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2023 Volume 39 Issue 6
2023, 39(6): 220803
doi: 10.3866/PKU.WHXB202208030
Abstract:
The problems associated with fossil fuel consumption are restricting human development and harming the environment. An effective way for solving the alluded problems is to develop technology for harnessing renewable clean energy. In recent years, hydrogen has been reported as a new source of clean energy. The combustion heat of hydrogen is very high and the product formed is only water, which fully conforms to the characteristics of green and sustainable energy. Therefore, finding a suitable method for producing hydrogen can effectively solve the current global energy crisis. Since titanium(IV) oxide was used as a photocatalyst to split water into hydrogen and oxygen in 1972, water splitting over semiconductor photocatalysts has been an interesting research topic in the past decades. Nevertheless, the inherent disadvantages of single-component photocatalysts limit their practical application and it is still challenging to circumvent those disadvantages. When compared with single-component photocatalysts, composite photocatalysts can more effectively separate photogenerated electrons and holes, thereby increasing the photocatalytic hydrogen evolution rate. Therefore, photocatalytic hydrogen evolution activity and stability can be optimized by selecting the appropriate photocatalytic mechanism (e.g., S-scheme) at the heterojunction of composites. In this study, many single-component CdSe-DETA photocatalysts with different band gaps were synthesized by varying certain synthesis conditions. The results obtained showed that adjusting the band gap (2.31 eV) of CdSe-DETA led to superior photocatalytic hydrogen production activity but the stability of the photocatalyst was poor. Thereafter, we constructed an In2O3/CdSe-DETA nanocomposite by attaching CdSe-DETA nanoflowers to the surface of porous In2O3 nanosheets to improve the photocatalytic hydrogen evolution activity, stability, and photocurrent response. The type of heterojunction in the In2O3/CdSe-DETA nanocomposite can be varied through the band energy gap of CdSe-DETA. More specifically, the type of heterojunction can be switched from Type-I to S-scheme in the case of swelling of the band energy gap of CdSe-DETA. When compared with single-component photocatalysts and Type-I photocatalysts, the S-scheme In2O3/CdSe-DETA nanocomposite exhibited higher photocatalytic activity and stability. Therefore, we chose the In2O3/CdSe-DETA nanocomposite with an S-scheme heterojunction to obtain optimal photocatalytic activity and stability. Additionally, we confirmed the existence of an S-scheme heterojunction via differential charge density calculations combined with experimental results. The S-scheme heterojunction In2O3/CdSe-DETA nanocomposite effectively separated photogenerated electrons and holes as well as maximized the use of the conduction and valence bands of the composite for efficient and stable photocatalytic hydrogen evolution. Therefore, this study demonstrates a novel strategy for modulating the carrier transfer mechanism, which provides a reference for the development of efficient hydrogen evolution photocatalysts.![]()
The problems associated with fossil fuel consumption are restricting human development and harming the environment. An effective way for solving the alluded problems is to develop technology for harnessing renewable clean energy. In recent years, hydrogen has been reported as a new source of clean energy. The combustion heat of hydrogen is very high and the product formed is only water, which fully conforms to the characteristics of green and sustainable energy. Therefore, finding a suitable method for producing hydrogen can effectively solve the current global energy crisis. Since titanium(IV) oxide was used as a photocatalyst to split water into hydrogen and oxygen in 1972, water splitting over semiconductor photocatalysts has been an interesting research topic in the past decades. Nevertheless, the inherent disadvantages of single-component photocatalysts limit their practical application and it is still challenging to circumvent those disadvantages. When compared with single-component photocatalysts, composite photocatalysts can more effectively separate photogenerated electrons and holes, thereby increasing the photocatalytic hydrogen evolution rate. Therefore, photocatalytic hydrogen evolution activity and stability can be optimized by selecting the appropriate photocatalytic mechanism (e.g., S-scheme) at the heterojunction of composites. In this study, many single-component CdSe-DETA photocatalysts with different band gaps were synthesized by varying certain synthesis conditions. The results obtained showed that adjusting the band gap (2.31 eV) of CdSe-DETA led to superior photocatalytic hydrogen production activity but the stability of the photocatalyst was poor. Thereafter, we constructed an In2O3/CdSe-DETA nanocomposite by attaching CdSe-DETA nanoflowers to the surface of porous In2O3 nanosheets to improve the photocatalytic hydrogen evolution activity, stability, and photocurrent response. The type of heterojunction in the In2O3/CdSe-DETA nanocomposite can be varied through the band energy gap of CdSe-DETA. More specifically, the type of heterojunction can be switched from Type-I to S-scheme in the case of swelling of the band energy gap of CdSe-DETA. When compared with single-component photocatalysts and Type-I photocatalysts, the S-scheme In2O3/CdSe-DETA nanocomposite exhibited higher photocatalytic activity and stability. Therefore, we chose the In2O3/CdSe-DETA nanocomposite with an S-scheme heterojunction to obtain optimal photocatalytic activity and stability. Additionally, we confirmed the existence of an S-scheme heterojunction via differential charge density calculations combined with experimental results. The S-scheme heterojunction In2O3/CdSe-DETA nanocomposite effectively separated photogenerated electrons and holes as well as maximized the use of the conduction and valence bands of the composite for efficient and stable photocatalytic hydrogen evolution. Therefore, this study demonstrates a novel strategy for modulating the carrier transfer mechanism, which provides a reference for the development of efficient hydrogen evolution photocatalysts.
