PHOTOSYNTHETIC MEMBRANES - PART-67 - PHOTOMINERALIZATION OF N-ALKANOIC ACIDS IN AQUEOUS-SOLUTION BY PHOTOCATALYTIC MEMBRANES - INFLUENCE OFRADIATION POWER

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, polychromat ic, radiant power, in the absorption range of semiconductor, between 0 .10 and 4.36 W.cm(-1), using PHOTOPERM(R) CPP/313 membranes, concentri c with the lamp. The membranes contained immobilized 30 +/- 3 wt.% TiO 2, and, in parallel runs, 7 wt.% of a synergic mixture of tri(t-butyl) - and tri-(i-propyl) vanadate(V) as photocatalytic promoter. Stoichiom etric H2O2 was used or, in some of the runs, O-3, at saturation, as ox ygen suppliers. Disappearance of total organic carbon (TOC) was follow ed as a function of time. Quantum yields, Phi(0), calculated from init ial rates, followed an apparently Langmuirian function of initial conc entration, by which Phi(infinity) values at ''infinite'' concentration could be obtained Both Phi(0) and Phi(infinity) values were a functio n of absorbed power per unit length of lamp (and membrane) (W.cm(-1)). given the geometrical configuration of the photoreactor. Limiting Phi (infinity) values at 0.10-0.35 W.cm(-1) substantially coincide with th ose measured at 0.32 W.cm(-1) of monochromatic 254 nm radiation in pre vious work, for the same substrates. The kinetic model, already used s uccessfully in previous studies, to interpret photodegradation curves up to complete mineralization, is further substantiated. (C) 1998 Publ ished by Elsevier Science Ltd. All rights reserved.