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2023 Volume 39 Issue 7
2023, 39(7): 220904
doi: 10.3866/PKU.WHXB202209043
Abstract:
As one of the most common bulk chemicals, propylene is widely used in industrial production. Given developments in shale gas exploration technology, propane direct dehydrogenation (PDH) has emerged as a potential route. Pt-based catalysts are considered highly active catalysts for PDH, but their use is limited by a number of challenges. Herein, in situ Fe-doped Silicalite-1 zeolite supports were synthesized using the hydrothermal method, after which the corresponding Pt-based catalysts were prepared by impregnation and used for PDH. For comparison, Pt/Silicalite-1 and co-impregnated Pt1Fe2/Silicalite-1 catalysts were also prepared. Compared with that of Pt/Silicalite-1, the catalytic performance of Pt/Fe-Silicalite-1 prepared by in situ Fe-doping was significantly enhanced, whereas that of the co-precipitated Pt1Fe2/Silicalite-1 catalyst decreased. The selectivity and catalytic stability of the reaction over the Pt/Fe-Silicalite-1 catalyst were greatly improved, although the initial conversion of propane was slightly low. After 8 h, the propane conversion rate stabilized at 43.7% and the propylene selectivity reached 98.0%. More importantly, the catalyst maintained its performance over 80 h without an obvious decline. Propane conversion increased with increasing reaction temperature, while propene selectivity was maintained at a comparable level. The reaction kinetics of PDH were determined, and the results demonstrated that the apparent activation energy of the Pt/Fe-Silicalite-1 catalyst was 97.0 kJ·mol−1; this value was the lowest obtained among the catalysts investigated and indicated the relative ease of propane activation over the catalyst. A series of characterization techniques, such as X-ray diffraction (XRD), N2 sorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), were used to explore the structural characteristics of the catalysts. The in situ Fe-doped Silicalite-1 zeolite supports retained their MFI structure but had a small particle size. UV-Vis spectroscopy revealed a large amount of Fe2O3 particles on the Pt1Fe2/Silicalite-1 surface; by contrast, Pt/Fe-Silicalite-1 possessed isolated tetrahedrally and octahedrally coordinated Fe3+ in the Fe-Silicalite-1 framework, as well as small oligomeric Fe species, such as FexOy, inside the zeolite pores. H2-TPR revealed strong interactions between the Fe species and support in the Pt/Fe-Silicalite-1 catalyst. CO-DRIFT and X-ray photoelectron spectroscopy (XPS) indicated that the in situ incorporation of Fe not only improved the formation of Pt on the platform sites with high saturation, which prevented the deep-cracking of propane, but also enriched the electron cloud density on Pt by promoting electron transfer from Fe to Pt, thus enhancing the desorption of propylene and preventing coke formation. In addition, Fe sites in the support could anchor Pt to prevent their aggregation and improve the stability of Pt/Fe-Silicalite-1. Thus, high conversion and selectivity were obtained even after 80 h of reaction. ![]()
As one of the most common bulk chemicals, propylene is widely used in industrial production. Given developments in shale gas exploration technology, propane direct dehydrogenation (PDH) has emerged as a potential route. Pt-based catalysts are considered highly active catalysts for PDH, but their use is limited by a number of challenges. Herein, in situ Fe-doped Silicalite-1 zeolite supports were synthesized using the hydrothermal method, after which the corresponding Pt-based catalysts were prepared by impregnation and used for PDH. For comparison, Pt/Silicalite-1 and co-impregnated Pt1Fe2/Silicalite-1 catalysts were also prepared. Compared with that of Pt/Silicalite-1, the catalytic performance of Pt/Fe-Silicalite-1 prepared by in situ Fe-doping was significantly enhanced, whereas that of the co-precipitated Pt1Fe2/Silicalite-1 catalyst decreased. The selectivity and catalytic stability of the reaction over the Pt/Fe-Silicalite-1 catalyst were greatly improved, although the initial conversion of propane was slightly low. After 8 h, the propane conversion rate stabilized at 43.7% and the propylene selectivity reached 98.0%. More importantly, the catalyst maintained its performance over 80 h without an obvious decline. Propane conversion increased with increasing reaction temperature, while propene selectivity was maintained at a comparable level. The reaction kinetics of PDH were determined, and the results demonstrated that the apparent activation energy of the Pt/Fe-Silicalite-1 catalyst was 97.0 kJ·mol−1; this value was the lowest obtained among the catalysts investigated and indicated the relative ease of propane activation over the catalyst. A series of characterization techniques, such as X-ray diffraction (XRD), N2 sorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), were used to explore the structural characteristics of the catalysts. The in situ Fe-doped Silicalite-1 zeolite supports retained their MFI structure but had a small particle size. UV-Vis spectroscopy revealed a large amount of Fe2O3 particles on the Pt1Fe2/Silicalite-1 surface; by contrast, Pt/Fe-Silicalite-1 possessed isolated tetrahedrally and octahedrally coordinated Fe3+ in the Fe-Silicalite-1 framework, as well as small oligomeric Fe species, such as FexOy, inside the zeolite pores. H2-TPR revealed strong interactions between the Fe species and support in the Pt/Fe-Silicalite-1 catalyst. CO-DRIFT and X-ray photoelectron spectroscopy (XPS) indicated that the in situ incorporation of Fe not only improved the formation of Pt on the platform sites with high saturation, which prevented the deep-cracking of propane, but also enriched the electron cloud density on Pt by promoting electron transfer from Fe to Pt, thus enhancing the desorption of propylene and preventing coke formation. In addition, Fe sites in the support could anchor Pt to prevent their aggregation and improve the stability of Pt/Fe-Silicalite-1. Thus, high conversion and selectivity were obtained even after 80 h of reaction.
