Acid-resistant thin-film composite nanofiltration membrane prepared from polyamide-polyurea and the behavior of density functional theory study

Acid-resistant nanofiltration membranes consisting of amide and urea groups have enhanced acid stability. A polyamide-polyurea NF membrane was fabricated by the interfacial polymerization reaction of linear ethylenediamine with toluene-diisocyanate and trimesoyl chloride on a polysulfone (PSf) support layer. The optimized EDA0.5/TMC0.05-TDI0.05 membrane has a MgSO4 rejection rate of 98% and was maintained over 98% for 83 days of exposure to 15 wt% H2SO4. The EDA0.5/TMC0.05-TDI0.05 membrane has acid resistance in an acidic solution (pH < 0), which was attributed to the stability of EDA as well as polyurea linkage having resonance, and resistance to hydrolysis due to greater hydrogen bonding. In addition, density functional theory (DFT) calculations were carried out to prove the acid-stability of the polyamide-polyurea NF membrane in terms of free energy (ΔG). The degradation of the membrane with EDA-TMC/TDI proceeds relatively slowly compared to a commercial polyamide nanofiltration membrane (PIP-TMC) due to the high energy barrier and the enhanced acid resistance of the prepared polyamide-polyurea membrane. This study introduces an NF membrane with a novel active layer with excellent performance and robust acid stability.