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Semiconductor-based Z-scheme heterojunction photocatalysts have received considerable attention for solar energy conversion and environmental purification due to their spatially separated reduction and oxidation sites, effective s...
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Semiconductor-based Z-scheme heterojunction photocatalysts have received considerable attention for solar energy conversion and environmental purification due to their spatially separated reduction and oxidation sites, effective separation and transportation of photo-excited charge carriers and strong redox ability. With their wide visible-light responsive range and high photocatalytic activity, metal sulphide is an important material in developing photocatalysts. This review summarizes and highlights recent research progress in sulphide-based direct Z-scheme photocatalysts, followed by analysis on the limitations over all-solid-state Z-scheme photocatalyst. Furthermore, the applications and characterization methods of sulphide-based direct Z-scheme photocatalyst are summarized. Finally, the challenges and perspectives of sulphide-based Z-scheme photocatalyst are discussed.
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A novel ternary photocatalyst with a Z-scheme heterojunction was successfully synthesized through the deposition of Ag nanoparticles onto the surface of a ZnO/g-C3N4 composite. The prepared photocatalysts were characterized by XRD...
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A novel ternary photocatalyst with a Z-scheme heterojunction was successfully synthesized through the deposition of Ag nanoparticles onto the surface of a ZnO/g-C3N4 composite. The prepared photocatalysts were characterized by XRD, FT-IR, XPS, HRSEM, TEM, DRS, PL, EIS, TPC, and M-S. The photocatalytic performance of the as-synthesized photocatalysts was systematically investigated through the photodegradation of norfloxacin (NOR) and rhodamine B (RhB) under visible light irradiation. The photodegradation efficiency of 5% Ag/ZnO/g-C3N4 (5AZCN) composite photocatalyst reached 86.7% (480 min) and 98.0% (60 min) for NOR and RhB, respectively. Moreover, the apparent rate constants of the 5AZCN composite photocatalysts for NOR and RhB were found to be 3.4 and 22.2 times higher than that of the ZCN composite photocatalysts, respectively. The significantly enhanced photocatalytic performance was ascribed to the widened range of visible light response and the efficient separation and migration of carriers facilitated by the introduction of Ag nanoparticles that functioned as electron transfer mediators. Based on the free radicals quenching experiment and electron spin resonance (ESR) spectroscopy characterization, superoxide radicals (center dot O-2(-)) were the main reactive species in the photodegradation process. Furthermore, the charge transfer process was proved to be a Z-scheme transfer mechanism. This work provides a promising approach to simply constructing novel efficient Z-scheme photocatalysts for the elimination of environmental pollutants.
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The degradation efficiency of photoelectrocatalytic (PEC) processes for the removal of organic pollutants is highly dependent on the performance of the photoelectroanode catalyst. The design of PEC systems with a direct Z-scheme c...
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The degradation efficiency of photoelectrocatalytic (PEC) processes for the removal of organic pollutants is highly dependent on the performance of the photoelectroanode catalyst. The design of PEC systems with a direct Z-scheme charge transfer mechanism and visible light excitation is essential to enhance the degradation efficiency of organic compounds. Here, a α-MnO2/BiOI direct Z-scheme heterojunction photocatalyst was successfully synthesized through a convenient and feasible method. It is remarkable that the photoanode exhibited excellent PEC performance under visible light irradiation; a 95% removal rate of tetracycline (TC) pollutants was achieved within 2 h, and it had excellent stability and reusability, which was expected to degrade antibiotics efficiently and environmentally in harsh environments. The presence of oxygen vacancies (OVs) in the α-MnO2/BiOI heterojunction was confirmed by electron spin resonance technique, and the OVs acted as electron traps that contributed substantially to the separation efficiency of photogenerated carriers. ESR characterization showed that the main reactive radicals during TC degradation were ?OH and ?O2?. By analyzing the intermediates, the possible degradation pathways of TC were further analyzed and a suitable degradation mechanism was proposed. The toxicity changes in the degradation process were explored by evaluating the toxicity of the intermediates. This study provides a new way to enhance the performance of Bi-based semiconductor photocatalysts for the effective degradation of TC in water.
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The rational design of interfacial contacts plays a decisive role in improving interfacial carrier transfer and separation in heterojunction photocatalysts. In Z-scheme photocatalysts, the recombination of photogenerated electron-...
