Carbon Nanotubes In Matrix Research Articles

Preparation of CuO@humic acid@carbon nanotube composite material using humic acid as a coupling agent and its lithium-ion storage performance.

The conventional Li-ion battery composite electrode material composed of CuO and carbon nanotubes (CNTs) suffer from poor contact between CuO and CNTs. This results in high electrode resistance and poor electrochemical performance. To solve this problem, CuO@humic acid (HA) @CNT anode material with cross-linked network structure was generated by linking CuO and CNT with HA as a coupling agent. For comparison, CuO@HA or CuO@CNT were also prepared in the absence of CNT or HA, respectively. The results showed that CuO@HA@CNT had lower charge transfer resistance, higher conductivity, lithium-ion diffusion coefficient, specific capacity, and rate capability than CuO@HA and CuO@CNT. The specific capacity of the CuO@HA@CNT electrode was significantly better than that of the composite electrode materials of CuO and CNT, which have been prepared by scientists using various methods. Due to the introduction of HA, not only was the uniformly distributed flower-like CuO obtained, but also the specific capacity and rate capability of the electrode material were substantially improved. This study thus provides a good strategy to optimize the capability of transition metal oxide lithium-ion anode materials.

Investigation of Carbon Nanotube Metal Zinc Oxide Nanoparticle Synthesis and its Applications

Background: Carbon nanotubes (CNT) synthesized by CVD method at 950 ℃. CNT and metal ZnO nanocomposites material synthesized by ball mill procedure have been examined. Stability of nanocomposite material has been attained by cationic ion liquid (IL), 1-tetradecyl-3 methylimidazolium chloride, structural morphology material characterized by Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), Ultraviolet visible (UV-Vis) spectroscopy. Furthermore, these materials were analyzed by Energy dispersive X-ray spectroscopy (EDX) to study for the percentage of elemental compositions. Current-Voltage (I-V) characterized by electrical properties are showing highly responsive of resistance variation and easy recoverable high sensitivity was the main feature of the CO2 gas sensing properties. Objective: Carbon nanotube and zinc oxide nanoparticle combined with different ratio and optimization of coating methods using for sensor applications. Methods: It is synthesized with chemical vapour deposition method and zinc nanoparticle developed by ball mill method. We have optimized spin coating and dip coating method on glass surface. Results: FTIR spectrum results are recommended that the existing hydroxyl group and C group CNT-ZnO nanoparticle covered by the surface active site of ZnO. The size and composition of the CNT-ZnO were confirmed by FESEM EDAX studies. The absorption and transmittance wavelength of CNT-ZnO nanoparticle were recorded by UV-Visible spectroscopy. The I-V property shows that the drain current and voltages are varied by gas implying the materials suitable for applications. Conclusion: This module can be used to monitor CO¬2 gas application instruments with help of software. In future, this module and techniques can be used to study stress sensor and piezoelectric applications

Switchable NaCl cages via a MWCNTs/Ni[Fe(CN)6]2 nanocomposite for high performance desalination.

With the application of nanomaterials in seawater desalination technology increasing, the adjustable characteristics of carbon-based nanomaterials make it possible to use multiwalled carbon nanotube (MWCNT) materials in seawater desalination technology. In this study, Ni[Fe(CN)6]2 is loaded onto the inner wall of MWCNTs by the co-precipitation method to prepare MWCNTs with variable pore size, making it a switchable cage for NaCl. During the procedure, most of the Ni[Fe(CN)6]2 is transferred to the outer surface of the MWCNTs after adsorption, and NaCl is stored inside the MWCNTs (which have been proved by characterization); at the same time, Ni can improve the cell stability of Ni[Fe(CN)6]2. The effect of adsorbent reaction time and addition amount on the desalination performance of MWCNTs/Ni[Fe(CN)6]2 has been tested. According to the results, the best desalination performance of MWCNTs/Ni[Fe(CN)6]2 is 1354.6 mg g-1 when the reaction time is 0.5 h and the addition amount is 20 mg. After 3 cycles of adsorption and desorption, its desalting performance decreased to 242.3 mg g-1.

