiological environments is of importance for biomedical applications. Among the existing crosslinking approaches for enhancing the structural integrity and stability, photocrosslinking has been considered to be an ideal crosslinking chemistry, as it is non-toxic and cost-effective, and does not require an additional crosslinker or generate by-products. Meanwhile, most current temperature-responsive nanocarriers are designed and synthesized for drug release by increasing temperature. However, heating may induce cell damage during triggered drug release. Therefore, lowering temperature-triggered nanocarriers need to be developed for drug delivery and safe drug release during therapeutic hypothermia. In this study, we prepared an amphiphilic block copolymer, poly(ethylene oxide)-block-poly[N-isopropyl acrylamide-stat-7-(2-methacryloyloxyethoxy)-4-methylcoumarin]-block-poly(acrylic acid) [PEO43-b-P(NIPAM71-stat-CMA8)-b-PAA13], by reversible addition fragmentation chain transfer (RAFT) polymerization. Successful synthesis of the polymer was verified by proton nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The copolymers self-assembled into vesicles in aqueous solution, with the P(NIPAM-stat-CMA) block forming an inhomogeneous membrane and the PEO chains and PAA chains forming mixed coronas. The cavity of this vesicle could be utilized to load hydrophilic drugs. The CMA groups could undergo photocrosslinking and enhance the stability of vesicles in biological applications, and the PNIPAM moiety endowed the vesicle with temperature-responsive properties. Upon decreasing the temperature, the vesicles swelled and released the loaded drugs. The size distribution and morphology of the vesicles were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) experiments. After staining with phosphotungstic acid, the hollow morphology of the vesicles with a phase-separated inhomogeneous membrane was observed by TEM and SEM. The DLS results showed that the hydrodynamic diameter of the vesicles was 208 nm and the polydispersity was 0.075. The size of the vesicles observed by TEM was between 180 and 200 nm, which was in accordance with that measured by DLS. To verify the drug loading capacity and controlled release ability of the vesicle, a water-soluble antibiotic was encapsulated in the vesicles. The experimental results showed that the drug loading content was 10.4% relative to the vesicles and the drug loading efficiency was approximately 32.7%. For vesicles containing the same amount of antibiotics, the release rate at 25 ℃ was 35% higher than that at 37 ℃ after 12 h in aqueous solution. Overall, this photocrosslinked vesicle with temperature-responsive properties facilitates lowering temperature-triggered drug release during therapeutic hypothermia.
2021, 37(10): 200100
doi: 10.3866/PKU.WHXB202001004
Abstract:
Vibrational spectroscopy is a powerful tool for studying the microstructure of liquids, and anatomizing the nature of the vibrational spectrum (VS) is promising for investigating changes in the properties of liquid structures under external conditions. In this study, molecular dynamics (MD) simulations have been performed to explore changes in the VS of 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF6]) ionic liquid (IL) under an external electric field (EEF) ranging from 0 to 10 V·nm-1 at 350 K. First, the vibrational spectra for [Emim][PF6] IL as well as its cation and anion are separately obtained, and the peaks are strictly assigned. The results demonstrate that the VS calculated by MD simulation can well reproduce the main characteristic peaks in the experimentally measured spectrum. Then, the vibrational spectra of the IL under various EEFs from 0 to 10 V·nm-1 are investigated, and the intrinsic origin of the changes in the vibrational bands (VBs) at 50, 183, 3196, and 3396 cm-1 is analyzed. Our simulation results indicate that the intensities of the VBs at 50 and 183 cm-1 are enhanced. In addition, the VB at 50 cm-1 is