Hydrogen storage in single-walled carbon nanotubes at room temperature

Catalytic Reforming of Oxygenates: State of the Art and Future Prospects

This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure-activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of heterogeneous catalysis, reaction engineering, and materials science can play in the near future. This Review aims to present insights into the intrinsic mechanism involved in catalytic reforming and provides guidance to the development of novel catalysts and processes for the efficient utilization of oxygenates for energy and environmental purposes.

Adsorption of Hydrogen Molecules on Carbon Nanotubes Using Quantum Chemistry and Molecular Dynamics

Physisorption and storage of molecular hydrogen on single-walled carbon nanotube (SWCNT) of various diameters and chiralities are studied by means of classical molecular dynamics (MD) simulations and a force field validated using DFT-D2 and CCSD(T) calculations. A nonrigid carbon nanotube model is implemented with stretching (C-C) and valence angle potentials (C-C-C) formulated as Morse and Harmonic cosine potentials, respectively. Our results evidence that the standard Lennard-Jones potential fails to describe the H2-H2 binding energies. Therefore, our simulations make use of a potential that contains two-body term with parameters obtained from fitting CCSD(T)/CBS binding energies. From our MD simulations, we have analyzed the interaction energies, radial distribution functions, gravimetric densities (% wt), and the distances of the adsorbed H2 layers to the three zigzag type of nanotubes (5,0), (10,0), and (15,0) at 100 and 300 K.

Band gap opening and semiconductor-metal phase transition in (n, n) single-walled carbon nanotubes with distinctive boron-nitrogen line defect

Band gap opening and modulating are critical in dictating the functionalities of single walled carbon nanotubes (SWCNTs) in a broad array of nano-devices. Using first-principles density functional theory calculations, a class of semiconducting armchair SWCNTs with a distinctive BN line defect are studied, showing a super capacity to open the band gap of (4, 4) SWCNT to as large as 0.86 eV, while the opened band gap are found decreasing with the increasing diameters of SWCNTs. The opened band gap of SWCNTs can also be successfully modulated through both mechanical and electrical approaches by applying compressive uniaxial strain and electric field. This study provides novel insights into the large band gap opening and modulating of SWCNTs and could be useful in facilitating future applications of SWCNTs in electronic, optical and thermoelectric devices.

A Ti-decorated boron monolayer: a promising material for hydrogen storage

A promising Ti-decorated boron monolayer (BM) system for hydrogen storage is proposed through the use of density functional theory. Our results suggest that the Ti-BM will be a promising material system for hydrogen storage.

Design and preparation of silica tube/poly(aryl ether ketone) composites with low dielectric constant

Low dielectric constant porous composites in which uniform nanosized silica tubes are covalently bonding onto fluoropoly(aryl ether ketone) are prepared.

Functionalization of single-walled (n,0) carbon and boron nitride nanotubes by carbonyl derivatives (n = 5, 6): a DFT study

By using density functional theory calculations, the chemical functionalization of finite-sized (5,0) and (6,0) carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) by different carbonyl derivatives –COX (X = H, CH3, OCH3, OH, and NH2) is studied in terms of geometrical and electronic structure properties. Also, the benefits of local reactivity descriptors is studied to characterize the reactive sites of the external surface of the tubes. These local reactivity descriptors include the electrostatic potential VS(r) and average local ionization energy ĪS(r) on the surfaces of these nanotubes. The estimated ĪS(r) values show that the functionalized CNTs tend to activate the surface toward electrophilic/radical attack. Results show that the chemical functionalization of CNTs leads to the reduction of VS(r) values and therefore enhances the surface reactivity. On the other hand, BNNTs resist chemical functionalization due to the negligible decrease in the VS,min and ĪS,min values. Generally, in contrast to BNNTs, the chemical functionalization of CNTs can considerably improve their surface reactivity. To verify the surface reactivity pattern based on the chosen reactivity descriptors, the reaction energies for the interaction of an H + ion or hydrogen radical with external surface of the functionalized CNTs and BNNTs are calculated. A general feature of all studied systems is that stronger potentials are associated with regions of higher curvature.

