Construction Of Ni-based Active Sites On C₃N₅ And Their Photocatalytic Performance

The ever-increasing issues of energy depletion and environmental degradation caused by rapid consumption of traditional fossil fuels have restricted the sustainable development of human society.Semiconductor-based photocatalytic technology is crucial for preparation of clean hydrogen energy,treatment of atmospheric pollutants,and realization of the national strategy of"carbon peaking in 2030-carbon neutralization in 2060".However,the low absorption efficiency of visible light and the fast recombination of photogenerated carriers limit their photocatalytic activity.Therefore,it is necessary to modify the semiconductor,in which the loading of metal-based active sites on the surface of the semiconductor is a typical surface modification strategy,which can not only enhance its visible light absorption ability,but also improve its photogenerated carrier separation efficiency,which become a research hotspot in this field.Traditional research mostly uses noble metals such as Pt as active sites,while their scarce and expensive properties are not conducive to practical applications.In this dissertation,C₃N₅ with narrow band gap（～2.2e V）,easy to coordinate with metals and wide visible light absorption region is selected as the research object,various Ni-based noble-metal-free active sites are loaded on its surface subsequently,and then its photocatalytic hydrogen production and NO removal performance are investigated.The main research contents are listed as follows:1.Highly dispersed Ni active sites loaded on C₃N₅（Ni-C₃N₅）material is prepared by a two-step calcination method.XRD,SEM/TEM,DRS,EDS and XPS etc are used to characterize the composition,morphology,light absorption properties and the existence of Ni.The results of visible-light-induced photocatalytic hydrogen production show that Ni-C₃N₅ with Ni loading amount of 0.1 wt%exhibits the best photocatalytic hydrogen production performance 1177μmol·h^-1.In addition,Ni-C₃N₅ also displays good photocatalytic cyclability and AQY values.Especially,a high AQY value of 24%at 420nm is obtained.This result provides a new idea for the design of highly active Ni sites.2.Three Ni-based active sites（the aforementioned highly dispersed Ni,S-Ni（OH）₂and Ni_xS_y）are loaded onto C₃N₅ to prepare Ni-C₃N₅,S-Ni（OH）₂-C₃N₅ and Ni_xS_y-C₃N₅catalytic materials,and their photocatalytic NO removal performance are studied.TRPL,EPR,and DRIFTS other methods are used to analyze photogenerated charge carriers separation,generation of reactive oxygen species and related mechanisms.The order of photocatalytic NO removal efficiencies under LED light irrdiation for the three materials follows:Ni-C₃N₅>S-Ni（OH）₂-C₃N₅>Ni_xS_y-C₃N₅.Under optimal conditions,the photocatalytic NO removal rates of Ni-C₃N₅,S-Ni（OH）₂-C₃N₅ and Ni_xS_y-C₃N₅ are 54%,42%and 40%,respectively.This result provides guidance for the design of Ni-based noble-metal-free active sites.