redshifted by about 16 cm-1 as the EEF is varied from 0 to 2 V·nm-1, and the redshift wavenumber increases to 33 cm-1 as the EEF is increased to 3 V·nm-1 and beyond. However, the intensities of the VBs at 3196 and 3396 cm-1 show an obvious decrease. Meanwhile, the VB at 3396 cm-1 is redshifted by about 16 cm-1 when the EEF increases to 3 V·nm-1, and the redshift increases to 33 cm-1 with an increase in the EEF beyond 4 V·nm-1. The intensity of the VB at 50 cm-1 increases because of the increase in the total dipole moment of each anion and cation (from 4.34 to 5.46 D), and the redshift is attributed to the decrease in the average interaction energy per ion pair (from -378.7 to -298.0 kJ·mol-1) with increasing EEF. The intensity of the VB at 183 cm-1 increases on account of the more consistent orientations for cations in the system with increasing EEF. The VB at 3196 cm-1 weakens visibly because a greater number of hydrogen atoms appear around the carbon atoms on the methyl/ethyl side chains and the vibrations of the corresponding carbon-hydrogen bonds are suppressed under the action of the EEF. Furthermore, the intensity of the VB at 3396 cm-1 decreases due to the decrease in the intermolecular +C-H···F- hydrogen bonds (HBs), while the relaxation effect that is beneficial for the formation of HBs simultaneously exists in the system under the varying EEF, thus causing a redshift of the VB at 3396 cm-1. ![]()
Vibrational spectroscopy is a powerful tool for studying the microstructure of liquids, and anatomizing the nature of the vibrational spectrum (VS) is promising for investigating changes in the properties of liquid structures under external conditions. In this study, molecular dynamics (MD) simulations have been performed to explore changes in the VS of 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF6]) ionic liquid (IL) under an external electric field (EEF) ranging from 0 to 10 V·nm-1 at 350 K. First, the vibrational spectra for [Emim][PF6] IL as well as its cation and anion are separately obtained, and the peaks are strictly assigned. The results demonstrate that the VS calculated by MD simulation can well reproduce the main characteristic peaks in the experimentally measured spectrum. Then, the vibrational spectra of the IL under various EEFs from 0 to 10 V·nm-1 are investigated, and the intrinsic origin of the changes in the vibrational bands (VBs) at 50, 183, 3196, and 3396 cm-1 is analyzed. Our simulation results indicate that the intensities of the VBs at 50 and 183 cm-1 are enhanced. In addition, the VB at 50 cm-1 is redshifted by about 16 cm-1 as the EEF is varied from 0 to 2 V·nm-1, and the redshift wavenumber increases to 33 cm-1 as the EEF is increased to 3 V·nm-1 and beyond. However, the intensities of the VBs at 3196 and 3396 cm-1 show an obvious decrease. Meanwhile, the VB at 3396 cm-1 is redshifted by about 16 cm-1 when the EEF increases to 3 V·nm-1, and the redshift increases to 33 cm-1 with an increase in the EEF beyond 4 V·nm-1. The intensity of the VB at 50 cm-1 increases because of the increase in the total dipole moment of each anion and cation (from 4.34 to 5.46 D), and the redshift is attributed to the decrease in the average interaction energy per ion pair (from -378.7 to -298.0 kJ·mol-1) with increasing EEF. The intensity of the VB at 183 cm-1 increases on account of the more consistent orientations for cations in the system with increasing EEF. The VB at 3196 cm-1 weakens visibly because a greater number of hydrogen atoms appear around the carbon atoms on the methyl/ethyl side chains and the vibrations of the corresponding carbon-hydrogen bonds are suppressed under the action of the EEF. Furthermore, the intensity of the VB at 3396 cm-1 decreases due to the decrease in the intermolecular +C-H···F- hydrogen bonds (HBs), while the relaxation effect that is beneficial for the formation of HBs simultaneously exists in the system under the varying EEF, thus causing a redshift of the VB at 3396 cm-1.
