Optimal configuration of a photocatalytic lab-reactor by using immobilized nanostructured TiO2

In this study, TiO2 nanoparticles (NPs) and glass balls coated by an N-doped TiO2 nanostructured layer were used for photocatalytic degradation of organic compounds in aqueous solutions. Preliminary batch photocatalytic experiments were carried out on the degradation of methylene blue (MB) in aqueous solutions by using two types of reactor: the first one was a cylindrical vessels fitted with a mechanical stirrer where the TiO2 NPs were suspended, whereas the second one consisted of a rectangular box with the glass spheres located at the bottom. For an initial MB concentration of 7 ppm a conversion of around 50 % was detected after 120 min for both the cases. An UV lamp was used for the light irradiation. Then, the catalytic effectiveness of the coated glass balls was checked on a system of industrial interest: the reduction of the organic compounds in an olive mill wastewater (OMW) stream. In this case a more performing configuration of the reactor was adopted by positioning the glass balls over a wire and feeding an air stream under the wire itself, moreover a visible light lamp was used alternatively to the UV lamp. For an initial COD of the OMW equal to 1100 mg/l, a conversion of 57 % was obtained after 120 minutes by using the UV lamp and a conversion of 99% with the use of a visible lamp. This latter result demonstrated the possibility of a strong purification of OMW by using the developed N-doped immobilized TiO2 catalyst under visible light.