Aqueous photocatalytic oxidation of lignin: The influence of mineral admixtures

The photocatalytic oxidation (PCO) of UV-irradiated aqueous solutions containing lignin on TiO2 was studied for the influence of ferrous ions. The addition of Fe2+, up to 2.8mg L-1, to the acidic lignin solution leads to the drastic, for about 25%, increase in PCO efficiency. A further increase in ferrous ion concentration results in a decrease in PCO efficiency of lignin. The maximum PCO efficiency, up to 9.2 mg W(-1)h(-1), was observed in neutral and slightly basic media: the oxidation mechanism with OH-radicals seems to prevail. Also, the difference in the PCO performance with a different attachment mode of titanium dioxide on the catalyst support was observed. Sprayed catalyst exhibited 1.5 times higher efficiency than the one attached by submersion, although sprayed one was easily resuspended in acidic lignin solutions. The efficiency of the N-doped photocatalyst active in visible light was observed to be negligible with lignin. Copyright (c) 2007.