Novel acid-free cross-linked polyvinyl alcohol NF membrane enhanced with a copolymer absorbent for wastewater treatment

Safe water is vital to human health. NF membrane technology has been demonstrated to be an effective solution for the remediation of water contamination in the environment. Polyvinyl alcohol (PVA) is one of the most promising materials for preparing NF membrane. The traditional PVA membrane preparation usually relies on sulfuric acid as a catalyst for crosslinking. However, strong acid raises safety and environmental concerns. In this study, we propose an acid-free cross-linking strategy to address the issue and improve the membrane flux simultaneously. Specifically, the cross-linking is achieved via the reaction between 4,4′-diaminodiphenyl sulfone and epoxy group which is grafted onto the PVA backbone. The epoxy group could reduce the crystallinity of PVA by disrupting its structure and then induce the improvement of membrane flux. The results showed that the flux was improved to 46.7 L·m −2 ·h −1 ·bar −1 and meanwhile the dye rejection was retained at high level (>96.79 %). Besides, in order to improve the salt rejection, the adsorption-enhanced membrane separation method was applied. An absorbent, acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer (AA-AMPSA), was added into the feed solution. Because salts were adsorbed by AA-AMPSA, which is big and could be rejected by the membrane, the rejection was improved. Due to the usage of AA-AMPSA, the salt rejection of the prepared membrane can reach a high level (98.5 %). This work provides new ideas to enhance the performance of PVA NF membrane and helps to promote the development of NF membrane technology for efficient wastewater treatment.