Removal of Cr(VI) by coupled adsorption and photocatalytic degradation based on Ag/ZIF-8/PVDF membrane

Abstract

In order to reduce the hazard of the heavy metal chromium, the reduction of Cr from Cr(VI) to Cr(III) for further removal was applied in this study. ZIF-8 modified with Ag was used as the photo-catalyst, and adsorption and degradation were further enhanced by deep penetration through in situ growth of Ag/ZIF-8 in the pores of polyvinylidene fluoride (PVDF) membrane. The composite Ag/ZIF-8/PVDF membrane was characterized by XRD, BET, SEM-EDS, UV–Vis and XPS, and the results proved that the nanoparticles of ZIF-8 and Ag were uniformly distributed inside the membrane pores. The removal efficiency of Cr(VI) was enhanced by 78 % after modification of Ag nanoparticles on the ZIF-8 surface, and further enhanced by 68 % after loading the composite particles (Ag/ZIF-8) into the PVDF membrane. Moreover, the removal mechanism was investigated by free radical trapping experiments, and the results showed that O₂·^- was the main factor in the photo-catalytic process, followed by ·OH. The results indicated that enhancement of coupled adsorption-degradation process by deep permeation is a feasible approach to improve the heavy metal removal performance due to the dispersive and domain-limiting effects of membrane pores. Ag/ZIF-8/PVDF material is expected to be applied in the field of practical Cr(VI)-containing industrial wastewater treatment.