Direct Z-Scheme Heterojunction of Semicoherent FAPbBr3/Bi2WO6 Interface for Photoredox Reaction with Large Driving Force

Integration of zirconium-based metal-organic framework with CdS for enhanced photocatalytic conversion of CO2 to CO

It is a promising strategy to prepare composite photocatalysts based on MOFs and semiconductors for enhancing photocatalytic reduction of carbon dioxide (CO₂). A family of binary composite photocatalysts (CdS@UiO-66-NH₂) with different CdS contents have been designed and synthesized, which have been explored for photocatalytic reduction of CO₂. CdS@UiO-66-NH₂ can efficiently convert CO₂ into CO under visible light irradiation via the solid-gas mode in the absence of sacrificial agents and photosensitizers. The generation rate of CO can reach up to 280.5 μmol g^-1 h^-1, which is 2.13-fold and 2.9-fold improvements over the pristine CdS and UiO-66-NH₂, respectively, and the selectivity for CO is very high. Furthermore, this kind of photocatalysts can still maintain great photocatalytic activity in CO₂/N₂ mixed atmosphere with different CO₂ concentrations. The outstanding performances of CdS@UiO-66-NH₂ may be attributed to the existence of the direct Z-scheme heterojunction, which possesses the enhanced separation and migration of photo-generated charge carriers between UiO-66-NH₂ and CdS, available specific surface areas and improved visible light absorption ability as well as abundant reaction active sites. This case reveals that MOF-based composite photocatalysts exhibit promising potential applications in the field of CO₂ conversion.

Photocatalytic Degradation of Tobacco Tar Using CsPbBr3 Quantum Dots Modified Bi2WO6 Composite Photocatalyst

Polycyclic aromatic hydrocarbons (PAHs) in tobacco tar are regarded as a significant threat to human health. PAHs are formed due to the incomplete combustion of organics in tobacco and cigarette paper. Herein, for the first time, we extended the application of CsPbBr3 quantum dots (CsPbBr3) to the photocatalytic degradation of tobacco tar, which was collected from used cigarette filters. To optimize the photoactivity, CsPbBr3 was coupled with Bi2WO6 for the construction of a type-II photocatalyst. The photocatalytic performance of the CsPbBr3/Bi2WO6 composite was evaluated by the degradation rate of PAHs from tobacco tar under simulated solar irradiation. The results revealed that CsPbBr3/Bi2WO6 possesses a large specific surface area, outstanding absorption ability, good light absorption and rapid charge separation. As a result, in addition to good stability, the composite photocatalyst performed remarkably well in degrading PAHs (over 96% were removed in 50 mins of irradiation by AM 1.5 G). This study sheds light on promising novel applications of halide perovskite.

Metal Halide Perovskites for Solar Fuel Production and Photoreactions

Photocatalysis is an easily configurable and cost-effective technology for the conversion of solar energy into chemical energy. Recently, increasing attention has been given to metal halide perovskite (MHP) photocatalysts because of the development of stabilization strategies for MHPs under reaction conditions. From this perspective, we first describe several substantial breakthroughs in the photocatalytic application of MHPs. Performance trends in the solar fuel production applications of MHPs, including photocatalytic H₂ generation and photocatalytic CO₂ reduction reactions, are then described. Recent developments to extend the use of MHPs to various photocatalytic organic transformations are also highlighted. Finally, we propose several scientific challenges for the practical implications of MHPs for solar fuel production and various photoreactions.

Ordered Macroporous Carbonous Frameworks Implanted with CdS Quantum Dots for Efficient Photocatalytic CO2 Reduction

