Browsing by Author "Ofomaja, Augustine E."

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    An Insight into the Adsorption Mechanism of Hexavalent Chromium onto Magnetic Pine Cone Powder
    (Springer, 2019-07-23) Ouma, Linda Immaculate A.; Naidoo, Eliazer B.; Ofomaja, Augustine E.
    The remediation of hexavalent chromium [Cr(VI)] contaminated water has been a challenge due to its high toxicity and mobility in the environment. Adsorption has so far been the most promising method for the treatment of chromium containing water due to the availability of low cost materials capable of chromium sequestration. The mechanism for hexavalent chromium removal has however not been fully understood with many studies pointing to a reduction-coupled mechanism. In this study, a composite material consisting of agricultural waste material (pine cone) and magnetite nanoparticles was used for the remediation of hexavalent chromium contaminated water with a focus on the removal mechanism and adsorbent regeneration studies. The mechanism was identified to be adsorption-coupled reduction where Cr(VI) was reduced on the adsorbent surface to the less toxic trivalent chromium [Cr(III)] before being adsorbed. The adsorbed chromium was successfully desorbed using NaOH allowing for concentration and chromium recovery. The adsorbent material was applied in three adsorption-desorption cycles without a significant loss in adsorption capacity.
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    Iron oxide nanoparticles stabilized by lignocellulosic waste as green adsorbent for Cr(VI) removal from wastewater
    (European Physical Journal of Applied Physics, 2017-07-06) Ouma, Linda Immaculate; Naidoo, Eliazer B.; Ofomaja, Augustine E.
    Magnetite nanoparticles and magnetite-pine cone nanocomposite were prepared and applied in the adsorption of hexavalent chromium from water. Pine cone powder stabilized the nanoparticles and acted as a support while simultaneously introducing functional groups which improved metal adsorption. The nanocomposite retained the nanoparticles magnetic properties while improving chromium adsorption efficiency. Adsorption of hexavalent chromium on both materials was pH and concentration dependent with the most efficient adsorption occurring at pH 2 and 75 mg/L. On both materials, chromium adsorption was spontaneous with Gibbs free energy values of −19.2 kJ mol−1 to −23.7 kJ mol−1 and −18.0 kJ mol−1 to −24.2 kJ mol−1 for nanoparticles and nanocomposite respectively between 298 K and 319 K. The changes in enthalpy and entropy were determined to be 44.4 kJ mol−1, 212.7 J K−1 mol−1 and 78.3 kJ mol−1, 323.3 J K−1 mol−1 for the prepared nanoparticles and nanocomposite respectively.