Monuron photodegradation using peroxymonosulfate activated by non-metal-doped TiO2 under visible LED and the modeling via a parallel-serial kinetic approach

Abstract N-doped TiO 2 (NT) was proven to be efficient for monuron decay via peroxymonosulfate (PMS) activation under visible LED (Vis LED). The activation mechanism revealed that OH and SO 4 − have a critical role in the monuron decay with a ratio of about 3 to 1, respectively; and the holes at the catalyst surface are the main precursors in forming SO 4 − . The NT/PMS/Vis LED hybrid process was found to be an effective approach under a wide solution pH range of 2.5–9.2 (>80% decay). Interestingly, the highest efficiency was observed at pH 9.2 due to the contribution of PMS/Vis LED process by generating both OH and SO 4 − at alkaline pH. However, the decay rate of monuron was inhibited at pH 11.6 due to the dissociation of OH into O − and the electrostatic repulsion among reagents. The process was also suitable for ion-rich wastewater since no significant reduction in the performance was induced in the presence of high concentrations of inorganic anions. Furthermore, the process was proven to be a promising approach for mineralization of monuron and its intermediates. Twenty reaction intermediates were detected and five of them are newly reported. A novel mathematical model was established based on reaction intermediates using a parallel-serial-irreversible reaction approach, which is helpful in predicting the detoxification extent of hazardous intermediates.