Surface Electron Localization in Cu-MOF-Bonded Double-Heterojunction Cu2O Induces Highly Efficient Photocatalytic CO2 Reduction

Zinc-doped C4N3/BiOBr S-scheme heterostructured hollow spheres for efficient photocatalytic degradation of tetracycline

Photocatalytic degradation of organic pollutants in water is of great significance to the sustainable development of the environment, but encounters limited efficiency when a single compound is used. Thus, there have been enormous efforts to find novel photocatalytic heterostructured composites with high performance. In this work, a novel S-scheme heterostructure is constructed with BiOBr and Zn2+ doped C4N3 (Zn-C4N3) by a solvothermal method for efficient photodegradation of tetracycline (TC), a residual antibiotic difficult to be removed from the aquatic environment. Thanks to Zn2+-doping induced improvement in chemical affinity between Zn-C4N3 and BiOBr, well-formed Zn-C4N3/BiOBr heterostructured hollow spheres are formed. This structure can efficiently suppress fast recombination of photogenerated electron-hole pairs to enhance the photocatalytic activity of BiOBr dramatically. At a room temperature of 25 °C and neutral pH 7, the catalyst can degrade a significant portion of TC pollutants within 30 min under visible light. Also, the Zn-C4N3/BiOBr heterostructure displays good stability after recycling experiments. Free radical capture experiments and ESR tests show that ˙O2- is the main active substance for photocatalytic degradation of TC. This study provides new insights for constructing heterostructures with an intimate interface between the two phases for photocatalytic applications.

Coupling Cu Coordination Polymers with CdS Forming an S-Scheme Heterojunction for Rapid Charge Separation and High Photocatalytic Activity

Energy and the environment are significant impacting factors for the future development of humankind. In order to improve the corrosion resistance of CdS and decrease the recombination of photogenerated carriers, a novel Cu-CPs@CdS heterojunction with high efficiency mesopores was constructed by a simple hydrothermal method. The effective interfacial contact formation between nano-CdS and Cu-CPs promotes the transfer of photogenerated carriers while exhibiting a high spatial separation rate of charges. The photocatalytic performance of the heterojunction was evaluated by the photocatalytic degradation of organic pollutants and photocatalytic hydrogen generation. The photocatalytic degradation of ciprofloxacin (CIP) could reach 90.34%, and the hydrogen generation was high as 9227.82 μmol·g-1 under simulated sunlight irradiation. The boosted photocatalytic activity of Cu-CPs@CdS results from (i) the formation of coordination bonds, which not only enhanced the stability of heterojunctions but also provided a path for photogenerated carrier migration, (ii) integrating Cu-CPs, which provided more active sites, and (iii) the matched energy band structure between CdS and Cu-CPs that promoted speedy S-scheme interfacial charge-transfer pathways, culminating in efficient photogenerated charge separation and transfer. This research offered a fresh tactic to restrict photocorrosion and enhance the production of photocatalytic H2 over CdS-based catalysts.

Surface CN bonds mediate photocatalytic CO2 reduction into efficient CH4 production in TiO2-decorated g-C3N4 nanosheets

Graphitic carbon nitride (g-C3N4, CN) has garnered considerable attention in the field of photocatalysis due to its favorable band gap and high specific surface area. However, its primary practical limitation lies in the strong radiative recombination of lone pair (LP) electronic states, leading to limited efficiency in separating photogenerated carriers and subsequently diminishing photocatalytic performance. In this study, we devised and synthesized a heterojunction photocatalytic system comprising TiO2 nanosheets supported on modified g-C3N4 (MCN), designated as MCN/TiO2. The presence of CN functional groups on the tri-s-triazine nitrogen captures photogenerated electrons by modifying LP electronic states, resulting in a reduction in the fluorescence emission intensity of g-C3N4. Simultaneously, it forms chemical bonds with the supported TiO2 nanosheets, creating an efficient electron transfer pathway for the accumulation of photogenerated electrons at the active Ti sites. Experimentally, the MCN/TiO2 photocatalytic system exhibited optimal performance in CO2 reduction. The CH4 production rate reached 26.59 μmol g-1 h-1, surpassing that of TiO2 and CN/TiO2 by approximately 8 and 3 times, respectively. Furthermore, this photocatalytic system demonstrated exceptional photostability over five cycles, each lasting 4 h. This research offers a valuable approach for the efficient separation and transfer of photogenerated carriers in composite materials based on g-C3N4.

An Overview of Metal-organic Framework Based Electrocatalysts: Design and Synthesis for Electrochemical Hydrogen Evolution, Oxygen Evolution, and Carbon Dioxide Reduction Reactions

Due to the increasing global energy demands, scarce fossil fuel supplies, and environmental issues, the pursued goals of energy technologies are being sustainable, more efficient, accessible, and produce near zero greenhouse gas emissions. Electrochemical water splitting is considered as a highly viable and eco-friendly energy technology. Further, electrochemical carbon dioxide (CO2 ) reduction reaction (CO2 RR) is a cleaner strategy for CO2 utilization and conversion to stable energy (fuels). One of the critical issues in these cleaner technologies is the development of efficient and economical electrocatalyst. Among various materials, metal-organic frameworks (MOFs) are becoming increasingly popular because of their structural tunability, such as pre- and post- synthetic modifications, flexibility in ligand design and its functional groups, and incorporation of different metal nodes, that allows for the design of suitable MOFs with desired quality required for each process. In this review, the design of MOF was discussed for specific process together with different synthetic methods and their effects on the MOF properties. The MOFs as electrocatalysts were highlighted with their performances from the aspects of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical CO2 RR. Finally, the challenges and opportunities in this field are discussed.

Designing Surface-Defect Engineering to Enhance the Solar-Driven Conversion of CO2 to C2 Products over Zn3In2S6/ZnS

The manipulation of electronic structure and prevention of photogenerated carriers from being quenched in bulk defects during the photocatalytic CO2 reduction reaction (CRR) have been effectively demonstrated through surface vacancy and defect engineering. In this work, the electronic structure on the surface of Zn3In2S6/ZnS (ZIS/ZnS) is significantly modified by the introduction and control of the surface S vacancies (SV) through Ar-plasma treatment. EPR and XPS analyses confirmed that SV was exclusively present on the ZIS/ZnS surface. The resulting ZIS/ZnS heterojunction photocatalysts demonstrate an impressive 46.6% selectivity toward C2 products even in the absence of cocatalysts. The mechanism of photocatalytic CRR is further elucidated through in situ analysis. Theoretical calculations demonstrate that the presence of In and Zn atoms adjacent to SV significantly enhances the adsorption of CO2 and facilitates C-C coupling.