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2023 Volume 39 Issue 12
2023, 39(12): 221203
doi: 10.3866/PKU.WHXB202212039
Abstract:
Bacterial infections cause various serious diseases including tuberculosis, meningitis, and cellulitis. Moreover, there is an increase in the number of drug-resistant bacterial strains, which has caused a global health issue. Thus, it is highly essential to develop more effective antibacterial agents. Currently, zinc oxide (ZnO) is commonly used as an inorganic antibacterial agent, but with a notable limit in efficiency. In this work, to improve ZnO antibacterial activity under visible light, bismuth oxyiodide (BiOI) with a narrow bandgap of 1.8 eV was used as a suitable refinement to ZnO. Four different BiOI/ZnO nanocomposites were designed and synthesized via a simple mechanical stirring method in an atmospheric environment; these were denoted as BiOI/ZnO-2.5%, BiOI/ZnO-5%, BiOI/ZnO-10%, and BiOI/ZnO-20%. The successful synthesis of the BiOI/ZnO nanocomposites was verified through X-ray powder diffraction, energy-dispersive X-ray analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A unique BiOI/ZnO heterojunction was also observed for the nanocomposites through high-resolution TEM, XPS, and selected area electron diffraction. Ultraviolet-visible diffuse reflectance spectroscopy revealed that all four BiOI/ZnO nanocomposites exhibited improved visible light absorption and possessed narrower bandgaps than the ZnO nanoparticles (nano-ZnO). Furthermore, the antibacterial activities of all BiOI/ZnO nanocomposites were investigated under visible light against both gram-positive and gram-negative bacteria strains. The results indicated a significant improvement in the antibacterial activities of BiOI/ZnO-10% and BiOI/ZnO-20% against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Strong light exposure was found to be attributable to an increase in the antibacterial activity against S. aureus. In addition, the antibacterial mechanistic investigation was conducted upon visible light activation. The SEM images showed completely broken bacterial cell walls for both bacteria strains after treatment with the BiOI/ZnO nanocomposites. Hydroxyl radicals (•OH), which are strong reactive oxygen species, generated by the BiOI/ZnO nanocomposites under visible light, were also trapped by 5,5-dimethyl-1-pyrroline-N-oxide. Furthermore, zeta potential analysis revealed the presence of more positively charged BiOI/ZnO nanocomposite surfaces than the surfaces of nano-ZnO. The metal ions released from the BiOI/ZnO nanocomposites under visible light were also studied through inductively coupled plasma mass spectrometry. Based on the above results, BiOI/ZnO nanocomposites were found to exhibit antibacterial mechanism similar to that of nano-ZnO. In the dark, E. coli growth was only inhibited by Zn2+ released from both BiOI/ZnO nanocomposites and pure nano-ZnO. After visible light activation, •OH generated from the BiOI/ZnO nanocomposites mainly contributed to the bacterial cell death of both E. coli and S. aureus. This study proposes an effective strategy to enhance the antibacterial activity of nano-ZnO under visible light upon the formation of nanocomposites with BiOI. Besides, this study indicates that the ZnO-based nanocomposites can be used as a more effective antibacterial agent in clinical applications. ![]()
Bacterial infections cause various serious diseases including tuberculosis, meningitis, and cellulitis. Moreover, there is an increase in the number of drug-resistant bacterial strains, which has caused a global health issue. Thus, it is highly essential to develop more effective antibacterial agents. Currently, zinc oxide (ZnO) is commonly used as an inorganic antibacterial agent, but with a notable limit in efficiency. In this work, to improve ZnO antibacterial activity under visible light, bismuth oxyiodide (BiOI) with a narrow bandgap of 1.8 eV was used as a suitable refinement to ZnO. Four different BiOI/ZnO nanocomposites were designed and synthesized via a simple mechanical stirring method in an atmospheric environment; these were denoted as BiOI/ZnO-2.5%, BiOI/ZnO-5%, BiOI/ZnO-10%, and BiOI/ZnO-20%. The successful synthesis of the BiOI/ZnO nanocomposites was verified through X-ray powder diffraction, energy-dispersive X-ray analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). A unique BiOI/ZnO heterojunction was also observed for the nanocomposites through high-resolution TEM, XPS, and selected area electron diffraction. Ultraviolet-visible diffuse reflectance spectroscopy revealed that all four BiOI/ZnO nanocomposites exhibited improved visible light absorption and possessed narrower bandgaps than the ZnO nanoparticles (nano-ZnO). Furthermore, the antibacterial activities of all BiOI/ZnO nanocomposites were investigated under visible light against both gram-positive and gram-negative bacteria strains. The results indicated a significant improvement in the antibacterial activities of BiOI/ZnO-10% and BiOI/ZnO-20% against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Strong light exposure was found to be attributable to an increase in the antibacterial activity against S. aureus. In addition, the antibacterial mechanistic investigation was conducted upon visible light activation. The SEM images showed completely broken bacterial cell walls for both bacteria strains after treatment with the BiOI/ZnO nanocomposites. Hydroxyl radicals (•OH), which are strong reactive oxygen species, generated by the BiOI/ZnO nanocomposites under visible light, were also trapped by 5,5-dimethyl-1-pyrroline-N-oxide. Furthermore, zeta potential analysis revealed the presence of more positively charged BiOI/ZnO nanocomposite surfaces than the surfaces of nano-ZnO. The metal ions released from the BiOI/ZnO nanocomposites under visible light were also studied through inductively coupled plasma mass spectrometry. Based on the above results, BiOI/ZnO nanocomposites were found to exhibit antibacterial mechanism similar to that of nano-ZnO. In the dark, E. coli growth was only inhibited by Zn2+ released from both BiOI/ZnO nanocomposites and pure nano-ZnO. After visible light activation, •OH generated from the BiOI/ZnO nanocomposites mainly contributed to the bacterial cell death of both E. coli and S. aureus. This study proposes an effective strategy to enhance the antibacterial activity of nano-ZnO under visible light upon the formation of nanocomposites with BiOI. Besides, this study indicates that the ZnO-based nanocomposites can be used as a more effective antibacterial agent in clinical applications.
2023, 39(12): 221206
doi: 10.3866/PKU.WHXB202212064
Abstract:
In recent years, gold nanoclusters have been widely used in catalysis, and alloying has become one of the most important methods for improving the catalytic performance of gold nanoclusters. As for the electrocatalytic reduction of CO2 (CO2RR), although many gold nanoclusters show fairly good Faraday efficiencies through Cd-doping, they still exhibit low current density. Furthermore, as an increasing number of Au-Cd alloy nanoclusters are reported, there is a growing interest in understanding the correlation between Cd coordination and catalysis performance. In most cases, Cd atoms are typically doped in the outer staples and connect with Au atoms through S coordinations. Are there any other unreported Cd coordination modes? Can novel or numerous Cd coordination modes be introduced into gold nanoclusters to increase the current density in the CO2RR? This study investigates these questions.Inspired by our previous work on surface sulfur doping, we employed a combined doping (S + Cd doping) strategy, developed a two-step synthesis method, and successfully synthesized a novel Au-Cd nanocluster—Au41Cd6S2(SCH2Ph)33. Precise formula and structure were determined by electrospray ionization mass spectrometry (ESI-MS), thermalgravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and single-crystal X-ray crystallography (SCXC). SCXC shows that the nanocluster contains a biicosahedral Au23 kernel, and all the Cd atoms are doped in the outer staples, providing a variety of coordination environments for Cd atoms. In addition to two common Au3(SR)4 trimers in the outer staples, two unusual Au5Cd2(SR)9S long staples were discovered cross-covering the top of the kernel, and a (S-Au-S)2(CdS-S-CdS) tetramer staple with two Cd atoms directly linked through S was also discovered for the first time. This alloy cluster shows robust stability in both high-temperature and oxidation environments. Compared with the "homo-kernel-hetero-staples" nanocluster Au38(SCH2Ph)24, Au41Cd6S2(SCH2Ph)33 exhibits distinct UV-Vis/NIR absorption and differential pulse voltammetry (DPV) results, indicating that the differences in the outer staples have a significant effect on the optical and electronic properties of gold nanoclusters. When used as an electrocatalyst, the Au41Cd6S2(SCH2Ph)33 exhibits a higher Faradaic efficiency for the CO2RR (99.3% at −0.7 V) and a higher CO partial current density (120 mA∙cm−2 at −0.9 V) than Au38(SCH2Ph)24, providing an ideal platform for investigating the roles of different Cd coordination modes in outer staples on CO2RR. DFT calculations interpret the experimental finding that Cd doping improves the catalytic performance and reveal that the Cd-Cd site is the most active site and the Au-Cd site furthest away from the kernel is the best-performing catalytic site given the consideration of both selectivity and activity.This work introduces a novel strategy to enhance the catalytic performance of gold nanoclusters, having important implications for future research on the syntheses and structural properties of metal nanoclusters, and is expected to inspire more work in related areas. ![]()
