Based On The Construction Of GC₃N₄ And ?-Ni(OH)₂ Monolithic Photocatalysts And The Research On The Photooxidation And Removal Of NOx

As a metal-free photocatalyst,graphitic carbon nitride(g-C3N4)with many advantages,such as stable physical and chemical properties,good visible light response ability,low cost and easy availability,is widely utilized in the field of nitrogen oxide(NOx)removal.However,the agglomeration of g-C3N4 leads to the decrease of its specific surface area,which affects the photocatalytic efficiency.Furthermore,the problems of powder g-C3N4,such as easy loss and difficult recovery,are difficult to meet the practical application.In order to immobilize g-C3N4 and enhance its photocatalytic activity,monolithic photocatalyst g-C3N4/Ni-foam was prepared via impregnation method.The mass loss ratio of g-C3N4 is only 6.4%after 60 hours continuous air direct blowing,which indicates that g-C3N4 can be firmly loaded on the surface of Ni-foam.Meanwhile,the g-C3N4/Ni-foam monolithic photocatalysts exhibited a 1.9 times higher NO removal ratio than powder g-C3N4,indicating the improvement of photocatalytic performance after introduction of Ni-foam.However,the inadequate oxidation ability of g-C3N4 results in the formation of a large number of toxic by-products(NO2).In order to inhibit the production of NO2,a-Ni(OH)2/Ni-foam monolithic photocatalyst was prepared through in situ hydrothermal growth method.Density functional theory and experiments confirm that the Ni 3d orbit band divides the wide bandgap of a-Ni(OH)2 into two parts,which acts as a bridge for electron transport(VB?Ni 3d?CB)and is beneficial visible light response.Meanwhile,we found a-Ni(OH)2 possesses favorable NO oxidation(21.2%)without any N02 generation(-1.2%)under visible light illumination.More importantly,the H atoms of a-Ni(OH)2 improve the activation of oxygen,leading to no toxic NO2 generation.Notably,the NO+was detected during the NO oxidation process,which is a crucial by-product to improve the oxidization of NO.Furthermore,the a-Ni(OH)2/Ni-foam monolithic photocatalysts exhibited a 3.2 times higher NO removal ratio than powder a-Ni(OH)2.Based on the study of g-C3N4 and ?-Ni(OH)2,the g-C3N4/a-Ni(OH)2 composite photocatalyst was successfully constructed by hydrothermal method.The introduction of?-Ni(OH)2 can enlarge the specific surface area and reduce the recombination rate of photogenerated carriers,thus increasing the removal rate of NO(50.1%)without any NO2 generation(-0.5%).At the same time,it was found that g-C3N4/a-Ni(OH)2 was a Z-type heterojunction by XPS valence band spectra and in situ infrared spectroscopy showed that g-C3N4/a-Ni(OH)2 had strong oxidation ability.In addition,the removal rate of NO by g-C3N4/a-Ni(OH)2@Ni-foam is 1.3 times that of g-C3N4/a-Ni(OH)2.Immobilization of g-C3N4,a-Ni(OH)2 and g-C3N4/a-Ni(OH)2 on Ni-foam can significantly improve the photocatalytic activity and stability.Firstly,the porous structure of Ni-foam can enlarge the dispersibility and provide more active sites for photocatalytic reaction,enhancing the adsorption capacity and photo-degradation efficiency of NO on the surface of photocatalyst;Secondly,the Ni-foam exhibited excellent electron transfer property which can strictly restrict the recombination efficiency of electron-hole pairs.This paper provides a new idea for the performance improvement and practical application of powder photocatalyst.