Hybrid adsorptive nanofiltration hollow fiber membranes with charge-patterned UiO-66 incorporated thin-film nanocomposite selective layer for enhanced boron removal

Herein, hybrid adsorptive nanofiltration (NF) hollow fiber (HF) membranes with the charge-patterned structure were fabricated and characterized for enhanced boron removal application. Mg–Al layer double hydroxide (LDH) and bentonite nanoparticles (NPs) were used as adsorbents in the support layer, while pristine and novel amine modified UiO-66 metal-organic frameworks (MOFs) were used to synthesize thin-film nanocomposite polyamide (PA) selective layer. UiO-66 was modified using triethylamine (TEA) and polyethylene imine (PEI) and the modification was approved through FTIR, DLS, and FESEM analyses. Prior to the performance evaluation of the fabricated membranes, the feasibility of boron removal by PA, and pristine and modified UiO-66 was investigated using molecular dynamics (MD) simulation and the diffusion coefficients were estimated. The structure of the fabricated thin film composite (TFC) and thin film nanocomposite (TFN) membranes were characterized by AFM, zeta potential and FESEM analyses showing agglomeration of the MOFs at 0.1 wt%. Membrane performance in boron removal was evaluated through brackish water condition at 4 bar in neutral and alkaline pH. The results showed that the contribution of the adsorptive support is 8 and 4% for the supports containing LDH and bentonite, respectively. Boron removal of the UiO-66 TFN membrane was achieved up to 58%, while the charge-patterned UiO-66/PEI TFN membrane was able to remove boron up to 87 and 91% at neutral and alkaline pH conditions.