In recent years, gold nanoclusters have been widely used in catalysis, and alloying has become one of the most important methods for improving the catalytic performance of gold nanoclusters. As for the electrocatalytic reduction of CO2 (CO2RR), although many gold nanoclusters show fairly good Faraday efficiencies through Cd-doping, they still exhibit low current density. Furthermore, as an increasing number of Au-Cd alloy nanoclusters are reported, there is a growing interest in understanding the correlation between Cd coordination and catalysis performance. In most cases, Cd atoms are typically doped in the outer staples and connect with Au atoms through S coordinations. Are there any other unreported Cd coordination modes? Can novel or numerous Cd coordination modes be introduced into gold nanoclusters to increase the current density in the CO2RR? This study investigates these questions.Inspired by our previous work on surface sulfur doping, we employed a combined doping (S + Cd doping) strategy, developed a two-step synthesis method, and successfully synthesized a novel Au-Cd nanocluster—Au41Cd6S2(SCH2Ph)33. Precise formula and structure were determined by electrospray ionization mass spectrometry (ESI-MS), thermalgravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and single-crystal X-ray crystallography (SCXC). SCXC shows that the nanocluster contains a biicosahedral Au23 kernel, and all the Cd atoms are doped in the outer staples, providing a variety of coordination environments for Cd atoms. In addition to two common Au3(SR)4 trimers in the outer staples, two unusual Au5Cd2(SR)9S long staples were discovered cross-covering the top of the kernel, and a (S-Au-S)2(CdS-S-CdS) tetramer staple with two Cd atoms directly linked through S was also discovered for the first time. This alloy cluster shows robust stability in both high-temperature and oxidation environments. Compared with the "homo-kernel-hetero-staples" nanocluster Au38(SCH2Ph)24, Au41Cd6S2(SCH2Ph)33 exhibits distinct UV-Vis/NIR absorption and differential pulse voltammetry (DPV) results, indicating that the differences in the outer staples have a significant effect on the optical and electronic properties of gold nanoclusters. When used as an electrocatalyst, the Au41Cd6S2(SCH2Ph)33 exhibits a higher Faradaic efficiency for the CO2RR (99.3% at −0.7 V) and a higher CO partial current density (120 mA∙cm−2 at −0.9 V) than Au38(SCH2Ph)24, providing an ideal platform for investigating the roles of different Cd coordination modes in outer staples on CO2RR. DFT calculations interpret the experimental finding that Cd doping improves the catalytic performance and reveal that the Cd-Cd site is the most active site and the Au-Cd site furthest away from the kernel is the best-performing catalytic site given the consideration of both selectivity and activity.This work introduces a novel strategy to enhance the catalytic performance of gold nanoclusters, having important implications for future research on the syntheses and structural properties of metal nanoclusters, and is expected to inspire more work in related areas.
2023, 39(12): 230103
doi: 10.3866/PKU.WHXB202301032
Abstract:
Fossil fuel depletion and environmental deterioration have created an urgent need to develop renewable and clean energy. Biomass, a sustainable organic carbon source, can meet the huge demand for energy and chemicals. Among them, 5-hydroxymethylfurfural (HMF) is an important biomass-derived platform molecule, which can be converted into various high-value chemicals. One of its oxidation products, 2,5-furandicarboxylic acid (FDCA), is expected to replace terephthalic acid as a raw material for the synthesis of bio-based degradable plastics. The electrooxidation of HMF emerges as a promising green route for preparing FDCA due to its advantages of mild conditions, fast reaction rate, and high selectivity. The theoretical potential of the HMF electrooxidation reaction (HMFOR, 0.3 V vs. reversible hydrogen electrode, RHE) is also lower than that of the oxygen evolution reaction (OER, 1.23 V vs. RHE). Coupling anodic HMFOR with cathodic hydrogen evolution reaction (HER) is expected to simultaneously produce valuable FDCA and reduce the cell voltage of hydrogen (H2) evolution. However, the construction of efficient and stable bifunctional catalysts for HMFOR-assisted H2 production is still challenging. In this study, Co-doped Ni-Mo-O porous nanorods grown on a nickel foam (Co-NiMoO/NF) is prepared by simple hydrothermal and calcination methods for both HMFOR and HER. Results of electrocatalytic studies indicate that Co-NiMoO/NF exhibits enhanced performance for HMFOR (E10/100 = 1.31/1.37 V vs. RHE) and HER (E−10/−100 = −35/−123 mV vs. RHE) and shows durable HMFOR/HER stability. In particular, Co-NiMoO/NF maintains high FDCA selectivity (~99.2%) and Faradaic efficiency (~95.7%) for 40 successive cycles at 1.36 V vs. RHE for HMFOR. Conversely, Co-NiMoO/NF maintains stable operation at −200 mA∙cm−2 for 50 h with no significant activity attenuation for HER. When coupled as a bifunctional electrode for overall HMF splitting, Co-NiMoO/NF reaches an electric flux of 50 mA∙cm−2 at 1.48 V, which is 290 mV lower than that of the overall water splitting. This confirms that the HMFOR-assisted H2 production over Co-NiMoO/NF significantly reduces the energy consumption. Moreover, the two-electrode system maintains good FDCA selectivity (97.6%) for 10 cycles at 1.45 V, implying good stability of HMFOR-assisted H2 evolution. The remarkable catalytic performance of Co-NiMoO/NF could be due to the introduction of Co, which optimizes the electronic structure of Ni-Mo-O and adsorption behaviors of the reactants, thereby enhancing the intrinsic activity and stability of the catalyst. Meanwhile, the porous nanorod structure enhanced the mass transport of substrates and desorption of bubbles, thereby elevating the HMFOR/HER kinetics. This study provides useful insights for designing efficient and durable bifunctional catalysts for HMFOR and HER. ![]()
Fossil fuel depletion and environmental deterioration have created an urgent need to develop renewable and clean energy. Biomass, a sustainable organic carbon source, can meet the huge demand for energy and chemicals. Among them, 5-hydroxymethylfurfural (HMF) is an important biomass-derived platform molecule, which can be converted into various high-value chemicals. One of its oxidation products, 2,5-furandicarboxylic acid (FDCA), is expected to replace terephthalic acid as a raw material for the synthesis of bio-based degradable plastics. The electrooxidation of HMF emerges as a promising green route for preparing FDCA due to its advantages of mild conditions, fast reaction rate, and high selectivity. The theoretical potential of the HMF electrooxidation reaction (HMFOR, 0.3 V vs. reversible hydrogen electrode, RHE) is also lower than that of the oxygen evolution reaction (OER, 1.23 V vs. RHE). Coupling anodic HMFOR with cathodic hydrogen evolution reaction (HER) is expected to simultaneously produce valuable FDCA and reduce the cell voltage of hydrogen (H2) evolution. However, the construction of efficient and stable bifunctional catalysts for HMFOR-assisted H2 production is still challenging. In this study, Co-doped Ni-Mo-O porous nanorods grown on a nickel foam (Co-NiMoO/NF) is prepared by simple hydrothermal and calcination methods for both HMFOR and HER. Results of electrocatalytic studies indicate that Co-NiMoO/NF exhibits enhanced performance for HMFOR (E10/100 = 1.31/1.37 V vs. RHE) and HER (E−10/−100 = −35/−123 mV vs. RHE) and shows durable HMFOR/HER stability. In particular, Co-NiMoO/NF maintains high FDCA selectivity (~99.2%) and Faradaic efficiency (~95.7%) for 40 successive cycles at 1.36 V vs. RHE for HMFOR. Conversely, Co-NiMoO/NF maintains stable operation at −200 mA∙cm−2 for 50 h with no significant activity attenuation for HER. When coupled as a bifunctional electrode for overall HMF splitting, Co-NiMoO/NF reaches an electric flux of 50 mA∙cm−2 at 1.48 V, which is 290 mV lower than that of the overall water splitting. This confirms that the HMFOR-assisted H2 production over Co-NiMoO/NF significantly reduces the energy consumption. Moreover, the two-electrode system maintains good FDCA selectivity (97.6%) for 10 cycles at 1.45 V, implying good stability of HMFOR-assisted H2 evolution. The remarkable catalytic performance of Co-NiMoO/NF could be due to the introduction of Co, which optimizes the electronic structure of Ni-Mo-O and adsorption behaviors of the reactants, thereby enhancing the intrinsic activity and stability of the catalyst. Meanwhile, the porous nanorod structure enhanced the mass transport of substrates and desorption of bubbles, thereby elevating the HMFOR/HER kinetics. This study provides useful insights for designing efficient and durable bifunctional catalysts for HMFOR and HER.
