Solar photocatalytic degradation of pesticides over TiO-rGO nanocomposites at pilot plant scale.

Two TiO-rGO nanocomposites were prepared by hydrothermal method from commercial TiO (P25 and Hombikat UV100, HBK). In both cases TiO nanoparticles appeared intimate and homogeneously distributed on rGO surface, but forming a dense network in P25-rGO nanocomposite, and a more open structure in HBK-rGO. Zeta potential and particle size distribution favored the ease of HBK-rGO nanocomposite to form stable suspensions. A comparative analysis of these two photocatalysts was performed on the pilot plant scale solar assisted photodegradation of a 200 μg·L or 5 mg·L mixture of persistent and biorecalcitrant pollutants in deionized water (methomyl, pyrimethanil, isoproturon and alachlor, all used as pesticides). Complete removal of pesticides was achieved, though faster with P25-rGO when O was the oxidant. However, the use of hydrogen peroxide (HO) dosage as oxidant speeded up pesticides removal, but HBK-rGO performance resulted much improved. Finally, at realistic very low concentrations of 200 μg·L, the complete removal of pesticides was achieved at very short times (<25 min), showing the efficiency of the synthetized TiO-rGO nanocomposites in this pilot-plat scale solar process to mitigate refractory and biorecalcitrant contaminants on effluents as a sustainable and efficient process.