Efficient photocatalytic reduction of CO2 by a rhenium-doped TiO2-x/SnO2 inverse opal S-scheme heterostructure assisted by the slow-phonon effect

Construction of Inverse-Opal ZnIn2S4 with Well-Defined 3D Porous Structure for Enhancing Photocatalytic H2 Production

The conversion of solar energy into hydrogen using photocatalysts is a pivotal solution to the ongoing energy and environmental challenges. In this study, inverse opal (IO) ZnIn2S4 (ZIS) with varying pore sizes is synthesized for the first time via a template method. The experimental results indicate that the constructed inverse opal ZnIn2S4 has a unique photonic bandgap, and its slow photon effect can enhance the interaction between light and matter, thereby improving the efficiency of light utilization. ZnIn2S4 with voids of 200 nm (ZIS-200) achieved the highest hydrogen production rate of 14.32 μ mol h-1. The normalized rate with a specific surface area is five times higher than that of the broken structures (B-ZIS), as the red edge of ZIS-200 is coupled with the intrinsic absorption edge of the ZIS. This study not only developed an approach for constructing inverse opal multi-metallic sulfides, but also provides a new strategy for enriching efficient ZnIn2S4-based photocatalysts for hydrogen evolution from water.

Build-in electric field in CuWO4/covalent organic frameworks S-scheme photocatalysts steer boosting charge transfer for photocatalytic CO2 reduction

Covalent organic frameworks (COFs) are crystalline porous materials with enormous potential for realizing solar-driven CO₂-to-fuel conversion, yet the sluggish transfer/separation of photoinduced electrons and holes remains a compelling challenge. Herein, a step (S)-scheme heterojunction photocatalyst (CuWO₄-COF) was rationally fabricated by a thermal annealing method for boosting CO₂ conversion to CO. The optimal CuWO₄/COF composite sample, integrating 10 wt% CuWO₄ with an olefin (C═C) linked COF (TTCOF), achieved a remarkable gas-solid phase CO yield as high as 7.17 ± 0.35 μmol g^-1h^-1 under visible light irradiation, which was significantly higher than the pure COF (1.6 ± 0.29 μmol g^-1h^-1). The enhanced CO₂ conversion rate could be attributable to the interface engineering effect and the formation of internal electric field (IEF) directing from TTCOF to CuWO₄ according to the theoretical calculation and experimental results, which also proves the electrons transfer from TTCOF to CuWO₄ upon hybridization. In addition, driven by the IEF, the photoinduced electrons can be steered from CuWO₄ to TTCOF under visible light irradiation as well-elucidated by in-situ irradiated X-ray photoelectron spectroscopy, verifying the S-scheme charge transfer pathway over CuWO₄/COF composite heterojunctions, which greatly foster the photoreduction activity of CO₂. The preparation technique of the S-scheme heterojunction photocatalyst in this study provides a paradigmatic protocol for photocatalytic solar fuel generation.

A review on TiO2-x-based materials for photocatalytic CO2 reduction

Photocatalytic CO₂ reduction technology has a broad potential for dealing with the issues of energy shortage and global warming. As a widely studied material used in the photocatalytic process, titanium dioxide (TiO₂) has been continuously modified and tailored for more desirable application. Recently, the defective/reduced titanium dioxide (TiO_2-x) catalyst has attracted broad attention due to its excellent photocatalytic performance for CO₂ reduction. In this perspective review, we comprehensively present the recent progress in TiO_2-x-based materials for photocatalytic CO₂ reduction. In detail, the review starts with the fundamentals of CO₂ photocatalytic reduction. Then, the synthesis of a defective TiO₂ structure is introduced for the regulation of its photocatalytic performance, especially its optical properties and dissociative adsorption properties. In addition, the current application of TiO_2-x-based photocatalysts for CO₂ reduction is also highlighted, such as metal-TiO_2-x, oxide-TiO_2-x and TiO_2-x-carbon-based photocatalysts. Finally, the existing challenges and possible scope of photocatalytic CO₂ reduction over TiO_2-x-based materials are discussed. We hope that this review can provide an effective reference for the development of more efficient and reasonable photocatalysts based on TiO_2-x.