2023, 39(12): 230104
doi: 10.3866/PKU.WHXB202301041
Abstract:
Bio-stimuli-responsive microspheres, which can encapsulate and release actives in response to physiological triggers, have attracted increasing attention in pharmaceutical, cosmetic, food biotechnology, and agricultural industries. However, most microspheres are based on synthetic polymers and suffer from a lack of biocompatibility due to the residues of harsh organic solvents or crosslinkers used in the synthesis process. Herein, we develop a simple and sustainable method for the construction of proteinaceous microspheres templated from Pickering double emulsions. Specifically, silica nanoparticles with a diameter of 100 nm were synthesized by Stöber method and modified by reacting with dichlorodimethylsilane. The Pickering emulsions are stabilized by hydrophobic silica nanoparticles, while zein protein is dissolved in the middle phase. Subsequent ethanol removal from the emulsion template precipitated the protein skeleton. First, we stained the aqueous ethanol phase with rhodamine B and the oil phase with pyrene to demonstrate the formation of double emulsions by confocal laser scanning microscopy (CLSM). The morphology of microspheres and silica nanoparticles was characterized by scanning electron microscopy (SEM). The obtained microspheres showed high sphericity and uniformity. In addition to acting as particulate stabilizers, the silica nanoparticles could improve the mechanical strength and monodispersity of microspheres. Herein, fluorescein isothiocyanate (FITC)-labeled dextran was chosen as the model active for encapsulation into microspheres. The CLSM images showed that it was uniformly dispersed in the microspheres and had no effect on the structure of the microspheres. Next, we investigated the pH tolerance of the microspheres. Through optical microscope, it was noted that the structure was intact under pH 3–11, and thus, it has a high resistance. Finally, we investigated the bio-stimuli-responsive behavior of microspheres. Zein is rich in sulfur-containing amino acids, which can form intra- and inter-molecular disulfide bonds. Because disulfide bonds can be reduced by glutathione (GSH) and the protein itself has enzymatic hydrolysis characteristics, the proteinaceous microspheres can be triggered release in response to GSH and protease. The release profiles of FITC-dextran from microspheres at different concentrations of GSH and protease were evaluated by fluorescence spectrophotometer. The decomposition behavior of microspheres under certain concentrations of GSH and protease was further verified by CLSM and SEM. To conclude, excellent stability and tunability of emulsion templates render the resulting proteinaceous microspheres with adjustable structures. Meanwhile, the proteinaceous microspheres have high encapsulation efficiency of model actives and have shown excellent bio-stimuli-responsiveness to protease and glutathione. ![]()
Bio-stimuli-responsive microspheres, which can encapsulate and release actives in response to physiological triggers, have attracted increasing attention in pharmaceutical, cosmetic, food biotechnology, and agricultural industries. However, most microspheres are based on synthetic polymers and suffer from a lack of biocompatibility due to the residues of harsh organic solvents or crosslinkers used in the synthesis process. Herein, we develop a simple and sustainable method for the construction of proteinaceous microspheres templated from Pickering double emulsions. Specifically, silica nanoparticles with a diameter of 100 nm were synthesized by Stöber method and modified by reacting with dichlorodimethylsilane. The Pickering emulsions are stabilized by hydrophobic silica nanoparticles, while zein protein is dissolved in the middle phase. Subsequent ethanol removal from the emulsion template precipitated the protein skeleton. First, we stained the aqueous ethanol phase with rhodamine B and the oil phase with pyrene to demonstrate the formation of double emulsions by confocal laser scanning microscopy (CLSM). The morphology of microspheres and silica nanoparticles was characterized by scanning electron microscopy (SEM). The obtained microspheres showed high sphericity and uniformity. In addition to acting as particulate stabilizers, the silica nanoparticles could improve the mechanical strength and monodispersity of microspheres. Herein, fluorescein isothiocyanate (FITC)-labeled dextran was chosen as the model active for encapsulation into microspheres. The CLSM images showed that it was uniformly dispersed in the microspheres and had no effect on the structure of the microspheres. Next, we investigated the pH tolerance of the microspheres. Through optical microscope, it was noted that the structure was intact under pH 3–11, and thus, it has a high resistance. Finally, we investigated the bio-stimuli-responsive behavior of microspheres. Zein is rich in sulfur-containing amino acids, which can form intra- and inter-molecular disulfide bonds. Because disulfide bonds can be reduced by glutathione (GSH) and the protein itself has enzymatic hydrolysis characteristics, the proteinaceous microspheres can be triggered release in response to GSH and protease. The release profiles of FITC-dextran from microspheres at different concentrations of GSH and protease were evaluated by fluorescence spectrophotometer. The decomposition behavior of microspheres under certain concentrations of GSH and protease was further verified by CLSM and SEM. To conclude, excellent stability and tunability of emulsion templates render the resulting proteinaceous microspheres with adjustable structures. Meanwhile, the proteinaceous microspheres have high encapsulation efficiency of model actives and have shown excellent bio-stimuli-responsiveness to protease and glutathione.
2023, 39(12): 230204
doi: 10.3866/PKU.WHXB202302041
Abstract:
With the increasing number of automobile vehicles, the exhaust emitted poses a severe menace to the environment and human health, necessitating the purification of exhaust pollutants. Meanwhile, the high price of noble metals and their limited supply require a decrease in noble metal loading to reduce the costs of three-way catalysts (TWCs). Therefore, improving the utilization efficiency of noble metals and their catalytic behavior is critical for the development of next-generation TWCs with low noble metal loading. Herein, the Rh micro-chemical state was modulated using the liquid-phase reduction method combined with atmospheric heat treatment to enhance the catalytic behavior of Rh-based catalysts with low Rh loading. The catalyst was characterized using X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), CO chemisorption, X-ray photoelectron spectroscopy (XPS), the FTIR spectroscopy of chemisorbed CO (CO-FTIR), transmission electron microscopy (TEM), and in situ diffuse reflectance IR (in-situ DRIFTS) to illustrate the relationship between Rh micro-chemical state (including valence state ratio and dispersion) and catalytic activity. The as-prepared catalyst re-Rh/CeO2-ZrO2-Al2O3-H2 (re-Rh/CZA-H2) exhibited better catalytic activity and a wider air/fuel ratio (λ) operating window with T90 values 30–73 ℃ and 51–86 ℃ lower than those of the catalysts synthesized by liquid-phase reduction and traditional impregnation method, respectively. In addition, aged samples prepared by the combined scheme also exhibited excellent activity and stability, where the T50 and T90 values were lower than the fresh catalyst. Structure-activity relationship results demonstrated that the better catalytic activity of re-Rh/CZA-H2 could be attributed to the optimal valence state ratio and highly dispersed Rh species, which increased the number of effective active sites. The considerable stability was attributed to the stable structure of the CeO2-ZrO2-Al2O3 (CZA) support, improved dispersion, and the high contents of active Rh species, which exposed more active sites to promote reactant conversion. In addition, the synergistic effect between the metallic Rh and oxygen vacancies could facilitate the anchoring of Rh nanoparticles to inhibit Rh sintering. Therefore, adjusting the micro-chemical state of noble metals by the combinatorial scheme developed herein provides a novel route for improving the catalytic activity, high-temperature stability, and air/fuel operating window of these catalysts. ![]()
With the increasing number of automobile vehicles, the exhaust emitted poses a severe menace to the environment and human health, necessitating the purification of exhaust pollutants. Meanwhile, the high price of noble metals and their limited supply require a decrease in noble metal loading to reduce the costs of three-way catalysts (TWCs). Therefore, improving the utilization efficiency of noble metals and their catalytic behavior is critical for the development of next-generation TWCs with low noble metal loading. Herein, the Rh micro-chemical state was modulated using the liquid-phase reduction method combined with atmospheric heat treatment to enhance the catalytic behavior of Rh-based catalysts with low Rh loading. The catalyst was characterized using X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), CO chemisorption, X-ray photoelectron spectroscopy (XPS), the FTIR spectroscopy of chemisorbed CO (CO-FTIR), transmission electron microscopy (TEM), and in situ diffuse reflectance IR (in-situ DRIFTS) to illustrate the relationship between Rh micro-chemical state (including valence state ratio and dispersion) and catalytic activity. The as-prepared catalyst re-Rh/CeO2-ZrO2-Al2O3-H2 (re-Rh/CZA-H2) exhibited better catalytic activity and a wider air/fuel ratio (λ) operating window with T90 values 30–73 ℃ and 51–86 ℃ lower than those of the catalysts synthesized by liquid-phase reduction and traditional impregnation method, respectively. In addition, aged samples prepared by the combined scheme also exhibited excellent activity and stability, where the T50 and T90 values were lower than the fresh catalyst. Structure-activity relationship results demonstrated that the better catalytic activity of re-Rh/CZA-H2 could be attributed to the optimal valence state ratio and highly dispersed Rh species, which increased the number of effective active sites. The considerable stability was attributed to the stable structure of the CeO2-ZrO2-Al2O3 (CZA) support, improved dispersion, and the high contents of active Rh species, which exposed more active sites to promote reactant conversion. In addition, the synergistic effect between the metallic Rh and oxygen vacancies could facilitate the anchoring of Rh nanoparticles to inhibit Rh sintering. Therefore, adjusting the micro-chemical state of noble metals by the combinatorial scheme developed herein provides a novel route for improving the catalytic activity, high-temperature stability, and air/fuel operating window of these catalysts.
