Gastrointestinal actions of orally-administered single-walled carbon nanohorns

Carbon nanomaterials, such as single-walled carbon nanohorns (SWCNHs) and carbon nanotubes, demonstrate great potential as drug delivery systems. However, no reports to date have detailed the use of SWCNHs as oral drug carriers. This study shows for the first time the actions of orally-administered SWCNHs in normal mice and mice with dextran sulfate sodium (DSS)-induced colitis. SWCNHs labeled with gadolinium oxide for quantification purposes were detected in the gastrointestinal tract and the feces of mice, but not in the blood or other bodily organs. These results indicate that the nanohorns were not absorbed into the body from the gastrointestinal tract. SWCNH absorption was not influenced by the functionalization or size control of SWCNH. Neither death nor behavioral aberrations were observed in normal mice following SWCNH administration. However, histological observation of mice with DSS-induced colitis at 24 h after oral administration of SWCNHs revealed the presence of black particles, presumed to be SWCNHs, in the inflamed areas of the colon and the cecum. Thus, SWCNHs might serve as efficacious drug delivery carriers for the treatment of ulcerative colitis.     

A novel fluorescent aptasensor based on single-walled carbon nanohorns

Single-walled carbon nanohorns have been used to construct an aptasensor for the first time. This novel aptasensor was successfully used for the detection of thrombin with high sensitivity and excellent selectivity. This thrombin aptasensor has a detection limit of as low as 100 pM.     

Characterization of single-walled carbon nanohorns using neon adsorption isotherms

Detailed volumetric neon adsorption isotherms were measured between 22.670 and 31.444 K on a sample of closed, mostly bud-like, aggregates of single-walled, carbon nanohorns, produced by NanoCraft, Inc. The results are compared to those recently reported on closed dahlia-like nanohorn aggregates. While for the closed dahlia-like aggregates the data shows that there are two groups of sites with different binding energies present at relatively low loadings, only one group of adsorption energies is present for the closed bud-like aggregates at comparable loadings. We measured the isosteric heat of adsorption and its dependence on substrate loading. From the low-loading limit of this quantity, we determined that the binding energy of the sites present on the bud-like aggregates have a value intermediate between that obtained for adsorption on planar graphite and that measured on the grooves of close-ended bundles on nanotubes for the same adsorbate.     

Physisorption of hydrogen in single-walled carbon nanotubes

The interaction of hydrogen with single-walled carbon nanotubes (SWNTs) was analysed. A SWNT sample was exposed to D₂ or H₂ at a pressure of 2 MPa for 1 h at 298 or 873 K. The desorption spectra were measured by thermal desorption spectroscopy (TDS). A main reversible desorption site was observed throughout the range 77 to 320 K. The activation energy of this peak at about 90 K was calculated assuming first-order desorption. This corresponds to physisorption on the surface of the SWNTs (19.2±1.2 kJ/mol). A desorption peak was also found for multi-walled carbon nanotubes (MWNTs), and also for graphite samples. The hydrogen desorption spectrum showed other small shoulders, but only for the SWNT sample. They are assumed to originate from hydrogen physisorbed at sites on the internal surface of the tubes and on various other forms of carbon in the sample. The nanosized metallic particles (Co:Ni) used for nanotube growth did not play any role in the physisorption of molecular hydrogen on the SWNT sample. Therefore, it is concluded that the desorption of hydrogen from nanotubes is related to the specific surface area of the sample.     

Adsorption of hydrogen on single-walled carbon nanotubes with defects

We present molecular dynamics (MD) simulations and density functional theory (DFT) calculations of hydrogen adsorption on single-walled carbon nanotubes (SWCNT) with various kinds of defects. The nature of defects, which is characterized here by the number of carbon atoms present in a ring on the surface of nanotube, plays a significant role in determining the hydrogen adsorption capacity of the SWCNT. Nanotubes containing the Stone–Wales defect with 5 and 8-member rings were found to have the largest hydrogen adsorption ability that increases further with the number of rings with such defects. Whereas, the presence of defects with 5, 3-5-8-member rings and the Stone–Wales defect with 5 and 7-member rings decreases the adsorption ability of the defective SWCNT significantly with respect to defect-free nanotubes. Our results indicate that the huge discrepancies in hydrogen storage capacities of SWCNT reported in the literature could be attributed to the nature of defects present in nanotubes. DFT calculations also reveal that the adsorption energy depends not only on the nature and number of defects present on the surface of nanotube but also on the equilibrium structure of rings.     

