Degradation Of Imidazolium Ionic Liquids In A Thermally Activated Persulfate System

Ionic liquids(ILs)have been widely used in synthetic chemistry,catalysis,electrochemistry,separation and purification because of their unique physical and chemical properties,such as low vapor pressure,high thermal stability,wide liquid range and good chemical stability.However,toxicological studies have shown that ILs were toxic and corrosive.Some ionic liquids are even more ecotoxic than traditional organic solvents,and they are difficult to be biodegraded.Therefore,it is of great significance to study the chemical degradation of ionic liquids.In this paper,thermally activated persulfate oxidation processes was used to degrade commonly used imidazolium ionic liquids.The degradation kinetics of four ILs with different alkyl side chain and three ILs with different anions were studied.The degradation intermediates of four ILs with different alkyl side chain were analyzed.The possible degradation pathways were speculated.The acute toxicities of the degradation products were evaluated using nematode Caenorhabditis elegans and luminescent bacterium Q67.The main research contents are as follows:1.In the thermally activated persulfate system,the effects of persulfate(PS)concentration,pH and temperature of the reaction system on the degradation of ILs were investigated with C41nimBr as a representative.The results showed that the degradation efficiency of C4mimBr increased with the increase of PS concentration,pH and temperature of the reaction system,and the degradation process accorded with pseudo-first-order kinetics.After 5 hours of reaction,more than 80%of C4mimBr was mineralized.Sulfate radical SO4·-was the dominant oxidant under neutral pH condition.2.The relationship between degradation rate and alkyl side chain length(CnmimBr,n=2,3,4,6)and anion type(C4mimX,X?Cl-,Br-,BF4-)of ILs was studied.The results showed that the length of alkyl side chain and the type of anions did not affect the degradation rate,but the mineralization ratio of ILs decreased with the increase of alkyl side chain length.The intermediate products of different ILs(CnmimBr,n=2,3,4,6)were analyzed,and the possible degradation pathways were speculated.The results showed that the degradation pathways of the four ILs were similar.3.Changes of acute toxicitdes of CnmimBr(n=2,3,4,6)during the thermally activated persulfate process were evaluated using luminescent bacterium Q67 and nematode Caenorhabditis elegans.The results showed that the toxicity of ILs degradation products decreased gradually with degradation time,which indicates that the degradation method provided in this paper is safe and reliable.