Degradation behavior of mixed and isolated aromatic ring containing VOCs: Langmuir-Hinshelwood kinetics, photodegradation, in-situ FTIR and DFT studies

Abstract

Abstract The photodegradation tendencies of mixed and isolated VOCs, e.g., benzene, toluene, and p-xylene were studied using TiO2 P25 as a model photocatalyst. The degradation of VOCs in the mixture is significantly affected by the existence of different organic pollutants. For example, benzene only showed 10% degradation efficiency in the mixture whilst 67% in the isolated mode. The conversion efficiency of benzene was 20% and 27% when mixed with p-xylene and toluene, respectively. It shows that the degradability of benzene is influenced more by the presence of p-xylene than toluene. The dynamic adsorption-desorption experiments and DFT calculations on stoichiometric and defective TiO2 surface revealed that benzene only weakly interacts with the stoichiometric TiO2 surface than toluene and p-xylene. This behavior could be the fundamental factor for the lower degradation efficiency of benzene. Furthermore, the presence of oxygen vacancy (Ov) in TiO2 surface tremendously improved the overall adsorption of VOCs. Several Langmuir-Hinshelwood kinetic models, which are based on different reaction dynamic assumptions, were used to determine rates of reactions, water adsorption equilibrium constant, and VOCs adsorption equilibrium constant. The results indicated that the oxidation of VOCs occurred on the catalyst surface, and the adsorption equilibrium constant of VOCs was higher than water adsorption equilibrium constant. The intermediate formation and hydroxyl groups consumption were further rationalized via in-situ FTIR study. This work provides a comprehensive analysis of VOCs degradation in the mixed and isolated mode, which will increase the possibility of implementing the photocatalytic oxidation technology for the VOCs abatement.