(754c) Mesopore Confinement Effects on Ionic Liquid Hydration

Room temperature ionic liquids (ILs) have been widely investigated as solvents due to their low volatility, good thermal stability, and tunable solvent properties, they have been employed as media for catalytic dehydration of glucose into 5-hydroxymethylfurfural (HMF). [1][2][3] However, their high price, unknown toxicity and difficulty of solute recovery inhibit their large-scale application. Supported ionic liquid systems (SILPs) are believed to be the key to overcome the disadvantages of ILs and allow their properties to be utilized in heterogeneous catalysis. [4][5] The long-term goal of the present study is to understand the interfacial science behind the functionalization of mesoporous silica films with IL and metal-based catalyst systems for heterogeneous catalysis, with dehydration of glucose to HMF as a representative reaction.

Here, in situ transmission FT-IR study is developed as a technique to characterize the interactions of water with IL (1-butyl-3-methylimidazolium chloride (BMIM-Cl)) supported by mesoporous silica films. The approach is to use thin silicon wafers as supports to allow direct transmission monitoring of ionic liquid response to solvent vapors. The development starts with investigation of structural changes of IL thin films on unmodified silicon wafers with respect to relative humidity (RH). This establishes the amount of water absorbed and the mode of interaction with the ionic liquid, as well as the reversibility of hydration upon changes in relative humidity. [6] Next, the effects of confining IL in silica films with mesopores of varying diameters is performed to isolate the effects of confinement on hydration of BMIM-Cl. The base case for this study uses silica films with pore diameter of 8-9 nm prepared using pores templated with Pluronic surfactant P123 that are vertically oriented by chemically modified using a crosslinked layer of P123. [7] Hydration of BMIM-Cl will be compared in films with smaller pores templated with CTAB, and larger pores formed by swelling the P123 templates with triisopropylbenzene. [7]

References

[1] Tariq, Mohammad, et al. "Ionic Liquids in Bulk and at an Interface." Ionic Liquid-Based Surfactant Science: Formulation, Characterization, and Applications (2015)

[2] Zhao, H., J. E. Holladay, H. Brown, and Z. C. Zhang. "Metal Chlorides in Ionic Liquid Solvents Convert Sugars to 5-Hydroxymethylfurfural."Science 316.5831 (2007)

[3] Stefanopoulos, Konstantinos L., George E. Romanos, Olga C. Vangeli, Konstantina Mergia, Nick K. Kanellopoulos, Alexandros Koutsioubas, and Didier Lairez. "Investigation of Confined Ionic Liquid in Nanostructured Materials by a Combination of SANS, Contrast-Matching SANS, and Nitrogen Adsorption." Langmuir 27.13 (2011)

[4] Stefanopoulos, Konstantinos L., et al. "Investigation of confined ionic liquid in nanostructured materials by a combination of SANS, contrast-matching SANS, and nitrogen adsorption." Langmuir 27.13 (2011)

[5] Gupta, Krishna M., and Jianwen Jiang. "Cellulose dissolution and regeneration in ionic liquids: a computational perspective." Chemical Engineering Science 121 (2015)

[6] Maiti, Amitesh, Arvind Kumar, and Robin D. Rogers. "Water-clustering in hygroscopic ionic liquids—an implicit solvent analysis." Physical Chemistry Chemical Physics 14.15 (2012)

[7] Das, Saikat. "Fundamental Studies of Surfactant Templated Metal Oxide Materials Synthesis and Transformation for Adsorption and Energy Applications." Ph.D. Thesis, University of Kentucky, 2015.