Equilibrium, Kinetic and Thermodynamic Studies of Dyes in Aqueous Solution onto Iron Nanocomposite Stabilized by <i>Irvingia gabonensis</i> Leaf Extract

Abstract

Elimination of dyes in contaminated water or wastewater has become a universal challenge because of their colouration, toxicity, mutagenicity and carcinogenicity when discharged into the recipient environment without treatment and several technologies have been developed to deal with this problem. This paper reports the potential of exploring the use and comparison of conventional iron zero-valent (nZVI) nanoparticle and Irvingia gabonensis stabilized iron nanocomposite (Ig-nZVI) for the elimination of methyl red (MR) and methyl orange (MO) dyes in aqueous solution under effect of different experimental conditions of adsorbent dosage, initial dye concentrations, pH, contact time and temperature. Data obtained show an increase in percent dye elimination as the amount of adsorbent increased. The optimal removal of MR and MO occurred in ˂ 60 min of the start of each experimentation, obtained at a maximum pH of 5.1 at 98.5% and 80.6% for adsorbent dosage of 0.3g/50 mL and 20 mg/L initial dye concentration at temperature of 27^oC. The experimental data fitted the Lamgmuir isotherm with maximum adsorption capacity (qmax) of 166.7mg/g (Ig-nZVI) and 83.35 mg/g (nZVI) for MR while 128.21 mg/g (Ig-nZVI) and 40.02.5 mg/g (nZVI) were obtained for MO. Kinetics studies showed that the removal of MR and MO fitted the pseudo second-order model. The adsorption of MR and MO were endothermic and spontaneous with enthalpy values of 3.39kJ/mol (Ig-nZVI) and 776.26kJ/mol (nZVI) and standard Gibbs free energy values of -5.95kJ/mol (Ig-nZVI) and -12.00kJ/mol (nZVI). Thermodynamic studies (ΔG < 0, ΔH < 0, ΔS > 0) implied a spontaneous and exothermic process in nature. The adsorption of MO was endothermic and spontaneous with enthalpy values of 31.70kJ/mol (Ig-nZVI) and 20.91kJ/mol (nZVI) and standard Gibbs free energy values of -5.92kJ/mol and -7.07kJ/mol for Ig-nZVI and nZVI respectively. Adsorbent produced from leaf extracts of African mango tree (Irvingia gabonensis) and stabilized by iron oxide could be an attractive option for elimination of dye from industrial effluents.