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

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 center dot- was the main factor in the photo-catalytic process, followed by center dot 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.