Abstract
Vertically-aligned nitrogen-doped carbon nanotubes (v-N-CNTs) were synthesized \textit{via} the chemical vapour deposition (CVD) technique. 1-ferrocenylmethyl(2-methylimidazole) was employed as the source of the Fe catalyst and was dissolved in different ratios of acetonitrile/benzophenone feedstock which served as both the carbon, nitrogen, and oxygen sources. The morphological difference in N-CNTs was as a result of increased oxygen concentration in the reaction mix and not due to water vapour formation as observed in the oxygen-free experiment, indicating specifically, the impact of oxygen. Raman and X-ray photoelectron spectroscopy (XPS) revealed surface defects and grafting of oxygen functional groups on the sidewall of N-CNTs. The FTIR data showed little or no effect as oxygen concentration increases. XPS analysis detected the type of nitrogen species (\textit{i.e.} pyridinic, pyrrolic, graphitic, or molecular nitrogen forms) incorporated in the N-CNT samples. Pyrrolic nitrogen was dominant and increased (from 8.6 to 11.8 at.\%) as oxygen concentration increases in the reaction precursor. An increase in N content was observed with the introduction of a lower concentration of oxygen, followed by a gradual decrease at higher oxygen concentration. Our result suggested that effective control of the reactant mixtures can manipulate the morphology of N-CNTs.
Highlights
Vertically-aligned nitrogen-doped carbon nanotubes (v-N-CNTs) were synthesized via the chemical vapour deposition (CVD) technique. 1ferrocenylmethyl(2-methylimidazole) was employed as the source of the Fe catalyst and was dissolved in different ratios of acetonitrile/benzophenone feedstock which served as both the carbon, nitrogen, and oxygen sources
Several methods have been employed in the synthesis of N-CNTs; namely arc-discharge [24], laser deposition [25] and chemical vapour deposition (CVD) [26]
Sakurai et al [37] reported that the introduction of the oxygencontaining molecule (e.g. H2O) during CVD synthesis enhanced the growth of CNTs and prolong catalyst lifetime at temperatures above 750 ◦C
Summary
Ferrocene (≥ 97%), ferrocenemethanol (98%), 2-methylimidazole (≥ 98.2%) and sodium borohydride (95%), potassium hydrogen phthalate (≥ 99.5%) were obtained from Sigma Aldrich Ltd. South Africa. 10% Hydrogen in argon (purchased from AFROX gases, South Africa) was used as a carrier gas for the synthesis of N-CNTs. Images of the synthesized N-CNTs were obtained by using scanning electron microscopy (SEM) (JOEL JEM 1010) and transmission electron microscopy (TEM) (JOEL JSM 6100). Boehm titration was conducted to quantify the acidic functional groups on the N-CNT surfaces. Bamboo-like structure typical of NThe use of FcMeCH3 as a catalyst in acetonitrile and benzophenone gave mainly clean N-CNTs water to remove the acetic acid and puried by column chromatography. (Figure 1) and in good yield (Table 1) This could be attributed to the cleaning effect of oxygen as it reacts with amorphous carnally dried under vacuum to obtain yellow crystals. N-CNTs and carbon sphere (CS) are obtained in toluene solvent
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