Adsorption Mechanisms of Typical Carbonyl-Containing Volatile Organic Compounds on Anatase TiO₂ (001) Surface: A DFT Investigation

The carbonyl-containing compounds (CCs) are typical volatile organic compounds (VOCs) and ubiquitously present in the environment. Therefore, the adsorption structures and properties of typical CCs on the anatase TiO₂ (001) surface were investigated systematically with density functional theory (DFT) to understand their further catalytic degradation mechanisms. The adsorption mechanisms show that three selected typical CCs, acetaldehyde, acetone, and methyl acetate, can easily be trapped on the anatase TiO₂ (001) surface via the interaction between the carbonyl group with Ti_5c sites of catalyst surface. Especially for acetaldehyde with the bare carbonyl group and the strongest adsorption energy, it is the most stable on the surface, because the bare carbonyl group can interact with not only the Ti_5c atom, but also the O_2c atom of the surface. The substituent effect of different CCs has less impact on its adsorption models in this studied system and the bare carbonyl group is the key functional group within studied CCs. The Ti_5c atoms of anatase TiO₂ (001) surface are active sites to trap CCs. Our theoretical results are expected to provide insight into the adsorption mechanisms of these carbonyl-containing VOCs on TiO₂ catalyst and also to help understand the further catalytic degradation mechanisms of air pollutants at the molecular level

Can Silica Particles Reduce Air Pollution by Facilitating the Reactions of Aliphatic Aldehyde and NO₂?

This study investigated the heterogeneous atmospheric reactions of acetaldehyde, propanal, and butanal with NO₂ onto silica (SiO₂) clusters using a theoretical approach. By analyzing spectral features and adsorption parameters, the formation of hydrogen bonds and negative adsorption energies provide evidence that an efficient spontaneous uptake of aliphatic aldehydes onto SiO₂ could occur. The atmospheric reaction mechanisms show that when aldehydes and NO₂ react on the surface model, the H atom abstraction reaction from the aldehydic molecule by NO₂ is an exclusive channel, forming nitrous acid and acyl radicals. This study included kinetics exploring the reaction of aldehydes with NO₂ using a canonical variational transition state theory. The reaction rate constants are increased in the presence of SiO₂ between the temperatures 217 and 298 K. This may explain how aldehydes can temporarily stay on mineral particles without chemical reactions. The results suggest that silica can depress the rate at which the studied aldehydes react with NO₂ and possibly reduce air pollution generated by these atmospheric reactions