Photodégradation du chlorure de 1-hexyl-3- methylimidazolium en milieu aqueux homogène et hétérogène.

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.