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2024 Volume 40 Issue 11
2024, 40(11): 231102
doi: 10.3866/PKU.WHXB202311026
Abstract:
Capacitive deionization (CDI) technology is considered to be an emerging water treatment technology in the 21st century, owing to its low energy consumption, absence of secondary pollution, and straightforward operation. The advancement of basic theory and computer science has facilitated the use of multi-angle numerical simulations for CDI. However, due to errors in experimental methods, a direct understanding of mechanisms such as the kinetic characteristics of ion diffusion inside electrode materials, structural evolution during charging and discharging, and the intrinsic connection between potentials and structures is lacking. Existing experimental methods fall short of providing clear theoretical explanations for these phenomena. In contrast, numerical simulations offer a better comprehension of the chemical and electrochemical evolution in CDI. Beyond electrode materials, the device configuration of CDI significantly impacts its performance. Utilizing numerical simulations to study the optimal device configuration is expected to enhance economic efficiency and promote the practical application of CDI. While current reviews of CDI focus primarily on electrode materials and device configurations, there is a dearth of comprehensive reviews on cutting-edge numerical simulation research in the CDI field. This review commences with the earliest continuous-scale model used to describe the dynamic process of CDI. It systematically categorizes multi-angle numerical simulations in CDI, summarizes the strengths and weaknesses of different numerical simulation methods, and anticipates future development directions. Continuous-scale models accurately characterize the ion dynamics of CDI, determining rate and process constraints. Pore-scale models analyze the microstructure of porous media, obviating the need for empirical formulas to preset transport parameters for continuous-scale models. Researchers have introduced molecular dynamics simulation and density functional theory into CDI research, effectively analyzing the influence of structural features at the molecular/atomic level of electrode materials on the CDI system. This aids researchers in enhancing the efficacy and ionic selectivity of CDI electrode materials through pore engineering, defect engineering, and electrochemical microcosmic modulation engineering. Finite element analysis guides improvements in ion diffusion and stability of electrode materials, while computational fluid dynamics provides references for designing high-performance CDI devices. Data-driven machine learning excels in handling nonlinear data and uncovering complex mechanisms of CDI water treatment processes, while digital twin technology can reduce operation and maintenance costs of CDI. Considering costs in practical applications, techno-economic analysis plays a pivotal role in promoting the practical application of CDI technology. This review, the first of its kind, provides an essential theoretical foundation and research ideas for the new paradigm of CDI research by summarizing the advantages and disadvantages of different numerical simulation methods and offering insights into cutting-edge perspectives in the field of CDI. ![]()
Capacitive deionization (CDI) technology is considered to be an emerging water treatment technology in the 21st century, owing to its low energy consumption, absence of secondary pollution, and straightforward operation. The advancement of basic theory and computer science has facilitated the use of multi-angle numerical simulations for CDI. However, due to errors in experimental methods, a direct understanding of mechanisms such as the kinetic characteristics of ion diffusion inside electrode materials, structural evolution during charging and discharging, and the intrinsic connection between potentials and structures is lacking. Existing experimental methods fall short of providing clear theoretical explanations for these phenomena. In contrast, numerical simulations offer a better comprehension of the chemical and electrochemical evolution in CDI. Beyond electrode materials, the device configuration of CDI significantly impacts its performance. Utilizing numerical simulations to study the optimal device configuration is expected to enhance economic efficiency and promote the practical application of CDI. While current reviews of CDI focus primarily on electrode materials and device configurations, there is a dearth of comprehensive reviews on cutting-edge numerical simulation research in the CDI field. This review commences with the earliest continuous-scale model used to describe the dynamic process of CDI. It systematically categorizes multi-angle numerical simulations in CDI, summarizes the strengths and weaknesses of different numerical simulation methods, and anticipates future development directions. Continuous-scale models accurately characterize the ion dynamics of CDI, determining rate and process constraints. Pore-scale models analyze the microstructure of porous media, obviating the need for empirical formulas to preset transport parameters for continuous-scale models. Researchers have introduced molecular dynamics simulation and density functional theory into CDI research, effectively analyzing the influence of structural features at the molecular/atomic level of electrode materials on the CDI system. This aids researchers in enhancing the efficacy and ionic selectivity of CDI electrode materials through pore engineering, defect engineering, and electrochemical microcosmic modulation engineering. Finite element analysis guides improvements in ion diffusion and stability of electrode materials, while computational fluid dynamics provides references for designing high-performance CDI devices. Data-driven machine learning excels in handling nonlinear data and uncovering complex mechanisms of CDI water treatment processes, while digital twin technology can reduce operation and maintenance costs of CDI. Considering costs in practical applications, techno-economic analysis plays a pivotal role in promoting the practical application of CDI technology. This review, the first of its kind, provides an essential theoretical foundation and research ideas for the new paradigm of CDI research by summarizing the advantages and disadvantages of different numerical simulation methods and offering insights into cutting-edge perspectives in the field of CDI.
2024, 40(11): 231101
doi: 10.3866/PKU.WHXB202311011
Abstract:
Metal halide perovskite (MHP) materials show great prospects in applications such as solar cells, luminescent displays, and biomedicines, owing to their outstanding visible light absorption, photoelectric conversion, adjustable energy level structure, and low energy consumption. Their exceptional properties, such as high visible light absorption, efficient photoelectric conversion, adjustable energy level structure, and low energy consumption, have attracted significant attention. However, the presence of ion migration in MHPs has been identified as a critical challenge, leading to reduced energy conversion efficiency and device instability. Overcoming this obstacle is crucial for the commercialization of perovskite-based technologies. In recent years, extensive research has been conducted to understand the conditions and mechanisms of ion migration in perovskite materials, as well as develop strategies to mitigate its adverse effects. This paper adopts a dialectical perspective on ion migration, with a specific focus on energy barriers. A comprehensive review is provided, covering the fundamental concepts and formation mechanisms of both irreversible unidirectional and reversible bidirectional ion migrations. This paper begins by presenting a detailed summary of the degradation processes caused by irreversible unidirectional ion migrations phenomena induced by external fields, including illumination, stress/strain, thermal and electrical fields. Understanding the underlying mechanisms of such degradation is essential to address the stability concerns associated with perovskite devices. Moreover, the overview of bidirectional reversible ion migration phenomena in perovskite is presented. The cyclic formation and restoration of Schottky barriers at the interface can significantly influence the photoelectrical properties and impact the overall performance of perovskite devices. Various strategies for regulating ion migrations under external fields are discussed, aiming to enhance device stability and performance. By understanding the energy landscape and migration pathways, researchers can develop effective strategies to control and optimize ion migrations, ultimately improving the photoelectric conversion performance of perovskite devices. This paper provides comprehensive analysis of ion migration in perovskite materials, addressing fundamental concepts, ion migration mechanisms, and strategies for regulating ion migrations. By providing a clear understanding of the challenges associated with ion migration, this work contributes to the advancement of perovskite-based technologies and facilitates their commercialization. Ultimately, the optimization of ion migration control will lead to improved performance and stability of perovskite devices, enabling their widespread adoption in various applications.![]()
Metal halide perovskite (MHP) materials show great prospects in applications such as solar cells, luminescent displays, and biomedicines, owing to their outstanding visible light absorption, photoelectric conversion, adjustable energy level structure, and low energy consumption. Their exceptional properties, such as high visible light absorption, efficient photoelectric conversion, adjustable energy level structure, and low energy consumption, have attracted significant attention. However, the presence of ion migration in MHPs has been identified as a critical challenge, leading to reduced energy conversion efficiency and device instability. Overcoming this obstacle is crucial for the commercialization of perovskite-based technologies. In recent years, extensive research has been conducted to understand the conditions and mechanisms of ion migration in perovskite materials, as well as develop strategies to mitigate its adverse effects. This paper adopts a dialectical perspective on ion migration, with a specific focus on energy barriers. A comprehensive review is provided, covering the fundamental concepts and formation mechanisms of both irreversible unidirectional and reversible bidirectional ion migrations. This paper begins by presenting a detailed summary of the degradation processes caused by irreversible unidirectional ion migrations phenomena induced by external fields, including illumination, stress/strain, thermal and electrical fields. Understanding the underlying mechanisms of such degradation is essential to address the stability concerns associated with perovskite devices. Moreover, the overview of bidirectional reversible ion migration phenomena in perovskite is presented. The cyclic formation and restoration of Schottky barriers at the interface can significantly influence the photoelectrical properties and impact the overall performance of perovskite devices. Various strategies for regulating ion migrations under external fields are discussed, aiming to enhance device stability and performance. By understanding the energy landscape and migration pathways, researchers can develop effective strategies to control and optimize ion migrations, ultimately improving the photoelectric conversion performance of perovskite devices. This paper provides comprehensive analysis of ion migration in perovskite materials, addressing fundamental concepts, ion migration mechanisms, and strategies for regulating ion migrations. By providing a clear understanding of the challenges associated with ion migration, this work contributes to the advancement of perovskite-based technologies and facilitates their commercialization. Ultimately, the optimization of ion migration control will lead to improved performance and stability of perovskite devices, enabling their widespread adoption in various applications.