Application of Carbon Nanotubes in Various Fields

There have been more studies on the characteristics and uses of carbon nanotubes (CNTs) in recent years as a result of the advancement of nanomaterials and nanotechnology. CNTs are used in a greater variety of applications due to their powerful adsorption, stable molecular structure, high thermal conductivity, and other qualities. This paper introduces the role of CNTs in textile, construction and environmental science. Specifically, in the textile industry, CNTs have the functions of electromagnetic signal shielding, UV protection and flexible sensing in the field of material strength and high-temperature resistance. In terms of building and construction, CNTs can be composite with cement and concrete to improve mechanical properties. In sewage treatment applications, CNTs are characterized by high specific surface area, high porosity, high hydrophobicity, and electrocatalysis. This paper provides a reference for the development of the above fields, refers to the problems existing in the practical application of CNTs, and prospects the deeper development of CNTs materials.

Portland Cement: An Overview as a Root Repair Material: Applications and Various Modifications

Background: Portland cement has promisingly been utilized for the reconstruction of root perforation and bone defects, although its key drawbacks, including low mechanical properties and radiopacity as well as long setting time, necessitate pragmatic modifications. Objective: The main objective of this review was an overview of portland cement as a root repair material, its applications and various modifications. Methods: The electronic search of the literature was done on the Pubmed and Google Scholar databases with the keywords of Portland cement, carbon nanotube, graphene oxide, MTA, pulp capping, and root repair material. Results: The first part of this paper presents the data published in the literature on applications of Portland cement in endodontic situations, including vital pulp therapy, root perforation repair, root canal filling and root-end filling following apical endodontic surgery. This bioactive endodontic cement has shown promising success rates compared to mineral trioxide aggregate (MTA), however, considerable modifications are required in order to improve its clinical performance and expand its application scope as a root repair material. Hence, nano-reinforcements (graphene oxide, carbon nanotube, silica and hydroxyapatite) and extensive chemical modifications incorporated into Portland cement composition to produce innovative bio-dental materials with superior rheological properties have been discussed. Moreover, the current knowledge of the microstructure, mechanical properties and durability of nanomaterial-incorporated cement has been summarized. Ultimately, this article outlines the main points of animal and clinical studies on resin-modified Portland cement (TheraCal) as a pulp capping material and suggests further investigations prior to marketing authorization. Conclusion: It can be concluded that Portland cement has the potential to be used as an acceptable pulp capping material with the least complaints in the long term.

Schottky-like photo/electro-catalytic carbon nanotube composite ultrafiltration membrane reactors

Stimuli-responsive membrane reactors offer advanced strategies towards simultaneous separation and degradation of persistent organic contaminants, allowing for triggered response through photo or electro stimuli. However, the scalable fabrication of stimuli-responsive nanoporous membranes with high selectivity and catalytic reactivity is still challenging in practical application. Here, photo-electro responsive membranes were designed by assembling carbon nanotubes (CNT) scaffolds decorated with conformal nanoscale SnO2 coatings. The membranes, built from spinnable CNT materials supported the generation of a unique class of ultrathin and flexible ultrafiltration membranes with thicknesses down to 25 nm and pore size as narrow as ∼20 nm. The CNTs were used as effective conductive photosensitizers to promote charge transfer from the graphitic to the SnO2 layer, supporting synergistic effects arising from generated Schottky-like diodes to improve the photo/electro-catalytic activity of nanocomposite membranes. The SnO2-CNT membranes exhibited high water permeance of 2.24 × 103 L m−2 h−1.bar−1, and faster reaction kinetics of 77.6 × 10−3 for acetaminophen degradation, which was 2–10 times higher than the kinetics achieved by currently available catalytic membrane reactors. The structural stability and outstanding performance of SnO2-CNT membranes were maintained over 8 reuse cycles with ∼99% degradation efficiency against acetaminophen in 60 min. The unique solid-state fabrication method of uniformly coated catalytic metal oxide on well aligned CNTs provides a scalable feasible approach to produce high-performance ultrafiltration photo/electro-catalytic membrane reactors towards cost-effective water purification at a competent reaction rate.

The New Reliable pH Sensor Based on Hydrous Iridium Dioxide and Its Composites.

The new reliable sensor for pH determination was designed with the use of hydrous iridium dioxide and its composites. Three different hIrO2-based materials were prepared and applied as solid-contact layers in pH-selective electrodes with polymeric membrane. The material choice included standalone hydrous iridium oxide; composite material of hydrous iridium oxide, carbon nanotubes, and triple composite material composed of hydrous iridium oxide; carbon nanotubes; and poly(3-octylthiophene-2,5-diyl). The paper depicts that the addition of functional material to standalone metal oxide is beneficial for the performance of solid-state ion-selective electrodes and presents the universal approach to designing this type of sensors. Each component contributed differently to the sensors' performance-the addition of carbon nanotubes increased the electrical capacitance of sensor (up to 400 µF) while the addition of conducting polymer allowed it to increase the contact angle of material changing its wetting properties and enhancing the stability of potentiometric response. Hydrous iridium oxide contacted electrodes exhibit linear response in wide linear range of pH (2-11) and stable potentiometric response (the lowest potential drift of 0.036 mV/h is attributed to the electrode with triple composite material).

