Study On The Band Structure Control And Photoelectrochemical Conversion Performance Of ZnMgO Solid Solution Photocatalysts

In recent years,ZnO semiconductor material has become a new research hotspot in the field of photocatalysis because of its many advantages,such as low cost,high stability,non-toxic,environmental friendly and so on.However,ZnO semiconductor also have two major issues,including insufficient conduction band（CB）potential and high recombination rate of photogenerated carriers.Therefore,on the basis of the high performance ZnO semiconductor materials with special morphologies,the energy band structure of ZnO can be adjusted by introducing the Mg elements to improve the photoelectrochemical（PEC）properties of the series of samples,and exploring the mechanism of the influence of the band structure change on the PEC properties of the series of samples.In this paper,pure ZnO nanoparticles and ZnMgO solid melt nanorods were prepared by oxalic acid co precipitation method.The results showed that the energy band structure of the ZnO can be tuned with the Mg elements doping in it.Especially,during this process,the CB potential of ZnMgO solid solution moved to more negative site gradually with the Mg content increasing,which is very important for semiconductor photocatalytic hydrogen evolution process.When the mole ratio of Mg reached to 50%,corresponding ZnMgO showed a much more negative CB potential（-0.46 V vs NHE）than pure ZnO（-0.05 V vs NHE）,and the photocatalytic for hydrogen evolution of ZnMgO increased dramatically than pure ZnO（from near zero of Zn O to1103.9μmol/g in 4 hours）.On the basis of ZnMgO solid solution material,we improved the photocatalytic degradation of Ag/ZnMgO solid solution composites by doping Ag.The results showed that doping Ag did not change the crystal structure and morphology of solid solution materials.However,under high temperature conditions,the Ag agglomerated to form nanoparticles.These Ag nanoparticles can effectively promoted the separation and migration of photo-generated carriers and further improved the photocatalytic degradation performance of Ag/ZnMgO solid solution composites.Among the composites,Ag/ZnMgO composite with doping ratio of 3%had the best degradation performance,which was twice as higher as ZnMgO solid solution material.In addition,magnesium hydroxide with thickness less than 10 nm were coated on the surface of Zn O tussock-like nanorods by in situ electrochemical multi-potential pulse deposition.With the post-annealing temperature increasing,the nano overlayer on the surface of ZnO tussock-like nanorods undergoes phase transition from amorphous Mg（OH）₂ to amorphous MgO particles,and finally a Zn_xMg_1-xO solid solution layer with high crystallinity forms.With the changing of the surface overlayer on Zn O nanorod,the energy band potential of the corresponding photoanodes showed gradual negative shift and the charge mobility were also improved.On the one hand,the dense Zn_xMg_1-xO solid solution coating can protect the Zn-Mg-O@ZnO 700composite from the corrosion of the surrounding acidic environment;on the other hand,the Zn_xMg_1-xO solid solution has a more negative conduction potential,so it can promote the migration and separation of photoinduced carriers,and then improve the PEC cathodic protection for 304 stainless steel（SS）.In conclusion,by regulating the band structure of the ZnMgO solid solution material,we can effectively shift the conduction band potential,enhance the photocatalytic hydrogen evolution and PEC cathodic protection performance of the composites.Such a method to optimize the properties of semiconductor by adjusting its energy band is of great importance in the research process of semiconductor materials.