2023, 39(7): 221103
doi: 10.3866/PKU.WHXB202211034
Abstract:
All-solid-state batteries have attracted significant attention as next-generation energy-storage devices for electric vehicles and smart grids because of their excellent safety and high energy density. Research on solid electrolytes with high ionic conductivity at room temperature, good chemical/electrochemical stability, and superior electrode compatibility is important for promoting the development of all-solid-state batteries. Sulfide electrolytes have become a hot topic among different inorganic solid electrolytes because of their relatively high Li-ion conductivity (~10-3 Sžcm-1) and low solid-solid interfacial resistance between the solid electrolytes and electrode particles. Among these sulfide electrolytes, lithium argyrodite solid electrolytes have attracted much attention owing to their high Li-ion conductivity at room temperature and relatively low cost. However, many problems still need to be solved before their practical application, such as difficulties in batch preparation, poor air stability, narrow chemical/electrochemical stability window, and poor interface stability towards high-voltage active materials. Extensive research has been conducted by many research groups to solve these problems and significant progress has been achieved. This review summarizes the current research on the structural information, ion conduction behaviors, synthesis routes, modification methods for improving the chemical/electrochemical stability properties, and applications of lithium argyrodite electrolytes combined with various cathode and anode materials in all-solid-state batteries based on our own research and published works of others. Two types of synthesis routes, the solid-state reaction route and the liquid solution route, are used to prepare lithium argyrodite electrolytes. Typically, electrolytes obtained by the former method deliver higher conductivities than those obtained by the latter. Multiple characterization methods, including alternating current (AC) impedance, molecular dynamics (MD) simulations, spin lattice relaxation in 7Li nuclear magnetic resonance (NMR), and 1D/2D Li exchange NMR, have been applied to probe Li-ion diffusion in the bulk of a signal particle across the interface section between two electrolyte particles, across the cathode, and across electrolyte particles. Increasing the number of Li vacancies via halogen substitution and element doping has been widely applied to increase the Li-ion conductivity of argyrodite electrolytes. Improvements in air stability for these argyrodite electrolytes have been achieved using element doping (such as O, Sb, and Sn) based on the hard-soft-acid-base theory and surface coating strategies. Interface contact and stability between the active materials and solid electrolytes play a key role in battery performance. Owing to the poor chemical/electrochemical stability of cathode materials, homogenous surface coatings and lithium halide electrolyte additives have been introduced into the configuration to isolate the direct contact between sulfides and active materials in the cathode mixture. Poor lithium metal compatibility inhibits the application of lithium argyrodite electrolytes in solid-state lithium metal batteries with high energy densities. Elemental doping in lithium argyrodites can form lithium alloys that impede the growth of lithium dendrites, and the surface modification of lithium metal anodes is helpful in constructing solid-state batteries with lithium metal anodes. Furthermore, research on lithium argyrodite electrolyte film preparation has also been conducted to develop a new solid-state battery construction route. In addition, the challenges and problems are analyzed, and possible research directions and development trends of lithium argyrodite solid electrolytes are proposed.![]()
All-solid-state batteries have attracted significant attention as next-generation energy-storage devices for electric vehicles and smart grids because of their excellent safety and high energy density. Research on solid electrolytes with high ionic conductivity at room temperature, good chemical/electrochemical stability, and superior electrode compatibility is important for promoting the development of all-solid-state batteries. Sulfide electrolytes have become a hot topic among different inorganic solid electrolytes because of their relatively high Li-ion conductivity (~10-3 Sžcm-1) and low solid-solid interfacial resistance between the solid electrolytes and electrode particles. Among these sulfide electrolytes, lithium argyrodite solid electrolytes have attracted much attention owing to their high Li-ion conductivity at room temperature and relatively low cost. However, many problems still need to be solved before their practical application, such as difficulties in batch preparation, poor air stability, narrow chemical/electrochemical stability window, and poor interface stability towards high-voltage active materials. Extensive research has been conducted by many research groups to solve these problems and significant progress has been achieved. This review summarizes the current research on the structural information, ion conduction behaviors, synthesis routes, modification methods for improving the chemical/electrochemical stability properties, and applications of lithium argyrodite electrolytes combined with various cathode and anode materials in all-solid-state batteries based on our own research and published works of others. Two types of synthesis routes, the solid-state reaction route and the liquid solution route, are used to prepare lithium argyrodite electrolytes. Typically, electrolytes obtained by the former method deliver higher conductivities than those obtained by the latter. Multiple characterization methods, including alternating current (AC) impedance, molecular dynamics (MD) simulations, spin lattice relaxation in 7Li nuclear magnetic resonance (NMR), and 1D/2D Li exchange NMR, have been applied to probe Li-ion diffusion in the bulk of a signal particle across the interface section between two electrolyte particles, across the cathode, and across electrolyte particles. Increasing the number of Li vacancies via halogen substitution and element doping has been widely applied to increase the Li-ion conductivity of argyrodite electrolytes. Improvements in air stability for these argyrodite electrolytes have been achieved using element doping (such as O, Sb, and Sn) based on the hard-soft-acid-base theory and surface coating strategies. Interface contact and stability between the active materials and solid electrolytes play a key role in battery performance. Owing to the poor chemical/electrochemical stability of cathode materials, homogenous surface coatings and lithium halide electrolyte additives have been introduced into the configuration to isolate the direct contact between sulfides and active materials in the cathode mixture. Poor lithium metal compatibility inhibits the application of lithium argyrodite electrolytes in solid-state lithium metal batteries with high energy densities. Elemental doping in lithium argyrodites can form lithium alloys that impede the growth of lithium dendrites, and the surface modification of lithium metal anodes is helpful in constructing solid-state batteries with lithium metal anodes. Furthermore, research on lithium argyrodite electrolyte film preparation has also been conducted to develop a new solid-state battery construction route. In addition, the challenges and problems are analyzed, and possible research directions and development trends of lithium argyrodite solid electrolytes are proposed.
