Polyhedral Oligomeric Silsesquioxane-Based Ionic Liquids: Syntheses, Properties, and Applications

Polyhedral oligomeric silsesquioxanes (POSS) and ionic liquids (ILs) have emerged as highly promising components for the design of advanced hybrid materials. The integration of ILs onto the POSS core has led to the development of a novel class of materials known as POSS-based ILs (POSS-ILs), which synergistically combine the thermal and mechanical stability of POSS with the tunable physicochemical properties of ILs. Despite their great potential, a detailed and unified review covering the synthesis, properties, and multifunctional applications of POSS-ILs remains limited. This review therefore presents a thorough discussion of their synthetic approaches such as direct functionalization, IL grafting, and sol–gel techniques alongside their distinctive physicochemical features, including high thermal and mechanical stability, ionic conductivity, viscosity control, tunability, solubility, and chemical resistance. Furthermore, the roles of POSS-ILs in catalysis, energy storage and conversion, smart materials, analytical applications, and wastewater treatment are systematically explored. The review also highlights current challenges related to structure–property relationships and multifunctionality, while outlining future perspectives for optimizing POSS-ILs as sustainable, high-performance materials. Overall, this review aims to serve as a comprehensive resource for researchers across materials science, nanotechnology, and environmental chemistry, supporting the continued innovation and application of POSS-ILs in next-generation functional systems.