The demonstration of low-temperature (350 °C) grown carbon nano-tubes for the applications of through silicon via in 3D stacking and power-via

Low temperature Carbon Nano-tubes (CNTs) growth technology is developed in this work with the insert of Al (Aluminum) between Ni (Nickel) and Ti (Titanium) as the reactant. The optimized Al thicknesses are also investigated. CNTs growth at the low temperature below 400 °C is the key factor for the back end of line compatible process integration. In this work, we grow the CNTs by thermal chemical vapor deposition process at 350 and 400 °C. The low ratio of peak ID/IG in Raman spectra and scanning electron microscope images proves the CNTs material quality. On the other hand, the high thermal conductivity (k) value of ∼50 W m − 1 K − 1 is also demonstrated. Both high material quality and k value on our low temperature grown CNTs show promising opportunities for the integration of semiconductor three dimensional packages and power-via related applications.

Highly Sensitive and Selective Formaldehyde Gas Sensors Based on Polyvinylpyrrolidone/Nitrogen-Doped Double-Walled Carbon Nanotubes

A highly sensitive and selective formaldehyde sensor was successfully fabricated using hybrid materials of nitrogen-doped double-walled carbon nanotubes (N-DWCNTs) and polyvinylpyrrolidone (PVP). Double-walled carbon nanotubes (DWCNTs) and N-DWCNTs were produced by high-vacuum chemical vapor deposition using ethanol and benzylamine, respectively. Purified DWCNTs and N-DWCNTs were dropped separately onto the sensing substrate. PVP was then dropped onto pre-dropped DWCNT and N-DWCNTs (hereafter referred to as PVP/DWCNTs and PVP/N-DWCNTs, respectively). As-fabricated sensors were used to find 1,2-dichloroethane, dichloromethane, formaldehyde and toluene vapors in parts per million (ppm) at room temperature for detection measurement. The sensor response of N-DWCNTs, PVP/DWCNTs and PVP/N-DWCNTs sensors show a high response to formaldehyde but a low response to 1,2-dichloroethane, dichloromethane and toluene. Remarkably, PVP/N-DWCNTs sensors respond sensitively and selectively towards formaldehyde vapor, which is 15 times higher than when using DWCNTs sensors. This improvement could be attributed to the synergistic effect of the polymer swelling and nitrogen-sites in the N-DWCNTs. The limit of detection (LOD) of PVP/N-DWCNTs was 15 ppm, which is 34-fold higher than when using DWCNTs with a LOD of 506 ppm. This study demonstrated the high sensitivity and selectivity for formaldehyde-sensing applications of high-performance PVP/N-DWCNTs hybrid materials.

Adsorption of different anionic and cationic dyes by hybrid nanocomposites of carbon nanotube and graphene materials over UiO-66

Amongst many chemical pollutants that cause environmental pollution, the presence of organic dyes in water resources can cause substantial health issues. Thus, owing to their mutagenicity and their adverse effects on human health, environment, and animals, they must be removed from industrial wastewater. In this study, UiO-66 metal–organic framework, as well as composite nanoparticles with carbonaceous materials such as MWCNTs-COOH and graphene oxide (GO) with different molar ratios (2.9 and 5.8 wt.%), were synthesized through solvothermal method since carbonaceous materials are an emerging material that demonstrates improvement in the properties of adsorbents. Then, the synthesized materials were utilized as a solid adsorbent for removing four different dyes including; anionic methyl red (MR), anionic methyl orange (MO), cationic methylene blue (MB), and cationic malachite green (MG) prepared from distilled water. The properties of prepared adsorbents were characterized via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), Photoluminescence spectroscopy (PL), Brunauer–Emmett–Teller (BET), as well as surface area analyzer and energy dispersive spectroscopy (EDS-MAP). Further, the influences of various factors including initial concentrations of the dyes and adsorption process time on adsorption of dyes were investigated. Adsorption experiments indicated that synthesized adsorbents exhibited the highest adsorption efficiency towards MR and MO dyes. Moreover, the experimental adsorption results revealed that MWCNTs-UiO-66 nanocomposites could adsorb 98% of MR and MO as well as 72% of MB and 46% of MG. Furthermore, the kinetic and stability of the materials over time were investigated. To reach a clear picture, adsorption experiments demonstrated that the amount of dye uptake on adsorbents was enhanced by increasing the contact time as well as uptake of materials with time were stable for both cationic and anionic dyes. The MR, MO, and MB adsorption isotherms were fitted with the Langmuir and Freundlich models. The Langmuir showed the highest agreement in these dyes and MWCNTs-UiO-66 (2.9 and 5.8 wt.%) exhibited a maximum adsorption capacity of 105.26 mg/g for MR, while the MG isotherm was in line with the Langmuir model.

