Thin-film composite nanofiltration membrane based on polysulfonamide for extremely acidic conditions

Increasing the acid stability and selectivity of nanofiltration (NF) membranes, which are used to treat acidic industrial effluents, is highly beneficial. A series of acid-stable NF membranes featuring polysulfonamide (PSA) separation layers were prepared through interfacial polymerization of branched polyethyleneimine (PEI), polyethylenepolyamine (PPA), and 1,3-benzenedisulfonyl chloride (BDSC) on a porous polyethersulfone (PES) substrate. The optimization of the membrane filtration performance involved analyzing the monomer content in both the aqueous and organic phases and adjusting the PEI-to-PPA ratio, thereby preparing ultrathin PSA layers. The influence of the PSA morphology and structure on the membrane filtration performance was examined. The most effectively optimized sample demonstrated a MgSO4 rejection rate of 95.4 +/- 0.4 % and a water flux of 55.4 +/- 1 L m-2h- 1 at a pressure of 2.0 MPa. The acid stability of the membrane was assessed by examining the permeation, separation, and physicochemical properties before and after undergoing static acid-soaking tests. Following a 5-month exposure to 20 % (w/v) HCl or 20 % (w/v) H2SO4 aqueous solution, the optimal membrane maintained a MgSO4 rejection of 92.6 % at neutral pH, with a permeation flux of 68.2 L m-2h- 1 under 2.0 MPa. Owing to their excellent selectivity, enhanced acid stability, structural controllability, and ease of functionalization, these PSA-NF membranes are promising for use in industries such as mining, semiconductor, and electroplating.