2021, 37(10): 200102
doi: 10.3866/PKU.WHXB202001025
Abstract:
Carbon materials have become one of the research hotspots in the field of catalysis as a typical representative of non-metallic catalytic materials. Herein, a facile synthetic strategy is developed to fabricate a series of hollow carbon nanoworms (h-NCNWs) that contain nitrogen up to 9.83 wt% by employing graphitic carbon nitride (g-C3N4) as the sacrificing template and solid nitrogen source. The h-NCNWs catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric (TG), Raman spectra, and X-ray photoelectron spectroscopies (XPS). The catalytic activities of the h-NCNWs catalysts for selective oxidation of benzyl alcohol with O2 were also evaluated. The characterization results revealed that the h-NCNWs catalysts displayed a unique hollow worm-like nanostructure with turbostratic carbon shells. The nitrogen content and shell thickness can be tuned by varying the relative ratio of resorcinol to g-C3N4 during the preparation process. Furthermore, nitrogen is incorporated to the carbon network in the form of graphite (predominantly) and pyridine, which is critical for the enhancement of the catalytic activity of carbon catalysts for the selective oxidation of benzyl alcohol. At a reaction temperature of 120 ℃, a 24.9% conversion of benzyl alcohol with > 99% selectivity to benzaldehyde can be achieved on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C3N4 of 0.5. However, the catalytic activities of the h-NCNWs catalysts were dependent on the amount of N dopants, in particular graphitic nitrogen species. The conversion of benzyl alcohol markedly decreased to 13.1% on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C3N4 of 1.5. Moreover, the h-NCNWs catalyst showed excellent stability during the reaction process. The conversion of benzyl alcohol and the high selectivity to aldehyde can be kept within five catalytic runs over the h-NCNWs0.5 catalyst. These results indicate that rationally designed carbon materials have great potential as highly efficient heterogeneous catalysts for oxidation reactions. ![]()
Carbon materials have become one of the research hotspots in the field of catalysis as a typical representative of non-metallic catalytic materials. Herein, a facile synthetic strategy is developed to fabricate a series of hollow carbon nanoworms (h-NCNWs) that contain nitrogen up to 9.83 wt% by employing graphitic carbon nitride (g-C3N4) as the sacrificing template and solid nitrogen source. The h-NCNWs catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), N2 adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric (TG), Raman spectra, and X-ray photoelectron spectroscopies (XPS). The catalytic activities of the h-NCNWs catalysts for selective oxidation of benzyl alcohol with O2 were also evaluated. The characterization results revealed that the h-NCNWs catalysts displayed a unique hollow worm-like nanostructure with turbostratic carbon shells. The nitrogen content and shell thickness can be tuned by varying the relative ratio of resorcinol to g-C3N4 during the preparation process. Furthermore, nitrogen is incorporated to the carbon network in the form of graphite (predominantly) and pyridine, which is critical for the enhancement of the catalytic activity of carbon catalysts for the selective oxidation of benzyl alcohol. At a reaction temperature of 120 ℃, a 24.9% conversion of benzyl alcohol with > 99% selectivity to benzaldehyde can be achieved on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C3N4 of 0.5. However, the catalytic activities of the h-NCNWs catalysts were dependent on the amount of N dopants, in particular graphitic nitrogen species. The conversion of benzyl alcohol markedly decreased to 13.1% on the h-NCNWs catalyst prepared with a mass ratio of resorcinol to g-C3N4 of 1.5. Moreover, the h-NCNWs catalyst showed excellent stability during the reaction process. The conversion of benzyl alcohol and the high selectivity to aldehyde can be kept within five catalytic runs over the h-NCNWs0.5 catalyst. These results indicate that rationally designed carbon materials have great potential as highly efficient heterogeneous catalysts for oxidation reactions.
2021, 37(10): 200202
doi: 10.3866/PKU.WHXB202002021
Abstract:
Ionic liquids (ILs) are thermally and chemically stable and have adjustable structures, which gives them the potential to be used as green, efficient biomolecular solvents. Given the critical role of ILs in dissolving biomolecules, the mechanism of interaction between them deserves further study. Herein, density functional theory (DFT) calculations, using the SMD implicit water solvent model, were employed to study the interaction and mechanism between a hydrophobic zwitterionic amino acid (Tyr) and a series of imidazolium ILs with different alkyl chain lengths and methylation sites. The contributions of hydrogen bonding (H-bonding), electrostatic effects, induction, and dispersion to the intermolecular interactions were determined by combining the symmetry-adapted perturbation theory (SAPT), the