2023, 39(7): 221105
doi: 10.3866/PKU.WHXB202211057
Abstract:
High-performance rechargeable lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and other fields of electrochemical energy storage. However, in order to achieve a wider range of commercial applications, the energy density of lithium-ion batteries needs to be further improved. Layered lithium-rich oxide materials with a high reversible specific capacity of over 250 mAh∙g−1 are regarded as commercially promising cathodes for next-generation high-energy lithium-ion batteries. The high capacity of layered lithium-rich materials can be attributed to its unique oxygen redox chemistry, which can achieve additional charge storage thus increasing its capacity. However, many challenges must be addressed, including high-voltage oxygen release, structural changes from layered to rock-salt phase and structural degradation owing to the migration of transition metal ions, before it can be applied practically. These existing challenges result in low initial Coulombic efficiency, voltage/capacity decay, and insufficient cycle life. In view of the above issues, the modification of layered lithium-rich materials is an effective method. This review systematically introduces the composition and structure of lithium-rich materials, and then analyzes the electrochemical mechanism and internal causes which affect the electrochemical performance of lithium-rich materials. Furthermore, recent material modification strategies are discussed with regards to the current challenges. In addition, current methods and developmental trends of modification strategies such as bulk doping, surface coating, defect design, ion exchange and microstructure regulation are summarized in detail. According to the different charge properties, the doping modification can be divided into cationic doping, anion doping and anion-cation co-doping. Among them, cationic doping can be further categorized into transition metal layer doping substitution and lithium layer doping substitution, depending on the doping site. Two tables for the doping and ion exchange modifications were tabulated, and the representative scientific research was summarized. Recent research conducted on hotspot high-entropy materials were also mentioned. Finally, design ideas for high-capacity, long-cycle layered lithium-rich materials and high specific energy lithium-ion batteries were prospected. This comprehensive review is expected to promote further lithium-rich oxide materials research.![]()
High-performance rechargeable lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and other fields of electrochemical energy storage. However, in order to achieve a wider range of commercial applications, the energy density of lithium-ion batteries needs to be further improved. Layered lithium-rich oxide materials with a high reversible specific capacity of over 250 mAh∙g−1 are regarded as commercially promising cathodes for next-generation high-energy lithium-ion batteries. The high capacity of layered lithium-rich materials can be attributed to its unique oxygen redox chemistry, which can achieve additional charge storage thus increasing its capacity. However, many challenges must be addressed, including high-voltage oxygen release, structural changes from layered to rock-salt phase and structural degradation owing to the migration of transition metal ions, before it can be applied practically. These existing challenges result in low initial Coulombic efficiency, voltage/capacity decay, and insufficient cycle life. In view of the above issues, the modification of layered lithium-rich materials is an effective method. This review systematically introduces the composition and structure of lithium-rich materials, and then analyzes the electrochemical mechanism and internal causes which affect the electrochemical performance of lithium-rich materials. Furthermore, recent material modification strategies are discussed with regards to the current challenges. In addition, current methods and developmental trends of modification strategies such as bulk doping, surface coating, defect design, ion exchange and microstructure regulation are summarized in detail. According to the different charge properties, the doping modification can be divided into cationic doping, anion doping and anion-cation co-doping. Among them, cationic doping can be further categorized into transition metal layer doping substitution and lithium layer doping substitution, depending on the doping site. Two tables for the doping and ion exchange modifications were tabulated, and the representative scientific research was summarized. Recent research conducted on hotspot high-entropy materials were also mentioned. Finally, design ideas for high-capacity, long-cycle layered lithium-rich materials and high specific energy lithium-ion batteries were prospected. This comprehensive review is expected to promote further lithium-rich oxide materials research.
