Kinetic study of photocatalytic degradation of the emerging contaminant bisphenol A using N–TiO2 in visible light: a study of the significance of dissolved oxygen

Abstract

This study compares the tracking of bisphenol A (BPA) degradation by three analytical techniques: liquid chromatography mass spectrometry (HPLC–MS), ultraviolet/visible (UV–Vis) spectroscopy and dissolved oxygen (DO) content. In each evaluation method, the photochemical behavior of TiO2 and N–TiO2 under visible light confirmed the relationship between the adsorption and photodegradation processes, with the reaction analysis indicating the possibility of two photocatalytic mechanisms: conventional photocatalyzed radical oxidation and lattice oxygen driven oxidation. The first one concerns HPLC, where the average half-lives (t1/2) were 38 min (5% N–TiO2), 60 min (1% N–TiO2) and 64 min (TiO2), these values vary in 12% if compared with the values obtained by UV–Vis spectroscopy. The second mechanism showed a decrease in the initial concentration by more than 50% (8 mg L−1) after 3 h. The solution of doped photocatalysts is tracked best by DO measurement. The results presented here confirm that the efficiency of photocatalytic oxidation (EPO) of a reaction is highly related to the DO content, given that dissolved O2 proactively causes the release of radicals on the surface of excited materials under the action of visible light, thus increasing the BPA degradation rate. The quantum yield of BPA disappearance was below 0.1 for all the materials.