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2024 Volume 40 Issue 1
2024, 40(1): 230204
doi: 10.3866/PKU.WHXB202302044
Abstract:
The GABAA receptor mainly mediates inhibitory signal transmission in mammalian central nervous systems and is the key target of sedative-hypnotics. However, the long-term use of sedative-hypnotics often leads to drug resistance, necessitating the development of novel sedative-hypnotics. This development can be achieved with novel scaffolds designed via the computer-aided drug design methods to obtain significant advantages. In this study, robust virtual screening models were established by identifying effective positive allosteric modulators of the GABAA receptor from ChEMBL and BindingDB databases. These compounds combined with randomly extracted negative compounds were firstly applied for a 10-fold cross validation and grid search to establish machine learning models which were subsequently evaluated in an independent test set. In this step, 4 machine learning methods and 6 fingerprints were used to establish 24 models. In the test set, the CDK_LR model performed the best (MCC = 0.751) and was used for subsequent virtual screening. Two effective molecular docking models were also established based on conformation 6D6T and 6D6U, wherein the root mean square deviation (RMSD) values of redocking experiments were 1.141 and 1.505 Å (1 Å = 0.1 nm), respectively. During the virtual screening, 41112 compounds from a commercial database were scanned by machine learning, molecular docking, and molecular mechanics-generalized Born surface area models. After the screening, 16 hits were obtained, 4 of which were structurally novel positive hits verified by whole-cell patch-clamp electrophysiology experiments. The compound GPR120 was verified experimentally at both the cell and animal levels. In cortical neurons recombinantly expressing α1β2γ2-type receptors, at 10 and 50 µmol∙L−1, GPR120 could potentiate GABA EC3-10 current by 71.5% and 163.8%, respectively. Total decomposition contribution analysis and point mutation experiment showed that the key binding site between GPR120 and the GABAA receptor is H102, similar to that of the positive drug Diazepam. To further verify GPR120 function at the animal level, locomotor activity and loss of righting reflex (LORR) tests were performed. GPR120 inhibited the locomotor activity of mice, which recovered after 6 h, indicating that GPR120 is a moderate sedative. In the pentobarbital sodium-induced righting reflex hour test, GPR120 (20 mg∙kg−1) significantly shortened the time to start LORR and prolonged its duration compared with the saline control group. In summary, using integrated virtual screening methods, GPR120 was identified as a moderate sedative with a novel scaffold. ![]()
The GABAA receptor mainly mediates inhibitory signal transmission in mammalian central nervous systems and is the key target of sedative-hypnotics. However, the long-term use of sedative-hypnotics often leads to drug resistance, necessitating the development of novel sedative-hypnotics. This development can be achieved with novel scaffolds designed via the computer-aided drug design methods to obtain significant advantages. In this study, robust virtual screening models were established by identifying effective positive allosteric modulators of the GABAA receptor from ChEMBL and BindingDB databases. These compounds combined with randomly extracted negative compounds were firstly applied for a 10-fold cross validation and grid search to establish machine learning models which were subsequently evaluated in an independent test set. In this step, 4 machine learning methods and 6 fingerprints were used to establish 24 models. In the test set, the CDK_LR model performed the best (MCC = 0.751) and was used for subsequent virtual screening. Two effective molecular docking models were also established based on conformation 6D6T and 6D6U, wherein the root mean square deviation (RMSD) values of redocking experiments were 1.141 and 1.505 Å (1 Å = 0.1 nm), respectively. During the virtual screening, 41112 compounds from a commercial database were scanned by machine learning, molecular docking, and molecular mechanics-generalized Born surface area models. After the screening, 16 hits were obtained, 4 of which were structurally novel positive hits verified by whole-cell patch-clamp electrophysiology experiments. The compound GPR120 was verified experimentally at both the cell and animal levels. In cortical neurons recombinantly expressing α1β2γ2-type receptors, at 10 and 50 µmol∙L−1, GPR120 could potentiate GABA EC3-10 current by 71.5% and 163.8%, respectively. Total decomposition contribution analysis and point mutation experiment showed that the key binding site between GPR120 and the GABAA receptor is H102, similar to that of the positive drug Diazepam. To further verify GPR120 function at the animal level, locomotor activity and loss of righting reflex (LORR) tests were performed. GPR120 inhibited the locomotor activity of mice, which recovered after 6 h, indicating that GPR120 is a moderate sedative. In the pentobarbital sodium-induced righting reflex hour test, GPR120 (20 mg∙kg−1) significantly shortened the time to start LORR and prolonged its duration compared with the saline control group. In summary, using integrated virtual screening methods, GPR120 was identified as a moderate sedative with a novel scaffold.
2024, 40(1): 230300
doi: 10.3866/PKU.WHXB202303003
Abstract:
Catalytic oxidation is a commonly employed technology in the industry for removing volatile organic compounds (VOCs) due to its exceptional efficiency under mild operating conditions. Although supported Pt-based nano-catalysts are recognized widely as one of the most promising and extensively used industrial catalysts for VOC abatement, their practical application, and development are restricted by their exorbitant cost. Single-atom catalyst (SAC) with maximized metal utilization and exclusive electronic character has been explored extensively in various catalytic reactions. However, Pt SAC is usually deemed to be inactive in hydrocarbon oxidation reactions in thermal catalysis, compared with its nanoparticle counterpart. Here, we demonstrate that the WO3-TiO2 supported Pt SAC (Pt1/WO3-TiO2) exhibits much higher activities than the corresponding nanoparticle catalyst (PtNP/WO3-TiO2) in photo-thermo catalytic oxidation of C3H8 and C3H6, which represent different kinds of typical VOCs. A key finding is that the activities of Pt1/WO3-TiO2 and PtNP/WO3-TiO2 can be accelerated in photo-thermo catalytic C3H8 oxidation by overcoming oxygen poisoning. Upon the light irradiation, the apparent active energy (Ea) of the Pt1/WO3-TiO2 and PtNP/WO3-TiO2 decline from 116 to 60 kJ·mol−1 and from 103 to 30 kJ·mol−1, respectively, substantiating their effectiveness in photo-thermo catalysis. Notably, a substantially higher reaction rate of 3792 μmol∙gPt−1∙s−1 on the Pt1/WO3-TiO2 is achieved, which should be a benchmark for C3H8 oxidation. More intriguingly, photo-thermo catalytic C3H6 oxidation on the PtNP/WO3-TiO2 is prohibited due to the strong adsorption-induced C3H6 poisoning on the Pt nanoparticles, for which the Ea of the PtNP/WO3-TiO2 catalyst for C3H6 oxidation is maintained at approximately 55 kJ·mol−1, regardless of the light irradiation. In comparison, the C3H6 poisoning on the Pt1/WO3-TiO2 can be mitigated by light illumination, where the Ea of the Pt1/WO3-TiO2 catalyst for C3H6 oxidation dramatically reduced from 49 to 16 kJ·mol−1, signifying that the high energy barrier of C3H6 oxidation can be mediated by the light. Profiting from the apt affinity between C3H6 and Pt single atoms, the photogenerated electrons accumulated on the Pt single atoms produce repulsive force towards the electron-rich C3H6 molecules, which is conducive to the C3H6 desorption from the Pt1/WO3-TiO2. Therefore, the Pt1/WO3-TiO2 exhibits enhanced activity in photo-thermo catalytic C3H6 oxidation. This study exemplifies that the advantages of SAC are not only saving the consumption of precious metals but also discovering new catalytic reactions on the account of the specific electronic characteristic. ![]()
