Adsorption of Methyl Orange and Amoxicillin from Water using Metal-organic Framework Prepared from Solvothermal Mixing of Zn ions and 1,4-Benzenedicarboxylic Acid Moieties

Abstract

In this study, we determined the capacity of metal organic framework, which we prepared by the solvothermal mixing of Zn ions and 1,4-benzenedicarboxylic acid (Zn/BDC) moieties to adsorb methyl orange (MO), and amoxicillin (AMX). Results obtained show that MO and AMX adsorption capacity by Zn/BDC (mg/g) was found to increase with increase in solution concentration, for each contaminant type. Three isotherm models were applied to the adsorption data: Freundlich, Langmuir, and Temkin.  R² values obtained for the adsorption of MO, 0.9778, 0.8589 and 0.9038 for Freundlich, Langmuir and Temkin plots respectively, indicates that all three models fit the adsorption data appreciably good, with the Freundlich isotherm providing the best fit. Those for AMX, 0.6737, 0.0616, and 0.5300 indicated a poor fit, but the Freundlich isotherm came out as best fitting isotherm for AMX, an indication of a multilayer adsorption process. Maximum possible amount of contaminant adsorbed per gram of Zn/BDC deduced from the Langmuir isotherm for the adsorption of both contaminants were 93.46 mg/g and 18.41 mg/g for MO and AMX respectively. This, among other indicators, showed the preference of Zn/BDC for MO relative to AMX. Adsorption kinetic models: pseudo first order, pseudo second order, and Weber-Morris intraparticle diffusion models, gave R² values that indicate that intraparticle diffusion dominated the adsorption of MO, while the adsorption of AMX followed pseudo second order kinetics, an indicator of chemisorptive mechanism. Calculated Q_e values, were in close agreement with experimental values.