2024, 40(11): 231100
doi: 10.3866/PKU.WHXB202311001
Abstract:
The construct of the internal electric field (IEF) is recognized as an effective driver for promoting charge migration and separation to enhance photocatalytic performance. In this study, one-dimensional nanorods of Mn0.2Cd0.8S (MCS) co-doped with interstitial chlorine (Clint) and substitutional chlorine (Clsub) were designed and synthesized using a one-step solvothermal method. The incorporation of Clint and Clsub led to an unbalanced charge distribution and the formation of IEF in the MCS nanorods, contributing to the improvement of photogenerated carrier kinetic behavior. Through density functional theory (DFT) calculations, the effect of Clint and Clsub doping on the activity of the MCS was visually explained by examining differences in electronic structure, charge distribution and H2 adsorption/desorption balance. Interestingly, the modulation of the energy band structure of MCS primarily resulted from the contribution of Clint, while Clsub playing a negligible role. Moreover, the Clsub further facilitated the optimization of Clint concerning the H2 adsorption-desorption Gibbs free energy (ΔGH*) of MCS. Ultimately, the ΔGH* of 0.9 Cl-MCS favored H2 production (1.14 vs. 0.17 eV), leading to a 9 times increase in photocatalytic H2 production activity compared to MCS. This investigation presents a valuable approach for constructing IEF in bimetallic sulfide photocatalysts.![]()
The construct of the internal electric field (IEF) is recognized as an effective driver for promoting charge migration and separation to enhance photocatalytic performance. In this study, one-dimensional nanorods of Mn0.2Cd0.8S (MCS) co-doped with interstitial chlorine (Clint) and substitutional chlorine (Clsub) were designed and synthesized using a one-step solvothermal method. The incorporation of Clint and Clsub led to an unbalanced charge distribution and the formation of IEF in the MCS nanorods, contributing to the improvement of photogenerated carrier kinetic behavior. Through density functional theory (DFT) calculations, the effect of Clint and Clsub doping on the activity of the MCS was visually explained by examining differences in electronic structure, charge distribution and H2 adsorption/desorption balance. Interestingly, the modulation of the energy band structure of MCS primarily resulted from the contribution of Clint, while Clsub playing a negligible role. Moreover, the Clsub further facilitated the optimization of Clint concerning the H2 adsorption-desorption Gibbs free energy (ΔGH*) of MCS. Ultimately, the ΔGH* of 0.9 Cl-MCS favored H2 production (1.14 vs. 0.17 eV), leading to a 9 times increase in photocatalytic H2 production activity compared to MCS. This investigation presents a valuable approach for constructing IEF in bimetallic sulfide photocatalysts.
2024, 40(11): 230904
doi: 10.3866/PKU.WHXB202309043
Abstract:
Olefins play a crucial role as fundamental raw materials in organic synthesis, particularly in the production of polyolefins and synthetic rubber. The conversion of alkynes to olefins is pivotal in both the polymer and fine chemical industries. However, this process faces significant challenges in terms of equilibrium selectivity and activity. The inherent low solubility of hydrogen, coupled with the thermodynamic ease of hydrogenating intermediate olefins compared to alkynes, contributes to a decline in olefin selectivity due to further hydrogenation leading to alkanes. Palladium-based catalysts, widely used for hydrogenation, exhibit robust hydrogen adsorption but lack selectivity. Researchers commonly modify catalyst structures by introducing other metals or non-metals to create intermetallic compounds, aiming to enhance olefin selectivity. This study focuses on synthesizing palladium-sulfur nanosheets (Pd-S NSs) using various sulfur sources to explore the impact of surface S species on the catalytic efficiency of selectively hydrogenating alkynes. Among these, Pd-S-PT NSs/C, utilizing 1,4-benzenedithiol (PT) as the sulfur source, demonstrated high styrene selectivity (92.3%–96.7%) following phenylacetylene hydrogenation for 2 h, showing notable selectivity for different alkynes' end-groups. Contrastingly, Pd-S-TU NSs/C, with thiourea (TU) as the sulfur source, exhibited poor olefin selectivity (72.4%). X-ray photoelectron spectroscopy (XPS) revealed that the improved olefin selectivity in Pd-S-PT NSs/C was attributed to hindered electron transfer from Pd to S, as well as the presence of surface S0 species, maintaining high hydrogenation activity while avoiding over-hydrogenation induced by oxidized S species (S4+). In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) demonstrated weak styrene adsorption on Pd-S-PT NSs, inhibiting further hydrogenation to ethylbenzene. The ease of styrene desorption on Pd-S-PT NSs, indicated by reduced adsorption strength with increasing desorption temperature, highlighted high olefin selectivity. Conversely, stronger styrene adsorption on Pd-S-TU NSs facilitated additional hydrogenation to produce ethylbenzene, suggesting that the presence of additional S4+ species hindered improved styrene selectivity. This study not only introduces efficient catalysts for olefin hydrogenation but also advances fundamental research on precisely controlling catalytic processes, particularly focusing on the nuanced control of catalytic surfaces.![]()
Olefins play a crucial role as fundamental raw materials in organic synthesis, particularly in the production of polyolefins and synthetic rubber. The conversion of alkynes to olefins is pivotal in both the polymer and fine chemical industries. However, this process faces significant challenges in terms of equilibrium selectivity and activity. The inherent low solubility of hydrogen, coupled with the thermodynamic ease of hydrogenating intermediate olefins compared to alkynes, contributes to a decline in olefin selectivity due to further hydrogenation leading to alkanes. Palladium-based catalysts, widely used for hydrogenation, exhibit robust hydrogen adsorption but lack selectivity. Researchers commonly modify catalyst structures by introducing other metals or non-metals to create intermetallic compounds, aiming to enhance olefin selectivity. This study focuses on synthesizing palladium-sulfur nanosheets (Pd-S NSs) using various sulfur sources to explore the impact of surface S species on the catalytic efficiency of selectively hydrogenating alkynes. Among these, Pd-S-PT NSs/C, utilizing 1,4-benzenedithiol (PT) as the sulfur source, demonstrated high styrene selectivity (92.3%–96.7%) following phenylacetylene hydrogenation for 2 h, showing notable selectivity for different alkynes' end-groups. Contrastingly, Pd-S-TU NSs/C, with thiourea (TU) as the sulfur source, exhibited poor olefin selectivity (72.4%). X-ray photoelectron spectroscopy (XPS) revealed that the improved olefin selectivity in Pd-S-PT NSs/C was attributed to hindered electron transfer from Pd to S, as well as the presence of surface S0 species, maintaining high hydrogenation activity while avoiding over-hydrogenation induced by oxidized S species (S4+). In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) demonstrated weak styrene adsorption on Pd-S-PT NSs, inhibiting further hydrogenation to ethylbenzene. The ease of styrene desorption on Pd-S-PT NSs, indicated by reduced adsorption strength with increasing desorption temperature, highlighted high olefin selectivity. Conversely, stronger styrene adsorption on Pd-S-TU NSs facilitated additional hydrogenation to produce ethylbenzene, suggesting that the presence of additional S4+ species hindered improved styrene selectivity. This study not only introduces efficient catalysts for olefin hydrogenation but also advances fundamental research on precisely controlling catalytic processes, particularly focusing on the nuanced control of catalytic surfaces.