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The rational design of interfacial contacts plays a decisive role in improving interfacial carrier transfer and separation in heterojunction photocatalysts. In Z-scheme photocatalysts, the recombination of photogenerated electron-hole pairs is prevented so that the redox capacity is maintained. Here, one-dimensional graphitic carbon nitride (g-C3N4)/CoFe2O4 fibres were synthesised as a new type of magnetic Z-scheme visible-light photocatalyst. Compared with pure g-C3N4 and CoFe2O4, the prepared composite photocatalysts showed considerably improved performance for the photooxidative degradation of tetracycline and methylene blue. In particular, the photodegradation efficiency of the g-C3N4/CoFe2O4 fibres for methylene blue was approximately two and seven times those of g-C3N4 and CoFe2O4, respectively. The formation mechanism of the Z-scheme heterojunctions in the g-C3N4/CoFe2O4 fibres was investigated using photocurrent spectroscopy and electrochemical impedance spectroscopy. We proposed that one of the reasons for the improved photodegradation performance is that the charge transport path in one-dimensional materials enables efficient photoelectron and hole transfer. Furthermore, the internal electric field of the prepared Z-scheme photocatalyst enhanced visible-light absorption, which provided a barrier for photoelectron-hole pair recombination.
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In this study, a novel tungsten disulfide/tungsten diselenide (WS2/WSe2) heterojunction photocatalyst by a facile hydrothermal process with great capable photocatalytic efficiency for hydrogen evolution from water and organic comp...
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In this study, a novel tungsten disulfide/tungsten diselenide (WS2/WSe2) heterojunction photocatalyst by a facile hydrothermal process with great capable photocatalytic efficiency for hydrogen evolution from water and organic compound removal was discussed. The WS2/WSe2 heterojunction photocatalyst to form heterojunctions to inhibit the quick recombination rate of photo-response holes and electrons is reflected to be a useful method to enhance the capability of photocatalysis hydrogen production. The hydrogen production rate of the WS2/WSe2 photocatalyst approach is 3856.7 μmol/g/h, which is 12 and 11 folds the efficiency of bare WS2 and WSe2, respectively. Moreover, the excellent photocatalytic performance for Congo Red (CR) removal (92.4%) was 2.4 and 2.1 times higher than those of bare WS2 and WSe2, respectively. The great photocatalytic efficiency was owing to the capable electrons and holes separation of WS2/WSe2 and the construction of Z-scheme heterostructure, which possessed vigorous photocatalytic oxidation and reduction potentials. The novel one-dimensional structure of WS2/WSe2 heterojunction shortens the transport pathway of photo-induced electrons and holes. This work provided an insight to the pathway of interfacial separation and transferring for induced charge carriers, which can refer to the interfacial engineering of developed nanocomposite photocatalysts. It possessed great capable photocatalytic efficiency of hydrogen production and organic dye removal. This study offers an insight to the route of interfacial migration and separation for induced charge carriers to generating clean hydrogen energy and solve environmental pollution issue.
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In this study, a systematic investigation on nitrogen photofixation over well-designed oxygen vacancies and interface coordinately modulated WO3/InVO4 samples has been performed to produce low-concentrated ammonia at room temperat...
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In this study, a systematic investigation on nitrogen photofixation over well-designed oxygen vacancies and interface coordinately modulated WO3/InVO4 samples has been performed to produce low-concentrated ammonia at room temperature and atmospheric pressure. This work reveals that the interface modulation based on the addition of various weight ratios of WO3 and InVO4 can significantly boost catalytic activity for the nitrogen photofixation. Impressively, the optimized 70 wt% WO3/InVO4 hybrid system with oxygen vacancies exhibits outstanding catalytic activity, with an ammonia production concentration of 8.37 ± 0.30 mg L~(-1) when irradiated by simulated sunlight for 1 h, which is around 9.30 and 3.23 times than those on relevant WO3 and InVO4, respectively. The present systematic work has conclusively proved that the ·CO2~- generated from an aqueous suspension of WO3/InVO4 nanocomposites in the light is responsible for the reaction and even enhancement in activity of nitrogen photofixation. This work further verifies that the synergistic effects of interface regulation and oxygen vacancies in the WO3/InVO4 samples play a significant role in the highly efficient nitrogen photofixation.
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A Z-scheme WO3/ZnIn2S4 photocatalyst was synthesized via a simple solvothermal method. Compared with pure WO3 and ZnIn2S4, photocatalytic experiments showed that these Z-scheme photocatalysts exhibited enhanced activity for the de...
