Ionic liquids (ILs) are considered a remarkable class of versatile compounds that have revolutionized materials science and green chemistry. They are considered designer solvents because the cation or anion pairs can be selected to modify the polarity, viscosity, acidity/basicity, hydrophilicity, coordination ability, and thermal stability. The ILs are not only used as solvents in the reaction but also play an active role in the synthesis, stabilization, and surface modification of nanomaterials (NMs). The capacity to design ILs with specific functionalities has made them essential tools in nanotechnology. When ILs are integrated with NMs, such as metal oxides, noble metals, carbon allotropes, and conducting polymers, it leads to improved colloidal stability, shape and size control, and tailored surface chemistry, often accompanied by novel functionalities, including enhanced catalytic selectivity, electrical conductivity, and redox activity etc. These features can be helpful for sustainable environmental applications. In this chapter, we have explored the synthesis, design, and properties of IL-modified nanomaterials, focusing on how ILs enhance the properties of NMs, promote green synthesis routes, and contribute to analysis, pollution control, and environmental monitoring.