Nickel And Carbon Cooperation In TiO₂ Based Photocatalyst:Material Preparation And Activity Enhancement

Heterogeneous photocatalysis and photoelectric catalysis has been extensively developed as a promising strategy to simultaneously address energy needs and environmental pollution.Since the first discovery of photocatalytic water splitting on a TiO₂ electrode under ultraviolet（UV）light,TiO₂ materials have been widely investigated due to its non-toxic,abundance,easy availability,and stability other unique properties.The optimizing of light absorption properties and charge transfer processes on semiconductor surfaces by doping heterogeneous elements and supported cocatalysts is an issue with wide universality and current applicability.Transition metal is one of the hot research materials due to its abundant reserves,low price,and convenient preparation.At the same time,the optimizing of electron transport by carbon materials with high conductivity has become the focus of attention.It is an important point to prepare highly efficient and stable photocatalyst to select the appropriate combination mode to control the energy band structure and charge transfer of TiO₂.Therefore,in this paper,taking abundant and inexpensive TiO₂as a model,using transition metal Ni and high conductivity carbon materials,the effects of synergistic enhancement effect of different composite modes on band matching,electron transport and photocatalytic hydrogen production of TiO₂ composite photocatalyst were investigated.The specific research content includes the following two aspects:1.The effects of heterogeneous element doping on the band structure,light absorption and photocatalytic performance of titanium dioxide were studied by using the atomic size effect of uniformly doped Ni element into the lattice of titanium dioxide.The effects of doping on band gap narrowing and introducing defects on photocatalytic hydrogen production performance were balanced by adjusting the content of doping elements.The highest photocatalytic efficiency（4.07 mmol/g/h）of Ni-doped TiO₂prepared by this method was obtained when the doping amount was 2%without supported cocatalyst.This rate is in the forefront of Ni/TiO₂ system.Then,in order to improve the electron transfer on its surface,carbon thin layer was selected as a cocatalyst and deposited on the material surface by secondary hydrothermal method without affecting the structure of Ni-doped TiO₂.The photocatalytic hydrogen production rate of C/Ni/TiO₂ was improved again.The highest photocatalytic hydrogen production rate is 10.26 mmol/g/h（the count of Ni doping is 2%）,is 2.52 times of that before carbon coating.2.The effect of NiO and TiO₂ heterojunction on electron transport was investigated.TiO₂ modified with 2-3 nm NiO nanocrystals was successfully prepared.The heterojunction formed by NiO and TiO₂ promoted the spatial separation of photogenerated electrons and holes,inhibited the recombination of carriers,and improved the photocatalytic hydrogen production activity.The photocatalytic activity was increased from 0.38 mmol/g/h of pure TiO₂ to 4.08 mmol/g/h of 2%-NiO/TiO₂ by adjusting Ni loading.Based on the previous work,Carbon thin layer can improve the surface electron transport,promote the charge transfer,and improve the photocatalytic activity.Using the same synthesis method,the carbon thin layer was deposited on the surface TiO₂ modified with NiO nanocrystalline.The experimental results show that the effect of carbon material on electron transport is also applicable to the heterojunction.The photocatalytic reaction rate was improved again,and the photocatalytic hydrogen production rate of TiO₂ co-modified by carbon thin layer and NiO nanocrystals reached 13.95 mmol/g/h,is 3.4 times higher than before the carbon load.