Highly hydrophilic loose nanofiltration membrane based on a novel diaminobenzamide monomer for efficient dye/salt separation

Loose nanofiltration (LNF) membranes with high dyes/salts selectivity and superior anti-fouling performance are urgently needed for treating textile wastewater. Herein, we prepared a polyamide (PA) LNF membrane through reaction of monomer 3,5-diaminobenzamide (3,5-DABA) with trimesoyl chloride (TMC). The presence of an electron-withdrawing and hydrophilic formamide substituent group on the 3,5-DABA monomer not only enhanced the membrane surface hydrophilicity, but also significantly influenced the IP film forming reaction process, leading to a looser and smoother separation layer. The optimized 3,5-DABA/TMC membrane exhibited a high water permeance of 24.62 LMH bar −1 and > 99 % retention for anionic dyes such as Eriochrome Black T (EBT), Methyl blue (MB), and Congo red (CR), as well as 97.5 % rejection for Acid Fuchsin (AF). Simultaneously, it also showed super-low (<5 %) rejection for monovalent anionic salts, achieving a superior selectivity (172.8) for CR/NaCl mixtures. Additionally, the membrane showed superior anti-fouling performance due to its negatively charged, hydrophilic, and relatively smooth surface. These results confirm its potential for saline textile wastewater treatment. This study presents a novel monomer candidate to fabricate outstanding LNF membranes.