The Research Of The Formation Mechanism Of Clay Minerals Supported Ionic Liquid Catalysts Based On Langmuir-blodgett Technique

The Langmuir-Blodgett technique has been employed for the construction ofinterfacial SIL (supported ionic liquid) catalyst. In our experiments, a hybrid LBfilms consist of two components: ionic liquid(IL) and catalyst carrier (saponite andlaponite) and of three components: ionic liquid, catalyst carrier and catalyst specieshave been constructed already.It was found that imidazolium chloride with carbon number more than six in thealkyl substituents can form stable Langmuir monolayer over diluted clay dispersions.By monitoring and recording surface pressure versus time (π-t) kinetic curves, wefound that the adsorption of imidazolium ILs or platinum nanocrystals by clayelementary layers reaches equilibrium within200s, and the molar Gibbs free energychange–dG for the adsorption lies in the range0.34-5.6kJ mol-1. Surface pressureversus area (π-A) isotherms which were obtained from compress the Langmuir filminferred that platinum nanocrystals are deposited in the IL-clay Langmuir films atthe air-water interface and two phase transition points in the π-A isotherms can beobserved during the compression of IL-clay-Pt films.Two methods: interfacial chemical methods (π-t, π-A) and spectroscopicmeasurements (UV-vis absorption, atomic absorption spectroscopy(AAS)) wereused to quantify the amount of imidazoliun IL and Pt that are presented in the LBfilms. Results showed that the amount of adsorbed1-hexadecyl-3-methylimidazolium chloride (C16MIM) in the hybridC16MIM-saponite-Pt film at the first deposition layer is around0.65ng mm-2.Laponite gives a higher adsorption capacity correspondingly. Attenuated totalreflectance (ATR)-Fourier transform infrared spectra (FTIR) confirmed the presenceof IL in the LB films which shares ordered vibrational conformation, however thedegree order of IL molecules becomes worse after incorporation of Pt nanocrystals.Transmission electron microscopy(TEM) verified that Pt nanocrystals with sizeof～5.0nm tend to be observed on the edges of clay layers, and the surfacecoverage of Pt particles can be tuned by the compression pressure. The LB filmscontained Pt nanocrystals were deposited on a glass carbon electrode (GCE), andthe electrocatalytic performance toward methanol electro-oxidation between thethree components have been studied by means of cyclic voltammetry (CV) and chronoamperometry (CA). Results showed that the IL-clay-Pt hybrid film exhibits aremarkable enhancement in catalytic and stability compared to clay-Pt hybrid film.In brief, this paper provide an idea that translate a complex phase adsorption intoLangmuir film surface adsorption, and the formation mechanism of SIL catalyst wasrevealed.