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Solar-energy-driven CO2 hydrogenation is a promising strategy to alleviate the climate crisis. Methane is a desirable derivative of CO2 reduction. However, developing a photocatalyst for highly active and selective CH4 generation remains challenging. Herein, we report a double Z-scheme Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S photocatalyst for efficient reduction of CO2 to CH4. In situ characterization techniques confirmed that the charge migration mechanism in Bi3O4Cl/g-C3N4/Cd0.5Zn0.5S promotes charge separation through double internal electric fields. As a result, the optimized C0.01B0.02C catalyst displayed a formation rate high up to 25.34 µmol g-1 h-1 and a selectivity of 96.52% of CH4. Moreover, the AQY of CO2 conversion on C0.01B0.02C (1.84%) was almost 41 times higher than that of the bare CN. This study provides a novel perspective to develop heterojunction photocatalysts for selective CO2 conversion to CH4.
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Covalent organic frameworks (COFs) are one type of porous organic materials linked by covalent bonds. COFs materials exhibit many outstanding characteristics such as high porosity, high chemical and thermal stability, large specific surface area, efficient electron transfer efficiency, and the ability for predesigned structures. These exceptional advantages enable COFs materials to exhibit remarkable performance in photocatalysis. Additionally, the activity of COFs materials as photocatalysts can be significantly upgraded by ion doping and the formation of heterojunctions. This paper summarizes the latest research progress on COF-based materials applied in photocatalytic systems. Initially, typical structures and preparation methods of COFs are analyzed and compared. Moreover, the essential principles of photocatalytic reactions over COFs-based materials and the latest research developments in photocatalytic hydrogen production, CO2 reduction, pollutants elimination, organic transformation, and overall water splitting are indicated. At last, the outlook and challenges of COF-based materials in photocatalysis are discussed. This review is intended to permit instructive guidance for the efficient use of photocatalysis based on COFs in the future.
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Converting CO2 into value-added products by photocatalysis, electrocatalysis, and photoelectrocatalysis is a promising method to alleviate the global environmental problems and energy crisis. Among the semiconductor materials applied in CO2 catalytic reduction, Cu2 O has the advantages of abundant reserves, low price and environmental friendliness. Moreover, Cu2 O has unique adsorption and activation properties for CO2 , which is conducive to the generation of C2+ products through CC coupling. This review introduces the basic principles of CO2 reduction and summarizes the pathways for the generation of C1 , C2 , and C2+ products. The factors affecting CO2 reduction performance are further discussed from the perspective of the reaction environment, medium, and novel reactor design. Then, the properties of Cu2 O-based catalysts in CO2 reduction are summarized and several optimization strategies to enhance their stability and redox capacity are discussed. Subsequently, the application of Cu2 O-based catalysts in photocatalytic, electrocatalytic, and photoelectrocatalytic CO2 reduction is described. Finally, the opportunities, challenges and several research directions of Cu2 O-based catalysts in the field of CO2 catalytic reduction are presented, which is guidance for its wide application in the energy and environmental fields is provided.
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Photocatalysis driven by solar energy is a feasible strategy to alleviate energy crises and environmental problems. In recent years, significant progress has been made in developing advanced photocatalysts for efficient solar-to-chemical energy conversion. Single-atom catalysts have the advantages of highly dispersed active sites, maximum atomic utilization, unique coordination environment, and electronic structure, which have become a research hotspot in heterogeneous photocatalysis. This paper introduces the potential supports, preparation, and characterization methods of single-atom photocatalysts in detail. Subsequently, the fascinating effects of single-atom photocatalysts on three critical steps of photocatalysis (the absorption of incident light to produce electron-hole pairs, carrier separation and migration, and interface reactions) are analyzed. At the same time, the applications of single-atom photocatalysts in energy conversion and environmental protection (CO2 reduction, water splitting, N2 fixation, organic macromolecule reforming, air pollutant removal, and water pollutant degradation) are systematically summarized. Finally, the opportunities and challenges of single-atom catalysts in heterogeneous photocatalysis are discussed. It is hoped that this work can provide insights into the design, synthesis, and application of single-atom photocatalysts and promote the development of high-performance photocatalytic systems.
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Photocatalytic CO2 reduction to valuable fuels is a promising way to alleviate anthropogenic CO2 emissions and energy crises. Perovskite oxides have attracted widespread attention as photocatalysts for CO2 reduction by virtue of their high catalytic activity, compositional flexibility, bandgap adjustability, and good stability. In this review, the basic theory of photocatalysis and the mechanism of CO2 reduction over perovskite oxide are first introduced. Then, perovskite oxides' structures, properties, and preparations are presented. In detail, the research progress on perovskite oxides for photocatalytic CO2 reduction is discussed from five aspects: as a photocatalyst in its own right, metal cation doping at A and B sites of perovskite oxides, anion doping at O sites of perovskite oxides and oxygen vacancies, loading cocatalyst on perovskite oxides, and constructing heterojunction with other semiconductors. Finally, the development prospects of perovskite oxides for photocatalytic CO2 reduction are put forward. This article should serve as a useful guide for creating perovskite oxide-based photocatalysts that are more effective and reasonable.
