Improving the performance of loose nanofiltration membranes by poly-dopamine/zwitterionic polymer coating with hydroxyl radical activation

Abstract

A growing number of sewage treatment plants are utilizing the membrane separation technology for wastewater bleaching and desalination. The surface characteristics of the membrane selective layer have a great impact on the filtration and separation performance. In this study, a facile mussel-inspired method was employed for fabricating loose NF membrane. Hydroxyl radical activation generated by CuSO4/H2O2 was used to realize a rapid polydopamine (PDA) deposition. To obtain an electroneutral, anti-fouling and anti-bacterial surface, a zwitterionic polymer (SBMA) was introduced for PDA/SBMA codeposition and polymerization. XPS, FTIR, SEM, AFM and water contact angle analysis were employed to investigate the characteristics of the selective layer. The RD-1S membrane (2 mg/mL PDA and 2 mg/mL SBMA utilized) shows the optimal surface property. In addition, the filtration and separation performance of multivalent salts (monovalent and divalent ion) and dyes (negatively and positively charged) were investigated in detail. The separation capability of membrane exhibited a high dye rejection and a low salt rejection. The anti-fouling performance of the RD-1S membrane was observed to be excellent, especially from the point of view of fouling resistance reversibility. The elevated surface charge might be the main reason for the significant decrease of irreversible fouling of the RD-1S membrane. Furthermore, the co-existence of chelated copper and SBMA resulted in a reliable anti-bacterial performance. Overall, the separation and anti-bacterial performance of the functional loose NF membrane were comprehensively investigated.