Carbon Nanotube Mesh Research Articles

Towards the superlubricity of polymer–steel interfaces with ionic liquids and carbon nanotubes

Frictional losses are responsible for significant energy waste in many practical applications, and superlubricity with a coefficient of friction lower than 0.01 is the goal of tribologists. In this paper, metal-on-polymer contact was analysed and close to superlubricity conditions for this material configuration were explored. A new lubricant has been proposed hinge on the phosphorus-based ionic liquid and carbon nanotubes as thickeners. Additionally, carbon nanotube mesh was doped with copper nanoparticles that allowed for the close to superlubricity state in a mild steel/polymer contact configuration under low normal load conditions. The adsorption of phosphorus onto metallic and polymer surfaces has been reported in EDS analysis. The formulation of the new lubricant allowed for stable dispersion with a carbon nanotube content as low as 0.1% wt. The carbon nanotubes and Cu nanoparticles have been analysed using TEM and SEM imaging. A tribological test in a block-on-ring system has been carried out. The wear of material, topography, and surface free energy have been analysed along with SEM/EDS images to explore the underlying mechanisms of friction and wear.

A Hygroscopic Janus Heterojunction for Continuous Moisture-Triggered Electricity Generators.

Moisture-triggered electricity generator (MEG) harvesting energy from the ubiquity of atmospheric moisture is one of the promising potential candidates for renewable power demand. However, MEG device performance is strongly dependent on the moisture concentration, which results in its large fluctuation of the electrical output. Here, a Janus heterojunction MEG device consisting of nanostructured silicon and hygroscopic polyelectrolyte incorporating hydrophilic carbon nanotube mesh is proposed to enable ambient moisture harvesting and continuous stable electrical output delivery. The nanostructured silicon with a large surface/volume ratio provides strong coupling interaction with water molecules for charge generation. A polyelectrolyte of polydiallyl dimethylammonium chloride (PDDA) can facilitate charge selective transporting and enhance the effectiveness of moisture-absorbing in an arid environment simultaneously. The conductive, porous, and hydrophilic carbon nanotube mesh allows water to be ripped through as well as the generated charges being collected timely. As such, any generated charge carriers in the Janus heterojunction can be efficiently swept toward their respective electrodes, because of the device asymmetric contact. A MEG device continuously delivers an open-circuit voltage of 1.0 V, short-circuit current density of 8.2 μA/cm2, and output power density of 2.2 μW/cm2 under an ambient environment (60% relative humidity, 25 °C), which is a record value over the previously reported values. Furthermore, the infrared thermal measurements also reveal that the moisture-triggered electricity generation power is likely ascribed to surrounding thermal energy collected by the MEG device. Our results provide an insightful rationale for the design of device structure and understanding of the working mechanism of MEG, which is of great importance to promote the efficient electricity conversion induced by moisture in the atmosphere.

Optimization and simulation of a carbon nanotube arrangement for transparent conductive electrodes with record-high direct current to optical conductive ratios

Carbon nanotube (CNT) meshes have optical and electrical properties that make them suitable for use in next-generation transparent conductive electrodes (TCEs). Although circuit modeling of CNT meshes has been studied widely, very few researchers have modeled the optical properties of the horizontally and regular arrangement of CNT arrays. The behavior of light propagating through a CNT mesh is complex, with no straightforward rules established to provide simple analytical solutions. In this study, we used the three-dimensional finite difference time domain (3D-FDTD) method to model the optical properties of regular arrays of CNTs, based on the calculated refractive indices and extinction coefficients of multi-walled CNTs (MWCNTs). One-dimensional regular arrays of CNTs displayed strong anisotropic optical behavior. Moreover, by adjusting the spacing and arrangement of two-dimensional regular arrays of CNTs, we could identify the optimal structure for a CNT-based TCE displaying excellent optical and electrical performance. We have also developed the concept of the “optical threshold,” which defines the most effective charge transport channels possessing sufficiently open areas. This concept solves the trade-off between the two key parameters—the light transmittance and the sheet resistance—in TCEs. The optimal geometry provided a CNT mesh with not only the most effective charge transport channels but also very high optical transmittance, CNT network with a diameter of 10 nm (specific conductivity of 0.385 Ω−1 nm−1) has light transparency and low sheet resistance T > 90% and Rs < 1.6 Ω/sq, such that the ratio of the direct current conductivity to the optical conductivity (σDC/σop) reached as high as 2077. This value is far greater than previously reported simulated and experimental values for TCEs based on various materials.

Supported graphene-based membranes

Membranes Porous graphene sheets have excellent filtration capabilities and are able to block most ions, but their fragility limits their scale-up beyond laboratory demonstrations. Yang et al. created a nanoporous graphene membrane reinforced by a network of single-walled carbon nanotubes (SWNTs) to provide mechanical stability (see the Perspective by Mi). The SWNT network also stopped the propagation of cracks in the graphene, effectively localizing the damage to a small area defined by a cell in the carbon nanotube mesh. The membranes showed high water flux rates as well as a high rejection rate for most ions. Science , this issue p. [1057][1]; see also p. [1033][2] [1]: /lookup/doi/10.1126/science.aau5321 [2]: /lookup/doi/10.1126/science.aax3103

Large-area graphene-nanomesh/carbon-nanotube hybrid membranes for ionic and molecular nanofiltration.

