Browsing by Author "Pholosi, Agnes"

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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.
Optimization studies of BTX removal by magnetite coated oleic acid obtained from microwave‑assisted synthesis using response surface methodology
(Scientific Reports, 2022-12-13) Masuku, Makhosazana; Ouma, Linda; Sanni, Saheed; Pholosi, Agnes
Benzene, toluene and xylene (BTX) are volatile organic compounds released into the environment, that require urgent removal to avoid adverse health effects. In this work, the modelling and optimization of the preparation factors for magnetite coated oleic acid (MNP-OA) composite from microwave synthesis using response surface methodology were conducted to maximize BTX removal, and iron content. The influence of five crucial preparation variables: the Fe3+/Fe2+ solution volumes, microwave power, volume of ammonia water (VAW), reaction time and volume of oleic acid (VOA) on the iron content (% Fe), and BTX adsorption capacity were investigated. The analysis of variance results revealed that VOA and VAW were the most influential factors for high % Fe content, and improved BTX removal. The % Fe, and BTX adsorption capacity for MNP-OA composite at optimized experimental conditions were estimated to be 85.57%, 90.02 mg/g (benzene), 90.07 mg/g (toluene), and 96.31 mg/g (xylene).
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.