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A photocatalytic system driven by solar light is one of the promising strategies for converting CO2 into valuable energy. The reduction of CO2 to CH4 is widely studied since CH4 has a high energy density as the main component of nonrenewable natural gas. Therefore, it is necessary to develop semiconductor materials with high photocatalytic activity and CH4 selectivity. Graphitic carbon nitride (g-C3N4/CN) has attracted widespread attention for photocatalytic CO2 reduction due to its excellent redox ability and visible light response. A hybrid system constructed by loading cocatalysts on g-C3N4 can significantly improve the yield of target products, and serve as a general platform to explore the mechanism of the CO2 reduction reaction. Herein, we briefly introduce the theory of selective CO2 photoreduction and the basic properties of cocatalysts. Then, several typical configurations and modification strategies of cocatalyst/CN systems for promoting CH4 selective production are presented in detail. In particular, we systematically summarize the application of cocatalyst/CN composite photocatalysts in the selective reduction of CO2 to methane, according to the classification of cocatalysts (monometal, bimetal, metal-based compound, and nanocarbon materials). Finally, the challenges and perspectives for developing cocatalyst/g-C3N4 systems with high CH4 selectivity are presented to guide the rational design of catalysts with high performance in the future.
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Converting CO2 into chemicals and fuels by solar energy can alleviate global warming and solve the energy crisis. In this work, CoAl-LDO/MoO3-x (LDO/MO) composites were successfully prepared and achieved efficient CO2 reduction under visible light. The CoAl-layered double oxides (CoAl-LDO) evolved from CoAl-layered double hydroxide (CoAl-LDH) exhibited a more robust structure, broader light absorption, and improved CO2 adsorption ability. The local surface plasmon resonance (LSPR) effect excited by nonstoichiometric MoO3-x broadened the photo-response range of CoAl-LDO/MoO3-x. In addition, constructing step-scheme (S-scheme) heterojunctions could simultaneously optimize the migration mechanism of photogenerated electrons and holes, and retain carriers with strong redox ability. Therefore, the production rates of CO and CH4 on the optimal LDO/MO composite were 7 and 9 times higher than the pristine CoAl-LDH, respectively. This work hybridizes oxidation photocatalysts and LDO-based materials to optimize the charge separation and migration mechanisms, which guides the modification of LDO-based materials.
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The photocatalytic reduction of CO2 to hydrocarbons is expected to simultaneously alleviate the energy crisis and greenhouse effect. Herein, the ternary BiOCl/C/Cu2O catalysts with different mass ratios were compounded using a simple hydrothermal method, revealing better photocatalytic activity than the monomer. In the absence of sacrificial agents and photosensitizers, 25% BiOCl/C/Cu2O showed optimal photocatalytic performance. The CO and CH4 yields over 25% BiOCl/C/Cu2O reached 26.77 and 9.86 µmol g-1 h-1, which is 2.9 and 8.7 times higher than that of the pristine Cu2O, respectively. The ameliorative activity can be attributed to the construction of the Z-scheme heterostructure and carbon layer, which are conducive to the transfer and separation of photogenerated carriers. This study offers valuable references for the design and investigation of a Z-scheme heterojunction using a carbon layer as an electron transfer medium.
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In this research, a ternary Cu-CuTCPP/Cu2O/CoAl-LDH composite with a dual Z-scheme heterostructure was fabricated based on a Cu2O photocatalyst and applied in photocatalytic CO2 reduction. The physicochemical properties of the prepared catalysts and the possible reaction mechanism in CO2 reduction were analyzed and studied by various characterization methods. The activity of CO2 reduction significantly increased, especially forming C2 products. The optimal yield of C2H4 and C2H6 reached 1.56 and 1.92 µmol g-1 h-1 respectively, which was 14.45 and 17.45 times that from using the Cu2O monomer. In addition, the selectivity of C2 products reached 37.4%. The satisfactory C2 yield was mainly due to the fact that Cu1+δ2(COO)3 nodes in Cu-CuTCPP contained adjacent Cu sites, which effectively promoted the C-C coupling reaction. Moreover, the dual Z-scheme heterojunction stimulated the separation of photogenerated electron-hole pairs and diminished the recombination rate. This work contributes to the development of novel photocatalysts with a dual Z-scheme heterojunction and facilitates the generation of valuable C2 products.
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OBJECTIVE: To investigate the therapeutic mechanism of Weiweifang (WWF, a Chinese herbal preparation) on gastric ulcer in rats viewing from metabonomics. METHODS: Wistar rats were made to gastric model by acetic acid cauterization and randomized into the model group, the spontaneously healing group and the three WWF treatment groups, and a group of normal rats was set for control. Metabolic spectra of gastric mucosa extraction of rats were acquired with gas chromatography-mass spectrometry (GC-MS) technique. After being pre-processing, data were subjected to partial least squares discriminant analysis (PLS-DA) to discover the biomarkers in rats of the normal group and the model group. The therapeutic effect of WWF on experimental gastric ulcer was assessed by principal component analyses (PCA), and its action of mechanism was explained viewing from the changes of biomarkers. RESULTS: Spectra of biomarkers, including organic acids, fatty acids, amino acids, etc. in model rats were statistically different to those in normal rats, which demonstrated that the energy and substance metabolisms were disordered in rats with gastric ulcer. WWF could cure gastric ulcer effectively by way of regulating the metabolism of gastric mucosa. CONCLUSION: The therapeutic mechanism of WWF on experimental gastric ulcer in rats is revealed integrally by metabonomics in this study, displaying prominently the characteristics of Chinese medicine multiple targets comprehensive therapy.