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

[Display omitted] •The wettability of pure GO and TiO2/GO composite membranes are dependent on the thermal reduction temperature.•UV activation increases the surface energy and hydrophilicity of the TiO2/GO membranes.•Principal component analysis of FTIR data was used to identify surface changes of the TiO2/GO membranes after activation.•The zeta potential of the TiO2/GO membrane surface decreases significantly after UV activation. 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.