Investigation of fullerene encapsulation in carbon nanotubes using a complex approach based on vibrational spectroscopy

Abstract

For carbon nanotubes filled with fullerenes (''peapods''), it is a key issue to find an analytical method that distinguishes the molecules inside the nanotube from those adsorbed on its surface. High-resolution transmission electron microscopy (HRTEM) detects both encapsulated and adsorbed molecules which are large enough (e.g., fullerenes), but being a localprobe method, it cannot be applied to large amounts of sample. In Raman spectroscopy, the empirical rules for line shifts and splitting are nanotube-type dependent and often ambiguous. We prepared C 60 peapods by nano-extraction using supercritical CO 2 as a solvent, and subsequently removed the adsorbed fullerene molecules by washing the samples. We analyzed the samples by the combination of HRTEM, Raman, and midinfrared attenuated total reflectance (MIR-ATR) spectroscopy. Although the TEM images proved that the nanotubes were filled with fullerenes, we did not observe any shift in the fullerene's A g (2) Raman mode compared to C 60 crystals. ATR spectra, on the other hand, were found to detect only the adsorbed molecules. Therefore, the combination of the two methods provide good basis for determining the success of nanotube filling by spectroscopy alone.

Fullerene-driven encapsulation of a luminescent Eu(iii) complex in carbon nanotubes

“…S9, S.I.). In fact, it has been previously shown [36] that ATR spectroscopy on CNT hybrids does not detect encapsulated species, but only 30 adsorbed ones. Thus the lack of the ATR signals of 1·[EuL 4 ], demonstrates the absence of adsorbed assemblies on the external surface in the purified hybrids.…”

“…[36] Prior to the encapsulation reaction, CNTs were 100 oxidized [37] to remove their endcaps. Subsequently, the carbonaceous species were annealed in air at 570 °C for 20 minutes to remove any carboxylic groups that could hamper the efficient insertion of the nano-carrier.…”

“…[33] Among these, supercritical CO 2 (scCO 2 ) revealed to be particularly efficient for preparing peapods, [34][35] and for this reason we have decided to use scCO 2 as a solvent in the preparation of this luminescent hybrid. [36] Prior to the encapsulation reaction, CNTs were 100 oxidized [37] to remove their endcaps. Subsequently, the carbonaceous species were annealed in air at 570 °C for 20 minutes to remove any carboxylic groups that could hamper the efficient insertion of the nano-carrier.…”

“…S10, S.I. ), the typical emission spectrum of the Eu(III) ion, characterized by 40 several emission features between λ = 570 and 700 nm, [36] The effect of the different packing motifs is further observable following the emission quantum yields and lifetimes. In fact, along the series from SWCNTs to MWCNTs, the hybrids result characterized by increasingly lower emission quantum yields and 5 shorter excited state lifetimes compared to reference 1·[EuL 4 ] (see Table 3).…”

Advances in tailoring the electronic properties of single-walled carbon nanotubes

“…The encapsulation of fullerene C 60 [240,357], organic molecules (TCNQ and F 4 TCNQ [48]) and endohedral fullerene Gd@C 82 [49,256] [14,241,275,276] or supercritical СО 2 [297][298][299], and by the plasma filling method [335].…”