| In recent years,with the increasing emphasis on environmental issues,the search for green and clean fossil energy has become the top priority of people's research.As a new type of energy,hydrogen energy can not only solve the energy crisis well,but also effectively avoid the environmental pollution caused by fossil fuel combustion,so it is favored by researchers all over the world.In the methods of generating hydrogen,photocatalytic decomposition of water to produce hydrogen by using sunlight is a simple and rapid method for producing hydrogen.As an important intermediate medium in photocatalytic reactions,semiconductor photocatalysts can convert sunlight into hydrogen energy,which is the focus of research.However,most of the semiconductor photocatalysts exhibit good catalytic activity only under ultraviolet light,such as TiO2,ZrO2,SrTiO3,etc.Therefore,it is necessary to find a suitable visible light catalyst.g-C3N4 can absorb light with a wavelength of less than 400 nm due to its internal high degree of polymerization and the presence of a heptazine ring,and exhibits excellent photocatalytic performance in the visible light region.Although g-C3N4 has a suitable forbidden band width and can effectively utilize visible light,but g-C3N4 also has some disadvantages:easy recombination of electron-hole pairs and low quantum efficiency.So it is necessary to improve its photocatalytic performance through modification techniques.CdS has a suitable forbidden band width and its direct transition performance band structure makes it has a high light absorption coefficient in the wavelength range of blue light and red light.Also,it exhibits good visible light responsiveness under sunlight,so it is considered to be a suitable photocatalytic material.However,CdS is subject to some defects,such as photocorrosion,which limits the application of CdS in photocatalytic hydrogen production.Based on this,this paper studied the modification of g-C3N4 and CdS by means of morphology control,semiconductor composite and cocatalyst loading,so as to enhance the photocatalytic hydrogen production performance of the catalyst under visible light.The details are as follows:1.Firstly,the visible light catalyst g-C3N4 was prepared by the high temperature thermal decomposition method.Subsequently,Cu2O/g-C3N4 was synthesized by in-situ synthesis.The results of transmission electron microscopy(TEM)and high resolution transmission electron microscope(HRTEM)proved that Cu2O semiconductor material was successfully combined with g-C3N4.Ultraviolet diffuse reflectance(Uv-vis)and photocurrent test results show that the electrons and holes are greatly accelerated because of the proper band gap of Cu2O and the obvious valence band and conduction band difference between g-C3N4.The transfer speed between the samples effectively improves the photocatalytic performance of the sample.2.CdS/g-C3N4 photocatalytic system was constructed by using a solvothermal method to load CdS on the surface of g-C3N4.X-ray diffraction and X-ray photoelectron spectroscopy results show that the combination of g-C3N4 and CdS semiconductors does not change the electronic structure of g-C3N4 and CdS.The photocatalytic hydrogen production experiments show that the CdS/g-C3N4 photocatalytic system exhibits good photocatalytic efficiency,which is attributed to the enhancement of the absorption of visible light and the light stability after modification by CdS.At the same time,by combining with the g-C3N4,the photogenerated hole-electrons of CdS are effectively separated,thereby alleviating the phenomenon of photocorrosion.3.The photocatalytic system Ni(dmgH)2/CdS was constructed by chemical injection method.Simple Ni(dmgH)2 does not exhibit photocatalytic hydrogen production activity under visible light,but exhibits better photocatalytic performance by loading with CdS.This is mainly because the reduction of the ligand excites the activity of Ni2+,which promotes the overall redox process of Ni(dmgH)2/CdS photocatalytic decomposition of water.At the same time,the CdS rod structure synthesized by ethylenediamine as a solvent provides more active sites for H reduction,thereby enhancing photocatalytic activity. |
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