atoms in molecules (AIM) theory, and reduced density gradient (RDG) analysis. The results indicate that the H-bonding between the IL cation and Tyr is stronger than that between the IL anion and Tyr; however, the binding between either ion and Tyr is dominated by electrostatic effects. By contrast, the difference between the induction and dispersion forces is small when methylation occurs on the C2 site of the imidazolium cation; whereas, it is significantly large when methylation takes place on the N3 site. This is rationalized by the interaction patterns that vary based on the methylation site. H-bonding and π+-π stacking interactions between the imidazole and benzene rings are dominant during C2-methylation, while H-bonding and CAlkyl-H…π interactions between the alkyl chain and benzene ring are dominant during N3-methylation. Increasing the side alkyl chain length has different effects on the interaction energy to cations with different methylation sites. During N3-methylation, when the side alkyl chain length increases from 4 to 12, there are significant van der Waals interactions between the Tyr benzene and the side alkyl chain. However, these van der Waals interactions are inapparent when methylation takes place on the C2 site. Finally, the synergetic effect of the H-bonding and the interaction between the benzene and the side alkyl chain for C2-methylation is greater than the H-bonding and the interaction between the imidazole and benzene rings for N3-methylation, when the side alkyl chain length n > 9. Therefore, the interaction strength and mechanism in these imidazolium-Tyr complexes can be regulated by changing the methylation site and the side alkyl chain length of the cation. Further study of ion-pair and Tyr reveals that the change tendency of the interaction energy of IL-Tyr systems is consistent with that of cation-Tyr cases, and the ion pair further stabilizes the binding with Tyr. These results illustrate the interaction mechanism of IL-Tyr systems and provide a novel strategy for the design and screening of functional ILs for amino acid extraction and separation in the future. ![]()
Ionic liquids (ILs) are thermally and chemically stable and have adjustable structures, which gives them the potential to be used as green, efficient biomolecular solvents. Given the critical role of ILs in dissolving biomolecules, the mechanism of interaction between them deserves further study. Herein, density functional theory (DFT) calculations, using the SMD implicit water solvent model, were employed to study the interaction and mechanism between a hydrophobic zwitterionic amino acid (Tyr) and a series of imidazolium ILs with different alkyl chain lengths and methylation sites. The contributions of hydrogen bonding (H-bonding), electrostatic effects, induction, and dispersion to the intermolecular interactions were determined by combining the symmetry-adapted perturbation theory (SAPT), the atoms in molecules (AIM) theory, and reduced density gradient (RDG) analysis. The results indicate that the H-bonding between the IL cation and Tyr is stronger than that between the IL anion and Tyr; however, the binding between either ion and Tyr is dominated by electrostatic effects. By contrast, the difference between the induction and dispersion forces is small when methylation occurs on the C2 site of the imidazolium cation; whereas, it is significantly large when methylation takes place on the N3 site. This is rationalized by the interaction patterns that vary based on the methylation site. H-bonding and π+-π stacking interactions between the imidazole and benzene rings are dominant during C2-methylation, while H-bonding and CAlkyl-H…π interactions between the alkyl chain and benzene ring are dominant during N3-methylation. Increasing the side alkyl chain length has different effects on the interaction energy to cations with different methylation sites. During N3-methylation, when the side alkyl chain length increases from 4 to 12, there are significant van der Waals interactions between the Tyr benzene and the side alkyl chain. However, these van der Waals interactions are inapparent when methylation takes place on the C2 site. Finally, the synergetic effect of the H-bonding and the interaction between the benzene and the side alkyl chain for C2-methylation is greater than the H-bonding and the interaction between the imidazole and benzene rings for N3-methylation, when the side alkyl chain length n > 9. Therefore, the interaction strength and mechanism in these imidazolium-Tyr complexes can be regulated by changing the methylation site and the side alkyl chain length of the cation. Further study of ion-pair and Tyr reveals that the change tendency of the interaction energy of IL-Tyr systems is consistent with that of cation-Tyr cases, and the ion pair further stabilizes the binding with Tyr. These results illustrate the interaction mechanism of IL-Tyr systems and provide a novel strategy for the design and screening of functional ILs for amino acid extraction and separation in the future.