2023, 39(7): 221104
doi: 10.3866/PKU.WHXB202211043
Abstract:
Recently, two-dimensional (2D) metal-organic framework (MOF) nanosheet-based composites have been extensively investigated as promising materials for biomedical applications, including antibacterial applications. This study reports the synthesis of silver nanoparticle (Ag NP)-modified 2D Zr-ferrocene-MOF (MOF-Ag) nanosheets by growing Ag NPs on 2D MOF nanosheets via light irradiation-induced reduction for photothermally enhanced silver ion (Ag+) release antibacterial treatment. The MOF nanosheets were synthesized by a hydrothermal method followed by ultrasonic treatment. Subsequently, Ag NPs were grown on the MOF nanosheets to obtain MOF-Ag nanosheets by in situ light irradiation-induced reduction. Various characterization results, including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS), showed that Ag NPs were successfully loaded onto the surface of the MOF nanosheets. Fourier transform infrared (FTIR) spectroscopy further confirmed the successful modification of the MOF-Ag surface with polyvinylpyrrolidone (PVP). The modification with of PVP not only enhanced the stability of MOF-Ag in solution, but also enhanced its biocompatibility. Under 808 nm near-infrared laser (NIR) irradiation, the MOF nanosheets exhibited good photothermal properties and photothermal conversion efficiency. The temperature increase induced by the photothermal effect accelerates the oxidation of Ag NPs to Ag+, and thus MOF-Ag continuously releases silver ions to kill bacteria. It was concluded that PVP-functionalized MOF-Ag (PVP@MOF-Ag) nanosheets have good antibacterial properties using experimental analyses such as bacterial growth curves, relative number of colonies, and morphological changes of bacteria. PVP@MOF-Ag nanosheets not only kills S. aureus but also inhibits E. coli growth more efficiently, exhibiting broad-spectrum bactericidal properties. Additionally, the good photothermal performance of the 2D MOF nanosheets enhanced Ag+ release and cell membrane permeability. Ag NPs release Ag+ in solution via an oxidation mechanism, and the released Ag+ is more likely to enter the bacteria via the cell membrane under light conditions. In bacteria, Ag+ induces the generation of endogenous reactive oxygen species to trigger oxidative stress, thus realizing efficient antibacterial performance. Based on the above-mentioned antibacterial mechanism and good in vitro antibacterial properties, the PVP@MOF-Ag nanosheets were used for wound healing in mice. By developing a mouse wound healing model and treating mouse wounds within a week, it was observed that PVP@MOF-Ag nanosheets have a good therapeutic effect and good biosafety during treatment. These results demonstrate that PVP@MOF-Ag nanosheets are an efficient platform for photothermally enhanced Ag+ release antibacterial therapy and wound healing. ![]()
Recently, two-dimensional (2D) metal-organic framework (MOF) nanosheet-based composites have been extensively investigated as promising materials for biomedical applications, including antibacterial applications. This study reports the synthesis of silver nanoparticle (Ag NP)-modified 2D Zr-ferrocene-MOF (MOF-Ag) nanosheets by growing Ag NPs on 2D MOF nanosheets via light irradiation-induced reduction for photothermally enhanced silver ion (Ag+) release antibacterial treatment. The MOF nanosheets were synthesized by a hydrothermal method followed by ultrasonic treatment. Subsequently, Ag NPs were grown on the MOF nanosheets to obtain MOF-Ag nanosheets by in situ light irradiation-induced reduction. Various characterization results, including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS), showed that Ag NPs were successfully loaded onto the surface of the MOF nanosheets. Fourier transform infrared (FTIR) spectroscopy further confirmed the successful modification of the MOF-Ag surface with polyvinylpyrrolidone (PVP). The modification with of PVP not only enhanced the stability of MOF-Ag in solution, but also enhanced its biocompatibility. Under 808 nm near-infrared laser (NIR) irradiation, the MOF nanosheets exhibited good photothermal properties and photothermal conversion efficiency. The temperature increase induced by the photothermal effect accelerates the oxidation of Ag NPs to Ag+, and thus MOF-Ag continuously releases silver ions to kill bacteria. It was concluded that PVP-functionalized MOF-Ag (PVP@MOF-Ag) nanosheets have good antibacterial properties using experimental analyses such as bacterial growth curves, relative number of colonies, and morphological changes of bacteria. PVP@MOF-Ag nanosheets not only kills S. aureus but also inhibits E. coli growth more efficiently, exhibiting broad-spectrum bactericidal properties. Additionally, the good photothermal performance of the 2D MOF nanosheets enhanced Ag+ release and cell membrane permeability. Ag NPs release Ag+ in solution via an oxidation mechanism, and the released Ag+ is more likely to enter the bacteria via the cell membrane under light conditions. In bacteria, Ag+ induces the generation of endogenous reactive oxygen species to trigger oxidative stress, thus realizing efficient antibacterial performance. Based on the above-mentioned antibacterial mechanism and good in vitro antibacterial properties, the PVP@MOF-Ag nanosheets were used for wound healing in mice. By developing a mouse wound healing model and treating mouse wounds within a week, it was observed that PVP@MOF-Ag nanosheets have a good therapeutic effect and good biosafety during treatment. These results demonstrate that PVP@MOF-Ag nanosheets are an efficient platform for photothermally enhanced Ag+ release antibacterial therapy and wound healing.
