Fabrication Of SiNW Covered With SiQD Or SnO₂ Protection Layer And Study Of Their Photoelectrocatalytic Properties

Photocatalysis is one of the most popular rising technologies to degrade pollutant,and has practical application potential as the main advantages of low cost,mild reaction condition,utilizing solar energy and mineralizing pollutant non-selectively.The core objective of this technology is to develop efficient photocatalysts with low price,non-toxic,visible light responsibility and high charge separation efficiency.Silicon is the second most abundant element in the earth's crust,with mature fabrication technique as well as biocompatibility.It responds to the light with wavelength less than 1100 nm,which matches solar spectrum well.Furthermore,its electron mobility and photoenergy conversion efficiency are higher than common metallic oxide photocatalysts.Thus it has high potential in water pollution controlment.However,in aqueous solution or humid air,silicon material will be oxidized into insulating silica,blocking photo-generated carriers transfering to pollutants in aqueous solution.Besides,for silicon photoanode,the overpotential should be enhanced to avoid oxygen evolution.This paper focused on the previous problems,took silicon nanowires?SiNW?as an object,used silicon quantum dots?SiQD?and SnO₂ as protection layers to endow silicon stability in water aqueous and improve photo-induced charges separation efficiency then resulted in degrading 4-chlorphenol efficiently.Experimental details are as below:SiQD protecting SiNW arrays electrode was prepared by electroless etching twice.Firstly,the effect of etching time for the shape of SiNW was investigated.SiNW arrays etched for 3 min was neater than the samples etched for 5-15 min,and the intensity of light absorption was also higher.The second etch formed SiQD on the surface with size ranging from 5 nm to 10 nm,the SiQD evenly spread over the top of SiNW with highly mechanical strength,and the intensity of light absorption increased.Secondly,photoelectrochemical test showed that the photocurrent of SiNW coated by SiQD?h-Si?increased 5 times compared to bare SiNW,and after 20 times cyclic voltammetry scanning,the photocurrent only decreased 1.8%,which meant h-Si was stable with high carrier separation efficiency.Using 4-chlorphenol as target contaminant,the first order reaction kinetics constant of h-Si during photoelectrocatalytic process was twice as high as that of SiNW.Chemical vapor deposition was used to deposit SnO₂ on SiNW?SiNW@SnO₂?to increase oxygen evolution overpotential.The deposition temperature and precursor weight were optimized,and according to the photoelectrochemical test results,the optimal conditions were 4 g precursor SnCl2 and reaction temperature from 375? to 425?.This photoanode in aqueous solution was stable,and onset potential for water splitting reached to 1.7 V?vs.SCE?.Due to most of the pollutants decomposition voltage is below 1.7 V,it can effectively avoid side effects and improve energy utilization.In summary,the advantages of SiQD and SnO₂ as protection layers include stable photocurrent and high overpotential.The results may promote the practical application process of silicon nanomaterials in aqueous.