TiO2-rGO photocatalytic degradation of an emerging pollutant: kinetic modelling and determination of intrinsic kinetic parameters

An intrinsic kinetic model, derived from a suggested reaction photo-mechanism and with an explicit dependence on the local volumetric rate of photon absorption (LVRPA), was developed to simulate the photocatalytic degradation of clofibric acid and the main reaction intermediates, with a new titania-reduced graphene oxide nanocomposite (TiO2-rGO), The proposed reaction mechanism takes into account that graphene behaves as an electron acceptor and, therefore, this effect was included in the derivation of the reaction rate expressions and in the parameters estimation of the kinetic model. The photodegradation of clofibric acid was performed in a slurry photoreactor under different irradiation levels and using several loadings of a TiO2-rGO nanocomposite, prepared by hydrothermal method with a 0.5 wt. % of GO. Absorbed radiation profiles inside the photoreactor were obtained by solving the radiation model with the Monte Carlo method. A photocatalyst loading of 100 mg L-1 gave place to the best photodegradation results. Mass balances were proposed for the main pollutant and their main detected intermediates: p-benzoquinone and 4-chlorophenol. The intrinsic kinetic parameters were obtained for the complete (6-parameters) and simplified (5-parameters) models by comparing the experimental and the theoretical concentration values of all the organic compounds detected. The model proved to be able to predict with good accuracy the concentration evolution of clofibric acid, 4-chlorophenol and p-benzoquinone under several photocatalyst concentrations and irradiation levels. Finally, a very good correlation between calculated and experimental values of clofibric acid concentration was obtained with root-mean-square errors below 11%.