This doctoral thesis explores the versatile chemistry of layered double hydroxides (LDHs), focusing on their modification through cationic and anionic engineering as well as covalent functionalization to enhance and understand their applications in catalysis, energy storage, and environmental remediation. The study begins by introducing the unique properties of LDHs stemming from their 2D layered structures and versatility, which allow for modifications at the atomic level that significantly impact their macroscopic properties. In the exploration of cationic engineering within LDHs, the thesis delves into how modifications in the metallic composition and cationic arrangement within LDH layers can significantly enhance their catalytic efficiency. The study rigorously synthesizes and characterizes several LDH variants, specifically MgAl-LDHs, MgFe-LDHs, and NiFe-LDHs, focusing on the impact of metal clustering within these structures on their catalytic performance. For MgAl-LDHs, the research demonstrates that the clustering of Al within the layers significantly boosts catalytic activity for the Baeyer-Villiger oxidation. This enhancement is linked to an increased number of Brönsted basic sites that facilitate the reaction mechanism, attributed to the unique distribution of Al in the LDH structure which optimizes the availability of active sites for catalysis. Similarly, the thesis examines MgFe-LDHs for their performance in the oxygen evolution reaction (OER), where the degree of Fe clustering is found to play a crucial role. It is observed that less clustered Fe environments lead to more favourable conversions to NiFe (oxo)hydroxide on Ni-foam collectors, enhancing the overall catalytic activity. This indicates that precise control over Fe clustering within the LDH can optimize electrocatalytic properties tailored for efficient hydrogen production. Additionally, NiFe-LDHs are analysed for their exceptional catalytic properties, particularly in OER applications. The arrangement of Fe and Ni in these structures significantly affects their electrocatalytic behaviour. Notably, the study observes how Fe clustering favours the conversion to more active catalytic phases, such as gamma-oxyhydroxide, enhancing the material's performance as catalyst for the OER in alkaline media. To achieve the precise control over the arrangement within LDH layers, various synthesis methods including hydrothermal methods and room-temperature synthesis are employed. These methods have been thoroughly investigated to understand how they influence metal clustering within LDHs. Each synthesis technique is pivotal, as it significantly impacts the structural properties of the LDHs, thereby affecting their catalytic efficiency. By experimenting with anions of varying lengths, the research demonstrates that increasing the interlayer spacing not only enhances the supercapacitive behaviour of CoAl-LDHs but also significantly alters the magnetic interactions within NiFe-LDHs, leading to distinct 2D magnetic behaviours. This part of the thesis underscores the critical role of interlayer spacing in tailoring the properties of LDHs for specific applications, revealing that broader interlayer spacings facilitate enhanced electron mobility and access for electrolyte ions, which are crucial for improving electrochemical performance. Additionally, the study explores how varying interlayer distances affect magnetic properties by modulating the magnetic interactions across the layers, which in turn influences the overall magnetic behaviour of the material. The thesis culminates with a detailed examination of covalent functionalization, a less common strategy in LDH chemistry. It introduces innovative approaches to integrate functional organic molecules like silanes and trisaminomethane (TRIS) into LDH structures, thereby enhancing their stability and utility. The functionalization processes investigated include both post-synthesis modifications for (3-Aminopropyl)triethoxysilane (APTES) and direct synthesis methods that incorporate functional groups during LDH formation for TRIS. The synthesis and characterization of NiFe-APTES LDHs reveal that covalent attachment of APTES molecules improves the material's capability for contaminant removal. This enhancement is attributed to the increased positive charge density of the LDHs, which allows for more effective adsorption of negative charge pollutants from water, such chromates. Conversely, the functionalization of NiFe-LDH with TRIS, demonstrates significant advantages in catalytic applications, specifically in the oxygen evolution reaction (OER). The study shows that the TRIS functionalization not only preserves its structural integrity in alkaline media but also enhances their stability under OER catalytic conditions. This stability is vital for OER processes, where the catalyst must withstand high oxidative environments. Overall, the thesis provides a comprehensive study on the strategic modification of LDHs to develop advanced materials for a range of scientific and industrial applications. By demonstrating the effects of cationic, anionic, and covalent modifications, this research significantly contributes to the field of materials science, offering insights into the design of new materials with tailored properties for specific applications.
