Developing thin film composite poly(piperazine-amide) and poly(vinyl-alcohol) nanofiltration membranes

In this work, two different thin film composite (TFC) nanofiltration (NF) membranes were fabricated for water softening: (i) poly(piperazine-amide) and (ii) poly(vinyl-alcohol) (PVA) nanofiltration membranes. The nanofiltration performance of membranes was evaluated by cross flow filtration using NaCl (1 g/l) and MgSO4 (1 g/l) solution at 5 and 10 bar, 25 °C and 10 l/min. The morphological and hydrophilicity studies were carried out with scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle, respectively. Thin film composite poly(piperazine-amide) nanofiltration membrane was prepared by interfacial polymerization of piperazine (PIP) with trimesoyl chloride (TMC). The SEM and AFM studies indicated that a rough and dense film was formed on the polyethersulfone (PES) support membrane by interfacial polymerization. The water permeability of this membrane was 53 and 101 kg m− 2 h− 1 (during salt solution filtration), 57 and 126 kg m− 2 h− 1 (during pure water filtration) at 5 and 10 bar. Moreover, the rejection to the MgSO4 as divalent salt (78 and 70%) was high compared to the NaCl as monovalent salt (44 and 35%). In second type, thin film composite poly(vinyl-alcohol) (PVA) nanofiltration membrane was prepared by dip coating and cross-linking with glutaraldehyde. In the case of PVA membrane, a thick and smooth film was formed. This membrane shows the water permeability of 60 and 109 kg m− 2 h− 1 (during salt solution filtration), 69 and 135 kg m− 2 h− 1 (during pure water filtration) and the rejection of 25 and 20% for NaCl and 72 and 63% for MgSO4 at two different pressures. Moreover, these two NF membranes exhibited structural and performance stabilities. The calculated pore radius and thickness-to-porosity (ΔX / AK) ratio by the modified Nernst–Plank equation confirmed the obtained results of rejection data of the synthesized membranes.