Photocatalytic reduction of vanadium(V) in TiO₂ suspension: chemometric optimization and application to wastewaters.

The photocatalytic reduction of V(V) to V(IV) over TiO₂ in aqueous solution is presented. Experiments were undertaken on air-equilibrated water spiked with V(V) (0.6-20 mgL(-1)), under UV-A or solar light. A chemometric study was performed to optimize the reduction yield, by considering the most important variables recognized to affect the photocatalytic process. Among pH, irradiation time and catalyst concentration, the two latter proved to be determinant. The good yields achieved (up to 98%), along with the possibility of working in aerated solution, make this procedure simple, rapid and efficient. Although a deep insight on the photochemical mechanisms was beyond our scope, the role of electron donors was investigated, proving the efficiency of 2-propanol, citric acid and formic acid in the acceleration and improvement of V(V) conversion. After irradiation, total vanadium and aqueous V(V) and V(IV) after solid-phase separation on Chelex-100 resin, were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). The procedure was applied to contaminated wastewaters, combining remediation and possible vanadium recovery as V(IV).