Synthesis in ionic liquids
4.3.2 Synthesis in ionic liquids
Ionic liquids are organic salts with a melting point below 100 °C. In general they consist of a bulky organic cation and a weakly-coordinating anion (figure 1). This leads to different properties from classical solvents, like a negligible vapor pressure. Electrostatic interactions between particle surface and ionic liquid stabilize nanoparticles, which renders surface modifying agents unnecessary.
Figure 1: Typical cations an ions used in ionic liquids.
ILs are thermally stable at high temperatures and are ideal solvents for microwave reactions due to their high polarisability and conductivity. In our current researches ionic liquids are used both as a solvent as well as a reactive reagent. For instance, [C4mim][BiI4] was prepared by reactioon of [C4mim]I with BiI3 and structurally characterized by single crystal X-ray diffraction using the in situ crystallization method.
Figure 2: Solid state structure of [C4mim][BiI4]
The combination of metal-containing ionic liquids and metal-organic precursors allows the synthesis of various materials. For instance, Bi2Te3 was successfully synthesized by thermolysis of bis(triethylsilyl)telluride in a mixture of 1-butyle-3-methyle-imidazolium iodide ([C4mim][I]) and 1-butyle-3-methyle-imidazolium tetraiododbismuthate ([C4mim][BiI4]).
Furthermore ternary phases (BixSb1-x)Te3 were successfully synthesized in the same medium by thermolysis of the single source precursor bis(diethylstibanyl)telluride.
The phase purity of the materials was proven by PXRD, while the composition was verified by EDX and AES. XPS studies and IR studies clearly showed thatthe material do not conatin any IL on the surface.
Figure 3: PXRD of different (BixSb1-x)2Te3 phases (x = 0.25, 0.5, 0.75, 1) as-synthesized in C4mimI/[C4mim][BiI4]; b) SEM picture of (Bi0.5Sb0.5)2Te3
In addition to the synthesis of group 15/16 materials, metal halide anions such as CoCl3- or SbCl4- are investigated as precursors for the synthesis of binary intermetallic materials including nanoparticular thermoelectric materials.
Figure 4: SEM picture of CoSb3 particles
References
[1] K. Richter et al., Phys. Status Solid B 2013, 6, 1152
[2] M. Antonietti et al., Angew. Chem. Int. Ed. 2004, 43, 4988
[3] J. Dupont et al., Chem. Rev. 2002, 102, 3667
[4] C. Janiak, Z.Naturforsch. 2013, 68b, 1059-1089
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