Photomineralization of n-alkanoic acids in aqueous solution by photocatalytic membranes. Influence of radiation power

Abstract

The TiO2-mediated photomineralization of 8–1000 ppm of methanoic acid, of 6–100 ppm of ethanoic acid. of 6–180 ppm of propanoic acid, and of 6–90 ppm of n-decanoic acid in aqueous solutions was studied at 308 ± 2 K, by a high pressure mercury arc lamp with variable. polychromatic, radiant power. in the absorption range of semiconductor, between 0.10 and 4.36 W.cm−1 , using PHOTOPERM® CPP/313 membranes. concentric with the lamp. The membranes contained immobilized 30±3 wt.% TiO2. and, in parallel runs, 7 wt.% of a synergic mixture of tri(t-butyl)- and tri-(i-propyl) vanadate(V) as photocatalytic promoter. Stoichiometric H2O2 was used or, in some of the runs, O3, at saturation, as oxygen suppliers. Disappearance of total organic carbon (TOC) was followed as a function of time. Quantum yields, θ0, calculated from initial rates. followed an apparently Langmuirian function of initial concentration, by which θ∞ values at “infinite” concentration could be obtained. Both θ0 and θ∞ values were a function of absorbed power per unit length of lamp (and membrane) (W.cm1), given the geometrical configuration of the photoreactor. Limiting θ∞ values at 0.10–0.35 W.cm−1 substantially coincide with those measured at 0.32 W.cm−1 of monochromatic 254 nm radiation in previous work, for the same substrates. The kinetic model, already used successfully in previous studies, to interpret photodegradation curves up to complete mineralization, is further substantiated.