Charge Transfer Of Zr-MOFs Based Photocatalysts For Photocatalytic Water Splitting Hydrogen Evolution

Metal-organic framework materials（MOFs）have the characteristics of porosity,large specific surface area,unsaturated metal sites,adjustable structure and function,and are also known as“future low band-gap semiconductor materials”,which have fulled lots of studies in the field of energy conversion and environment.However,their relative poor light-harvesting capability and high recombination probability of photo-generated electron-hole pairs limit the efficient application,espacially in photocatalytic water splitting hydrogen evolution.Therefore,the design and construction of novel materials with fast separation of photo-generated electron-hole pairs and accelerated charge carrier transfer is vital for the development of efficient photocatalysts.Therefore,porous Zr-based MOFs（UiO-66-NH₂）with excellent water stability are chosen as the substrat to design UiO-66-NH₂ based photocatalysts with effective charge separation and transfer efficiency.The structure,morphology and photocatalytic performance are systematically characterized,combining with the photoelectrochemical performance test,transient/steady state fluorescence spectra,electron paramagnetic resonance,first-principle calculation analysis,the separation and transfer of photo-generated electrons and holes pairs mechanism are investigated in detail.Relevant research results are as following:（1）PW₁₂@UiO-NH₂ was prepared by incorporating PW₁₂ units inside porous UiO-66-NH2 framework through one-step solvothermal method,aiming to construct POM@MOFs materials by utilizing tuneable redox properties and reversible multi-electrons transformation characteristic of polyoxometalates（POMs）,which can effectively impede the recombination of photo-generated electron-hole pairs of pure MOFs.The results showed that PW₁₂@UiO-NH₂ presented superior photocatalytic HER performance and degradation of RhB than the pristine UiO-66-NH₂.Systematical characterizations including photoelectrochemical tests and transient/steady-state fluorescence spectrum indicated that PW12 can be served as electron acceptor to enable photo-generated electrons to be effectively transferred from UiO-66-NH₂ to PW₁₂,thus improving the separation and transfer efficiency of charge carriers and optimizing photocatalytic HER performance.（2）TU series with Schottky barrier effect heterostructure were prepared by integrated Ti₃C₂ nanosheets into UiO-66-NH₂ through one-step hydrothermal method,which can profit from the excellent conductivity and hydrophilicity of 2D MXenes and construct the Schottky junction at the metal/catalyst interface,so as to improve the separation and transfer efficiency of photo-generated electron-hole pairs.First principles calculation results showed that Ti₃C₂ nanosheets（O-TC）possessed favorable Fermi level and relatively low Gibbs free energy(|ΔG_H*|=0.08≈0).The constructed Schottky barrier at the interface between Ti₃C₂ and UiO-66-NH₂ may not only facilitate the spatial separation and transfer of charge carriers but also accumulate the photo-generated electrons on the surface of Ti3C2 nanosheets,leading to the optimization the photocatalytic HER performance.（3）Ti₃C₂/TiO₂/UiO-66-NH₂ hybrid was rationally designed with multiple charge transfer pathways by introducing annealed Ti₃C₂T_x MXenes over UiO-66-NH₂ through a facile hydrothermal process.It demonstrated the formation of multi-interfaces in Ti₃C₂/TiO₂/UiO-66-NH₂,including Ti₃C₂/TiO₂/UiO-66-NH₂,Ti₃C₂/TiO₂ and Ti₃C₂/UiO-66-NH₂ interfaces was benefit for the construction of multiple pathways at the interfaces with Schottky junctions to accelerate the separation and transfer of charge carriers and endowed the accumulation of photo-generated electrons on the surface of Ti₃C₂.It optimized the charge carriers transfer and effectively improving photocatalytic HER performance.