碳基吸附储氢材料

本文综述了活性炭、活性碳纤维、碳纳米纤维和碳纳米管的结构与储氢性能．活性炭只是在低温下才有好的吸附储氢性能,碳纳米材料吸附储氢对于工业应用还不成熟．活性碳纤维是一种可大规模生产且成本较低的微孔吸附材料,其作为储氢材料具有一定的工业前景．     

Transformation from single-walled carbon nanotubes to nanohorns by simple heating with Pd at 1600 °C

A route to synthesize single-wall carbon nanohorns (SWCNHs) at a lower than normal temperature is reported. SWCNHs were synthesized at 1600 °C by a transformation from single-walled carbon nanotubes as the result of the catalytic effect of molten Pd. Observations by transmission electron microscope (TEM) on the remaining precursors suggested that SWCNTs were first deformed to highly curled shapes, and then were fragmentized into independent horns. Typical structures of SWCNHs were formed by merging these horn-like fragments.     

Molybdenum carbide-derived carbon for hydrogen storage

Physisorption of hydrogen in microporous molybdenum carbide (Mo₂C)-derived carbons has been studied as a function of synthesis conditions. Changes in local structure induced by varying the chlorination temperature afford controllable variations in average pore size and specific surface area. Optimal hydrogen storage capacity of 4.3 wt%, measured at −196 °C and 35 bar pressure, is obtained from a sample chlorinated at 660 °C for 3 h. This optimum correlates with the largest fraction of total pore volume having average pore sizes in the 0.6–0.8 nm range.     

Molecular hydrogen and spiltover hydrogen storage on high surface area carbon sorbents

A series of templated carbons with various high surface areas (2033–3798 m²/g) have been prepared using various microporous zeolites as hard templates. Molecular hydrogen storage and spiltover hydrogen storage on these templated carbons were investigated and compared with superactivated carbon AX-21 and other reported porous carbon sorbents at 298 K and 100 atm. Two relationships between the surface areas of these carbons and their hydrogen capacities were obtained. The relationship between molecular hydrogen capacity and surface area showed a 0.23 wt.% H₂/1000 m²/g of carbon sorbent at 298 K and 100 atm, indicating that merely increasing surface areas of the carbon sorbents cannot achieve a significant molecular hydrogen capacity at ambient temperature. Spiltover hydrogen storage was achieved by doping Pt nanoparticles (as dissociative hydrogen source) on these carbons (spiltover hydrogen receptor). Our first result on the relationship between the spiltover hydrogen capacity and surface area showed 0.4 wt.% H₂/1000 m²/g of carbon sorbent at 298 K and 100 atm, which indicated that storage via spillover can lead to an average of 70% enhancement compared to molecular hydrogen storage.     

Aryl diazonium functionalization of carbon nanohorns

Carbon nanohorns (CNHs) are a relatively new material within the family of elongated carbon nanostructures. A strategy for their solubilization is presented here. Aryl diazonium functionalization of CNHs has been achieved giving rise to soluble materials in common organic solvents as well as water. The modified CNHs have been characterized by complementary spectroscopic and microscopic means as well as thermal gravimetric analysis and dynamic light scattering measurements.     

Single-walled carbon nanohorns and their applications

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.     

Activation of carbon nanofibres for hydrogen storage

The present study was aimed to investigate different methods of activation of carbon nanofibres, CNF, in order to determine the beneficial effect on the hydrogen sorption capacities of increasing the surface area. Two activation systems were used: physical activation with CO₂ and chemical activation with KOH. A range of potential adsorbents were thus prepared by varying the temperature and time of activation. The structure of the CNF proved more suitable to activation by KOH than by CO₂, with the former yielding higher surface area carbons (up to 1000 m² g⁻¹). The increased surface area, however, did not correspond directly with a proportional increase in hydrogen adsorption capacity. Although high surface areas are important for hydrogen storage by adsorption on solids, it would appear that it is essential that not only the physical, but also the chemical, properties of the adsorbents have to be considered in the quest for carbon based materials, with high hydrogen storage capacities.     

Effect of surface acidity of activated carbon on hydrogen storage

Hydrogen adsorption studies at 78 K and pressures up to 40 atmosphere were conducted on nine commercial activated carbon samples. The amount of hydrogen adsorbed increased with increasing surface area. Surface modification consisting of controlled high-temperature reduction and oxidation revealed that BET surface area was not affected by these treatments. The surface acidity, however, increased with increasing oxygen treatment. The amount of hydrogen adsorbed also increased as the surface acidity of the activated carbons increased.     

Electrochemical lithium ion storage properties of single-walled carbon nanotubes containing organic molecules

The Li ion storage properties of single-walled carbon nanotube peapods containing one of three organic molecules (9,10-dichloroanthracene, β-carotene, coronene) were measured. It was found by electrochemical charge-discharge measurements that the reversible storage capacity of the SWCNTs significantly increased as a result of the inclusion, although unfortunately the samples are still not appropriate for the practical use as an anode material in Li ion battery because of the high irreversible capacity (>900 mAh/g). In the most effective case, the tube containing the organic molecule can store about 2.5 times more Li ions compared to an empty tube.     

