Free-standing Carbon Nanotube Research Articles

Free-standing carbon nanotubes as non-metal electrocatalyst for oxygen evolution reaction in water splitting

Oxygen evolution reaction (OER) has significant impact on the overall electrochemical water splitting. We introduce, for the first time, a facile approach towards the fabrication of versatile electrode composed of free-standing multiwalled carbon nanotubes (MWCNTs) as electrocatalyst for the water splitting reaction. Directly extracted MWCNTs as sheets from vertically grown arrays transferred over the glass substrate, are used without any post treatment as a working electrode for OER. Onset potential of 1.60 V was achieved for MWCNTs which is significantly reduced as compared to platinum based metal electrode (1.72 V) with excellent current density. No surface modification, metal-free nature, flexibility and low cost with excellent catalytic activity proved this material as a promising candidate for the replacement of metal based electrodes in electrochemical water splitting.

All-solid state symmetric supercapacitors based on compressible and flexible free-standing 3D carbon nanotubes (CNTs)/poly(3,4-ethylenedioxythiophene) (PEDOT) sponge electrodes

Flexible supercapacitors that maintain electrochemical performance under deformation have attracted much attention for the potential application in the flexible electronics market. A compressible and flexible free-standing electrodes sponge and all-solid-state symmetric supercapacitors based on as-prepared electrodes are presented. The carbon nanotubes (CNTs) framework is synthesized by chemical vapor deposition (CVD) method, and then composited with poly (3,4-ethylenedioxythiophene) PEDOT by the electrodeposition. This CNTs/PEDOT sponge electrode shows highest mass-specific capacitance of 147 Fg-1 at 0.5 A g−1, tuned by the PEDOT mass loading, and exhibits good cyclic stability with the evidence that more than 95% of capacitance is remained after 3000 cycles. Furthermore, the symmetric supercapacitor shows the highest energy density of 12.6 Wh kg−1 under the power density of 1 kW kg−1 and highest power density of 10.2 kW kg−1 with energy density of 8 Wh kg−1, which exhibits both high energy density and power density. The electrochemical performance of composite electrode also indicates that the operate voltage of device could be extend to 1.4 V by the n-doping and p-doping process in different potential of PEDOT component. This flexible supercapacitor maintains stable electrochemical performance working on different bending condition, which shows promising prospect for wearable energy storage applications.

Field emission properties of SiO2-wrapped CNT field emitter

Carbon nanotubes (CNTs) exhibit unstable field emission (FE) behavior with low reliability due to uneven heights of as-grown CNTs. It has been reported that a mechanically polished SiO2-wrapped CNT field emitter gives consistent FE performance due to its uniform CNT heights. However, there are still a lack of studies on the comparison between the FE properties of freestanding and SiO2-wrapped CNTs. In this study, we have performed a comparative study on the FE properties of freestanding and SiO2-wrapped CNT field emitters. From the FE measurements, freestanding CNT field emitter requires lower applied voltage of 5.5 V μm−1 to achieve FE current density of 22 mA cm−2; whereas SiO2-wrapped field emitter requires 8.5 V μm−1 to achieve the same current density. This can be attributed to the lower CNT tip electric field of CNTs embedded in SiO2, as obtained from the electric field simulation. Nevertheless, SiO2-wrapped CNTs show higher consistency in FE current than freestanding CNTs. Under repeated FE measurement, SiO2-wrapped CNT field emitter achieves consistent FE behavior from the 1st voltage sweep, whereas freestanding field emitter only achieved consistent FE performance after 3rd voltage sweep. At the same time, SiO2-wrapped CNTs exhibit better emission stability than freestanding CNTs over 4000 s continuous emission.

Photoluminescence from an individual double-walled carbon nanotube

We report direct and unambiguous evidence of the existence of inner semiconducting tube (ISCT) photoluminescence (PL) from measurements performed on four individual freestanding index-identified double-walled carbon nanotubes (DWNTs). Based on thorough Rayleigh scattering, Raman scattering, and PL experiments, we are able to demonstrate that the ISCT PL is observed with a quantum yield estimated to be a few ${10}^{\ensuremath{-}6}$ independent of the semiconducting or metallic nature of the outer tube. This result is mainly attributed to ultrafast exciton transfer from the inner to outer tube. Furthermore, by carrying out PL excitation experiments on the (14,1)@(15,12) DWNT, we show that the ISCT PL can be detected through the optical excitation of the outer tube, indicating that the exciton transfer can also occur in the opposite way.