2023, 39(6): 220901
doi: 10.3866/PKU.WHXB202209012
Abstract:
The peroxymonosulfate (PMS) activation reaction based on photocatalysts has been widely employed for the removal of tetracycline (TC) and other antibiotics. The photocatalyst comprising CuWO4 decorated with oxygen vacancies has attracted research attention owing to its narrow band gap, favorable oxidation ability, and good charge transfer efficiency. A single-component photocatalyst can influence the PMS activation efficiency due to the rapid recombination between photogenerated electron and hole pairs. Herein, oxygen vacancy-decorated CuWO4−x/Bi12O17Cl2 (CovB) photocatalysts were fabricated, and enabled an enhancement in the PMS activation efficiency for TC removal under visible-light irradiation. The crystalline structures and optical properties of CovB were measured by field-emission scanning electron microscopy, transmission electron microscopy, and UV-visible diffuse reflectance spectroscopy. Characterization of the O 1s bond by electron paramagnetic resonance (EPR) analyses and X-ray photoelectron spectra (XPS) showed that the oxygen vacancies were successfully introduced into the composites. CovB-30 (mass ratio of CuWO4−x to Bi12O17Cl2 was 3 : 7) achieved a TC removal rate of 94.74% in 30 min in the PMS activation system. The degradation efficiencies of CovB-30 were 2.67 and 2.21 times higher than those of CuWO4 and Bi12O17Cl2, respectively. The enhanced TC elimination performance can be ascribed to the synergetic effect between photocatalysis and the PMS activation reaction, which were promoted by the S-scheme heterojunction. The S-scheme heterojunction structure could maintain an excellent redox ability under light irradiation and generate an internal electric field, which possessed the ability to prevent the recombination of photogenerated carriers. The photoluminescence (PL) measurements and time-resolved photoluminescence (TRPL) spectra confirmed that the formation of the S-scheme heterojunction effectively increased the migration rates and separation efficiency of photogenerated hole and electron pairs, facilitating the activation of PMS for TC removal. CovB-30 retained the ability to eliminate TC in a wide pH range of 3.0–11.0 and different inorganic anion systems. The XPS profiles of fresh and used samples indicated that the Cu2+/Cu+ redox cycle and oxygen vacancies both participated in the activation of PMS. XPS analysis and experimental capture results illustrated that the charge transfer mechanism of the CovB composite followed that of an S-scheme heterojunction photocatalyst. CovB-30 maintained excellent PMS activation ability over a wide pH range of 3.0–11.0. This paper discusses the possible TC degradation pathways in the PMS activation system on the basis of the generated intermediates. Quenching experiments were conducted, and demonstrated that SO4•−/∙OH/∙O2−/h+/1O2 served as the reactive species in TC removal. The CovB-30 composite possessed remarkable photocatalytic activity after five consecutive cycles, illustrating that it could be utilized for practical antibiotic degradation. This work proposes a promising method of introducing oxygen vacancies into an S-scheme photocatalyst for efficient PMS activation.![]()
The peroxymonosulfate (PMS) activation reaction based on photocatalysts has been widely employed for the removal of tetracycline (TC) and other antibiotics. The photocatalyst comprising CuWO4 decorated with oxygen vacancies has attracted research attention owing to its narrow band gap, favorable oxidation ability, and good charge transfer efficiency. A single-component photocatalyst can influence the PMS activation efficiency due to the rapid recombination between photogenerated electron and hole pairs. Herein, oxygen vacancy-decorated CuWO4−x/Bi12O17Cl2 (CovB) photocatalysts were fabricated, and enabled an enhancement in the PMS activation efficiency for TC removal under visible-light irradiation. The crystalline structures and optical properties of CovB were measured by field-emission scanning electron microscopy, transmission electron microscopy, and UV-visible diffuse reflectance spectroscopy. Characterization of the O 1s bond by electron paramagnetic resonance (EPR) analyses and X-ray photoelectron spectra (XPS) showed that the oxygen vacancies were successfully introduced into the composites. CovB-30 (mass ratio of CuWO4−x to Bi12O17Cl2 was 3 : 7) achieved a TC removal rate of 94.74% in 30 min in the PMS activation system. The degradation efficiencies of CovB-30 were 2.67 and 2.21 times higher than those of CuWO4 and Bi12O17Cl2, respectively. The enhanced TC elimination performance can be ascribed to the synergetic effect between photocatalysis and the PMS activation reaction, which were promoted by the S-scheme heterojunction. The S-scheme heterojunction structure could maintain an excellent redox ability under light irradiation and generate an internal electric field, which possessed the ability to prevent the recombination of photogenerated carriers. The photoluminescence (PL) measurements and time-resolved photoluminescence (TRPL) spectra confirmed that the formation of the S-scheme heterojunction effectively increased the migration rates and separation efficiency of photogenerated hole and electron pairs, facilitating the activation of PMS for TC removal. CovB-30 retained the ability to eliminate TC in a wide pH range of 3.0–11.0 and different inorganic anion systems. The XPS profiles of fresh and used samples indicated that the Cu2+/Cu+ redox cycle and oxygen vacancies both participated in the activation of PMS. XPS analysis and experimental capture results illustrated that the charge transfer mechanism of the CovB composite followed that of an S-scheme heterojunction photocatalyst. CovB-30 maintained excellent PMS activation ability over a wide pH range of 3.0–11.0. This paper discusses the possible TC degradation pathways in the PMS activation system on the basis of the generated intermediates. Quenching experiments were conducted, and demonstrated that SO4•−/∙OH/∙O2−/h+/1O2 served as the reactive species in TC removal. The CovB-30 composite possessed remarkable photocatalytic activity after five consecutive cycles, illustrating that it could be utilized for practical antibiotic degradation. This work proposes a promising method of introducing oxygen vacancies into an S-scheme photocatalyst for efficient PMS activation.
2023, 39(6): 220901
doi: 10.3866/PKU.WHXB202209016
Abstract:
The construction of heterojunctions is a method employed to inhibit the rapid recombination of photogenerated carriers. In this work, zero-dimensional (0D) g-C3N4 quantum dots (CNQDs) were composited with two-dimensional (2D) BiOBr for the first time using the typical hydrothermal method under the conditions of a high temperature and high pressure, and a 0D/2D CNQD/BiOBr S-scheme heterojunction with an intimate-contact interface was formed. The π-electrons in the heterocycle of the CNQDs were bound to BiOBr by interaction. The apparent reaction rate constants generated by CNQDs/BiOB-1.50% for tetracycline (TC) and ciprofloxacin (CIP) degradation and H2O2 production were 2.02, 2.91, and 1.54 times that of the original BiOBr, respectively. In the cycle test, CNQDs/BiOBr-1.50% displayed a relatively high photocatalytic activity and structural stability. X-ray photoelectron spectroscopy (XPS) analysis showed that the π electrons in the CNQDs interacted with BiOBr, and also confirmed the flow of photogenerated electrons in this heterojunction. This successfully constructed S-scheme exhibited extraordinary photocatalytic activity and stability. The more active species and stable catalytic activity were attributed to the distinctive transfer mechanism of the carriers. This work will provide reference for constructing 0D/2D S-scheme heterojunctions for the degradation of organic pollutants and in situ production of H2O2. ![]()
The construction of heterojunctions is a method employed to inhibit the rapid recombination of photogenerated carriers. In this work, zero-dimensional (0D) g-C3N4 quantum dots (CNQDs) were composited with two-dimensional (2D) BiOBr for the first time using the typical hydrothermal method under the conditions of a high temperature and high pressure, and a 0D/2D CNQD/BiOBr S-scheme heterojunction with an intimate-contact interface was formed. The π-electrons in the heterocycle of the CNQDs were bound to BiOBr by interaction. The apparent reaction rate constants generated by CNQDs/BiOB-1.50% for tetracycline (TC) and ciprofloxacin (CIP) degradation and H2O2 production were 2.02, 2.91, and 1.54 times that of the original BiOBr, respectively. In the cycle test, CNQDs/BiOBr-1.50% displayed a relatively high photocatalytic activity and structural stability. X-ray photoelectron spectroscopy (XPS) analysis showed that the π electrons in the CNQDs interacted with BiOBr, and also confirmed the flow of photogenerated electrons in this heterojunction. This successfully constructed S-scheme exhibited extraordinary photocatalytic activity and stability. The more active species and stable catalytic activity were attributed to the distinctive transfer mechanism of the carriers. This work will provide reference for constructing 0D/2D S-scheme heterojunctions for the degradation of organic pollutants and in situ production of H2O2.
