Effect of functionalized nanodiamonds and surfactants mediation on the nanofiltration performance of polyamide thin-film nanocomposite membranes

Thin film nanocomposite (TFN) membranes have drawn intensive attention for desalination. Herein, we investigate the effect of addition of different kinds of functionalized (Amine, Carboxylic acid, Hydrogen) nanodiamonds (NDs) and their dispersion enhanced by surfactants mediation on polypiperazineamide selective layer synthesized on polyamide membrane via Piperazine (PIP) and Trimesoyl chloride (TMC) interfacial polymerization (IP). The addition of functionalized NDs not only enhanced the surface roughness, hydrophilicity, and degree of crosslinking of selective layer but also enhanced the water flux and salt rejection performance of the membranes. The optimum NH2-ND400/PIP/TMC membrane enhanced the water flux by 14 % and MgSO4 rejection by 2.4 % with respect to the conventional PIP/TMC membrane. To further enhance the performance, different chain length surfactants such as Sodium Octyl Sulfate (SOS) and Sodium Dodecyl Sulfate (SDS) were added to the aqueous phase of IP system. The optimum SDS1/NH2-ND400/PIP/TMC membrane showed improved flux and MgSO4 rejection of 8.87 Lm−2h−1b−1 and 98.68 %. It was further investigated for long term stability performance, which resulted in maximum flux and salt rejection of 15 Lm−2h−1b−1 and 99.57 % respectively, leading to increase of water flux by 87.5 % and MgSO4 rejection by 0.5 % with respect to the conventional PIP/TMC membrane. Overall, the highlight was that the SDS addition improved the membrane performance with well retained stability, indicating that the SDS has significantly improved the degree of crosslinking of selective layer via improved dispersion of PIP and NH2-NDs in aqueous phase during IP, making it mechanically more stable, hydrophilic and effective for MgSO4 rejection as compared to the conventional PIP/TMC membrane. The SDS1/NH2-ND400/PIP/TMC membranes show great potential to be used in nanofiltration.