Utilization Of Nickel-based Cocatalyst For Improving Photocatalytic Hydrogen Production Activity Over Cadmium

It is well known that hydrogen is an environmental-friendly and sustainable alternative to fossil fuel,and the utilization of photocatalysts to split water driven by sunlight is a critical pathway to product hydrogen.A prerequisite for effective solar energy conversion is to develop efficent photocatalysts that can use the spectral wavelength range of sunlight.Photocatalysts can split water usually containing a photocatalytic semiconductor and one or more cocatalysts.Semiconductors are mainly responsible for light absorption and charge transfer,while catalytic reaction mainly occurs on the surface of the cocatalyst.CdS semiconductor is a promising photocatalytic material with narrow band gap and adjustable band structure.However,CdS compounds have the disadvantages of high photogenic carrier recombination rate and serious photocorrosion.Many ways can be used to improve the photocatalytic performance,including increasing the specific surface area,constructing heterojunction,doping and modification of co-catalyst.In this thesis,different nickel-based cocatalysts were designed to modify the CdS-based semiconductor to improve its photogenic carrier separation rate and corrosion resistance.The main research contents and results are as follows:?1?The urchin-shaped CdS were synthesized by hydrothermal method,then ball grinding to load NiC cocatalyst.It is apparently that the water splitting performance of pure CdS can be improved by using NiC as cocatalyst.Under visible light irradiation,the hydrogen production rate of CdS-4%NiC photocatalyst reached 12.84mmol·g^-11 in 3 hours,which was 6 times of pure CdS.This is due to the fact that the NiC promotes the transfer rate of photogenic carriers on the CdS surface and provides more active sites of hydrogen production.?2?Trimetal doped Cd_0.5Zn_0.5Ni_xS_1+x+x photocatalyst was synthesized by one-step hydrothermal method.In the subsequent test,it was shown that there exists Ni nanoparticles as cocatalyst on the surface of the photocatalyst.Under visible light irradiation,the hydrogen production rate of Cd_0.5Zn_0.5Ni_xS_1+x+x photocatalyst reached53.4 mmol·g^-11 in 3 hours,which was 25 times higher than that of CdS photocatalyst.It is because Zn and Ni are doped into CdS,which changes the conduction band and valence band position of CdS,and Ni is used as an cocatalyst to accelerate electron transport and provide active sites.?3?The photocatalyst composed of CN and Cd_0.5Zn_0.5S was synthesized by hydrothermal method,and then NiS was supported by ion-exchange method.Under visible light irradiation,the hydrogen production rate of CN/CdZnS-15%NiS photocatalyst reached 19.3 mmol·g^-11 in 3 hours,which was 9 times than that of CdS photocatalyst.The results showed that the photogenic carrier separation was enhanced and the catalytic activity of photocatalyst was improved after the modification of NiS as cocatalyst.Moreover,its stability was greatly improved,and the catalytic activity remained basically unchanged after five cycles.