2023, 39(6): 221000
doi: 10.3866/PKU.WHXB202210003
Abstract:
Excessive CO2 emissions have led to serious environmental problems. The photocatalytic reduction of CO2 to value-added chemicals is a promising strategy to reduce carbon emissions and alleviate the energy crisis simultaneously. Photocatalysts is crucial in the reduction process. Nanostructure engineering and heterojunction construction have been identified as prospective approaches to develop efficient photocatalysts for CO2 reduction. Step-scheme (S-scheme) heterojunctions are novel systems composed of a reduction catalyst and an oxidation catalyst. In these systems, the charge separation at the interface between the two catalysts could be enhanced by an internal electric field directed from the reduction photocatalyst to the oxidation photocatalyst on account of their matched Fermi levels (Ef). The S-scheme transfer mode can not only efficaciously inhibit the recombination of photoinduced carriers but also accumulate electrons and holes with greater redox potential. Cu2O and BiOI materials, as typical reduction and oxidation catalysts, are endowed with efficient visible-light absorption and favorable band position for catalyzing the coupling reaction of CO2 reduction and H2O oxidation. In this study, a series of S-scheme catalysts consisting of polyhedral Cu2O-modified BiOI flakes were synthesized onto a fluorine-doped tin oxide substrate via the electrodeposition method. The structure, morphology, and surface composition of the as-obtained samples were then studied using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. 13C/18O isotope tracer experiments indicated that the BiOI/Cu2O composite achieved CO2 conversion with water vapor under visible-light irradiation (λ > 400 nm). The CO, CH4, H2, and O2 yields of the optimal BiOI/Cu2O-1500 catalyst reached 53.03, 30.75, 8.49, and 82.73 μmol∙m−2, respectively, after 11 h of visible-light illumination. The photocatalytic activity of BiOI/Cu2O-1500 slightly decreased at the eighth cycling, but its CO, CH4, and O2 yields still reached 27.38, 34.08, and 75.52 μmol∙m−2, respectively. The XPS and XRD results confirmed the excellent cycling stability of the catalysts, and analysis using the XPS core-level (CL) alignment method revealed that a staggered band structure was formed in the BiOI/Cu2O heterojunction. The direction of the built-in electric field in the heterojunction was determined using UPS measurements, and the S-scheme mechanism of charge transfer was verified via the in situ XPS results. In addition, the production of HCO3−, CO32−, HCOO−, and •CH3 species during CO2 reduction was confirmed using in situ diffuse reflectance Fourier transform spectrometry, and a possible mechanism of CO2 conversion under water vapor was proposed. Benefiting from its S-scheme BiOI/Cu2O heterojunction, the prepared catalyst showed improved photoinduced charge separation, and its photogenerated carriers with strong redox ability were preserved, thereby leading to enhanced photocatalytic performance.![]()
Excessive CO2 emissions have led to serious environmental problems. The photocatalytic reduction of CO2 to value-added chemicals is a promising strategy to reduce carbon emissions and alleviate the energy crisis simultaneously. Photocatalysts is crucial in the reduction process. Nanostructure engineering and heterojunction construction have been identified as prospective approaches to develop efficient photocatalysts for CO2 reduction. Step-scheme (S-scheme) heterojunctions are novel systems composed of a reduction catalyst and an oxidation catalyst. In these systems, the charge separation at the interface between the two catalysts could be enhanced by an internal electric field directed from the reduction photocatalyst to the oxidation photocatalyst on account of their matched Fermi levels (Ef). The S-scheme transfer mode can not only efficaciously inhibit the recombination of photoinduced carriers but also accumulate electrons and holes with greater redox potential. Cu2O and BiOI materials, as typical reduction and oxidation catalysts, are endowed with efficient visible-light absorption and favorable band position for catalyzing the coupling reaction of CO2 reduction and H2O oxidation. In this study, a series of S-scheme catalysts consisting of polyhedral Cu2O-modified BiOI flakes were synthesized onto a fluorine-doped tin oxide substrate via the electrodeposition method. The structure, morphology, and surface composition of the as-obtained samples were then studied using X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements. 13C/18O isotope tracer experiments indicated that the BiOI/Cu2O composite achieved CO2 conversion with water vapor under visible-light irradiation (λ > 400 nm). The CO, CH4, H2, and O2 yields of the optimal BiOI/Cu2O-1500 catalyst reached 53.03, 30.75, 8.49, and 82.73 μmol∙m−2, respectively, after 11 h of visible-light illumination. The photocatalytic activity of BiOI/Cu2O-1500 slightly decreased at the eighth cycling, but its CO, CH4, and O2 yields still reached 27.38, 34.08, and 75.52 μmol∙m−2, respectively. The XPS and XRD results confirmed the excellent cycling stability of the catalysts, and analysis using the XPS core-level (CL) alignment method revealed that a staggered band structure was formed in the BiOI/Cu2O heterojunction. The direction of the built-in electric field in the heterojunction was determined using UPS measurements, and the S-scheme mechanism of charge transfer was verified via the in situ XPS results. In addition, the production of HCO3−, CO32−, HCOO−, and •CH3 species during CO2 reduction was confirmed using in situ diffuse reflectance Fourier transform spectrometry, and a possible mechanism of CO2 conversion under water vapor was proposed. Benefiting from its S-scheme BiOI/Cu2O heterojunction, the prepared catalyst showed improved photoinduced charge separation, and its photogenerated carriers with strong redox ability were preserved, thereby leading to enhanced photocatalytic performance.
