Microplastic separation and degradation via transition metal-based nanomaterials

Microplastic (MP) pollution has triggered a serious concern due to its severe impact on the water environment and human health. To mitigate this issue, effective and sustainable remediation methods are urgently needed. Although there are a large number of accessible strategies, the scalable synthesis of high-performance nanomaterials for both MP capture and degradation is still lacking. This thesis aims to address these challenging issues by developing new strategies to synthesize advanced nanomaterials for MP remediation, including magnetic adsorption nanomaterials (Fe3O4 nanodiscs (NDs)), hydrothermal catalytic degradation nanomaterials (layered double hydroxides (LDHs)), and peroxymonosulfate (PMS)-activated advanced oxidation nanomaterials (Oxygen vacancy-rich CoFeOx nanosheets anchored on graphene oxide (CFGO)). Chapter 1 introduces the environmental context of MP pollution, detailing the current remediation methods and their inherent limitations, such as high operational costs, limited scalability, and insufficient effectiveness in complex water matrices. This highlights the necessity for advanced materials-based solutions combining physical adsorption and catalytic degradation. In Chapter 2, the recent MP removal technologies and their limitations are reviewed in detail. The advantages of nanotechnology-based approaches are highlighted. It is essential to develop environmentally friendly, low cost and scalable strategies for efficient MP remediation combining both capture and degradation processes. In Chapter 3, the synthesis and application of ultrathin Fe3O4 NDs with magnetic vortex domains are reported. The magnetic vortex Fe3O4 NDs exhibited high magnetic adsorption efficiency for MPs at different size scales. Characterisations results demonstrated the structural stability, high adsorption capacity and recyclability of Fe3O4 NDs, which are ideal candidates for scalable MPs removal. In Chapter 4, transition-metal based LDHs (NiFe, CoFe, MnFe) were investigated as catalysts for MPs degradation via hydrothermal Fenton-like oxidation. NiFe-LDH exhibited outstanding catalytic activity for MPs removal. The advanced oxidation process could achieve efficient MPs degradation at relatively moderate temperature. The mechanism study demonstrated that •OH was the dominant reactive species. The LDH technology is simple, low cost and has excellent potential for scalability. In Chapter 5, CFGO composites with abundant oxygen vacancies were designed for selective ¹O₂ generation in PMS based advanced oxidation. The CFGO exhibited remarkable catalytic performance for MPs removal. The advanced oxidation process could efficiently degrade different types of MPs, including polyethylene, polystyrene and polyamide. Density functional theory (DFT) calculations further demonstrated the important role of oxygen vacancies in PMS activation and 1O2 production. However, the scalability and process optimization are still important issues for its practical application. Comparatively, Fe3O4 nanodiscs and LDHs are scalable and cost-effective for larger remediation applications, while CFGO catalysts are capable of precise control of ROS generation and structural functionalities for targeted and high-value treatments. Overall, these two approaches are great advances beyond conventional MP remediation applications for scalable, reusable, and environmentally friendly remediation. The results from this thesis can guide further research towards optimization of synthetic conditions, incorporation of adsorption and degradation strategies into hybrid systems, and detailed characterizations in real wastewater samples to further promote the translation of advanced nanomaterials from fundamental explorations towards practical large-scale environmental applications.