Investigating the mechanism behind the synergistic ultraviolet photooxidation degradation of gaseous benzene through modified ACF

Abstract

The effects of relative humidity were studied on the direct conversion efficiency, mineralization rate and components of waste gas from benzene photooxidation degradation. The adsorption energies, adsorption types, and molecular interaction forces of activated carbon fiber (ACF) modified with nitrogen and oxygen-containing functional groups were calculated using quantum chemical density functional theory (DFT) calculations and wave function analysis. Five polar intermediate products including acetone, acetol, hexanal, benzaldehyde, and acetophenone generated from benzene photooxidation degradation were selected as the computational object. The independent gradient model method based on Hirshfeld partition was used to study the weak interactions among the five equilibrium molecular adsorption configurations. The results demonstrated that the direct conversion efficiency of benzene increased first and then decreased with increasing relative humidity. The maximum direct conversion efficiency was 82% observed at a relative humidity of 50%. The mineralization rate decreased significantly at higher relative humidity, and the lowest value was 2%. The overall adsorption effect of nitrogen-containing functional groups on the modified ACF surface is higher than that of oxygen-containing functional groups. The functional groups with the best adsorption effect are ACF modified by pyridone, amino and carboxyl groups. Combined with electron localization function (ELF) analysis and Mayer bond-level calculation, it was found that all the modified ACF surfaces do not form chemical bonds for the equilibrium molecular adsorption configurations of the five organic compounds, which belong to physical adsorption. The adsorption of five intermediate products by modified ACF mainly depended on hydrogen bonds or van der Waals forces. The existence of hydrogen bonds greatly improved the adsorption capacity of modified ACF to organic molecules.