Copper (II) ions adsorption by untreated and chemically modified Tectona grandis (teak bark): kinetics, equilibrium and thermodynamic studies

Abstract

In this study, untreated Tectona grandis (UTG) and citric acid- modified T. grandis (CAMTG) bark powder were used for the adsorption of Cu (II) ions from aqueous solution. The UTG and CAMTG were characterized by Fourier Transform Infrared (FTIR), and scanning electron microscopy (SEM). The adsorption characteristics were carried out by determining the solution pH, initial concentration of Cu (II) ions, effect of time and temperature. Langmuir, Freundlich and Temkin isotherms were used to describe the equilibrium model with Freundlich isotherm giving the best fit. The maximum monolayer adsorption capacity for CAMTG was higher than that of UTG. Also, there was about a four-fold increase in the adsorption of Cu(II) ions by CAMTG (Ao = 87.0 mg/g) over UTG (Ao = 22.9 mg/g). The kinetic data were explained by employing the pseudo-first and pseudo-second order models. The pseudo-second order kinetic model has an outstanding suitability to the experimental data. The positive enthalpy and negative free energy are indications of the endothermic and spontaneous nature of the copper (II) ion adsorption process. CAMTG is therefore, a more viable adsorbent for the removal of Cu(II) ions from aqueous solution than UTG.