2021, 37(10): 200407
doi: 10.3866/PKU.WHXB202004071
Abstract:
Six ternary lanthanide complexes formulated as [Ln(2, 4, 6-TMBA)3(5, 5'-DM-2, 2'-bipy)]2 (Ln = Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Dy 6; 2, 4, 6-TMBA = 2, 4, 6-trimethylbenzoate; 5, 5'-DM-2, 2'-bipy = 5, 5'-dimethyl-2, 2'-bipyridine) have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, etc. The results of crystal diffraction analysis show that complexes 1–6 are binuclear units, crystallizing in the triclinic Pī space group. Complexes 1–5 are isostructural, and each of the central metal ions has a coordination number of 9. The asymmetric unit of complexes 1–5 consists of one Ln3+, one 5, 5'-DM-2, 2'-bipy ligand, and three 2, 4, 6-TMBA- moieties with three coordination modes: chelation bidentate, bridging bidentate, and bridging tridentate. The coordination geometry of Ln3+ is distorted monocapped square antiprismatic. The binuclear units of complexes 1–5 form a one-dimensional (1D) supramolecular chain along the c-axis via π–π stacking interactions between the 2, 4, 6-trimethylbenzoic acid rings. The 1D chains are linked to form a supramolecular two-dimensional (2D) sheet in the bc plane via π–π stacking interactions between the pyridine rings. Although the molecular formulae of complex 6 and complexes 1–5 are similar, the coordination environment of the lanthanide ions is different in the two cases. The asymmetric unit of complex 6 contains a Dy3+ ion coordinated by a bidentate 5, 5'-DM-2, 2'-bipy and three 2, 4, 6-TMBA- ligands adopting bidentate and bridging bidentate coordination modes. The Dy3+ metal center has a coordination number of 8, with distorted square antiprismatic molecular geometry. The binuclear molecule of 6 is assembled into a six-nuclear unit by π–π weak staking interactions between two 5, 5'-DM-2, 2'-bipy ligands; then, adjacent six-nuclear units form a 1D chain via offset π–π interactions between 5, 5'-DM-2, 2'-bipy ligands on different adjacent units. The adjacent 1D chains are linked by C―H···O hydrogen bonding interactions to form a 2D supramolecular structure. The thermal stability and thermal decomposition mechanism of all the complexes are investigated by the combination of thermogravimetry and infrared spectroscopy (TG/FTIR) techniques under a simulated air atmosphere in the temperature range of 298–973 K at a heating rate of 10 K·min-1. Thermogravimetric studies show that this series of complexes have excellent thermal stability. During the thermal decomposition of the complex, the neutral ligand is lost first, followed by the acid ligand, and finally, the complex is decomposed into rare earth oxides. The three-dimensional infrared results are consistent with the thermogravimetric results. The photoluminescence spectra of complex 4 show the strong characteristic luminescence of Eu3+. The five typical emission peaks at 581, 591, 621, 651, and 701 nm correspond to the 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 electronic transitions of Eu3+, respectively. The emission at 621 nm is due to the electric dipole transition 5D0 → 7F2, while that at 591 nm is assigned to the 5D0 → 7F1 the magnetic dipole transition. The lifetime (τ) of complex 4 is calculated as 1.15 ms based on the equation τ = (B1τ12 + B2τ22))/(B1τ1 + B2τ2), and the intrinsic quantum yield is calculated to be 45.1%. Further, the magnetic properties of complex 6 in the temperature range of 2–300 K are studied under an applied magnetic field of 1000 Oe. ![]()
Six ternary lanthanide complexes formulated as [Ln(2, 4, 6-TMBA)3(5, 5'-DM-2, 2'-bipy)]2 (Ln = Pr 1, Nd 2, Sm 3, Eu 4, Gd 5, Dy 6; 2, 4, 6-TMBA = 2, 4, 6-trimethylbenzoate; 5, 5'-DM-2, 2'-bipy = 5, 5'-dimethyl-2, 2'-bipyridine) have been synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, etc. The results of crystal diffraction analysis show that complexes 1–6 are binuclear units, crystallizing in the triclinic Pī space group. Complexes 1–5 are isostructural, and each of the central metal ions has a coordination number of 9. The asymmetric unit of complexes 1–5 consists of one Ln3+, one 5, 5'-DM-2, 2'-bipy ligand, and three 2, 4, 6-TMBA- moieties with three coordination modes: chelation bidentate, bridging bidentate, and bridging tridentate. The coordination geometry of Ln3+ is distorted monocapped square antiprismatic. The binuclear units of complexes 1–5 form a one-dimensional (1D) supramolecular chain along the c-axis via π–π stacking interactions between the 2, 4, 6-trimethylbenzoic acid rings. The 1D chains are linked to form a supramolecular two-dimensional (2D) sheet in the bc plane via π–π stacking interactions between the pyridine rings. Although the molecular formulae of complex 6 and complexes 1–5 are similar, the coordination environment of the lanthanide ions is different in the two cases. The asymmetric unit of complex 6 contains a Dy3+ ion coordinated by a bidentate 5, 5'-DM-2, 