Enzyme-MOFs for biocatalytic degradation of organic pollutants
| dc.contributor.author | Dlamini, Mbongiseni Lungelo | |
| dc.date.accessioned | 2024-01-29T09:33:02Z | |
| dc.date.available | 2024-01-29T09:33:02Z | |
| dc.date.issued | 2024 | |
| dc.description | A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Chemistry, University of the Witwatersrand, Johannesburg, 2023 | |
| dc.description.abstract | The widespread use of pharmaceutically active compounds (PhACs) and the incidental discharge of endocrine-disrupting chemicals (EDCs) into surface water has resulted in the detection of such compounds in effluents of wastewater treatment plant effluents (WWTPs). This indicates that such contaminants are highly stable and recalcitrant, defying total elimination by traditional technologies. These compounds have been designated as emerging contaminants, and involuntary exposure to them may have negative consequences for humans and aquatic life. As a result, there is a need to investigate potential strategies for effectively eliminating such contaminants from water. Among the various remediation technologies, enzymatic biotransformation of these organic pollutants by oxidative enzymes is a green, cost-effective, and considerably sustainable approach. In this study, an Aspergillus-based laccase, immobilized on zeolitic imidazolate frameworks (ZIF) was investigated for its potential to biodegrade three model PhACs (carbamazepine (CBZ), diclofenac (DFC), and norfloxacin (NOR)), and dimethyl phthalate (DMP) - a potential endocrine-disrupting chemical. The laccase was immobilized via a facile one-pot biomineralization covalent binding procedure. The success of this attachment was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy analysis, demonstrating peaks and proton shifts attributable to functional groups present in the protein structure of the enzyme. Furthermore, Powder XRay Diffraction (PXRD) analysis revealed a preserved crystallographic structure of the ZIF particles after the laccase attachment. Additionally, the characteristic rhombic dodecahedral morphologies of ZIF crystals were retained after enzyme attachment, confirmed by Scanning Electron Microscope (SEM) micrographs, with slightly agglomerated particles. The immobilized laccase (Lac-ZIF) demonstrated significant resistance to adverse environmental conditions such as extreme pH, elevated temperatures of up to 70 ℃ (relatively higher deactivation energies (Ed)), and harsh organic solvents in comparison to the free laccase. Also, the Lac-ZIF proved to be quite recyclable retaining high efficiencies (>70%) for up to 5 reuse cycles, as well as remarkable storage stabilities of up to 15 d. Even though the immobilization of the laccase resulted in diminished affinities for the substrates (analytes) as illustrated by increasing Michaelis constant (Km) values, the Lac-ZIF still outperformed the free laccase in the removal of all the investigated contaminants. This was attributed to the synergistic adsorption and biodegradation effects provided by the ZIF backbone and the attached laccase enzyme. For the optimization of operational parameters for DFC and NOR removal, the quadratic response surface methodology (RSM) regression model proved effective and viable with high accuracy as confirmed by experimental results. In this sense, the experimental values (93.5% for DFC and 94.9% for NOR) were found to be very close to the predicted removal efficiencies, 93.9 and 95.1% for DFC and NOR, respectively. Finally, the synthesized biocatalyst was used to decontaminate the investigated compounds in real river water samples, and it significantly outperformed the free laccase. Due to its remarkable attributes such as thermal and storage stabilities, strong pH resistance, recyclability, and high degradation potential, the Lac-ZIF is a potential candidate for application in greener and more effective wastewater remediation approaches. | |
| dc.description.librarian | TL (2024) | |
| dc.description.sponsorship | Council for Scientific and Industrial Research (CSIR) Department of Science and Innovation (DSI) WITS postgraduate merit award (PMA) Inter-bursary Support Programme (IBS) | |
| dc.faculty | Faculty of Science | |
| dc.identifier.uri | https://hdl.handle.net/10539/37461 | |
| dc.language.iso | en | |
| dc.phd.title | PhD | |
| dc.school | Chemistry | |
| dc.subject | Biocatalytic degradation | |
| dc.subject | Endocrine-disrupting chemicals (EDCs) | |
| dc.subject | Aspergillus-based laccase | |
| dc.title | Enzyme-MOFs for biocatalytic degradation of organic pollutants | |
| dc.type | Thesis |