Preparation of MOFs/Chitosan Positively Charged Nanofiltration Membrane by Electrospray Method

Electrospray technology can solve the problems of long membrane formation period, thicker membrane layer and low flux of traditional chitosan nanofiltration membranes. In this study, the NH₂-UIO-66(Zr)/chitosan positively charged nanofiltration membrane based on NH₂-UIO-66(Zr)/chitosan was successfully prepared by combining the direct membrane-forming properties of chitosan with electrospray technology and introducing metal-organic frameworks (MOFs). This membrane has achieved efficient separation and enrichment of Ni²⁺. The morphology, structure and properties of membrane were investigated by SEM, EDS, Zeta potential, water contact angle measurements, etc. The results show that compared with the traditional coating process, the permeability of the chitosan composite membrane prepared by the electrospray method is increased by 634%, and the membrane can still maintain a good rejection. However, pure chitosan matrix membranes are usually affected by trade-off effect, and it is difficult to further improve the separation performance. The introduction of NH₂-UIO-66 (Zr) as a filler could effectively alleviate the trade-off effect. Hybridization improved the hydrophilicity of the separation layer and formed a special membrane surface structure, thereby increasing permeability of the composite membrane. Experiments showed that the limit of NH₂-UiO-66(Zr) loading was 5% (the mass fraction of MOFs to chitosan). The optimized NH₂-UIO-66(Zr)/chitosan membrane had a higher flux than pristine chitosan membrane (increased by 38%). The prepared membrane exhibited a high NiCl₂ rejection of 92% and a water permeability of 4.7×10⁻⁵ L/(m²·h·Pa) (test pressure: 4×10⁵ Pa; feed concentration: 0.5 g/L). In addition, the hybrid membrane exhibited excellent mechanical strength and had the potential to separate a single solution of MgCl₂, ZnCl₂ and Pb(NO₃)₂.