ZnO particles and their derivative, Zn-based layered double hydroxides (LDHs), are widely used in fields such as photocatalysis, energy storage, drug delivery, and adsorption due to their tunable properties and cost-effectiveness. Their performance is closely tied to crystal morphology, influenced by factors like surface area, exposed crystal planes, active sites, and structural complexity. Controlling morphology during synthesis is essential but conventional methods, such as hydrothermal, co-precipitation, and sol-gel processes, face challenges like high energy consumption and complex operations. Thus, greener, more economical approaches hold great promise.
This study uses the Oxidative Ionothermal Synthesis (OIS) method, employing ionic liquids as solvents to oxidise metallic Zn for ZnO and Zn-based LDH synthesis. Ionic liquids, such as Betaine Hydrochloride ([Betaine]·HCl) and 1-Butyl-3-methylimidazolium chloride ([BMIM]Cl), act as both solvents and structure-directing agents, facilitating the control of crystal morphology while reducing energy consumption by enabling room-temperature reactions. The study explores the effects of ionic liquid concentration and reaction time on the morphology and composition of Zn-based nanocrystals. The findings indicate that the presence of ionic liquids facilitates the formation of crystal nanoparticles with enhanced uniformity in both morphology and size.
Relying solely on the reaction between ionic liquids and metallic Zn presents challenges such as slow reaction rates, low yields, and limited morphology selectivity. Building on this, the research further explores the interactions between metal ions and ionic liquids, examining their influence on crystallisation mechanisms and morphological control. Notably, the incorporation of heterometallic ions effectively addresses the slow synthesis rate and limited selectivity of the OIS method, improving both efficiency and structural precision.
Additionally, this method aims to efficiently recover Zn from metal-impure waste streams, specifically targeting the separation of slag generated during steel processing for the synthesis of high-value Zn-based LDH nanomaterials. By leveraging multi-metal doping and ionic liquids, this work regulates crystallization and self-assembly behaviours, providing a foundation for potential industrial applications.
