Supported Vanadium Oxide as a Photocatalyst in the Liquid Phase: Dissolution Studies and Selective Laser Excitation

Supported vanadium oxide species are tested for their capability to perform photocatalytic methyl orange degradation in the aqueous phase. Excitation is performed with a frequency-tripled (λ=270 nm) or frequency-doubled (λ=405 nm) Ti:sapphire laser in a newly designed 15 ml photoreactor. Photocatalytic activity in dye degradation is only observed at 270 nm excitation, indicating that larger vanadium oxide structures (V₂O₅ nanoparticles, decavanadates) are either not present in sufficient quantities, or not active in the reaction. Reference experiments exclude pure photodegradation of the dye. It is found that a major part of the supported vanadium oxide species becomes detached from the silica support, and a very small fraction detaches from alumina. Considerations of the aqueous phase chemistry of dissolved vanadate ions allow to identify the formed dissolved species to be predominantly H₂VO₄⁻ ions. These doubly protonated monovanadates are the main active species in the photocatalytic reaction, together with small anchored species on alumina.