Impact of TiO 2 nanoparticles on morphology and performance of crosslinked polyimide organic solvent nanofiltration (OSN) membranes

Abstract

Chemically crosslinked polyimide organic–inorganic composite nanofiltration membranes suitable for application in harsh organic solvents were successfully prepared by phase inversion of dope solutions. TiO 2 nanoparticles were dispersed in these dope solutions, comprising polyimide (PI) in N, N-dimethylformamide/1,4-dioxane. The impact of TiO 2 on the resulting PI membranes was investigated using SEM, TGA, water contact angle, dope viscosity measurements and mechanical strength. The presence of TiO 2 nanoparticles within the membrane matrix was proved by the detection of a peak characteristic of TiO 2 in the WAXS pattern. SEM pictures of the cross-section of the PI/TiO 2 membranes showed dramatically changed morphology compared to reference membranes with no TiO 2 addition. Macrovoids present in reference membranes were suppressed by increasing loading of TiO 2 nanoparticles, and eventually disappeared completely at a TiO 2 loading above 3 wt.%. Decreasing water contact angle and an increase in ethanol flux indicated that hydrophilicity increased as nanoparticle loading increased. The effect of TiO 2 on the functional performance of the membranes was evaluated by measuring flux and rejection using cross-flow filtration. Perhaps surprisingly, the presence of TiO 2 improved the compaction resistance of the membranes, whereas rejection and steady flux were almost unaltered.