Query: carbon nanotube arrays

title: Nitrogen Doped Carbon Nanotube Arrays for High Efficiency Electrochemical Reduction of CO2: On the Understanding of Defects, Defect Density, and Selectivity.
abstract: Nitrogen doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon dioxide reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. 0.18 V) and increases the selectivity (ca. 80% towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO2. However, for graphitic like nitrogen, electrons are located in the p* antibonding orbital, making them less accessible for CO2 binding.

title: Physical properties of carbon nanotube sheets drawn from nanotube arrays
abstract: We report mechanical, thermal, and electrical properties of novel sheet materials composed of multiwalled carbon nanotubes, drawn from a CNT array. At low loading there is some slippage of CNTs but at higher loading tensile strength s 0 7.9 MPa and Young's modulus E 310 MPa. The room temperature thermal conductivity of the CNT sheet was 2.5 0.5 W m 1 K 1 giving a thermal conductivity to density ratio of k r 65 W m 1 K 1 g 1 cm 3 The heat capacity shows 1D behavior for T 40 K, and 2D or 3D behavior at lower temperatures. The room temperature specific heat was 0.83 J g 1 K 1 The iV curves above 10 K have Ohmic behavior while the iV curve at T 2 K is non Ohmic, and a model to explain both ranges is presented. Negative magnetoresistance was found, increasing in magnitude with decreasing temperature 15% at T 2 K and B 9 T) The tensile strength, Young's modulus and electrical conductivity of the CNT sheet are low, in comparison with other CNT materials, likely due to defects. Thermal conductivity is dominantly phononic but interfacial resistance between MWCNTs prevents the thermal conductivity from being higher.

title: Generic Synthesis of Carbon Nanotube Branches on Metal Oxide Arrays Exhibiting Stable High Rate and Long Cycle Sodium Ion Storage.
abstract: A new and generic strategy to construct interwoven carbon nanotube (CNT) branches on various metal oxide nanostructure arrays (exemplified by V2 O3 nanoflakes, Co3 O4 nanowires, Co3 O4 CoTiO3 composite nanotubes, and ZnO microrods) in order to enhance their electrochemical performance, is demonstrated for the first time. In the second part, the V2 O3 /CNTs core/branch composite arrays as the host for Na( storage are investigated in detail. This V2 O3 /CNTs hybrid electrode achieves a reversible charge storage capacity of 612 mAh g( 1) at 0.1 A g( 1) and outstanding high rate cycling stability (a capacity retention of 100% after 6000 cycles at 2 A g( 1) and 70% after 10 000 cycles at 10 A g( 1) Kinetics analysis reveals that the Na( storage is a pseudocapacitive dominating process and the CNTs improve the levels of pseudocapacitive energy by providing a conductive network.

title: The effects of plasma treatment on bacterial biofilm formation on vertically aligned carbon nanotube arrays
abstract: Carbon nanotubes (CNTs) can be fabricated with an ordered microstructure by controlling their growth process. Unlike dispersed carbon nanotubes, these vertically aligned arrays have the ability to support or inhibit bacteria biofilms. Here, we show that by treating the carbon nanotube arrays with plasma, different effects on biofilms of Gram positive (Bacillus subtilis, Staphylococcus epidermidis) and Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa) can be observed.

title: Water transport control in carbon nanotube arrays
abstract: AbstractBased on a recent scaling law of the water mobility under nanoconfined conditions, we envision novel strategies for precise modulation of water diffusion within membranes made of carbon nanotube arrays (CNAs) In a first approach, the water diffusion coefficient D may be tuned by finely controlling the size distribution of the pore size. In the second approach, D can be varied at will by means of externally induced electrostatic fields. Starting from the latter strategy, switchable molecular sieves are proposed, where membranes are properly designed with sieving and permeation features that can be dynamically activated/deactivated. Areas where a precise control of water transport properties is beneficial range from energy and environmental engineering up to nanomedicine.

title: Ultrasmall graphitic carbon nitride quantum dots decorated self organized TiO2 nanotube arrays with highly efficient photoelectrochemical activity
abstract: In the present study, a novel graphitic carbon nitride quantum dots (CNQDs) modified TiO 2 nanotube arrays (NTAs) photoelectrode was successfully synthesized by a simple two step method which includes an electrochemical anodization technique followed by a facile organic molecular linkage. The successful modification of TiO 2 by CNQDs was found to improve the photoelectrochemical activity significantly because of enhanced light absorption and improved separation of photo generated electron hole pairs. The optimized CNQDs/TiO 2 NTAs showed nearly 3.5 fold photocurrent of that from TiO 2 NTAs alone at 0.3 V vs Ag/AgCl and the maximum photoconversion efficiency reaches up to 0.63% in neutral solution under simulated solar light irradiation. Furthermore, the prepared CNQD/TiO 2 NTAs demonstrated superior photoelectrocatalytic activity and stability in the degradation of RhB, with kinetic constants 3.0 times of that from TiO 2 NTAs. The hydroxyl and superoxide radicals were proved to be the dominant active radicals during pollutants degradation. Additionally, the prepared CNQD/TiO 2 sample was used as photoanodes for direct photoelectrochemical water splitting to produce H 2 and O 2 under simulated solar light illumination, achieving a H 2 production rate with 22.0 mmol h 1 cm 2 at 0.3 V vs Ag/AgCl.

