Comparison of different advanced oxidation processes for the degradation of room temperature ionic liquids

Imidazolium ionic liquids have been widely researched as possible “green” replacements for organic solvents. The “green” aspect is related mainly to their non-measurable vapor pressure, which is obviously not enough to justify calling a technology cleaner. Some quantities of ionic liquids will soon be present in technological wastewater, where, because of their great stability, they could become persistent pollutants and break through classical treatment systems into natural waters. In order to verify future possibilities of their cleanup, three common advanced oxidation processes (UV, UV/H2O2 and UV/TiO2) were studied for their applicability in the degradation of imidazolium ionic liquids in aqueous solution. The greatest degradation efficiency for all the compounds studied was achieved with the H2O2/UV system. The stability of imidazolium ionic liquids with respect to all the tested oxidation processes is structure-related. Except for direct photolysis, where the least degradable compounds were OMIM and HMIM, 1-ethyl-3-ethylimidazolium was found to be most stable entity among the compounds studied in enhanced photodegradation systems.