Photocatalytic mineralisation of humic acids using TiO₂ modified by tungsten dioxide/ hydrogen peroxide

TiO₂ of anatase structure was modified by tungsten dioxide and H₂O₂ in order to obtain WO₃-TiO₂ photocatalyst with enhanced photocatalytic activity under both, UV and artificial solar light irradiations. WO₂ was dissolved in 30% H₂O₂ and mixed with TiO₂ in a vacuum evaporator at 70°C. Such modified TiO₂ was dried and then calcinated at 400 and 600°C.

The prepared samples and unmodified TiO₂ were used for the photocatalytic decomposition of humic acids (Leonardite standard IHSS) in the aqueous solution under irradiations of both, UV and artificial solar light. Modification of TiO₂ with tungsten dioxide and H₂O₂ improved separation of free carriers in TiO₂ which resulted in the increase of OH radicals formation. Calcination caused an increase of anatase crystals and higher yield in OH radicals. The uncalcined samples showed high abilities for the adsorption of HA. Combination of adsorption abilities and photocatalytic activity of photocatalyst caused that the uncalcined TiO₂ modified with WO₂/H₂O₂ showed the shortest time of HA mineralisation. The mineralisation of HA under the artificial solar light was much lower than under the UV. It was proved that, although OH radicals are powerful in the decomposition of HA, adsorption can facilitate the contact of the adsorbed molecules with the photocatalyst surface and accelerate their photocatalytic decomposition.