Oxidation state selective sorption behavior of plutonium using N,N-dialkylamide functionalized carbon nanotubes: experimental study and DFT calculation

Selective phase separation of Pu⁴⁺ and PuO₂²⁺ was performed using N,N-dialkylamide functionalized multi-walled carbon nanotubes (AFMWCNTs).

Theoretical study of the interaction between molecular hydrogen and [MC60]+ complexes

In this work we present a density functional theory study of the interaction between a positively charged exohedral metallofullerene and several hydrogen molecules.

High Stability Electron Field Emitters Synthesized via the Combination of Carbon Nanotubes and N₂-Plasma Grown Ultrananocrystalline Diamond Films

An electron field emitter with superior electron field emission (EFE) properties and improved lifetime stability is being demonstrated via the combination of carbon nanotubes and the CH4/N2 plasma grown ultrananocrystalline diamond (N-UNCD) films. The resistance of the carbon nanotubes to plasma ion bombardment is improved by the formation of carbon nanocones on the side walls of the carbon nanotubes, thus forming strengthened carbon nanotubes (s-CNTs). The N-UNCD films can thus be grown on s-CNTs, forming N-UNCD/s-CNTs carbon nanocomposite materials. The N-UNCD/s-CNTs films possess good conductivity of σ = 237 S/cm and marvelous EFE properties, such as low turn-on field of (E0) = 3.58 V/μm with large EFE current density of (J(e)) = 1.86 mA/cm(2) at an applied field of 6.0 V/μm. Moreover, the EFE emitters can be operated under 0.19 mA/cm(2) for more than 350 min without showing any sign of degradation. Such a superior EFE property along with high robustness characteristic of these combination of materials are not attainable with neither N-UNCD films nor s-CNTs films alone. Transmission electron microscopic investigations indicated that the N-UNCD films contain needle-like diamond grains encased in a few layers of nanographitic phase, which enhanced markedly the transport of electrons in the N-UNCD films. Moreover, the needle-like diamond grains were nucleated from the s-CNTs without the necessity of forming the interlayer that facilitate the transport of electrons crossing the diamond-to-Si interface. Both these factors contributed to the enhanced EFE behavior of the N-UNCD/s-CNTs films.

A Review of Patterned Organic Bioelectronic Materials and their Biomedical Applications

Organic electronic materials are rapidly emerging as superior replacements for a number of conventional electronic materials, such as metals and semiconductors. Conducting polymers, carbon nanotubes, graphenes, organic light-emitting diodes, and diamond films fabricated via chemical vapor deposition are the most popular organic bioelectronic materials that are currently under active research and development. Besides the capability to translate biological signals to electrical signals or vice versa, organic bioelectronic materials entail greater biocompatibility and biodegradability compared to conventional electronic materials, which makes them more suitable for biomedical applications. When patterned, these materials bring about numerous capabilities to perform various tasks in a more-sophisticated and high-throughput manner. Here, we provide an overview of the unique properties of organic bioelectronic materials, different strategies applied to pattern these materials, and finally their applications in the field of biomedical engineering, particularly biosensing, cell and tissue engineering, actuators, and drug delivery.

Charge Modulation in Graphitic Carbon Nitride as a Switchable Approach to High-Capacity Hydrogen Storage

Electrical charging of graphitic carbon nitride nanosheets (g-C4 N3 and g-C3 N4 ) is proposed as a strategy for high-capacity and electrocatalytically switchable hydrogen storage. Using first-principle calculations, we found that the adsorption energy of H2 molecules on graphitic carbon nitride nanosheets is dramatically enhanced by injecting extra electrons into the adsorbent. At full hydrogen coverage, the negatively charged graphitic carbon nitride achieves storage capacities up to 6-7 wt %. In contrast to other hydrogen storage approaches, the storage/release occurs spontaneously once extra electrons are introduced or removed, and these processes can be simply controlled by switching on/off the charging voltage. Therefore, this approach promises both facile reversibility and tunable kinetics without the need of specific catalysts. Importantly, g-C4 N3 has good electrical conductivity and high electron mobility, which can be a very good candidate for electron injection/release. These predictions may prove to be instrumental in searching for a new class of high-capacity hydrogen storage materials.

