Synthesis, Characterization, and Application of Activated Biomaterials as Potential Adsorbents for the Removal of Cr(VI), Pb(II), and Cu(II) Ions from Aqueous Solution

Piliostigma thonningii (PSH), Perqutinia negrecrecens (PNS), and Hildegardia barteri (HB) activated carbon bio-sorbents were prepared for removal of Cr(VI), Pb(II) and Cu(II) ions from aqueous solutions. The bio-sorbents were characterized using SEM, EDX, FTIR, and CHN methods. The SEM results showed crystalline material with flake-like structures. Effect of concentrations, contact time, pH, adsorbent dosage and temperature were studied to determine the optimal conditions of adsorption. The adsorption capacities of Pb (II) ions was 14.29, 13.74 and 16.67, while Cu(II) ions was 24.88, 17.21 and 25.13 mg/g onto HB, PSH and PNS respectively. Optimum temperature of adsorption was recorded at 40 oC in the pH range between 6 and 7. The thermodynamic study revealed that ∆G◦ values were between -20 and 0 KJmol-1 suggesting spontaneous adsorption. The ∆H for Cr(VI) ions adsorption was +0.067, +0.168, and +0.025 kJ/mol, while Pb(II) ions was +0.137, +0.095, and +0.178 kJ/mol, with that of Cu(II) ions as +0.005, +0.002, and +0.0400 kJ/mol onto PSH, PNS and HB respectively. The ∆S for Cr(VI) ions was found to be +0.320, +0317 and +0.378 kJ/mol, with that of Pb(II) ions as +0.261, 0.244 and 0.188 kJ/mol, while Cu(II) ions was +0.236, +0.210 and +0.193 kJ/mol respectively, showing endothermic and randomness of all the adsorption. The Langmuir isotherm model and pseudo-second order kinetics fitted well to all the adsorption processes. The results demonstrated that the activated carbon bio-sorbents from the three biomasses have the potential to be employed as low-cost adsorbents.