2023, 39(7): 221202
doi: 10.3866/PKU.WHXB202212028
Abstract:
All-fiber functional devices are superior to conventional optical crystals for next-generation integrated optics owing to their natural compatibility with optical fiber systems. Nonlinear optical fiber devices play an important role in frequency conversion and optical parametric amplification. However, optical fibers are unsuitable for all-optical systems owing to the intrinsic properties of pure quartz. Optical second harmonic generation (SHG), which is significant in practical optical applications, is theoretically forbidden in traditional centrosymmetric non-crystalline fused silica fibers. Consequently, generating giant second-order optical processes in optical fibers remains challenging. Many studies have attempted to artificially break the centrosymmetry of fused silica fibers using various poling techniques, such as thermal or electric field poling, which can enhance the second-order nonlinear optical susceptibility. However, these methods require difficult and complicated fabrication processes, and the corresponding hybrid optical fibers exhibit an inefficient harmonic generation process, which greatly increases the cost and limits the development of all-fiber nonlinear functionalization. Therefore, there is an urgent need for new fabrication methods and technical means for functionalizing optical fiber devices that can improve the second-order nonlinear effect while remaining simple and practical. Herein, we propose an improved solution-filling method that can effectively deposit highly nonlinear GaSe nanoflakes directly on the inner walls of hollow-core fibers (HCF) with a length of up to half a meter. In addition, the as-fabricated hollow-core fiber integrated with GaSe nanoflakes (GaSe-HCF) is used to demonstrate that the second-order nonlinear effect of the optical fiber is enhanced by the ultrahigh nonlinear effect of the GaSe materials. Compared to previously reported MoS2-embedded hollow-core fibers (MoS2-HCF) and conventional optical fibers, the SHG of the GaSe-HCF is three and two orders of magnitude stronger than that of bare HCF and MoS2-HCF, respectively. A GaSe-HCF with a length of up to half a meter was successfully prepared using the new filling method and exhibited good expansibility. The pressure process was exploited by adding a short length of air column to effectively fill the HCF with the highly nonlinear GaSe suspension, and expand the applicability of this method. Our results will provide a novel and highly efficient strategy to manufacture nonlinear optical fibers integrated with other nanomaterials and can be used to fabricate new all-fiber devices with strongly enhanced second-order nonlinear optical processes, thus broadening nonlinear optics and optoelectronics applications. ![]()
All-fiber functional devices are superior to conventional optical crystals for next-generation integrated optics owing to their natural compatibility with optical fiber systems. Nonlinear optical fiber devices play an important role in frequency conversion and optical parametric amplification. However, optical fibers are unsuitable for all-optical systems owing to the intrinsic properties of pure quartz. Optical second harmonic generation (SHG), which is significant in practical optical applications, is theoretically forbidden in traditional centrosymmetric non-crystalline fused silica fibers. Consequently, generating giant second-order optical processes in optical fibers remains challenging. Many studies have attempted to artificially break the centrosymmetry of fused silica fibers using various poling techniques, such as thermal or electric field poling, which can enhance the second-order nonlinear optical susceptibility. However, these methods require difficult and complicated fabrication processes, and the corresponding hybrid optical fibers exhibit an inefficient harmonic generation process, which greatly increases the cost and limits the development of all-fiber nonlinear functionalization. Therefore, there is an urgent need for new fabrication methods and technical means for functionalizing optical fiber devices that can improve the second-order nonlinear effect while remaining simple and practical. Herein, we propose an improved solution-filling method that can effectively deposit highly nonlinear GaSe nanoflakes directly on the inner walls of hollow-core fibers (HCF) with a length of up to half a meter. In addition, the as-fabricated hollow-core fiber integrated with GaSe nanoflakes (GaSe-HCF) is used to demonstrate that the second-order nonlinear effect of the optical fiber is enhanced by the ultrahigh nonlinear effect of the GaSe materials. Compared to previously reported MoS2-embedded hollow-core fibers (MoS2-HCF) and conventional optical fibers, the SHG of the GaSe-HCF is three and two orders of magnitude stronger than that of bare HCF and MoS2-HCF, respectively. A GaSe-HCF with a length of up to half a meter was successfully prepared using the new filling method and exhibited good expansibility. The pressure process was exploited by adding a short length of air column to effectively fill the HCF with the highly nonlinear GaSe suspension, and expand the applicability of this method. Our results will provide a novel and highly efficient strategy to manufacture nonlinear optical fibers integrated with other nanomaterials and can be used to fabricate new all-fiber devices with strongly enhanced second-order nonlinear optical processes, thus broadening nonlinear optics and optoelectronics applications.