2023, 39(6): 221105
doi: 10.3866/PKU.WHXB202211051
Abstract:
As a higher oxidation state compound of carbon, more electrons and protons are needed to reduce CO2. While the step-scheme (S-scheme) heterojunction driven by semiconductors performs excellently in the excitation and transport of electrons, which has strong redox ability while inhibiting electron hole recombination, and has exhibited excellent results in photocatalytic CO2 reduction. Herein, Ag/CN was prepared by an optical deposition method, and the Ag/CN/ZnIn2S4 S-scheme heterojunction composite photocatalyst was prepared by a hydrothermal method. The crystal structure, morphology and elements valences of the materials were analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and other characterization methods, and the composite of the monomer was successfully verified. According to the electron spin resonance (ESR) and ultraviolet photoelectron spectroscopy (UPS) studies, formation of the S-scheme heterojunction was observed. Based on photoelectrochemical results and photoluminescence (PL) studies, the enhanced CO2 reduction can be attributed to the S-scheme electron transfer at the interface, which promotes charge separation. In the S-scheme electronic transmission system, CN acts as the reductive photocatalyst (RP) and ZnIn2S4 as the oxidative photocatalyst (OP). Owing to the difference in Fermi energy levels, the electron cloud density changes until the Fermi levels match after contact between the RP and OP. This process generates internal electric fields and band bending at the interface, facilitating hole separation and the transfer of photo-induced carriers and photogenerated electrons. The plasmonic effect of the interfacial Ag NPs of the composite was proven using UV-Vis diffuse reflectance spectroscopy (DRS). When exposed to light, Ag NPs, as reactive sites of the reaction, act as receptors for electron transport. The excitation of high-energy thermal electrons on the surface of Ag NPs leads to the generation of localized electromagnetic fields between CN and Ag NPs, which subsequently accelerates the electron transport rate on the CB of CN and enhances light absorption, thus improving the photoreduction performance of hybrid materials. Under the combined action of the S-scheme heterojunction and plasmonic effect, the interface carrier transfer efficiency can be improved. Finally, the charge transfer mechanism was analyzed. Simultaneously, the possible reaction paths of photocatalytic CO2 reduction were explained by comparing the in situ Fourier-transform infrared spectroscopy (FT-IR) spectra of the monomer and compound. The CO2 reduction capability of composite materials was better compared to that of monomer materials. The best yields of CO and CH4 of ACZ-60 were 5.63 μmol·g−1 and 0.23 μmol·g−1, which were 6.5 and 2.1 times that of CN, respectively. Across four cycles, the CO and CH4 yields and XRD patterns of ACZ-60 showed excellent stability. This study provides a scheme for the rational design of photocatalytic CO2 reduction S-scheme catalysts. ![]()
As a higher oxidation state compound of carbon, more electrons and protons are needed to reduce CO2. While the step-scheme (S-scheme) heterojunction driven by semiconductors performs excellently in the excitation and transport of electrons, which has strong redox ability while inhibiting electron hole recombination, and has exhibited excellent results in photocatalytic CO2 reduction. Herein, Ag/CN was prepared by an optical deposition method, and the Ag/CN/ZnIn2S4 S-scheme heterojunction composite photocatalyst was prepared by a hydrothermal method. The crystal structure, morphology and elements valences of the materials were analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and other characterization methods, and the composite of the monomer was successfully verified. According to the electron spin resonance (ESR) and ultraviolet photoelectron spectroscopy (UPS) studies, formation of the S-scheme heterojunction was observed. Based on photoelectrochemical results and photoluminescence (PL) studies, the enhanced CO2 reduction can be attributed to the S-scheme electron transfer at the interface, which promotes charge separation. In the S-scheme electronic transmission system, CN acts as the reductive photocatalyst (RP) and ZnIn2S4 as the oxidative photocatalyst (OP). Owing to the difference in Fermi energy levels, the electron cloud density changes until the Fermi levels match after contact between the RP and OP. This process generates internal electric fields and band bending at the interface, facilitating hole separation and the transfer of photo-induced carriers and photogenerated electrons. The plasmonic effect of the interfacial Ag NPs of the composite was proven using UV-Vis diffuse reflectance spectroscopy (DRS). When exposed to light, Ag NPs, as reactive sites of the reaction, act as receptors for electron transport. The excitation of high-energy thermal electrons on the surface of Ag NPs leads to the generation of localized electromagnetic fields between CN and Ag NPs, which subsequently accelerates the electron transport rate on the CB of CN and enhances light absorption, thus improving the photoreduction performance of hybrid materials. Under the combined action of the S-scheme heterojunction and plasmonic effect, the interface carrier transfer efficiency can be improved. Finally, the charge transfer mechanism was analyzed. Simultaneously, the possible reaction paths of photocatalytic CO2 reduction were explained by comparing the in situ Fourier-transform infrared spectroscopy (FT-IR) spectra of the monomer and compound. The CO2 reduction capability of composite materials was better compared to that of monomer materials. The best yields of CO and CH4 of ACZ-60 were 5.63 μmol·g−1 and 0.23 μmol·g−1, which were 6.5 and 2.1 times that of CN, respectively. Across four cycles, the CO and CH4 yields and XRD patterns of ACZ-60 showed excellent stability. This study provides a scheme for the rational design of photocatalytic CO2 reduction S-scheme catalysts.
