Acid stability of polyamide membranes

Abstract

This study systematically focused on the conditions for acid resistance of polyamide membranes using seven types of polyamide membranes fabricated manually via interfacial polymerization. A 15 wt% sulfuric acid solution was used as the model wastewater of the smelting process to investigate the effect of the acidic solution on the physical and chemical properties of the membranes. Successful synthesis of the polyamide layer on the polysulfone support layer was confirmed by the changes in hydrophilicity and charge of the membrane surface using a contact angle analyzer and an electrophoretic light scattering spectrophotometer, respectively. To accelerate the degradation of polyamide membranes by acid solution, the membrane samples were gradually exposed to an acidic feed solution at 25, 45, and 65 °C. According to the surface characterizations and permeation properties of polyamide membranes, each result showed a high correlation in terms of the acid stability order. Additionally, through density functional theory calculations, we found that the lower out-of-plane deformation of the N-protonated amide bond showed higher acid stability, which is consistent with previous work. Through experimental characterization and theoretical study, we demonstrated the acid-stability trend of various polyamide membranes and proposed an important condition for acid stability.