Ahmed, Diana Salah Raie;
(2022)
Chemical effects of magnetic nanoparticles on heavy metal removal.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The safe removal of hexavalent chromium (Cr<sup>6+</sup>) from waste streams is in increasing demand because of environmental, economic and health considerations. The integrated adsorption and bio-reduction method can eliminate the carcinogenic Cr<sup>6+</sup>and detoxify Cr<sup>6+</sup> to the less toxic trivalent state (Cr<sup>3+</sup>). This work describes a synthetic protocol for achieving the best chemical composition of spherical and flower-like manganese ferrite (Mn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub>) nanostructures (NS) for Cr<sup>6+</sup> adsorption. NS, with the highest adsorption performance, was selected to study its efficiency in the extracellular reduction of Cr<sup>6+</sup> to Cr<sup>3+</sup> by Shewanella oneidensis (S. oneidensis) MR-1. Mn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub>NS were prepared by a polyol solvothermal synthesis process. They were characterised by powder X-Ray Diffraction, Transmission Electron Microscopy, X-ray Photoelectron Spectrometry (XPS), Dynamic Light Scattering and Fourier Transform-Infrared Spectroscopy. Inductively Coupled Plasma Atomic Emission Spectroscopy evaluated the elemental composition of Mn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub>NS. Our results revealed that the oxidation state of the manganese precursor significantly affects the Cr<sup>6+</sup> adsorption efficiency of Mn<sub>x</sub>Fe<sub>3-x</sub>O<sub>4</sub>NS. The best adsorption capacity for Cr<sup>6+</sup> is 16.8 ± 1.6 mg Cr<sup>6+</sup>/g by the spherical Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> at pH 7, which was 1.4 times higher than that by Mn<sub>0.8</sub><sup>3+</sup>Fe<sub>2.2</sub><sup>3+</sup>O<sub>4</sub> nanoflowers. A chemical redox reaction took place between the adsorbent surface of Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs and Cr<sup>6+</sup> solution as was approved by XPS. The redox-based interaction was attributed to the relative excess of divalent manganese in Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs based on our XPS analysis. The lethal concentration of Cr<sup>6+</sup>for S. oneidensis MR-1 was 60 mg/L. Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs improved the viability of S. oneidensis MR-1 by 3.3 times at the sub-lethal dose of Cr<sup>6+</sup> (50 mg/L). The addition of Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs to S. oneidensis MR-1 enhanced Cr<sup>6+</sup>bio-removal by 2.66 times compared to using bacteria alone and by 1.37 times of applying Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs. To gain insights into the enhancing impact of Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs on the microbial reduction of Cr<sup>6+</sup>by S. oneidensis MR-1, the change of the morphology of S. oneidensis MR-1 cells in response to their treatment with a sub-lethal dose of Cr<sup>6+</sup>was monitored using Scanning Electron Microscopy. The oxidation state of Cr was studied using XPS, which revealed that integrating both S. oneidensis MR-1 and Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs boosted the detoxification of the removed Cr<sup>6+</sup> by 2.1 times by using S. oneidensis MR-1 alone and by 1.4 times by applying Mn<sub>0.2</sub><sup>2+</sup>Fe<sub>2.8</sub><sup>3+</sup>O<sub>4</sub> NPs alone. This has opened up a new route for research using nanomaterials for enhancing the bio-reduction of more Cr<sup>6+</sup> using bacteria. This work provides a cost-effective method for Cr<sup>6+</sup> removal with less Cr-containing sludge.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Chemical effects of magnetic nanoparticles on heavy metal removal |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10161913 |
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