Preparation and characterization of ZIF-8 and ZIF-67 engineered PVDF mixed-matrix membranes: stability enhancement in pervaporation study

Abstract

In this work, mono-(ZIF-8 and ZIF-67) and bi-metallic (ZIF-8-67) metal–organic frameworks (MOFs) are prepared using the sol–gel method. The prepared MOFs are successfully applied to prepare mixed-matrix membranes. The prepared MOFs and MOF-incorporated mixed-matrix membranes are characterized by thickness and porosity, field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), water contact angle, and X-ray diffraction (XRD) analysis. The performance evaluation of the prepared mixed-matrix membranes is carried out to study the effect of fillers, feed temperature, salt concentration, and stability of the membranes on the permeate flux and salt rejection. FESEM confirms the regular spherical shape of the nanoparticles. FTIR and XRD confirm the presence of the various functional groups and crystallinity of the nanofillers. The prepared mixed-matrix membranes are tested for desalination performance. It is observed that with an increase in temperature from 55 °C to 75 °C, the water flux increases for all the modified membranes with high salt rejection (>99%). The total flux of the prepared mixed-matrix membranes is enhanced when different ZIFs are incorporated into the pristine membrane. The total flux of M2, M3, and M4 varies from 34.1–96.5 L m⁻² h⁻¹, 46.8–109.2 L m⁻² h⁻¹, and 55.4–117.8 L m⁻² h⁻¹, respectively. The M4 membrane has the highest water flux and salt rejection of 117.8 L m⁻² h⁻¹ and >99.6%, respectively. The long-term separation performance of the mixed-matrix membranes shows stable performance up to 220 h of the desalination experiment.