Heterostructure of AuAg nanoparticles tipping on Ag2S quantum tubes

We report synthesis of a novel metal-semiconductor heterostructure, in which AuAg alloy nanoparticles locate at Ag2S quantum tube tips. Ag2S quantum tubes have ultrathin walls below 1 nm thickness. The formation mechanism, UV-vis, luminescence and photoelectrochemical activity of the prepared heterostructure were further studied.

Structural, Vibrational and Electronic Properties of Defective Single-Walled Carbon Nanotubes Functionalised with Carboxyl Groups: Theoretical Studies

Covalent sidewall functionalisation of defective zigzag single-walled carbon nanotubes [SWCNTs(10,0)] with COOH groups is investigated by using DFT. Four types of point defects are considered: vacancy (V), divacancy [V₂ (5-8-5), V₂ (555-777)], adatom (AA) and Stone-Wales (SW). The energetic, structural, electronic and vibrational properties of these systems are analysed. Decreasing reactivity is observed in the following order: AA>V>V₂ (555-777)>V₂ (5-8-5)>SW. These studies also demonstrate that the position in which a carboxyl group is attached to a defective SWCNT is of primary importance. Saturation of two-coordinate carbon atoms in systems with the vacancy V-7 and with the adatom AA-1(2) is 3.5-4 times more energetically favourable than saturation of three-coordinate carbon atoms for all studied systems. Vibrational analysis for these two systems shows significant redshifts of the ν(CO) stretching vibration of 96 and 123 cm^-1 compared to that for carboxylated pristine systems. Detailed electronic-structure analysis of the most stable carboxylated systems is also presented.

DFT, QTAIM, and NBO investigations of the ability of the Fe or Ni doped CNT to absorb and sense CO and NO

The structures and intramolecular interactions of complexes (FeCNT-CO, FeCNT-NO, NiCNT-CO, and NiCNT-NO) formed by the Fe or Ni doped single-wall carbon nanotube (FeCNT or NiCNT) and gas CO or NO were studied using density functional theory, quantum theory of atom in molecule (QTAIM), and natural bond orbital methods. The adsorption processes of CO and NO on surfaces of FeCNT and NiCNT are chemisorption, energetically favored, exothermic, and spontaneous. High temperature is not good for adsorption. Introducing NO more obviously elongates the distances between Fe/Ni and C atoms and decreases ∠CFe(Ni)C than adding CO. QTAIM analysis shows that the covalent bonding interactions of FeCNT-NO (NiCNT-NO) are stronger than that of FeCNT-CO (NiCNT-CO). NO plays a role of electron acceptor while CO is electron donator in complexes. Electrostatic interaction of FeCNT-NO (NiCNT-NO) is stronger than that of FeCNT-CO (NiCNT-CO). The stronger intramolecular interactions of FeCNT-NO and NiCNT-NO reveal that FeCNT and NiCNT are more effective to adsorb and sense NO than CO. CO and NO considerably change the electronic properties of FeCNT and NiCNT, which is useful for designing sensors for CO and NO.

"H₂ sponge": pressure as a means for reversible high-capacity hydrogen storage in nanoporous Ca-intercalated covalent organic frameworks

We explore the potential and advantages of Ca-intercalated covalent organic framework-1 (CaCOF-1) as a 3-dimensional (3D) layered material for reversible hydrogen storage. Density functional theory calculations show that by varying the interlayer distance of CaCOF-1, a series of metastable structures can be achieved with the interlayer distance falling in the range of 4.3-4.8 Å. When four hydrogen molecules are adsorbed on each Ca, a high hydrogen uptake of 4.54 wt% can be produced, with the binding energy falling in the ideal range of 0.2-0.6 eV per H2. While H2 absorption is a spontaneous process under H2 rich conditions, tuning the interlayer distance by reasonable external pressure could compress CaCOF-1 to release all of the hydrogen molecules and restore the material to its original state for recyclable use. This provides a new method for gradual, controllable extraction of hydrogen molecules in covalent organic frameworks, satisfying the practical demand for reversible hydrogen storage at ambient temperatures.

