Synthesis of nanofiltration membranes with enhanced monovalent and divalent selectivity using β-cyclodextrin, tannic acid and ZIF-8.

β-cyclodextrin (β-CD) and tannic acid (TA) together as an organic phase and zeolitic imidazolate framework-8 (ZIF-8) as an additive can be used along with trimesoyl chloride (TMC) as a monomer to synthesize nanofiltration (NF) membranes. Those membranes have better separation performance and provide higher flux. In this study, a new NF membrane was synthesized using them to investigate the effects of monomer concentration, substrate morphology, and reaction temperature on membrane performance. The results showed that when the concentrations of both β-CD and TA were 1 wt%, the membranes had the highest selectivity (2.99) for monovalent and divalent salts. A 10-fold increase in TMC concentration (0.05 to 0.5 wt%) optimized membrane selectivity and flux. When both spongy and cavernous structures were present in the substrate, the membranes could achieve >85 % removal of monovalent and divalent salts. After the introduction of ZIF-8, the roughness of the membrane increased, and the removal rate of monovalent salts decreased significantly, resulting in a salt selectivity of 7.97 and a flux up to 27.81 ± 1.17 L/(m2 h). The growth of ZIF-8 on the membrane surface was assisted by an increase in the reaction temperature. • The selectivity for monovalent and divalent salts of synthesized membrane reached 7.97. • The substrate with both spongy and cavernous structures aided in the removal of monovalent and divalent salts. • Increasing the synthesizing temperature from 20 to 70 °C promoted ZIF-8 growth on membrane surfaces. [ABSTRACT FROM AUTHOR]