2'-bipy and three 2, 4, 6-TMBA- ligands adopting bidentate and bridging bidentate coordination modes. The Dy3+ metal center has a coordination number of 8, with distorted square antiprismatic molecular geometry. The binuclear molecule of 6 is assembled into a six-nuclear unit by π–π weak staking interactions between two 5, 5'-DM-2, 2'-bipy ligands; then, adjacent six-nuclear units form a 1D chain via offset π–π interactions between 5, 5'-DM-2, 2'-bipy ligands on different adjacent units. The adjacent 1D chains are linked by C―H···O hydrogen bonding interactions to form a 2D supramolecular structure. The thermal stability and thermal decomposition mechanism of all the complexes are investigated by the combination of thermogravimetry and infrared spectroscopy (TG/FTIR) techniques under a simulated air atmosphere in the temperature range of 298–973 K at a heating rate of 10 K·min-1. Thermogravimetric studies show that this series of complexes have excellent thermal stability. During the thermal decomposition of the complex, the neutral ligand is lost first, followed by the acid ligand, and finally, the complex is decomposed into rare earth oxides. The three-dimensional infrared results are consistent with the thermogravimetric results. The photoluminescence spectra of complex 4 show the strong characteristic luminescence of Eu3+. The five typical emission peaks at 581, 591, 621, 651, and 701 nm correspond to the 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4 electronic transitions of Eu3+, respectively. The emission at 621 nm is due to the electric dipole transition 5D0 → 7F2, while that at 591 nm is assigned to the 5D0 → 7F1 the magnetic dipole transition. The lifetime (τ) of complex 4 is calculated as 1.15 ms based on the equation τ = (B1τ12 + B2τ22))/(B1τ1 + B2τ2), and the intrinsic quantum yield is calculated to be 45.1%. Further, the magnetic properties of complex 6 in the temperature range of 2–300 K are studied under an applied magnetic field of 1000 Oe.
2021, 37(10): 200500
doi: 10.3866/PKU.WHXB202005008
Abstract:
This study concentrated on the production of a two-dimensional and two-dimensional (2D/2D) Ti3C2/Bi4O5Br2 heterojunction with a large interface that applied as one of the novel visible-light-induced photocatalyst via the hydrothermal method. The obtained photocatalysts enhanced the photocatalytic efficiency of the NO removal. The crystal structure and chemical state of the composites were characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that Ti3C2, Bi4O5Br2, and Ti3C2/Bi4O5Br2 were successfully synthesized. The experimental results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the prepared samples had a 2D/2D nanosheet structure and large contact area. This structure facilitated the transfer of electrons and holes. The solar light absorptions of the samples were evaluated using the UV-Vis diffuse reflectance spectra (UV-Vis DRS). It was found that the absorption band of Ti3C2/Bi4O5Br2 was wider than that of Bi4O5Br2. This represents the electrons in the Ti3C2/Bi4O5Br2 nanosheet composites were more likely to be excited. The photocatalytic experiments showed that the 2D/2D Ti3C2/Bi4O5Br2 composite with high photocatalytic activity and stability. The photocatalytic efficiency of pure Bi4O5Br2 for the NO removal was 30.5%, while for the 15%Ti3C2/Bi4O5Br2 it was 57.6%. Moreover, the catalytic reaction happened in a short period. The concentration of NO decreased exponentially in the first 5 min, which approximately reached the final value. Furthermore, the stability of 15%Ti3C2/Bi4O5Br2 was favorable: the catalytic rate was approximately 50.0% after five cycles of cyclic catalysis. Finally, the scavenger experiments, electron spin resonance spectroscopy (ESR), transient photocurrent response, and surface photovoltage spectrum (SPS) were applied to analyze the photocatalytic mechanism of the composite. The results indicated that the 2D/2D heterojunction Ti3C2/Bi4O5Br2 improved the separation rate of the electrons and holes, thus enhancing the photocatalytic efficiency. In the photocatalytic reactions, the photogenerated electrons (e−) and superoxide radical (·O2−) were critical active groups that had a significant role in the oxidative removal of NO. The in situ Fourier-transform infrared spectroscopy (in situ FTIR) showed that the photo-oxidation products were mainly NO2− and NO3−. Based on the above experimental results, a possible photocatalytic mechanism was proposed. The electrons in Bi4O5Br2 were excited by visible light. They jumped from the valence band (VB) of Bi4O5Br2 to the conduction band (CB). Then, the photoelectrons transferred from the CB of Bi4O5Br2 to the Ti3C2 surface, which significantly promoted the separation of the electron-hole pairs. Therefore, the photocatalytic efficiency of Ti3C2/Bi4O5Br2 on NO was significantly improved. This study provided an effective method for preparing 2D/2D Ti3C2/Bi4O5Br2 nanocomposites for the photocatalytic degradation of environmental pollutants, which has great potential in solving energy stress and environmental pollution. ![]()