2024, 40(11): 240200
doi: 10.3866/PKU.WHXB202402006
Abstract:
Organic-inorganic halide perovskite solar cells (PSCs) have received widespread attention due to their outstanding photovoltaic performance and straightforward preparation process. However, charge recombination at the interface is a crucial factor limiting further enhancement of the power conversion efficiency (PCE) of the PSCs. In this study, we report the interfacial modification between the electron transport layer and the perovskite film (PSK) using ammonium hexachlorostannate (AH) crystals synthesized via the room temperature spin-coating method. AH as an inorganic tin-based perovskite material, can passivate defects in the PSK and establish a better lattice match, thereby enhancing the quality and crystallinity of the PSK. Kelvin probe force microscopy results confirm that AH promotes the directional migration of photogenerated electrons. Femtosecond transient absorption spectroscopy results verify that AH effectively shortens the lifetime of electron extraction and facilitates interfacial electron transfer. Based on the benefits of AH modification, AH-based PSCs exhibit higher PCE and reduced hysteresis effect.![]()
Organic-inorganic halide perovskite solar cells (PSCs) have received widespread attention due to their outstanding photovoltaic performance and straightforward preparation process. However, charge recombination at the interface is a crucial factor limiting further enhancement of the power conversion efficiency (PCE) of the PSCs. In this study, we report the interfacial modification between the electron transport layer and the perovskite film (PSK) using ammonium hexachlorostannate (AH) crystals synthesized via the room temperature spin-coating method. AH as an inorganic tin-based perovskite material, can passivate defects in the PSK and establish a better lattice match, thereby enhancing the quality and crystallinity of the PSK. Kelvin probe force microscopy results confirm that AH promotes the directional migration of photogenerated electrons. Femtosecond transient absorption spectroscopy results verify that AH effectively shortens the lifetime of electron extraction and facilitates interfacial electron transfer. Based on the benefits of AH modification, AH-based PSCs exhibit higher PCE and reduced hysteresis effect.
2024, 40(11): 240300
doi: 10.3866/PKU.WHXB202403009
Abstract:
Hydrogen peroxide (H2O2) plays a significant role as an industrial chemical and potential energy carrier. However, common H2O2 photosynthesis catalysts face challenges such as limited solar spectrum absorption, severe agglomeration, and difficulty in reuse, hindering their widespread application. In this study, an inorganic/organic heterojunction photocatalyst comprising g-C3N4 nanosheets and Bi4Ti3O12 nanofibers is synthesized using electrospinning assisted self-assembly methods. The Bi4Ti3O12/g-C3N4 heterojunction exhibits significantly enhanced H2O2 yield of 1650 μmol∙g−1∙h−1 and efficient H2O2 photosynthesis directly from pure water. The improved performance is attributed to enhanced visible light absorption, charge separation efficiency, and boosting redox properties of photoinduced carriers in S-scheme heterojunctions. Additionally, the utilization of in situ X-ray photoelectron spectroscopy (ISXPS) enables the investigation of the S-scheme mechanism and dynamics of inorganic/organic Bi4Ti3O12/g-C3N4 heterojunctions. This research presents a novel approach for designing inorganic/organic heterojunction photocatalysts for solar-driven H2O2 production.![]()
Hydrogen peroxide (H2O2) plays a significant role as an industrial chemical and potential energy carrier. However, common H2O2 photosynthesis catalysts face challenges such as limited solar spectrum absorption, severe agglomeration, and difficulty in reuse, hindering their widespread application. In this study, an inorganic/organic heterojunction photocatalyst comprising g-C3N4 nanosheets and Bi4Ti3O12 nanofibers is synthesized using electrospinning assisted self-assembly methods. The Bi4Ti3O12/g-C3N4 heterojunction exhibits significantly enhanced H2O2 yield of 1650 μmol∙g−1∙h−1 and efficient H2O2 photosynthesis directly from pure water. The improved performance is attributed to enhanced visible light absorption, charge separation efficiency, and boosting redox properties of photoinduced carriers in S-scheme heterojunctions. Additionally, the utilization of in situ X-ray photoelectron spectroscopy (ISXPS) enables the investigation of the S-scheme mechanism and dynamics of inorganic/organic Bi4Ti3O12/g-C3N4 heterojunctions. This research presents a novel approach for designing inorganic/organic heterojunction photocatalysts for solar-driven H2O2 production.