Partially reduced CeO2/C@CNT with high oxygen vacancy boosting phosphate adsorption as CDI anode

Phosphorus in water is the main inducement for eutrophication and deterioration of water quality. Cerium oxide has excellent adsorption ability for phosphate, but its activity and conductivity need to be improved for capacitive deionization (CDI) application. Herein, a carbon nanotube (CNT)-twined CeO2/C composite was synthesized by in-situ growth of Ce-BTC in CNT matrix followed by carbonization. The ultrafine CeO2 particles were uniformly dispersed in carbon matrix, improving the electrical conductivity and effective active sites. Via hydrazine reduction, the content of Ce(III) and oxygen vacancy of the obtained CeO2/C-R@CNT were enhanced, boosting the activity of electrode for phosphate adsorption. As an anode, CeO2/C-R@CNT delivered the maximum phosphate removal capacity of 109.5 mg P/g. The adsorption performance was investigated by analyzing adsorption kinetics and adsorption isotherms. The corresponding adsorption mechanism was studied by pH analysis, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The electrode showed high selectivity to phosphate adsorption, and the separation factor arrived at 8.7 in the mixture solution with the Cl–/P concentration ratio of 15. In addition, CeO2/C-R@CNT retains the P adsorption capacity of 95 % in 30 cycles. The phosphate in actual water was totally removed with good repeatability, proving the high practicability for water treatment.

Agglomeration effects of CNTs on the energy harvesting performance of multifield interactive magneto-electro-elastic/nanocomposite unimorph smart beam

In this article, the effect of agglomeration of carbon nanotubes (CNTs) on the energy harvesting behavior of a unimorph multifunctional cantilever beam (UMCB) subjected to transverse and rotational vibrations is investigated analytically using a distributed parameter model. The top layer of the UMCB consists of the magneto-electro-elastic (MEE) material, formed by reinforcing a piezoelectric matrix with CNTs, acting as a piezomagnetic phase. The substructure of the UMCB is composed of a nanocomposite CNTs material. To address the issue of dispersion of the material, agglomeration or cluster formation of the CNTs in the substrate layer is considered. The agglomeration is modeled using the modified Eshelby-Mori-Tanaka (EMT) method. The ideal case of no agglomeration, partial and complete agglomeration, is considered for evaluation. The various distributions of the CNTs in the substrate and its volume fractions are also considered in the analysis. The coupled governing equations of motion and the subsequent frequency-response functions (FRFs) for the output parameters are derived based on the distributed parameter approach, in conjunction with the Euler-Bernoulli beam theory, Gauss and Faraday’s laws. Various material and geometrical parametric studies are discussed in detail to understand the output response of the UMCB. Special focus is placed on the effect of the agglomerated CNTs substrate and the influence of various agglomeration parameters on the overall output response. The article is a stepping stone to developing and utilizing advanced composite structure-based energy harvesting devices and paves the way for further research into utilizing CNTs-based composite structures for various engineering applications.

Cu/Cu3P@CNT Flexible Film Electrode for Highly Efficient Electrocatalytic Hydrogen Evolution in Alkaline Solution

AbstractGlobal warming and the global energy crisis are worsening owing to the increasing consumption of fossil fuels; thus, there is a need to explore renewable and clean energy sources. The energy conversion efficiency of water electrolysis – an important and feasible means to obtain green hydrogen energy – can be improved by developing catalytic electrode materials with high activity and low overpotential. Herein, low‐temperature phosphating of copper deposited on flexible carbon nanotube (CNT) films was conducted to fabricate high‐performance Cu/Cu3P@CNT electrocatalysts for the hydrogen evolution reaction (HER). The optimal conditions for the preparation of catalytic electrodes were determined by adjusting the electrodeposition time. Owing to the porous CNT framework and the heterostructure of the Cu3P/Cu nanoparticles, the Cu/Cu3P@CNT exhibited long‐term stability and highly efficient catalytic HER in an alkaline electrolyte with an overpotential of only 77 mV at 10 mA cm−2. This study provided a facile strategy for designing inexpensive and efficient electrocatalytic HER systems using highly active transition metal phosphides heterostructures and CNT materials.

