Generation of Free OHaq Radicals by Black Light Illumination of Degussa (Evonik) P25 TiO2 Aqueous Suspensions

Abstract

This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e.,• OH aq , formation, in black light illuminated Degussa P25 TiO 2 aerated suspensions in the pH range from 3 to 11. The • OH aq formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of • OH aq formation was estimated to be at the ~10 −2 level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the • OH aq production in the acidic pH range. It is suggested that • OH aq -radical formation in TiO 2 photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO 2 surfaces.

Impact of natural organic matter on the degradation of 2,4-dichlorophenoxy acetic acid in a fluidized bed photocatalytic reactor

“…At pH > pH zpc hydroxyl radicals can diffuse into the solution to produce Å OH bulk . In contrast, at acidic pH (pH 3) the diffusion rate is very low [30]. In addition, at pH 7 because of the limited adsorption, most of the decomposition is likely mediated by Å OH bulk .…”

Eight-lamp externally irradiated bench-scale photocatalytic reactor: Scale-up and performance prediction

“…Regarding the mathematical and kinetic scheme under consideration, adsorbed free radicals are assumed to be the ones mainly responsible for photocatalytic activity [22], Hanan and Bahnemann (2012). This is the case given that the probability of having a free radical adsorbed on the photocatalyst surface determines, among other factors, the rate at which adsorbed chemical species can be photodegraded.…”

“…These models are described in Section 3.4. Furthermore, after charge separation at the photocatalyst surface, adsorbed hydroxyl free radicals and desorbed aqueous hydroxyl free radicals, within the particle vicinity, are generated [22]. Through these hydroxyl radicals [21], a great number of photocatalytic reactions are made possible [29].…”

E. coli inactivation by visible light irradiation using a Fe–Cd/TiO 2 photocatalyst: Statistical analysis and optimization of operating parameters

“…Photocatalyst particles at pH lower than the PZC are charged positively and can induce electrostatic interactions with the bacteria (such as E. coli), being negatively charged at these pH values. Hence, a lower pH favors inactivation of E. coli [47][48][49][50][51].…”