2023, 39(6): 221200
doi: 10.3866/PKU.WHXB202212009
Abstract:
The increased global demand for energy and the enhanced deterioration of the environment are the two urgent challenges of the 21st century on the way to sustainable development for human society. Currently, green and renewable energy conversion technology has received much attention as a substitute for limited and non-renewable fossil fuels. Hydrogen energy is advantageous because of its high energy capacity (142 MJ·kg−1) and its production by green conversion technology, consisting of H2 reacting with O2 to generate H2O. It can establish a clean and sustainable hydrogen economic system, as well as reduce the utilization of fossil fuels and carbon dioxide emissions. Water splitting technology is an efficient approach to acquire the featured H2 energy of the green reaction (2H2O → 2H2 + O2) through electrocatalytic and photocatalytic reactions. Photocatalysis technology, with the advantage of huge solar energy utilization, has been widely regarded as a promising method for the realization of this chemical synthesis. Among photocatalysis technologies, photocatalytic H2 production from water is considered a promising approach to obtain H2 energy due to its environmentally friendly energy conversion. However, the effectiveness of acquiring H2 energy through photocatalytic water splitting is intimately related with photocatalysts. In general, photocatalysts still face the big challenge of their low solar energy utilization efficiency, which restricts the large-scale application of photocatalytic technology to obtain H2 energy. Thus, developing highly efficient photocatalysts for H2 production is critical in promoting this technology moving forward, and obtaining renewable energy. Herein, we successfully construct the S-scheme MnCo2S4/g-C3N4 heterojunction through an expedient physical mixing process at a low temperature, which can be separately obtained via the pyrolysis process and hydrothermal method. The H2 production rate of MnCo2S4/g-C3N4 heterojunction can achieve up to 2979 µmol·g−1·h−1, which is 26.4 and 8.7 times higher than those of g-C3N4 (113 µmol·g−1·h−1) and MnCo2S4 (341 µmol·g−1·h−1), respectively, and presents a superior stability in three continuous cycles during H2 production tests. The high H2 production of MnCo2S4/g-C3N4 heterojunction is mainly ascribed to the following three reasons: i) The light absorption region of the heterojunction is extended to visible light. ii) MnCo2S4/g-C3N4 possesses low impedance during the reaction, high photocurrent density, and more exposed sites in solution. iii) The efficient reservation of active electron-hole pairs greatly enhances the ratio of electrons reacting with H* species to generate H2 over MnCo2S4/g-C3N4 heterojunction. This work provides an efficient approach to constructing advanced g-C3N4-based photocatalysts through hybridization with metal sulfides to form S-scheme heterojunctions. ![]()
The increased global demand for energy and the enhanced deterioration of the environment are the two urgent challenges of the 21st century on the way to sustainable development for human society. Currently, green and renewable energy conversion technology has received much attention as a substitute for limited and non-renewable fossil fuels. Hydrogen energy is advantageous because of its high energy capacity (142 MJ·kg−1) and its production by green conversion technology, consisting of H2 reacting with O2 to generate H2O. It can establish a clean and sustainable hydrogen economic system, as well as reduce the utilization of fossil fuels and carbon dioxide emissions. Water splitting technology is an efficient approach to acquire the featured H2 energy of the green reaction (2H2O → 2H2 + O2) through electrocatalytic and photocatalytic reactions. Photocatalysis technology, with the advantage of huge solar energy utilization, has been widely regarded as a promising method for the realization of this chemical synthesis. Among photocatalysis technologies, photocatalytic H2 production from water is considered a promising approach to obtain H2 energy due to its environmentally friendly energy conversion. However, the effectiveness of acquiring H2 energy through photocatalytic water splitting is intimately related with photocatalysts. In general, photocatalysts still face the big challenge of their low solar energy utilization efficiency, which restricts the large-scale application of photocatalytic technology to obtain H2 energy. Thus, developing highly efficient photocatalysts for H2 production is critical in promoting this technology moving forward, and obtaining renewable energy. Herein, we successfully construct the S-scheme MnCo2S4/g-C3N4 heterojunction through an expedient physical mixing process at a low temperature, which can be separately obtained via the pyrolysis process and hydrothermal method. The H2 production rate of MnCo2S4/g-C3N4 heterojunction can achieve up to 2979 µmol·g−1·h−1, which is 26.4 and 8.7 times higher than those of g-C3N4 (113 µmol·g−1·h−1) and MnCo2S4 (341 µmol·g−1·h−1), respectively, and presents a superior stability in three continuous cycles during H2 production tests. The high H2 production of MnCo2S4/g-C3N4 heterojunction is mainly ascribed to the following three reasons: i) The light absorption region of the heterojunction is extended to visible light. ii) MnCo2S4/g-C3N4 possesses low impedance during the reaction, high photocurrent density, and more exposed sites in solution. iii) The efficient reservation of active electron-hole pairs greatly enhances the ratio of electrons reacting with H* species to generate H2 over MnCo2S4/g-C3N4 heterojunction. This work provides an efficient approach to constructing advanced g-C3N4-based photocatalysts through hybridization with metal sulfides to form S-scheme heterojunctions.
2023, 39(6): 221202
doi: 10.3866/PKU.WHXB202212026
Abstract:
Photocatalytic CO2 reduction to renewable hydrocarbon fuels provides a feasible protocol for alleviating the greenhouse effect and addressing energy shortage. However, the CO2 reduction activity of a single-component photocatalyst is very low because of two problems. One is the fast recombination of photogenerated charge carriers, which leads to low photon efficiency, while the other is the large energy barrier to CO2 activation. There have been considerable research efforts to develop photocatalysts with improved CO2 reduction performance. For example, step-scheme (S-scheme) heterojunctions have been developed to improve charge carrier separation and enhance the redox abilities of photocatalysts. Single-atom metals have also been applied cocatalysts to optimize the reaction thermodynamics. Thus, the synergy between S-scheme heterojunctions and single-atom metal cocatalysts is anticipated to promote both charge carrier transfer and CO2 reduction reaction processes. In this study, a Pt-C3N4/BiOCl heterojunction photocatalyst is modeled, composed of single-atom Pt-loaded g-C3N4 and BiOCl, and its photocatalytic properties are studied using density functional theory calculations. Its structure and electronic property are explored, and the process of CO2 conversion is also simulated. The charge density difference results show that electrons in g-C3N4 are transferred to BiOCl owing to the higher Fermi level of g-C3N4 than that of BiOCl. Therefore, an interfacial electric field from g-C3N4 to BiOCl is established at the g-C3N4/BiOCl interface. Under light irradiation, charge carrier transfer in the g-C3N4/BiOCl composite is consistent with the S-scheme mechanism. Specifically, the photogenerated electrons in the CB of BiOCl recombine with the photogenerated holes in the VB of g-C3N4, while the photogenerated electrons in the CB of g-C3N4 and the photogenerated holes in the VB of BiOCl are retained. After the loading of Pt atom at each sixfold cavity of g-C3N4, the work function of g-C3N4 decreases, thereby enlarging the difference between the Fermi levels of the two semiconductors. Consequently, more electrons are transferred from Pt-C3N4 to BiOCl, and the strength of the interfacial electric field is increased. This enhanced electric field is beneficial to the S-scheme charge transfer in Pt-C3N4/BiOCl heterojunctions. Besides, based on the calculated variation in reaction energy, the rate-limiting step involved in CO2 reduction on g-C3N4/BiOCl heterojunction is the hydrogenation of CO2 to COOH, which has an energy barrier of 1.13 eV. After Pt loading, the hydrogenation of CO to HCO is the rate-limiting step and the corresponding energy increase is 0.71 eV. These results manifest that the introduction of Pt single-atom cocatalysts improves the CO2 reduction performance of g-C3N4/BiOCl S-scheme photocatalysts by strengthening the interfacial electric field and reducing the energy barrier. This study provides guidance for constructing metal-atom-incorporated S-scheme heterojunction photocatalysts to realize efficient CO2 reduction. ![]()
