Degradation Of Nitric Oxide By Coal-based Graphene Quantum Dots Compounded With Bismuth Halide Oxide

In the past few years,the use of fossil fuels has increased rapidly with the rapid development of industry,but the use of fossil fuels can cause serious air pollution.Among the many air pollutants,nitrogen oxides(NO_x)have been shown to be an air pollutant that can both cause environmental hazards and affect human health.In the industrial field,the treatment of NO_x mainly includes selective catalytic reduction(SCR)and selective non-catalytic reduction(SNCR),but these methods have some drawbacks,such as high reaction temperature and ammonia escape when ammonia is used as the reductant,which can bring secondary pollution,so the development of a NO_xdegradation method with mild reaction conditions,fast and without secondary pollution to the environment Therefore,it is urgent to develop a method for NO_x degradation with mild reaction conditions,fast and no secondary pollution to the environment.Semiconductor photocatalysis has been gaining wide attention in the degradation of nitrogen oxides because of its mild reaction conditions,easy operation,low cost and without causing secondary pollution to the environment.As a new visible light-driven catalyst,bismuth halide oxide has been widely used in photocatalytic degradation of nitrogen oxides due to its simple preparation,non-toxicity and good stability.However,for monomeric bismuth halide oxides due to their wide forbidden band width leads to their small visible light absorption range and the low separation efficiency of photogenerated electrons and holes of monomeric bismuth halide oxides,which will affect their photocatalytic activity.Therefore,it has become a current research hotspot to improve these drawbacks and enhance the performance of photocatalytic degradation of nitrogen oxides by constructing novel bismuth halide oxide-based photocatalytic semiconductors.In this study,we will obtain efficient visible photocatalysts for NO degradation by modifying bismuth chloride oxide(Bi OCl)and bismuth bromide oxide(Bi OBr)with coal-based graphene quantum dots(C-GQDs),and investigate the mechanism of photocatalytic NO degradation by the prepared composite catalysts through various characterization methods.Firstly,the visible light composite catalyst CG/BOC was prepared by compounding C-GQDs with Bi OCl by semi-solventothermal method.The characterization results by XPS,EDS and HR-TEM demonstrated that the C-GQDs were successfully loaded onto the Bi OCl surface.Compared with pure Bi OCl,the BET results showed that the specific surface area and pore volume of the 0.15CG/BOC composite increased by 6.70 and 3.22 times,respectively.This provided more adsorption and reactive active sites for the photocatalytic degradation of NO.In the photocatalytic degradation of 32 ppm NO,the CG/BOC composite catalyst increased the NO degradation rate from 34.41%to 75.15%and the denitrification index from 0.06to 0.35 compared with pure Bi OCl.By combining the results of UV-Vis DRS,MS tests and DFT calculations,the C-GQDs in the CG/BOC composite under light as photoelectron acceptor under light accelerates the separation of photo-generated electrons and holes.The prepared catalysts were shown to be stable and reusable by five cycles of experiments.Next,the visible-light composite catalyst CG/BOB was prepared by semi-solventothermal method of compounding C-GQDs with Bi OBr.Characterization results by XPS,EDS and HR-TEM demonstrated that the C-GQDs were successfully loaded onto the Bi OBr surface.In the photocatalytic degradation of 35 ppm NO,the CG/BOB composite increased the NO degradation rate from 45.30%to 81.42%and the denitrification index from-0.73 to 0.34 compared with pure BOB.By combining the results of UV-Vis DRS,MS,XPS-VB tests and DFT calculations,the CG/BOB composite in which C GQDs and BOB constitute a type-Ⅱ heterojunction,which will greatly promote the separation of photogenerated carriers and is beneficial to improve the photocatalytic activity of the composite catalyst.The cycling experiments showed that the prepared composite catalysts have good stability and can be reused.