Theoretical investigation of rare gas adsorption on and inside B-doped carbon nanotubes by DFT, QTAIM and NBO

Structures and intramolecular interactions of complexes formed by 1–2 boron atom doped CNTs with rare gases were studied.

High-resolution Raman imaging of bundles of single-walled carbon nanotubes by tip-enhanced Raman spectroscopy

Bundles of single-walled carbon nanotubes (SWCNTs) prepared by plasma torch method and further purified, are deposited over a glass coverslip to estimate the spatial resolution of tip-enhanced Raman spectroscopy measurements. For this purpose, near-field Raman maps and spectra of isolated bundles of carbon nanotubes are collected using optimized experimental conditions such as a tightly focused beam using a 1.4 numerical aperture oil immersion microscope objective and a gold coated atomic force microscope probe illuminated by a radially polarized 632.8 nm wavelength to selectively excite the localized surface plasmon confined at the extremity of the tip. The near-field nature of the collected Raman signals is evaluated through measuring the decay of the Raman signal with respect to the tip-sample separation.

Ionic liquid functionalized multi-walled carbon nanotubes/zeolitic imidazolate framework hybrid membranes for efficient H2/CO2 separation

A ZIF-9 membrane covered by ionic liquid (IL) functionalized carbon nanotubes (CNTs) was prepared with a high selectivity for H₂/CO₂.

Evaluation of Hydrophilized Graphite Felt for Electrochemical Heavy Metals Detection (Pb2+, Hg2+)

Hydrophilized graphite felt has been used,for the first time, for the electrochemical detection of Hg2+ions both as single metal species and via its simultaneous detection with Pb2+. To do so, square wave voltammetry (SWV) method was developed with alginate modified graphite felt as working electrode. The structure of the graphite felt such as its high porosity and specific surface area coupled with its good electrical conductivity allows achieving large peak currents via the SWV method, suggesting that the alginate coating helps to preconcentrate metals at the carbon surface. The as-described electrode has low cost, it is easy to manipulate, and the electrochemical analysis can be performed by simple immersion of the felt in the metal solution.

Boron nitride nanotubes for spintronics

With the end of Moore's law in sight, researchers are in search of an alternative approach to manipulate information. Spintronics or spin-based electronics, which uses the spin state of electrons to store, process and communicate information, offers exciting opportunities to sustain the current growth in the information industry. For example, the discovery of the giant magneto resistance (GMR) effect, which provides the foundation behind modern high density data storage devices, is an important success story of spintronics; GMR-based sensors have wide applications, ranging from automotive industry to biology. In recent years, with the tremendous progress in nanotechnology, spintronics has crossed the boundary of conventional, all metallic, solid state multi-layered structures to reach a new frontier, where nanostructures provide a pathway for the spin-carriers. Different materials such as organic and inorganic nanostructures are explored for possible applications in spintronics. In this short review, we focus on the boron nitride nanotube (BNNT), which has recently been explored for possible applications in spintronics. Unlike many organic materials, BNNTs offer higher thermal stability and higher resistance to oxidation. It has been reported that the metal-free fluorinated BNNT exhibits long range ferromagnetic spin ordering, which is stable at a temperature much higher than room temperature. Due to their large band gap, BNNTs are also explored as a tunnel magneto resistance device. In addition, the F-BNNT has recently been predicted as an ideal spin-filter. The purpose of this review is to highlight these recent progresses so that a concerted effort by both experimentalists and theorists can be carried out in the future to realize the true potential of BNNT-based spintronics.

