Kinetic study and model of the photocatalytic degradation of rhodamine B (RhB) by a TiO2-coated activated carbon catalyst: Effects of initial RhB content, light intensity and TiO2 content in the catalyst

Heterogeneous photocatalysis has proved to be a useful tool for the degradation of water pollutants over the past 30 years. Despite notable achievements in this domain, a more satisfactory and accurate kinetic model has to be developed further. In this work, to clarify the dependence of the apparent rate constant kapp of the first-order kinetics on the initial organic content, light intensity and TiO2 content of TiO2/AC (TiO2-coated activated carbon, TA), the photocatalytic treatment of rhodamine B (RhB) as a model compound has been studied by using TA in suspension as a photocatalyst. The photocatalytic degradation kinetic characteristics were experimentally investigated under different reaction conditions (light intensity, initial organic content and TiO2 content of TA). To account for the experimental results, a new kinetic model is proposed on the basis of intrinsic element reactions, which takes into account the effect of light intensity, reaction intermediates, and the absorption performance on h+ forming, organic compound combining with OH and degradation rate, respectively. The new kinetic model fairly resembles the classic Langmuir–Hinshelwood equation from its expression. However, it does predict that both kr−1 and KS are linearly proportional to the reciprocal of the square root of the light intensity in a rather large intensity range. The model fits quite well with the experimental data and elucidates phenomena about the effects of the TiO2 content of TA on the degradation rate.