ZIF-8 membrane supported on alumina hollow fiber with enhanced salt removal by forward osmosis

This work describes the development of ZIF-8 membranes supported on alumina hollow fiber via electroless deposition (ELD) of ZnO followed by solvothermal synthesis for water desalination. The relatively low operating temperature of ELD of ZnO provided an alternative method to fabricate pure-phase ZIF-8 membrane. As-prepared ZnO and ZIF-8 samples were characterized using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), water contact angle, and Fourier transform infrared spectroscopy (FTIR). The performance of ZIF-8 membrane was evaluated using forward osmosis (FO) using active layer facing feed solution. The well-intergrown membrane provided high water flux up to 12.25 L/m2h with reverse solute flux as low as 0.029 kg/m2h when using 100,000 ppm NaCl solution and water as the draw and feed solutions, respectively. Furthermore, the membrane showed high KCl (87.8%) and NaCl (88%) rejection and excellent CaCl2 (95%) and MgCl2 (98%) salt rejection in FO using 1.0 M dextrose solution as the draw solution. Interestingly, the rejection of AlCl3 salt was only as high as 46% due to the instability of ZIF-8 in the AlCl3 solution causing the loss of its crystallinity. The ZIF-8 material showed no degradation in various saline solutions (e.g., KCl, NaCl, CaCl2, and MgCl2) except for AlCl3 solution even at a high concentration of 40,000 ppm for 720 h. The findings suggest that the prepared ZIF-8 membrane is a potential membrane for desalination application due to its excellent separation performance toward certain salts.