Imidazolium modified carbon nanohorns: switchable solubility and stabilization of metal nanoparticles

Abstract

Imidazolium-modified carbon nanohorn-based hybrid materials have been prepared and characterized by complementary spectroscopic, thermal and microscopy techniques, while the counter-anion of the positively charged imidazolium fragment has been identified by electron dispersive X-ray analysis. In particular, oxidized carbon nanohorns, activated upon reaction with oxalyl chloride, have been initially covalently coupled with (3-aminopropyl)imidazole, while further reaction with n-butyl bromide resulted to the formation of the N-n-butylimidazolium-modified carbon nanohorns as a stable dispersion in aqueous media. Moreover, the bromide anion of the imidazolium-based hybrid material, can be exchanged by [PF₆⁻], [ClO₄⁻] and [BF₄⁻] anions upon treatment with the corresponding salts, resulting on switching of the solubility of the hybrid material from aqueous to organic solvents. On the other hand, when the [PF₆⁻] N-n-butylimidazolium-modified carbon nanohorn hybrid material was treated with Na₂SO₄, NaNO₃ or NaCl, the solubility of the as prepared hybrid materials was switched to aqueous media again. Thus, the nature of the counter-anion on the imidazolium-modified carbon nanohorns modulates the wettability of the material (i.e. switchable hydrophilic vs. lipophilic counter-anion and vice versa). In addition, the newly prepared hybrid materials have been employed as effective stabilizers to grow platinum and palladium nanoparticles, while their presence has been proved both by HR-TEM and EDX analysis.