Single-walled carbon nanotubes in superacid: partly ordered H$_{2}$SO$_{4}$, nanotube-templated crystallization and evidence for protonation

Liquid anhydrous sulfuric acid forms a partly ordered structure in the presence of single-walled carbon nanotubes (SWNTs). Room temperature x-ray scattering from well-aligned nanotube fibers immersed in acid shows that H$_{2}$SO$_{4}$ molecules align along the nanotube axis and form cylindrical ``shells'' wrapped around nanotubes and ropes. Differential scanning calorimetry of SWNT-acid suspensions exhibits concentration-dependent supercooling/melting behavior, confirming that the partly ordered molecules are a new phase. Temperature-dependent x-ray scattering further shows that crystallization of the bulk-like acid surrounding the structured acid shells is templated by the aligned SWNTs, while the structured shells remain partly ordered, at least for temperatures from 100K to 500K. The (2 0 0) or (-2 0 2) planes of the templated H$_{2}$SO$_{4}$ crystallites are parallel to the nanotube axes. This provides solid evidence for the direct protonation of SWNT since these planes display exposed hydrogen bonds.