Synergy of Ligands in Tailoring the Photocatalytic Properties of Zirconium Metal–Organic Framework-Impregnated Membranes for Water Treatment

The Zr-based metal–organic framework (MOF) nanoparticles by varying three different ligands (2-methylimidazole, 2-aminoterephthalic acid, and terephthalic acid) are synthesized using a solvothermal method and impregnated into polysulfone membranes. These MOF membranes served as photocatalytic membranes and facilitated both the separation and degradation of dyes in water. Both the XRD and IR analysis revealed that the MOFs are well interacting with the membrane matrix, manifesting effective hydrophilic and surface potential properties confirmed by contact angle, water uptake, and zeta potential analyses. The FESEM images revealed that the MOFs are exposed on the surface, supporting the enhanced dye separation and photocatalytic properties. Further, the cross-sectional images showed that the pore channels in MOF membranes are block-free, smooth, and uniform. These features facilitated the enhanced flux and antifouling properties of MOF membranes compared to bare ones. As a result, the optimized MOF membrane (i.e., amine functionalized Zr-MOF-impregnated membrane) showed an enhanced water flux of around 57 L/m2 h, while it is ∼25 L/m2 h in the case of the bare membrane. The dye (rhodamine B and Congo red) rejection efficacy values of this MOF membrane are around 81.6 and 75.8%, respectively, which are around 2-fold higher than the bare one. Similarly, the RhB/CR dye solution flux of the MOF membrane is around 39.6/33.3%, respectively, while it is only around 10.2/10.4% in the case of the bare membrane. These MOF membranes also showed enhanced fouling resistance compared to bare ones, estimated through reversible and irreversible fouling estimations. Furthermore, the photocatalytic efficiency of the MOF membrane is appreciable, which degraded around 10.7/8.2% of RhB/CR dye, respectively. These add-on features induced by MOFs can considerably reduce the overall process cost of the membrane separation and, especially, the cost involving not only the regeneration and self-cleaning of the membranes but also the safe disposal of the dyes separated on the membrane surface.