Organic solvent nanofiltration with Grignard functionalised ceramic nanofiltration membranes

In this paper the use of functionalised ceramic nanofiltration membranes in solvent filtration is described. The membranes were grafted using a novel method for surface modification based on Grignard chemistry. Commercially available 1 nm TiO2 membranes were differently functionalised with a series of alkyl groups (methyl, pentyl, octyl, dodecyl) in order to generate a more hydrophobic membrane surface. The properties of the modified membranes were examined by physico-chemical characterisation (contact angle measurements, micro-ATR/FTIR-spectroscopy) in addition to performance characterisation (flux measurements for solvents ranging from highly polar to non-polar, next to polyethylene glycol retentions in water and polystyrene retentions in acetone). All observations for modified membranes are consistent with the assumed partial replacement of the OH-groups on the membrane surface and the consequent amphiphilic character of the modified membrane surface. The retentions of modified and unmodified membranes in acetone confirm the recent findings in organic solvent nanofiltration (OSN): an increase in the hydrophobicity of the membrane leads to an increase in the retentions. A comparison with reference polymeric membranes shows that the newly developed membranes are a good alternative, having the advantage of the absence of effects of swelling. This new grafting technique for ceramic membranes allows to further explore solvent–membrane–solute interactions in OSN in a controlled way without the extra complexity of swelling.