High-performance thin film nanocomposite membranes enabled by nanomaterials with different dimensions for nanofiltration

The incorporation of nanomaterials into a polyamide (PA) matrix has been demonstrated to be effective in the design of advanced thin film nanocomposite (TFN) membranes. In this study, a novel TFN membrane was developed by simultaneous introduction of two nanofillers with different dimensions. Graphitic carbon nitride (g-C3N4) and halloysite nanotubes (HNTs) were co-deposited onto a substrate surface with piperazine (PIP) monomers via vacuum filtration, followed by interfacial polymerization (IP) with trimesoyl chloride (TMC). A series of characterizations showed that the pre-loaded g-C3N4 was present as nanoaggregates wrapped by the formed PA film, while one-dimensional HNTs inclined to be horizontally aligned as a hydrophilic interlayer. This unique architecture led to a crumpled membrane surface with convex and ridged structures, and provided additional water transport channels. The surface roughness and hydrophilicity of the TFN membranes were also enhanced with the addition of nanomaterials. Although g-C3N4 and HNTs were able to elevate the water permeance, a superior separation performance could only be achieved by simultaneously incorporating these two nanofillers. The best performing TFN membrane containing 16.4 μg cm−2 g-C3N4 and 19.7 μg cm−2 HNTs exhibited a water permeance of 20.5 L m−2 h−1 bar−1, nearly twice as high as that of the thin film composite (TFC) membrane, while maintaining a comparably high Na2SO4 rejection of 94.5%. This demonstrated the effectiveness of g-C3N4 and HNTs in developing high-performance TFN membranes, which were ascribed to their respective advantages as well as the combined effect in the regulation of the PA layer microstructure.