A critical review on the oxidation-property-performance of polyamide membranes for water treatment

Despite the wide deployment of polyamide nanofiltration (NF) and reverse osmosis (RO) membranes in water treatment, their poor resistance to oxidants (e.g., hypochlorite) often results in compromised separation performance. In this review, we extracted physicochemical properties and separation performance of polyamide NF/RO membranes before and after oxidation from the literature for systematic data analysis. The results showed that the fully-aromatic membranes are more prone to oxidation compared to the semi-aromatic membranes. Severe oxidation could significantly damage polyamide network, leading to deteriorated polyamide nanofeatures, varied hydrophilicity depending on pH (e.g., more hydrophilic after alkaline oxidation), increased negative charge, and enhanced O/N ratio. Moreover, the fully-aromatic polyamide membranes often demonstrate enhanced water permeance after neutral and alkaline oxidation due to the degradation of polyamide. Meanwhile, the membranes showed deceased rejection and selectivity of salts after severe oxidation. In addition, an initial evaluation of micropollutant rejection was performed based on the currently limited available literature data, but a comprehensive and systematic investigation into the oxidation impact on water-micropollutant selectivity is still lacking and represents a critical area for future research. We further analyzed the chlorination-properties-performance relationship to highlight the importance of oxidation-induced O/N ratio change on membrane separation performance. In addition, the Janus impacts of oxidation (e.g., damaging membranes with compromised performance and polishing membranes for enhanced performance) were highlighted. Moreover, we outlooked the development of novel anti-oxidation membranes and oxidation polished membranes for specific applications in water treatment.