Filling Single-Walled Carbon Nanotubes with Lutetium Chloride: A Sustainable Production of Nanocapsules Free of Nonencapsulated Material

Abstract

Filled carbon nanotubes are of interest for a wide variety of applications ranging from sensors to magnetoelectronic devices and going through the development of smart contrast and therapeutic agents in the biomedical field. In general, regardless of the method employed, bulk filling of carbon nanotubes results in the presence of a large amount of external nonencapsulated material. Therefore, further processing is needed to achieve a sample in which the selected payload is present only in the inner cavities of the nanotubes. Here, we report on a straightforward approach that allows the removal of nonencapsulated compounds in a time efficient and environmentally friendly manner, using water as a "green" solvent, while minimizing the residual waste. The results presented herein pave the way toward the production of large amounts of high-quality closed-ended filled nanotubes, also referred to as carbon nanocapsules, readily utilizable in the foreseen applications

Enter the Tubes: Carbon Nanotube Endohedral Catalysis

“…In a recent example, Nieto et al adapted a previously reported protocol [25,26] to encapsulate viologen derivatives in 1.6-2.2-nm-thick metallic SWCNTs causing a band-gap opening of the nanomaterials [27]. Following a completely different approach, Kierkowicz et al prepared SWCNTs filled with LuCl 3 whose radioactive isotope 177 Lu is largely used in medicine [28]. To do so and in line with most recent reports, SWCNTs were purified i.e., (i) oxidation; (ii) acid treatment to remove the catalyst; and (iii) annealing to restore the graphitic nature) and then grinded in the presence of the salts.…”

Epoxidation of Carbon Nanocapsules: Decoration of Single-Walled Carbon Nanotubes Filled with Metal Halides

“…Chemical vapour deposition SWCNTs (Elicarb ® ) were provided by Thomas Swan & Co. Ltd. (Consett, UK) with an average diameter of 2.1 nm (value provided by the supplier). LuCl 3 @SWNCTs were prepared following the protocol previously described [ 27 ]. Briefly, pristine SWCNTs were steam treated at 900 °C for 4 h followed by an HCl wash [ 28 ], which leads to a median length of 420 nm.…”

Structure of inorganic nanocrystals confined within carbon nanotubes

“…In most cases, the encapsulation protocol involves using a large excess of filler (compared to the available space inside the nanotubes). During the filling procedure the material not only crystallizes within the inner channels of the nanotubes, but also a significant amount of the inorganic precursor remains external to the carbon nanotubes [24,25]. Since the presence of external material will generally interfere with the properties of the sample, further washing is required to clean the nanotubes.…”

“…Having samples free of external material allows the quantitative determination of the encapsulated compounds [26]. It has been experimentally shown that the material encapsulated within narrow SWCNT and few-walled CNT by melt filling cannot be removed during the washing step, even when harsh conditions are involved [25,27]. This is because the ends of the CNTs close upon cooling, thus inhibiting the dissolution of the crystals [28].…”