2023, 39(12): 230205
doi: 10.3866/PKU.WHXB202302051
Abstract:
Rapid intrinsic carrier recombination severely restricts the photocatalytic activity of CeO2-based catalytic materials. In this study, a heterogeneous interfacial engineering strategy is proposed to rationally perform interface modulation. A 2D/3D S-scheme heterojunction with strong electronic interactions was constructed. A composite photocatalyst was synthesized for the 3D Cu2O particles anchored at the edge of 2D CeO2. First-principles calculations (based on density functional theory) and the experimental results show that a strongly coupled S-scheme heterojunction electron transport interface is formed between CeO2 and Cu2O, resulting in efficient carrier separation and transfer. The photocatalytic hydrogen evolution activity of the composite catalyst is significantly improved in the system with triethanolamine as the sacrificial agent and is 48 times as that of CeO2. In addition, the resulting CeO2-Cu2O photocatalyst affords highly stable photocatalytic hydrogen activity. This provides a general technique for constructing unique interfaces in novel nanocomposite structures. ![]()
Rapid intrinsic carrier recombination severely restricts the photocatalytic activity of CeO2-based catalytic materials. In this study, a heterogeneous interfacial engineering strategy is proposed to rationally perform interface modulation. A 2D/3D S-scheme heterojunction with strong electronic interactions was constructed. A composite photocatalyst was synthesized for the 3D Cu2O particles anchored at the edge of 2D CeO2. First-principles calculations (based on density functional theory) and the experimental results show that a strongly coupled S-scheme heterojunction electron transport interface is formed between CeO2 and Cu2O, resulting in efficient carrier separation and transfer. The photocatalytic hydrogen evolution activity of the composite catalyst is significantly improved in the system with triethanolamine as the sacrificial agent and is 48 times as that of CeO2. In addition, the resulting CeO2-Cu2O photocatalyst affords highly stable photocatalytic hydrogen activity. This provides a general technique for constructing unique interfaces in novel nanocomposite structures.
2023, 39(12): 230302
doi: 10.3866/PKU.WHXB202303028
Abstract:
'Green hydrogen' is a promising clean energy carrier for use instead of traditional fuels. For obtaining 'green hydrogen', electrochemical water splitting has been receiving considerable attention due to its eco-friendly and low-cost properties. However, the sluggish kinetics of the anodic oxygen evolution reaction (OER) reduces the efficiency of hydrogen production. Accordingly, the hydrazine oxidation reaction (HzOR) with low theoretical potential (−0.33 V vs. RHE) has been proposed as a reasonable alternative for the OER. In this study, graphene aerogel (GA) was utilized as a conductive substrate with a 3D porous framework. RuⅢ-polyethyleneimine (RuⅢ-PEI) complexes were adsorbed on the GA surface. Phytic acid (PA) was further adsorbed to form RuⅢ-PEI-GA-PA hybrids through the hydrogen bond interaction between PA and PEI, which can serve as a precursor to synthesize RuP nanoparticles anchored on N-doped GA (RuP/N-GA) through the phosphorization reaction. In the pyrolysis process, the ultra-small RuP was formed at the GA surface. Additionally, the decomposition of PEI and PA can introduce abundant N and P heteroatoms into the structure of GA. As a result, RuP/N-GA hybrids achieve efficient HzOR with a low working potential of −54 mV at 10 mA∙cm−2. Moreover, the novel RuP/N-GA hybrids with low Ru loading also exhibit a promising hydrogen evolution reaction (HER) activity with an overpotential of −19.6 mV at 10 mA∙cm−2. Among various RuP/N-GA hybrids, the Tafel plot of HER at RuP/N-GA-900 reveals the smallest value to be 37.03 mV∙dec−1, which affords the fastest HER kinetics. Meanwhile, the result suggests that the HER at RuP/N-GA-900 undergoes a Heyrovsky mechanism similar to that of Pt. The theoretical results revealed that the anchored structure and the presence of N heteroatoms can promote the HzOR on RuP nanoparticles. The free energy of hydrazine molecular adsorption on RuP/N-GA was −0.68 eV, indicating that N-doping in the RuP/N-GA structure can adjust the electronic structure of the Ru active site, which also contributes to the enhanced HzOR activity of the Ru site. Additionally, RuP/N-GA hybrids exhibited excellent cycling and long-term stability for both HER and HzOR, superior to those of commercial Pt/C. Based on the bifunctional activity of RuP/N-GA hybrids, the constructed two-electrode hydrazine split system exhibits an extremely low cell voltage of 41 mV at 10 mA∙cm−2 for the hydrogen production, which achieves the goal of energy-saved hydrogen production at low voltage. The excellent electrocatalytic activity of RuP/N-GA hybrids is attributed to the ultrasmall RuP nanoparticles for abundant Ru active sites. Meanwhile, the synergistic effect between N-doping in GA frameworks with RuP nanoparticles contributes to the activity enhancement of RuP/N-GA hybrids, in which the 3D porous N-GA with few-layer morphology accelerates the electron and mass transfer and the electron interaction between N-GA and RuP nanoparticles promotes the electrocatalytic activity of RuP nanoparticles for both HER and HzOR. This study extends the bifunctional electrocatalyst for the HER and HzOR to achieve energy-saved hydrogen production and sheds new light on the design and synthesis of advanced electrocatalysts via the adsorption-phosphatization method. ![]()
'Green hydrogen' is a promising clean energy carrier for use instead of traditional fuels. For obtaining 'green hydrogen', electrochemical water splitting has been receiving considerable attention due to its eco-friendly and low-cost properties. However, the sluggish kinetics of the anodic oxygen evolution reaction (OER) reduces the efficiency of hydrogen production. Accordingly, the hydrazine oxidation reaction (HzOR) with low theoretical potential (−0.33 V vs. RHE) has been proposed as a reasonable alternative for the OER. In this study, graphene aerogel (GA) was utilized as a conductive substrate with a 3D porous framework. RuⅢ-polyethyleneimine (RuⅢ-PEI) complexes were adsorbed on the GA surface. Phytic acid (PA) was further adsorbed to form RuⅢ-PEI-GA-PA hybrids through the hydrogen bond interaction between PA and PEI, which can serve as a precursor to synthesize RuP nanoparticles anchored on N-doped GA (RuP/N-GA) through the phosphorization reaction. In the pyrolysis process, the ultra-small RuP was formed at the GA surface. Additionally, the decomposition of PEI and PA can introduce abundant N and P heteroatoms into the structure of GA. As a result, RuP/N-GA hybrids achieve efficient HzOR with a low working potential of −54 mV at 10 mA∙cm−2. Moreover, the novel RuP/N-GA hybrids with low Ru loading also exhibit a promising hydrogen evolution reaction (HER) activity with an overpotential of −19.6 mV at 10 mA∙cm−2. Among various RuP/N-GA hybrids, the Tafel plot of HER at RuP/N-GA-900 reveals the smallest value to be 37.03 mV∙dec−1, which affords the fastest HER kinetics. Meanwhile, the result suggests that the HER at RuP/N-GA-900 undergoes a Heyrovsky mechanism similar to that of Pt. The theoretical results revealed that the anchored structure and the presence of N heteroatoms can promote the HzOR on RuP nanoparticles. The free energy of hydrazine molecular adsorption on RuP/N-GA was −0.68 eV, indicating that N-doping in the RuP/N-GA structure can adjust the electronic structure of the Ru active site, which also contributes to the enhanced HzOR activity of the Ru site. Additionally, RuP/N-GA hybrids exhibited excellent cycling and long-term stability for both HER and HzOR, superior to those of commercial Pt/C. Based on the bifunctional activity of RuP/N-GA hybrids, the constructed two-electrode hydrazine split system exhibits an extremely low cell voltage of 41 mV at 10 mA∙cm−2 for the hydrogen production, which achieves the goal of energy-saved hydrogen production at low voltage. The excellent electrocatalytic activity of RuP/N-GA hybrids is attributed to the ultrasmall RuP nanoparticles for abundant Ru active sites. Meanwhile, the synergistic effect between N-doping in GA frameworks with RuP nanoparticles contributes to the activity enhancement of RuP/N-GA hybrids, in which the 3D porous N-GA with few-layer morphology accelerates the electron and mass transfer and the electron interaction between N-GA and RuP nanoparticles promotes the electrocatalytic activity of RuP nanoparticles for both HER and HzOR. This study extends the bifunctional electrocatalyst for the HER and HzOR to achieve energy-saved hydrogen production and sheds new light on the design and synthesis of advanced electrocatalysts via the adsorption-phosphatization method.
