KMnO4 modified magnetic hydrochar for efficient adsorption of malachite green and methylene blue from the aquatic environment

Abstract

This study exploited magnetic citrus peel hydrochar (MHC) modified by KMnO4 (MHC/Mn) for the removal of methylene blue (MB) and malachite green (MG). Effects of initial concentration, pH, dosage, temperature, and ion strength on MHC/Mn adsorption properties were investigated. The adsorption kinetics, isotherm, and mechanism were further explored. The results indicated that Fe3O4 was successfully embedded and MnO2 was coated on MHC after modification. The experiment data were well fitted to the pseudo-second-order kinetic model and Langmuir isotherm model. Thermodynamic parameters showed that the adsorption of MHC/Mn to MB is spontaneous and endothermic, and the adsorption of MG is spontaneous and exothermic. The mechanism of MB and MG interaction with MHC/Mn includes electrostatic interaction, hydrogen bond, surface complexation, and π-π interaction. The maximum adsorption capacity of MB and MG calculated were 175.63 mg/g and 1402.17 mg/g. After four adsorption–desorption cycles, the removal rate of MB and MG were 85.11 % and 69.29 %. MHC/Mn is an economical and environmentally favorable adsorbent for the removal of MB and MG in wastewater.