Sulfur-doped carbon nanohorn bifunctional electrocatalyst for water splitting

Sulfur-doped carbon nanohorns (S-CNHs) were prepared by an easy one-pot solvothermal process and were employed as efficient electrocatalysts towards water splitting. Initially, oxidation of CNHs followed by thermal treatment with the Lawesson’s reagent resulted in the formation of S-CNHs with the sulfur content determined as high as 3%. The S-CNHs were thoroughly characterized by spectroscopic, thermal and electron microscopy imaging means and then electrocatalytically screened. Specifically, S-CNHs showed excellent activity and durability for both O2 and H2 evolution reactions, by showing low overpotential at 1.63 and -0.2 V vs. RHE for oxygen and hydrogen evolution reaction, respectively. Additionally, S-CNHs showed significantly lower Tafel slope value and lower current resistance compared to oxidized and pristine CNHs for both electrocatalytic reactions. The outstanding electrocatalytic properties and high conductivity, along with the high S-doping level, render S-CNHs a promising bifunctional electrocatalyst for water splitting

In vitro and in vivo biocompatibility of boron/nitrogen co-doped carbon nano-onions

Boron/nitrogen, co-doped, carbon nano-onions (BN-CNOs) have recently shown great promise as catalysts for the oxygen reduction reaction, due to the improved electronic properties imparted by the dopant atoms; however, the interactions of BN-CNOs with biological systems have not yet been explored. In this study, we examined the toxicological profiles of BN-CNOs and oxidized BN-CNOs (oxi-BN-CNOs) in vitro in both healthy and cancer cell lines, as well as on the embryonic stages of zebrafish (Danio rerio) in vivo. The cell viabilities of both cell lines cells were not affected after treatment with different concentrations of both doped CNO derivatives. On the other hand, the analysis of BN-CNOs and oxidized BN-CNO interactions with zebrafish embryos did not report any kind of perturbations, in agreement with the in vitro results. Our results show that both doped CNO derivatives possess a high biocompatibility and biosafety in cells and more complex systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Optoelectronic properties of calcium cobalt oxide misfit nanotubes

We report on the optoelectronic properties of a recently discovered nanotubular phase of misfit-layered calcium cobalt oxide, CaCoO2-CoO2. Individual nanotubes are investigated by spatially resolved electron energy-loss spectroscopy experiments performed in a transmission electron microscope, and complementary first-principles, time-dependent hybrid density-functional theory calculations are performed to elucidate the electronic structure and optical spectra. We find that the band gap is independent of the geometry of the nanotubes, and experimental and calculated results independently confirm an optical gap of 1.9-2.1 eV for the CaCoO2-CoO2 nanotubes. The time-dependent hybrid density-functional theory calculations also suggest the existence of strongly bound intralayer excitons (up to 0.5 eV binding energy), which could allow for optoelectronic applications of these nanotubes at near-infrared to visible (~1.5-2 eV) wavelengths

The physical and chemical properties of heteronanotubes

Carbon nanotubes undoubtedly take a leading position in nanotechnology research owing to their well-known outstanding structural and electronic properties. Inspired by this, hybrid and functionalized tubular structures have been constructed via several modification paths that involve the presence of molecules, generation of defects, and partial or full replacement of the carbon atoms, always maintaining a nanotube structure. The possibilities are countless. However, this review is mainly dedicated to giving a fundamental insight into the concepts behind wall modification, doping, and formation of a carbon nanotube structure. Theoretical concepts and experimental achievements ranging from carbon nanotubes with low B or N doping to the new physics behind boron nitride nanotubes are covered. Furthermore, special attention is devoted to the bulk and local characterization tools employed with these materials, their suitability and limitations. The theoretical approaches to describing the physical and chemical properties of heteronanotubes are objectively analyzed versus the materials available at this moment

Resonant Raman scattering in cubic and hexagonal boron nitride

We measured first- and second-order Raman scattering in cubic and hexagonal boron nitride using excitation energies in the visible and in the UV. The nonresonant first-order Raman susceptibilities for cubic and hexagonal BN are 1 and 10Å2, respectively. Raman scattering is thus very powerful in detecting the hexagonal phase in mixed thin boron nitride films. In cubic BN the constant Raman sucseptibility in the visible and the UV is due to its indirect band gap. For hexagonal BN a Raman enhancement is found at 5.4eV. It is well explained by the energy dependence of the dielectric function of hexagonal BN. The second-order spectrum of cubic boron nitride is in excellent agreement with first-principles calculations of the phonon density of states. In hexagonal BN the overbending of the LO phonon is ˜100cm-1, five times larger than in graphite

Raman spectroscopy of boron nitride nanotubes and boron nitride-carbon composites

Boron nitride nanotubes (BN-NT) are topological analoges to single wall carbon nanotubes (SWCNT). We analysed and refined the filling process for SWCNTs and applied it to the BN-NTs. BN-NTs were first annealed in air to open the ends and to remove BN particles. A filling procedure with C60 fullerene via vapour phase was applied. Subsequently high temperature treatment was performed to transform the fullerenes. Some spectral features in the Raman spectra of the reaction products in the low frequency range may be assigned to small diameter carbon nanotubes inside the BN-NTs

Raman spectroscopy of BN-SWNTs

We present results on the vibrational properties of BN-SWNTs together with a study of the synthesis material by transmission electron microscopy. Phonon modes have been investigated by Raman spectroscopy with laser excitation wavelengths in the range from 363.8 to 676.44 nm. The assignment of the modes is guided by ab-initio calculations

EELS measurements in single wall Boron Nitride nanotubes

We present here the results of an electron energy loss spectroscopy (EELS) study in scanning transmission electron microscopy (STEM) on boron nitride nanotubes (BN-NTs). The low and core-loss regions have been analyzed to provide by the same technique a combined information about chemical bonding in the different materials in the sample and the electronic properties of individual BN-NTs. In particular, we deduce an optical gap value of about 5.8 eV for single walled nanotubes, which is independent on diameter

Electron Energy Loss Spectroscopy Measurement of the Optical Gaps on Individual Boron Nitride Single-Walled and Multiwalled Nanotubes

Spatially resolved electron energy loss spectroscopy experiments have been performed in an electron microscope on several individual boron nitride (BN) single-, double-, and triple-walled nanotubes, whose diameters and number of shells have been carefully measured. In the low-loss region (from 2 to 50 eV) the spectra have been analyzed within the framework of the continuum dielectric theory, leading to the conclusion of a weak influence of out-of-plane contribution to the dielectric response of the tubes. The gap has been measured to be independent of the nanotubes geometry, and close to the in-plane gap value of hexagonal BN (5.8±0.2¿¿eV)