Comparing potentiostatic and galvanostatic anodization of titanium membranes for hybrid photocatalytic/microfiltration processes

Hybrid photocatalysis/membrane processes constitute promising alternatives for water and wastewater treatment because they combine the efficiencies of filtration membranes technology and the oxidative effect of the photocatalytic process, increasing the lifetime of the membranes. The main challenge of these systems is the incorporation of the titanium dioxide (TiO2) catalyst without altering the filtration properties of the membrane and the photocatalytic activity of the catalyst. One way to achieve this goal is generating the TiO2 layer by direct anodization of titanium supports under controlled conditions to form titanium dioxide nanotubes (TiO2-NTs). This work reports the development of novel photocatalytic titanium membranes based on the formation of TiO2-NT arrays by anodization under both potentiostatic and galvanostatic conditions, and the scaling-up of the most promising systems to operational membrane photoreactors. The results demonstrated that the galvanostatic method displays more controlled tuneability to obtain NTs formation than the potentiostatic method on porous surfaces. However, despite the formation of TiO2-NTs structures, the observed photocatalytic activity is lower than that exhibited by TiO2 nanoparticles deposited directly on the membrane, although in this case the transmembrane pressure is significantly higher, and therefore the operational pumping costs are greater. Synergistic effects of photocatalysis and microfiltration are clearly demonstrated in the application of the hybrid system to the removal of bacteria for water disinfection processes, showing a significant improvement in the inactivation of E. coli bacteria in water with respect to the bare membrane.