Regulating composition and structure of nanofillers in thin film nanocomposite (TFN) membranes for enhanced separation performance: A critical review

Thin film nanocomposite (TFN) membranes, comprising nanofillers and nanoscale dense polymeric barriers, were prepared by introducing nanomaterials into a polyamide layer during interfacial polymerization for diverse separations. The versatile nanofillers allow the TFN membranes to go beyond the longstanding trade-off limitation and alleviate the fouling propensity by tailoring the membrane surface properties, i.e., pore characteristics, hydrophilicity, charge, and compactness, even when applied in low dose. The enhanced performance is primarily determined by the composition and structure of the nanofillers. Therefore, in this review, particular attention is paid to the compositional and structural evolution of nanofillers. Starting from the functionality, some emerging and prevalent nanofillers are emphatically introduced, followed by discussing their selection criteria for targeted separation. Furthermore, the encouraging applications of TFN membrane in the past 5 years for gas separation, nanofiltration (in water and organic solvents), reverse osmosis, forward osmosis, and pervaporation are outlined. Moreover, current challenges and further prospects of fabricating TFN membranes are proposed. Through this critical review, a fundamental guide of designing unique nanofillers with specific composition and structure for advanced TFN membrane separation technologies is provided.