Catalytic oxidation is a commonly employed technology in the industry for removing volatile organic compounds (VOCs) due to its exceptional efficiency under mild operating conditions. Although supported Pt-based nano-catalysts are recognized widely as one of the most promising and extensively used industrial catalysts for VOC abatement, their practical application, and development are restricted by their exorbitant cost. Single-atom catalyst (SAC) with maximized metal utilization and exclusive electronic character has been explored extensively in various catalytic reactions. However, Pt SAC is usually deemed to be inactive in hydrocarbon oxidation reactions in thermal catalysis, compared with its nanoparticle counterpart. Here, we demonstrate that the WO3-TiO2 supported Pt SAC (Pt1/WO3-TiO2) exhibits much higher activities than the corresponding nanoparticle catalyst (PtNP/WO3-TiO2) in photo-thermo catalytic oxidation of C3H8 and C3H6, which represent different kinds of typical VOCs. A key finding is that the activities of Pt1/WO3-TiO2 and PtNP/WO3-TiO2 can be accelerated in photo-thermo catalytic C3H8 oxidation by overcoming oxygen poisoning. Upon the light irradiation, the apparent active energy (Ea) of the Pt1/WO3-TiO2 and PtNP/WO3-TiO2 decline from 116 to 60 kJ·mol−1 and from 103 to 30 kJ·mol−1, respectively, substantiating their effectiveness in photo-thermo catalysis. Notably, a substantially higher reaction rate of 3792 μmol∙gPt−1∙s−1 on the Pt1/WO3-TiO2 is achieved, which should be a benchmark for C3H8 oxidation. More intriguingly, photo-thermo catalytic C3H6 oxidation on the PtNP/WO3-TiO2 is prohibited due to the strong adsorption-induced C3H6 poisoning on the Pt nanoparticles, for which the Ea of the PtNP/WO3-TiO2 catalyst for C3H6 oxidation is maintained at approximately 55 kJ·mol−1, regardless of the light irradiation. In comparison, the C3H6 poisoning on the Pt1/WO3-TiO2 can be mitigated by light illumination, where the Ea of the Pt1/WO3-TiO2 catalyst for C3H6 oxidation dramatically reduced from 49 to 16 kJ·mol−1, signifying that the high energy barrier of C3H6 oxidation can be mediated by the light. Profiting from the apt affinity between C3H6 and Pt single atoms, the photogenerated electrons accumulated on the Pt single atoms produce repulsive force towards the electron-rich C3H6 molecules, which is conducive to the C3H6 desorption from the Pt1/WO3-TiO2. Therefore, the Pt1/WO3-TiO2 exhibits enhanced activity in photo-thermo catalytic C3H6 oxidation. This study exemplifies that the advantages of SAC are not only saving the consumption of precious metals but also discovering new catalytic reactions on the account of the specific electronic characteristic.
2024, 40(1): 230300
doi: 10.3866/PKU.WHXB202303004
Abstract:
The increasing global demand for energy and the detrimental effects of using fossil fuels highlight the urgent need for alternative and sustainable energy sources. Metal halide perovskites have gained significant research attention over the last few years, primarily for solar energy storage, light emission, and thermoelectrics, due to their low cost and high efficiency. To understand the thermoelectric transport characteristics of halide perovskites and improve their practical applications, precise knowledge of their heat transport mechanism is necessary. In this study, we used density functional theory (DFT) and different exchange-correlation functionals, namely the Perdew-Burke-Ernzerhof (PBE) and modified Becke Johnson (mBJ) schemes, to screen three inorganic halide perovskites, Rb2SnI6, Rb2PdI6, and Cs2PtI6, in their pristine forms for thermoelectric energy conversion. Here, we report the mechanical stability, effective masses, Seebeck coefficient, power factor, and thermoelectric figure of merit. Both PBE and mBJ functionals successfully determined the most stable geometry and accurate electronic structure for each halide perovskite. Initially, we optimized the crystal structures of all three compounds using the PBE functional and obtained the corresponding lattice parameters. The optimized lattice constants are in good agreement with the experimental values. We are the first to calculate the elastic constants and other mechanical parameters, such as the elastic moduli, Poisson's ratio, Pugh index, elastic anisotropy, and Grüneisen parameter, to determine the elastic and mechanical stability of these compounds. All three compounds (Rb2SnI6, Rb2PdI6, and Cs2PtI6) are mechanically stable and ductile. The effective mass of the electrons at the conduction band minimum was smaller than that of the holes at the valence band maximum. Electronic band structure calculations showed that all three compounds are narrow band gap semiconductors (with band gaps ranging from 0.47 to 1.22 eV) with degenerate band extrema. The low effective masses and favorable band gap feature make them ideal for thermoelectric applications. Our study reveals a high Seebeck coefficient of 0.76 mV·K−1 for Cs2PtI6 for hole doping at maximum temperature. Due to the high Seebeck coefficient and maximum power factor, we found high figure of merit (ZT) of 0.98 for Cs2PtI6, 0.96 for Rb2PdI6, and 0.97 for Rb2SnI6, upon p-type doping. With this study, we provide new insights into the thermoelectric performance of halide perovskites and can offer inspiration for the experimental synthesis of these compounds. Our results may also contribute to developing practical energy conversion and storage devices, which can significantly affect the renewable energy sector. ![]()
The increasing global demand for energy and the detrimental effects of using fossil fuels highlight the urgent need for alternative and sustainable energy sources. Metal halide perovskites have gained significant research attention over the last few years, primarily for solar energy storage, light emission, and thermoelectrics, due to their low cost and high efficiency. To understand the thermoelectric transport characteristics of halide perovskites and improve their practical applications, precise knowledge of their heat transport mechanism is necessary. In this study, we used density functional theory (DFT) and different exchange-correlation functionals, namely the Perdew-Burke-Ernzerhof (PBE) and modified Becke Johnson (mBJ) schemes, to screen three inorganic halide perovskites, Rb2SnI6, Rb2PdI6, and Cs2PtI6, in their pristine forms for thermoelectric energy conversion. Here, we report the mechanical stability, effective masses, Seebeck coefficient, power factor, and thermoelectric figure of merit. Both PBE and mBJ functionals successfully determined the most stable geometry and accurate electronic structure for each halide perovskite. Initially, we optimized the crystal structures of all three compounds using the PBE functional and obtained the corresponding lattice parameters. The optimized lattice constants are in good agreement with the experimental values. We are the first to calculate the elastic constants and other mechanical parameters, such as the elastic moduli, Poisson's ratio, Pugh index, elastic anisotropy, and Grüneisen parameter, to determine the elastic and mechanical stability of these compounds. All three compounds (Rb2SnI6, Rb2PdI6, and Cs2PtI6) are mechanically stable and ductile. The effective mass of the electrons at the conduction band minimum was smaller than that of the holes at the valence band maximum. Electronic band structure calculations showed that all three compounds are narrow band gap semiconductors (with band gaps ranging from 0.47 to 1.22 eV) with degenerate band extrema. The low effective masses and favorable band gap feature make them ideal for thermoelectric applications. Our study reveals a high Seebeck coefficient of 0.76 mV·K−1 for Cs2PtI6 for hole doping at maximum temperature. Due to the high Seebeck coefficient and maximum power factor, we found high figure of merit (ZT) of 0.98 for Cs2PtI6, 0.96 for Rb2PdI6, and 0.97 for Rb2SnI6, upon p-type doping. With this study, we provide new insights into the thermoelectric performance of halide perovskites and can offer inspiration for the experimental synthesis of these compounds. Our results may also contribute to developing practical energy conversion and storage devices, which can significantly affect the renewable energy sector.
