Efficient separation of phosphate ions from water across a wide pH range using a triphenylamine-p-phenylenediamine/TMC composite membrane

Abstract

The persistent accumulation of phosphate ions in wastewater, which leads to eutrophication, has garnered substantial attention within the scientific community. Nanofiltration (NF) membranes are widely used for water treatment due to their simplicity, effective multivalent ion rejection, and absence of phase change; however, their practical application is limited by the “trade-off effect” and poor antifouling performance. Therefore, the development of membrane materials that simultaneously enhance rejection efficiency, flux, and anti-fouling performance is of great practical significance. In this study, polyaniline (Ani) and para-phenylenediamine (pPD) were polymerized in situ on a polyethersulfone (PES) support using ammonium persulfate as the oxidant to synthesize PAPD. Subsequently, PAPD was integrated with trimesoyl chloride through interfacial polymerization, thereby fabricating a PAPD/PES composite nanofiltration membrane specifically designed for phosphate separation. The membrane surface featured protruding structures with nanoscale particulate characteristics. At ambient temperature, under an operational pressure of 2.5 bar, with a solution pH of 9 and an initial phosphate concentration of 10 mg L^–1, the membrane flux reached 58.15 L m^–2h⁻¹ bar⁻¹, with a phosphate rejection of 81.86 %. Stability tests confirmed excellent structural durability. In real wastewater containing 1.03 mg P L^–1, the membrane reduced phosphate to 0.51 mg P L^–1, meeting China’s Grade B discharge standard (1.0 mg P L^–1). This work demonstrates that the PAPD/PES composite membrane, modified with Ani and pPD, provides enhanced phosphate rejection, high flux, and robust antifouling performance, offering a promising strategy for efficient water treatment and potential industrial-scale applications.