Degradation of ibuprofen by UVA-LED/TiO2/persulfate process: Kinetics, mechanism, water matrix effects, intermediates and energy consumption

Abstract

In this study, UVA-LED/TiO2/persulfate process was used to degrade ibuprofen (IBP). The results showed that addition of persulfate into the UVA-LED/TiO2 system significantly enhanced the degradation of IBP by inhibiting the electron-hole recombination, with a pseudo-first-order rate constant (kobs) increased by 2.7 times when 0.5 mM persulfate was added. The kobs increased linearly with the concentration of TiO2, while higher IBP initial concentration lowered the degradation rate. HO• contributed most to IBP degradation as suggested by a steady-state kinetic model. The investigation of the effects of water matrix indicated that alkaline condition, existence of humic acid, bicarbonate ion, chloride ion and sulfate ion inhibited the IBP degradation. The mineralization of IBP and decay of PS by UVA-LED/TiO2/persulfate process were both quite slow. Five intermediates were detected and the decomposition pathways were proposed based on the frontier electron densities (FEDs) theory. The electrical energy per order (EEO) of IBP was varied from 0.029 kWh/m3 to 0.243 kWh/m3, showing a relatively low energy cost of UVA-LED/TiO2/persulfate process. The results of this work indicate that UVA-LED/TiO2/persulfate is a powerful and promising process for the degradation of IBP.