2024, 40(1): 230303
doi: 10.3866/PKU.WHXB202303034
Abstract:
The conversion of renewable solar energy into chemical energy is an important topic in research. Recently, bismuth chromate (Bi2CrO6) has attracted attention in photocatalytic research, particularly for its potential applications in pollutant degradation and water splitting. This layered metal oxide exhibits a narrow optical band gap of approximately 1.9 eV and can utilize most of visible light in the solar spectrum. However, the photocatalytic activity of Bi2CrO6 is relatively low, and its poor charge separation properties restrict its practical applications. Herein, we report a microwave-assisted hydrothermal method for the fabrication of Bi2CrO6 crystals with high crystallinity and uniform morphology. Compared with the conventional preparations, microwave irradiation induces rapid volumetric heating and greatly accelerates nucleation and growth reactions, forming Bi2CrO6 crystals within minutes. Multiple characterization methods, including X-ray diffraction, Raman scattering, and scanning electron microscopy, were employed to examine the crystallinity and morphologies of the samples. Microwave-assisted synthesized Bi2CrO6 crystals showed better water oxidation activity in photocatalytic and photoelectrochemical tests than the conventional samples. Oxygen evolution rates were boosted 7.2 and 3.1 times using AgNO3 and Fe(NO3)3 as electron acceptors, respectively. Further investigations showed that microwave-assisted Bi2CrO6 crystals exhibited improved photogenerated charge separation. The average lifetime of photogenerated carriers, calculated from time-resolved photoluminescence results, also showed an increase. Furthermore, using photodeposition of metals and oxides as probes, the spatial separation of photogenerated electrons and holes was demonstrated to take place between {001} top and side facets of the Bi2CrO6 crystal samples. Loading reduction and oxidation cocatalysts onto different facets significantly enhanced the photocatalytic activities. These results enforce the promise of microwave-assisted Bi2CrO6 crystal synthesis for photocatalytic water-splitting applications and present a solution for efficient solar-energy conversion. ![]()
The conversion of renewable solar energy into chemical energy is an important topic in research. Recently, bismuth chromate (Bi2CrO6) has attracted attention in photocatalytic research, particularly for its potential applications in pollutant degradation and water splitting. This layered metal oxide exhibits a narrow optical band gap of approximately 1.9 eV and can utilize most of visible light in the solar spectrum. However, the photocatalytic activity of Bi2CrO6 is relatively low, and its poor charge separation properties restrict its practical applications. Herein, we report a microwave-assisted hydrothermal method for the fabrication of Bi2CrO6 crystals with high crystallinity and uniform morphology. Compared with the conventional preparations, microwave irradiation induces rapid volumetric heating and greatly accelerates nucleation and growth reactions, forming Bi2CrO6 crystals within minutes. Multiple characterization methods, including X-ray diffraction, Raman scattering, and scanning electron microscopy, were employed to examine the crystallinity and morphologies of the samples. Microwave-assisted synthesized Bi2CrO6 crystals showed better water oxidation activity in photocatalytic and photoelectrochemical tests than the conventional samples. Oxygen evolution rates were boosted 7.2 and 3.1 times using AgNO3 and Fe(NO3)3 as electron acceptors, respectively. Further investigations showed that microwave-assisted Bi2CrO6 crystals exhibited improved photogenerated charge separation. The average lifetime of photogenerated carriers, calculated from time-resolved photoluminescence results, also showed an increase. Furthermore, using photodeposition of metals and oxides as probes, the spatial separation of photogenerated electrons and holes was demonstrated to take place between {001} top and side facets of the Bi2CrO6 crystal samples. Loading reduction and oxidation cocatalysts onto different facets significantly enhanced the photocatalytic activities. These results enforce the promise of microwave-assisted Bi2CrO6 crystal synthesis for photocatalytic water-splitting applications and present a solution for efficient solar-energy conversion.
2024, 40(1): 230304
doi: 10.3866/PKU.WHXB202303040
Abstract:
CO2 molecules can be converted into various fuels and industrial chemicals through electrochemical reduction, effectively addressing the problems of global warming, desertification, ocean acidification, and other adverse environmental changes and energy supply issues such as excessive utilization of nonrenewable fossil fuels. Generally, the pathway of the CO2 reduction reaction (CO2RR) involves multiple proton–electron pairs transferred to the reactants, resulting in the production of multiple reduction products. Here, protons are derived from water molecules under aqueous solvent conditions. Therefore, exploring the effect of water molecules on the proton–electron pair transfer process in CO2RRs is essential. In this study, we developed a water-mediated hydrogen shuttle model (H-shuttling) as a hydrogenation model to investigate the effect of water molecules on the proton–electron pair transfer process in CO2RRs and compared it with the widely used water-free direct hydrogenation model (H-transfer), wherein the hydrogen atom is used as a proton. Because copper is a metal electrode material capable of producing hydrocarbons from CO2 electroreduction with a high faraday efficiency, and nitrogen-doped graphene (C2N) exhibits excellent catalytic CO2 activation, we selected a single copper atom-embedded C2N (Cu@C2N) as the catalyst. Furthermore, to study the effect of graphene on the CO2RR activity of Cu@C2N/G, we selected a graphene-loaded Cu@C2N composite (Cu@C2N/G) as the catalyst because graphene was utilized as a substrate to boost the conductivity of the catalyst. In the two hydrogenation models, we investigated the mechanisms of CO2RRs on Cu@C2N and Cu@C2N/G catalysts through density functional theory calculations. Notably, in the H-shuttling model, the H atom combines with the water molecule to form H3O, which transfers one of its own H atoms to a reactant on the catalyst surface, yielding a reaction intermediate. The H-shuttling model enhances the interaction between the catalyst and intermediate. Graphene, as a substrate, transfers electrons to the Cu@C2N surface of the Cu@C2N/G catalyst, which is demonstrated by calculations of the Bader charge transferred between the reaction intermediate and catalyst, as well as the Gibbs free energy of the CO2 reduction elementary reaction. This effectively lowers the Gibbs free energy of the potential-determining step and enhances the CO2RR catalytic activity of Cu@C2N/G. Moreover the limiting potentials of the CO2RR and hydrogen evolution reaction are determined to obtain the activity and selectivity of the Cu@C2N and Cu@C2N/G catalysts. The results indicate that CO2 molecules on the Cu@C2N and Cu@C2N/G catalysts generate HCOOH at low applied potentials, and are able to produce CO, CH3OH, CH4, and H2 as the applied potentials increases. ![]()
CO2 molecules can be converted into various fuels and industrial chemicals through electrochemical reduction, effectively addressing the problems of global warming, desertification, ocean acidification, and other adverse environmental changes and energy supply issues such as excessive utilization of nonrenewable fossil fuels. Generally, the pathway of the CO2 reduction reaction (CO2RR) involves multiple proton–electron pairs transferred to the reactants, resulting in the production of multiple reduction products. Here, protons are derived from water molecules under aqueous solvent conditions. Therefore, exploring the effect of water molecules on the proton–electron pair transfer process in CO2RRs is essential. In this study, we developed a water-mediated hydrogen shuttle model (H-shuttling) as a hydrogenation model to investigate the effect of water molecules on the proton–electron pair transfer process in CO2RRs and compared it with the widely used water-free direct hydrogenation model (H-transfer), wherein the hydrogen atom is used as a proton. Because copper is a metal electrode material capable of producing hydrocarbons from CO2 electroreduction with a high faraday efficiency, and nitrogen-doped graphene (C2N) exhibits excellent catalytic CO2 activation, we selected a single copper atom-embedded C2N (Cu@C2N) as the catalyst. Furthermore, to study the effect of graphene on the CO2RR activity of Cu@C2N/G, we selected a graphene-loaded Cu@C2N composite (Cu@C2N/G) as the catalyst because graphene was utilized as a substrate to boost the conductivity of the catalyst. In the two hydrogenation models, we investigated the mechanisms of CO2RRs on Cu@C2N and Cu@C2N/G catalysts through density functional theory calculations. Notably, in the H-shuttling model, the H atom combines with the water molecule to form H3O, which transfers one of its own H atoms to a reactant on the catalyst surface, yielding a reaction intermediate. The H-shuttling model enhances the interaction between the catalyst and intermediate. Graphene, as a substrate, transfers electrons to the Cu@C2N surface of the Cu@C2N/G catalyst, which is demonstrated by calculations of the Bader charge transferred between the reaction intermediate and catalyst, as well as the Gibbs free energy of the CO2 reduction elementary reaction. This effectively lowers the Gibbs free energy of the potential-determining step and enhances the CO2RR catalytic activity of Cu@C2N/G. Moreover the limiting potentials of the CO2RR and hydrogen evolution reaction are determined to obtain the activity and selectivity of the Cu@C2N and Cu@C2N/G catalysts. The results indicate that CO2 molecules on the Cu@C2N and Cu@C2N/G catalysts generate HCOOH at low applied potentials, and are able to produce CO, CH3OH, CH4, and H2 as the applied potentials increases.
