PHOTOMINERALIZATION OF N-ALKANOIC ACIDS IN AQUEOUS-SOLUTION BY PHOTOCATALYTIC MEMBRANES - INFLUENCE OF TRIALKYL VANADATES AS CATALYTIC PROMOTERS OF IMMOBILIZED TITANIUM-DIOXIDE

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 296 /- 2 K or 308 +/- 2 K, with low and high pressure mercury are lamps (r adiant power in the absorption range 8 and 145 W respectively), using PHOTOPERM(R) CPP/313 membranes containing 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. Stoichiome tric H2O2 was used or, in some of the runs, O-3, at saturation, as oxy gen suppliers. Disappearance of total organic carbon (TOC) was followe d as a function of time. To fit kinetic curves up to complete photomin eralization, a kinetic model was employed, already used successfully i n previous studies, which considers appearance and disappearance of al l intermediates, as if they were represented by a hypothetical single molecule, mediating all of them. The photocatalytic activity of trialk yl vanadates was evaluated from quantum yields at ''infinite'' concent ration, with respect to the maximum allowable efficiencies. When using O-3, a dark catalysis effect clearly appeared towards intermediate sp ecies produced during the photocatalysed degradation. (C) 1997 Elsevie r Science Ltd.