Multi-stimuli activation of TiO2/α-alumina membranes for degradation of Methylene Blue

TiO2/α-Al2O3 porous membranes were prepared and tested under different stimuli including: UV and solar radiation, with or without H2O2 and by using Methylene Blue (MB) as indicator of the catalytic activity of the membranes. An ultrathin TiO2 layer was deposited on porous α-Al2O3 substrates through the combination of the sol-gel route and spin coating technique. Uniform TiO2 coverage onto the alumina membrane surface was achieved resulting in an increased pollutant adsorption responding to the crucial requirements of an optimal catalytic performance. The photoactivity of these functionalised membranes was proved in a Photocatalytic Membrane Reactor (PMR) monitoring the photodegradation of MB in water. Under UV irradiation, 80% of MB degradation was reached in 4 h, with the residual pollutant completely retained by the membrane, providing a pollutant-free permeate. Noteworthy, the TiO2/α-Al2O3 membranes displayed self-cleaning properties and have shown to be reusable in successive catalytic runs without reduction of their photocatalytic activity. Under irradiation (UV or solar light), the addition of H2O2 increased, as expected, the efficiency of MB degradation, but for the first time in dark conditions, a catalytic activity of a TiO2 coated membrane in presence of H2O2 was also demonstrated. Enhanced membrane performances were obtained under solar-light irradiation, where the synergic action of H2O2 together with the TiO2/α-Al2O3 photocatalytic activity allowed total MB degradation in only 40 min. The excellent performance of these TiO2/α-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. These findings demonstrate that these catalytic membranes possess a great potential for the sunlight-driven degradation of organic compounds, thus meeting the requirements of future environmental applications.