2024, 40(1): 230305
doi: 10.3866/PKU.WHXB202303055
Abstract:
Electrochemical water splitting proves critical to sustainable and clean hydrogen fuel production. However, the anodic water oxidation reaction—the major half-reaction in water splitting—has turned into a bottleneck due to the high energy barrier of the complex and sluggish four-electron transfer process. Nickel-iron layered double hydroxides (NiFe-LDHs) are regarded as promising non-noble metal electrocatalysts for oxygen evolution reaction (OER) catalysis in alkaline conditions. However, the electrocatalytic activity of NiFe-LDH requires improvement because of poor conductivity, a small number of exposed active sites, and weak adsorption of intermediates. As such, tremendous effort has been made to enhance the activity of NiFe-LDH, including introducing defects, doping, exfoliation to obtain single-layer structures, and constructing arrayed structures. In this study, researchers controllably doped NiFe-LDH with tungsten using a simple one-step alcohothermal method to afford nickel-iron-tungsten layered double hydroxides (NiFeW-LDHs). X-ray powder diffraction analysis was used to investigate the structure of NiFeW-LDH. The analysis revealed the presence of the primary diffraction peak corresponding to the perfectly hexagonal-phased NiFe-LDH, with no additional diffraction peaks observed, thereby ruling out the formation of tungsten-based nanoparticles. Furthermore, scanning electron microscopy (SEM) showed that the NiFeW-LDH nanosheets were approximately 500 nm in size and had a flower-like structure that consisted of interconnected nanosheets with smooth surfaces. Additionally, it was observed that NiFeW-LDH had a uniform distribution of Ni, Fe, and W throughout the nanosheets. X-ray photoelectron spectra (XPS) revealed the surface electronic structure of the NiFeW-LDH catalyst. It was determined that the oxidation state of W in NiFeW-LDH was +6 and that the XPS signal of Fe in NiFeW-LDH shifted to a higher oxidation state compared to NiFe-LDH. These results suggest electron redistribution between Fe and W. Simultaneously, the peak area of surface-adsorbed OH increased significantly after W doping, suggesting enhanced OH adsorption on the surface of NiFeW-LDH. Furthermore, density functional theory (DFT) calculations indicated that W(Ⅵ) facilitates the adsorption of H2O and O*-intermediates and enhances the activity of Fe sites, which aligns with experimental results. The novel NiFeW-LDH catalyst displayed a low overpotential of 199 and 237 mV at 10 and 100 mA∙cm−2 in 1 mol∙L−1 KOH, outperforming most NiFe-based colloid catalysts. Furthermore, experimental characterizations and DFT+U calculations suggest that W doping plays an important role through strong electronic interactions with Fe and facilitating the adsorption of important O-containing intermediates. ![]()
Electrochemical water splitting proves critical to sustainable and clean hydrogen fuel production. However, the anodic water oxidation reaction—the major half-reaction in water splitting—has turned into a bottleneck due to the high energy barrier of the complex and sluggish four-electron transfer process. Nickel-iron layered double hydroxides (NiFe-LDHs) are regarded as promising non-noble metal electrocatalysts for oxygen evolution reaction (OER) catalysis in alkaline conditions. However, the electrocatalytic activity of NiFe-LDH requires improvement because of poor conductivity, a small number of exposed active sites, and weak adsorption of intermediates. As such, tremendous effort has been made to enhance the activity of NiFe-LDH, including introducing defects, doping, exfoliation to obtain single-layer structures, and constructing arrayed structures. In this study, researchers controllably doped NiFe-LDH with tungsten using a simple one-step alcohothermal method to afford nickel-iron-tungsten layered double hydroxides (NiFeW-LDHs). X-ray powder diffraction analysis was used to investigate the structure of NiFeW-LDH. The analysis revealed the presence of the primary diffraction peak corresponding to the perfectly hexagonal-phased NiFe-LDH, with no additional diffraction peaks observed, thereby ruling out the formation of tungsten-based nanoparticles. Furthermore, scanning electron microscopy (SEM) showed that the NiFeW-LDH nanosheets were approximately 500 nm in size and had a flower-like structure that consisted of interconnected nanosheets with smooth surfaces. Additionally, it was observed that NiFeW-LDH had a uniform distribution of Ni, Fe, and W throughout the nanosheets. X-ray photoelectron spectra (XPS) revealed the surface electronic structure of the NiFeW-LDH catalyst. It was determined that the oxidation state of W in NiFeW-LDH was +6 and that the XPS signal of Fe in NiFeW-LDH shifted to a higher oxidation state compared to NiFe-LDH. These results suggest electron redistribution between Fe and W. Simultaneously, the peak area of surface-adsorbed OH increased significantly after W doping, suggesting enhanced OH adsorption on the surface of NiFeW-LDH. Furthermore, density functional theory (DFT) calculations indicated that W(Ⅵ) facilitates the adsorption of H2O and O*-intermediates and enhances the activity of Fe sites, which aligns with experimental results. The novel NiFeW-LDH catalyst displayed a low overpotential of 199 and 237 mV at 10 and 100 mA∙cm−2 in 1 mol∙L−1 KOH, outperforming most NiFe-based colloid catalysts. Furthermore, experimental characterizations and DFT+U calculations suggest that W doping plays an important role through strong electronic interactions with Fe and facilitating the adsorption of important O-containing intermediates.