2023, 39(12): 230100
doi: 10.3866/PKU.WHXB202301009
Abstract:
The development of energy storage technologies with high safety, low cost, and high energy densities is essential for the widespread use of renewable energy sources. Battery technology is one of the most promising candidates because of its pollution-free operation, high round-trip efficiency, flexible power and energy characteristics, long cycle life, and low maintenance cost. Although most batteries operate at room temperature, high-temperature systems are expected to perform better owing to improved electrolyte conductivity, faster reaction kinetics, and reduced interface impedance. The reported high-temperature batteries can be classified into liquid and solid electrolyte-based systems, with the latter having the potential to achieve higher energy densities while avoiding self-discharge effects. This review summarizes solid electrolyte-based liquid sodium and lithium batteries (SELS and SELL batteries). SELS batteries primarily use beta-Al2O3 and NASICON electrolytes, while SELL battery systems use garnet electrolytes. Because the microstructures and compositions of ceramic electrolytes significantly affect their conductivity and stability, novel manufacturing and element doping methods are being intensively investigated. Surface modification technology is also a major research focus to improve the wetting properties of molten alkali metals on the ceramic electrolyte, which assists to decrease interfacial resistance and increase the rate performance and power density of the battery. In addition, the selection of the cathode materials of SELS and SELL batteries has a significant impact on the energy and power densities, cycling stability, material cost, and application scenarios of the real devices. Until now, lead alloys, metal chlorides, sulfur, selenium, and iodine have been reported as potential choices. We describe in detail the reaction mechanisms, existing problems, and the latest research progress of these battery systems, with their electrochemical performance and raw material costs systematically summarized and compared. It is worth noting that the SELS and SELL batteries have different levels of technological maturity. In 2019, an energy storage system using SELS batteries with a capacity of 108 MW/648 MWh was built, whereas SELL battery research is a relatively emerging field. However, SELL batteries demonstrate promising application prospects because of their higher energy densities, lower operating temperatures, and competitive raw material costs. In addition, we believe that several research advancements and technical achievements related to these two types of batteries can be shared, with the future research directions listed in the conclusion section.![]()
The development of energy storage technologies with high safety, low cost, and high energy densities is essential for the widespread use of renewable energy sources. Battery technology is one of the most promising candidates because of its pollution-free operation, high round-trip efficiency, flexible power and energy characteristics, long cycle life, and low maintenance cost. Although most batteries operate at room temperature, high-temperature systems are expected to perform better owing to improved electrolyte conductivity, faster reaction kinetics, and reduced interface impedance. The reported high-temperature batteries can be classified into liquid and solid electrolyte-based systems, with the latter having the potential to achieve higher energy densities while avoiding self-discharge effects. This review summarizes solid electrolyte-based liquid sodium and lithium batteries (SELS and SELL batteries). SELS batteries primarily use beta-Al2O3 and NASICON electrolytes, while SELL battery systems use garnet electrolytes. Because the microstructures and compositions of ceramic electrolytes significantly affect their conductivity and stability, novel manufacturing and element doping methods are being intensively investigated. Surface modification technology is also a major research focus to improve the wetting properties of molten alkali metals on the ceramic electrolyte, which assists to decrease interfacial resistance and increase the rate performance and power density of the battery. In addition, the selection of the cathode materials of SELS and SELL batteries has a significant impact on the energy and power densities, cycling stability, material cost, and application scenarios of the real devices. Until now, lead alloys, metal chlorides, sulfur, selenium, and iodine have been reported as potential choices. We describe in detail the reaction mechanisms, existing problems, and the latest research progress of these battery systems, with their electrochemical performance and raw material costs systematically summarized and compared. It is worth noting that the SELS and SELL batteries have different levels of technological maturity. In 2019, an energy storage system using SELS batteries with a capacity of 108 MW/648 MWh was built, whereas SELL battery research is a relatively emerging field. However, SELL batteries demonstrate promising application prospects because of their higher energy densities, lower operating temperatures, and competitive raw material costs. In addition, we believe that several research advancements and technical achievements related to these two types of batteries can be shared, with the future research directions listed in the conclusion section.
2023, 39(12): 230203
doi: 10.3866/PKU.WHXB202302037
Abstract:
Human activities primarily rely on the consumption of the fossil energy, which has led to an energy crisis and environmental pollution. Since the industrial revolution, the atmospheric CO2 concentration has been continuously increasing, and reached 414 × 10−6 in 2020, which has resulted in global warming and glacial ablation. Converting CO2 into high-value-added fuels and chemicals can alleviate environmental problems, enable the storage of intermittent renewable energy (wind and solar power), and provide a new route for fuel synthesis. The electrochemical CO2 reduction reaction (CO2RR) has attracted extensive attention owing to its mild reaction conditions, controllability, environmental friendliness, and the ability to generate various products. There are four key steps in a typical CO2RR: (1) charge transport (electrons are transported from the conductive substrate to the electrocatalyst); (2) surface conversion (CO2 is adsorbed and activated on the surface of the catalyst); (3) charge transfer (electrons are transferred from the catalyst surface to the CO2 intermediate); and (4) mass transfer (CO2 diffuses from the electrolyte to the catalyst surface, and the products diffuse in the reverse pathway). The former two steps depend on the type of membrane and the development of highly conductive catalysts with abundant active sites, while the latter two steps rely on the properties of the electrolyte and the optimization of the electrolytic cell configuration. To meet the high-selectivity (> 90%), superior-activity (> 200 mA·cm−2), and excellent-stability (> 1000 h) requirements of the CO2RR as per industrial standards, the design of efficient electrocatalysts has been a key research area in recent decades. However, other factors have rarely been investigated. In this review, we systematically summarize the development of electrocatalysts, effect of the electrolyte, progress in the development of the reactor, and type of membrane in the CO2RR from industrial and commercial perspectives. First, we discuss how first-principles calculations can be used to determine the chemical rate for CO2 reduction. Additionally, we discuss how in situ or operando techniques such as X-ray absorption measurements can reveal the theoretically proposed reaction pathway. The microenvironment (e.g., pH, anions, and cations) at the three-phase interface plays a vital role in achieving a high CO2RR performance, which can be controlled by changing the electrolyte properties. Further, the suitable design and development of the reactor is very critical for commercial CO2RR technology because CO2RR reactors must efficiently utilize the CO2 feedstock to minimize the cost of upstream CO2 capture. Finally, different types of membranes based on different ion-transfer mechanisms can affect the CO2RR performance. The development opportunities and challenges toward the practical application of the CO2RR are also highlighted.![]()
Human activities primarily rely on the consumption of the fossil energy, which has led to an energy crisis and environmental pollution. Since the industrial revolution, the atmospheric CO2 concentration has been continuously increasing, and reached 414 × 10−6 in 2020, which has resulted in global warming and glacial ablation. Converting CO2 into high-value-added fuels and chemicals can alleviate environmental problems, enable the storage of intermittent renewable energy (wind and solar power), and provide a new route for fuel synthesis. The electrochemical CO2 reduction reaction (CO2RR) has attracted extensive attention owing to its mild reaction conditions, controllability, environmental friendliness, and the ability to generate various products. There are four key steps in a typical CO2RR: (1) charge transport (electrons are transported from the conductive substrate to the electrocatalyst); (2) surface conversion (CO2 is adsorbed and activated on the surface of the catalyst); (3) charge transfer (electrons are transferred from the catalyst surface to the CO2 intermediate); and (4) mass transfer (CO2 diffuses from the electrolyte to the catalyst surface, and the products diffuse in the reverse pathway). The former two steps depend on the type of membrane and the development of highly conductive catalysts with abundant active sites, while the latter two steps rely on the properties of the electrolyte and the optimization of the electrolytic cell configuration. To meet the high-selectivity (> 90%), superior-activity (> 200 mA·cm−2), and excellent-stability (> 1000 h) requirements of the CO2RR as per industrial standards, the design of efficient electrocatalysts has been a key research area in recent decades. However, other factors have rarely been investigated. In this review, we systematically summarize the development of electrocatalysts, effect of the electrolyte, progress in the development of the reactor, and type of membrane in the CO2RR from industrial and commercial perspectives. First, we discuss how first-principles calculations can be used to determine the chemical rate for CO2 reduction. Additionally, we discuss how in situ or operando techniques such as X-ray absorption measurements can reveal the theoretically proposed reaction pathway. The microenvironment (e.g., pH, anions, and cations) at the three-phase interface plays a vital role in achieving a high CO2RR performance, which can be controlled by changing the electrolyte properties. Further, the suitable design and development of the reactor is very critical for commercial CO2RR technology because CO2RR reactors must efficiently utilize the CO2 feedstock to minimize the cost of upstream CO2 capture. Finally, different types of membranes based on different ion-transfer mechanisms can affect the CO2RR performance. The development opportunities and challenges toward the practical application of the CO2RR are also highlighted.
