Sorptive Removal of Phenol from Aqueous Solution by Ammonium Chloride-Treated and Carbonized Moringa oleifera Seed Shells

Ammonium chloride-activated (AMSS) and carbonized (CMSS) adsorbents were prepared from Moringa oleifera seed shells, characterized and evaluated for aqueous phase removal of phenol. The effect of operational parameters such as initial phenolic solution pH and adsorbent dosage on equilibrium sorption were studied. Adsorption isotherms and kinetic experiments performed at 25 - 40oC furnished some thermodynamic and kinetic parameters, respectively. Both AMSS and CMSS showed favorable attributes (pH, bulk density, attrition, iodine number/surface area, surface charge/functional groups). Phenol uptake decreased with increase in solution pH for both adsorbents. Across the temperatures, equilibrium removal efficiencies were AMSS (48.21-RE ( %) -79.3) and CMSS (39.88-RE ( %) -81.45). Maximum adsorption capacities, Qmax (mg/g) were AMSS (6.21-Qmax-6.76) and CMSS (10.75-Qmax-13.16). Free energy change (Go) and enthalpy change (Ho) indicated that phenol uptake was feasible and exothermic for both adsorbents, but occurred via the physisorptive and chemisorptive modes for AMSS and CMSS, respectively. Adsorption kinetics obeyed the pseudo-second-order model. The adsorbents show a promise of applicability in dephenolation of aqueous effluents/wastewater.