Highly Selective Production of Ethanol Over Hierarchical Bi@Bi2 MoO6 Composite via Bicarbonate-Assisted Photocatalytic CO2 Reduction

Highly Efficient and Selective Photocatalytic CO2 Reduction to Ethanol by Cu4 Clusters with Adjacent Cu Single Atoms Anchored on Carbon Nitride

An efficient photocatalyst for CO2-to-CH3CH2OH conversion comprising atomically dispersed Cu clusters (Cu4) and single Cu sites coordinated with 2 N and 1 O anchored on two-step calcinated C3N4 (Cu4/Cu1@CN) is reported. It was found to catalyze the reduction of CO2 to ethanol with production rate of 154 µmol g-1 h-1 and selectivity of 98%, the yield rate and selectivity exceed most of the reported results for ethanol production. Experimental and theoretical calculations indicate that the high efficiency of this catalyst arises from the strong synergy between Cu4 clusters and adjacent Cu single atoms, which facilitates OC─CO coupling and promotes ethanol production.

Rationally Designed S-Scheme CeO2/g-C3N4 Heterojunction for Promoting Visible Light Driven CO2 Photoreduction into Syngas

Exploring low-cost visible light photocatalysts for CO2 reduction to produce proportionally adjustable syngas is of great significance for meeting the needs of green chemical industry. A S-Scheme CeO2/g-C3N4 (CeO2/CN) heterojunction was constructed by using a simple two-step calcination method. During the photocatalytic CO2 reduction process, the CeO2/CN heterojunction can present a superior photocatalytic performance, and the obtained CO/H2 ratios in syngas can be regulated from 1 : 0.16 to 1 : 3.02. In addition, the CO and H2 production rate of the optimal CeO2/CN composite can reach 1169.56 and 429.12 μmol g-1 h-1, respectively. This superior photocatalytic performance is attributed to the unique S-Scheme photogenerated charge transfer mechanism between CeO2 and CN, which facilitates rapid charge separation and migration, while retaining the excellent redox capacity of both semiconductors. Particularly, the variable valence Ce3+/Ce4+ can act as electron mediator between CeO2 and CN, which can promote electron transfer and improve the catalytic performance. This work is expected to provide a new useful reference for the rational construction of high efficiency S-Scheme heterojunction photocatalyst, and improve the efficiency of photocatalytic reduction of CO2, promoting the photocatalytic reduction of CO2 into useful fuels.

Recent advances of metal active sites in photocatalytic CO2 reduction

Photocatalytic CO2 reduction captures solar energy to convert CO2 into hydrocarbon fuels, thus shifting the dependence on rapidly depleting fossil fuels. Among the various proposed photocatalysts, systems containing metal active sites (MASs) possess obvious advantages, such as effective photogenerated carrier separation, suitable adsorption and activation of intermediates, and achievable C-C coupling to generate multi-carbon (C2+) products. The present review aims to summarize the typical photocatalytic materials with MAS, highlighting the critical role of different formulations of MAS in CO2 photoreduction, especially for C2+ product generation. State-of-the-art progress in the characterization and theoretical calculations for MAS-containing photocatalysts is also emphasized. Finally, the challenges and prospects of catalytic systems involving MAS for solar-driven CO2 conversion are outlined, providing inspiration for the future design of materials for efficient photocatalytic energy conversion.

Boosting Solar-Driven CO2 Conversion to Ethanol via Single-Atom Catalyst with Defected Low-Coordination Cu-N2 Motif

Cu-based catalysts have been shown to selectively catalyze CO2 photoreduction to C2+ solar fuels. However, they still suffer from poor activity and low selectivity. Herein, we report a high-performance carbon nitride supported Cu single-atom catalyst featuring defected low-coordination Cu-N2 motif (Cu-N2-V). Lead many recently reported photocatalysts and its Cu-N3 and Cu-N4 counterparts, Cu-N2-V exhibits superior photocatalytic activity for CO2 reduction to ethanol and delivers 69.8 μmol g-1 h-1 ethanol production rate, 97.8 % electron-based ethanol selectivity, and a yield of ~10 times higher than Cu-N3 and Cu-N4. Revealed by the extensive experimental investigation combined with DFT calculations, the superior photoactivity of Cu-N2-V stems from its defected Cu-N2 configuration, in which the Cu sites are electron enriched and enhance electron delocalization. Importantly, Cu in Cu-N2-V exist in both Cu+ and Cu2+ valence states, although predominantly as Cu+. The Cu+ sites support the CO2 activation, while the co-existence of Cu+/Cu2+ sites are highly conducive for strong *CO adsorption and subsequent *CO-*CO dimerization enabling C-C coupling. Furthermore, the hollow microstructure of the catalyst also promotes light adsorption and charge separation efficiency. Collectively, these make Cu-N2-V an effective and high-performance catalyst for the solar-driven CO2 conversion to ethanol. This study also elucidates the C-C coupling reaction path via *CO-*CO to *COCOH and rate-determining step, and reveals the valence state change of partial Cu species from Cu+ to Cu2+ in Cu-N2-V during CO2 photoreduction reaction.