Solar-driven photocatalytic CO₂ reduction is regarded as a promising way to simultaneously mitigate the energy crisis and CO₂ pollution. However, achieving high efficiency of photocatalytic CO₂ reduction, especially without the assistance of sacrifice reagents or extra alkaline additives, remains a critical issue. Herein, a photocatalyst of 3D ordered macroporous N-doped carbon (NC) supported CdS quantum dots (3DOM CdSQD/NC) is successfully fabricated toward photocatalytic CO₂ reduction via an in situ transformation strategy. Additionally, an amines oxidation reaction is introduced to replace the H₂ O oxidation process to further boost the photocatalytic CO₂ reduction efficiency. Impressively, 3DOM CdSQD/NC exhibits superior activity and selectivity in photocatalytic CO₂ reduction coupled with amines oxidation, affording a CO production rate as high as 5210 µmol g^-1 h^-1 in the absence of any sacrificial agents and alkaline additives. Moreover, 3DOM CdSQD/NC achieves an apparent quantum efficiency of 2.9% at 450 nm. Mechanism studies indicate that the 3D ordered macropores in the NC matrix are beneficial to the transfer of photogenerated carriers. Furthermore, the highly dispersed CdS QDs on the NC skeleton are able to significantly promote the adsorption of both CO₂ and amine molecules and depress the CO₂ activation energy barriers by stabilizing the *COOH intermediate, directly contributing to the high activity.

Two-dimensional halide perovskites: synthesis, optoelectronic properties, stability, and applications

Halide perovskites are promising materials for light-emitting and light-harvesting applications. In this context, two-dimensional perovskites such as nanoplatelets or Ruddlesden-Popper and Dion-Jacobson layered structures are important because of their structural flexibility, electronic confinement, and better stability. This review article brings forth an extensive overview of the recent developments of two-dimensional halide perovskites both in the colloidal and non-colloidal forms. We outline the strategy to synthesize and control the shape and discuss different crystalline phases and optoelectronic properties. We review the applications of two-dimensional perovskites in solar cells, light-emitting diodes, lasers, photodetectors, and photocatalysis. Besides, we also emphasize the moisture, thermal, and photostability of these materials in comparison to their three-dimensional analogs.

Geometric, electronic, and optical properties of MoS2/WSSe van der Waals heterojunctions: a first-principles study

Van der Waals (vdW) heterojunctions constructed by vertical stacking two-dimensional transition metal dichalcogenides hold exciting promise in realizing future atomically thin electronic and optoelectronic devices. Recently, a Janus WSSe structure has been successfully synthesized by using chemical vapor deposition, selective epitaxy atomic replacement, and pulsed laser deposition methods. Herein, based on first-principles calculations, we introduce the structures and performances of MoS₂/WSSe vdW heterojunctions with different interfaces and stacking modes. The vdW heterojunctions possess indirect band gaps for S-S interfaces, while direct band gaps for Se-S interfaces. Besides, the potential drop indicates an efficient separation of photogenerated charges. Interestingly, the opposite built-in electric fields formed in the vdW heterojunctions with a S-S interface and a Se-S interface suggest different charge transfer paths, which would motivate further theoretical and experimental investigations on charge transfer dynamics. Moreover, the electronic property is adjustable by applying external in-plane strains, accomplishing with indirect to direct bandgap transition and semiconductor to metal transition. The findings are helpful for the design of multi-functional high-performance electronic and optoelectronic devices based on the MoS₂/WSSe vdW heterojunctions.

Prospects of Z-Scheme Photocatalytic Systems Based on Metal Halide Perovskites

Considering the attractive optoelectronic properties of metal halide perovskites (MHPs), their introduction to the field of photocatalysis was only a matter of time. Thus far, MHPs have been explored for the photocatalytic generation of hydrogen, carbon dioxide reduction, organic synthesis, and pollutant degradation applications. Of growing research interest and possible applied significance are the currently emerging developments of MHP-based Z-scheme heterostructures, which can potentially enable efficient photocatalysis of highly energy-demanding redox processes. In this Perspective, we discuss the advantages and limitations of MHPs compared to traditional semiconductor materials for applications as photocatalysts and describe emerging examples in the construction of MHP-based Z-scheme systems. We discuss the principles and material properties that are required for the development of such Z-scheme heterostructure photocatalysts and consider the ongoing challenges and opportunities in this emerging field.

