Remediation of industrial dye by Fenton-activated biogenic waste

This research work gave details on the application of Malacantha alnifolia tree bark as a low-cost adsorbent and a heterogeneous Fenton-catalyst for the removal of methylene blue from aqueous solution. The tree bark was modified using different ratios of ferrous sulphate and hydrogen peroxide (Fenton's reagent). Fenton modification of the adsorbent was more effective at lower concentration of ferrous sulphate solution (100 mg.L ^{− 1}) and at higher concentration of hydrogen peroxide solution (60,000 mg.L ^{− 1}). The modified adsorbent was characterised by x-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR) and pH of point of zero charge (pHpzc). Applying batch experimental method, the effects of various parameters such as pH, Fe²⁺/H₂O₂ concentration ratio, contact time, initial methylene blue (adsorbate) concentration and adsorbent dose were studied. The experimental data were best described by Freundlich isotherm model (R²=0.972) and the adsorption kinetics followed the pseudo-second order kinetic model (R²=1.000). The thermodynamic analysis of the adsorption processes indicated a spontaneous adsorption process (ΔG° at 25 °C= –5.335 kJ/mol); change in enthalpy showed that the remediation process was exothermic (ΔH°= –1.964 kJ/mol) and change in entropy indicated that the adsorption process was disorderly (ΔS°=+11.314 J/mol/K). Desorption studies showed that the modified adsorbent can be regenerated effectively and re-used. Fenton-modification improved the adsorption capacity of Malacantha alnifolia tree bark and prevented bleeding of the tree bark into the dye solution.