Leaf-like ZIF-L as self-sacrificed template via acid induced removal for stronger negatively charged PES membranes based on RTIPS method

In this paper, ZIF-L was blended with citric acid (CA) and polyethersulfone (PES) to prepare a casting solution. A novel negatively charged ultrafiltration (UF) membrane (ZIF-L/CA/PES) was obtained using the reverse thermally induced phase separation (RTIPS) method. The hydrophilic carboxyl groups present in CA not only imparted high hydrophilicity and negative charge to the membrane surface, enhancing the membrane’s selectivity and contamination resistance, but also created an acidic environment to attack the Zn atoms in ZIF-L by the ionized H+ from CA, resulting in the generation of micro-defective pores and an improvement in permeability. Additionally, the results showed that membranes generated through the RTIPS process exhibit uniform porous surfaces and spongy cross-sections, enhancing membrane performance. The optimized membranes demonstrated the capability to achieve a pure water flux of up to 2267 L/m2h with 93.1 % humic acid (HA) retention, and a remarkable membrane flux recovery rate of 75.8 %, suggesting the crucial roles played by CA and ZIF-L in the separation process. In conclusion, hydrophilic anti-fouling UF membranes with a high negative charge and excellent permeation selectivity were fabricated by establishing micro-defective channels through the incorporation of carboxylic acid and ZIF-L, combined with the RTIPS process.