CdS quantum dots-decorated InOOH: Facile synthesis and excellent photocatalytic activity under visible light

For the first time, CdS quantum dots (QDs)-decorated InOOH (CdS-In for short) was synthesized by a facile photodeposition method. The experiment results showed that CdS-In samples exhibited excellent activity and stability towards photocatalytic reduction of nitro aromatics. The conversion ratio of 4-nitroaniline (4-NA) over CdS-In sample that was prepared with photodeposition time of 120 min (CdS-In-120) reached up to 99.4% under visible light irradiation for 40 min, which was even higher than that achieved over commercial CdS (86.2%). Besides the significant enhancement of visible light absorption, quantum sized CdS were decorated evenly on the surface of InOOH, which was very beneficial for the high activity. Furthermore, the heterogeneous junction formed at the interface of CdS QDs and InOOH can significantly increase the separation efficiency of photogenerated charge carriers. Active species control experiment and electron spin resonance (ESR) technique have proved that photogenerated electrons are the main active species towards photocatalytic reduction of nitro aromatics. It is anticipated that our study would offer meaningful insights for exploring novel InOOH-based visible light photocatalysts towards efficient reduction of nitro aromatics.

Direct Z-Scheme Heterojunction of Ligand-Free FAPbBr3/α-Fe2O3 for Boosting Photocatalysis of CO2 Reduction Coupled with Water Oxidation

Up to now, the majority of the developed photocatalytic CO₂ reduction systems need to use expensive sacrificial reductants as electron source. It is still a huge challenge to drive the photocatalytic CO₂ reduction using water as an electron source. Herein, we report a facile strategy for the construction of direct Z-scheme heterojunction of LF-FAPbBr₃/α-Fe₂O₃, which is manufactured by the in situ and two-step controlled growth of ligand-free formamidinium lead bromide (LF-FAPbBr₃) nanocrystals on the surface of α-Fe₂O₃ nanorods. The matchable energy levels and direct contact between LF-FAPbBr₃ and α-Fe₂O₃ significantly accelerate the interfacial charge transfer, with a charge separation efficiency (η_separation) of 93%, much higher than that of 11% shown by the ligand-capped FAPbBr₃/α-Fe₂O₃ heterojunction. The resulting efficient separation and raised redox ability of photogenerated carriers endow the LF-FAPbBr₃/α-Fe₂O₃ heterojunction with an outstanding photocatalytic performance for CO₂ reduction (to CO and CH₄) coupled with water oxidation (to O₂), achieving a highest electron consumption rate of 175.0 μmol g^-1 h^-1 among the reported metal halide perovskite-based photocatalysts, which are 5 and 11 times higher in comparison with those of sole LF-FAPbBr₃ and ligand-capped FAPbBr₃/α-Fe₂O₃, respectively.

Coupling Strategy for CO2 Valorization Integrated with Organic Synthesis by Heterogeneous Photocatalysis

Photocatalytic reduction of CO₂ to solar fuels and/or fine chemicals is a promising way to increase the energy supply and reduce greenhouse gas emissions. However, the conventional reaction system for CO₂ photoreduction with pure H₂ O or sacrificial agents usually suffers from low catalytic efficiency, poor stability, or cost-ineffective atom economy. A recent surge of developments, in which photocatalytic CO₂ valorization is integrated with selective organic synthesis into one reaction system, indicates an efficient modus operandi that enables sufficient utilization of photogenerated electrons and holes to achieve the goals for sustainable economic and social development. In this Review we discuss current advances in cooperative photoredox reaction systems that integrate CO₂ valorization with organics upgrading based on heterogeneous photocatalysis. The applications and virtues of this strategy and the underlying reaction mechanisms are discussed. The ongoing challenges and prospects in this area are critically discussed.

g-C3N4-Stabilised Organic–Inorganic Halide Perovskites for Efficient Photocatalytic Selective Oxidation of Benzyl Alcohol

The outstanding optoelectronic performance and facile synthetic approach of metal halide perovskites has inspired additional applications well beyond efficient solar cells and light emitting diodes (LEDs). Herein, we present an alternative option available for the optimisation of selective and efficient oxidation of benzylic alcohols through photocatalysis. The materials engineering of hybrids based on formamidine lead bromide (FAPbBr3) and graphic carbon nitride (g-C3N4) is achieved via facile anti-solvent approach. The photocatalytic performance of the hybrids is highly reliant on weight ratio between FAPbBr3 and g-C3N4. Besides, the presence of g-C3N4 dramatically enhances the long-term stability of the hybrids, compared to metal oxides hybrids. Detailed optical, electrical and thermal studies reveal the proposed novel photocatalytic and stability behaviours arising in FAPbBr3 and g-C3N4 hybrid materials.

