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Microwave assisted synthesis of oleic acid modifed magnetite nanoparticles for benzene adsorption
(Environmental Nanotechnology, Monitoring & Management, 2021-01-30) Masuku, Makhosazana; Ouma, Linda Immaculate; Pholosi, Agnes
Benzene is a carcinogenic, mutagenic and highly toxic nonpolar organic compound, its presence in water occurs as a result of leakage of underground pipes and improper effluent disposal. Adsorption techniques have proven to be efficient for benzene removal from water providing a low maintenance method with high removal efficiencies. Nanoparticles provide high surface areas for adsorption and magnetite particles are specifically advantageous owing to their magnetic characteristics. Magnetite surfaces require modification with hydrophobic compounds for the adsorption of nonpolar pollutants. Herein, magnetite nanoparticles (MNP) were modified with oleic acid to form a magnetite-oleic acid composite (MNP-OA) via microwave synthesis for the adsorption of benzene from simulated wastewater. Infrared analysis confirmed the interaction between magnetite and oleic acid and particle
diameters were determined by XRD analysis as 19.7 nm and 17.1 nm for MNP and MNP-OA respectively. Magnetic measurements indicated that both materials were superparamagnetic with a decrease in saturation magnetization after modification due to the non-magnetic layer on the surface. Oleic acid modification improved the benzene uptake of magnetite nanoparticles by approximately 30 % while kinetic studies suggested that a concentration driving force controlled the adsorption process. The adsorbent was regenerated and was efficient for five adsorption-desorption cycles.
Monitoring of Annual Effective Dose (Aed) in Surface Soils of Ahero Rice Fields, Kenya
(Journal of Engineering and Technology for Industrial Applications, 2023-12-30) Wanyama, Mukanda Kere; Waswa, Michael Nakitare; Ouma, Linda Immaculate
The annual effective doses (AED) both AED (in) and AED (out) in the surface soils of Ahero rice fields, Kenya were investigated. The associated health risk of the soils from the four fields Field 1, Field 2, Field 3 and Field 4 was measured using gamma ray spectrometric technique employing Sodium Iodide Thallium doped detector. Five surface soil samples were collected at a depth of 15 – 20 cm from the Field 1, Field 2, Field 3 and two samples from Field 4. The average AED (in) of 0.30 ± 0.01 mSv/y and an average AED (out) of 0.20 ± 0.01 mSv/y for field 1, an average AED (in) of 0.19 ± 0.01 mSv/y, an average AED (out) of 0.20 ± 0.01 mSv/y for field 2, an average AED (in) of 0.28 ± 0.01 mSv/y and an average AED (out) of 0.18 ± 0.01 mSv/y for field 3 and an average AED (in) of 0.34 ± 0.01 mSv/y and an average AED (out) of 0.23 ± 0.01 mSv/y for field 4. All the AED values both in and out from the four fields were below the recommended level of 1mSv/y. The values indicate that there is no health hazard associated with the surface soils of the study area to the farmers and the general population.
Optimizing Cr(VI) adsorption parameters on magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles
(Physical Sciences Review, 2023-07-23) Ouma, Linda Immaculate A.; Pholosi, Agnes; Onani, Martin
Magnetite as an adsorbent is efficient since iron oxides have high affinities for heavy metal pollutants and are environmentally friendly. Manganese oxides provide catalytic properties which are desirable during the remediation of multi valent pollutants. Magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles were synthesized and characterized to determine the manganese doping effects on magnetite’s crystal and surface properties. Fe3O4 and MnxFe(3-x)O4 showed similarities in crystal morphology indicating that manganese doping did not alter the nature of Fe3O4 nanoparticles. Manganese doping improved magnetite’s thermal properties as well as its surface area providing improved adsorption characteristics. The as-synthesized particles were applied in the optimization of hexavalent chromium adsorption. Adsorption proceeded under similar conditions for both adsorbents indicating their structural similarities. Higher efficiencies were observed on the doped adsorbent due to increased surface area and the presence of additional functional groups. Solution pH significantly affected the adsorption process aiding in the
reduction of Cr(VI) ions to the less toxic Cr(III) species. The adsorption distribution coefficient KD indicated that manganese doping significantly improved magnetite’s affinity for hexavalent chromium. Adsorption and reduction were determined to responsible for pollutant reduction in solution at optimal conditions of pH 2, 5 g/L and 100 mg/L for adsorbent mass and solution concentration.
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.
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.