INHIBITION OF THE ADSORPTION AND PHOTOCATALYTIC DEGRADATION OF AN ORGANIC CONTAMINANT IN AN AQUEOUS SUSPENSION OF TIO2 BY INORGANIC-IONS

The effect of the inhibition of various adsorbed inorganic ions on the adsorption of dichloroethane (DCE) in a titanium dioxide aqueous susp ension was studied. The adsorption of the ions was competitive with th at of DCE and the adsorption kinetic constant k(a) varied only slightl y around a value of 0.08 min(-1). The kinetics of adsorption were cont rolled by DCE mass transfer, since the ion mass transfer was much more rapid. The affinity of the ions for TiO2 and the competition with DCE for adsorption were in the order: Cl- <NO3- < [HCO3-, CO32-] < SO42- < [H2PO4-, HPO42-]. The Langmuir model of adsorption was unsatisfactor y for the whole set of experiments, thus suggesting a non-uniform surf ace. The photodegradation occurred on the surface according to an appa rent Langmuir-Hinshelwood mechanism, and the inhibition of the ions fo r this reaction was in the order: NO3- < Cl- < HCO3-, CO32- < SO42- < H2PO4-, HPO42-. The effect of inhibition on the photocatalytic degrada tion was about half that on the adsorption of DCE, which could be attr ibuted to the surface heterogeneity and/or to a mass transfer phenomen on. (C) 1997 Elsevier Science S.A.