Fabrication of modified carbon nano tubes based composite using ionic liquid for phenol removal

Carbon nano tubes are functionalized to enhance their surface properties and target specificity. In this research, a novel ionic liquid functionalized carbon nanotube (IL-CNT) material was synthesized using 1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide and investigated for the phenol removal. The parametric experiments were performed to identify the optimal conditions for high removal performance. With an initial concentration of 50 mg/L and an IL-CNT dosage level 100 mg, 95.36% phenol removal was attained at optimal pH 6.0. The occurrence of monolayer attachment was verified through equilibrium studies. The Langmuir isotherm parameters are evaluated as qm =109.9 mg/g and KL = 0.196 L/mg. The kinetic experiments followed Pseudo Second Order model (R2 > 0.990). The synthesized nanomaterial was characterized using Scanning Electron Microscopic imaging, Fourier Transform Infra-Red spectra, X-Ray Diffraction analysis and Thermo Gravimetric Analysis.

Combined Atomic and Molecular Layer Deposition Surface Modification of Carbon Nanotubes for CNT–Epoxy Polymer Composites

Optimizing the interactions between the matrix and reinforcement components is key to attaining high-performance composite materials. Yet, balancing the reinforcing–matrix phase interactions for synthetic composites remains a great challenge. Here, a combined methodology using molecular and atomic layer deposition (M/ALD) is demonstrated for tailoring carbon nanotube (CNT) interfacial interactions, yielding high-performance-reinforced polymer composites. CNT mats are used as a model system to systematically study the molecular details as they do not involve powder processing and other aspects which obscure the understanding of molecular level effects. Noncovalent attachment of the M/ALD layer at the interface allows good wetting of the CNTs, provides an effective means for stress dissipation without compromising the CNTs’ Csp2–Csp2 network which remains intact, while introducing amine functionalities to facilitate the cross-linking polymer matrix (epoxy). M/ALD-modified CNT mat–epoxy composites showed an increase in the maximal tensile strength and toughness of up to 32 and 247%, respectively. These findings may pave the way to systematically develop high CNT loading composites as well as other nano-reinforced composite systems showing both high strength and toughness as well as numerous other desirable properties related to nanomaterial composites in general.

Flexible Bonding of Polymer Substrates By Microwave Heating of Carbon Nanotubes

Recently, as research on developing electronic devices for simultaneous implementation of flexibility and conductivity has been continuously conducted, ensuring stable and high reliability of devices in preparation for various mechanical deformation is becoming important. When a physical force such as bending, twisting, or folding is applied, the bonding area between two substrates should ensure stability due to high stress generation. Epoxy resin materials used as standard adhesive agents have brittleness due to the nature of the material, and are weak in terms of flexibility due to increased bonding thickness due to high temperature hardening. In addition, it is difficult to apply as a bonding material in consideration of thermal deformation of the polymer substrate exposed to high temperatures during the process. To improve both flexibility and durability against fatigue deformation, Flexible bonding process is required without adhesive such as epoxy resin with poor brittleness. Surface activation bonding technologies by ion beams and vacuum ultraviolet rays have been developed in previous studies, bonding between plastic substrates by activating thin metal films surface of adhesive layer with ion beam or improving adhesive force by direct-UV radiation on the surface of the polymer substrate. In this study, a flexible bonding process between polymer substrates was developed by heating carbon nanotubes (CNTs) through microwave irradiation. High microwave absorption properties of CNT lead to heat dissipation behavior and light emission characteristics. Heat transfer mechanism of CNT applied to CNT-polymer composites, CNT electrodes fields and has been microwave assisted purification. By utilizing the microwave heating effect, we selected CNT materials for flexible substrates. Multi-walled carbon nanotubes (MWNTs) were coated on a bonded PET polymer substrate and then local heating was performed by microwaves to induce mechanical entanglement between the CNTs and the PET. In the bonding process, the output power of the microwave was adjusted to 600,800 and 1000 Watt, and the bonding strength was evaluated by quantifying the bonding strength was evaluated. For the analysis of the bonding mechanism in the area where mechanical entanglement took place, the CNT-PET bonding interface was analyzed through electron scanning microscope (SEM) measurement, and further analysis was performed for each process condition. In addition, a fracture mechanism analysis that occurred at the junction was performed after the overlapping shear strength test. Acknowledgments This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020M3H4A3106413, Development of Evaluation Method for Mechanical Deformation of Micro-joints in Micro-LED Module) Figure 1

