Chemical pretreatment of Lagenaria breviflora seeds used as biosorbents for the removal of aqueous-bound Ni2+

Abstract Lagenaria breviflora (LB) seeds were modified with acid (AMLB) and base (BMLB) for the sorption of Ni2+ from an aqueous solution. It was characterized by Fourier transformation infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analyzer (TGA), and Brunauer–Emmett–Teller (BET). Kinetic, isotherm thermodynamic, and effects of pH were also studied. The FTIR revealed a shift and formation of new functional groups on the pretreated biosorbent surface which could be attributed to the adsorption of Ni2+ onto the modified LB. SEM analysis under different magnifications revealed that the external surface of the modified LB exhibited several cracked surfaces and different pore structures which could be involved in the adsorption of Ni2+. The XRD showed an amorphous structure, while the BET revealed a large surface area (BMLB-360.430 and AMLB-322.965 m2/g). The experimental conditions – contact time, pH, and initial metal ion concentration indicated that the maximum adsorption was attained at 30 min at pH 6, while the adsorption efficiency increased as the concentration of the biosorbents increased. Kinetic studies indicated that the sorption process correlates with the pseudo-second-order kinetic model suggesting a chemosorption mechanism. The isotherm data obtained obeyed a Langmuir model suggesting monolayer adsorption of Ni2+. The calculated sorption thermodynamic factors showed the adsorption of Ni2+ to be exothermic and spontaneous.