In situ growth and crystallization of TiO2 on polymeric membranes for the photocatalytic degradation of diclofenac and 17α-ethinylestradiol

TiO2 in situ growth on three commercial membranes (polysulfone - PS, polyvinylidene fluoride - PVDF and polytetrafluoroethylene - PTFE) and its hydrothermal post-crystallization to transform TiO2 into a photocatalytically-active phase, were investigated under mild synthesis conditions to preserve the textural properties of the supports. The membranes were successfully prepared and characterized by scanning electron microscopy, thermogravimetry analysis, N2 physisorption, X-ray diffraction, and water contact angle measurements, among other techniques. Membrane supports with a more opened porosity and high hydrophilicity allowed to enhance the content and distribution of the anatase TiO2 nanoparticles on the membrane surface. The efficiency and the permeate flux of the developed membranes were investigated to simultaneously remove diclofenac (DCF) and 17 alpha-ethinylestradiol (EE2) from water by adsorption and UV-LED (light-emitting diode) photocatalysis under continuous recirculating mode. All TiO2 membranes achieved removal efficiencies above 90% for both contaminants, EE2 being always preferentially adsorbed over DCF due to electrostatic repulsions between the DCF molecules and the surface of these membranes. The permeate flux of TiO2 membranes was enhanced after UV-LED exposure as a consequence of the degradation of the contaminants adsorbed on the membrane surface during the dark phase. Moreover, the stability of TiO2 nanoparticles on these membranes was studied by static tests under sonication and several consecutive reaction cycles. The TiO2 membrane prepared with PVDF was the most stable, also presenting a high photocatalytic activity.