2023, 39(7): 221204
doi: 10.3866/PKU.WHXB202212043
Abstract:
Lignocellulose utilization has the unique feature of net-zero carbon emissions. Thus, the utilization of lignocellulose as a renewable alternative to fossil-based carbon resources is one of the most promising strategies to achieve "carbon neutrality". Lignin has been recognized as the most abundant aromatic biopolymer on Earth; hence, it could be the most promising alternative to fossil-based aromatics. The efficient dissolution of lignin is crucial for lignin upgrading, which relies on the design of innovative and robust solvents. Herein, we designed several biomass-derived acidic deep eutectic solvents (DESs) using choline chloride, betaine, and L-carnitine as hydrogen bond acceptors (HBAs), and four protic compounds as hydrogen bond donors (HBDs), namely, oxalic acid, benzoic acid, ethyl gallate, and 5-methoxysalicylic acid. The designed DESs can dissolve different types of lignin, including alkali lignin (AL), dealkaline lignin (DAL), enzymatic hydrolysis lignin (EHL), and Kraft lignin (KL). Lignin dissolution was found to be affected by the relative contents of three phenylpropanoid monomers in lignin: syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units. More S and fewer H units in lignin could result in higher solubility. G-, S-, and H-type structural units were found in EHL, while AL, KL, and DAL had only G-type structural units. Therefore, EHL could be more easily dissolved than AL, KL, and DAL in the most developed DESs. The hydroxyl group content of the four lignin samples had a significant impact on lignin dissolution. AL (1.98 mmol·g−1) and EHL (1.93 mmol·g−1) had much higher contents of phenolic hydroxyl groups than DAL (0.62 mmol·g−1), implying that AL and EHL had higher polarity than DAL. This resulted in different dissolution behaviors in different DESs with varying polarities. However, the sulfonate groups afforded KL with much higher polarity, thus resulting in the special dissolution behavior of KL. It is to be noted that not all cases of dissolving lignin in the developed DESs conformed to the above rules. Therefore, it is necessary to further explore the effect of the properties of the DESs on the dissolution of different lignins. Choline chloride was the preferred HBA to construct DESs with good performance and adaptability to lignin dissolution, whereas suitable acidity enabled benzoic acid and ethyl gallate to be favorable HBDs. Systematic investigation revealed that an efficient DES for lignin dissolution should possess stronger hydrogen-bonding acidity (α > 0.95) and appropriate polarity matching with the dissolved lignin. In addition, the pKa value of the HBD and the acidity of the DESs were also efficient indices for estimating the performance of an acidic DES in dissolving lignin, and the pKa value and acidity could be well correlated with the polarity. Generally, HBDs (e.g., BA and EG in this study) with moderate pKa values can be employed to construct robust DESs to dissolve lignin with satisfactory solubility. Additionally, the viscosity of the DESs should have an impact on lignin dissolution, and a lower viscosity is helpful for dissolving lignin. Therefore, the better performance of the developed ChCl-based DESs than the Betaine- and L-Carnitine-based DESs was partially because of the lower viscosity of the ChCl-based DESs. ![]()
Lignocellulose utilization has the unique feature of net-zero carbon emissions. Thus, the utilization of lignocellulose as a renewable alternative to fossil-based carbon resources is one of the most promising strategies to achieve "carbon neutrality". Lignin has been recognized as the most abundant aromatic biopolymer on Earth; hence, it could be the most promising alternative to fossil-based aromatics. The efficient dissolution of lignin is crucial for lignin upgrading, which relies on the design of innovative and robust solvents. Herein, we designed several biomass-derived acidic deep eutectic solvents (DESs) using choline chloride, betaine, and L-carnitine as hydrogen bond acceptors (HBAs), and four protic compounds as hydrogen bond donors (HBDs), namely, oxalic acid, benzoic acid, ethyl gallate, and 5-methoxysalicylic acid. The designed DESs can dissolve different types of lignin, including alkali lignin (AL), dealkaline lignin (DAL), enzymatic hydrolysis lignin (EHL), and Kraft lignin (KL). Lignin dissolution was found to be affected by the relative contents of three phenylpropanoid monomers in lignin: syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units. More S and fewer H units in lignin could result in higher solubility. G-, S-, and H-type structural units were found in EHL, while AL, KL, and DAL had only G-type structural units. Therefore, EHL could be more easily dissolved than AL, KL, and DAL in the most developed DESs. The hydroxyl group content of the four lignin samples had a significant impact on lignin dissolution. AL (1.98 mmol·g−1) and EHL (1.93 mmol·g−1) had much higher contents of phenolic hydroxyl groups than DAL (0.62 mmol·g−1), implying that AL and EHL had higher polarity than DAL. This resulted in different dissolution behaviors in different DESs with varying polarities. However, the sulfonate groups afforded KL with much higher polarity, thus resulting in the special dissolution behavior of KL. It is to be noted that not all cases of dissolving lignin in the developed DESs conformed to the above rules. Therefore, it is necessary to further explore the effect of the properties of the DESs on the dissolution of different lignins. Choline chloride was the preferred HBA to construct DESs with good performance and adaptability to lignin dissolution, whereas suitable acidity enabled benzoic acid and ethyl gallate to be favorable HBDs. Systematic investigation revealed that an efficient DES for lignin dissolution should possess stronger hydrogen-bonding acidity (α > 0.95) and appropriate polarity matching with the dissolved lignin. In addition, the pKa value of the HBD and the acidity of the DESs were also efficient indices for estimating the performance of an acidic DES in dissolving lignin, and the pKa value and acidity could be well correlated with the polarity. Generally, HBDs (e.g., BA and EG in this study) with moderate pKa values can be employed to construct robust DESs to dissolve lignin with satisfactory solubility. Additionally, the viscosity of the DESs should have an impact on lignin dissolution, and a lower viscosity is helpful for dissolving lignin. Therefore, the better performance of the developed ChCl-based DESs than the Betaine- and L-Carnitine-based DESs was partially because of the lower viscosity of the ChCl-based DESs.