Nanoporous two-dimensional materials are attractive for ionic and molecular nanofiltration but limited by insufficient mechanical strength over large areas. We report a large-area graphene-nanomesh/single-walled carbon nanotube (GNM/SWNT) hybrid membrane with excellent mechanical strength while fully capturing the merit of atomically thin membranes. The monolayer GNM features high-density, subnanometer pores for efficient transport of water molecules while blocking solute ions or molecules to enable size-selective separation. The SWNT network physically separates the GNM into microsized islands and acts as the microscopic framework to support the GNM, thus ensuring the structural integrity of the atomically thin GNM. The resulting GNM/SWNT membranes show high water permeance and a high rejection ratio for salt ions or organic molecules, and they retain stable separation performance in tubular modules.

Antishear Stress Bionic Carbon Nanotube Mesh Coating with Intracellular Controlled Drug Delivery Constructing Small-Diameter Tissue-Engineered Vascular Grafts.

Small-diameter (<6 mm) tissue-engineered blood vessels (TEBVs) have a low patency rate due to chronic inflammation mediated intimal hyperplasia. Functional coating with drug release is a promising solution, but preventing the released drug from being rushed away by blood flow remains a great challenge. A single-walled carboxylic acid functionalized carbon nanotube (C-SWCNT) is used to build an irregular mesh for TEBV coating. However, an interaction between the released drug and the cells is still insufficient due to the blood flow. Thus, an intracellular drug delivery system mediated by macrophage cellular uptake is designed. Resveratrol (RSV) modified CNT is used for macrophage uptake. M1 macrophage uptakes CNT-RSV and then converts to the M2 phenotype upon intracellular RSV release. Prohealing M2 macrophage inhibits the chronic inflammation thus maintains the contractile phenotype of the vascular smooth muscle cell (VSMC), which reduces intimal hyperplasia. Additionally, RSV released from the mesh coating also directly protects the contractile VSMCs from being converted to a secretory phenotype. Through antishear stress coating and macrophage-based intracellular drug delivery, CNT-RSV TEBVs exhibit a long-term anti-intimal hyperplasia function. Animal transplantation studies show that the patency rate remains high until day 90 after grafting in rat carotid arteries.

Ubiquitous Low-Cost Functionalized Multi-Walled Carbon Nanotube Sensors for Distributed Methane Leak Detection

This paper presents a highly sensitive, energy efficient, and low-cost distributed methane (CH4) sensor system (DMSS) for continuous monitoring, detection, and localization of CH4 leaks in natural gas infrastructure, such as transmission and distribution pipelines, wells, and production pads. The CH4 sensing element, a key component of the DMSS, consists of a metal–oxide nanocrystal functionalized multi-walled carbon nanotube mesh, which, in comparison with the existing literature, shows stronger relative resistance change while interacting with lower parts per million concentration of CH4. A Gaussian plume triangulation algorithm has been developed for the DMSS. Given a geometric model of the surrounding environment, the algorithm can precisely detect and localize a CH4 leak as well as estimate its mass emission rate. A UV-based surface recovery technique making the sensor recover ten times faster than the reported ones is presented for the DMSS. A control algorithm based on the UV-accelerated recovery is developed, which facilitates faster leak detection.

(Invited) Fabrication of Implantable Glucose Fuel Cells on Silicon Wafers

Well-known silicon micro fabrication techniques are used to create biocompatible abiotic glucose fuel cells, suitable for powering ultra-low-power bioelectronics on a silicon wafer. Measured continuous outputs of 2.3 µW/cm2 at 0.243V were achieved and maintained for a period of at least 48 hr with an open circuit voltage of 0.55V. Fabrication processes are discussed to address the difficulty in depositing and patterning Nafion separation membranes robustly and in the creation of a uniform carbon nanotube mesh catalyst.

Enhanced field emission from vertically aligned carbon nanotubes on metal mesh electrode

A vertically aligned carbon nanotube (CNT) mesh emitter array on metal mesh electrode has been fabricated with a low temperature growth process, from which a current density of up to 5A/cm2, and a threshold field of 0.9V/μm for a current density 1mA/cm2 were obtained, which show much better performance than CNT mesh on a flat electrode. This result was attributed to the enhanced edge effect of CNT mesh on metal mesh electrode. The numerical calculation results proved that the electric field on top of CNT emitter on mesh electrode was enhanced compared to that on flat electrode.

