Synthesis and modification methods of metal-organic frameworks and their application in modification of polymeric ultrafiltration membranes: A review

Metal-organic frameworks (MOFs) with highly flexible structures and extraordinary surface area are one of the most prominent promising materials for separation processes. Although MOFs have attracted attention in water technology applications, synthesis methods and rational combination of MOFs with polymeric membranes are still challenges to improve MOFs' stability and recyclability in void-free membranes with optimum performance, avoiding secondary potential contamination. Nowadays, the most crucial problem in membrane separation technologies is fouling. Membrane fouling happens when the adsorbed or precipitated solutes on the membrane surface clog the membrane surface pores or form a cake/gel layer on the membrane surface. This phenomenon not only deteriorates the membrane performance (permeability and rejection) but also declines membrane porosity, shortens membrane life, and ultimately causes an exorbitant energy cost. Fouling phenomenon strongly depends on chemistry, roughness, charge, and hydrophilicity of the membrane surface and interactions between the membrane surface and the solutes. Researchers have proposed different methods to overcome this challenge, such as using nanoparticles (NPs) in membrane structure as one of the most common methods. Among numerous NPs, water-stable metal-organic frameworks (MOFs) have attracted great attention thanks to their approved affinity with organic polymers and distinctive physiochemical properties, including extraordinary surface area, highly controllable porosity, and designable structure. This article presents an overview of current progress in the MOFs' synthesis and modification. Also, the effects of MOFs addition on the structure, performance, and properties of the MOFs-based mixed matrix ultrafiltration (UF) membranes are deeply investigated with particular emphasis on their challenges and advances in water treatment applications.