2023, 39(12): 230204
doi: 10.3866/PKU.WHXB202302049
Abstract:
With the continuous consumption of non-renewable energy and increasing exacerbation in associated environmental problems, there is a growing demand for clean renewable energy. This demand has led to the development of many energy conversion technologies to alleviate the energy crisis and related environmental problems. The development of high-efficiency electrocatalysts is crucial for the progress of renewable energy conversion and storage technologies. Over the past decade, researchers have gradually understood the intrinsic reaction mechanism and structure-performance relationships in electrocatalysis, and made significant progress in synthesizing high-performance electrocatalysts. Detailed analysis of the relationship between the intrinsic activity and electronic structure of active sites, including the deeper levels of electronic spin distribution of catalyst active sites, has been the focus of electrocatalysis research. Spin is an inherent property of particles and can have a unique impact on chemical reactions. Therefore, using electron spin to further study the electronic structure of active sites is expected to bring new development opportunities to catalyst design theory. Spin control in electrocatalysts is undoubtedly an effective method to improve catalytic performance. This review article introduces the progress status of electron spin in electrocatalysis, summarizes the common strategies for controlling electron spin at the active sites in electrocatalysis, and expound the mechanism of spin effect in electrocatalysis from both thermodynamic and kinetic aspects. Further, the article reviews the latest research progress concerning the spin effect on several reactions such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), nitrogen reduction reaction (NRR) and carbon dioxide reduction reaction (CO2RR). It explains the important role of spin in catalyst activity and catalyst promotion of the aforementioned reactions, and then discusses the spin stability of the catalyst active sites in ORR. In addition, the article reviews the advanced methods widely used for characterizing electron spin in electrocatalysis, such as vibrating sample magnetometry, electron paramagnetic resonance spectroscopy, Mossbauer spectroscopy, and X-ray spectroscopy, and discusses the first-principle calculation methods employed in spin catalysis. Finally, the article summarizes the current development of spin electronics in electrocatalysis and proposes future development directions regarding the spin effect in electrocatalysis. In summary, understanding the role of spin effect is instrumental for improving the understanding of the mechanism of electrocatalytic reaction, and can guide the design of high-efficiency catalysts, which has broad research prospects. This review presents for the first time a comprehensive summary of the latest research progress on the spin effect in the field of electrocatalysis, which provides theoretical guidance for the design of spin-regulated high-efficiency electrocatalysts.![]()
With the continuous consumption of non-renewable energy and increasing exacerbation in associated environmental problems, there is a growing demand for clean renewable energy. This demand has led to the development of many energy conversion technologies to alleviate the energy crisis and related environmental problems. The development of high-efficiency electrocatalysts is crucial for the progress of renewable energy conversion and storage technologies. Over the past decade, researchers have gradually understood the intrinsic reaction mechanism and structure-performance relationships in electrocatalysis, and made significant progress in synthesizing high-performance electrocatalysts. Detailed analysis of the relationship between the intrinsic activity and electronic structure of active sites, including the deeper levels of electronic spin distribution of catalyst active sites, has been the focus of electrocatalysis research. Spin is an inherent property of particles and can have a unique impact on chemical reactions. Therefore, using electron spin to further study the electronic structure of active sites is expected to bring new development opportunities to catalyst design theory. Spin control in electrocatalysts is undoubtedly an effective method to improve catalytic performance. This review article introduces the progress status of electron spin in electrocatalysis, summarizes the common strategies for controlling electron spin at the active sites in electrocatalysis, and expound the mechanism of spin effect in electrocatalysis from both thermodynamic and kinetic aspects. Further, the article reviews the latest research progress concerning the spin effect on several reactions such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), nitrogen reduction reaction (NRR) and carbon dioxide reduction reaction (CO2RR). It explains the important role of spin in catalyst activity and catalyst promotion of the aforementioned reactions, and then discusses the spin stability of the catalyst active sites in ORR. In addition, the article reviews the advanced methods widely used for characterizing electron spin in electrocatalysis, such as vibrating sample magnetometry, electron paramagnetic resonance spectroscopy, Mossbauer spectroscopy, and X-ray spectroscopy, and discusses the first-principle calculation methods employed in spin catalysis. Finally, the article summarizes the current development of spin electronics in electrocatalysis and proposes future development directions regarding the spin effect in electrocatalysis. In summary, understanding the role of spin effect is instrumental for improving the understanding of the mechanism of electrocatalytic reaction, and can guide the design of high-efficiency catalysts, which has broad research prospects. This review presents for the first time a comprehensive summary of the latest research progress on the spin effect in the field of electrocatalysis, which provides theoretical guidance for the design of spin-regulated high-efficiency electrocatalysts.
2023, 39(12): 230102
doi: 10.3866/PKU.WHXB202301024
Abstract:
Quasi-two-dimensional (quasi-2D) perovskites are one of the most promising luminescent layer candidates for light-emitting diodes (LEDs) because of their excellent optoelectronic properties such as large exciton binding energy, efficient energy transfer, high photoluminescence quantum yield, and adjustable band gap. However, the formation of a large number of low-dimensional phases and surface/interface defects during solution processing of quasi-two-dimensional perovskite films gives rise to an increase in non-radiative recombination, resulting in deteriorated light-emitting diode performance. It is highly desirable to simultaneously realize low-dimensional phase formation inhibition and surface/interface defect passivation during quasi-two-dimensional perovskite film formation. Herein, we report a multifunctional additive, 1, 6-bis(acryloyloxy)-2, 2, 3, 3, 4, 4, 5, 5-octafluorohexane (OFHDODA), which has strong physical and chemical interactions with the PEA2Cs2Pb3Br10 precursor that can effectively suppress non-radiative recombination in the perovskite films. The distinct C＝C peak in the Fourier transform infrared spectroscopy (FTIR) spectra and the F 1s peak in the X-ray photoelectron spectroscopy (XPS) spectra showed that OFHDODA molecules were successfully incorporated into the perovskite films, and most OFHDODA molecules existed as monomers. With the addition of OFHDODA, the photoluminescence quantum yield (PLQY) of the perovskite film increased from 19.7% to 49.0%, and the PL emission wavelength red-shifted from 508 to 511 nm. It was demonstrated that hydrogen bond interactions between the polyfluorine structure and PEA+ can tune perovskite crystallization dynamics, which inhibit the formation of low-dimensional phases, as shown by the reduced peak intensities at 403 nm (n = 1), 434 nm (n = 2), and 465 nm (n = 3) in the absorption spectra. The strong Lewis base moiety of the ester groups passivates the unsaturated Pb2+ defects at the surface and grain boundaries of the perovskite films, as evidenced by the Pb 4f peak shift in the XPS spectra and the C＝O shift in the FTIR spectra. The trap-filled limiting voltage (VTFL) decreased in both hole-only and electron-only devices, which also proves the reduction of Pb2+ defects. At the optimized OFHDODA concentration, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) results from the perovskite films show lower roughness and smoother surface potential, which promotes superior interfacial contact. As a result, perovskite LEDs with a device structure of indium tin oxide glass/poly (9-vinylcarbazole)/perovskite/1, 3, 5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene/8-hydroxyquinolinolato-lithium/Al exhibited an improved maximum external quantum efficiency (EQE) from 8.55% to 13.76%, improved maximum brightness from 16400 to 17620 cd∙m−2, and increased lifetime from 8 min to 12 min. This process provides an effective way to suppress non-radiative recombination in quasi-2D perovskites via additive molecular structure design, leading to superior electroluminescence performance. ![]()
Quasi-two-dimensional (quasi-2D) perovskites are one of the most promising luminescent layer candidates for light-emitting diodes (LEDs) because of their excellent optoelectronic properties such as large exciton binding energy, efficient energy transfer, high photoluminescence quantum yield, and adjustable band gap. However, the formation of a large number of low-dimensional phases and surface/interface defects during solution processing of quasi-two-dimensional perovskite films gives rise to an increase in non-radiative recombination, resulting in deteriorated light-emitting diode performance. It is highly desirable to simultaneously realize low-dimensional phase formation inhibition and surface/interface defect passivation during quasi-two-dimensional perovskite film formation. Herein, we report a multifunctional additive, 1, 6-bis(acryloyloxy)-2, 2, 3, 3, 4, 4, 5, 5-octafluorohexane (OFHDODA), which has strong physical and chemical interactions with the PEA2Cs2Pb3Br10 precursor that can effectively suppress non-radiative recombination in the perovskite films. The distinct C＝C peak in the Fourier transform infrared spectroscopy (FTIR) spectra and the F 1s peak in the X-ray photoelectron spectroscopy (XPS) spectra showed that OFHDODA molecules were successfully incorporated into the perovskite films, and most OFHDODA molecules existed as monomers. With the addition of OFHDODA, the photoluminescence quantum yield (PLQY) of the perovskite film increased from 19.7% to 49.0%, and the PL emission wavelength red-shifted from 508 to 511 nm. It was demonstrated that hydrogen bond interactions between the polyfluorine structure and PEA+ can tune perovskite crystallization dynamics, which inhibit the formation of low-dimensional phases, as shown by the reduced peak intensities at 403 nm (n = 1), 434 nm (n = 2), and 465 nm (n = 3) in the absorption spectra. The strong Lewis base moiety of the ester groups passivates the unsaturated Pb2+ defects at the surface and grain boundaries of the perovskite films, as evidenced by the Pb 4f peak shift in the XPS spectra and the C＝O shift in the FTIR spectra. The trap-filled limiting voltage (VTFL) decreased in both hole-only and electron-only devices, which also proves the reduction of Pb2+ defects. At the optimized OFHDODA concentration, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) results from the perovskite films show lower roughness and smoother surface potential, which promotes superior interfacial contact. As a result, perovskite LEDs with a device structure of indium tin oxide glass/poly (9-vinylcarbazole)/perovskite/1, 3, 5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene/8-hydroxyquinolinolato-lithium/Al exhibited an improved maximum external quantum efficiency (EQE) from 8.55% to 13.76%, improved maximum brightness from 16400 to 17620 cd∙m−2, and increased lifetime from 8 min to 12 min. This process provides an effective way to suppress non-radiative recombination in quasi-2D perovskites via additive molecular structure design, leading to superior electroluminescence performance.