Facile Preparation of Hydrogen-Bonded Organic Framework/Cu2O Heterostructure Films via Electrophoretic Deposition for Efficient CO2 Photoreduction

Photocatalytic CO₂ reduction is one of the most cost-effective and environmentally friendly techniques of converting CO₂ into high-value compounds and/or fuels. However, the performance of most current photocatalytic CO₂ reduction catalysts is less than satisfactory for practical applications. Here, we synthesized a heterogeneous structure by integrating Cu₂O and a porphyrin hydrogen-bonded organic framework (PFC-45), which was then fabricated into a thin-film catalyst on carbolic paper (CP) using a facile electrophoretic deposition technology. With improved electron-hole separation efficiency and visible-light-harvesting ability, this film (PFC-45/Cu₂O@CP) significantly enhanced CO₂-to-CO photoreduction, exceeding 2.4 and 3.2 times that of PFC-45@CP and PFC-45/Cu₂O particles, respectively. Remarkably, PFC-45/Cu₂O@CP also exhibited high selectivity (99%) and outstanding activity (11.81 μmol g^-1 h^-1) for photocatalytic CO₂ reduction in pure water without any sacrificial agent. This work demonstrates a new strategy to design photocatalysts for efficient CO₂ reduction.

Ag Decoration and SnO2 Coupling Modified Anatase/Rutile Mixed Crystal TiO2 Composite Photocatalyst for Enhancement of Photocatalytic Degradation towards Tetracycline Hydrochloride

The anatase/rutile mixed crystal TiO₂ was prepared and modified with Ag decoration and SnO₂ coupling to construct a Ag@SnO₂/anatase/rutile composite photocatalytic material. The crystal structure, morphology, element valence, optical properties and surface area were characterized, and the effects of Ag decoration and SnO₂ coupling on the structure and photocatalytic properties of TiO₂ were studied. Ag decoration and SnO₂ coupling are beneficial to reduce the recombination of photogenerated electrons and holes. When the two modification are combined, a synergistic effect is produced in suppressing the photogenerated charge recombination, making Ag@SnO₂/TiO₂ exhibits the highest quantum utilization. After 30 min of illumination, the degradation degree of tetracycline hydrochloride (TC) by pure TiO₂ increased from 63.3% to 83.1% with Ag@SnO₂/TiO₂.

Accelerated charge transfer in well-designed S-scheme Fe@TiO2/Boron carbon nitride heterostructures for high performance tetracycline removal and selective photo-reduction of CO2 greenhouse gas into CH4 fuel

Designing and fabrication of smart hybrid multifunctional materials for energy/fuel production and environmental detoxification is indeed of great significance for sustainable development. Herein, we synthesized a new well-structured S-scheme heterostructure Fe@TiO₂/Boron Carbon nitride (FT/BCN) with high performance tetracycline degradation and selective CO₂ photo-reduction to CH₄. Under visible light irradiation, 96.3% tetracycline was degraded in 60 min using best performing FT30/BCN sample with a high 83.2% total organic carbon removal in 2 h. The tetracycline degradation rate for FT30/BCN composite catalyst was ∼7 times than bare boron carbon nitride (BCN). The impact of reaction parameters as pH, presence of interfering electrolytes, light source and water matrix was also investigated. The FT30/BCN photocatalyst shows dramatic improvement in CO₂ photoreduction as exhibited in 24.7 μmol g^-1 h^-1 CH₄ and 2.4 μmol g^-1 h^-1 CO evolutions with optimal 91.1% CH₄ selectivity. Pure BCN shows a poor 39.1% selectivity. Further, effect of alkali activation, CO₂/H₂O feed ratio, reducing agent and light source onto CH₄ production and selectivity was also investigated. The CH₄ evolution and selectivity was improved because of enhanced visible light absorption, high adsorption potential, charge carrier separation and high reducing power of photogenerated electrons induced by an effective S-scheme heterojunction between Fe@TiO₂ and boron carbon nitride. An S-scheme (step-scheme) charge transfer mechanism is here operative both during tetracycline removal and CO₂ reduction. The drug degradation route and photocatalytic mechanism for antibiotic removal and CO₂ reduction was also predicted.