Recent advances on bismuth oxyhalides for photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into fuels such as CO, CH4, and CH3OH, is a promising approach for achieving carbon neutrality. Bismuth oxyhalides (BiOX, where X = Cl, Br, and I) are appropriate photocatalysts for this purpose due to the merits of visible-light-active, efficient charge separation, and easy-to-modify crystal structure and surface properties. For practical applications, multiple strategies have been proposed to develop high-efficiency BiOX-based photocatalysts. This review summarizes the development of different approaches to prepare BiOX-based photocatalysts for efficient CO2 reduction. In the review, the fundamentals of photocatalytic CO2 reduction are introduced. Then, several widely used modification methods for BiOX photocatalysts are systematacially discussed, including heterojunction construction, introducing oxygen vacancies (OVs), Bi-enrichment, heteroatom-doping, and morphology design. Finally, the challenges and prospects in the design of future BiOX-based photocatalysis for efficient CO2 reduction are examined.

Micro-Spherical BiOI Photocatalysts for Efficient Degradation of Residual Xanthate and Gaseous Nitric Oxide

BiOI microspheres were synthesized using the solvothermal method for the degradation of residual xanthate and gaseous nitric oxide (NO) under visible light irradiation. The as-prepared BiOI nanomaterials were then characterized using various technologies, including XRD, FE-SEM, TEM, UV-Vis DRS, and XPS. The photodegradation results show that the removal efficiency of isobutyl sodium xanthate can reach 98.08% at an initial xanthate concentration of 120 mg/L; that of NO is as high as 96.36% at an inlet NO concentration of 11 ppm. Moreover, the effects of operational parameters such as catalyst dosage, initial xanthate concentration, and pH value of wastewater on the removal of xanthate were investigated. The results of scavenging tests and full-spectrum scanning indicate that ·O2- radicals are the main active species in xanthate degradation, and peroxide xanthate is an intermediate. The reusability of BiOI was explored through cyclic experiments. Furthermore, the reaction path and the mechanism of NO removal using BiOI were analyzed, and the main active species was also ·O2-. It is concluded that BiOI photocatalysts have high potential for wastewater treatment and waste gas clean-up in the mineral industry.

Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation

Traditional NO_x treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NO_x at low concentration, especially at ppb levels. Fortunately, low concentration NO_x can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NO_x oxidation. This review focused on typical layered Bi-based photocatalysts (Bi₂WO₆, Bi₂O₂CO₃, BiOY (YCl, Br, and I), BiOIO₃, and BiOCOOH) with the structure of [Bi₂O₂]²⁺ layer for photocatalytic NO_x oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NO_x was proposed. In addition, the non-NO₂ selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NO_x oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO₂ selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NO_x.

Non-Noble Plasmonic Metal-Based Photocatalysts

Solar-to-chemical energy conversion via heterogeneous photocatalysis is one of the sustainable approaches to tackle the growing environmental and energy challenges. Among various promising photocatalytic materials, plasmonic-driven photocatalysts feature prominent solar-driven surface plasmon resonance (SPR). Non-noble plasmonic metals (NNPMs)-based photocatalysts have been identified as a unique alternative to noble metal-based ones due to their advantages like earth-abundance, cost-effectiveness, and large-scale application capability. This review comprehensively summarizes the most recent advances in the synthesis, characterization, and properties of NNPMs-based photocatalysts. After introducing the fundamental principles of SPR, the attributes and functionalities of NNPMs in governing surface/interfacial photocatalytic processes are presented. Next, the utilization of NNPMs-based photocatalytic materials for the removal of pollutants, water splitting, CO₂ reduction, and organic transformations is discussed. The review concludes with current challenges and perspectives in advancing the NNPMs-based photocatalysts, which are timely and important to plasmon-based photocatalysis, a truly interdisciplinary field across materials science, chemistry, and physics.

Enhancing Green Product Generation of Photocatalytic NO Oxidation: A Case of WO3 Nanoplate/g-C3N4 S-Scheme Heterojunction

Nitric oxide (NO) removal by photocatalytic oxidation over g-C₃N₄ has achieved more efficient results. However, there is a concern about the high NO-to-NO₂ conversion yield of products, which is not suitable for the photocatalytic NO reaction. In this study, we modify g-C₃N₄ by WO₃ nanoplates for the first time for photocatalytic NO oxidation over a WO₃/g-C₃N₄ composite to enhance the green product selectivity under atmospheric conditions. The results indicate that the photocatalytic efficiency for NO removal by the WO₃/g-C₃N₄ composite is drastically improved and achieves 52.5%, which is approximately 2.1 times higher than that of pure g-C₃N₄. Significantly, the green product (NO₃^-) selectivity of the WO₃/g-C₃N₄ composite is 8.7 times higher than that of pure g-C₃N₄, and the selectivity remained high even after five cycles of photocatalytic tests. We also conclude that the enhanced green product selectivity of photocatalytic NO oxidation by the WO₃/g-C₃N₄ composite is due to the separation and acceleration of the photogenerated charges of the WO₃/g-C₃N₄ S-scheme heterojunction.

ZIF-67-Derived 3D Hollow Mesoporous Crystalline Co3 O4 Wrapped by 2D g-C3 N4 Nanosheets for Photocatalytic Removal of Nitric Oxide

ZIF-67-derived 3D hollow mesoporous crystalline Co₃ O₄ wrapped by 2D graphitic carbon nitride (g-C₃ N₄ ) nanosheets are prepared by low temperature annealing, and are used for the photocatalytic oxidation of nitric oxide (NO) at a concentration of 600 ppb. The p-n heterojunction between Co₃ O₄ and g-C₃ N₄ forms a spatial conductive network frame and results in a broad visible light response range. The hollow mesoporous structure of Co₃ O₄ contributes to the circulation and adsorption of NO, and the large specific surface area exposes abundant active sites for the reaction of active species. A maximum NO degradation efficiency of 57% is achieved by adjusting the mass of the Co₃ O₄ precursor. Cycling tests and X-ray diffraction indicate the high stability and recyclability of the composite, making it promising in environmental purification applications.