Constructing Of Insulator-based Heterojunction And Photocatalytic NO_X Reaction Mechnism

Air pollution has become a serious problem that cannot be ignored in the sustainable development of society.The low concentration of nitrogen oxides emitted into the air not only threatens human health,but also causes environmental problems,such as acid rain,photochemical smog and PM2.5.Visible light photocatalysis technology can be directly drived by clean solar energy,which has great application prospects for the purification of low concentration pollutants.Therefore,in order to realize the environmental application of photocatalytic technology,the photocatalyst used not only needs to have high-efficiency visible light photocatalytic performance,but also meets the requirements of stablility,low cost,abundant reserves,and easy preparation.Ceramics,glass and building cement are cheap materials that can be seen everywhere.The main components of them are mostly rich and cheap insulators on the earth,such as CaSO₄,SrCO₃,BaCO₃ and so on.These materials are called insulators simply because their band gap is wider than that of semiconductor materials,and the photon energy in sunlight is not enough to excite them.Therefore,researchers have hardly considered insulators as photocatalysts.Recently,Dong Fan et al.found that a defective insulator exhibits good photocatalytic activity under ultraviolet light irradiation due to the formation of a defect-mediated intermediate level in the forbidden band.If the insulator material is modified to have high efficiency visible light photocatalysis,the insulator will be the best photocatalyst candidate.Therefore,referring to the method of modifying the wide-bandgap semiconductor photocatalyst,in this paper,we constructed insulator-based heterojunction to induce the photogenerated electrons to be efficiently separated from the semiconductor and transferred to the insulator to achieve excellent visible light photocatalytic performance.We use a chemical precipitation method to prepare an insulator-semiconductor heterojunction composed of an insulator BaCO₃ and BiOI.The charge transport channel is formed in advance by the covalent interaction between atoms at the interface,and the photogenerated electrons are separated and directionally transferred to the conduction band of insulator.These large amounts of free electrons promote the generation of free radicals,preferentially oxidizing NO to high-valence intermediates.The interface of insulator-based heterojunction containing a large amount of free electron was constructed.The combination of experimental and theoretical calculations was used to investigate the effect of the electron-rich environment at the interface of the insulator-based heterojunction on the photocatalytic NO purification process.The abundant electronic environment can effectively activate the inert pollutants to promote the conversion and can generate new active species to provide new conversion pathways for inert pollutants,thereby achieving an efficient and non-toxic photocatalytic purification process.In addition,the mechanism of photocatalytic NOx purification by insulator-based heterojunction has not been explored.Based on in situ DRIFT characterization,we clarify the mechanism of photocatalytic NO purification by insulator-based heterojunction.It is found that the insulator-based heterojunction can pass pathway（NO→NO⁺or NO₂⁺→nitrate or nitrite）to efficiently convert NO to final products.This provides a number of opportunities for exploring earth-rich insulators as visible light photocatalysis,and also offers a new understanding of the mechanisms of gas phase photocatalysis and control of air pollution...