Photocatalytic Oxidation of Organic Micro-Pollutants: Pilot Plant Investigation and Mechanistic Aspects of the Degradation Reaction

An innovative pilot plant based on UVB and TiO2 (Anatase) allowed for photocatalytic degradation of organic micro-pollutants. The catalyst was immobilized onto a channel through which the solution containing a target molecule (methylene blue, MB) was re-circulated. Due to the cationic nature of the MB substrate, the adsorption reaction onto the catalyst surface provided a significant contribution to the overall degradation mechanism due to the negatively charged surface at neutral pH (TiO2 pHzpc=6.8). The influence of the initial MB concentration was investigated in the range 0.3-2.0mg/L with the Langmuir-Hinshelwood (LH) model showing good data correlations at concentrations up to 0.7 mg/L, whereas at higher concentrations a pure zero-order (catalytic) kinetic trend was observed. Flow rate of the re-circulating solution sensibly influenced kinetics after the larger volumes of liquid exposed to UVB=TiO2 and to the better oxygen saturation in the liquid phase. UV-vis and HPLC-MS=MS experimental determinations allowed for identification of MB residual concentration and by-products.