Abstract
Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO2 into cyclic carbonate under high temperature and CO2 pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved catalytic activity. Beside the low catalytic loading (0.05–0.09 mol%) and the absence of Lewis acid co-catalysts, all the materials showed high TON values (up to 1154 for epichlorohydrin with SW-1:2). Interestingly, despite the loss of part of the polymeric coating for crumbling or peeling, the activity increases upon recycling of the materials, and this behaviour was ascribed to their change in morphology, which led to materials with higher surface areas and with more accessible catalytic sites. Transmission electron microscopy analysis, along with different experiments, have been carried out in order to elucidate these findings.
Highlights
IntroductionSome features of Carbon nanoforms (CNFs), namely outstanding mechanical strength, as well as the possibility of their functionalization, are responsible for certain applications concerning the preparation of carbon nanotubes (CNTs)-reinforced composites [8,9,10] or their use as a support for catalysts [11,12]
Three different Carbon nanoforms (CNFs), namely SWCNTs, MWCNTs, and carbon nanohorns (CNHs) were used as support for the polymerization of a bis-vinylimidazolium salt
All the materials prepared were characterized by means of several analytical and spectroscopic techniques and tested in the reaction between CO2 and epoxides to form cyclic carbonates with the aim to investigate their stability under the reaction conditions adopted under repeated use
Summary
Some features of CNFs, namely outstanding mechanical strength, as well as the possibility of their functionalization, are responsible for certain applications concerning the preparation of CNT-reinforced composites [8,9,10] or their use as a support for catalysts [11,12]. CNFs can be functionalized through non-covalent bonding [13,14,15], or through a defined portfolio of chemical reactions that offer the possibility of introducing specific functional groups [12,16,17,18,19]. Covalent attachment of appropriate chemical entities is a good strategy to improve dispersibility in liquid. Nanomaterials 2021, 11, 2243 media by disruption of the sp system and lowering of the van der Waals forces responsible for the bundling [20]. Oxidative pre-treatment is not the only way to modify CNFs and other techniques to functionalize covalently pristine
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