2024, 40(11): 240303
doi: 10.3866/PKU.WHXB202403032
Abstract:
Increasing the CO2 concentration on the surface of the photocatalysts helps to increase the reaction dynamic rate of the photocatalytic CO2 reduction. However, the low solubility and poor mass transfer of CO2 in aqueous phase seriously hinder the adsorption and conversion of CO2 at the active site. In this work, the porous liquid photocatalyst (NH2-UIO-66 PL) with strong hydrophobicity has been synthesized by grafting the hydrophobic liquid end long-chain (PDMS) onto the amino site of metal-organic framework (NH2-UIO-66). It is found that the NH2-UIO-66 PL with permanent porosity causes a large amount of CO2 to be concentrated in the porous liquid cavity for transporting and diffusing CO2 onto the photocatalyst surface rapidly, and then the CO2 affinity surface with high positive potential and key intermediates for activation reduction reactions are formed with the grafting of hydrophobic PDMS, leading to stronger electron enrichment Zr active sites for enhancement of the overall CO2 reduction ability. As a result, NH2-UIO-66 PL achieved CO2 photoreduction with a CO yield of 24.70 μmol∙g−1∙h−1 and CH4 yield of 7.93 μmol∙g−1∙h−1, which is 2.3-fold and 2.7-fold compared to hydrophilic NH2-UIO-66, respectively. This research provides a novel design of hydrophobic porous liquids to provide industrial possibilities for high CO2 adsorption and reduction.![]()
Increasing the CO2 concentration on the surface of the photocatalysts helps to increase the reaction dynamic rate of the photocatalytic CO2 reduction. However, the low solubility and poor mass transfer of CO2 in aqueous phase seriously hinder the adsorption and conversion of CO2 at the active site. In this work, the porous liquid photocatalyst (NH2-UIO-66 PL) with strong hydrophobicity has been synthesized by grafting the hydrophobic liquid end long-chain (PDMS) onto the amino site of metal-organic framework (NH2-UIO-66). It is found that the NH2-UIO-66 PL with permanent porosity causes a large amount of CO2 to be concentrated in the porous liquid cavity for transporting and diffusing CO2 onto the photocatalyst surface rapidly, and then the CO2 affinity surface with high positive potential and key intermediates for activation reduction reactions are formed with the grafting of hydrophobic PDMS, leading to stronger electron enrichment Zr active sites for enhancement of the overall CO2 reduction ability. As a result, NH2-UIO-66 PL achieved CO2 photoreduction with a CO yield of 24.70 μmol∙g−1∙h−1 and CH4 yield of 7.93 μmol∙g−1∙h−1, which is 2.3-fold and 2.7-fold compared to hydrophilic NH2-UIO-66, respectively. This research provides a novel design of hydrophobic porous liquids to provide industrial possibilities for high CO2 adsorption and reduction.
2024, 40(11): 240403
doi: 10.3866/PKU.WHXB202404030
Abstract:
Photocatalytic hydrogen evolution by heterojunction photocatalysts is considered an effective way to address environmental and energy crises. In this work, a novel ZnCoP/CdLa2S4 Schottky heterojunction was prepared via a physical mixing method assisted by water bath heating and used to enhance the efficiency of photocatalytic hydrogen production. Owing to the higher work function and metallic conductivity of ZnCoP, the photoinduced electrons can transfer from CdLa2S4 to ZnCoP through the ZnCoP/CdLa2S4 interface, which suppresses the recombination of photoinduced electrons and holes. Moreover, the Schottky heterojunction formed at the interface between ZnCoP and CdLa2S4 inhibits electron backflow from ZnCoP to CdLa2S4, which further promotes the separation of electron-hole pairs. Meanwhile, the ZnCoP/CdLa2S4 heterojunction exhibited enhanced visible light absorption compared to CdLa2S4. In addition, ZnCoP acts as an electron acceptor and hydrogen evolution active site. The synergistic effect of the tight ZnCoP/CdLa2S4 interface, the higher work function and metallic conductivity of ZnCoP, and the formation of Schottky junctions significantly enhance the photocatalytic hydrogen production evolution performance of CdLa2S4. When the amount of ZnCoP was 30 wt% (wt%, mass fraction), the 30ZCP/CLS composite showed the highest photocatalytic performance, and the hydrogen production rate reached 10.26 mmol·g-1·h-1 under visible light irradiation and with Na2S and Na2SO3 as sacrificial agents, which was 7.7 times that of CdLa2S4. Combined with the activity data and characterization results, a potential mechanism for photocatalytic hydrogen production over ZnCoP/CdLa2S4 Schottky heterojunctions was proposed.
Photocatalytic hydrogen evolution by heterojunction photocatalysts is considered an effective way to address environmental and energy crises. In this work, a novel ZnCoP/CdLa2S4 Schottky heterojunction was prepared via a physical mixing method assisted by water bath heating and used to enhance the efficiency of photocatalytic hydrogen production. Owing to the higher work function and metallic conductivity of ZnCoP, the photoinduced electrons can transfer from CdLa2S4 to ZnCoP through the ZnCoP/CdLa2S4 interface, which suppresses the recombination of photoinduced electrons and holes. Moreover, the Schottky heterojunction formed at the interface between ZnCoP and CdLa2S4 inhibits electron backflow from ZnCoP to CdLa2S4, which further promotes the separation of electron-hole pairs. Meanwhile, the ZnCoP/CdLa2S4 heterojunction exhibited enhanced visible light absorption compared to CdLa2S4. In addition, ZnCoP acts as an electron acceptor and hydrogen evolution active site. The synergistic effect of the tight ZnCoP/CdLa2S4 interface, the higher work function and metallic conductivity of ZnCoP, and the formation of Schottky junctions significantly enhance the photocatalytic hydrogen production evolution performance of CdLa2S4. When the amount of ZnCoP was 30 wt% (wt%, mass fraction), the 30ZCP/CLS composite showed the highest photocatalytic performance, and the hydrogen production rate reached 10.26 mmol·g-1·h-1 under visible light irradiation and with Na2S and Na2SO3 as sacrificial agents, which was 7.7 times that of CdLa2S4. Combined with the activity data and characterization results, a potential mechanism for photocatalytic hydrogen production over ZnCoP/CdLa2S4 Schottky heterojunctions was proposed.
2024, 40(11): 240501
doi: 10.3866/PKU.WHXB202405019
Abstract:
Designing heterojunctions using two semiconductors with aligned band structures is a promising strategy for solar energy-driven photocatalytic hydrogen production. Particularly, S-scheme heterojunctions exhibit significant promise for accelerating spatial separation and migration of photoexcited charge carriers while maintaining strong redox capacity. Herein, a hierarchical S-scheme composite of red phosphorus (RP) nanoparticles decorated flower-like CeO2 (CeO2/RP) was synthesized via the chemical vapor deposition process. Under simulated solar light irradiation, the optimized CeO2/RP S-scheme heterojunction exhibited a highly efficient photocatalytic hydrogen production rate of 297.8 μmol·h-1·g-1, which is approximately 8.8 and 5.7 times greater than that of pure CeO2 and RP, respectively. After decoration with RP, the optical absorption of CeO2/RP is greatly expanded to the visible light region. The effective photocatalytic performance can be primarily attributed to the presence of interfacial P-O-Ce bonds providing charge transfer pathways, as well as the development of a built-in electric field between CeO2 and RP at the intimate interface. The photogenerated electrons follow an S-scheme mechanism, the electric field drives directional charge transfer from the conduction band (CB) of CeO2 to the valence band (VB) of RP upon exposure to light, thus enabling the retention of photoexcited electrons and holes with higher redox potential at the CB of RP and the VB of CeO2, respectively. This work provides a novel vision in the fabrication of S-scheme photocatalytic heterojunction systems with great photocatalytic hydrogen production performance.