2023, 39(12): 230103
doi: 10.3866/PKU.WHXB202301033
Abstract:
Photoelectric resistive switching memory (RRAM) is the most promising competitor in the next generation of non-volatile memory (NVM) owing to its miniaturization, integration, and versatility advantages. A low-temperature spin coating method is deployed to synthesize inorganic CsPbBr3 quantum dots (QDs) with green fluorescence. Then, flexible photoelectrical dual-controlled Ag/CsPbBr3 QDs/indium tin oxide (ITO) RRAM devices with high efficiency are prepared, in which the switching behavior is modified by both electric field and light illumination. The as-prepared device demonstrated forming-free bipolar resistive switching behavior in the presence and absence of light. The switching voltages (VSET) show significant reductions compared to the dark condition, and the hysteresis windows considerably increase under illumination. These indicate a higher ON/OFF ratio and lower energy consumption under illumination than in the dark for the Ag/CsPbBr3 QDs /ITO device. The ON/OFF ratio of the Ag/CsPbBr3 QDs /ITO device is about 3.2×103 under illumination, about 24 times higher than that in the dark state. The VSET is 2.88 V, approximately 13.3% lower than the dark state. These results are further confirmed by the resistive switching behavior of the 36 memory cells randomly selected in the Ag/CsPbBr3 QDs /ITO device. Moreover, the devices exhibit good fatigue and retention performance. No noticeable degradation occurre in the high resistance state (HRS) and low resistance state (LRS) even after 500 consecutive cycles. The resistance remain stable for a long retention time exceeding 5000 s. The large ON/OFF ratio, good endurance, and retention properties of the Ag/CsPbBr3 QDs: GO/ITO device are sufficient for a photoelectric regulation NVM device. Based on the double logarithmic fitting curves during the switching process, it is assumed that the device has the same conduction mechanism under dark and illumination conditions, which is dominated by both ohmic behavior and space charge limited current (SCLC) mechanism in the HRS, and only by the ohmic conduction in the LRS. The primary resistive switching mechanism in the Ag/CsPbBr3 QDs/ITO devices is enabled by the formation and rupture of the hybrid conductive filament composed of Br- vacancies and Ag atom owing to both Br- and Ag+ ion migration under an electric field. The main reason for the declining LRS resistance, resulting in the increment of the ON/OFF ratio and VSET of the above devices, is derived from the increasing photocurrent promoted by the decreasing defect density in CsPbBr3 QDs films under illumination. High-efficiency photoelectronic regulatory perovskite materials will improve the development of high-density memory RRAM technology. ![]()
Photoelectric resistive switching memory (RRAM) is the most promising competitor in the next generation of non-volatile memory (NVM) owing to its miniaturization, integration, and versatility advantages. A low-temperature spin coating method is deployed to synthesize inorganic CsPbBr3 quantum dots (QDs) with green fluorescence. Then, flexible photoelectrical dual-controlled Ag/CsPbBr3 QDs/indium tin oxide (ITO) RRAM devices with high efficiency are prepared, in which the switching behavior is modified by both electric field and light illumination. The as-prepared device demonstrated forming-free bipolar resistive switching behavior in the presence and absence of light. The switching voltages (VSET) show significant reductions compared to the dark condition, and the hysteresis windows considerably increase under illumination. These indicate a higher ON/OFF ratio and lower energy consumption under illumination than in the dark for the Ag/CsPbBr3 QDs /ITO device. The ON/OFF ratio of the Ag/CsPbBr3 QDs /ITO device is about 3.2×103 under illumination, about 24 times higher than that in the dark state. The VSET is 2.88 V, approximately 13.3% lower than the dark state. These results are further confirmed by the resistive switching behavior of the 36 memory cells randomly selected in the Ag/CsPbBr3 QDs /ITO device. Moreover, the devices exhibit good fatigue and retention performance. No noticeable degradation occurre in the high resistance state (HRS) and low resistance state (LRS) even after 500 consecutive cycles. The resistance remain stable for a long retention time exceeding 5000 s. The large ON/OFF ratio, good endurance, and retention properties of the Ag/CsPbBr3 QDs: GO/ITO device are sufficient for a photoelectric regulation NVM device. Based on the double logarithmic fitting curves during the switching process, it is assumed that the device has the same conduction mechanism under dark and illumination conditions, which is dominated by both ohmic behavior and space charge limited current (SCLC) mechanism in the HRS, and only by the ohmic conduction in the LRS. The primary resistive switching mechanism in the Ag/CsPbBr3 QDs/ITO devices is enabled by the formation and rupture of the hybrid conductive filament composed of Br- vacancies and Ag atom owing to both Br- and Ag+ ion migration under an electric field. The main reason for the declining LRS resistance, resulting in the increment of the ON/OFF ratio and VSET of the above devices, is derived from the increasing photocurrent promoted by the decreasing defect density in CsPbBr3 QDs films under illumination. High-efficiency photoelectronic regulatory perovskite materials will improve the development of high-density memory RRAM technology.