Carbon-nanotube-templated deposition of amorphous aluminum oxide with linear photo transmittance

Atomic layer deposition on free-standing carbon nanotube (CNT) sheets produced highly amorphous Al2O3 nanostructures. The hybrid sheets maintained amorphousness for Al2O3 at 700 °C and robustness as well by thermally decomposing the CNTs. Higher temperatures (above 1000 °C) induced crystalline transformations into γ- and α Al2O3 phases. As each amorphous structure could contribute an absorption peak, the hybrid sheets with a mixture of amorphousness interestingly showed a linear photo-transmittance/absorbance when increasing the wavelength from 200 to 800 nm.

Fabrication of a high-resolution electron beam with a carbon nanotube cold-cathode

High-resolution electron microscopy requires electron beams with high-brightness. Hence, the authors used a resist-assisted patterning process to fabricate a new high-resolution cold-cathode electron beam with carbon nanotube (CNT) electron emitters. Herein, the authors successfully prepared one free-standing CNT emitter containing no impurities. The authors calculated the electron beam properties of the CNT emitter and found a reduced brightness of 1.7 × 107 A m−2 sr−1 V−1 at a current of 1.5 μA with a spatial resolution of 50 μm in a diode configuration. The one free-standing CNT emitter cold-cathode electron beam could be applied to a variety of electron microscope devices.

Thermoacoustic sound projector: Beyond the fundamental efficiency of carbon nanotubes

Advances in thermophone transduction from the perspective of novel nanostructured materials, device design, and signal processing will be presented. The comparison of studied 2D and 3D networks of nanostructured materials with aerogel structures will be given. The energy conversion efficiency of encapsulated thermoacoustic devices excited by short pulses with varying duty cycle, shape of pulse, and carrier signal frequency will be analyzed for a variety of fabricated devices. I will provide an extensive experimental study of pulse excitation in different thermodynamic regimes for freestanding carbon nanotube sheets with varying thermal inertias (single-wall, multi-wall with varying diameters, and number of superimposed sheets) in vacuum and in air. The experimental observations are rationalized within a basic theoretical framework. The acoustical and geometrical parameters providing further increase in efficiency and transduction performance for open and closed resonant systems will be discussed. [Research supported by ONR, Grant No.: N00014-17-1-2521.]

Janus Electrochemistry: Asymmetric Functionalization in One Step.

Janus structures represent an overwhelming member of materials with adaptable chemical and physical properties. Development of new synthesis routes has allowed the fabrication of Janus architectures with specific characteristics depending on the final applications. In the case of the membranes, the improvement of wet routes has been limited to the capillary effect, in which the solution can gradually penetrate through the membrane, avoiding a double modification different at each face of the membrane. In this work, we propose a new electrochemical methodology to circumvent the capillary limitation and obtain a double electrochemical functionalization in only one step in a controlled way. This innovative methodology has been validated using a tridirectional spectroelectrochemistry setup. Moreover, the information provided by this optical arrangement should be especially useful for the study of the different processes (ion transfer, assisted ion transfer, and electron transfer) that can take place at liquid/liquid interfaces. Janus electrochemistry allows us to modify the two faces of a free-standing single-walled carbon nanotube electrode in a single experiment. As proof of concept, the free-standing films have been functionalized with two different conducting polymers, polyaniline and poly(3-hexylthiophene), in one electrochemical experiment. According to the obtained results, this new electrochemical methodology will open new gates for the design and functionalization of Janus materials.

The formation of Cr2O3 nanoclusters over graphene sheet and carbon nanotubes

Carbon supported metal oxide nanoparticles hold promise for various future applications in diverse areas including spintronics, catalysis and biomedicine. These applications, however, typically depend on the structure and morphology of the nanoparticles. In this contribution, we employ classical molecular dynamic simulations based on a recently developed force field to study the structural properties of Cr2O3 nanoclusters over graphene and carbon nanotubes. We observe that Cr2O3 nanoclusters tend to aggregate over both freestanding graphene and carbon nanotubes and form larger nanoclusters. These large nanoclusters are characterized by their worm-like shape with a lattice constant similar to that of bulk Cr2O3. We also investigate the structural deformation induced in graphene due to the presence of Cr2O3 nanoclusters.

Highly biocompatible carbon nanocapsules derived from plastic waste for advanced cancer therapy

Carbon nanotubes (CNT) are increasingly being investigated for their use in biomedical applications and nanomedicine. In order to be used as nano-carriers for delivering anti-cancer drugs (drug delivery), smart free standing carbon nanotubes (CNTs) with hydrophilic core were prepared from recycled plastic bags. These CNTs were loaded with doxorubicin (Dox) and its external surface was chemically functionalized with a biodegradable polymer (chitosan) by anchoring its polymeric chains to functional groups on the external surface of CNTs. The obtained Chitosan-coated CNTs (Ch-CNCs) nanocomposites were then tested for their localized and slow drug eluting property using the cellular vicinity of MDA-MB-231 TXSA, human breast cancer cell line. The preliminary results are very promising and confirm a 500 fold enhanced death rate in case of cells treated with Ch-CNCs compared to the pro-drug alone. This work shows that it is possible to develop a highly biocompatible carbon nanocapsules (CNCs) derived from plastic bags and further used them as cargo transporters to study an intra-tumoral delivery of an anti-neoplastic drug is possible.