2024, 40(1): 230400
doi: 10.3866/PKU.WHXB202304002
Abstract:
Organic-organic heterostructures have been widely applied in various organic electronic devices, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells. A thorough understanding of the interface effect in these heterostructures is of crucial importance for device design and optimization. However, owing to the diverse chemical properties and weak van der Waals interactions of organic semiconductors, interface charge transport is critically related to the organic-organic electronic structure and environmental atmosphere. Therefore, an in situ real-time investigation of the electrical properties in vacuum could efficiently avoid atmospheric influence and aid determination of the instinct interactions at the organic-organic interface. Herein, we report in situ real-time electrical property monitoring of the pentacene/vanadyl phthalocyanine (VOPc) heterostructure with top layer pentacene growth. The hole mobility of the heterostructure transistors decreases from 0.4 cm2∙V−1∙s−1 to approximately 0.2 cm2∙V−1∙s−1, while the electron mobility increases rapidly from 0.01 cm2∙V−1∙s−1 to approximately 0.9 cm2∙V−1∙s−1 as the pentacene thickness increases. This enhanced electron transport is attributed to the interface electron transfer from pentacene to VOPc, leading to filling of trap states in the VOPc layer and an improvement in the charge mobility and n-channel current. In contrast, the ex situ processing results indicate that atmospheric exposure will significantly suppress this charge transfer effect, resulting to a negligible improvement in the electron transport. The film morphology, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy characterizations suggest electron transfer occurs from pentacene to VOPc. Additionally, density functional theory (DFT) calculations confirm that the interaction between pentacene and VOPc is strong and the pentacene molecule tends to transfer electrons to VOPc with a calculated charge transfer value of approximately 0.15 e. Moreover, this interface charge transfer is significantly suppressed with the presence of either O2 or H2O, which is highly consistent with our experiment results. In this paper, we provide a clear understanding of the instinct organic-organic interface charge transfer effect by using in situ characterization, which will be helpful for further device performance optimization and analysis. ![]()
Organic-organic heterostructures have been widely applied in various organic electronic devices, including organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells. A thorough understanding of the interface effect in these heterostructures is of crucial importance for device design and optimization. However, owing to the diverse chemical properties and weak van der Waals interactions of organic semiconductors, interface charge transport is critically related to the organic-organic electronic structure and environmental atmosphere. Therefore, an in situ real-time investigation of the electrical properties in vacuum could efficiently avoid atmospheric influence and aid determination of the instinct interactions at the organic-organic interface. Herein, we report in situ real-time electrical property monitoring of the pentacene/vanadyl phthalocyanine (VOPc) heterostructure with top layer pentacene growth. The hole mobility of the heterostructure transistors decreases from 0.4 cm2∙V−1∙s−1 to approximately 0.2 cm2∙V−1∙s−1, while the electron mobility increases rapidly from 0.01 cm2∙V−1∙s−1 to approximately 0.9 cm2∙V−1∙s−1 as the pentacene thickness increases. This enhanced electron transport is attributed to the interface electron transfer from pentacene to VOPc, leading to filling of trap states in the VOPc layer and an improvement in the charge mobility and n-channel current. In contrast, the ex situ processing results indicate that atmospheric exposure will significantly suppress this charge transfer effect, resulting to a negligible improvement in the electron transport. The film morphology, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy characterizations suggest electron transfer occurs from pentacene to VOPc. Additionally, density functional theory (DFT) calculations confirm that the interaction between pentacene and VOPc is strong and the pentacene molecule tends to transfer electrons to VOPc with a calculated charge transfer value of approximately 0.15 e. Moreover, this interface charge transfer is significantly suppressed with the presence of either O2 or H2O, which is highly consistent with our experiment results. In this paper, we provide a clear understanding of the instinct organic-organic interface charge transfer effect by using in situ characterization, which will be helpful for further device performance optimization and analysis.
2024, 40(1): 230401
doi: 10.3866/PKU.WHXB202304018
Abstract:
Hydrogen is an important zero-pollution green energy source with potential for alleviating environmental contamination and energy shortages. Hydrogen evolution via solar-energy-induced semiconducting water splitting is among the most environmentally friendly methods available to date. In this study, a metal–organic-framework-derived, Ni-decorated carbon nanotube (Ni-CNT) is used as a non-noble co-catalyst. This Ni-CNT is grown in situ on ZnIn2S4 nanosheets using a simple one-step oil bath strategy, wherein Ni nanoparticles are wrapped around the top and cross sections of the nanotubes, preventing their agglomeration. Notably, Ni-CNT/ZnIn2S4 heterostructures feature intimate contact interfaces that promote charge transfer, facilitating their use as efficient photocatalysts for hydrogen evolution. The 38Ni-CNT/ZnIn2S4 sample exhibits a high H2 production rate (12267 μmol·h−1·g−1), with an apparent quantum efficiency (AQE) of 11.3% under 420 nm monochromatic light irradiation, which is nearly 6.4 times that of pure ZnIn2S4. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) corroborate the observations on Ni-CNT/ZnIn2S4 heterostructures. Electrochemical measurements reveal that the combination of the Ni-CNT and ZnIn2S4 facilitates the transfer of photogenerated electrons and effectively prevents rapid recombination of photocarriers, thus improving the hydrogen evolution performance of ZnIn2S4. Electron spin resonance (ESR) results further prove that co-catalyst Ni-CNTs are beneficial for prolonging the lifetimes of ZnIn2S4 photogenerated electrons, thereby achieving effective charge separation. A charge transfer pathway in the heterojunction interfaces is further explored and confirmed by density functional theory (DFT) calculations. The difference in the Fermi level energy (Ef) contributes to both charge migration and the generation of a built-in electronic field (BEF), indicating that the energy band of ZnIn2S4 bends downward, which is favorable for photogenerated electron flow from ZnIn2S4 to the Ni-CNT electron acceptor. The results of planar-averaged electron density difference analysis confirm that the hot electrons are transferred from Ni nanoparticles to the CNT and then to the ZnIn2S4 nanosheets, indicating the formation of a photogenerated electron transfer pathway of ZnIn2S4 → CNT → Ni. Furthermore, Gibbs free energy of H* adsorption (ΔGH*) and crystal orbital Hamilton population (COHP) analysis indicate that Ni nanoparticles can serve as active sites, promoting H2 evolution. Thus, the present study formulates a new strategy for developing low-cost, high-efficiency, non-noble-metal co-catalysts for photocatalytic hydrogen production. ![]()
Hydrogen is an important zero-pollution green energy source with potential for alleviating environmental contamination and energy shortages. Hydrogen evolution via solar-energy-induced semiconducting water splitting is among the most environmentally friendly methods available to date. In this study, a metal–organic-framework-derived, Ni-decorated carbon nanotube (Ni-CNT) is used as a non-noble co-catalyst. This Ni-CNT is grown in situ on ZnIn2S4 nanosheets using a simple one-step oil bath strategy, wherein Ni nanoparticles are wrapped around the top and cross sections of the nanotubes, preventing their agglomeration. Notably, Ni-CNT/ZnIn2S4 heterostructures feature intimate contact interfaces that promote charge transfer, facilitating their use as efficient photocatalysts for hydrogen evolution. The 38Ni-CNT/ZnIn2S4 sample exhibits a high H2 production rate (12267 μmol·h−1·g−1), with an apparent quantum efficiency (AQE) of 11.3% under 420 nm monochromatic light irradiation, which is nearly 6.4 times that of pure ZnIn2S4. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) corroborate the observations on Ni-CNT/ZnIn2S4 heterostructures. Electrochemical measurements reveal that the combination of the Ni-CNT and ZnIn2S4 facilitates the transfer of photogenerated electrons and effectively prevents rapid recombination of photocarriers, thus improving the hydrogen evolution performance of ZnIn2S4. Electron spin resonance (ESR) results further prove that co-catalyst Ni-CNTs are beneficial for prolonging the lifetimes of ZnIn2S4 photogenerated electrons, thereby achieving effective charge separation. A charge transfer pathway in the heterojunction interfaces is further explored and confirmed by density functional theory (DFT) calculations. The difference in the Fermi level energy (Ef) contributes to both charge migration and the generation of a built-in electronic field (BEF), indicating that the energy band of ZnIn2S4 bends downward, which is favorable for photogenerated electron flow from ZnIn2S4 to the Ni-CNT electron acceptor. The results of planar-averaged electron density difference analysis confirm that the hot electrons are transferred from Ni nanoparticles to the CNT and then to the ZnIn2S4 nanosheets, indicating the formation of a photogenerated electron transfer pathway of ZnIn2S4 → CNT → Ni. Furthermore, Gibbs free energy of H* adsorption (ΔGH*) and crystal orbital Hamilton population (COHP) analysis indicate that Ni nanoparticles can serve as active sites, promoting H2 evolution. Thus, the present study formulates a new strategy for developing low-cost, high-efficiency, non-noble-metal co-catalysts for photocatalytic hydrogen production.