2023, 39(7): 221200
doi: 10.3866/PKU.WHXB202212006
Abstract:
Owing to the advantages of broad absorption, semitransparency, and large-area solution processing, organic solar cells based on a nonfullerene blend system have attracted wide attention and become an important aspect of clean energy. At present, the power conversion efficiency of organic solar cells based on nonfullerene blends is more than 19% because of the molecular design, device structure optimization, and morphology regulation. Organic solar cells consist of a cathode, an anode, the corresponding interface layers, and the active layer. Research shows that the morphology of the active layer has significant influence on the device performance. For example, the phase separation structure affects the charge transport, exciton diffusion efficiency is dependent on the domain sizes of the donor and acceptor, crystallinity has a considerable impact on photon absorption and carrier mobility, and molecular orientation affects the dissociation of the charge-transfer state and carrier mobility. Owing to the rigidity of conjugated molecules, the coupling of crystallization between the donor and acceptor always occurs during the film-forming and/or post-annealing processes. Moreover, crystallization and phase separation are inclined to occur simultaneously, leading to poor morphology control. Although many methods, such as post-annealing, solution-state, solvent or solid additive, and solvent engineering, have been exploited, forming the ideal structure morphology of the active layer is still difficult. This is particularly challenging in nonfullerene blends owing to the asymmetric phase separation behavior. This feature article summarizes the recently developed crystallization kinetics strategy in morphology control, which made precise morphology control possible. In this strategy, the interpenetrating network can be constructed by applying modified film-forming kinetics, which inhibits the liquid–liquid phase separation and induces liquid–solid phase separation. The domain size can be reduced by employing sequential crystallization, where the donor and acceptor crystallize in different stages through the combination of the solution-state and post-annealing treatments, surpassing the driving force of phase separation. In addition, the crystallinity of small nonfullerene molecules in the polymer/nonfullerene blends can be effectively enhanced by prioritizing their crystallization. This shift in crystallization priority can reduce the confinement of crystalline framework polymers and benefit the diffusion of the small nonfullerene molecules. Moreover, the ordered stacking of molecules in crystals can be improved by regulating the matching degree between the crystal nucleation rate and growth rate. Molecular orientation can be regulated by combining the motion scale and heterogeneous nucleation. The optimized morphology is beneficial to device performance as it suppresses exciton quenching, recombination of the charge-transfer state, and bimolecular recombination and improves charge mobility, thereby laying the foundation for high-performance organic solar cells.![]()
Owing to the advantages of broad absorption, semitransparency, and large-area solution processing, organic solar cells based on a nonfullerene blend system have attracted wide attention and become an important aspect of clean energy. At present, the power conversion efficiency of organic solar cells based on nonfullerene blends is more than 19% because of the molecular design, device structure optimization, and morphology regulation. Organic solar cells consist of a cathode, an anode, the corresponding interface layers, and the active layer. Research shows that the morphology of the active layer has significant influence on the device performance. For example, the phase separation structure affects the charge transport, exciton diffusion efficiency is dependent on the domain sizes of the donor and acceptor, crystallinity has a considerable impact on photon absorption and carrier mobility, and molecular orientation affects the dissociation of the charge-transfer state and carrier mobility. Owing to the rigidity of conjugated molecules, the coupling of crystallization between the donor and acceptor always occurs during the film-forming and/or post-annealing processes. Moreover, crystallization and phase separation are inclined to occur simultaneously, leading to poor morphology control. Although many methods, such as post-annealing, solution-state, solvent or solid additive, and solvent engineering, have been exploited, forming the ideal structure morphology of the active layer is still difficult. This is particularly challenging in nonfullerene blends owing to the asymmetric phase separation behavior. This feature article summarizes the recently developed crystallization kinetics strategy in morphology control, which made precise morphology control possible. In this strategy, the interpenetrating network can be constructed by applying modified film-forming kinetics, which inhibits the liquid–liquid phase separation and induces liquid–solid phase separation. The domain size can be reduced by employing sequential crystallization, where the donor and acceptor crystallize in different stages through the combination of the solution-state and post-annealing treatments, surpassing the driving force of phase separation. In addition, the crystallinity of small nonfullerene molecules in the polymer/nonfullerene blends can be effectively enhanced by prioritizing their crystallization. This shift in crystallization priority can reduce the confinement of crystalline framework polymers and benefit the diffusion of the small nonfullerene molecules. Moreover, the ordered stacking of molecules in crystals can be improved by regulating the matching degree between the crystal nucleation rate and growth rate. Molecular orientation can be regulated by combining the motion scale and heterogeneous nucleation. The optimized morphology is beneficial to device performance as it suppresses exciton quenching, recombination of the charge-transfer state, and bimolecular recombination and improves charge mobility, thereby laying the foundation for high-performance organic solar cells.
