MATHEMATICAL-MODELING OF PHOTOMINERALIZATION OF PHENOLS IN AQUEOUS-SOLUTION, BY PHOTOCATALYTIC MEMBRANES IMMOBILIZING TITANIUM-DIOXIDE

Photomineralization of phenol, 2,6-dimethyl phenol, 1,2,3-benzenetriol , 4-chloro phenol, and 2,4-dichloro phenol, in 9.9x10(-3) - 5.6x10(-5) M aqueous solutions, in the presence of stoichiometric hydrogen perox ide, was studied, using PHOTOPERM(R) CPP/313 membranes containing immo bilized 30+/-3 wt.% TiO2, by analysis of total organic carbon (TOC) co ntent. With phenol and 2,6-dimethyl phenol also the rate of disappeara nce of the substrate molecules was measured fluorimetrically. Polychro matic or monochromatic irradiation was carried out (radiant power in t he absorption range 145 and 8 W respectively). The initial rate of pho todegradation was studied as a function of the initial concentration o f substrate using the linearized form of the Langmuir-Hinshelwood equa tion, from which the rate constants k and apparent adsorption constant s K were evaluated. These parameters, which are unable to fit the whol e photomineralization kinetic curves, were employed to optimize, by nu merical integration, a kinetic model which considers appearance and di sappearance of all intermediates, as if they were represented by a hyp othetical single molecule, mediating all of them. By this way, two cou ples of parameters, K-1 and K-1, k(2) and K-2 were obtained, relative to the two successive steps of the model (substrate disappearance and mineralization), able to reproduce satisfactorily well the whole kinet ics. Experimental data, as compared to modelling, show evidence of a m ain rate determining path, and of another, minor but not unsignificant , parallel path leading to a faster mineralization. Mean quantum yield s of organic carbon mineralization, calculated by k(2) parameters, rea ch 10-20% of the maximum allowable efficiencies. Copyright (C) 1996 El sevier Science Ltd