Tuning the microstructure and permeation property of thin film nanocomposite membrane by functionalized inorganic nanospheres for solvent resistant nanofiltration

Herein, a series of thin film nanocomposite (TFN) membranes are prepared by incorporating functionalized silica nanospheres into polyethyleneimine (PEI) matrix for solvent resistant nanofiltration (SRNF). Three functional groups are grafted onto the nanospheres in form of polymer layer via distillation-precipitation polymerization for manipulating the free volume cavities of PEI matrix by interfacial interactions along PEI-nanosphere domains. The effects of nanospheres on the microstructures, physicochemical and permeation properties of TFN membranes are investigated systematically. The tested data suggest that the nanospheres are uniformly dispersed in PEI matrix without obvious defects, offering the excellent thermal stability and appropriate solvent resistance to the membranes. The microstructures of TFN membranes are elaborately regulated by varying the fractional free volume (FFV) and surface hydrophilic/hydrophobic nature, jointly yielding the tunable permeation properties. In particular, the permeate flux of ethanol is elevated from 21.2 to 30.8 L m^-1 h^-1 with the increase of FFV from 0.452% to 0.473% by incorporating various hydrophilic nanospheres. Meanwhile, the addition of hydrophobic nanospheres provided much higher fluxes for n-heptane from 0.1 to 21.7 L m^-1 h^-1, due to the enhanced solution capability. Moreover, the presence of nanospheres donates high rejection ability and promising operation stability to the TFN membranes.