Many desalination technologies have been developed, but they usually require a large amount of energy. Forward osmosis (FO) has the potential to become an excellent alternative desalination technology due to its lower energy consumption. Nano structured materials have also attracted attention, particularly metal organic frameworks (MOFs), due to their exceptional separation properties, controllable pore sizes, adsorption affinities and high porosity. To use an MOF as an effective membrane, an MOF is deposited onto an inorganic support to provide mechanical strength and chemical resistance. Increased attention has been given to a subclass of MOFs: the zeolitic imidazolate frameworks (ZIFs) that consist of zinc or cobalt ions coordinated by an imidazole-based linker. Under this group, ZIF-8 has been the most commonly studied for various separation applications.
Now a team from Universiti Teknologi Malaysia (Skudai, Malaysia; www.utm.my) has carried out the in-situ synthesis of ZIF-8 membranes using the solvothermal process onto alumina hollow fiber in the presence of ZnO, NiO and polydopamine (PDA). In addition, the different molar ratio of sodium formate in synthesis solution was studied on the membrane characterization and performance. The team evaluated the performance of ZIF-8 membranes in desalination, using FO. “To the best of our knowledge, no studies have reported on ZIF-8 membranes for desalination using forward osmosis,” says the team.
The team found ZIF-8 to be a promising membrane material for desalination using FO. However, it said, improvements in membrane morphology to prepare a well-intergrown, continuous and thin membrane are needed to enhance its performance in terms of water flux, reverse-solute flux and salt rejection.