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A Z-scheme WO3/ZnIn2S4 photocatalyst was synthesized via a simple solvothermal method. Compared with pure WO3 and ZnIn2S4, photocatalytic experiments showed that these Z-scheme photocatalysts exhibited enhanced activity for the degradation of nitenpyram (NTP). The apparent rate constant (k) of NTP degradation on 50WZ (WO3/50 wt% Znln(2)S(4)) was 0.042 min(-1) (similar to 3.8 times higher than WO3 and similar to 2.5 times higher than ZnIn2S4). Photoluminescence (PL), photocurrent (PC), and electrochemical impedance spectroscopy (EIS) showed that the separation and transfer efficiency of photogenerated carriers in SOWZ was markedly enhanced, which was favorable for improving its photocatalytic activity. Active species capture experiments and electron spin resonance (ESR) measurements showed that superoxide radicals and holes were the main active species for NIP degradation, and they confirmed the formation of the Z-scheme structure. Furthermore, a possible NTP degradation pathway was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS).
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A three-component BiVO4/Ag/CdS Z-scheme photocatalyst was synthesized through a two-step in-situ deposition method. Ag nanoparticles obtained from photoreduction are distributed on the BiVO4 (010) facets with a low LUMO level. CdS...
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A three-component BiVO4/Ag/CdS Z-scheme photocatalyst was synthesized through a two-step in-situ deposition method. Ag nanoparticles obtained from photoreduction are distributed on the BiVO4 (010) facets with a low LUMO level. CdS is gradually deposited onto BiVO4/Ag composites by electrostatic self-assembly. The unique structural configuration with closely integrated triple points among BiVO4, Ag, and CdS, facilitates the transfer of charge carriers, and thus improves the photocatalytic ability and stability. Based on the trapping test, the all-solid-state Z-scheme photocatalytic mechanism is proposed and further validated with photoelectrochemical measurements.
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The energy band alignments, charge transfers and distributions of square of electronic wavefunctions of g-C3N4/(101)-TiO2 and g-C3N4/(001)-TiO2 heterojunctions with oxygen vacancies are investigated with first principles calculati...
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The energy band alignments, charge transfers and distributions of square of electronic wavefunctions of g-C3N4/(101)-TiO2 and g-C3N4/(001)-TiO2 heterojunctions with oxygen vacancies are investigated with first principles calculations. Our theoretical results show that TiO2 and g-C3N4 can contact with each other to form a van der Waals heterojunction. Three heterostructures for g-C3N4/(101)-TiO2, g-C3N4/V-O-(101)-TiO2, and g-C3N4/(001)-TiO2 are Z-scheme heterojunctions while g-C3N4/V-O-(001)-TiO2 is type-II heterojunction. The energy levels of (001) surface is higher than that of (101) surface in titanium dioxide, and the donor level formed by oxygen vacancy further increases its Fermi level. So in the process of forming heterojunction, the electrons will transfer from titanium dioxide to carbon nitride instead of from carbon nitride to titanium dioxide to form type-II heterojunction for g-C3N4/V-O-(001)-TiO2. There exist several localized and delocalized shallow defect levels in energy gap of the g-C3N4/V-O-(101)-TiO2 heterojunction. Its wavefunction of delocalized shallow defect level can span both sides of the heterojunction and play an important role in promoting photogenerated electrons migration from titanium dioxide to carbon nitride. However, there are partially localized deep defect levels in the energy gap of g-C3N4/V-O-(001)-TiO2 heterojunction, whose wavefunctions only distribute over titania. They only act as the recombination centers of electron-hole pairs and makes the photocatalytic effect worse. Our calculations reveal the effects of delocalized wavefunction of shallow defect level covering both sides of heterojunction on photocatalytic activity in g-C3N4/TiO2 heterojunctions and provide a way to convert the transfer scheme of heterojunctions by introducing impurities.
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Global warming is caused by excessive CO2 production, and reducing CO2 emissions is a viable way to counteract this. It has been extensively studied how light-driven processes, particularly photocatalytic systems, can trans-form s...
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Global warming is caused by excessive CO2 production, and reducing CO2 emissions is a viable way to counteract this. It has been extensively studied how light-driven processes, particularly photocatalytic systems, can trans-form solar energy into chemical energy. In the present review exercise, the mechanism of CO2 reduction is described using calculations based on density functional theory (DFT), and comparisons are also made with regard to typical light-driven devices. Additionally, the traits of potential materials-including metal-organic frameworks (MOFs), metal complexes, metal oxide, Z-scheme (metal complexes/semiconductors, two semi-conductors, dye-sensitized semiconductors), improved S-scheme and organic photocatalyst etc.-are described in depth to show how these traits affect the CO2 adsorption, activation, and desorption processes. Also summarized are a number of methods for enhancing the selectivity and efficiency of catalytic reactions. Lastly, the challenges and future outlook of light-driven reactions for CO2 reduction are presented.
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