Glycine-Functionalized CsPbBr3 Nanocrystals for Efficient Visible-Light Photocatalysis of CO2 Reduction

Capping ligands are indispensable for the preparation of metal-halide-perovskite (MHP) nanocrystals (NCs) with good stability; however, the long alkyl-chain capping ligands in conventional MHP NCs will be unfavorable for CO₂ adsorption and hinder the efficient carrier separation on the surface of MHP NCs, leading to inferior catalytic activity in artificial photosynthesis. Herein, CsPbBr₃ nanocrystals with short-chain glycine as ligand are constructed through a facile ligand-exchange strategy. Owing to the reduced hindrance of glycine and the presence of the amine group in glycine, the photogenerated carrier separation and CO₂ uptake capacity are noticeably improved without compromising the stability of the MHP NCs. The CsPbBr₃ nanocrystals with glycine ligands exhibit a significantly increased yield of 27.7 μmol g^-1  h^-1 for photocatalytic CO₂ -to-CO conversion without any organic sacrificial reagents, which is over five times higher than that of control CsPbBr₃ NCs with conventional long alkyl-chain capping ligands.

Photocorrosion at Irradiated Perovskite/Electrolyte Interfaces

Metal-halide perovskites transformed optoelectronics research and development during the past decade. They have also gained a foothold in photocatalytic and photoelectrochemical processes recently, but their sensitivity to the most commonly applied solvents and electrolytes together with their susceptibility to photocorrosion hinders such applications. Understanding the elementary steps of photocorrosion of these materials can aid the endeavor of realizing stable devices. In this Perspective, we discuss both thermodynamic and kinetic aspects of photocorrosion processes occurring at the interface of perovskite photocatalysts and photoelectrodes with different electrolytes. We show how combined in situ and operando electrochemical techniques can reveal the underlying mechanisms. Finally, we also discuss emerging strategies to mitigate photocorrosion (such as surface protection, materials and electrolyte engineering, etc.).

A Microorganism Bred TiO2/Au/TiO2 Heterostructure for Whispering Gallery Mode Resonance Assisted Plasmonic Photocatalysis

The TiO₂/Au nanostructure has been acknowledged as one of the most classic visible-light active photocatalysts due to the surface plasmon resonance (SPR) of Au nanoparticles. In many cases, the SPR effect only features weak visible light absorption in conventional TiO₂/Au nanostructures. Here, we demonstrate a design of TiO₂/Au/TiO₂ with a combination of whispering gallery mode (WGM) resonances and SPR for efficient visible-light-driven photocatalysis. Escherichia coli (E. coli) were used as natural reactants as well as a template to construct an E. coli-like TiO₂/Au/TiO₂ nanostructure. Using numerical simulations, we show that the E. coli-like TiO₂ capsule acts as the WGM resonator to interplay with the SPR effect of the Au NPs on TiO₂ surface, which leads to a significant increase of visible light absorption and the local field enhancement at the Au-TiO₂ interface. Accordingly, with the synergistic effect of WGM and SPR, the E. coli-like TiO₂/Au/TiO₂ nanostructure exhibits enhanced photocatalytic activity in the visible range. Our work reveals a promising bioapproach to a design highly visible light active plasmonic photocatalyst.

Solar-Driven Hydrogen Generation by Metal Halide Perovskites: Materials, Approaches, and Mechanistic View

Solar-driven photocatalysis by metal halide perovskites (MHPs) is emerging as an exciting and promising field to promote several relevant catalytic reactions taking advantage of the superior optical properties of MHPs. Their electronic structure is suitable to run reduction reactions (H₂ generation, CO₂ reduction) and even oxidation reactions, in particualr for perovskites with higher band gap values, and further extends their possible use in the field of photochemical organic syntheses. This Mini-Review focuses on the application of MHPs in the solar-driven hydrogen generation with particular emphasis on the materials' design and mechanistic features involved in the catalytic reactions.