Sequestered uptake of chromium(VI) by Irvingia gabonensis stem bark extract anchored silica gel

Abstract

In this research, the mechanism and efficiency of Cr(VI) uptake onto Irvingia gabonensis stem bark extract modified silica gel (IGMS) was reported for the first time. The pristine silica gel (PS) and IGMS adsorbents were characterized by the XRD, FTIR, FESEM, EDX, BET, and TGA techniques. The characterizations proved the successful coating of the plant extract onto silica gel. The FTIR spectra showed the Si–O–Si bands present on the silica gel materials. The FESEM revealed an increase in surface roughness of IGMS after coating with the plant extract, while TGA showed a high thermal stability of both PS and IGMS with over 65% of the initial weight retained at 800 °C. The batch Cr(VI) adsorption revealed optimum uptake at pH 2.0, with a maximum monolayer uptake capacity of 23.26–26.18 mg/g for IGMS at temperatures of 295 to 318 K. The kinetic modeling of Cr(VI) uptake onto PS and IGMS was best fitted by the Elovich model in comparison to the pseudo-second-order, pseudo-first-order, and intraparticle diffusion model. The Langmuir and Freundlich isotherms gave the best fit to the adsorption of Cr(VI) onto IGMS and PS, respectively. Adsorption thermodynamics revealed endothermic, increased randomness and spontaneous removal of Cr(VI) onto IGMS and PS adsorbents. The results revealed that Irvingia gabonensis stem bark extract modified silica gel is a viable and highly efficient adsorbent for the removal of Cr(VI) from Cr(VI)-contaminated effluents.