Investigation of surface energy, wettability and zeta potential of titanium dioxide/graphene oxide membranes

This research aims to study the wettability and zeta potential of photoactive TiO₂/GO composite membranes. Full factorial design was utilized for the investigation of the influence of TiO₂ content, reduction temperature and UV activation on the surface energy and zeta-potential of TiO₂/GO composite membranes. Multivariate data analysis of FTIR data was used to correlate the changes in wettability and zeta-potential after UV irradiation to changes in surface functional groups of the TiO₂/GO membranes. The hydrophilic properties of pure GO (D) and TiO₂/GO composite membranes (A, B, and C) is highly dependent on reduction temperature; membranes reduced at 140 °C have significantly higher surface energy than membranes reduced at 160 °C. Principal component analysis (PCA) of Fourier transformation infrared spectroscopy (FT-IR) data, thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) analysis shows that the change in surface energy was a result of loss of carboxylic acid and hydroxyl groups when reduced at 160 °C. The largest change in surface energy was observed after UV activation of the TiO₂/GO membranes. From the PCA model the increase in surface energy is caused by an increase in OH groups on the TiO₂ after activation of the TiO₂/GO membrane. Moreover higher TiO₂ content was found to significantly increase the surface energy of the membranes. TiO₂/GO membranes with higher TiO₂ contents showed faster hydrophilic conversion rates. In addition the Zeta potential of the membranes changes significantly resulting in more negative zeta potentials after UV activation which enhances the electrostatic repulsion of negatively charged fouling components. The zeta potential of the individual TiO₂/GO membranes was found to be almost constant in the pH interval 4–9.