Degradation of carbamazepine by UVA/WO3/hypochlorite process: Kinetic modelling, water matrix effects, and density functional theory calculations

Abstract

The rapid recombination of electron/hole pairs is a major setback in the application of WO3-based photocatalysis in water treatment. In this study, hypochlorite (ClO−) was used as an electron acceptor to enhance the photocatalytic degradation of carbamazepine (CBZ) using UVA-excited WO3. The results showed that CBZ degradation in the UVA/WO3/ClO− system followed a pseudo-first order reaction kinetic model. The addition of 0.1 mM ClO− to the UVA/WO3 system at pH values of 8.2 and 6.2 increased the rate constant (kobs) of the degradation process 5.3- and 11.5-fold, respectively. Further, increasing the WO3 dosage or decreasing the initial CBZ concentration resulted in an increase in kobs. However, at high concentrations, ClO− inhibited CBZ degradation. Based on the kinetic model, it could be suggested that ClO played a dominant role in the degradation process. Furthermore, the water matrix effects were as follows: the optimal pH was 6.2; humic acid, chloride, bicarbonate, and ammonium exhibited inhibitory effects on CBZ degradation; and sulfate ion significantly enhanced the degradation. Density functional theory (DFT) calculations indicated a strong affinity between ClO− and the WO3 surface. Specifically, the electrical energy per order that was associated with the use of ClO− varied in the range of 0.100–1.617 kWh/m3. In summary, this study shows that ClO− is an excellent electron acceptor for excited WO3, while clarifying the CBZ degradation-enhancing effect of ClO− as well as the kinetic model and DFT calculations. These findings can be employed in the degradation of recalcitrant contaminants in a cost-effective manner, while being significant for the development of more effective catalysts of UV-assisted advanced oxidation processes.