High performance in-situ tuned self-doped polyaniline (PANI) membranes for organic solvent (nano)filtration

Cross-linked polyaniline (PANI) membranes are attractive for organic solvent nanofiltration (OSN). However, inadequate tuneability to cover the full nanofiltration (NF) separation range, prolonged post-treatment cross-linking using hazardous organic chemicals and poor permeance limit their widespread application. This work introduces a new strategy to tune the transport properties of PANI membranes to suit the rejection spectrum of NF membranes without compromising permeance. Incorporating different molecular weight organic acids, metanilic acid (MA) and poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), facilitated cross-linking during polymer precipitation at different aqueous coagulation bath acidic strength using non-solvent induced phase separation (NIPS). Static ageing tests for PANI membranes immersed in tetrahydrofuran (THF) for 30 days showed no physical or chemical deterioration. All membranes were stable during long-term dynamic crossflow filtration tests over 250 h with sequential feed of methanol, acetonitrile and THF. THF permeance was 2.1–16.4 L m−2 h−1 bar−1 with apparent molecular weight cut off (MWCO) between 250 and 1000 g mol−1. PAMPSA doped membranes were successfully cross-linked but required wet annealing post-treatment to obtain membranes in NF range. The MA doped membranes surpassed the performance of cross-linked PANI membranes with glutaraldehyde (organic cross-linker) showing a 2.5 times higher permeance with better rejection. In comparison to commercial polyimide membranes, PANI membranes prepared in coagulation bath ≥0.5 M HCl(aq) were stable in N,N-dimethylformamide (DMF) whereas the former suffered complete damage. This work represents a simplified technique to in-situ optimise permselective properties of OSN self-doped PANI membranes for various applications in food, pharmaceutical and petrochemical industries.