Investigation Of Photocatalytic NO Oxidation And Reaction Mechanism Via La Doping In Photocatalyst

NOx includes NO and NO₂,which is the main reason for air pollution,such as photochemical smog,acid rain,et all.Recently,semiconductor photocatalysis technology has attracted much attention in the environmental governance field due to the advantage,such as low cost,mild reaction conditions,etc.However,it still has a weak point that toxic byproduct NO₂will be generated during photocatalytic purification of NO and low removal efficiency in common semiconductor photocatalyst.Besides,NO₂has strong irritation to human respiratory organs,which is 5-8 times as toxic as NO.Therefore,the development and design of the new efficient photocatalyst is the key to promote the application of photocatalyst technology.In recent years,ion doping exhibits excellently modified efficiency.Among all kinds of doped modified elements,rare earth element shows excellent photoelectric and magnetic properties,in which La has no variable valence state and is stable as La³⁺.Hence,the La element is an ideal dopant.Therefore,it is an important topic to modify semiconductor photocatalyst by doping La to realize the safe and efficient oxidation of NO to nitrate.To improve the photocatalytic efficiency and clarify the mechanism of La doping.La-doped Zn O photocatalysts were prepared by a simple precipitation method.The UV photocatalytic NO removal efficiency increases from 36.2%to 53.6%after La doping.Most importantly,a significant suppressed NO₂production also has been realized.According to the experimental and theoretical results,the doping of La on Zn O results in the formation of V_Zn,which induces the redistribution of charge carriers in Zn O.Besides,La promotes the production of·O₂^-and V_Znaccelerates the formation of·OH respectively,contributing to the complete oxidation of NO to nitrate.However,visible light accounts for 43%of sunlight,while ultraviolet light only accounts for 8.7%.Therefore,it is of great significance to develop a visible light catalyst with high catalytic efficiency and selectivity.To further promote the practical application of photocatalytic technology and clarify the key role of La.（Bi O）₂CO₃with the visible light response is selected as a base catalyst.La-doped（Bi O）₂CO₃was prepared by hydrothermal method to improve the performance and selectivity of NO oxidation under visible light irradiation.The results indicate that local excess electrons（Ex）are formed on the surface of（Bi O）₂CO₃after La doping.Besides,the Ex could effectively accelerate the activation of reactants and promote charge separation and transfer.Under visible light,the gas molecules could capture the Ex and get activated to produce reactive oxygen species（ROS）with high oxidation ability,which enables complete oxidation of NO to target products（NO₂^-/NO₃^-）instead of producing other toxic byproducts.Combining experimental and theoretical methods,the pathway of charge carriers transportation/transformation and the photocatalytic NO oxidation mechanism have been fully unraveled.This work paves a new way to simultaneously realize the photocatalytic pollutants removal and the inhibition of toxic intermediates generation for efficient and safe air purification.Furthermore,the La-doped photocatalyst preparation method can also be extended to other semiconductors for guiding the rare earth elements doped experiment to improve photocatalytic efficiency and inhibit toxic byproduct.Moreover,the provided mechanism of NO oxidation and toxic byproduct inhibition also can be referenced for future research.