Heterogeneous photocatalytic reduction of ferrate(VI) in UV-irradiated titania suspensions: Role in enhancing destruction of nitrogen-containing pollutants

The results of the heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated TiO2 suspensions are presented and suggest indirect observation of the formation of Fe(V) by the photoreduction of Fe(VI) with e(cb)(-) at TiO2 surfaces. Because Fe(V) selectively and rapidly oxidizes low reactivity pollutants with the production of the non-toxic by-product, Fe(III), the photocatalytic reduction of Fe(VI) has a role in pollution remediation processes. The experiments were conducted as a function of TiO2 suspension concentrations, Fe(VI) concentrations, and pH in basic media. The initial rate of Fe(VI) reduction gave a fractional order with respect to initial Fe(VI) concentrations and adheres to simple Langmuir-Hinshelwood kinetics. Results suggest that the surface reaction (Fe(VI) + (-)(ecb) --> Fe(V)) is the rate-controlling step. The photocatalytic reduction of Fe(VI) in the presence of less reactive nitrogen-containing species (ammonia, cyanate, and fulvic acid) were also investigated. Enhancement in the rate of Fe(VI) reduction was observed. A reaction scheme involving Fe(V) as an intermediate is presented which explains the faster photocatalytic oxidation of pollutants in the presence of Fe(VI).