- Title
- Graphene@microalgae-based nanohybrid structures as adsorbents for removal of Cr(VI) ions in aqueous solutions
- Creator
- Mulovhedzi, Rolivhuwa
- Subject
- Nanoscience
- Subject
- Nanotechnology
- Subject
- Nonaqueous solvents
- Date Issued
- 2024-12
- Date
- 2024-12
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/69404
- Identifier
- vital:77252
- Description
- iv ABSTRACT The efficient removal of heavy metals using carbon-based nanoadsorbents poses a substantial challenge in the domain of water purification. Graphene-based materials have been extensively utilised in the treatment of water and wastewater due to their tremendous surface areas, porosity, turntable nature to different functional groups, and photo-catalytic properties. In this project, graphene oxide (GO) was synthesised via the modified Hummers method. A similar method was used to produce nitrogen-doped graphene oxide (NGO), with urea as the nitrogen precursor. Utilising biomass materials to dope graphene-based nanocomposites can effectively enhance their application in water treatment. In this work, graphene oxide-microalgae (GO@Algae) and N-doped graphene oxide-microalgae (NGO@Algae) nanocomposites were synthesised by combining GO or NGO with green Scenedesmus microalgae. This was done through a solution self-assembly mixing method using ultrasonication. The resulting nanocomposites were used to remove Cr(VI) from water solutions. The influence of microalgae content deposited on GO and NGO nanosheets at different weight ratios (1:1, 3:1, and 1:3) on the chemical, structural, morphological, and thermal characteristics of nanoadsorbents was evaluated using various techniques such as Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The flat nanosheet-like morphology of GO@Algae and NGO@Algae nanostructured materials was observed through SEM, confirming microalgae's incorporation within the GO and NGO matrices. The thermal stability and surface area properties of GO and NGO nanocomposite materials decreased with the incorporation of microalgae content. The incorporation of microalgae into GO nanosheets showed enhancements in chemical and structural properties due to the presence of the strong covalent interaction (oxygen and nitrogen-containing groups) between the interfaces of nanocomposites. XPS and FT-IR analyses revealed the existence of amides, carboxylic acids, and phosphates, which exhibited positive charges below the pH 2.03 point-of-zero charge. The second phase of the study involved assessing the adsorption capabilities of the GO, NGO nanosheets, and GO@Algae and NGO@Algae nanocomposites in removing Cr(VI)from the water solution. Adsorption parameters such as the effect of solution pH, contact time, adsorbent dosage and metal ion concentrations were evaluated for Cr(VI) removal. When comparing GO, NGO, GO@Algae, and NGO@Algae, it was found that GO@Algae and NGO@Algae exhibited superior adsorption performance due to the available functional groups and well-developed pores. Additionally, a mixed ratio of GO or NGO and algae at a ratio of 1:3 was found to be the most suitable for GO@Algae and NGO@Algae. The adsorption efficiency of nanostructured materials for Cr(VI) is significantly influenced by their surface charge, porosity and specific surface area. The results revealed that the adsorption capabilities of GO@Algae (1:3) and NGO@Algae (1:3) were 2.24 and 2.01 times higher than GO and NGO which were 1.64 and 1.89, respectively, at a solution of pH 2 where HCrO4− species are predominant compared to a solution of pH 5 which predominate a mix of Cr2O72− and CrO42- species. The enhanced performance of the GO@Algae and NGO@Algae nanocomposites is attributed due to their increased surface functionalities and porosity. The adsorption of Cr(VI) ions by the GO/NGO@Algae nanocomposites declined with increasing initial concentration of Cr(VI) species in the water medium. The adsorption kinetics data for GO, NGO, GO@Algae (1:3), and NGO@Algae (1:3) exhibited a good fit with the pseudo-second-order model (R2 > 0.995) suggesting that chemisorption governed the adsorption process. Similarly, the isotherm adsorption findings showed a good fit with the Freundlich model (R2 > 0.961). The findings indicated that the adsorption mechanism process was characterised by monolayer adsorption onto a heterogeneous adsorbent surface. Furthermore, the GO@Algae (1:3) was found to have the maximum adsorption capacity of 10.85 mg/g surpassing the capacities of both unmodified and NGO@Algae counterparts. The application of GO@Algae and NGO@Algae has the potential to promote the green reuse of graphene-based nanomaterials. In summary, GO@Algae and NGO@Algae show great potential as eco-friendly adsorbents for the feasible treatment of heavy metal-contaminated water.
- Description
- Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (111 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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Collections
NMU School of BioMolecular and Chemical Sciences
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | MULOCHEDZI, R.pdf | 4 MB | Adobe Acrobat PDF | View Details Download |