Conversion of chicken feather waste to N-doped carbon nanotubes for the catalytic reduction of 4-nitrophenol

Poultry feather is renewable, inexpensive and abundantly available. It holds great business potentials if poultry feather can be converted into valuable functional materials. Herein, we describe a strategy for the catalytic conversion of chicken feather waste to Ni3S2-carbon coaxial nanofibers (Ni3S2@C) which can be further converted to nitrogen doped carbon nanotubes (N-CNTs). Both Ni3S2@C and N-CNTs exhibit high catalytic activity and good reusability in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 with a first-order rate constant (k) of 0.9 × 10(-3) s(-1) and 2.1 × 10(-3) s(-1), respectively. The catalytic activity of N-CNTs is better than that of N-doped graphene and comparable to commonly used noble metal catalysts. The N content in N-CNTs reaches as high as 6.43%, which is responsible for the excellent catalytic performance. This strategy provides an efficient and low-cost method for the comprehensive utilization of chicken feathers. Moreover, this study provides a new direction for the application of N-CNTs.

Three-dimensional metal-intercalated covalent organic frameworks for near-ambient energy storage

A new form of nanoporous material, metal intercalated covalent organic framework (MCOF) is proposed and its energy storage property revealed. Employing density functional and thermodynamical analysis, we find that stable, chemically active, porous materials could form by stacking covalent organic framework (COF) layers with metals as a gluing agent. Metal acts as active sites, while its aggregation is suppressed by a binding energy significantly larger than the corresponding cohesive energy of bulk metals. Two important parameters, metal binding and metal-metal separation, are tuned by selecting suitable building blocks and linkers when constructing COF layers. Systematic searches among a variety of elements and organic molecules identify Ca-intercalated COF with diphenylethyne units as optimal material for H2 storage, reaching a striking gravimetric density ~ 5 wt% at near-ambient conditions (300 K, 20 bar), in comparison to < 0.1 wt% for bare COF-1 under the same condition.

Detailed atomistic simulation of the nano-sorption and nano-diffusivity of water, tyrosol, vanillic acid, and p-coumaric acid in single wall carbon nanotubes

We report results from a detailed computer simulation study for the nano-sorption and mobility of four different small molecules (water, tyrosol, vanillic acid, and p-coumaric acid) inside smooth single-wall carbon nanotubes (SWCNTs). Most of the results have been obtained with the molecular dynamics (MD) method, but especially for the most narrow of the CNTs considered, the results for one of the molecules addressed here (water) were further confirmed through an additional Grand Canonical (μVT) Monte Carlo (GCMC) simulation using a value for the water chemical potential μ pre-computed with the particle deletion method. Issues addressed include molecular packing and ordering inside the nanotube for the four molecules, average number of sorbed molecules per unit length of the tube, and mean residence time and effective axial diffusivities, all as a function of tube diameter and tube length. In all cases, a strong dependence of the results on tube diameter was observed, especially in the way the different molecules are packed and organized inside the CNT. For water for which predictions of properties such as local structure and packing were computed with both methods (MD and GCMC), the two sets of results were found to be fully self-consistent for all types of SWCNTs considered. Water diffusivity inside the CNT (although, strongly dependent on the CNT diameter) was computed with two different methods, both of which gave identical results. For large enough CNT diameters (larger than about 13 Å), this was found to be higher than the corresponding experimental value in the bulk by about 55%. Surprisingly enough, for the rest of the molecules simulated (phenolic), the simulations revealed no signs of mobility inside nanotubes with a diameter smaller than the (20, 20) tube. This is attributed to strong phenyl-phenyl attractive interactions, also to favorable interactions of these molecules with the CNT walls, which cause them to form highly ordered, very stable structures inside the nanotube, especially under strong confinement. The interaction, in particular, of the methyl group (present in tyrosol, vanillic acid, and p-coumaric acid) with the CNT walls seems to play a key role in all these compounds causing them to remain practically immobile inside nanotubes characterized by diameters smaller than about 26 Å. It is only for larger-diameter CNTs that tyrosol, vanillic acid, and p-coumaric acid were observed to demonstrate appreciable mobility.