Photocatalytic degradation of metoprolol tartrate in suspensions of two TiO 2-based photocatalysts with different surface area. Identification of intermediates and proposal of degradation pathways

Abstract

This study investigates the efficiency of the photocatalytic degradation of metoprolol tartrate (MET), a widely used β 1-blocker, in TiO 2 suspensions of Wackherr's " Oxyde de titane standard" and Degussa P25. The study encompasses transformation kinetics and efficiency, identification of intermediates and reaction pathways. In the investigated range of initial concentrations (0.01-0.1mM), the photocatalytic degradation of MET in the first stage of the reaction followed approximately a pseudo-first order kinetics. The TiO 2 Wackherr induced a significantly faster MET degradation compared to TiO 2 Degussa P25 when relatively high substrate concentrations were used. By examining the effect of ethanol as a scavenger of hydroxyl radicals (OH), it was shown that the reaction with OH played the main role in the photocatalytic degradation of MET. After 240min of irradiation the reaction intermediates were almost completely mineralized to CO 2 and H 2O, while the nitrogen was predominantly present as NH4+. Reaction intermediates were studied in detail and a number of them were identified using LC-MS/MS (ESI+), which allowed the proposal of a tentative pathway for the photocatalytic transformation of MET as a function of the TiO 2 specimen.