Utilization of carboxyl group-grafted molybdenum disulfide for enhancing the performance of thin-film nanocomposite nanofiltration membranes

The incompatibility between inorganic nanoparticles and polyamide matrix in thin film nanocomposite (TFN) nanofiltration membranes tends to generate defects in the selective layer and further sacrifice the membrane separation performance, which can be promisingly mitigated by modifying nanoparticles with hydrophilic functional groups. In this study, carboxyl group-grafted molybdenum disulfide (COOH-MoS2) nanoparticles were prepared via organic functionalization grafting reaction and then incorporated into membrane polyamide layers. The resultant TFN membranes exhibited a rougher surface with unique globule structures, which greatly contributed to the enhancement of water permeance. The optimal membrane obtained at the COOH-MoS2 depositing density of 50.0 μg/cm2 exhibited a high Na2SO4 rejection of 98.5 %, a low NaCl rejection of 23.8 %, and an excellent water permeance of 27.7 LMH/bar, which was 2.8 and 1.5 times higher than that of the control membrane (9.6 LMH/bar) and the original MoS2 modified TFN membrane (18.4 LMH/bar), respectively. The more superior membrane performance enabled by COOH-MoS2 was mainly due to the enhanced hydrophilicity of the nanoparticles, which effectively inhibited the piperazine monomer diffusion and resulted a thinner and properly looser selective layer. This work provides an effective strategy to improve the performance of TFN nanofiltration membranes via graft of proper functional groups on nanomaterials.