碳纳米管储氢性能的研究进展

介绍了单壁碳纳米管和多壁碳纳米管对氢气的吸附实验和模拟计算研究进展;综述了该领域的最新研究成果;讨论了碳纳米管储氢性能的可行性和应用前景。     

Hydrogen storage on Li-doped single-walled carbon nanotubes: Computer simulation using the density functional theory

The first principal calculation based on the density functional theory was performed to investigate the hydrogen storage behavior of Li-doped single-walled carbon nanotubes (SWCNTs). It was found that, through Li-doping, two new adsorption sites for hydrogen molecules are created in addition to the inherent three adsorptive sites which are exterior, interior and interstitial regions of pristine SWCNTs: the first site (denoted ‘region 1’) is the nanotube's sidewall whose electronic distribution status is influenced by the doped Li atoms. The second site (denoted ‘region 2’) exists on the positively charged Li atoms which result from the transfer of electrons from the Li atoms to the SWCNTs. The calculations show that although the adsorption energy in region 1 increases somewhat, the adsorption behavior of hydrogen is marginally different from that of pristine SWCNTs. However, in region 2, at least three hydrogen molecules can be adsorbed by each charged Li-atom, and based on the maximum Langmuir coverage (of 0.55), 1.1 hydrogen molecules can be adsorbed onto each charged Li-atom. When this result is considered together with the effective specific surface area, the hydrogen storage capacities of Li-doped SWCNTs with the doping ratio of LiC₁₅ are approximately 0.1 wt% in region 1 and 1.17 wt% in region 2 at 10 MPa and 300 K so that the total H₂ storage capability is 1.27 wt%, which agrees well with previously reported results.     

Arm length dependency of Pt-decorated CdSe tetrapods on the performance of photocatalytic hydrogen generation

Pt-decorated CdSe tetrapods with different arm lengths were tested for the photocatalytic hydrogen generation reaction. Well-defined CdSe tetrapods with controlled wurtzite arm lengths were synthesized by the continuous precursor injection (CPI) approach. Pt nanocrystals with an extremely small size of ～1 nm were directly decorated on the overall surfaces of CdSe tetrapods. Ligand-exchanged Pt-decorated CdSe tetrapods with different arm lengths were employed as photocatalysts for photocatalytic hydrogen generation reaction in the presence of hole scavengers. Pt-decorated CdSe tetrapods with shorter arm length showed the highest photocatalytic efficiency, which is due to higher probability of charge separation.     

Adsorption properties of hydrogen on (10,0) single-walled carbon nanotube through density functional theory

The density functional theory (DFT) has been used to simultaneously investigate physi-/chemi-sorption properties of hydrogen on the (10,0) single-walled carbon nanotube (SWCNT) walls. Physisorption of H₂ outside the CNT with a vertical orientation to the tube axis above the center of a hexagon surface is the most stable state of physisorption and its binding energy is very weak, −0.792 kcal/mol. In the chemisorption of two hydrogen atoms the most stable state is above two adjacent carbon atoms of a hexagon with a C-H bond length of 1.10 Å and one C-H bond energy of −45.761 kcal/mol. Based on these results, we have also investigated the transition state and the reaction pathway from physisorption to chemisorption of hydrogen on the CNT. The energy barrier of the reaction from physisorption to chemisorption is about 78.837 kcal/mol and the reaction is not spontaneous at 0 K. Through the calculations of the Gibbs free energy change from physisorption to chemisorption with temperatures, we learned that it is not easy for the reaction to occur, which is a major obstacle for the practical use of the CNT as a hydrogen storage medium.     

Single-step synthesis and characterization of single-walled carbon nanohorns hybridized with Pd nanoparticles using N2 gas-injected arc-in-water method

Single-walled carbon nanohorns (SWCNHs) hybridized with palladium (Pd) nanoparticles were synthesized by a single-step gas-injected arc-in-water method (GI-AIW) with a Pd wire inserted inside the anode hole. In the arc zone, carbon and Pd were vaporized simultaneously, leading to the formation of hybrid material of SWCNHs and Pd nanoparticles due to effective quenching. Based on TEM and CO chemisorption analyses, Pd nanoparticles were found to be embedded inside SWCNH aggregates. The size of Pd nanoparticles, determined by X-ray diffraction, was in the range of 3–6 nm when Pd wires with diameters of 0.1 and 0.3 mm were used. Using a Pd wire with a diameter larger than 0.5 mm results in larger Pd nanoparticles which tend to be exposed to the outer surface of the hybrid material. According to thermogravimetric analyses, the weight fraction of Pd nanoparticles is increased by increasing the Pd wire diameter although the yield of Pd nanoparticles decreased. SWCNHs hybridized with dispersed Pd nanoparticles, synthesized with 0.1 mm Pd wire, exhibited strong anti-oxidation resistance with a highly graphitic structure.