2023, 39(12): 230103
doi: 10.3866/PKU.WHXB202301034
Abstract:
Antigen tests and nucleic acid detection via the reverse transcription quantitative polymerase chain reaction (RT-qPCR) have been widely used amid the spread of the new coronavirus disease (COVID-19). Despite its superior detection performance, RT-qPCR requires long detection times, expensive professional equipment, and detection personnel. By contrast, antigen tests can produce results within 15 min but often lack in terms of specificity and sensitivity. Therefore, the realization of accurate and rapid detection remains a crucial challenge. In this study, guanidine-modified fluorescent carbon dots (GCDs) were synthesized via a hydrothermal method using o-phenylenediamine and arginine as precursors for the rapid, highly sensitive, and specific detection of nucleic acids. The crude CDs were purified using combined silica gel and neutral alumina column chromatographies until yellow fluorescent GCDs with guanidine-modified edges were obtained. Notably, the yellow fluorescence of the GCDs, with a quantum yield of 9.8%, represents the main detection principle of this study. After incubating the GCDs with a molecular beacon (Bea) for 15 min to create hydrogen-bonded GCD-Bea pairs, a transfer of fluorescence resonance energy was initiated between the GCDs and the ROX fluorescence groups carried by the Bea. During this process, GCDs fluorescence was quenched, thus weakening the fluorescence of the GCD-Bea pairs. When the GCD-Bea pairs encountered target DNA molecules, the Beas and target DNAs underwent base complementary pairing, causing the GCDs and Bea to detach; the latter recovered the self-fluorescence of the GCDs, enabling qualitative detection of the target DNAs in the system. Fluorescence analyses revealed that the fluorescence of the target DNA group was enhanced by more than 20% compared with that of the control group. The entire fluorescence "off-on" DNA detection process described above was accomplished within 5 min, achieving a specificity of 95.45%. Furthermore, the lowest DNA detection concentration in the system was 0.005 fmol∙L−1 (approximately 300 copys∙mL−1), and no acid amplification process was required. More importantly, after replacing the Bea sequence with the DNA sequences of other viruses or diseases, the obtained GCD-Bea pairs could still detect the corresponding target DNAs, confirming their capability of identifying target DNA sequences in a mixed system without the need for nucleic acid extraction. Additionally, compared with the 2–4 h typically required by qPCR, our GCD-Bea system could achieve considerably shortened detection times while also maintaining high specificity and sensitivity after Bea sequence replacements. Collectively, these characteristics are expected to provide a convenient and effective method for the detection of multiple viruses or diseases. ![]()
Antigen tests and nucleic acid detection via the reverse transcription quantitative polymerase chain reaction (RT-qPCR) have been widely used amid the spread of the new coronavirus disease (COVID-19). Despite its superior detection performance, RT-qPCR requires long detection times, expensive professional equipment, and detection personnel. By contrast, antigen tests can produce results within 15 min but often lack in terms of specificity and sensitivity. Therefore, the realization of accurate and rapid detection remains a crucial challenge. In this study, guanidine-modified fluorescent carbon dots (GCDs) were synthesized via a hydrothermal method using o-phenylenediamine and arginine as precursors for the rapid, highly sensitive, and specific detection of nucleic acids. The crude CDs were purified using combined silica gel and neutral alumina column chromatographies until yellow fluorescent GCDs with guanidine-modified edges were obtained. Notably, the yellow fluorescence of the GCDs, with a quantum yield of 9.8%, represents the main detection principle of this study. After incubating the GCDs with a molecular beacon (Bea) for 15 min to create hydrogen-bonded GCD-Bea pairs, a transfer of fluorescence resonance energy was initiated between the GCDs and the ROX fluorescence groups carried by the Bea. During this process, GCDs fluorescence was quenched, thus weakening the fluorescence of the GCD-Bea pairs. When the GCD-Bea pairs encountered target DNA molecules, the Beas and target DNAs underwent base complementary pairing, causing the GCDs and Bea to detach; the latter recovered the self-fluorescence of the GCDs, enabling qualitative detection of the target DNAs in the system. Fluorescence analyses revealed that the fluorescence of the target DNA group was enhanced by more than 20% compared with that of the control group. The entire fluorescence "off-on" DNA detection process described above was accomplished within 5 min, achieving a specificity of 95.45%. Furthermore, the lowest DNA detection concentration in the system was 0.005 fmol∙L−1 (approximately 300 copys∙mL−1), and no acid amplification process was required. More importantly, after replacing the Bea sequence with the DNA sequences of other viruses or diseases, the obtained GCD-Bea pairs could still detect the corresponding target DNAs, confirming their capability of identifying target DNA sequences in a mixed system without the need for nucleic acid extraction. Additionally, compared with the 2–4 h typically required by qPCR, our GCD-Bea system could achieve considerably shortened detection times while also maintaining high specificity and sensitivity after Bea sequence replacements. Collectively, these characteristics are expected to provide a convenient and effective method for the detection of multiple viruses or diseases.
2023, 39(12): 230301
doi: 10.3866/PKU.WHXB202303012
Abstract:
Seawater electrolysis is a promising and sustainable technology for green hydrogen production. However, some disadvantages include sluggish kinetics, competitive chlorine evolution reaction at the anode, chloride ion corrosion, and surface poisoning, which has led to a decline in activity and durability and low oxygen evolution reaction (OER) selectivity of the anodic electrodes. Benefiting from the lower interface resistance, larger active surface, and superior stability, the self-supported nanoarrays have emerged as advanced catalysts compared to conventional powder catalysts. Self-supported catalysts have more advantages than powder catalysts, particularly in practical large-scale hydrogen production applications requiring high current density. During electrolysis, due to the influx of bubbles generated on the electrode surface, the powdered nanomaterial is peeled off easily, resulting in reduced catalytic activity and even frequent replacement of the catalyst. In contrast, self-supported nanoarray possessing strong adhesion between the active species and the substrates ensures good electronic conductivity and high mechanical stability, which is conducive to long-term use and recycling. This minireview summarizes the recent progress of self-supported transition-metal-based catalysts for seawater oxidation, including (oxy)hydroxides, nitrides, phosphides, and chalcogenides, emphasizing the strategies in response to the corrosion and competitive reactions to ensure high activity and selectivity in OER processes. In general, constructing three-dimensional porous nanostructures with high porosity and roughness can enlarge the surface areas to expose more active sites for oxygen evolution, which is an efficient strategy for improving mass transfer and catalytic efficiency. Furthermore, the Cl− barrier layer on the surface of catalyst, particularly that with both catalytic activity and protection, can effectively inhibit the competitive oxidation and corrosion of Cl−, thereby delivering enhanced catalytic activity, selectivity, and stability of the catalysts. Moreover, developing super hydrophilic and hydrophobic surfaces is a promising strategy to increase the permeability of electrolytes and avoid the accumulation of large amounts of bubbles on the surface of the self-supported electrodes, thus promoting the effective utilization of active sites. Finally, perspectives and suggestions for future research in OER catalysts for seawater electrolysis are provided. In particular, the medium for seawater electrolysis should be transferred from simulated saline water to natural seawater. Considering the challenges faced in natural seawater splitting, in addition to designing and synthesizing self-supported catalysts with high activities, selectivity, and stability, developing simple and low-cost natural seawater pretreatment technologies to minimize corrosion and poisoning issues is also an important topic for the future development of seawater electrolysis. More importantly, a standardized, feasible evaluation system for self-supported electrocatalysts should be established. In addition, factors such as the intrinsic activity, density of accessible active sites, size, mass loading, substrate effects, and test conditions of the catalyst should be fully considered.![]()
Seawater electrolysis is a promising and sustainable technology for green hydrogen production. However, some disadvantages include sluggish kinetics, competitive chlorine evolution reaction at the anode, chloride ion corrosion, and surface poisoning, which has led to a decline in activity and durability and low oxygen evolution reaction (OER) selectivity of the anodic electrodes. Benefiting from the lower interface resistance, larger active surface, and superior stability, the self-supported nanoarrays have emerged as advanced catalysts compared to conventional powder catalysts. Self-supported catalysts have more advantages than powder catalysts, particularly in practical large-scale hydrogen production applications requiring high current density. During electrolysis, due to the influx of bubbles generated on the electrode surface, the powdered nanomaterial is peeled off easily, resulting in reduced catalytic activity and even frequent replacement of the catalyst. In contrast, self-supported nanoarray possessing strong adhesion between the active species and the substrates ensures good electronic conductivity and high mechanical stability, which is conducive to long-term use and recycling. This minireview summarizes the recent progress of self-supported transition-metal-based catalysts for seawater oxidation, including (oxy)hydroxides, nitrides, phosphides, and chalcogenides, emphasizing the strategies in response to the corrosion and competitive reactions to ensure high activity and selectivity in OER processes. In general, constructing three-dimensional porous nanostructures with high porosity and roughness can enlarge the surface areas to expose more active sites for oxygen evolution, which is an efficient strategy for improving mass transfer and catalytic efficiency. Furthermore, the Cl− barrier layer on the surface of catalyst, particularly that with both catalytic activity and protection, can effectively inhibit the competitive oxidation and corrosion of Cl−, thereby delivering enhanced catalytic activity, selectivity, and stability of the catalysts. Moreover, developing super hydrophilic and hydrophobic surfaces is a promising strategy to increase the permeability of electrolytes and avoid the accumulation of large amounts of bubbles on the surface of the self-supported electrodes, thus promoting the effective utilization of active sites. Finally, perspectives and suggestions for future research in OER catalysts for seawater electrolysis are provided. In particular, the medium for seawater electrolysis should be transferred from simulated saline water to natural seawater. Considering the challenges faced in natural seawater splitting, in addition to designing and synthesizing self-supported catalysts with high activities, selectivity, and stability, developing simple and low-cost natural seawater pretreatment technologies to minimize corrosion and poisoning issues is also an important topic for the future development of seawater electrolysis. More importantly, a standardized, feasible evaluation system for self-supported electrocatalysts should be established. In addition, factors such as the intrinsic activity, density of accessible active sites, size, mass loading, substrate effects, and test conditions of the catalyst should be fully considered.
