Sequestration of Pb2+ from aqueous solution using bio-based-alkaline modified sorbent from waste Irvingia gabonensis seed husk

The unmodified and modified Irvingia gabonensis (IG) were characterized with Fourier transform infrared (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), thermogravimetric analyzer (TGA), and scanning electron microscope (SEM). The experimental conditions revealed that the optimum adsorption efficiency was achieved at pH 6 within 30 min. FTIR spectra showed an observable shift in peaks which are attributed to the pretreatment with NaOH that necessitated the breakdown of the organic compounds. It was established from the SEM image under different magnifications that the surface morphology of the biosorbent consists of heterogeneous layers and pore cavities which acted as potential sites for Pb2+ adsorption. However, there was a considerable increase in the BET surface area, pore size, and pore width on the modified biosorbent compared to the unmodified biosorbent though this did not translate into higher adsorption capacity. The experimental data were best fitted with the Temkim isotherm model suggesting heterogeneous uptake of Pb2+ onto the base-modified Irvingia gabonensis seed husk. The maximum adsorption capacity was 2.58 mg/g and the kinetic model is best described with the pseudo-second-order reaction suggesting a chemical adsorption mechanism. Also, the two error functions (HYBRID and MPSD) suggested the pseudo-second-order reaction mechanism in the adsorption of Pb2+ onto the base-modified Irvingia gabonensis.