Free-standing flexible MWCNTs bucky paper: Extremely stable and energy efficient supercapacitive electrode

Due to highly conducting and extraordinary stable nature, carbon based materials expand the arms of energy storage devices in terms of supercapacitor. Hence, emphasis has been made to use flexible and free-standing multi-walled carbon nanotubes (MWCNTs) bucky paper synthesized by chemical vapor deposition for electrochemical supercapacitive electrode. The high specific capacitance of 270F/g (2mV/s) with superb stable behavior (88% at 10000 cycles) of bucky paper has promised as decent electrode in energy storage application. Aqueous symmetric supercapacitor (ASSC) device developed through bucky paper exhibits voltage frame of 1.6V yielding specific capacitance of 91F/g along with specific energy of 32 Wh/kg at a current density of 1mA/cm2 with trustworthy stability of 107% at 6000 cycles. The hands-on practicability to light up a red LED offers its promising approach in energy storage domain.

From mesoscale to nanoscale mechanics in single-wall carbon nanotubes

The analysis of the radial collapse of individualized and isolated single-wall carbon nanotubes under high pressure as function of their diameter, d, distinguishes their mesoscale and their nanoscale mechanics. The evolution with pressure of the Raman spectra for nine tube chiralities and the theoretical modelling reveal a deviation from the continuum mechanics prediction of a collapse pressure PC∝d−3. Nanotubes show a normalized collapse pressure PN=PCd3=24αD(1−β2/d2) both in experiment and in very different theoretical models. In this expression β=0.44±0.04nm represents the smallest diameter for a stable freestanding single-wall carbon nanotube and D is the bending stiffness of graphene. From the experimental data D=1.7±0.2eV. Deviations from the continuum mechanics predictions start to be of significance for diameters smaller than ∼1nm. The associated reduction of their collapse pressure is attributed to the discretization of the elastic compliances around the circumference of the tubes.

Influence of the Interface on the Photoluminescence Properties in ZnO Carbon-Based Nanohybrids

We report on the synthesis of free-standing ZnO nanoparticles (NPs) and ZnO NPs-decorated multiwalled carbon nanotubes (MWCNTs) via nonhydrolytic sol–gel (NHSG) routes. The role of the hydrates in the zinc precursor on the structure and surface termination of ZnO NPs via NHSG routes has already been reported in our earlier study. In the present work, the synthesis has been carried out in ambient air without using a glovebox, whereupon the effects of the synthesis temperature have been studied systematically. The structure, morphology, and optical properties of the free-standing ZnO-NPs are compared with those of the carbon nanotube-based nanocomposites, ZnO:MWCNTs, synthesized under identical conditions. The observed efficient and broad luminescence covering the entire visible spectrum points toward the high potential of the hybrid nanocomposites in optoelectronic and photovoltaic applications.

Subwoofer and nanotube butterfly acoustic flame extinction

Nonchemical flame control using acoustic waves from a subwoofer and a lightweight carbon nanotube thermoacoustic projector was demonstrated. The intent was to manipulate flame intensity, direction and propagation. The mechanisms of flame suppression using low frequency acoustic waves were discussed. Laminar flame control and extinction were achieved using a thermoacoustic ‘butterfly’ projector based on freestanding carbon nanotube sheets.

Fabrication of Millimeter-Long Carbon Tubular Nanostructures Using the Self-Rolling Process Inherent in Elastic Protein Layers.

Millimeter-long conducting fibers can be fabricated from carbon nanomaterials via a simple method involving the release of a prestrained protein layer. This study shows how a self-rolling process initiated by polymerization of a micropatterned layer of fibronectin (FN) results in the production of carbon nanomaterial-based microtubular fibers. The process begins with deposition of carbon nanotube (CNT) or graphene oxide (GO) particles on the FN layer. Before polymerization, particles are discrete and nonconducting, but after polymerization the carbon materials become entangled to form an interconnected conducting network clad by FN. Selective removal of FN using high-temperature combustion yields freestanding CNT or reduced GO microtubular fibers. The properties of these fibers are characterized using atomic force microscopy and Raman spectroscopy. The data suggest that this method may provide a ready route to rapid design and fabrication of aligned biohybrid nanomaterials potentially useful for future electronic applications.

