The Role of Temperature on the Degree of End-Closing and Filling of Single-Walled Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs), owing to their high surface area-to-volume ratio and hollow core, can be employed as hosts for adsorbed and/or encapsulated molecules. At high temperatures, the ends of CNTs close spontaneously, which is relevant for several applications, including catalysis, gas storage, and biomedical imaging and therapy. This study highlights the influence of the annealing temperature in the range between 400 and 1100 °C on the structure and morphology of single-walled CNTs. The nitrogen adsorption and density functional theory calculations indicate that the fraction of end-closed CNTs increases with temperature. Raman spectroscopy reveals that the thermal treatment does not alter the tubular structure. Insight is also provided into the efficacy of CNTs filling from the molten phase, depending on the annealing temperature. The CNTs are filled with europium (III) chloride and analyzed by using electron microscopy (scanning electron microscopy and high-resolution transmission electron microscopy) and energy-dispersive X-ray spectroscopy, confirming the presence of filling and closed ends. The filling yield increases with temperature, as determined by thermogravimetric analysis. The obtained results show that the apparent surface area of CNTs, fraction of closed ends, and amount of encapsulated payload can be tailored via annealing.

Highly active ZIF-8@CNT composite catalysts as cathode materials for anion exchange membrane fuel cells

“…Since the ZNT-900 material contains an equal amount of CNTs along with ZIF-8, after annealing at 900 °C Zn evaporates, creating hollow ZIF crystals, and the ends of the CNTs start to close, which results in a decrease in its S BET . 55 CNTs tend to form bundles due to van der Waals interactions and only the outer area, interstitial channels, and grooves are the available sites left for O 2 adsorption, which in turn decreases the overall surface area of the material. The DFT micropores/mesopores surface area ratio was close to 1.1 for ZNT-900, representing that both micropores and mesopores were equally present in the catalyst materials.…”

UV-Vis quantification of the iron content in iteratively steam and HCl purified single-walled carbon nanotubes

“…The use of steam also results in the end opening of carbon nanotubes [52] thus allowing their posterior filling with a wide variety of payloads [53][54][55]. The carbon nanotube ends can then be sealed/closed thus allowing to remove the compounds that have not been encapsulated [56][57][58][59]. The confinement of materials inside the cavities of carbon nanotubes not only allows the formation of unprecedented structures but also expands their range of application [60][61][62][63][64].…”

Advanced Carbon Nanostructures: Synthesis, Properties, and Applications

“…The papers presented with discuss aspects of synthesis, sorting, functionalization, and characterization of chemical and physical properties, leading to many interesting applications being highlighted and experimental, theoretical, and modelling aspects being discussed. In the Special Issue, 15 papers were published, consisting of 2 reviews [ 4 , 5 ] and 13 research papers [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ].…”

“…In [ 12 ], the authors investigated the morphology of annealed SWCNTs ( Figure 9 ). The SWCNTs were filled with europium (III) chloride and then were investigated by SEM, TEM, and energy-dispersive X-ray analysis, confirming the filling and closed ends.…”