Removal of methyl orange and methylene blue by bimetallic zinc/cobalt metal–organic skeleton/carbon nanotubes (Zn/Co-ZIF@CNTs)

Abstract

Zinc/cobalt metal–organic skeleton/carbon nanotubes (Zn/Co-ZIF@CNTs) were prepared by solvothermal method using Zn/Co-ZIF as the main raw material and CNTs as the carrier. The results showed that Zn/Co-ZIF@CNTs retained the high specific surface area and large porosity of ZIFs while exhibiting a stable cubic crystal structure. At the optimal initial dye concentration, the removal rates for methyl orange (MO) and methylene blue (MB) reached over 85%. When the dosage of Zn/Co-ZIF@CNTs was 30 mg in a 30 mL solution, the removal of MO and MB reached the maximum. The MO removal rate in mixed solution was generally lower than that in unmixed solution, and the removal rate of MB was the opposite. The second-order kinetic model was the most suitable for describing the adsorption of MO and MB by Zn/Co-ZIF@CNTs, and it was dominated by chemisorption. The reaction isotherms for the adsorption of MO were well fitted by the Langmuir model. The adsorption process for MB was consistent with the Freundlich adsorption isotherm model. The adsorption mechanism for MO and MB was mainly electrostatic interactions and π–π stacking; moreover, competitive adsorption and synergistic adsorption effects might be involved.