Photocatalytic CO2 reduction to renewable hydrocarbon fuels provides a feasible protocol for alleviating the greenhouse effect and addressing energy shortage. However, the CO2 reduction activity of a single-component photocatalyst is very low because of two problems. One is the fast recombination of photogenerated charge carriers, which leads to low photon efficiency, while the other is the large energy barrier to CO2 activation. There have been considerable research efforts to develop photocatalysts with improved CO2 reduction performance. For example, step-scheme (S-scheme) heterojunctions have been developed to improve charge carrier separation and enhance the redox abilities of photocatalysts. Single-atom metals have also been applied cocatalysts to optimize the reaction thermodynamics. Thus, the synergy between S-scheme heterojunctions and single-atom metal cocatalysts is anticipated to promote both charge carrier transfer and CO2 reduction reaction processes. In this study, a Pt-C3N4/BiOCl heterojunction photocatalyst is modeled, composed of single-atom Pt-loaded g-C3N4 and BiOCl, and its photocatalytic properties are studied using density functional theory calculations. Its structure and electronic property are explored, and the process of CO2 conversion is also simulated. The charge density difference results show that electrons in g-C3N4 are transferred to BiOCl owing to the higher Fermi level of g-C3N4 than that of BiOCl. Therefore, an interfacial electric field from g-C3N4 to BiOCl is established at the g-C3N4/BiOCl interface. Under light irradiation, charge carrier transfer in the g-C3N4/BiOCl composite is consistent with the S-scheme mechanism. Specifically, the photogenerated electrons in the CB of BiOCl recombine with the photogenerated holes in the VB of g-C3N4, while the photogenerated electrons in the CB of g-C3N4 and the photogenerated holes in the VB of BiOCl are retained. After the loading of Pt atom at each sixfold cavity of g-C3N4, the work function of g-C3N4 decreases, thereby enlarging the difference between the Fermi levels of the two semiconductors. Consequently, more electrons are transferred from Pt-C3N4 to BiOCl, and the strength of the interfacial electric field is increased. This enhanced electric field is beneficial to the S-scheme charge transfer in Pt-C3N4/BiOCl heterojunctions. Besides, based on the calculated variation in reaction energy, the rate-limiting step involved in CO2 reduction on g-C3N4/BiOCl heterojunction is the hydrogenation of CO2 to COOH, which has an energy barrier of 1.13 eV. After Pt loading, the hydrogenation of CO to HCO is the rate-limiting step and the corresponding energy increase is 0.71 eV. These results manifest that the introduction of Pt single-atom cocatalysts improves the CO2 reduction performance of g-C3N4/BiOCl S-scheme photocatalysts by strengthening the interfacial electric field and reducing the energy barrier. This study provides guidance for constructing metal-atom-incorporated S-scheme heterojunction photocatalysts to realize efficient CO2 reduction.
2023, 39(6): 220903
doi: 10.3866/PKU.WHXB202209037
Abstract:
The photoconversion of CO2 to carbon-containing fuels, splitting water into H2, selective organic synthesis, reduction of N2 to NH3, and hazardous organic contaminant degradation represent feasible schemes for solving environmental and energy issues. In 1972, TiO2 was applied for decomposing water into H2 and O2 via photocatalysis. Owing to its the low visible-light utilization, fast charge recombination, and high energy barrier for water oxidation, overall photocatalytic water-splitting efficiency is extremely low. Because H2 is more economically valuable than O2, sacrificial agent-assisted photocatalytic H2 evolution has been extensively investigated. Because the sacrificial agent can quickly consume photoexcited holes and effectively reduce the water oxidation energy barrier, photocatalytic H2 evolution efficiency can be increased by 3–4 orders of magnitude compared to photocatalytic water splitting. However, the overuse of sacrificial agents contributes to wasted photoexcited holes and expensive processes, while presenting potential environmental issues. Recently, overall charge utilization and improved redox efficiency have been achieved by coupling photocatalytic reduction with oxidation reactions. Moreover, overall charge utilization can boost charge separation and increase photocatalyst durability. However, the photocatalytic mechanism of the overall redox reactions remains unclear, owing to the complex reaction processes and design difficulties. Herein, the basic principles of photocatalysis are discussed from the perspective of light harvesting, photoexcited charge separation, thermodynamics, and redox reaction kinetics. Photocatalytic redox reactions, including overall water photodecomposition, photocatalytic H2 evolution coupled with organic oxidation, photocatalytic CO2 reduction coupled with organic oxidation, photocatalytic H2O2 production coupled with organic oxidation, photocatalytic N2 reduction coupled with N2 oxidation, and photocatalytic organic reduction coupled with organic oxidation, can be systematically classified according to the coupling of photocatalytic oxidation reactions with photocatalytic reduction reactions. Subsequently, the design of photocatalytic redox reactions is considered in terms of the modulation of photocatalyst materials, reaction conditions, and diversity of reactants and products. In addition, the vital role of density functional theory (DFT) calculations for unveiling photoexcited charge transfer, rate-determining steps, and redox reaction barriers are discussed in the context of the work function, electron density difference, Bader charge, and variation in the intermediate adsorption free energy profiles. The activity and mechanism of various photocatalytic redox reactions were elaborately analyzed through in situ characterizations and DFT calculations using representative cases. Finally, the overall photocatalytic redox reactions were summarized with a focus on the construction of an S-scheme heterojunction photocatalyst, reasonable loading of co-catalysts, photocatalyst morphology regulation, novel photocatalyst development, reasonable selection of the oxidation half-reaction and reduction half-reaction for coupling, and combined in situ characterization and DFT calculations. This work provides a reference for promising design strategies and insight into the mechanism of overall photocatalytic redox reactions. ![]()