Designing heterojunctions using two semiconductors with aligned band structures is a promising strategy for solar energy-driven photocatalytic hydrogen production. Particularly, S-scheme heterojunctions exhibit significant promise for accelerating spatial separation and migration of photoexcited charge carriers while maintaining strong redox capacity. Herein, a hierarchical S-scheme composite of red phosphorus (RP) nanoparticles decorated flower-like CeO2 (CeO2/RP) was synthesized via the chemical vapor deposition process. Under simulated solar light irradiation, the optimized CeO2/RP S-scheme heterojunction exhibited a highly efficient photocatalytic hydrogen production rate of 297.8 μmol·h-1·g-1, which is approximately 8.8 and 5.7 times greater than that of pure CeO2 and RP, respectively. After decoration with RP, the optical absorption of CeO2/RP is greatly expanded to the visible light region. The effective photocatalytic performance can be primarily attributed to the presence of interfacial P-O-Ce bonds providing charge transfer pathways, as well as the development of a built-in electric field between CeO2 and RP at the intimate interface. The photogenerated electrons follow an S-scheme mechanism, the electric field drives directional charge transfer from the conduction band (CB) of CeO2 to the valence band (VB) of RP upon exposure to light, thus enabling the retention of photoexcited electrons and holes with higher redox potential at the CB of RP and the VB of CeO2, respectively. This work provides a novel vision in the fabrication of S-scheme photocatalytic heterojunction systems with great photocatalytic hydrogen production performance.
2024, 40(11): 240602
doi: 10.3866/PKU.WHXB202406027
Abstract:
Photocatalytic technology harnesses clean, non-polluting solar energy to synthesize hydrogen peroxide (H2O2). In this study, ZnO/PBD S-scheme heterojunction composites, featuring ZnO nanoparticles on a donor-acceptor conjugated polymer substrate (PBD), were synthesized via the Suzuki-Miyaura reaction and hydrothermal method. The optimal ZnO/PBD composite achieved an H2O2 production efficiency of 4.07 mmol·g-1·h-1, which is 5.4 times higher than that of pristine ZnO. This significant enhancement is attributed to the formation of S-scheme heterojunctions. The successful construction of S-scheme heterojunctions was confirmed through UV-visible absorption spectroscopy and in situ irradiated X-ray photoelectron spectroscopy. Steady-state photoluminescence and femtosecond transient absorption (fs-TA) spectroscopies identified and verified the presence of defect states in ZnO. These defect states trap photogenerated electrons, adversely affecting the photocatalytic reaction. However, the S-scheme heterojunction effectively promotes the separation and transfer of electrons, mitigating this issue. The measured lifetimes of photogenerated electrons in these defect states, as determined by fitted fs-TA decay kinetics, provided further evidence of the carrier transfer mechanism in S-scheme heterojunctions. This work introduces a novel approach for studying organic/inorganic S-scheme heterojunctions using fs-TA spectroscopy.
Photocatalytic technology harnesses clean, non-polluting solar energy to synthesize hydrogen peroxide (H2O2). In this study, ZnO/PBD S-scheme heterojunction composites, featuring ZnO nanoparticles on a donor-acceptor conjugated polymer substrate (PBD), were synthesized via the Suzuki-Miyaura reaction and hydrothermal method. The optimal ZnO/PBD composite achieved an H2O2 production efficiency of 4.07 mmol·g-1·h-1, which is 5.4 times higher than that of pristine ZnO. This significant enhancement is attributed to the formation of S-scheme heterojunctions. The successful construction of S-scheme heterojunctions was confirmed through UV-visible absorption spectroscopy and in situ irradiated X-ray photoelectron spectroscopy. Steady-state photoluminescence and femtosecond transient absorption (fs-TA) spectroscopies identified and verified the presence of defect states in ZnO. These defect states trap photogenerated electrons, adversely affecting the photocatalytic reaction. However, the S-scheme heterojunction effectively promotes the separation and transfer of electrons, mitigating this issue. The measured lifetimes of photogenerated electrons in these defect states, as determined by fitted fs-TA decay kinetics, provided further evidence of the carrier transfer mechanism in S-scheme heterojunctions. This work introduces a novel approach for studying organic/inorganic S-scheme heterojunctions using fs-TA spectroscopy.
2024, 40(11): 240600
doi: 10.3866/PKU.WHXB202406005
Abstract:
Graphitic carbon nitride (g-C3N4) has gained growing attention in hydrogen peroxide (H2O2) photosynthesis, but the low activity of two-electron oxygen reduction reaction (2e--ORR) still restricts its photocatalytic H2O2-generation performance. Herein, traditional g-C3N4 photocatalysts are recrystallized on KI crystal surfaces by a secondary calcination route to synthesize K incorporated highly-crystalline g-C3N4 photocatalysts. The synthesized CN-K photocatalyst exhibits improved inter-plane crystallization, narrowed bandgap structure, and smaller particle size from 20 to 50 nm. Moreover, the incorporated K atoms, as excellent catalytic sites, can enhance O2 adsorption and stabilize the *OOH intermediates, thus improving the 2e--ORR activity of the K incorporated high-crystallization g-C3N4 photocatalysts. Consequently, the optimized CN-K(1:6) photocatalyst exhibits a remarkably improved H2O2-generation rate of 7.8 mmol·L-1·h-1 with an AQE value of 5.17% at 420 nm, outperforming the traditional g-C3N4 sample by a factor of 220. This work uncovers the roles of heteroatoms in promoting the 2e--ORR selectivity of the g-C3N4 photocatalyst, and offers novel insights to construct highly-active g-C3N4-based materials for H2O2 photosynthesis.
Graphitic carbon nitride (g-C3N4) has gained growing attention in hydrogen peroxide (H2O2) photosynthesis, but the low activity of two-electron oxygen reduction reaction (2e--ORR) still restricts its photocatalytic H2O2-generation performance. Herein, traditional g-C3N4 photocatalysts are recrystallized on KI crystal surfaces by a secondary calcination route to synthesize K incorporated highly-crystalline g-C3N4 photocatalysts. The synthesized CN-K photocatalyst exhibits improved inter-plane crystallization, narrowed bandgap structure, and smaller particle size from 20 to 50 nm. Moreover, the incorporated K atoms, as excellent catalytic sites, can enhance O2 adsorption and stabilize the *OOH intermediates, thus improving the 2e--ORR activity of the K incorporated high-crystallization g-C3N4 photocatalysts. Consequently, the optimized CN-K(1:6) photocatalyst exhibits a remarkably improved H2O2-generation rate of 7.8 mmol·L-1·h-1 with an AQE value of 5.17% at 420 nm, outperforming the traditional g-C3N4 sample by a factor of 220. This work uncovers the roles of heteroatoms in promoting the 2e--ORR selectivity of the g-C3N4 photocatalyst, and offers novel insights to construct highly-active g-C3N4-based materials for H2O2 photosynthesis.
2024, 40(11): 240601
doi: 10.3866/PKU.WHXB202406019
Abstract:
The generation of hydrogen peroxide (H2O2) from water and oxygen redox reaction by photocatalysis has acquired increasing attention owing to its green and clean properties. Aiming at the low intrinsic photocatalytic activity of carbon nitride (g-C3N4), here, an ultrathin g-C3N4 nanosheet photocatalyst with a large surface area and enhanced crystallinity was fabricated by a two-step thermal polymerization technique. The calcination parameters showed a significant impact on the structural properties and catalytic performance of g-C3N4. The remarkable H2O2 yield (3177.0 µmol·g-1·h-1) of CN-T-1 (by two-step calcination, 1 ℃·min-1 optimal heating rate) was 3.7 times that (858.6 µmol·g-1·h-1) of CN-O-1 (by one-step calcination, 1 ℃·min-1 heating rate) and higher than those of pure g-C3N4 in literature. Most of the H2O2 yield for CN-T-1 remained after five cycles, showing good stability. The enhanced catalytic performance of CN-T-1 than CN-O-1 is owing to its larger specific surface area, enhanced crystallinity, higher oxygen adsorption ability and photogenerated carrier separation efficiency, longer lifetime of carriers, and slightly larger bandgap (3.07 eV, +0.26 eV bigger than CN-O-1) with more positive valence band position owing to ultrathin layers. The •O2- radicals were verified to be the primary active species. A two-step single electron ORR pathway (O2 + e- → •O2- → H2O2) was confirmed for H2O2 production over CN-T-1.
