Physicochemical properties of nitrogen-doped carbon nanotubes from metallocenes and ferrocenyl imidazolium compounds

Effects of Ionic Liquid and Biomass Sources on Carbon Nanotube Physical and Electrochemical Properties

The ongoing research toward meeting global energy demands requires novel materials from abundant renewable resources. This work involves an investigation on nitrogen-doped carbon nanotubes (N-CNTs) synthesized from relatively low-cost and readily available biomass as carbon precursors and their use as electrodes for supercapacitors. The influence of the ionic liquid 1-butyl-3-methylimidazolium chloride, or its combination with either sugarcane bagasse or cellulose (IL-CNTs, ILBag-CNTs, and ILCel-CNTs, respectively), in the synthesis of N-CNTs and the resultant effect on their physical and electrochemical properties was studied. Systematic characterizations of the N-CNTs employing transmission electron microscopy (TEM), thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), elemental analysis, nitrogen sorption analysis, cyclic voltammetry, and electrochemical impedance spectroscopy were performed. TEM data analysis showed that the mean outer diameters decreased, in the order of IL-CNTs > ILBag-CNTs > ILCel-CNTs. The N-CNTs possess only pyridinic and pyrrolic nitrogen-doping moieties. The pyridinic nitrogen-doping content is lowest in IL-CNTs and highest in ILCel-CNTs. The N-CNTs are mesoporous with surface areas in the range of 21–52 m2 g−1. The ILCel-CNTs had the highest specific capacitance of 30 F g−1, while IL-CNTs has the least, 10 F g−1. The source of biomass is beneficial for tuning physicochemical properties such as the size and surface areas of N-CNTs, the pyridinic nitrogen-doping content, and ultimately capacitance, leading to materials with excellent properties for electrochemical applications.

Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives

Six ferrocenyl imidazole derivatives substituted with -Cl, -NO₂ and -CH₃ on the 2-position of the 1H-imidazole ring have been synthesized. Of the six compounds, the di-substituted ferrocenes, i.e. compounds 4 (1,1′-ferrocenylmethyl(2-chloroimidazole)), 5 (1,1′-ferrocenyl(2-nitroimidazole)), and 6 (1,1′-ferrocenylmethyl(2-methylimidazole)) are reported for the first time. The structure-property relationships of compounds 4, 5 and 6 were investigated by means of UV-visible, FTIR, ¹H-NMR, ¹³C-NMR spectroscopy and electrochemical studies. UV-visible analysis in acetonitrile showed that the π -π* band of compounds 2 (1-ferrocenylmethyl(2-nitroimidazole)) and 5 appeared at longer wavelength compared to 1 (1-ferrocenylmethyl(2-chloroimidazole)), 3 (1-ferrocenylmethyl(2-methylimidazole)), 4 and 6. This phenomenon is due to the different electronics around the imidazole moieties. In cyclic voltammetry analysis, all compounds exhibited a quasi-reversible redox wave for the ferrocenyl and imidazole moieties. Density functional theoretical (DFT) calculations with the B3LYP/6-311+G(d) basis set were performed on compounds 1–6, and the calculated HUMO-LUMO band gap energies correlated with those obtained from electrochemical and spectroscopic data. The X-ray crystallographic analysis highlighted the effect of electron-withdrawing and electron-donating substituents on the conformation of the cyclopentadienyl rings attached to the ferrocenyl moiety.