Multistimuli Activation of TiO2/?-alumina membranes for degradation of methylene blue

TiO2/?-Al2O3 porous membranes were prepared and tested under different stimuli, including UV and simulated solar irradiation, with or without the addition of hydrogen peroxide (H2O2), and by using Methylene Blue (MB) as a model organic pollutant to probe the oxidative catalytic activity of the membranes. An ultrathin TiO2 layer was coated on porous ?- Al2O3 substrates by combining a sol-gel process with a spin coating technique. Uniform TiO2-coated alumina surfaces were obtained, which resulted in an increased pollutant adsorption on the semiconductor surface, a crucial requirement for achieving enhanced catalytic performances. The photocatalytic activity of these functionalized membranes was tested in a photocatalytic membrane reactor (PMR), by monitoring the photodegradation of MB in water. Under UV irradiation, 80% of MB degradation was achieved in 4 h. Concomitantly, the residual pollutant is completely retained by the membrane in the feed solution, and a pollutant-free permeate can be recovered. Noteworthily, the TiO2/?-Al2O3 membranes displayed self-cleaning properties allowing their reuse in successive catalytic runs without reduction of their photocatalytic activity. Under irradiation (UV or solar light), the addition of H2O2 in the feed solution increased the efficiency of MB degradation. Furthermore, and for the first time, the ability of a TiO2 coated membrane to perform catalytic oxidation in the presence of H2O2 was demonstrated in dark conditions. Enhanced membrane performances were obtained under solar light irradiation, expecially when the TiO2/?-Al2O3 photocatalytic activity was synergically combined with the H2O2-assisted oxidative reaction, allowing the complete MB degradation in only 40 min. The excellent performance of these TiO2/?-Al2O3 membranes under solar light was mainly ascribed to the absorption and in situ dye-sensitization of the thin TiO2 layer, allowing the visible photon harvesting, as well as to the occurrence of lattice disorder and defects. These findings demonstrate that these catalytic membranes possess a great potential for the sunlight-driven degradation of organic compounds, thus meeting the requirements for future environmental applications.