Fabrication of nanofiltration membrane on MoS2 modified PVDF substrate for excellent permeability, salt rejection, and structural stability

A thin-film composite polyamide membrane has been widely implemented in water desalination. However, the balance between permeability and selectivity by decreasing structural stability has restricted their larger-scale applications in water desalination. Here, we fabricated nanofiltration membranes (NFMs) by interfacial polymerization on polyvinylidene fluoride (PVDF) substrates modified with hierarchical flower-like molybdenum disulfide (HF–MoS2). The thin-film nanocomposite (TFN) NFMs exhibited a water flux up to 21.5 LMH/bar and rejection rates of 98.6% for Na2SO4. Steric hindrance and Donnan exclusion together contributed to high salt rejection rates, as evidenced by a less polyamide layer thickness such as 56 nm and a high surface negative charge at pH 3–10. Note that the nanocomposite substrate became more porous, more hydrophilic, and rougher than the non-nanocomposite one, due to an increase in the fraction of macroporous on the surface, which was known to affect the performance of the polyamide layer. The high content of HF-MoS2 incorporated in PVDF substrate led to enhanced hydrophilicity and, consequently, a cross-linking degree of defect-free polyamide, resulting in declines in thickness and increases in water permeability and salt rejection. Furthermore, TFN NFMs exhibited an excellent organic solvent resistance and long-term stability, indicating that HF-MoS2 incorporation had no adverse effect but even improved their structural stability. Compared to NFMs without MoS2 modification, NFMs with MoS2 modification showed a better performance for desalination of real seawater and excellent anti-biofouling properties for lysozyme and bovine serum albumin. Taking together, the TFN NFMs provide high permeability and rejection rate without a decline in structural stability. Therefore, TFN NFMs were promising candidates for practical water desalination treatment.