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 recirculated. 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 0.3-2.0 mgL-1 with the Langmuir–Hinshelwood model showing good data correlations at concentrations up to 0.7 mgL-1, whereas at higher concentrations a pure zero-order (catalytic) kinetic trend was observed. Flow-rate of the recirculating 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.