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

Magdalena Kierkowicz,Gerard Tobias,Elzbieta Pach,Belén Ballesteros,Julio Fraile,Concepción Domingo

doi:10.3390/nano11123365

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.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Single-walled carbon nanotubes (SWCNTs) were studied by conducting low-temperature nitrogen adsorption tests
To estimate the cumulative pore volume (VC ), only the pores in the range of 0.3–1.5 nm were considered. This range was chosen by observing the representation of the nonlocal density functional theory (NLDFT) differential pore volume vs. pore width (Figure 1b). This range of pore diameters is in agreement with the diameters of the SWCNTs used, previously determined by employing

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Single-walled carbon nanotubes (SWCNTs) are cylindrical nanostructures composed of individual rolled-up carbon sp sheets arranged as adjacent hexagons. SWCNTs are usually closed with hemifullerene caps. The diameter ranges between 0.7 and 3 nm, depending on the method of synthesis. Owing to their high surface area-tovolume ratio, SWCNTs have strong potential for water purification, drug delivery, tissue engineering, catalysis, sensors, and photovoltaics to name some of their applications [1,2,3,4,5]

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Conclusion