This study concentrated on the production of a two-dimensional and two-dimensional (2D/2D) Ti3C2/Bi4O5Br2 heterojunction with a large interface that applied as one of the novel visible-light-induced photocatalyst via the hydrothermal method. The obtained photocatalysts enhanced the photocatalytic efficiency of the NO removal. The crystal structure and chemical state of the composites were characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that Ti3C2, Bi4O5Br2, and Ti3C2/Bi4O5Br2 were successfully synthesized. The experimental results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the prepared samples had a 2D/2D nanosheet structure and large contact area. This structure facilitated the transfer of electrons and holes. The solar light absorptions of the samples were evaluated using the UV-Vis diffuse reflectance spectra (UV-Vis DRS). It was found that the absorption band of Ti3C2/Bi4O5Br2 was wider than that of Bi4O5Br2. This represents the electrons in the Ti3C2/Bi4O5Br2 nanosheet composites were more likely to be excited. The photocatalytic experiments showed that the 2D/2D Ti3C2/Bi4O5Br2 composite with high photocatalytic activity and stability. The photocatalytic efficiency of pure Bi4O5Br2 for the NO removal was 30.5%, while for the 15%Ti3C2/Bi4O5Br2 it was 57.6%. Moreover, the catalytic reaction happened in a short period. The concentration of NO decreased exponentially in the first 5 min, which approximately reached the final value. Furthermore, the stability of 15%Ti3C2/Bi4O5Br2 was favorable: the catalytic rate was approximately 50.0% after five cycles of cyclic catalysis. Finally, the scavenger experiments, electron spin resonance spectroscopy (ESR), transient photocurrent response, and surface photovoltage spectrum (SPS) were applied to analyze the photocatalytic mechanism of the composite. The results indicated that the 2D/2D heterojunction Ti3C2/Bi4O5Br2 improved the separation rate of the electrons and holes, thus enhancing the photocatalytic efficiency. In the photocatalytic reactions, the photogenerated electrons (e−) and superoxide radical (·O2−) were critical active groups that had a significant role in the oxidative removal of NO. The in situ Fourier-transform infrared spectroscopy (in situ FTIR) showed that the photo-oxidation products were mainly NO2− and NO3−. Based on the above experimental results, a possible photocatalytic mechanism was proposed. The electrons in Bi4O5Br2 were excited by visible light. They jumped from the valence band (VB) of Bi4O5Br2 to the conduction band (CB). Then, the photoelectrons transferred from the CB of Bi4O5Br2 to the Ti3C2 surface, which significantly promoted the separation of the electron-hole pairs. Therefore, the photocatalytic efficiency of Ti3C2/Bi4O5Br2 on NO was significantly improved. This study provided an effective method for preparing 2D/2D Ti3C2/Bi4O5Br2 nanocomposites for the photocatalytic degradation of environmental pollutants, which has great potential in solving energy stress and environmental pollution.
2021, 37(10): 191103
doi: 10.3866/PKU.WHXB201911036
Abstract:
The rapid development of industrialization has resulted in severe environmental problems. A comprehensive assessment of air quality is urgently required all around the world. Among various technologies used in gas molecule detection, including Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, mass spectroscopy (MS), electrochemical sensors, and metal oxide semiconductor (MOS) gas sensors, MOS gas sensors possess the advantages of small dimension, low power consumption, high sensitivity, low production cost, and excellent silicon chip compatibility. MOS sensors hold great promise for future Internet of Things (IoT) sensors, which will have a profound impact on indoor and outdoor air quality monitoring. The development of nanotechnology has significantly enhanced the development of MOS gas sensors. Among various nanostructures like nanoparticles, nanosheets and nanowires, the emergence of quasi-one-dimensional (q1D) nanowires/nanorods/nanofibers, with unique q1D geometry (facilitating fast carrier transport) and large surface-to-volume ratio, potentially act as ideal sensing channels for MOS sensors with extremely small dimension, and good stability and sensitivity. These structures have thus been the focus of extensive research. Among the various MOS nanomaterials available, tungsten oxide (WO3-x, 0 ≤ x < 1) nanowires feature the characteristic properties (multiple oxidation states, rich substoichiometric oxides with distinct properties, photo/electrochromism, (photo)catalytic properties, etc.), and unique q1D geometry (single-crystalline pathway for fast carrier transport, large surface-to-volume ratio, etc.). WO3-x