Porous Zr-Based Metal-Organic Frameworks (Zr-MOFs)-Incorporated Thin-Film Nanocomposite Membrane toward Enhanced Desalination Performance

Abstract

Four different thin-film nanocomposite (TFN) membranes were prepared by adding different concentrations of porous Zr-metal-organic frameworks (MOFs) (UiO-66 and UiO-66-NH₂) to piperazine aqueous solution (aqueous phase) or 1,3,5-benzenetricarbonyl trichloride-n-hexane solution (organic phase) by interfacial polymerization. The main purpose is to study the specific effects of different addition methods and addition amounts of nanoparticles on the structure and performance of the TFN membranes by interfacial polymerization. All four TFN membranes exhibited a higher water permeability while maintaining high salt rejection compared to thin-film composite membrane. On the one hand, the TFN membranes behave differently, which are prepared by adding the same kind of nanoparticles to the aqueous phase or organic phase, respectively. The TFN membrane prepared by adding 0.2 w/v% UiO-66 to the organic phase had a high water flux of 87.86 L m^-2 h^-1, compared to 46.31 L m^-2 h^-1 of the membrane prepared by adding 0.3 w/v% UiO-66 in the aqueous phase. This is due to the fact that UiO-66 greatly slows the interfacial polymerization rate when UiO-66 is added to the organic phase, resulting in a thinner and wider-aperture polyamide thin-film layer, reducing the water transmission resistance during filtration. Therefore, it is more economical by adding nanoparticles to organic phase than aqueous phase under the same filtering effect. On the other hand, different nanoparticles can also cause differences in performance and structure of the TFN membranes even in the same preparation manner. TFN membrane with UiO-66-NH₂ in the aqueous phase has higher water permeance than the one with UiO-66 in the aqueous phase, owing to the good hydrophilicity of the amino group, which improves the water dispersibility of UiO-66-NH₂ so that the TFN membrane is more uniform. In addition, UiO-66-NH₂ slows down the process of interface polymerization, making the membrane more porous. The monomers in the aqueous phase and organic phase can be adsorbed in the pores of Zr-MOFs, which makes the interfacial polymerization occur both in the pores and on the surface of the pores. Thus, the compatibility between the polyamide and MOFs was enhanced and less defects were formed in the thin-film layer, resulting in a high salt rejection even when the concentration of Zr-MOFs increased. This is the first time to explain that polyamide membrane has not obvious salt rejection attenuation with increasing porous material content using pore adsorption reaction monomer principle. Also, the Zr-MOFs-based TFN membrane exhibited good heat resistance and antifouling property. This work shows that porous Zr-MOFs nanomaterials have significant advantages in the development of nanofiltration membranes with high water flux and rejection.