Mechanistic insights into the role of nanoparticles towards the enhanced performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are promising in improving water treatment due to their high permeability and selectivity. However, little is known about the mechanism by which nanoparticles enhance their performance. In this study, we prepared two series of TFN membranes containing ∼40 nm-sized zeolitic imidazolate framework (ZIF-8) nanoparticles, one with a hydrophobic porous form and the other with a nonporous amorphous form (aZIF-8). The TFN membranes containing 0.15 w/v% ZIF-8 exhibited a 100% increase in water permeance while maintaining a similar NaCl rejection (98.38%) compared to thin-film composite (TFC) membranes used in brackish water reverse osmosis (BWRO). In contrast, adding the same amount of aZIF-8 resulted in almost no water permeance enhancement. By comparing the physicochemical properties of the two materials and the two series of membranes, we found that the only difference was the presence or absence of internal hydrophobic pore structures. We proposed that the hydrophobic internal pores of nanoparticles served as extra water channels while preventing the passage of NaCl during BWRO.