Abstract
Multiwalled carbon nanotubes (MWCNTs) were easily and efficiently functionalised with highly cross-linked polyamines. The radical polymerisation of two bis-vinylimidazolium salts in the presence of pristine MWCNTs and azobisisobutyronitrile (AIBN) as a radical initiator led to the formation of materials with a high functionalisation degree. The subsequent treatment with sodium borohydride gave rise to the reduction of imidazolium moieties with the concomitant formation of secondary and tertiary amino groups. The obtained materials were characterised by thermogravimetric analysis (TGA), elemental analysis, solid state 13C-NMR, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), potentiometric titration, and temperature programmed desorption of carbon dioxide (CO2-TPD). One of the prepared materials was tested as a heterogeneous base catalyst in C–C bond forming reactions such as the Knoevenagel condensation and Henry reaction. Furthermore, two examples concerning a sequential one-pot approach involving two consecutive reactions, namely Knoevenagel and Michael reactions, were reported.
Highlights
Given the extremely high versatility of aminofunctionalised carbon-based materials, and in the context of the current interest aroused by the production of heterogeneous base catalysts, which can nd application in the catalysis of some relevant C–C bond forming reactions such as Knoevenagel condensation and Henry reaction,[84,85,86] we propose a new method for obtaining highly loaded cross-linked polyamine– Multiwalled carbon nanotubes (MWCNTs) materials through the reduction of the corresponding accessible cross-linked polyimidazolium salt–MWCNT hybrids
Two bis-vinylimidazolium salts (1a,b) were used for the direct functionalisation of pristine MWCNTs by means of free-radical polymerisation initiated by azobisisobutyronitrile (AIBN), as reported in Scheme 1
The as-prepared materials Imi-ButMWCNT and Imi-Xyl-MWCNT were reduced with sodium borohydride in re uxing ethanol leading to the opening of the imidazolium rings and the subsequent formation of secondary and tertiary amino groups
Summary
The outstanding electrical and mechanical features of carbon nanotubes (CNTs) are well known and explain why CNT-based materials have aroused signi cant interest for use in plenty of applications such as energy storage,[1,2,3] electronics,[4,5,6] catalysis,[7,8,9] structural reinforcement,[3,10,11] and nanomedicine,[12,13,14,15] among others. It is not surprising that many research efforts have been made aimed at efficiently functionalising CNTs both to improve their handling and to impart other speci c features. Depending on the strength of the oxidative/ acid treatment of pristine CNTs, nanotube fragmentation along with their decoration with various oxygenated functional groups (carboxyl, carbonyl, hydroxyl, etc.) can be obtained. Shortening of the pristine CNTs can be minimized by adopting milder conditions, such as the use of re uxing nitric acid, preserving their electronic and mechanical properties. The second step involves the postfunctionalisation of the primary oxygenated functional groups added onto the surface of CNTs by means of standard amidation and esteri cation reactions
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