Tailoring morphology for improved dispersibility of hydrophilic silica nanoparticles to fabricate thin-film nanocomposite membranes

Improving the dispersibility of nanomaterials is a promising approach to enhance the performance of thin-film nanocomposite (TFN) membranes. In this study, hydrophilic nonporous, mesoporous, and dendritic mesoporous silica nanoparticles (NSNs, MSNs, and DMSNs) with a uniform particle size were utilized as aqueous phase additives to prepare TFN membranes through in-situ polymerization. The electrostatic adsorption of nanoparticles increased the concentration of amine monomers on the surface of the polysulfone (PSF) substrate. In collaboration with the steric hindrance effect, nanoparticles restricted the diffusion of piperazine (PIP) into the organic phase to polymerize with the acyl chloride monomers. Compared to TFC-0, the TFN membranes exhibited a rougher surface with increased negative charge and had more channels that facilitated the transportation of water molecules. Among the nanoparticles, DMSNs exhibited excellent dispersibility, ensuring their uniform distribution within the polyamide (PA) matrix. Furthermore, DMSNs possessed an open central-radial pore structure, offering more efficient channels for water molecules to cross the membrane. Therefore, a highly crosslinked, defect-free, and hydrophilic PA layer of TFN-DMSNs was achieved. In the performance characterization, TFN-DMSNs demonstrated a high water/salt permselectivity (A/B) of up to 32.25 bar-1, and exhibited good resistance to acidic/alkaline environments as well as foulants during the operation. This study proposes a novel approach to prepare advanced TFN membranes by optimizing the morphological structure of nanoparticles.