Tetra-n-octylammonium iodide is widely used as a phase transfer catalyst in organic synthesis. It facilitates the transfer of reactants between immiscible phases, enhancing reaction rates and yields in various chemical processes. This compound is particularly effective in nucleophilic substitution reactions, where it helps to solubilize ionic reagents in organic solvents. Additionally, it finds application in the preparation of nanoparticles and in the synthesis of polymers, where it aids in controlling particle size and distribution. Its role in electrochemical studies is also notable, as it serves as an electrolyte additive in batteries and supercapacitors, improving ionic conductivity and stability. In the field of material science, it is utilized in the development of ionic liquids and in the modification of surface properties of materials.