The photoconversion of CO2 to carbon-containing fuels, splitting water into H2, selective organic synthesis, reduction of N2 to NH3, and hazardous organic contaminant degradation represent feasible schemes for solving environmental and energy issues. In 1972, TiO2 was applied for decomposing water into H2 and O2 via photocatalysis. Owing to its the low visible-light utilization, fast charge recombination, and high energy barrier for water oxidation, overall photocatalytic water-splitting efficiency is extremely low. Because H2 is more economically valuable than O2, sacrificial agent-assisted photocatalytic H2 evolution has been extensively investigated. Because the sacrificial agent can quickly consume photoexcited holes and effectively reduce the water oxidation energy barrier, photocatalytic H2 evolution efficiency can be increased by 3–4 orders of magnitude compared to photocatalytic water splitting. However, the overuse of sacrificial agents contributes to wasted photoexcited holes and expensive processes, while presenting potential environmental issues. Recently, overall charge utilization and improved redox efficiency have been achieved by coupling photocatalytic reduction with oxidation reactions. Moreover, overall charge utilization can boost charge separation and increase photocatalyst durability. However, the photocatalytic mechanism of the overall redox reactions remains unclear, owing to the complex reaction processes and design difficulties. Herein, the basic principles of photocatalysis are discussed from the perspective of light harvesting, photoexcited charge separation, thermodynamics, and redox reaction kinetics. Photocatalytic redox reactions, including overall water photodecomposition, photocatalytic H2 evolution coupled with organic oxidation, photocatalytic CO2 reduction coupled with organic oxidation, photocatalytic H2O2 production coupled with organic oxidation, photocatalytic N2 reduction coupled with N2 oxidation, and photocatalytic organic reduction coupled with organic oxidation, can be systematically classified according to the coupling of photocatalytic oxidation reactions with photocatalytic reduction reactions. Subsequently, the design of photocatalytic redox reactions is considered in terms of the modulation of photocatalyst materials, reaction conditions, and diversity of reactants and products. In addition, the vital role of density functional theory (DFT) calculations for unveiling photoexcited charge transfer, rate-determining steps, and redox reaction barriers are discussed in the context of the work function, electron density difference, Bader charge, and variation in the intermediate adsorption free energy profiles. The activity and mechanism of various photocatalytic redox reactions were elaborately analyzed through in situ characterizations and DFT calculations using representative cases. Finally, the overall photocatalytic redox reactions were summarized with a focus on the construction of an S-scheme heterojunction photocatalyst, reasonable loading of co-catalysts, photocatalyst morphology regulation, novel photocatalyst development, reasonable selection of the oxidation half-reaction and reduction half-reaction for coupling, and combined in situ characterization and DFT calculations. This work provides a reference for promising design strategies and insight into the mechanism of overall photocatalytic redox reactions.
2023, 39(6): 221201
doi: 10.3866/PKU.WHXB202212010
Abstract:
Rapid industrialization throughout the 20th and 21st centuries has led to the excessive consumption of fossil fuels to satisfy global energy demands. The dominant use of these fuel sources is the main cause of the ever-increasing environmental issues that greatly threaten humanity. Therefore, the development of renewable energy sources is fundamental to solving environmental issues. Solar energy has received widespread attention over the past decades as a green and sustainable energy source. Solar radiation-induced photocatalytic processes on the surface of semiconductor materials are able to convert solar energy into other energy sources for storage and further applications. However, the preparation of highly efficient and stable photocatalysts remains challenging. Recently, a new step-scheme (S-scheme) carrier migration mechanism was reported that solves the drawbacks of carrier migration in conventional heterojunction photocatalysts. The S-scheme heterojunction not only effectively solves the carrier migration problem and achieves fast separation but also preserves the powerful redox abilities and improves the catalytic performance of the photocatalytic system. To date, various S-scheme heterojunctions have been developed and employed to convert solar energy into useful chemical fuels to decrease the reliance on fossil fuels. Furthermore, these systems can also be used to degrade pollutants and reduce the harmful impact on the environment associated with the consumption of fossil fuels, including H2 evolution, pollutant degradation, and the reduction of CO2. H2O2 has been used as an effective, multipurpose, and green oxidizing agent in many applications including pollutant purification, medical disinfection, and chemical synthesis. It has also been used as a high-density energy carrier for fuel cells, with only water and oxygen produced as by-products. Photocatalytic technology provides a low-cost, environmentally friendly, and safe way to produce H2O2, requiring only solar energy, H2O, and O2 gas as raw materials. This paper reviews new S-scheme heterojunction designs for photocatalytic H2O2 production, including g-C3N4-, sulfide-, TiO2-, and ZnO-based S-scheme heterojunctions. The main principles of photocatalytic H2O2 production and the formation mechanism of the S-scheme heterojunction are also discussed. In addition, effective advanced characterization methods for S-scheme heterojunctions have been analyzed. Finally, the challenges that need to be addressed and the direction of future research are identified to provide new methods for the development of high-performance photocatalysts for H2O2 production.![]()
Rapid industrialization throughout the 20th and 21st centuries has led to the excessive consumption of fossil fuels to satisfy global energy demands. The dominant use of these fuel sources is the main cause of the ever-increasing environmental issues that greatly threaten humanity. Therefore, the development of renewable energy sources is fundamental to solving environmental issues. Solar energy has received widespread attention over the past decades as a green and sustainable energy source. Solar radiation-induced photocatalytic processes on the surface of semiconductor materials are able to convert solar energy into other energy sources for storage and further applications. However, the preparation of highly efficient and stable photocatalysts remains challenging. Recently, a new step-scheme (S-scheme) carrier migration mechanism was reported that solves the drawbacks of carrier migration in conventional heterojunction photocatalysts. The S-scheme heterojunction not only effectively solves the carrier migration problem and achieves fast separation but also preserves the powerful redox abilities and improves the catalytic performance of the photocatalytic system. To date, various S-scheme heterojunctions have been developed and employed to convert solar energy into useful chemical fuels to decrease the reliance on fossil fuels. Furthermore, these systems can also be used to degrade pollutants and reduce the harmful impact on the environment associated with the consumption of fossil fuels, including H2 evolution, pollutant degradation, and the reduction of CO2. H2O2 has been used as an effective, multipurpose, and green oxidizing agent in many applications including pollutant purification, medical disinfection, and chemical synthesis. It has also been used as a high-density energy carrier for fuel cells, with only water and oxygen produced as by-products. Photocatalytic technology provides a low-cost, environmentally friendly, and safe way to produce H2O2, requiring only solar energy, H2O, and O2 gas as raw materials. This paper reviews new S-scheme heterojunction designs for photocatalytic H2O2 production, including g-C3N4-, sulfide-, TiO2-, and ZnO-based S-scheme heterojunctions. The main principles of photocatalytic H2O2 production and the formation mechanism of the S-scheme heterojunction are also discussed. In addition, effective advanced characterization methods for S-scheme heterojunctions have been analyzed. Finally, the challenges that need to be addressed and the direction of future research are identified to provide new methods for the development of high-performance photocatalysts for H2O2 production.
