Photodegradation of doxycycline in water induced by TiO2-MCM-41: Kinetics, TOC evolution and reusability

Abstract

UV-VIS spectroscopy was used as a fast, easy-implementation and novel method to monitor and quantify the photodegradation kinetics of the emergent pollutant doxycycline (DXC) in water. TiO2 nanoparticles (NPs), bare and supported on MCM-41 type silica (TiO2-MCM-41), were used as catalysts, with the silica used in order to enhance the polydispersion of the NPs. pH played a crucial role in both, the decomposition rate and the mechanism, i.e., via hydroxyl radicals at alkaline pH or presumably via hydroperoxyl radicals at acidic pH. At constant pH, the photodegradation efficiency strongly increased as initial DXC concentration and MCM-41 loadings decreased. All data were well fitted using a pseudo first-order kinetic model. The effects of such variables on the DXC mineralization and the stability of the catalyst after UV irradiation were also studied and discussed. TiO2-MCM-41 resulted highly effective after three times reuse.