The generation of hydrogen peroxide (H2O2) from water and oxygen redox reaction by photocatalysis has acquired increasing attention owing to its green and clean properties. Aiming at the low intrinsic photocatalytic activity of carbon nitride (g-C3N4), here, an ultrathin g-C3N4 nanosheet photocatalyst with a large surface area and enhanced crystallinity was fabricated by a two-step thermal polymerization technique. The calcination parameters showed a significant impact on the structural properties and catalytic performance of g-C3N4. The remarkable H2O2 yield (3177.0 µmol·g-1·h-1) of CN-T-1 (by two-step calcination, 1 ℃·min-1 optimal heating rate) was 3.7 times that (858.6 µmol·g-1·h-1) of CN-O-1 (by one-step calcination, 1 ℃·min-1 heating rate) and higher than those of pure g-C3N4 in literature. Most of the H2O2 yield for CN-T-1 remained after five cycles, showing good stability. The enhanced catalytic performance of CN-T-1 than CN-O-1 is owing to its larger specific surface area, enhanced crystallinity, higher oxygen adsorption ability and photogenerated carrier separation efficiency, longer lifetime of carriers, and slightly larger bandgap (3.07 eV, +0.26 eV bigger than CN-O-1) with more positive valence band position owing to ultrathin layers. The •O2- radicals were verified to be the primary active species. A two-step single electron ORR pathway (O2 + e- → •O2- → H2O2) was confirmed for H2O2 production over CN-T-1.
2024, 40(11): 240602
doi: 10.3866/PKU.WHXB202406021
Abstract:
To eliminate the additional assistance of previously reported strategies for the synthesis of g-C3N4 nanosheets such as templates, strong acids and alkalis, in this study, an innovative pattern for transportation of molten g-C3N4 intermediates, without any additional substance assistance, has been resoundingly established to produce amino-rich g-C3N4 nanosheets. The innovative pattern concretely contains the preliminary placement of melamine onto the top platform of an inverted crucible and their subsequent one-step calcination. During the calcination process, melamine and its subsequently formed g-C3N4 intermediate can transform into a molten state and gradually stream down along the outer surface of inverted crucible. This molten intermediate transportation pattern contributes to remarkably resist severe aggregation, resulting in the final polymerization into amino-rich g-C3N4 nanosheets in sequence. Moreover, the resultant amino-rich g-C3N4 nanosheets exhibit an evidently enhanced photocatalytic H2O2-production rate of ca. 85.8 μmol·L–1·h–1, over 2 times superior to bulk g-C3N4, mainly due to the fact that in addition to their nanosheet structures with enhanced specific surface areas, their amino-rich structures can efficiently reinforce the adsorption of O2 and *OOH intermediates to accelerate their effective transformation into H2O2. This work delivers an innovative pattern to synthesize amino-rich g-C3N4 nanosheets with an insight into the photocatalytic mechanism.
To eliminate the additional assistance of previously reported strategies for the synthesis of g-C3N4 nanosheets such as templates, strong acids and alkalis, in this study, an innovative pattern for transportation of molten g-C3N4 intermediates, without any additional substance assistance, has been resoundingly established to produce amino-rich g-C3N4 nanosheets. The innovative pattern concretely contains the preliminary placement of melamine onto the top platform of an inverted crucible and their subsequent one-step calcination. During the calcination process, melamine and its subsequently formed g-C3N4 intermediate can transform into a molten state and gradually stream down along the outer surface of inverted crucible. This molten intermediate transportation pattern contributes to remarkably resist severe aggregation, resulting in the final polymerization into amino-rich g-C3N4 nanosheets in sequence. Moreover, the resultant amino-rich g-C3N4 nanosheets exhibit an evidently enhanced photocatalytic H2O2-production rate of ca. 85.8 μmol·L–1·h–1, over 2 times superior to bulk g-C3N4, mainly due to the fact that in addition to their nanosheet structures with enhanced specific surface areas, their amino-rich structures can efficiently reinforce the adsorption of O2 and *OOH intermediates to accelerate their effective transformation into H2O2. This work delivers an innovative pattern to synthesize amino-rich g-C3N4 nanosheets with an insight into the photocatalytic mechanism.
2024, 40(11): 240602
doi: 10.3866/PKU.WHXB202406020
Abstract:
This work illustrates the novelty of double S-scheme ZnS/ZnO/CdS ternary heterojunction photocatalyst with efficient photocatalytic activity. The sample with optimal CdS content, ZnS/ZnO/CdS-14% (ZZC14%), displayed the maximum H2 evolution rate of 4.1 mmol·g‒1·h‒1. The maximum photocatalytic performance was approximately 2 and 13 times higher than their corresponding counterparts, ZnS/CdS and ZnO/ZnS, respectively. A high AQE of 19.8% under 420 nm was obtained. Additionally, the slight changes in H2 evolution activities and retentions of crystal structures after six successive cycles indicate the stability of the photocatalyst. In accordance with the theoretical calculations and experimental results, the remarkable enhancement in photocatalytic activity is attributed to fast electron transfer and separation as well as the intimate contact due to mutual interaction between S-scheme. This work highlights an innovative approach to constructing a dual S-scheme photocatalytic system with high separation and fast migration capabilities of photogenerated charge carriers for splitting water to produce hydrogen. ![]()
This work illustrates the novelty of double S-scheme ZnS/ZnO/CdS ternary heterojunction photocatalyst with efficient photocatalytic activity. The sample with optimal CdS content, ZnS/ZnO/CdS-14% (ZZC14%), displayed the maximum H2 evolution rate of 4.1 mmol·g‒1·h‒1. The maximum photocatalytic performance was approximately 2 and 13 times higher than their corresponding counterparts, ZnS/CdS and ZnO/ZnS, respectively. A high AQE of 19.8% under 420 nm was obtained. Additionally, the slight changes in H2 evolution activities and retentions of crystal structures after six successive cycles indicate the stability of the photocatalyst. In accordance with the theoretical calculations and experimental results, the remarkable enhancement in photocatalytic activity is attributed to fast electron transfer and separation as well as the intimate contact due to mutual interaction between S-scheme. This work highlights an innovative approach to constructing a dual S-scheme photocatalytic system with high separation and fast migration capabilities of photogenerated charge carriers for splitting water to produce hydrogen.
