Investigation of the wettability changes of graphene oxide/TiO2 Membranes upon UV activation

One of the major limitations in the application of membrane filtration is fouling resulting in a decreased flux. One solution to this limitation is development of antifouling or self-cleaning membranes based on photocatalysis. Graphene oxide has recently attracted a lot of attention because of its excellent membrane properties such as high permeability and selectivity of components in both liquid and gas phase [1,2]. Moreover GO/TiO2 composite membranes have been produced which display promising results in respect to obtain self-cleaning properties [3,4].
In this study the changes in surface energy and zeta potential of photoactivated TiO2/GO composite membranes is investigated. A full factorial experimental design was used to investigate the influence of TiO2 loading, reduction temperature and UV activation on the surface energy and zeta-potential of TiO2/GO membranes. Moreover multivariate data analysis of FTIR data was used to relate the changes in wettability and zeta-potential after UV irradiation to changes in the surface functional groups of the TiO2/GO membranes.
The hydrophilicity of pure GO and TiO2/GO composite membranes (TiO2 load 6.7 - 13.4 w/w%) was found to be 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 FT-IR data combined with TGA and DSC analysis suggest that the change in surface energy is due to a decrease in carboxylic acid and hydroxyl groups when reduced at 160 °C. The most significant change in surface energy was observed after UV activation of the TiO2/GO membranes. The PCA model based on the FTIR data before and after UV activation suggests that the increase in surface energy is caused by an increase in OH groups on the TiO2 after activation of the TiO2/GO membrane. In addition an increase in TiO2 loading was found to significantly increase the surface energy of the membranes. The TiO2/GO membranes with high TiO2 loading provided faster hydrophilic conversion rates.
The Zeta potential of the membrane surface changes significantly after UV activation resulting in more negative values, which enhance the electrostatic repulsion of negatively, charged fouling components.