A Review of the Effect of Defect Modulation on the Photocatalytic Reduction Performance of Carbon Dioxide

Constructive defect engineering has emerged as a prominent method for enhancing the performance of photocatalysts. The mechanisms of the influence of defect types, concentrations, and distributions on the efficiency, selectivity, and stability of CO2 reduction were revealed for this paper by analyzing the effects of different types of defects (e.g., metallic defects, non-metallic defects, and composite defects) on the performance of photocatalysts. There are three fundamental steps in defect engineering techniques to promote photocatalysis, namely, light absorption, charge transfer and separation, and surface-catalyzed reactions. Defect engineering has demonstrated significant potential in recent studies, particularly in enhancing the light-harvesting, charge separation, and adsorption properties of semiconductor photocatalysts for reducing processes like carbon dioxide reduction. Furthermore, this paper discusses the optimization method used in defect modulation strategy to offer theoretical guidance and an experimental foundation for designing and preparing efficient and stable photocatalysts.

Schottky Junctions with Bi@Bi2MoO6 Core-Shell Photocatalysts toward High-Efficiency Solar N2-to-Ammonnia Conversion in Aqueous Phase

The photocatalytic nitrogen reduction reaction (NRR) in aqueous solution is a green and sustainable strategy for ammonia production. Nonetheless, the efficiency of the process still has a wide gap compared to that of the Haber-Bosch one due to the difficulty of N2 activation and the quick recombination of photo-generated carriers. Herein, a core-shell Bi@Bi2MoO6 microsphere through constructing Schottky junctions has been explored as a robust photocatalyst toward N2 reduction to NH3. Metal Bi self-reduced onto Bi2MoO6 not only spurs the photo-generated electron and hole separation owing to the Schottky junction at the interface of Bi and Bi2MoO6 but also promotes N2 adsorption and activation at Bi active sites synchronously. As a result, the yield of the photocatalytic N2-to-ammonia conversion reaches up to 173.40 μmol g-1 on core-shell Bi@Bi2MoO6 photocatalysts, as much as two times of that of bare Bi2MoO6. This work provides a new design for the decarbonization of the nitrogen reduction reaction by the utilization of renewable energy sources.

Photocatalytic Enhancement Strategy with the Introduction of Metallic Bi: A Review on Bi/Semiconductor Photocatalysts

Semiconductor photocatalysis has great potential in the fields of solar fuel production and environmental remediation. Nevertheless, the photocatalytic efficiency still constrains its practical production applications. The development of new semiconductor materials is essential to enhance the solar energy conversion efficiency of photocatalytic systems. Recently, the research on enhancing the photocatalytic performance of semiconductors by introducing bismuth (Bi) has attracted widespread attention. In this review, we briefly overview the main synthesis methods of Bi/semiconductor photocatalysts and summarize the control of the micromorphology of Bi in Bi/semiconductors and the key role of Bi in the catalytic system. In addition, the promising applications of Bi/semiconductors in photocatalysis, such as pollutant degradation, sterilization, water separation, CO2 reduction, and N2 fixation, are outlined. Finally, an outlook on the challenges and future research directions of Bi/semiconductor photocatalysts is given. We aim to offer guidance for the rational design and synthesis of high-efficiency Bi/semiconductor photocatalysts for energy and environmental applications.

Advances in the Application of Bi-Based Compounds in Photocatalytic Reduction of CO2

Bi-based semiconductor materials have special layered structure and appropriate band gap, which endow them with excellent visible light response ability and stable photochemical characteristics. As a new type of environment-friendly photocatalyst, they have received extensive attention in the fields of environmental remediation and energy crisis resolution and have become a research hotspot in recent years. However, there are still some urgent issues that need to be addressed in the practical large-scale application of Bi-based photocatalysts, such as the high recombination rate of photogenerated carriers, limited response range to visible spectra, poor photocatalytic activity, and weak reduction ability. In this paper, the reaction conditions and mechanism of photocatalytic reduction of CO₂ and the typical characteristics of Bi-based semiconductor materials are introduced. On this basis, the research progress and application results of Bi-based photocatalysts in the field of reducing CO₂, including vacancy introduction, morphological control, heterojunction construction, and co-catalyst loading, are emphasized. Finally, the future prospects of Bi-based photocatalysts are prospected, and it is pointed out that future research directions should be focused on improving the selectivity and stability of catalysts, deeply exploring reaction mechanisms, and meeting industrial production requirements.

Recent Advances in Electrochemical, Photochemical, and Photoelectrochemical Reduction of CO2 to C2+ Products

Environmental problems such as global warming are one of the most prominent global challenges. Researchers are investigating various methods for decreasing CO₂ emissions. The CO₂ reduction reaction via electrochemical, photochemical, and photoelectrochemical processes has been a popular research topic because the energy it requires can be sourced from renewable sources. The CO₂ reduction reaction converts stable CO₂ molecules into useful products such as CO, CH₄ , C₂ H₄ , and C₂ H₅ OH. To obtain economic benefits from these products, it is important to convert them into hydrocarbons above C₂ . Numerous investigations have demonstrated the uniqueness of the CC coupling reaction of Cu-based catalysts for the conversion of CO₂ into useful hydrocarbons above C₂ for electrocatalysis. Herein, the principle of semiconductors for photocatalysis is briefly introduced, followed by a description of the obstacles for C₂₊ production. This review presents an overview of the mechanism of hydrocarbon formation above C₂ , along with advances in the improvement, direction, and comprehension of the CO₂ reduction reaction via electrochemical, photochemical, and photoelectrochemical processes.

Photocatalytic CO2 Conversion to Ethanol: A Concise Review

Photo-catalytically converting the greenhouse gas CO2 into ethanol is an important avenue for the mitigation of climate issues and the utilization of renewable energies. Catalysts play critical roles in the reaction of photocatalytic CO2 conversion to ethanol, and a number of catalysts have been investigated, including semiconductors and plasmonic metal-based catalysts, as well as several other catalysts. In this review, the progress in the development of each category of catalysts is summarized, the current status is reviewed, the remaining challenges are pointed out, and the future research directions are prospected, with the aim being to pave pathways for the rational design of better catalysts.

Recent review of BixMOy (M=V, Mo, W) for photocatalytic CO2 reduction into solar fuels

The utilization of solar energy for CO₂ conversion not only enables a green and low-carbon recycling of CO₂ with renewable energy, but also solves ecological problems. Bi_xMO_y (M = V, Mo, W) materials have typical layered structures and unique electronic properties that provide suitable band gaps and potential to meet the basic conditions for CO₂ reduction. However, pristine Bi_xMO_y faces with problems such as small specific surface area, insufficient active sites, low charge carriers' separation and utilization efficiency. This review comprehensively described the basic principles and reaction pathways of photocatalytic CO₂ reduction, and further presented the research progress of Bi_xMO_y catalysts in CO₂ conversion reactions. In this perspective, we further focus on the design concepts and modification strategies to improve the photocatalytic CO₂ reduction activity of Bi_xMO_y, such as morphology control, constructing surface vacancies and heterojunction fabrication. Finally, based on representative researches, the present review will be expected to provide updated information and insights for developing advanced Bi_xMO_y materials to further improve CO₂ reduction activity and selectivity.

Selective Photocatalytic Reduction of CO2 to Syngas Over Tunable Metal-Perovskite Interface

The extensive emission of CO₂ results in critical environmental issues, such as global warming. Photocatalytic CO₂ conversion is a meaningful route to convert CO₂ into useful chemicals. However, the highly selective reduction of CO₂ with the avoidance of hydrogen evolution is still challenging. Herein, the photocatalytic reduction CO₂ to synthesis gas (syngas) was achieved on a metal Ag socketed perovskite LaFeO₃ (LFO) catalytic interface prepared by an in-situ exsolution method. The conduction band of Ag-exsolved LFO is more negative than LFO, benefiting efficient CO₂ reduction. By tuning the dopant Ag cation in the lattice to nanoparticles pinned on the surface, the CO formation rate was improved around five-fold from 0.51 to 2.41 μmol g^-1  h^-1 . Meanwhile, the H₂ /CO molar ratio also showed strong dependence on the modality of Ag at the metal-perovskite interface. The design offers a promising pathway for transforming CO₂ to valuable chemicals based on efficient photocatalysts design.

Light-driven carbon dioxide reduction over the Ag-decorated modified TS-1 zeolite

Cu species doped defective Ag/TS-1 owns Ti3+–Vo which could play an vital part in stabilizing Cu2O. It shows high selectivity for CO and C2H5OH under light excitation and photoelectric condition. The possible pathway of CO2RR process is proposed.