2024, 40(11): 240602
doi: 10.3866/PKU.WHXB202406024
Abstract:
Photocatalytic hydrogen production is one of the effective ways to address environmental pollution and energy crises. Herein, Nix-MoS2/ZnIn2S4 heterojunctions were constructed to improve the separation efficiency of photogenerated electrons and holes and increase the number of active sites for hydrogen evolution. According to the catalyst characterization and theoretical calculations, the Ni at the interface between Nix-MoS2 and ZnIn2S4 can act as a bridge for charge transfer, the Ni―S bond is the active site for H2O dissociation, and the S site near the S vacancy on the Nix-MoS2 surface enhances the hydrogen evolution reaction. Benefiting from the synergistic effect of the S vacancy and the Ni-doped MoS2 cocatalyst, the optimal Ni0.08-MoS2/ZnIn2S4 exhibited the best hydrogen production rate of 7.13 mmol∙h−1∙g−1, which is 12.08 times than that of ZnIn2S4. This work provides a new strategy for enhancing photocatalytic efficiency through the synergistic effect of surface vacancies and doping and the optimization of heterojunctions. ![]()
Photocatalytic hydrogen production is one of the effective ways to address environmental pollution and energy crises. Herein, Nix-MoS2/ZnIn2S4 heterojunctions were constructed to improve the separation efficiency of photogenerated electrons and holes and increase the number of active sites for hydrogen evolution. According to the catalyst characterization and theoretical calculations, the Ni at the interface between Nix-MoS2 and ZnIn2S4 can act as a bridge for charge transfer, the Ni―S bond is the active site for H2O dissociation, and the S site near the S vacancy on the Nix-MoS2 surface enhances the hydrogen evolution reaction. Benefiting from the synergistic effect of the S vacancy and the Ni-doped MoS2 cocatalyst, the optimal Ni0.08-MoS2/ZnIn2S4 exhibited the best hydrogen production rate of 7.13 mmol∙h−1∙g−1, which is 12.08 times than that of ZnIn2S4. This work provides a new strategy for enhancing photocatalytic efficiency through the synergistic effect of surface vacancies and doping and the optimization of heterojunctions.
2024, 40(11): 240701
doi: 10.3866/PKU.WHXB202407013
Abstract:
Covalent organic framework (COF) materials are promising photocatalysts because of their fantastic structural and physicochemical features. To enhance photocatalytic performance, numerous metal single atoms (MSA) are loaded on COF to improve molecule adsorption. However, the inherent mechanisms and dominant factors of the heightened adsorption property are not deeply unveiled. Herein, four MSA-COF systems were constructed by severally introducing Fe, Co, Ni, and Cu single atoms in monolayer TpBpy-COF. The effect of various metal atoms modification on the electronic property and O2 adsorption of COF was investigated using density functional theory calculations. The results show that the metal atoms are bonded to the pyridinic N atoms, forming stable MSA-COF configurations. The anchoring of metal atoms reduces the band gap and raises the Fermi level of COF. Moreover, as the atomic number of the metals increases, the d orbitals of the metal atoms gradually move to lower energy levels, manifesting a negative shift of the d-band centers. After metal atoms loading, the weak physical adsorption of O2 on pristine COF is converted to robust chemisorption with the formation of M―Oads bonds and intense electron transfer. Intriguingly, the adsorption energy presents a strong correlation with the d-band centers of the metal atoms. This finding is comprehended from the perspective of electron occupancy in antibonding orbitals in the adsorption systems. This work provides a feasible approach for modifying molecule adsorption on MSA-COF by regulating the d-band centers of metal atoms. ![]()
Covalent organic framework (COF) materials are promising photocatalysts because of their fantastic structural and physicochemical features. To enhance photocatalytic performance, numerous metal single atoms (MSA) are loaded on COF to improve molecule adsorption. However, the inherent mechanisms and dominant factors of the heightened adsorption property are not deeply unveiled. Herein, four MSA-COF systems were constructed by severally introducing Fe, Co, Ni, and Cu single atoms in monolayer TpBpy-COF. The effect of various metal atoms modification on the electronic property and O2 adsorption of COF was investigated using density functional theory calculations. The results show that the metal atoms are bonded to the pyridinic N atoms, forming stable MSA-COF configurations. The anchoring of metal atoms reduces the band gap and raises the Fermi level of COF. Moreover, as the atomic number of the metals increases, the d orbitals of the metal atoms gradually move to lower energy levels, manifesting a negative shift of the d-band centers. After metal atoms loading, the weak physical adsorption of O2 on pristine COF is converted to robust chemisorption with the formation of M―Oads bonds and intense electron transfer. Intriguingly, the adsorption energy presents a strong correlation with the d-band centers of the metal atoms. This finding is comprehended from the perspective of electron occupancy in antibonding orbitals in the adsorption systems. This work provides a feasible approach for modifying molecule adsorption on MSA-COF by regulating the d-band centers of metal atoms.
2024, 40(11): 240700
doi: 10.3866/PKU.WHXB202407002
Abstract:
S-scheme heterojunction system represents a highly efficient strategy for photocatalytic applications as it can simultaneously facilitate photogenerated charge carrier separation and enhance the reduction-oxidation potentials of the photocatalyst. Despite its gigantic potential, the photocatalytic CO2 conversion efficiency of the S-scheme heterojunction remains limited mainly attributed to the sluggish interfacial charge carrier migration and poor light utilization efficiency. Herein, we prepare an InOOH/ZnIn2S4 hollow sphere S-scheme heterojunction with 0D/2D contact interface for enhancing photocatalytic CO2 conversion performance. Specifically, the hollow sphere morphology can cause the multireflection of incident light within the photocatalyst leading to enhanced light absorption of the photocatalyst. In addition, the 0D/2D contact interface can facilitate the photogenerated charge carrier migration transfer over the InOOH/ZnIn2S4 S-scheme heterojunction. Furthermore, combining in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) characterization and radicals trapping test, it is affirmed the accumulation of photogenerated holes and electrons respectively on InOOH and ZnIn2S4, which is beneficial for the effective utilization of photogenerated charge carriers. As a result, the photocatalytic CO2 conversion performance of the optimized InOOH/ZnIn2S4 is ca. 25.8 times higher than that of pristine ZnIn2S4. Our reported results demonstrate a facile yet effective strategy for enhancing the interfacial photogenerated charge carrier migration and light utilization efficiency of S-scheme heterojunction. ![]()
S-scheme heterojunction system represents a highly efficient strategy for photocatalytic applications as it can simultaneously facilitate photogenerated charge carrier separation and enhance the reduction-oxidation potentials of the photocatalyst. Despite its gigantic potential, the photocatalytic CO2 conversion efficiency of the S-scheme heterojunction remains limited mainly attributed to the sluggish interfacial charge carrier migration and poor light utilization efficiency. Herein, we prepare an InOOH/ZnIn2S4 hollow sphere S-scheme heterojunction with 0D/2D contact interface for enhancing photocatalytic CO2 conversion performance. Specifically, the hollow sphere morphology can cause the multireflection of incident light within the photocatalyst leading to enhanced light absorption of the photocatalyst. In addition, the 0D/2D contact interface can facilitate the photogenerated charge carrier migration transfer over the InOOH/ZnIn2S4 S-scheme heterojunction. Furthermore, combining in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) characterization and radicals trapping test, it is affirmed the accumulation of photogenerated holes and electrons respectively on InOOH and ZnIn2S4, which is beneficial for the effective utilization of photogenerated charge carriers. As a result, the photocatalytic CO2 conversion performance of the optimized InOOH/ZnIn2S4 is ca. 25.8 times higher than that of pristine ZnIn2S4. Our reported results demonstrate a facile yet effective strategy for enhancing the interfacial photogenerated charge carrier migration and light utilization efficiency of S-scheme heterojunction.
