An innovative NH2-UiO-66/NH2-MIL-125 MOF-on-MOF structure to improve the performance and antifouling properties of ultrafiltration membranes

The careful design of distinctive membrane layers with specific pore structures is a crucial aspect of membrane fabrication. Previous efforts in metal–organic framework (MOF) based membranes have predominantly employed a single MOF material for improving membrane resistance to fouling due to microplastics and proteins. Here, a novel, highly specialised ultrafiltration (UF) membrane is developed through the in-situ growth of NH2-UiO-66 on the NH2-MIL-125 (MOF-on-MOF) crystals to improve membranes' performance such as pure water flux (PWF), rejection, and antifouling properties. The developed membranes displayed multidimensional pores, leading to a significant enhancement in fouling resistance while achieving remarkable improvements in water flux. The improved MOF-on-MOF UF membranes showed increased PWF from 247 (controlled membrane) to 401 L.m−2.h−1 while maintaining rejection rates above the 94% threshold. The MOF-on-MOF particles displayed a strong hydrophilic nature and a higher negative surface charge compared to the individual MOFs due to synergistic effect of both MOFs. That, together with their interconnected structure, contributed to their significant impact on the membranes' performance and antifouling properties. Given that the MOF-on-MOF integration with UF membranes has not been extensively explored in existing literature, the outcome of this study offers new insights into the dynamics of these interactions and the potential to enhance these intricate membrane structures for more effective separation and purification processes.