Photocatalytic Degradation Pathways of the Valsartan Drug by TiO2 and g-C3N4 Catalysts

Abstract

The photocatalytic degradation of the valsartan (VLS) pharmaceutical using TiO2 and g-C3N4 catalysts under simulated solar light is studied in this paper by high-resolution Orbitrap mass spectrometry. •OH radicals were the major oxidant species for the degradation of valsartan using TiO2, while positive holes (h+), followed by a much lesser amount of •OH radicals, were the major species in the case of g-C3N4. Valsartan degradation followed first order kinetics by both catalysts with TiO2 being the catalyst with the better photocatalytic efficiency. The transformation products (TPs) and their evolution profiles are identified and monitored, respectively, by means of LC-HRMS. Based on TPs identification, the degradation mechanisms are discussed. The major degradation pathways for g-C3N4 include decarboxylation and subsequent oxidation, hydroxylation, and cleavage of C–N bond, while for TiO2 cyclization, TPs are abundant and the hydroxylation occurs in the first stage products. The study highlights the complex nature of TPs formed during such processes, the different mechanisms involved and the necessity for the identification of TPs for the assessment of the treatment and the tracking of such TPs in different environmental compartments.