2024, 40(11): 240701
doi: 10.3866/PKU.WHXB202407014
Abstract:
Photocatalytic wastewater decontamination techniques hold eminent promise in mitigating environmental deterioration, yet the lack of distinctive photocatalysts prevents their further large-scale application. Herein, an S-scheme heterojunction photocatalyst BiOBr/C3N5 (BBN) was fabricated for efficiently dislodging micropollutants under visible light. Among the BBN samples, the optimal BBN-2 demonstrated exceptional activity in photocatalytic TC removal with a rate constant of 0.0139 min‒1, which surpassed that of pure BiOBr and C3N5 by 0.6 and 2.8 times, respectively. The spatially segregated photoredox sites and efficient photo-carrier separation propelled by an internal electric field are found to play a cardinal role in promoting photoreaction kinetics. Moreover, BBN-2 exhibited remarkable resistance to environmental interference and stability, retaining a high activity level after five runs. Through active radical detection, •O2‒, h+ and •OH were identified as the primary active species in the photocatalytic reaction process. This research would encourage the exploration of C3N5-based photocatalysts for environmental protection. ![]()
Photocatalytic wastewater decontamination techniques hold eminent promise in mitigating environmental deterioration, yet the lack of distinctive photocatalysts prevents their further large-scale application. Herein, an S-scheme heterojunction photocatalyst BiOBr/C3N5 (BBN) was fabricated for efficiently dislodging micropollutants under visible light. Among the BBN samples, the optimal BBN-2 demonstrated exceptional activity in photocatalytic TC removal with a rate constant of 0.0139 min‒1, which surpassed that of pure BiOBr and C3N5 by 0.6 and 2.8 times, respectively. The spatially segregated photoredox sites and efficient photo-carrier separation propelled by an internal electric field are found to play a cardinal role in promoting photoreaction kinetics. Moreover, BBN-2 exhibited remarkable resistance to environmental interference and stability, retaining a high activity level after five runs. Through active radical detection, •O2‒, h+ and •OH were identified as the primary active species in the photocatalytic reaction process. This research would encourage the exploration of C3N5-based photocatalysts for environmental protection.
2024, 40(11): 240602
doi: 10.3866/PKU.WHXB202406026
Abstract:
Photocatalytic hydrogen generation through water splitting driven by solar energy is regarded as a highly promising strategy to tackle the challenges of the energy crisis and environmental contamination. Tuning the electronic properties and band structures of photocatalysts is critical to improving the efficiency of charge separation and the activity of hydrogen production. Herein, donor-acceptor modified polymeric carbon nitride (CN)-based copolymers are synthesized via the introduction of 4-amino-1H-imidazole-5-carbonitrile (AICN) into the molecular skeleton of CN. The incorporation of electron donor AICN units can broaden the π-conjugated system and promote the spatial charge separation in the catalysts, thus resulting in enhanced light utilization and improved intramolecular charge carrier transfer rate. As a consequence, the AICN modified CN samples exhibit an increased photocatalytic hydrogen evolution rate, and the optimal photocatalytic activity can reach 3204 μmol·h−1·g−1. This molecular engineering strategy provides an effective avenue to develop high-performance CN-based photocatalysts for hydrogen evolution. ![]()
Photocatalytic hydrogen generation through water splitting driven by solar energy is regarded as a highly promising strategy to tackle the challenges of the energy crisis and environmental contamination. Tuning the electronic properties and band structures of photocatalysts is critical to improving the efficiency of charge separation and the activity of hydrogen production. Herein, donor-acceptor modified polymeric carbon nitride (CN)-based copolymers are synthesized via the introduction of 4-amino-1H-imidazole-5-carbonitrile (AICN) into the molecular skeleton of CN. The incorporation of electron donor AICN units can broaden the π-conjugated system and promote the spatial charge separation in the catalysts, thus resulting in enhanced light utilization and improved intramolecular charge carrier transfer rate. As a consequence, the AICN modified CN samples exhibit an increased photocatalytic hydrogen evolution rate, and the optimal photocatalytic activity can reach 3204 μmol·h−1·g−1. This molecular engineering strategy provides an effective avenue to develop high-performance CN-based photocatalysts for hydrogen evolution.
2024, 40(11): 240701
doi: 10.3866/PKU.WHXB202407012
Abstract:
Solar photocatalysis is a green, economical, and sustainable method for H2O2 synthesis, which has been regarded as the most promising alternative to the traditional anthraquinone oxidation method. However, single-component photocatalyst exhibits moderate activity owing to the limited light-harvesting range, fast charge recombination and inadequate redox capacity. Moreover, the addition of sacrificial agents is required in the reaction system. Herein, we present the development of an S-scheme heterojunction, achieved through photodepositing Bi2O3 nanoparticles (BO) on ionic covalent organic framework nanofiber (iCOF). The optimized photocatalyst iCOF/BO10 shows the highest H2O2 production performance in pure water, achieving an H2O2 yield of 9.76 mmol·g−1·h−1 with an apparent quantum yield (AQY) of 5.5% at 420 nm. This photocatalytic performance is approximately 2.2 and 5.6 times as high as that of pristine iCOF and BO, respectively. In-depth characterizations including in situ irradiated XPS, DFT-calculations, active species trapping experiments and in situ DRIFTS, reveal that the obtained sample not only facilitates charge carrier separation and enhances light absorption capability, but also maximizes the redox ability to concurrently achieve indirect 2e− ORR and 4e− WOR for H2O2 production. Additionally, the generated O2 from the 4e− WOR is capable of accelerating the reaction kinetics for H2O2 formation via the indirect 2e− ORR pathway, enabling overall photocatalytic H2O2 synthesis. This work provides a new insight into creating innovative catalysts for achieving high-efficiency photosynthesis of H2O2. ![]()
Solar photocatalysis is a green, economical, and sustainable method for H2O2 synthesis, which has been regarded as the most promising alternative to the traditional anthraquinone oxidation method. However, single-component photocatalyst exhibits moderate activity owing to the limited light-harvesting range, fast charge recombination and inadequate redox capacity. Moreover, the addition of sacrificial agents is required in the reaction system. Herein, we present the development of an S-scheme heterojunction, achieved through photodepositing Bi2O3 nanoparticles (BO) on ionic covalent organic framework nanofiber (iCOF). The optimized photocatalyst iCOF/BO10 shows the highest H2O2 production performance in pure water, achieving an H2O2 yield of 9.76 mmol·g−1·h−1 with an apparent quantum yield (AQY) of 5.5% at 420 nm. This photocatalytic performance is approximately 2.2 and 5.6 times as high as that of pristine iCOF and BO, respectively. In-depth characterizations including in situ irradiated XPS, DFT-calculations, active species trapping experiments and in situ DRIFTS, reveal that the obtained sample not only facilitates charge carrier separation and enhances light absorption capability, but also maximizes the redox ability to concurrently achieve indirect 2e− ORR and 4e− WOR for H2O2 production. Additionally, the generated O2 from the 4e− WOR is capable of accelerating the reaction kinetics for H2O2 formation via the indirect 2e− ORR pathway, enabling overall photocatalytic H2O2 synthesis. This work provides a new insight into creating innovative catalysts for achieving high-efficiency photosynthesis of H2O2.