Effects of Electron Density Variation of Active Sites in CO2 Activation and Photoreduction: A Review
2024, 40(1): 230302
doi: 10.3866/PKU.WHXB202303029
Abstract:
Photocatalytic reduction of CO2 into value-added chemicals is a feasible approach to harvest solar light energy and storing energy in the form of chemical fuels as well as to mitigate the effects of global climate change and help achieve an artificial carbon cycle. However, the efficiency of CO2 photoreduction is low for commercial purposes. This is mainly due to the difficult adsorption and activation process of CO2 molecules, the unsatisfactory selectivity of target products, and the uncontrolled-subsequent reaction process of the generated carbon products. CO2 photoreduction requires substantial electrons for participation. Hence, these issues are due to the electron density modulation of the active sites of catalysts. Unfortunately, the CO2 photoreduction process involves multi-fundamental steps, which leads to different requirements in electron density modulation. The performance might not be effectively improved by directly enhancing or weakening the total electron density of active sites. In this paper, we summarize recent advances in the influence of electron density variation of the active sites in strengthening the adsorption and activation of CO2 molecules, enhancing the selectivity of target carbon products and modulating the subsequent reaction process of the generated carbon products. This review begins with the effect of different types of active sites in strengthening the adsorption and activation of the CO2 molecules and the related methods for modulating the electron density of active sites. Active sites with high electron densities can significantly enhance the adsorption and activation of CO2. Introducing metal and fabricating the defects on catalyst surfaces are effective strategies for fabricating the electron-rich active sites. After that, we discuss the influence of electron density variation in enhancing the selectivity of target carbon products in detail. In this part, the related effects in the multielectron donation from the catalyst surface, the reactive intermediates, and the competition hydrogen evolution reaction are summarized. Enhancing the electron density of active sites strengthens the former two processes. For multielectron donation, introducing cocatalysts or fabricating heterostructures are the most effective methods for enhancing the electron density of active sites. The adsorption and conversion process of intermediates are mainly affected by the accumulation sites of electrons. The active sites with low coordination are more favorable to achieving the generation of multi-electronic carbon products. In contrast, the hydrogen evolution reaction is significantly inhibited by reducing the electron density of active sites. Moreover, elemental doping is considered one of the most effective strategies. Finally, we describe the method for weakening the electron density of active sites to promote product desorption and inhibit the photooxidation of reactive products. ![]()
Photocatalytic reduction of CO2 into value-added chemicals is a feasible approach to harvest solar light energy and storing energy in the form of chemical fuels as well as to mitigate the effects of global climate change and help achieve an artificial carbon cycle. However, the efficiency of CO2 photoreduction is low for commercial purposes. This is mainly due to the difficult adsorption and activation process of CO2 molecules, the unsatisfactory selectivity of target products, and the uncontrolled-subsequent reaction process of the generated carbon products. CO2 photoreduction requires substantial electrons for participation. Hence, these issues are due to the electron density modulation of the active sites of catalysts. Unfortunately, the CO2 photoreduction process involves multi-fundamental steps, which leads to different requirements in electron density modulation. The performance might not be effectively improved by directly enhancing or weakening the total electron density of active sites. In this paper, we summarize recent advances in the influence of electron density variation of the active sites in strengthening the adsorption and activation of CO2 molecules, enhancing the selectivity of target carbon products and modulating the subsequent reaction process of the generated carbon products. This review begins with the effect of different types of active sites in strengthening the adsorption and activation of the CO2 molecules and the related methods for modulating the electron density of active sites. Active sites with high electron densities can significantly enhance the adsorption and activation of CO2. Introducing metal and fabricating the defects on catalyst surfaces are effective strategies for fabricating the electron-rich active sites. After that, we discuss the influence of electron density variation in enhancing the selectivity of target carbon products in detail. In this part, the related effects in the multielectron donation from the catalyst surface, the reactive intermediates, and the competition hydrogen evolution reaction are summarized. Enhancing the electron density of active sites strengthens the former two processes. For multielectron donation, introducing cocatalysts or fabricating heterostructures are the most effective methods for enhancing the electron density of active sites. The adsorption and conversion process of intermediates are mainly affected by the accumulation sites of electrons. The active sites with low coordination are more favorable to achieving the generation of multi-electronic carbon products. In contrast, the hydrogen evolution reaction is significantly inhibited by reducing the electron density of active sites. Moreover, elemental doping is considered one of the most effective strategies. Finally, we describe the method for weakening the electron density of active sites to promote product desorption and inhibit the photooxidation of reactive products.
2024, 40(1): 230400
doi: 10.3866/PKU.WHXB202304004
Abstract:
Rapid population growth and the demand for energy, which is powered by unrestricted fossil fuel exploitation, have caused severe environmental problems. Thus, it is crucial to effectively exploit alternative clean energy sources. Solar energy, which is a sustainable renewable energy source, provides an effective strategy for mitigating the energy crisis and greenhouse effect without resulting in additional carbon emissions. The concept of converting carbon dioxide (CO2) into synthetic fuels is a promising solution towards realizing a sustainable carbon-neutral economy. Photocatalysis is a favorable approach for CO2 conversion, but it has limitations in terms of conversion rates, efficiency, and scalability. Therefore, the novel concept of photothermal catalysis has been proposed based on the photothermal effect of catalysts, which allows for the complete exploitation of the solar spectrum, especially infrared light that is typically wasted during photochemical catalysis. Photothermal catalysis, combining photochemical and photothermal effects, can effectively catalyze chemical reactions under mild conditions. Although various metal structures can serve as the light-absorbing and active centers for photothermal catalysis, they suffer from disadvantages such as insufficient light utilization, high cost, and poor stability. Recently, naturally abundant silicon has emerged as a prospective photothermal catalyst, especially silicon nanostructure arrays, which outperform other conventional silicon materials owing to their excellent light-harvesting ability and efficient catalytic performance. Compared with conventional photothermal catalysts, silicon nanostructure arrays have demonstrated unique catalytic performance advantages in the photothermal CO2 reduction reaction. As a platform, silicon nanostructure arrays exhibit an excellent light-harvesting ability, high specific surface area, and versatile hybridization possibilities. This review discusses the fundamental concepts and principles related to the theory and applications of photothermal catalytic CO2 conversion, the functionalities of silicon nanostructure arrays in conventional photothermal CO2 catalytic reduction, and the recent developments in photothermal CO2 catalysis using silicon nanostructure arrays. Ultimately, it provides a guide for the development direction of high-performance nanostructure arrays-based photothermal CO2 catalysts. ![]()
Rapid population growth and the demand for energy, which is powered by unrestricted fossil fuel exploitation, have caused severe environmental problems. Thus, it is crucial to effectively exploit alternative clean energy sources. Solar energy, which is a sustainable renewable energy source, provides an effective strategy for mitigating the energy crisis and greenhouse effect without resulting in additional carbon emissions. The concept of converting carbon dioxide (CO2) into synthetic fuels is a promising solution towards realizing a sustainable carbon-neutral economy. Photocatalysis is a favorable approach for CO2 conversion, but it has limitations in terms of conversion rates, efficiency, and scalability. Therefore, the novel concept of photothermal catalysis has been proposed based on the photothermal effect of catalysts, which allows for the complete exploitation of the solar spectrum, especially infrared light that is typically wasted during photochemical catalysis. Photothermal catalysis, combining photochemical and photothermal effects, can effectively catalyze chemical reactions under mild conditions. Although various metal structures can serve as the light-absorbing and active centers for photothermal catalysis, they suffer from disadvantages such as insufficient light utilization, high cost, and poor stability. Recently, naturally abundant silicon has emerged as a prospective photothermal catalyst, especially silicon nanostructure arrays, which outperform other conventional silicon materials owing to their excellent light-harvesting ability and efficient catalytic performance. Compared with conventional photothermal catalysts, silicon nanostructure arrays have demonstrated unique catalytic performance advantages in the photothermal CO2 reduction reaction. As a platform, silicon nanostructure arrays exhibit an excellent light-harvesting ability, high specific surface area, and versatile hybridization possibilities. This review discusses the fundamental concepts and principles related to the theory and applications of photothermal catalytic CO2 conversion, the functionalities of silicon nanostructure arrays in conventional photothermal CO2 catalytic reduction, and the recent developments in photothermal CO2 catalysis using silicon nanostructure arrays. Ultimately, it provides a guide for the development direction of high-performance nanostructure arrays-based photothermal CO2 catalysts.
