UV-VIS photocatalytic degradation of cyclophosphamide on nitrogen doped TiO2 thin film. Kinetics and possible degradation pathway

Abstract

Cyclophosphamide (CP) is a cytostatic drug prescribed on a large scale, which proved to induce a toxic effect on ecosystems and cannot be removed by conventional wastewater treatment processes. Therefore, there is a need to test advanced degradation processes for its removal from wastewater discharges. CP photocatalytic degradation via UV-VIS irradiation was studied using a Nitrogen-doped TiO2 catalyst. The catalyst was synthesized as a thin film deposited on a glass substrate under the nitrogen atmosphere technique. The influence of N2 flow rate and annealing temperature on the CP degradation efficiency was investigated and the best photocatalytic activity was obtained for catalyst with 1.8 %wt nitrogen content, synthesized at N2 flow rate=10 sccm, annealed at 550 oC for 1 hour. Its use assures the CP degradation with a pseudo-first order rate constant of 5.262 x 10-4 s-1 and an efficiency of 98 % for an irradiation time of 120. Based on the obtained experimental results in the presence of various scavengers it was found that superoxide radicals are representing the main oxidizing reactive species involved in CP degradation, but the contribution of free hydroxyl radicals from bulk solution is also possible. Degradation intermediates were identified using LC-MS and a possible degradation pathway consisting of three conversion routes was proposed.