The influence of Fe(III) speciation on supported TiO2 efficiency: example of monuron photocatalytic degradation

The degradation of herbicide monuron (initial concentration 5×10−5 M) in plate photoreactor with laminar flow of the solution using heterogeneous (TiO2) and/or homogeneous photocatalyst (Fe(ClO4)3) was investigated. For the rate of photoinduced degradation with Fe(III) aquacomplexes, the initial concentration of monomer Fe(OH)2+, which is the most photocatalytically active form of Fe(III), is crucial. The degradation rate for combination of both photocatalysts is higher than the sum of the rates for separately taken single catalysts. This is caused not only by the addition of the two effects but also by the fact that Fe(III) acts as scavanger of electrons photogenerated in TiO2 particles thus let down hole-electron recombination. Fe(OH)2+ appears to be the most photoactive trap for electrons.