2023, 39(7): 221206
doi: 10.3866/PKU.WHXB202212061
Abstract:
Enantioselective catalysis is ubiquitous in biological organisms and closely related to biological production and metabolism. The design and development of nanozymes with high enantioselectivities are essential for various bio-related applications. Currently, investigations of nanozymes are primarily focused on their catalytic activity. However, the enantioselectivity of nanozymes, a significant feature, has been rarely studied. In view of the few reports related to enantioselective catalysis, nanozymes have mainly been constructed with chiral molecule-modified nanoparticles. Because the selectivity of natural enzymes not only depends on the molecular chirality of chiral species, such as amino acids, but is also closely related to the chiral supramolecular microenvironment generated by the spatial arrangement and folding of proteins, the construction of active chiral substances with chiral supramolecular microenvironment for nanozymes is also an effective way to design nanozymes with excellent enantioselectivities. Additionally, to improve the enantioselectivity, an understanding of the influencing parameters for select factor of chiral nanozymes is essential. Herein, we report the successful construction of nanocomposites composed of supramolecular M-polyaniline (M-PANI) twisted nanoribbons assembled without any chiral molecules, and Au nanoparticles (NPs) of three different sizes (3, 10, and 16 nm). The characterization results from scanning electron microscopy, transmission electron microscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful fabrication of M-PANI-Au nanocomposites. The evident signals in the circular dichroism spectra of the M-PANI-Au nanocomposites indicated their potential as chiral nanozymes. Considering the catalytic oxidation of chiral R-/S-3, 4-dihydroxyphenylalanine (R-/S-DOPA) enantiomers as a model reaction, the three M-PANI supported Au NPs demonstrated higher catalytic selectivity for R-DOPA than for S-DOPA, as confirmed by the kinetic absorption curves, revealing the high potential of M-PANI-Au nanocomposites as enantioselective nanozymes. Interestingly, according to the kinetic assay study, the M-PANI nanocomposite with 3 nm Au NPs had a higher selection factor (2.59) than those of 10 nm Au NPs (1.46) and 16 nm Au NPs (1.58), which could be attributed to the strongest chirality transfer effect from the supramolecular chiral PANI to 3 nm Au NPs. Therefore, chirality transfer from chiral supramolecular scaffolds to nanozymes is a key factor influencing the enantioselective catalysis and can provide direct guidance for the future design and construction of chiral supramolecular nanozymes with high enantioselectivities.![]()
Enantioselective catalysis is ubiquitous in biological organisms and closely related to biological production and metabolism. The design and development of nanozymes with high enantioselectivities are essential for various bio-related applications. Currently, investigations of nanozymes are primarily focused on their catalytic activity. However, the enantioselectivity of nanozymes, a significant feature, has been rarely studied. In view of the few reports related to enantioselective catalysis, nanozymes have mainly been constructed with chiral molecule-modified nanoparticles. Because the selectivity of natural enzymes not only depends on the molecular chirality of chiral species, such as amino acids, but is also closely related to the chiral supramolecular microenvironment generated by the spatial arrangement and folding of proteins, the construction of active chiral substances with chiral supramolecular microenvironment for nanozymes is also an effective way to design nanozymes with excellent enantioselectivities. Additionally, to improve the enantioselectivity, an understanding of the influencing parameters for select factor of chiral nanozymes is essential. Herein, we report the successful construction of nanocomposites composed of supramolecular M-polyaniline (M-PANI) twisted nanoribbons assembled without any chiral molecules, and Au nanoparticles (NPs) of three different sizes (3, 10, and 16 nm). The characterization results from scanning electron microscopy, transmission electron microscopy, UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful fabrication of M-PANI-Au nanocomposites. The evident signals in the circular dichroism spectra of the M-PANI-Au nanocomposites indicated their potential as chiral nanozymes. Considering the catalytic oxidation of chiral R-/S-3, 4-dihydroxyphenylalanine (R-/S-DOPA) enantiomers as a model reaction, the three M-PANI supported Au NPs demonstrated higher catalytic selectivity for R-DOPA than for S-DOPA, as confirmed by the kinetic absorption curves, revealing the high potential of M-PANI-Au nanocomposites as enantioselective nanozymes. Interestingly, according to the kinetic assay study, the M-PANI nanocomposite with 3 nm Au NPs had a higher selection factor (2.59) than those of 10 nm Au NPs (1.46) and 16 nm Au NPs (1.58), which could be attributed to the strongest chirality transfer effect from the supramolecular chiral PANI to 3 nm Au NPs. Therefore, chirality transfer from chiral supramolecular scaffolds to nanozymes is a key factor influencing the enantioselective catalysis and can provide direct guidance for the future design and construction of chiral supramolecular nanozymes with high enantioselectivities.