Flash-evaporation printing methodology for perovskite thin films

Printing solutions have attracted wide attention from various research fields, but thin films made by printing technologies still cannot match the quality of the films made by conventional thin-film deposition methods. In this study, a flash-evaporation printing (FEP) technology, which employed a freestanding carbon nanotube (CNT) flash evaporator, was developed to address this issue and to achieve a compact physical vapor deposition geometry. The target material precoated on the CNT flash evaporator was printed onto a substrate by gas-phase transportation. The FEP methodology presented a printable solution for hybrid perovskite thin films. The as-fabricated photovoltaic devices showed power conversion efficiencies of ∼10.3%, and the thin films were also utilized as potential photodetectors. In addition, this technology can also be used to print patterns and a wide variety of materials on large panels. The environmentally friendly and cost-effective FEP technology will be of significant benefit to printed electronics, organic electronics and future flexible electronics.

SnO2@a-Si core–shell nanowires on free-standing CNT paper as a thin and flexible Li-ion battery anode with high areal capacity

Here, we report 3D hierarchical SnO2 nanowire (NW) core-amorphous silicon shell on free-standing carbon nanotube paper (SnO2@a-Si/CNT paper) as an effective anode for flexible lithium-ion battery (LIB) application. This binder-free electrode exhibits a high initial discharge capacity of 3020 mAh g−1 with a large reversible charge capacity of 1250 mAh g−1 at a current density of 250 mA g−1. Compared to other SnO2 NW or its core–shell nanostructured anodes, the fabricated SnO2@a-Si/CNT structure demonstrates an outstanding performance with high mass loading (∼5.9 mg cm−2), high areal capacity (∼5.2 mAh cm−2), and large volumetric capacity (∼1750 mAh cm−3) after 25 cycles. Due to the incorporation of CNT paper as the current collector, the weight and thickness of the total electrode is effectively reduced with respect to the conventional LIB anodes. The fabricated electrode has a total thickness of only 30 μm and considering the total weight of the electrode (active mass + current collector), an initial discharge/charge capacity of 2460/1018 mAh g−1 is obtained. Hence, this thin, lightweight and highly flexible structure is proposed as an excellent candidate for high-performance LIB anode materials, especially in flexible electronics.

Silver nanoparticles/free-standing carbon nanotube Janus membranes.

Janus materials are attracting intense interest due to their exceptional possibilities in the design of structures with specific properties. In this work, Janus structures were constructed by the functionalization of free-standing single-walled carbon nanotube (FS-SWCNT) membranes with silver nanoparticles (AgNPs) electrodeposited on one face of the free-standing structure. The modification of the FS-SWCNT films with AgNPs was carried out from an ionic liquid solution, a green and environmentally friendly procedure. Before the functionalization of the free-standing membranes, the optimal electrodeposition conditions of AgNPs from an ionic liquid in different carbon substrates were studied. We demonstrate by UV–vis spectroelectrochemistry that the functionalization of the FS-SWCNT membranes on only one face is achieved, remaining unmodified the other face, as SEM images confirm. Moreover, the morphology of AgNPs, and, consequently, the properties of the Janus structures strongly depend on the specific electrodeposition conditions selected, determining their future applicability.

Directed synthesis of carbon nanotube arrays based on layered double hydroxides toward highly-efficient bifunctional oxygen electrocatalysis

The exploration of highly-efficient, low-cost bifunctional oxygen electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) is critical for renewable energy storage and conversion technologies (e.g., fuel cells and metal–air batteries). Here we report the design and fabrication of free-standing nitrogen-doped carbon nanotube (NCNT) arrays via a directed growth approach as a high-performance bifunctional oxygen electrocatalyst. By virtue of the unique hierarchical nanoarray structure, uniform N-doping and decreased charge-transfer resistance, the as-prepared NCNT array exhibits rather high activity and stability in both ORR and OER, even superior to the mono-functional commercial Pt/C (for ORR) and IrO2 (for OER). A flexible, rechargeable all-solid-state zinc–air battery is successfully fabricated by using this self-supporting NCNT electrode as air-cathode, which gives excellent discharge-charge performance and mechanical stability.

Laser-induced graphitic healing of carbon nanotubes aligned in a sheet

A laser scanning method was developed to heal the graphitic defects of carbon nanotubes (CNTs). The laser beam was controlled to longitudinally scan CNTs aligned in the freestanding CNT sheets. The localized heating zone generated by the laser beam moved along the CNT axes and exhibited the extreme thermal conditions of fast-heating and fast-cooling. This unique laser-CNT interaction was beneficial to quickly heal the CNT defects and limited the undesired structural transformation of CNTs. The effectiveness of the introduced laser method in healing CNTs was confirmed by comparing with the conventional furnace annealing method and also verified by treating the plasma-bombarded CNTs. The generated localized heating zone and the scanning pattern controllability of the laser irradiation method are favorable to thermally treat the 1D-structured nanomaterials having the dominant longitudinal thermal conductivities such as CNTs or nanowires.