Exploring the Structure of Nitrogen-Rich Ionic Liquids and Their Binding to the Surface of Oxide-Free Boron Nanoparticles

The structure of two different energetic ionic liquids and the nature of their binding to elemental boron surfaces were investigated by a combination of X-ray photoelectron spectroscopy, IR spectroscopy, zeta potential measurements, thermogravimetric analysis, and first-principles theory. It was found that both 1-methyl-4-amino-1,2,4-triazolium dicyanamide ([MAT][DCA]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]) ionic liquids bind to boron well enough to resist removal by ultrasonic washing and to protect the boron surface from oxidation during air exposure of the washed powder. The data suggest that both the cation and the anion of the ionic liquids interact with the boron surface; however, for [MAT][DCA], the interaction of the cation appears to dominate, while for [BMIM][DCA] the interaction with the [DCA]− anion dominates. The difference is attributed to the binding of boron to the amino group of [MAT]+, and the amino group also appears to help bind a thicker ionic liquid (IL) capping layer.