2024, 40(1): 230303
doi: 10.3866/PKU.WHXB202303037
Abstract:
The continuous developments in physical chemistry, improved methodology, and advanced techniques have spurred interest in chemical reaction at the microscopic scale. Experimental manipulation techniques at the microscopic level are demanded to enable in-depth studies regarding the regulation of chemical reactions, material structures, and properties. The development and application of microscopic research methods have become an emerging trend in physical chemistry. Techniques featuring the use of optical, magnetic, and acoustic tweezers have been developed to manipulate objects at the microscopic scale. Optical tweezers use momentum transfer between light and objects to manipulate objects and can stably trap and manipulate mesoscopic particles, even single molecules, by exerting pico-newton force. With advantages including non-invasiveness, non-damaging, and ultra-high sensitivity, optical tweezers are ideal for studying individual molecules, molecular aggregates, condensed matter, chemical bonds, and intermolecular interactions. This technique has the potential to revolutionize the fields of chemistry, physics, information technology, and life sciences. Arthur Ashkin was awarded the 2018 Nobel Prize in Physics for his contribution to the development of this technique. The trapping force of the conventional optical tweezers technique originates from the light intensity gradient. Because of the diffraction limit of light, the trapping and manipulation of micro-nano objects < 100 nm in size with traditional optical tweezers is difficult. However, simply increasing the optical power used for trapping induces serious thermal effects and photodamage. By developing unique materials and structures coupled with optical tweezers, researchers have broken the diffraction limit of light and achieved sub-nanometer single-molecule trapping. In this review, we summarize the recent advances in the application of various optical tweezers techniques in physical chemistry and demonstrate the technical principles of fiber, photonic crystal, and plasmonic optical tweezers, respectively. We focus on the development and application of plasmonic optical tweezers and single-molecule plasmonic optical trapping based on tunable nanogaps. Generally, optical tweezers can realize the trapping and manipulation of molecular-scale particles via two main technical routes. The first route is improving the laser focusing ability through unique optical path design and optical component fabrication. The second involves enhancing the trapping field through ingenious auxiliary structure design. Finally, we present the promising future developments and applications of optical tweezers technology. ![]()
The continuous developments in physical chemistry, improved methodology, and advanced techniques have spurred interest in chemical reaction at the microscopic scale. Experimental manipulation techniques at the microscopic level are demanded to enable in-depth studies regarding the regulation of chemical reactions, material structures, and properties. The development and application of microscopic research methods have become an emerging trend in physical chemistry. Techniques featuring the use of optical, magnetic, and acoustic tweezers have been developed to manipulate objects at the microscopic scale. Optical tweezers use momentum transfer between light and objects to manipulate objects and can stably trap and manipulate mesoscopic particles, even single molecules, by exerting pico-newton force. With advantages including non-invasiveness, non-damaging, and ultra-high sensitivity, optical tweezers are ideal for studying individual molecules, molecular aggregates, condensed matter, chemical bonds, and intermolecular interactions. This technique has the potential to revolutionize the fields of chemistry, physics, information technology, and life sciences. Arthur Ashkin was awarded the 2018 Nobel Prize in Physics for his contribution to the development of this technique. The trapping force of the conventional optical tweezers technique originates from the light intensity gradient. Because of the diffraction limit of light, the trapping and manipulation of micro-nano objects < 100 nm in size with traditional optical tweezers is difficult. However, simply increasing the optical power used for trapping induces serious thermal effects and photodamage. By developing unique materials and structures coupled with optical tweezers, researchers have broken the diffraction limit of light and achieved sub-nanometer single-molecule trapping. In this review, we summarize the recent advances in the application of various optical tweezers techniques in physical chemistry and demonstrate the technical principles of fiber, photonic crystal, and plasmonic optical tweezers, respectively. We focus on the development and application of plasmonic optical tweezers and single-molecule plasmonic optical trapping based on tunable nanogaps. Generally, optical tweezers can realize the trapping and manipulation of molecular-scale particles via two main technical routes. The first route is improving the laser focusing ability through unique optical path design and optical component fabrication. The second involves enhancing the trapping field through ingenious auxiliary structure design. Finally, we present the promising future developments and applications of optical tweezers technology.
