Abstract
The encapsulation of CdSe nanocrystals within single‐walled carbon nanotube (SWNT) cavities of varying dimensions at elevated temperatures under strictly air‐tight conditions is described for the first time. The structures of CdSe nanocrystals under confinement inside SWNTs was established in a comprehensive study, combining both experimental and DFT theoretical investigations. The calculated binding energies show that all considered polymorphs [(3:3), (4:4), and (4:2)] may be obtained experimentally. The most thermodynamically stable structure (3:3) is directly compared to the experimentally observed CdSe structures inside carbon nanotubes. The gas‐phase DFT‐calculated energy difference between “free” 3:3 and 4:2 structures (whereby 3:3 models a novel tubular structure in which both Cd and Se form three coordination, as observed experimentally for HgTe inside SWNT, and 4:2 is a motif derived from the hexagonal CuI bulk structure in which both Cd and Se form 4 or 2 coordination) is surprisingly small, only 0.06 eV per formula unit. X‐ray powder diffraction, Raman spectroscopy, high‐resolution transmission electron microscopy, and energy‐dispersive X‐ray analyses led to the full characterization of the SWNTs filled with the CdSe nanocrystals, shedding light on the composition, structure, and electronic interactions of the new nanohybrid materials on an atomic level. A new emerging hybrid nanomaterial, simultaneously filled and beta‐d‐glucan coated, was obtained by using pristine nanotubes and bulk CdSe powder as starting materials. This displayed fluorescence in water dispersions and unexpected biocompatibility was found to be mediated by beta‐d‐glucan (a biopolymer extracted from barley) with respect to that of the individual inorganic material components. For the first time, such supramolecular nanostructures are investigated by life‐science techniques applied to functional nanomaterial characterization, opening the door for future nano‐biotechnological applications.
Highlights
Single-walled carbon nanotubes (SWNTs) have unique structural and electronic properties, which render them very promising materials for device fabrication
An earlier structural analysis of HgTe@SWNT showed that coordination of Hg and Te was altered significantly from the tetrahedral coordination found in the bulk HgTe zinc blende structure to trigonal planar and trigonal pyramidal geometries, respectively, in a SWNT composite.[1g,j] In some cases, the encapsulation of 1D crystals (e.g. KI) in SWNTs yields a structure without an overall change, but with a systematic reduction of coordination mode.[1e]. In high-resolution transmission electron microscopy (HRTEM), heavy atoms can be observed at higher resolution; the positions of light atoms are a challenge, so theoretical model structures must be proposed to generate images for comparison with experimental data
Two different batches of SWNTs [electric arc growth (ArcSWNT) and chemical vapor deposition (CVD-SWNT)] were used for comparison purposes. Both SWNT samples were filled with CdSe nanocrystals and purified following the method described by Salzmann and co-workers[4] as well as Green and coworkers[5]
Summary
Single-walled carbon nanotubes (SWNTs) have unique structural and electronic properties, which render them very promising materials for device fabrication. An earlier structural analysis of HgTe@SWNT showed that coordination of Hg and Te was altered significantly from the tetrahedral coordination found in the bulk HgTe zinc blende structure to trigonal planar and trigonal pyramidal geometries, respectively, in a SWNT composite.[1g,j] In some cases, the encapsulation of 1D crystals (e.g. KI) in SWNTs yields a structure without an overall change, but with a systematic reduction of coordination mode.[1e] In HRTEM, heavy atoms can be observed at higher resolution; the positions of light atoms are a challenge, so theoretical model structures must be proposed to generate images for comparison with experimental data In this sense, first principles calculations have been supportive in predicting the structures of nanocrystals found inside the nanotube and have the bonus of elucidating physical and chemical properties of the composites. This aims at understanding the nature of the CdSe crystals when confined within the SWNT cavities, the impact on their likely optical properties, and considerations of the biocompatibility mediated by this glucan.[3]
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