Degradation of diphenhydramine pharmaceutical in aqueous solutions by using two highly active TiO2 photocatalysts: operating parameters and photocatalytic mechanism

Abstract

In the present work the efficiency of a new TiO2 catalyst (ECT), synthesized by means of an optimized sol–gel method, is studied for degradation of an important pharmaceutical water pollutant, diphenhydramine (DP). Its activity is compared to P25, the benchmark catalyst, produced by Evonik Degussa Corporation, under different catalyst loadings (up to 2.00 g L−1) and initial solution pH (3.0–11.0). The results show that DP is very stable under non-catalytic conditions but complete degradation and considerable mineralization (ca. 60–70%) under near UV to visible irradiation (∼50 mW cm−2) can be achieved in 60 min by selecting the appropriate TiO2 loading. ECT is significantly more active than the benchmark catalyst for loadings higher than 1.00 g L−1 while the pseudo-first order rate constant increased with the initial solution pH from 3.0 to 11.0. The highest rate constant was obtained with ECT at pH 11 (173 × 10−3 min−1 against 116 × 10−3 min−1 for P25). Scavenger agents were used as a diagnostic tool for the analysis of the photocatalytic mechanism and it was possible to prove that holes were crucial active species participating in the photocatalytic mechanism as well as that ECT has a higher availability than P25 to generate reactive radicals, such as hydroxyl (HO•) and hydroperoxyl (HOO•) radicals.