2024, 40(1): 230304
doi: 10.3866/PKU.WHXB202303047
Abstract:
Phenothiazines (PTZs), have received a lot of attention for many optoelectronic applications, such as hole-transporting layers, functioning as host materials for organic light-emitting diodes; dye sensitizers in dye-sensitized solar cells; and hole-transporting materials for perovskite solar cells. However, studies on benzophenothiazine materials are limited. In this study, we synthesize three isomeric bis-benzophenothiazine compounds (D-PTZa, D-PTZb, and D-PTZc), all bearing an aromatic ring at the 1, 2-, 2, 3-, and 3, 4-positions, respectively. Next, we systematically investigate the relationship between their structures and properties and compare them with bis-phenothiazine compounds (D-PTZ). The highest occupied molecular orbital (HOMO) distributions for D-PTZb and D-PTZc are dispersed over benzophenothiazine moities, whereas the lowest unoccupied molecular orbitals (LUMOs) are localized at the middle phenyl- and naphthyl-groups, which are similar frontier orbital distribuitions to the D-PTZ case. For D-PTZa, the steric hindrance between the phenyl groups at the 1, 2- and middle positions increases, significantly distorting its spatial structure. Therefore, its HOMO and LUMO distributions differ from those of D-PTZb and D-PTZc. Notably, the HOMOs in D-PTZa are dispersed over the middle phenyl group and nitrogen atom, whereas the LUMOs are localized at the naphthyl group. The hole/electron excitation and frontier orbital analyses demonstrate that strong local π → π* transition mixing with weak charge transfer transition is responsible for the luminescence of D-PTZb and D-PTZc. Interestingly, the ultraviolet–visible absorption spectra of all samples exhibit strong π → π* transition absorption and weak n → π* transition absorption. Furthermore, the conjugated length of the molecule can be effectively increased with the introduction of an aromatic ring, resulting in a red-shift in the maximum absorption wavelength. Compared to D-PTZ, D-PTZa emits yellow-green light with a photoluminescence quantum efficiency (PLQE) of 14%. In addition, the introduction of a phenyl group at the 2, 3-position effectively stabilizes the HOMO energy level, slightly increasing its π → π* transition gap, while also emitting blue light with a PLQE of 1.7%. For D-PTZc, the introduction of a phenyl group at the 3, 4-position better linearizes the LUMO distribution, thereby stabilizing the LUMO energy level and reducing its π → π* transition gap. The maximum emission peak is observed at 520 nm, emitting yellow-green light with a PLQE of 13%. Overall, our molecular design and results on structure–property relationships can provide fundamental guidance for the design of phenothiazine derivatives with specific photoelectric performance. ![]()
Phenothiazines (PTZs), have received a lot of attention for many optoelectronic applications, such as hole-transporting layers, functioning as host materials for organic light-emitting diodes; dye sensitizers in dye-sensitized solar cells; and hole-transporting materials for perovskite solar cells. However, studies on benzophenothiazine materials are limited. In this study, we synthesize three isomeric bis-benzophenothiazine compounds (D-PTZa, D-PTZb, and D-PTZc), all bearing an aromatic ring at the 1, 2-, 2, 3-, and 3, 4-positions, respectively. Next, we systematically investigate the relationship between their structures and properties and compare them with bis-phenothiazine compounds (D-PTZ). The highest occupied molecular orbital (HOMO) distributions for D-PTZb and D-PTZc are dispersed over benzophenothiazine moities, whereas the lowest unoccupied molecular orbitals (LUMOs) are localized at the middle phenyl- and naphthyl-groups, which are similar frontier orbital distribuitions to the D-PTZ case. For D-PTZa, the steric hindrance between the phenyl groups at the 1, 2- and middle positions increases, significantly distorting its spatial structure. Therefore, its HOMO and LUMO distributions differ from those of D-PTZb and D-PTZc. Notably, the HOMOs in D-PTZa are dispersed over the middle phenyl group and nitrogen atom, whereas the LUMOs are localized at the naphthyl group. The hole/electron excitation and frontier orbital analyses demonstrate that strong local π → π* transition mixing with weak charge transfer transition is responsible for the luminescence of D-PTZb and D-PTZc. Interestingly, the ultraviolet–visible absorption spectra of all samples exhibit strong π → π* transition absorption and weak n → π* transition absorption. Furthermore, the conjugated length of the molecule can be effectively increased with the introduction of an aromatic ring, resulting in a red-shift in the maximum absorption wavelength. Compared to D-PTZ, D-PTZa emits yellow-green light with a photoluminescence quantum efficiency (PLQE) of 14%. In addition, the introduction of a phenyl group at the 2, 3-position effectively stabilizes the HOMO energy level, slightly increasing its π → π* transition gap, while also emitting blue light with a PLQE of 1.7%. For D-PTZc, the introduction of a phenyl group at the 3, 4-position better linearizes the LUMO distribution, thereby stabilizing the LUMO energy level and reducing its π → π* transition gap. The maximum emission peak is observed at 520 nm, emitting yellow-green light with a PLQE of 13%. Overall, our molecular design and results on structure–property relationships can provide fundamental guidance for the design of phenothiazine derivatives with specific photoelectric performance.
2024, 40(1): 230401
doi: 10.3866/PKU.WHXB202304015
Abstract:
Currently, the world is at the intersection of the energy and computer revolutions. The electronic information industry, driven by the fields of 5G communication, smartphones, and new energy vehicles, is booming and has become an important pillar of the economic market. Multilayer ceramic capacitors (MLCC), which are passive electronic components with the highest market share, are one of the key products that require breakthroughs in key technologies in the basic electronic component industry, with wide applications in automotive electronics, power grid frequency modulation, aerospace, and other fields. With the trend of miniaturization and thin lamination, the thickness of the dielectric layer in the MLCC is decreasing continuously, whereas the electric field on the single dielectric layer is increasing significantly when the MLCC is applied under the same voltage, particularly for the ultrathin-layered MLCC served under medium/high voltage. Consequently, the reliability of MLCC has become a key product quality indicator. In this study, the deterioration mechanism of ultrathin-layer MLCC is systematically studied via accelerated aging tests, high-temperature impedance spectroscopy, and leakage current tests. During the accelerated aging test, the ceramic dielectrics degrades under the applied strict electric field and temperature, and the oxygen vacancies gradually migrate in grains and transgranularly, finally accumulating near the cathode, as observed by transmission electron microscopy. Consequently, a semiconducting layer with poor insulation performance near the cathode is formed, and the barrier height at the interface is reduced. Based on the results of the high-temperature impedance spectroscopy and leakage current test, the activation energy at the grain boundary and dielectric-electrode interface decreases, and the leakage current density increases significantly for the aged MLCC. The formation of an oxygen-vacancy-enriched semiconducting layer is a great threat to the reliability of MLCC, particularly under the trend of developing increasingly thinner dielectric layers. Therefore, inhibiting the migration and enrichment of oxygen vacancies is a top priority for ensuring the reliability of MLCC. To improve the reliability of ultrathin-layered MLCC, the oxygen vacancy concentration in ceramic dielectrics should be reduced, the activation energy required for its migration should be increased, and the Schottky barrier at the interface should be improved. All these results provide a powerful guide for the design of ultrathin-layered MLCC dielectric materials, which is expected to promote the upgrade iteration of high-end MLCC. ![]()
Currently, the world is at the intersection of the energy and computer revolutions. The electronic information industry, driven by the fields of 5G communication, smartphones, and new energy vehicles, is booming and has become an important pillar of the economic market. Multilayer ceramic capacitors (MLCC), which are passive electronic components with the highest market share, are one of the key products that require breakthroughs in key technologies in the basic electronic component industry, with wide applications in automotive electronics, power grid frequency modulation, aerospace, and other fields. With the trend of miniaturization and thin lamination, the thickness of the dielectric layer in the MLCC is decreasing continuously, whereas the electric field on the single dielectric layer is increasing significantly when the MLCC is applied under the same voltage, particularly for the ultrathin-layered MLCC served under medium/high voltage. Consequently, the reliability of MLCC has become a key product quality indicator. In this study, the deterioration mechanism of ultrathin-layer MLCC is systematically studied via accelerated aging tests, high-temperature impedance spectroscopy, and leakage current tests. During the accelerated aging test, the ceramic dielectrics degrades under the applied strict electric field and temperature, and the oxygen vacancies gradually migrate in grains and transgranularly, finally accumulating near the cathode, as observed by transmission electron microscopy. Consequently, a semiconducting layer with poor insulation performance near the cathode is formed, and the barrier height at the interface is reduced. Based on the results of the high-temperature impedance spectroscopy and leakage current test, the activation energy at the grain boundary and dielectric-electrode interface decreases, and the leakage current density increases significantly for the aged MLCC. The formation of an oxygen-vacancy-enriched semiconducting layer is a great threat to the reliability of MLCC, particularly under the trend of developing increasingly thinner dielectric layers. Therefore, inhibiting the migration and enrichment of oxygen vacancies is a top priority for ensuring the reliability of MLCC. To improve the reliability of ultrathin-layered MLCC, the oxygen vacancy concentration in ceramic dielectrics should be reduced, the activation energy required for its migration should be increased, and the Schottky barrier at the interface should be improved. All these results provide a powerful guide for the design of ultrathin-layered MLCC dielectric materials, which is expected to promote the upgrade iteration of high-end MLCC.
