Flame Synthesis And First-principles Study Of CuO_x/TiO₂ Photocatalysts

Ever since the find of the photocatalysis phenomenon in 1972,semiconductor photocatalysis has been perceived as one of the most promising technologies confronting global energy shortage and environmental degradation.To promote the industrialization and large-scale application of photocatalysis technology in the future,systematic knowledge framework in photocatalysts preparation,characterization and theoretical simulation need be further explored.This work adopts an state-of-the-art one-step flame spray pyrolysis method to prepare high-performance CuO_x/TiO₂ photocatalysts and explore its application in water-splitting hydrogen production.X-ray diffraction?XRD?patterns indicate TiO₂ in the as-prepared samples are the mixture of rutile and anatase.X-ray photoluminescence spectra?XPS?and high-resolution transmission electron microscopy?HRTEM?indicate Cu species exist simultaneously in the TiO₂ lattice and the surface,and those surface Cu species are the mixture of CuO and Cu₂O nanoclusters.Photocatalytic hydrogen production tests show that the hydrogen production rate of the best flame-made CuO_x/TiO₂ photocatalysts is²2 times higher than that of commercial P25 TiO₂.To understand the photocatalytic mechanisms of CuO_x/TiO₂ catalysts,this work investigates the properties of Cu ion modified TiO₂ lattice.A 72-atom rutile model is adopted during density functional theory?DFT?calculation as a prototype taking into consideration the effects of intrinsic defects?oxygen vacancies,V_O?.It is found that the modification of either Cu ion or V_O can induce the formation of band-gap energy states.The substitutional dope of Cu ion in TiO₂ lattice can promote the formation of V_O.The relative position of the Cu&V_O pair has significant influence on the electronic properties of the structure.The results suggest that the short distance between the Cu&V_O pair induces deep band-gap energy level,unfavorable to charge carrier separation and utilization in photocatalytic processes,while the long distance induces a shallow band-gap energy level,which is beneficial to high charge separation efficiency.This thesis further investigates the photocatalytic properties of TiO₂ catalysts modified with?CuO?_n clusters?n=1⁶?,also adopting first principle DFT method.We study the energetic evolution of these clusters and determine the most stable atomic configuration using a combined simulated annealing-DFT method.The electronic structures of these clusters are investigated to reveal the quantum size effect of the clusters.By supporting the?CuO?_n clusters on rutile TiO₂?110?facet,we examine changes in the aggregation behaviors of those clusters during the deposition and reveal the charge transportation in?CuO?_n-TiO₂heterojunction.These results suggest the narrowing of band-gap energy with the enlargement of the cluster size and the size-dependent tradeoff between electron transportation efficiency and electron-hole recombination rate.Photocatalytic hydrogen evolution reaction may be favored on the?CuO?₃ cluster modified TiO₂?equivalent to⁷.7mol%of doped Cu?due to its suitable band-edge position and structural stability.