Preparation And Photocatalytic Activity Of Titanium Dioxide-based Composite Photocatalysts

Energy and environmental issues raise people’s awareness of potential global crises.Semiconductor photocatalytic technology is a "green" approach to solving environmental and energy problems and is expected to play an important role in solving these problems.TiO2 is widely used material because of its low cost,high chemical stability and environmental friendly.However,some negative aspects of TiO2 nanostructures still exist,including a relatively low specific surface area and a broad band gap,which in turn lead to the lack of an active site,poor quantum efficiency,and a shortage of visible light photocatalytic activity.Effectively harvesting light to generate long-lived charge carriers to suppress the recombination of electrons and holes is crucial for photocatalytic reactions.Constructing the heterostructure and exposing the highly active facets have been regarded as powerful approaches to high-performance photocatalysts.The research results were obtained as follows:(1)In this paper,a three-dimensional(3D)double-heterostructured photocatalyst was constructed by connecting a TiO2-MoS2 core-shell nanosheets(NSs)assembled on a graphite fiber(GF@MoS2-TiO2)via a facile two-step hydrothermal method.The highly active(001)facets of TiO2 NSs vertically grown on the GFs and uniformly ultrathin MoS2 NSs on the surface of TiO2 NSs(rich in active edge sites)afford high-efficiency photogeneration of electron-hole pairs under UV and visible light.Meanwhile,the carrier separation is substantially promoted by the Ohmic contact between TiO2 NSs and the efficiently channeling electrons of zero-bandgap GFs,and the two-dimensional(2D)nano-junction with intimate and large contact interface between TiO2 NSs and MoS2 NSs.The improved charge separation and exposed active facets dramatically boost the photocatalytic degradation of methyl orange dye.(2)A novel 2D-2D nanojunction of MoS2 nanosheets(NSs)deposited on the TiO2 NSs with mainly exposed high-active(001)facets was prepared via a hydrothermal method combined with an annealing treatment using carbon fiber(CF)as templates.The prepared MoS2@TiO2 composite photocatalyst exhibits a greatly enhanced photocatalytic H2 production activity at the optimal weight percentage of MoS2(15 wt%),exceeding that of pure TiO2 NSs by 33 times.The superior photoactivity of MoS2@TiO2 composites is attributed to the synergistic promoting effects of the following factors:(i)the mainly exposed(001)facets of Ti02 NSs with higher surface energy in MoS2@TiO2 composites facilitate the activation of water molecules and the photocatalytic reduction;(ii)the coexposed(101)and(001)facets can form a surface heterojunction within single TiO2 NSs,which is beneficial for the transfer and separation of charge carriers.This study presents an inexpensive photocatalyst for energy conversion to achieve highly efficient H2 evolution without noble metals.(3)Synthesis of titanium-organic composite nanoflowers with Ti(OBu)4 as the titanium source by hydrothermal method and calcinations at different temperatures.As calcination temperature is increased to 350℃,titanium-organic composite start to transform into a bicrystalline mixture consisting of Ti02(B)and anatase.The content of TiO2(B)and anatase phase in TiO2 NFs was changed by changing the calcination temperature.The Ti02 NFs were analyzed by DSC,XRD,BET and TEM.By investigating the hydrogen production of bicrystalline TiO2 NFs,it was found that when Pt was used as a cocatalyst,TiO2 NFs-550℃ had the best hydrogen production effect compared to other samples.The carrier separation is substantially promoted by the nano-junction with intimate contact interface between TiO2(B)and anatase.The improved charge separation and exposed active facets dramatically boost the photocatalytic.