Performance Enhancement And Reaction Mechanism Of Metal Ion-doped SnO₂ For VOCs Degradation

In recent years,the pollution of volatile organic compounds(VOCs)has attracted much attention and has become one of the most urgent environmental pollution problems to be solved.As an environmentally friendly green technology,photocatalytic oxidation technology can directly degrade VOCs into harmless carbon dioxide and water under mild conditions.This method is one of the most promising technologies for VOCs purification.Tin oxide(Tin Oxide,SnO₂),as a typical n-type semiconductor material,not only has excellent stability,but also has excellent optoelectronic properties,so it shows good prospects in the field of catalysis.However,pristine SnO₂ has problems such as rapid recombination of photogenerated electron holes,low charge separation efficiency,and insufficient oxidation ability,which restrict its application in photocatalytic technology.In addition,VOCs in actual emission occasions are mainly in the form of a mixture of various pollutant components,so it is of great practical significance to explore the photocatalytic degradation of mixed components of VOCs.In this work,we use metal doping to modify SnO₂.By adjusting the types of doping metal elements and the doping ratio,the electronic structure of SnO₂ is optimized,which effectively inhibits the photo-generated electron-hole recombination and improves the charge.Separation efficiency,thereby significantly enhancing the efficiency of photocatalytic acetone degradation,the best is more than 92.8%.The reasons for the enhanced photocatalytic activity of SnO₂ after metal doping modification were revealed by experimental data and density functional theory calculations,and the reaction pathway of photocatalytic acetone degradation was revealed by combining in situ infrared spectroscopy,which provided a new perspective for understanding the mechanism of acetone degradation.In addition,in order to further promote the practical application of photocatalytic degradation of VOCs,we explored the purification process and mechanism of metal-doped SnO₂ on typical pharmaceutical industry VOCs waste gas,including the degradation of toluene and acetone mixtures and single-component VOCs.Through experimental characterization and density functional theory calculations,it was found that toluene and acetone would compete for adsorption on limited active sites to inhibit each other's photocatalytic degradation efficiency.It was found by in-situ infrared spectroscopy and gas chromatography-mass spectrometry that no addition reaction occurred during the mixed degradation of toluene and acetone,that is,the photocatalytic degradation paths of the mixture of toluene and acetone were independent.Through density functional theory calculations,we found that when the system contains both toluene and acetone,the stability of the conjugated?bond of toluene will be relatively enhanced,and it is not easy to obtain effective activation,which is not conducive to the ring opening and oxidation reaction of toluene.This study helps to better understand the photocatalytic degradation process and mechanism of mixed VOCs,and lays a solid theoretical and practical foundation for the practical application of photocatalytic technology.