The photodegradation tendencies of mixed and isolated VOCs, e.g., benzene, toluene, and p -xylene were studied using TiO 2 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 TiO 2 surface revealed that benzene only weakly interacts with the stoichiometric TiO 2 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 ( O v ) in TiO 2 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.