A review on the evolution of ionic liquids: Sustainable synthesis, applications, and future prospects

Ionic liquids (ILs) have emerged as a transformative class of materials, offering unique physicochemical properties such as low volatility, high thermal stability, and tunable solubility. Their evolution is categorized into four generations: first-generation ILs, primarily used as green solvents; second-generation ILs, designed for specific applications in catalysis and electrochemical systems; third-generation ILs, incorporating bio-derived and task-specific functionalities for biomedical and environmental applications; and fourth-generation ILs, focusing on sustainability, biodegradability, and multifunctionality. This review explores the synthesis, applications, and future scope of ILs across various domains, including biomedicine, renewable energy, industrial processes, and current industry applications. In biomedical sciences, ILs enhance drug solubility, improve targeted drug delivery, and serve as antimicrobial agents, offering novel solutions to pharmaceutical challenges. In the energy sector, ILs play a critical role as electrolytes in fuel cells, supercapacitors, and advanced battery technologies, facilitating efficient energy conversion and storage. Additionally, ILs contribute to CO 2 capture and utilization, addressing global environmental concerns. Current industrial applications of ILs include their use as solvents and catalysts in petrochemical processing, biodiesel production, pharmaceutical synthesis, and metal extraction in mining industries. ILs are also employed in gas separation, electroplating, cellulose processing, and as lubricants in high-performance machinery due to their thermal and chemical stability. Their role in improving battery efficiency, polymer processing, and corrosion protection further highlights their industrial significance. The future of ILs lies in the development of smart, biodegradable, and recyclable materials with tailored functionalities for next-generation applications. Innovations in IL-based energy storage, precision medicine, and sustainable industrial processes will further expand their potential. As research progresses, ILs are expected to drive advancements in green chemistry, renewable energy, and biocompatible technologies, positioning them as key enablers of a sustainable and technologically advanced future. • Comprehensive synthesis and characterization of ionic liquids (ILs). • Tailoring IL properties through customizable cation-anion combinations. • Exceptional stability and durability of IL-based catalytic systems. • Multidisciplinary applications of ILs in biomedicine, energy, and industry. • ILs as sustainable solutions for green technologies and environmental challenges.