Noble metal and sulfuric acid modified TiO₂ photocatalysts: Mineralization of organophosphorous compounds

Photocatalytic oxidation by oxygen of air in water suspension of TiO ₂-based catalysts was carried out for dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) - simulants of warfare agents. Active photocatalysts were prepared via surface modification of standard photocatalyst Degussa P25 with platinum and palladium. The developed catalysts were about three-fold more active than traditionally best photocatalyst Degussa P25. Kinetic curves of DMMP oxidation on TiO₂ and Pt/TiO₂ are well approximated by the Langmuir-Hinshelwood model with competitive adsorption of oxygen and organophosphorus compound. The increase of activity of Pt/TiO ₂ is linked with higher oxygen adsorption constant or reaction rate coefficient. Photocatalytic oxidation can be scaled up to a larger reactor with the same reaction rates expressed as mmol l^-1 min^-1 in mineralization of DMMP. The batch recirculating reactor with total volume 3 l utilizes photocatalyst deposited over porous support and demonstrated higher oxidation rate and catalyst stability compared to suspended photocatalyst. Main criteria for mass-transfer process in the batch recirculating reactor were calculated to understand how concentration cross gradient depends on flow rate. The concentration of oxygen in reaction mixture changed with the stirring or recirculation rate and exerts strong influence on the oxidation rate.