Removal of iodine from aqueous solution by PVDF/ZIF-8 nanocomposite membranes

Abstract

Metal-organic frameworks (MOFs) are capable in capture and storage of iodine ions with high efficiency, and polymer/MOF nanocomposite membrane has the potential to be used for efficient removal of iodine from radioactive wastewater. In this work, we have reported a PVDF/ZIF-8 nanocomposite adsorption membrane prepared by contra-diffusion method. The combination of surface graft of poly(4-vinylpyridien) brushes and optimal addition of sodium formate into ligand contributes to the formation of a well-intergrown and continuous ZIF-8 layer on the metal ions side surface of PVDF-g-P4VP membrane. In the batch adsorption, the PVDF/ZIF-8 nanocomposite membrane exhibits high affinity for iodine following a pseudo-second-order kinetics and fitting the Freundlich isotherm model with a maximum adsorption capacity of 73.33 mg/g. In the dynamic adsorption, the PVDF/ZIF-8 nanocomposite membrane exhibits a high flux of 66.19 L/(m2⋅h⋅MPa) and an iodine removal efficiency of 73% until 180 min. Initial iodine concentration has a little influence on the iodine removal efficiency, but solution pH shows a significant effect. The iodine removal efficiency can be maintained around 92% in a weakly alkaline medium of pH = 8. The PVDF/ZIF-8 nanocomposite membrane possesses an excellent reusability with an iodine removal efficiency of 73.4% after five cycles.