2023, 39(6): 221201
doi: 10.3866/PKU.WHXB202212016
Abstract:
With the gradual depletion of conventional fossil fuels, serious energy shortage has become a major societal challenge. Among the numerous new energy generation technologies, photocatalytic water splitting for hydrogen production only requires abundant solar energy as the driving force and the process conditions are mild, green, and pollution-free. Thus, this technology has been proposed as an effective strategy to solve the current energy shortage crisis. The core of the photocatalytic hydrogen production technology is the photocatalyst. Therefore, it is necessary to develop efficient and stable photocatalysts. However, single-component photocatalysts usually exhibit insufficient photocatalytic H2 evolution efficiencies owing to its rapid hole-electron recombination, limited redox ability and low solar energy utilization efficiency. Therefore, various modification approaches have been designed to improve the photocatalytic H2 evolution efficiency of single-component photocatalysts, such as element doping, cocatalyst modification, heterojunction construction, etc. Generally, element doping and cocatalyst modification improve the photocatalytic hydrogen production activity but cannot effectively solve the drawbacks of single-component photocatalysts, which limits their ability to improve the photocatalytic performance. However, constructing heterojunctions between two or more semiconductors simultaneously resolves these drawbacks. Compared with currently used conventional type-Ⅱ all-solid-state Z-scheme, and liquid-phase Z-scheme heterojunctions, S-scheme heterojunctions present a more reasonable charge transfer mechanism, which is of great concern to and extensively used by several researchers. Therefore, this review firstly introduces the research background on S-scheme heterojunction photocatalytic systems, including the photocatalytic charge transfer mechanism of conventional type-Ⅱ, all-solid-state Z-scheme, and liquid-phase Z-scheme heterojunction systems. Subsequently, the photocatalytic mechanism of S-scheme heterojunctions is meticulously explained. Additionally, the corresponding characterization methods, including in situ irradiated X-ray photoelectron spectroscopy (ISIXPS), Kelvin probe force microscopy (KPFM), selective deposition, electron paramagnetic resonance (EPR), density functional theory (DFT) calculations, etc., are briefly summarized. Moreover, currently reported photocatalytic water splitting S-scheme heterojunctions and the corresponding significant enhancement in the hydrogen evolution mechanism are systematically summarized, including g-C3N4-, metal sulfide-, TiO2-, other oxide-, and other S-scheme heterojunction-based photocatalysts. Notably, S-scheme heterojunction photocatalysts typically exhibit highly improved photocatalytic H2 evolution performance owing to their effective carrier separation and enhanced photoredox capacities. Finally, the bottlenecks of developing S-scheme heterojunctions for photocatalytic H2 production are presented, which require further investigation to enhance the photocatalytic efficiency of S-scheme heterojunctions for achieving industrial application standards.![]()
With the gradual depletion of conventional fossil fuels, serious energy shortage has become a major societal challenge. Among the numerous new energy generation technologies, photocatalytic water splitting for hydrogen production only requires abundant solar energy as the driving force and the process conditions are mild, green, and pollution-free. Thus, this technology has been proposed as an effective strategy to solve the current energy shortage crisis. The core of the photocatalytic hydrogen production technology is the photocatalyst. Therefore, it is necessary to develop efficient and stable photocatalysts. However, single-component photocatalysts usually exhibit insufficient photocatalytic H2 evolution efficiencies owing to its rapid hole-electron recombination, limited redox ability and low solar energy utilization efficiency. Therefore, various modification approaches have been designed to improve the photocatalytic H2 evolution efficiency of single-component photocatalysts, such as element doping, cocatalyst modification, heterojunction construction, etc. Generally, element doping and cocatalyst modification improve the photocatalytic hydrogen production activity but cannot effectively solve the drawbacks of single-component photocatalysts, which limits their ability to improve the photocatalytic performance. However, constructing heterojunctions between two or more semiconductors simultaneously resolves these drawbacks. Compared with currently used conventional type-Ⅱ all-solid-state Z-scheme, and liquid-phase Z-scheme heterojunctions, S-scheme heterojunctions present a more reasonable charge transfer mechanism, which is of great concern to and extensively used by several researchers. Therefore, this review firstly introduces the research background on S-scheme heterojunction photocatalytic systems, including the photocatalytic charge transfer mechanism of conventional type-Ⅱ, all-solid-state Z-scheme, and liquid-phase Z-scheme heterojunction systems. Subsequently, the photocatalytic mechanism of S-scheme heterojunctions is meticulously explained. Additionally, the corresponding characterization methods, including in situ irradiated X-ray photoelectron spectroscopy (ISIXPS), Kelvin probe force microscopy (KPFM), selective deposition, electron paramagnetic resonance (EPR), density functional theory (DFT) calculations, etc., are briefly summarized. Moreover, currently reported photocatalytic water splitting S-scheme heterojunctions and the corresponding significant enhancement in the hydrogen evolution mechanism are systematically summarized, including g-C3N4-, metal sulfide-, TiO2-, other oxide-, and other S-scheme heterojunction-based photocatalysts. Notably, S-scheme heterojunction photocatalysts typically exhibit highly improved photocatalytic H2 evolution performance owing to their effective carrier separation and enhanced photoredox capacities. Finally, the bottlenecks of developing S-scheme heterojunctions for photocatalytic H2 production are presented, which require further investigation to enhance the photocatalytic efficiency of S-scheme heterojunctions for achieving industrial application standards.
2023, 39(6): 221100
doi: 10.3866/PKU.WHXB202211009
Abstract:
