A Review of Phosphorus Structures as CO2 Reduction Photocatalysts

S-scheme heterojunction Cu-porphyrin/TiO2 nanosheets with highly efficient photocatalytic reduction of CO2 in ambient air

Directly capturing CO2 in ambient air and converting it into value-added fuels using photocatalysis is a potentially valuable technology. In this study, Cu-porphyrin (tetrakis-carboxyphenyl porphyrin copper, CuTCPP) was innovatively anchored on the surface of TiO2 (titanium dioxide) nanosheets to form an S-scheme heterojunction. Based on this, a photocatalytic reaction system for stably converting CO2 in ambient air into value-added fuels at the gas-solid interface was constructed without addition of sacrificial agents and alkaline liquids. Under the illumination of visible light and sunlight, the evolution rate of CO is 56 μmol·g-1·h-1 and 73 μmol·g-1·h-1, respectively, with a potential CO2 conversion rate of 35.8 % and 50.4 %. The enhanced of photocatalytic performance is attributed to the introduction of CuTCPP, which provides additional active sites, significantly improves capture capacity of CO2 and the utilization of electrons. Additionally, the formation of S-scheme heterojunction expands the redox range and improves the separation efficiency of photo-generated charges.

Molecular Terpyridine-Lanthanide Complexes Modified Carbon Nitride for Enhanced Photocatalytic CO2 Reduction

Molecule/semiconductor hybrid catalysts, which combine molecular metal complexes with semiconductors, have shown outstanding performances in photocatalytic CO2 reduction. In this work, we report two hybrid catalysts for the selective photoreduction of CO2 to CO. One is composed of carbon nitride and a terpyridine-Lu complex (denoted as LutpyCN), and the other is composed of carbon nitride and a terpyridine-Ce complex (denoted as CetpyCN). Compared with pristine carbon nitride, the hybrid catalysts LutpyCN and CetpyCN display a noteworthy increase in CO generation, boosting the yield by approximately 176 times and 106 times, respectively. Mechanistic studies demonstrate that such significant enhancement in photocatalysis is primarily due to more efficient separation of photogenerated carriers for hybrid catalysts after modifying CN with molecular terpyridine-lanthanide species.

Zintl Clusters as a Platform for Lewis Acid Catalysis

Clusters of the main group elements phosphorus and arsenic, commonly categorized as Zintl clusters, have been known for over a century. And, only now is the application of these systems as catalysts for organic synthesis being investigated. In this work, boranes are tethered via an aliphatic linker to Zintl-based clusters and their Lewis acidity is examined experimentally, by the Gutmann-Beckett test and competency in the hydroborative reduction of six organic substrates, as well as computationally, by fluoride ion affinity and hydride ion affinity methods. The effects of tuning the aliphatic linker length, substituents at the boron, and changing the cluster from a seven-atom phosphorus system to a seven-atom arsenic system on reactivity are studied.

Dynamics of Electron Transfer in CdS Photocatalysts Decorated with Various Noble Metals

To address charge recombination in photocatalysis, the prevalent approach involves the use of noble metal cocatalysts. However, the precise factors influencing this performance variability based on cocatalyst selection have remained elusive. In this study, CdS hollow spheres loaded with distinct noble metal nanoparticles (Pt, Au, and Ru) are investigated by femtosecond transient absorption (fs-TA) spectroscopy. A more pronounced internal electric field leads to the creation of a larger Schottky barrier, with the order Pt-CdS > Au-CdS > Ru-CdS. Owing to these varying Schottky barrier heights, the interface electron transfer rate (Ke) and efficiency (ηe) of metal-CdS in acetonitrile (ACN) exhibit the following trend: Ru-CdS > Au-CdS > Pt-CdS. However, the trends of Ke and ηe for metal-CdS in water are different (Ru-CdS > Pt-CdS > Au-CdS) due to the influence of water, leading to the consumption of photogenerated electrons and affecting the metal/CdS interface state. Although Ru-CdS displays the highest Ke and ηe, its overall photocatalytic performance, particularly in H2 production, lags behind that of Pt-CdS due to the electron backflow from Ru to CdS. This work offers a fresh perspective on the origin of performance differences and provides valuable insights for cocatalyst design and construction.

Research progress of dual-atom site catalysts for photocatalysis

Dual-atom site catalysts (DASCs) have sparked considerable interest in heterogeneous photocatalysis as they possess the advantages of excellent photoelectronic activity, photostability, and high carrier separation efficiency and mobility. The DASCs involved in these important photocatalytic processes, especially in the photocatalytic hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2/nitrate reduction, etc., have been extensively investigated in the past few years. In this review, we highlight the recent progress in DASCs that provides fundamental insights into the photocatalytic conversion of small molecules. The controllable preparation and characterization methods of various DASCs are discussed. Subsequently, the reaction mechanisms of the formation of several important molecules (hydrogen, hydrocarbons and ammonia) on DASCs are introduced in detail, in order to probe the relationship between DASCs's structure and photocatalytic activity. Finally, some challenges and outlooks of DASCs in the photocatalytic conversion of small molecules are summarized and prospected. We hope that this review can provide guidance for in-depth understanding and aid in the design of efficient DASCs for photocatalysis.

Advances in zeolitic-imidazolate-framework-based catalysts for photo-/electrocatalytic water splitting, CO2 reduction and N2 reduction applications

Harnessing electrical or solar energy for the renewable production of value-added fuels and chemicals through catalytic processes (such as photocatalysis and electrocatalysis) is promising to achieve the goal of carbon neutrality. Owing to the large number of highly accessible active sites, highly porous structure, and charge separation/transfer ability, as well as excellent stability against chemical and electrochemical corrosion, zeolite imidazolate framework (ZIF)-based catalysts have attracted significant attention. Strategic construction of heterojunctions, and alteration of the metal node and the organic ligand of the ZIFs effectively regulate the binding energy of intermediates and the reaction energy barriers that allow tunable catalytic activity and selectivity of a product during reaction. Focusing on the currently existing critical issues of insufficient kinetics for electron transport and selective generation of ideal products, this review starts from the characteristics and physiochemical advantages of ZIFs in catalytic applications, then introduces promising regulatory approaches for advancing the kinetic process in emerging CO2 reduction, water splitting and N2 reduction applications, before proposing perspective modification directions.

Pivotal Impact Factors in Photocatalytic Reduction of CO2 to Value-Added C1 and C2 Products

Over the past decades, CO2 greenhouse emission has been considerably increased, causing global warming and climate change. Indeed, converting CO2 into valuable chemicals and fuels is a desired option to resolve issues caused by its continuous emission into the atmosphere. Nevertheless, CO2 conversion has been hampered by the ultrahigh dissociation energy of C=O bonds, which makes it thermodynamically and kinetically challenging. From this prospect, photocatalytic approaches appear promising for CO2 reduction in terms of their efficiency compared to other traditional technologies. Thus, many efforts have been made in the designing of photocatalysts with asymmetric sites and oxygen vacancies, which can break the charge distribution balance of CO2 molecule, reduce hydrogenation energy barrier and accelerate CO2 conversion into chemicals and fuels. Here, we review the recent advances in CO2 hydrogenation to C1 and C2 products utilizing photocatalysis processes. We also pin down the key factors or parameters influencing the generation of C2 products during CO2 hydrogenation. In addition, the current status of CO2 reduction is summarized, projecting the future direction for CO2 conversion by photocatalysis processes.

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.

Screening of Transition Metal Supported on Black Phosphorus as Electrocatalysts for CO2 Reduction

The electrocatalytic CO2 reduction (CO2RR) is an effective and economical strategy to eliminate CO2 through conversion into value-added chemicals and fuels. However, exploring and screening suitable 2D material-based single-atom catalysts (SACs) for CO2 reduction are still a great challenge. In this study, 27 (3d, 4d, and 5d, except Tc and Hg) transition metal (TM) atom-doped black phosphorus (TM@BP) electrocatalysts were systematically investigated for CO2RR by density functional theory calculations. According to the stability of SACs and their effectiveness in activating the CO2 molecule, three promising catalysts, Zr@BP, Nb@BP, and Ru@BP, were successfully screened out, exhibiting outstanding catalytic activity for the production of carbon monoxide (CO), methyl alcohol (CH3OH), and methane (CH4) with limiting potentials of -0.79, -0.49, and -0.60 V, respectively. A catalytic relationship between the d-band centers of SACs and the limiting potential of CO2RR was used to estimate the catalytic activity of catalysts. Furthermore, Nb@BP has high selectivity for CO2RR to CH3OH compared to H2 formation, while the hydrogen evolution reaction significantly impacts the synthesis of CO and CH4 on Zr@BP and Ru@BP. Nitrogen atom doping in BP is beneficial for enhancing the selectivity of CO2RR, but it is detrimental to the activity of CO2RR. This study offers theoretical guidance for synthesizing highly efficient CO2RR electrocatalysts and further enhances structural modulation methods for layered 2D materials.

Constructing Dual Cocatalysts of Ni2P-NiS-Decorated TiO2 for Boosting Photocatalytic H2 Evolution

The loading of cocatalysts is an effective approach to optimize the separation of carriers during photocatalytic processes. Among them, cocatalysts often work independently during the photocatalytic production of H2. However, an investigation of the synergistic effect of dual cocatalysts is beneficial for further promoting photocatalytic H2 production activity. In this work, dual cocatalyst Ni2P-NiS-modified TiO2 nanosheets were fabricated through a solvent evaporation method. The investigation indicates that Ni2P-NiS can widen the light absorption range and reduce the contact angle between TiO2 and water from 26.71 to 8.27°, which facilitates the adsorption of water molecules. Besides, the introduction of Ni2P-NiS can decrease the overpotential of H2 evolution and induce more electrochemically active surface area. The photocatalytic tests show that the H2 production rate of 15% Ni2P-NiS/TiO2 can reach up to 4891.6 μmol·g-1·h-1, which is 30.2, 4.4, and 1.3 times than pure TiO2 (161.8 μmol·g-1·h-1), 15% Ni2P/TiO2 (1112.1 μmol·g-1·h-1), and 15% NiS/TiO2 (3678.1 μmol·g-1·h-1), respectively. The enhancement mechanism of photocatalytic H2 production is attributed to the Schottky barrier effect between Ni2P-NiS nanoparticles and TiO2 nanosheets, which can enormously promote the interface charge separation and transfer, and enhance the kinetics of H2 production. This work provides a potential strategy for enhancement H2 production using appropriate dual cocatalyst-decorated semiconductor materials.

Metal to non-metal sites of metallic sulfides switching products from CO to CH4 for photocatalytic CO2 reduction

The active center for the adsorption and activation of carbon dioxide plays a vital role in the conversion and product selectivity of photocatalytic CO2 reduction. Here, we find multiple metal sulfides CuInSnS4 octahedral nanocrystal with exposed (1 1 1) plane for the selectively photocatalytic CO2 reduction to methane. Still, the product is switched to carbon monoxide on the corresponding individual metal sulfides In2S3, SnS2, and Cu2S. Unlike the common metal or defects as active sites, the non-metal sulfur atom in CuInSnS4 is revealed to be the adsorption center for responding to the selectivity of CH4 products. The carbon atom of CO2 adsorbed on the electron-poor sulfur atom of CuInSnS4 is favorable for stabilizing the intermediates and thus promotes the conversion of CO2 to CH4. Both the activity and selectivity of CH4 products over the pristine CuInSnS4 nanocrystal can be further improved by the modification of with various co-catalysts to enhance the separation of the photogenerated charge carrier. This work provides a non-metal active site to determine the conversion and selectivity of photocatalytic CO2 reduction.