nanowires have broad applications in smart windows, energy conversation & storage, and gas sensing devices, and have thus become a focus of attention. In this paper, the fundamental properties of tungsten oxide, synthesis methods and growth mechanism of tungsten oxide nanowires are reviewed. Among various (vapor-liquid-solid (VLS), vapor-solid (VS) and thermal oxidation) growth methods, the thermal oxidation method enables an in situ integration of WO3-x nanowires on predefined electrodes (so-called bridged nanowire devices) via the oxidation of lithographically patterned W film at relatively low growth temperature (~500 ℃) because of interfacial strain, defects and oxygen on the surface of the W film. The novel bridged nanowire-based sensor devices outperform traditional lateral nanowire devices in terms of larger exposure area, low power consumption via self-heating, and greater convenience in device processing. Recent progress in bridged WO3-x nanowire devices and sensitive NOx molecule detection under low power consumption have also been reviewed. Power consumption of as low as a few milliwatts was achieved, and the detection limit of NO2 was reduced to 0.3 ppb (1 ppb = 1 × 10-9, volume fraction). In situ formed bridged WO3-x nanowire devices potentially satisfy the strict requirements of IoT sensors (small dimension, low power consumption, high integration, low cost, high sensitivity, and selectivity), and hold great promises for future IoT sensors. ![]()
The rapid development of industrialization has resulted in severe environmental problems. A comprehensive assessment of air quality is urgently required all around the world. Among various technologies used in gas molecule detection, including Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, mass spectroscopy (MS), electrochemical sensors, and metal oxide semiconductor (MOS) gas sensors, MOS gas sensors possess the advantages of small dimension, low power consumption, high sensitivity, low production cost, and excellent silicon chip compatibility. MOS sensors hold great promise for future Internet of Things (IoT) sensors, which will have a profound impact on indoor and outdoor air quality monitoring. The development of nanotechnology has significantly enhanced the development of MOS gas sensors. Among various nanostructures like nanoparticles, nanosheets and nanowires, the emergence of quasi-one-dimensional (q1D) nanowires/nanorods/nanofibers, with unique q1D geometry (facilitating fast carrier transport) and large surface-to-volume ratio, potentially act as ideal sensing channels for MOS sensors with extremely small dimension, and good stability and sensitivity. These structures have thus been the focus of extensive research. Among the various MOS nanomaterials available, tungsten oxide (WO3-x, 0 ≤ x < 1) nanowires feature the characteristic properties (multiple oxidation states, rich substoichiometric oxides with distinct properties, photo/electrochromism, (photo)catalytic properties, etc.), and unique q1D geometry (single-crystalline pathway for fast carrier transport, large surface-to-volume ratio, etc.). WO3-x nanowires have broad applications in smart windows, energy conversation & storage, and gas sensing devices, and have thus become a focus of attention. In this paper, the fundamental properties of tungsten oxide, synthesis methods and growth mechanism of tungsten oxide nanowires are reviewed. Among various (vapor-liquid-solid (VLS), vapor-solid (VS) and thermal oxidation) growth methods, the thermal oxidation method enables an in situ integration of WO3-x nanowires on predefined electrodes (so-called bridged nanowire devices) via the oxidation of lithographically patterned W film at relatively low growth temperature (~500 ℃) because of interfacial strain, defects and oxygen on the surface of the W film. The novel bridged nanowire-based sensor devices outperform traditional lateral nanowire devices in terms of larger exposure area, low power consumption via self-heating, and greater convenience in device processing. Recent progress in bridged WO3-x nanowire devices and sensitive NOx molecule detection under low power consumption have also been reviewed. Power consumption of as low as a few milliwatts was achieved, and the detection limit of NO2 was reduced to 0.3 ppb (1 ppb = 1 × 10-9, volume fraction). In situ formed bridged WO3-x nanowire devices potentially satisfy the strict requirements of IoT sensors (small dimension, low power consumption, high integration, low cost, high sensitivity, and selectivity), and hold great promises for future IoT sensors.
2021, 37(10): 200801
doi: 10.3866/PKU.WHXB202008014
Abstract:
2021, 37(10): 201102
doi: 10.3866/PKU.WHXB202011026
Abstract:
2021, 37(10): 201104
doi: 10.3866/PKU.WHXB202011045
Abstract:
2021, 37(10): 201105
doi: 10.3866/PKU.WHXB202011054
Abstract:
2021, 37(10): 201107
doi: 10.3866/PKU.WHXB202011078
Abstract:
