Abstract:
1-hexyl-3-methylimidazolium chloride (HMImCl) removal from aqueous solution has been
achieved by different advanced oxidation processes (AOPs).
HMImCl direct photolysis at 254 nm showed that oxygen mainly intervenes to give O2–·, it
can then react with water to form hydrogen peroxide, capable to photolyze and lead to the
formation of radicals HO•. On the other hand, singlet oxygen does not participate in the
oxidation reaction.
HMImCl degradation rate is appreciably increased by combining the strong oxidant H2O2
with UV light. The H2O2/UV process efficiency is enhanced by increasing H2O2 concentration
up to a limit value imposed by self-quenching reactions. High alkalinity favors the
disappearance while current inorganic anions chlorides, in acidic medium, inhibit it. Very
similar results are obtained with S2O82-/UV process with, in particular, a rate that increases up
to a limiting value of the oxidant concentration.
The reaction rate constants of the hydroxyl radicals determined for the two ionic liquids
studied, transcribe the high reactivity and the speed of reaction of hydroxyl radicals on ionic
liquid. The reaction rate constant of hydroxyl radicals on HMImCl is the same whatever the
concentration of HMImCl
Heterogeneous photocatalysis on TiO2 proved to be efficient to degrade HMImCl. The
process is further improved by H2O2 or S2O82- addition up to an optimum but inhibited by
anion chloride in acidic medium. The process is adequately described by the LangmuirHinshelwood kinetic model.
Selective heterogeneous photocatalysis of HMImCl in presence of benzoic acid has
demonstrated that benzoic acid affect HMImCl’s degradation. A good selectivity was
obtained in acidic medium, where only benzoic acid has been degraded.
