Metal selectivity and effects of co-existing ions on the removal of Cd, Cu, Ni, and Cr by ZIF-8-EGCG nanoparticles

Recently, the developments of MOFs and their applications on heavy metal removal have attracted much attention. In this paper, we focused on the influence of co-existing ions on the adsorbability of epigallo-catechin gallate (EGCG) modified ZIF-8 in a multi-metal system (Cd(II), Cu(II), Ni(II), and Cr(VI)). It was found that the adsorption of Cd(II), Cu(II), Ni(II), and Cr(VI) on the ZIF-8-EGCG fitted well with the pseudo second-order kinetic model and Langmuir isotherm. The adsorption selectivity of ZIF-8-EGCG in the mixed metal solution followed the order of Cu(II) >> Cr(VI) > Cd(II) > Ni(II). Besides, Cu(II) was the most attractive substance with a maximum capacity of 232.97 mg.g(-1). Copper also disturbed the adsorption of Cd(II) and Ni(II) and contributed the most to the Cr(VI) removal. The natural anions (e.g., Cl, NO3-, AsO2, SO42) significantly impeded Cr(VI) adsorption, while low concentrations of natural cations (e.g., K+, Na+, Ca2+, and Mg2+) facilitated the adsorption of Cd(II), Cu(II) and Ni(II). (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This paper focused on the influence of co-existing ions on the adsorption performance of epigallo-catechin gallate (EGCG) modified ZIF-8 in a multi-metal system. It was found that Cu(II) exhibited the highest adsorption capacity and interfered with the adsorption of other metals. Natural anions significantly impeded Cr(VI) adsorption, while natural cations facilitated the adsorption of Cd(II), Cu(II) and Ni(II).