Stable and uniform field emission from zinc oxide nanowires grown on carbon nanotube mesh template

Zinc oxide nanowires (ZNW) were grown on a vertically-aligned carbon nanotube mesh array (VACM), of which the field emission properties were determined and compared with bare ZNW and bare VACM, respectively. The ZNW–VACM combined structure produced a macroscopic turn-on field of 0.8V/μm and a threshold field of 2.3V/μm, which was found to be much lower than that of bare ZNW. Crucially, field emission from ZNW–VACM was much more stable and uniform than that from bare VACM and exhibits a current fluctuation of less than 0.5% in 80h with a current density of ~1mA/cm2, making it a promising field emitter for field emission backlighting and displays.

Synthesis of graphene–carbon nanotube hybrid foam and its use as a novel three-dimensional electrode for electrochemical sensing

Three-dimensional (3D) graphene–carbon nanotube (CNT) hybrids are synthesized by two-step chemical vapor deposition (CVD) under atmospheric pressure. As revealed by scanning electron microscopy (SEM), the hybrid is a monolithic graphene foam with conformal coverage of a dense CNT mesh. We further demonstrate that the obtained graphene–CNT hybrid foams can be used as novel 3D electrochemical electrodes for sensing applications. Specifically, the 3D graphene–CNT electrodes exhibit a high sensitivity (∼470.7 mA M−1 cm−2) and low detection limit (∼20 nM with S/N ≈ 9.2) for dopamine detection. Modified with horseradish peroxidase and Nafion, the 3D hybrid electrodes are also used to detect H2O2 with a high sensitivity (137.9 mA M−1 cm−2), low detection limit (∼1 μM with S/N ≈ 17.4), and wide linear detection range (10 μM–1 mM).

High emission current density, vertically aligned carbon nanotube mesh, field emitter array

A vertically aligned carbon nanotube mesh emitter array has been fabricated and tested, giving a current density of up to 1.5 A/cm2, and a threshold field of 1.5 V/μm for a current density 1 mA/cm2. Low temperature carbon nanotube growth is used to fabricate the carbon nanotube mesh emitter arrays significantly reducing the cost of the fabrication of large area electron emitters. This system exhibits ultralong lifetime.

Wetting of carbon nanotubes by aluminum oxide

Most ceramic–carbon nanotube (CNT) composite processing utilizessolid state sintering, hence the concept of wetting of CNTs by moltenceramic is absolutely new. In the present work on a plasma sprayedAl2O3–CNT nanocomposite, it is observed that moltenAl2O3 spreads uniformly on the CNT surface by forming a thin(∼20–25 nm) ceramic layer without any cracks. The wettability of theAl2O3–CNT system is associated with the surface tension and capillary forces as captured from theevolution of microstructure. The dynamic equilibrium between melting and solidification ofAl2O3 was deduced from the meniscus height, curvature, contact perimeter and projection area of solidifiedAl2O3 onthe CNT surface. This interfacial phenomenon illuminates the mechanisms of microstructure evolutionfrom Al2O3-coated CNT bridge structures to CNT mesh formation. Consequent ab initio modeling depicteddistorted iso-surface contours at the interface, suggesting partial bonding and good wettability ofAl2O3 on the CNT surface.

Role of Powder Treatment and Carbon Nanotube Dispersion in the Fracture Toughening of Plasma-Sprayed Aluminum Oxide—Carbon Nanotube Nanocomposite

Al2O3 ceramic reinforced with 4-wt% multiwalled carbon nanotube (CNT) is plasma sprayed for improving the fracture toughness of the nanocomposite coating. Two different methodologies of CNT addition have been adopted in the powder feedstock to assist CNT dispersion in the nano-Al2O3 matrix. First, spray-dried nano-Al2O3 agglomerates are blended with 4 wt% CNT as powder-feedstock, which is subsequently plasma sprayed resulting in the fracture toughness improvement of 19.9%. Secondly, spray dried composite nano-Al2O3 and 4 wt% CNT powder was used as feedstock for attaining improved dispersion of CNTs. Plasma sprayed coating of composite spray dried powder resulted in increase of 42.9% in the fracture toughness. Coating synthesized from the blended powder displayed impact alignment of CNTs along splat interface, and CNTs chain loop structure anchoring the fused Al2O3 melt whereas coating synthesized from composite spray dried powder evinced anchoring of CNTs in the solid state sintered region and CNT mesh formation. Enhanced fracture toughness is attributed to significance of CNT dispersion.

High-Sensitivity NO&lt;SUB&gt;2&lt;/SUB&gt; Detection with Carbon Nanotube–Gold Nanoparticle Composite Films

Composite films of single-walled carbon nanotube mesh doped with alkanethiol monolayer protected gold clusters (MPCs) have been investigated for ultrahigh sensitivity detection of nitrogen dioxide. The response to NO2 (measured as increased conductance) of the composite materials increased with MPC loading until a threshold MPC loading level was achieved, after which no further enhancement of sensor response is observed. The total of about ten droplets of MPC solution had been cast atop the SWNT mesh. The detection limit for NO2 has been improved 9.6-fold, to 4.6 ppb, compared with that obtained with pure SWNT sensors. Ultraviolet illumination helps to speed up the sensor recovery. All tests were done under ambient conditions.