Degradation of organophosphorus flame retardant tris (1-chloro-2-propyl) phosphate (TCPP) by visible light N,S-codoped TiO2 photocatalysts

Abstract N and N,S co-doped TiO 2 catalysts were prepared by a simple sol–gel method and were characterized by various techniques such as X-ray diffraction, scanning electron microscopy, UV–vis spectroscopy, porosimetry and particle size distribution. The photocatalytic efficiency of the prepared catalysts was evaluated for the degradation of organophosphorus flame retardant TCPP in aqueous solutions at environmental relevant concentrations under UV–vis and visible light irradiation. All the prepared N and N,S doped catalysts showed lowered crystallite size and higher visible-light response compared to the undoped TiO 2 catalyst. An increased surface acidity was observed for N,S co-doped catalysts as a result of surface sulfate species which play a crucial role in the photocatalytic performance. N-doped TiO 2 was found to be the most photoactive catalyst for the removal of TCPP, under UV–vis irradiation. Among N,S co-doped TiO 2 catalysts, the one prepared with equimolar Ti:N,S ratio showed the higher performance for the removal of TCPP under both UV–vis and visible irradiation. Its higher activity was attributed to the higher surface area, larger pore volume, well-crystallized anatase and red shift in light absorption. Under visible light irradiation the degradation kinetics of TCPP were slower than under UV–vis irradiation due probably to reduced production of hydroxyl radicals.