title: En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen doped carbon nanotube arrays
abstract: The catalytic chemical vapour deposition (c CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen doped carbon nanotubes (N CNTs) A mixture of toluene (main carbon source) pyrazine (1,4 diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N CNT arrays, we investigated the influence of key parameters, i.e. growth temperature (660, 760 and 860 degC) composition of the feedstock and time of growth, on morphology and properties of N CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N CNTs down to about one twentieth compared to the growth rate of multi wall CNTs (MWCNTs) As revealed by electron microscopy studies (SEM, TEM) the individual N CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e. 5 x 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor) In turn, the internal crystallographic order of the N CNTs was found to be of a 'bamboo' like or 'membrane' like (multi compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2 hybridisation of graphene C atoms. As studied by XRD, the temperature and the [pyrazine][ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N CNTs into a 'mixed base and tip' (primarily of the base type) type as compared to the purely 'base' type for undoped MWCNTs.

title: Single molecule detection of protein efflux from microorganisms using fluorescent single walled carbon nanotube sensor arrays.
abstract: A distinct advantage of nanosensor arrays is their ability to achieve ultralow detection limits in solution by proximity placement to an analyte. Here, we demonstrate label free detection of individual proteins from Escherichia coli (bacteria) and Pichia pastoris (yeast) immobilized in a microfluidic chamber, measuring protein efflux from single organisms in real time. The array is fabricated using non covalent conjugation of an aptamer anchor polynucleotide sequence to near infrared emissive single walled carbon nanotubes, using a variable chemical spacer shown to optimize sensor response. Unlabelled RAP1 GTPase and HIV integrase proteins were selectively detected from various cell lines, via large near infrared fluorescent turn on responses. We show that the process of E. coli induction, protein synthesis and protein export is highly stochastic, yielding variability in protein secretion, with E. coli cells undergoing division under starved conditions producing 66% fewer secreted protein products than their non dividing counterparts. We further demonstrate the detection of a unique protein product resulting from T7 bacteriophage infection of E. coli, illustrating that nanosensor arrays can enable real time, single cell analysis of a broad range of protein products from various cell types.

title: CO2 Adsorption on Charged Carbon Nanotube Arrays: A Possible Functional Material for Electric Swing Adsorption
abstract: The adsorption and orientational ordering of carbon dioxide molecules on parallel bundles of charged as well as uncharged carbon nanotubes were investigated at 300 K using grand canonical Monte Carlo and molecular dynamics. Zigzag and armchair single walled carbon nanotubes of radius ~1.5 nm and different intertube distances between 0 and 2 nm were used. A fixed charge of 0.01 0.04e was placed on each carbon to investigate the effect of charge. Adding a positive charge to the carbon nanotubes causes a significant increase in adsorption (up to 35% at a pressure of 1.88 bar) while the gas adsorption decreases by up to 15% on negatively charged carbon nanotubes. The increase or decrease of adsorption upon charging is attributed to the change in potential energy for the interaction between the individual carbon dioxide molecule and the nanotube. The higher adsorption on positively charged nanotubes leads to thicker adsorbed layers and a lower orientational order of the adsorbed molecules.

title: Vertically Aligned Carbon Nanotube Arrays Co doped with Phosphorus and Nitrogen as Efficient Metal Free Electrocatalysts for Oxygen Reduction.
abstract: Using a mixture of ferrocene, pyridine, and triphenylphosphine as precursors for injection assisted chemical vapor deposition (CVD) we prepared the first vertically aligned multiwalled carbon nanotube array co doped with phosphorus (P) and nitrogen (N) with a relatively high P doping level (designated as PN ACNT) We have also demonstrated the potential applications of the resultant PN ACNTs as high performance electrocatalysts for the oxygen reduction reaction (ORR) PN ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P (P ACNT) or N (N ACNT) only and even comparable to the commercially available Pt C catalyst (45 wt Pt on Vulcan XC 72R; E TEK) due to a demonstrated synergetic effect arising from the co doping of CNTs with both P and N.