Degradation impact of low pH mineral acids and long exposure period on the active layer of semi-aromatic polyamine-based nanofiltration membrane

Rapid degradation of the active layer of nanofiltration (NF) membranes by acids contained in water and wastewater during industrial processes, needs to be understood to develop acid-resistant membranes with prolonged stability and durability. This study focuses on the degradation impact of a typical semi-aromatic polyamine-based NF membrane excited by two mineral acids (HCl and H₂SO₄) having pH ≤ 0. Selected analytical tools were systematically engaged to investigate the morphological change, chemical composition, hydrophilicity and surface charge of the degraded membrane at varying and elongated exposure periods up to 150 days. The neat membrane was examined for comparison and the reaction mechanism between individual acid and the degraded membrane active layer was also studied. At early exposure periods of 7, 15 and 30 days, corresponding deterioration changes were noticed in both the HCl and H₂SO₄ degraded membranes. However, at extended exposure periods of 90 and 150 days, the impact of degradation was more severe on the H₂SO₄ degraded membrane as revealed by the SEM and XPS analyses. This was envisaged to be triggered by the prolonged dissociation of the acid which gradually weakens the bonds and the polymer structures, hence making it more vulnerable to further degradation. HCl and H₂SO₄ readily dissociate to form hydrogen ions; a condition that favors the acid-catalyzed hydrolysis reaction pathway of the degraded membranes. This study thus serves as a reference to the expected behavioral change of semi-aromatic polyamine-based NF membrane used in acidic wastewater treatment and reclamation for extended periods.