Surface Structure Modification Of Bismuth Oxychloride And Its Performance On Photocatalytic Water Splitting

The problem of energy shortage restricts the sustainable development of modern society.A major challenge facing scientific research is to develop the new energy technologies.Benefit from the clean and unlimited solar energy,more and more scientists try to transfer the solar energy to other forms of energy by catalytic technique,such as hydrogen energy.Semiconductor photocatalysis technology is a kind of technology which can use solar energy to catalyse many kinds of reactions conveniently and effectively.A lot of researches are devoted to using semiconductor to catalyse water splitting into hydrogen to obtain clean hydrogen energy.While there are many factors restricting the application of photocatalytic water splitting:firstly,semiconductor catalysts should satisfy the effective absorption of sunlight,but most of them have wide band gap and weak absorption of the visible light which accounts for 47 percent of solar light;secondly,catalysts usually can not effectively absorb and activate water;apart from that,photogenerated charges often have low separation efficiency,and the separated electrons and holes are still need strong oxidability and reducibility to realize the effective occurrence of two half-reactions of oxidation and reduction in water splitting.These factors all lead to the low efficiency of the final conversion of solar energy to hydrogen energy.Bismuth oxychloride(BiOCl)is a semiconductor photocatalyst with typical layered structure.It has been widely used in photocatalytic reactions due to its low toxicity,low cost and easy availability,unique crystal plane effect and easy regulation of electronic band structure.Because of the local electron-rich property of surface oxygen vacancies,it can be used to activate many small molecules such as N2,NO,and H2O,which improves the possibility of small molecules being catalysed thermodynamically.These unique properties provide new research ideas for its application in photocatalytic technology.Therefore,the purpose of this paper is to improve the photocatalytic performance of BiOCl in water splitting by changing its surface structure,and to provide new research ideas for its conversion from solar energy to hydrogen energy.Specific research contents are as follows:1.Photocatalytic water splitting undergoes two main semi-reaction processes:oxidation of water into oxygen and reduction of water into hydrogen.Oxygen production needs to undergo four-hole oxidation process.If this half-reaction is not carried out effectively,it will limit the occurrence of reduction reaction.Therefore,we first focus on improving the reaction efficiency of water oxidation process.BiOCl exhibits some unique properties in the presence of oxygen vacancies on the surface,such as effective adsorption of water molecules and promotion of their decomposition process,obvious tailing of visible light absorption,which provide a prerequisite for photocatalytic water splitting.Because the surface oxygen vacancy concentration will greatly affect the catalytic reaction,we try to explore the effect of different surface oxygen vacancy concentration on the process of water oxidation under visible light.Different oxidation products are obtained according to the change of oxygen vacancy concentration.We also try to combine photocatalytic water oxidation with pollutant removal,so as to realize the development of various applications of catalysts by adjusting oxygen vacancy concentration on BiOCl surface.2.After improving the efficiency of oxidation reaction under visible light to a certain extent,we try to modify the catalyst surface structure with other materials,such as supported cocatalyst,to assist its reduction semi-reaction,that is,hydrogen production process.Noble metal catalysts,which we know well,often do not prevent the reverse reaction of water splitting,or even promote it to a certain extent.While transition metal oxides do not show this phenomenon.Ruthenium oxide(RuO2)and nickel oxide(NiO)catalysts are the best transition metal oxide catalysts for hydrogen production at present,but Ni has strong adsorption for H compared with Ru,which may not be conducive to the subsequent hydrogen evolution process.The surface of BiOCl is rich in oxygen,metals are easy to form oxides on the surface of BiOCl,and Ru is easy to grow into small RuO2 particles by epitaxy growth on the surface of oxygen-rich catalyst.Therefore,we try to use RuO2 as hydrogen production cocatalyst to improve the hydrogen production performance of BiOCl under visible light.