Conjugated polyaniline derivative membranes enable ultrafast nanofiltration and organic-solvent nanofiltration

The separation and recovery of small molecules from aqueous or organic solvents via engineered membranes are facing huge challenge. Herein, conjugated polyaniline derivative membranes were designed through the polymerization of ammonia-rich monomers and post-crosslinking treatment, exhibiting superior performance for ultrafast nanofiltration (NF) and organic-solvent nanofiltration (OSNF). Specifically, p-phenylenediamine (pPD), as one of aniline derivative with conjugate structure was in-situ growth onto porous substrate to fabricate PpPD/HPAN NF membrane, showing ultrahigh water permeance of 297 L m−2 h−1 bar−1, congo red (CR) and direct red 23 (DR23) rejections above 98.5%. The separation mechanisms of PpPD/HPAN NF membrane were controlled by the co-effects of size sieving and charge repulsion, which had potential application prospects for dye removal and desalination. Subsequently, the chain-like polymer PpPD was post-crosslinking treated by trimesoyl chloride (TMC) to generate (PpPD-TMC)/HPAN OSNF membrane with rigid interconnected network structure, which displayed excellent permeance to organic solvent with ethanol permeance up to 242 L m−2 h−1 bar−1, and CR rejection of ∼90%. The solvent's permeance was inversely proportional to solvent's viscosity, and the separation mechanism was mainly controlled by size sieving effect. Furthermore, a two-stage OSNF process was designed and operated with simulated industrial waste liquid, successfully achieving 75% solute recovery and 60% solvent recovery after the 1st and 2nd stage treatments.