Three-channel capillary nanofiltration membrane with quaternary ammonium incorporated for efficient heavy metals removal

Abstract High-performance nanofiltration (NF) membranes have profound implications for water purification. Here, we reported a novelty polyamide NF membrane through introducing bis (2-hydroxyethyl) dimethyl-ammonium chloride (BHDA) in interfacial polymerization (IP) process on three-channel substrate membrane. This new monomer bearing abundant quaternary ammonium (N+) and hydroxyl could participate in the reaction between piperazine (PIP) and trimesoyl chloride (TMC). Then, not only was positive charge introduced into the NF membrane, but the hydrophilic of the resultant NF membrane was also significantly improved. Thus, the as-prepared PIP/BHDA-TMC (MPQ) membrane exhibited enhanced pure water flux (12.9 L·m−2·h−1·bar−1) which is 2.4 times as high as that of the PIP-TMC (MP) membrane, coupled with the salt rejection sequence as MgSO4 (93.46%) > Na2SO4 (91.61%) > MgCl2 (88.15%) > NaCl (22.03%). Meanwhile, MPQ exhibited a promising separation performance to various heavy metal salts (96.43% CuSO4, 96.16% ZnSO4, 91.69% Cu(NO3)2, 89.69% ZnCl2, 88.37% Pb(NO3)2). The stability of MPQ was tested with simulated wastewater, and the results illustrated that it has a potential applicability for heavy metals removal.