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.
Highlights
During the last few years, the studies on the fate and transformation of pharmaceutical compounds are gaining scientific attention because of their continuous occurrence and increasing concentrations in different types of water, such as wastewater, surface water, ground water and even drinking water [1,2,3,4,5]
The major degradation pathways for g-C3 N4 include decarboxylation and subsequent oxidation, hydroxylation, and cleavage of C–N bond, while for TiO2 cyclization, transformation products (TPs) are abundant and the hydroxylation occurs in the first stage products
The photocatalytic degradation pathways of the valsartan pharmaceutical were studied in the presence of g-C3 N4 and TiO2 catalysts using LC-MS-Orbitrap high resolution accurate mass spectrometry
Summary
During the last few years, the studies on the fate and transformation of pharmaceutical compounds are gaining scientific attention because of their continuous occurrence and increasing concentrations in different types of water, such as wastewater, surface water, ground water and even drinking water [1,2,3,4,5]. G-C3 N4 , an alternative and promising polymeric semiconductor nanostructure demonstrates high thermal (up to 600 °C, in air) and chemical stability in photocatalyst with visible light response (band gap 2.7 eV), has gained attention in recent acidic and basic media due to its s-triazinic structure, while it is insoluble in common years. This metal-free catalyst with a two-dimensional (2D) nanostructure demonstrates solvents (ethanol, DMF, water) [15,16]. Holes by two(hdifferent oxidant species, OH radicals and positive holes (h+ )
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