Highly-efficient cathodic lysis of biofilm on conductive carbon nanotube membranes

Biofouling is a major problem observed with membrane-based water treatment systems. In this work, cathodic lysis of bacteria and biofilms on carbon nanotube (CNT) membrane was investigated as a novel mechanism for biofouling reduction. Considering the biofilm growth cycle, electrolysis of sessile bacteria and established bacterial biofilms were separately investigated. The results showed that cathodic electrolysis at 3.0 V for 3 h effectively eliminated 99.23% of the sessile bacteria on the CNT membrane. An extended treatment of mature biofilm for 21 h led to 93.92% reduction in viable bacterial density and 98.6% decrease in biofilm coverage. Besides, analyses of the membrane permeate revealed that the biofilm lysis released cell contents into the CNT matrix, which were subsequently removed by electrolysis. As a result, the normalized transmembrane pressure for the fouled membrane decreased from 4.23 to 2.06 after 21 h of electrolysis. Moreover, the cathodic lysis of bacteria and biofilm by the low-voltage electric field was mainly ascribed to the electro-generated H2O2 and the associated bio-electrochemical effects. This work provided a facile approach for in-situ mitigation of biofouling caused by chlorine-resistant bacteria, which was conducive to energy-efficient operation of membrane-based water treatment facilities.

A supersensitive wearable sensor constructed with PDMS porous foam and multi-integrated conductive pathways structure

In recent years, wearable multifunctional strain sensors have attracted attention for their promising applications in wearable electronics and portable devices. To achieve a high-performance wearable strain sensor with a wide sensing range and high gauge factor (GF), wisely choosing appropriate conductive materials and a rational structural design is essential. Herein, we develop a supersensitive sensor that contains one-dimensional conductive material CNT and two-dimensional material MXene built on a PDMS porous foam that is made based on a sugar template. The one-dimensional carbon nanotube (CNT) functionalizes as a conductive scale layer through solvent swelling and evaporation on the surface of the PDMS skeleton. The two-dimensional MXene is applied on top of the CNT layer to form final conductive pathways. The PDMS/CNT@MXene (PCM) sensor has a wide sensing range (150%), high sensitivity (GF = 26438), rapid response speed (response/recovery time of 60/71 ms), and exceptional durability (>1000 cycles) owing to its unique porous structure with scale layers and graded fracture of conductive pathways. Moreover, the PCM sensor is capable of monitoring subtle and significant human activities and is used for wireless sensing and medical diagnostics, even for solvent identification. The superior performance of the PCM sensor provides vast application potential in human movement, health monitoring, and warning devices.

Purification of dense carbon nanotube networks by subcritical hydrothermal processing

Carbon nanotube (CNT)-reinforced composites are promising materials for high-performance, lightweight structures; however, homogeneous infiltration of CNTs by a matrix material is necessary to achieve desired mechanical properties. Critical to overcoming this challenge at scale is purification of CNT materials produced by floating-catalyst chemical vapor deposition. Here, we present a hydrothermal processing technique for purification of CNT yarns, wherein as-received material is exposed to superheated, subcritical water in a hydrothermal reactor. This process selectively removes amorphous carbon and acid impurities while preserving the yarn structure. We find this technique to be consistent and tunable, with processing time directly correlating to linear density reduction up to a saturation limit. Using commercially-available yarns, we find that after 4 h of treatment at 200 °C, the weight loss of the yarn under inert atmosphere is reduced from 12% to 5%, the atomic percentage of oxygen at the surface by 42%, and the I D /I G by 30%. In addition, the yarn specific strength (1.3 N/tex) is preserved, while the specific Young's modulus is significantly increased by 20% (79 to 95 N/tex). At longer treatment times, we obtain greater purity and higher specific Young's modulus, but at a substantial reduction in tensile strength, which we hypothesize results from eliminating amorphous carbon toughening CNT bundles. The reported method could be scaled to continuous processing in tandem with post-purification treatments, and appears broadly applicable to different continuous CNT networks.

Nanostructural Engineering of Electrospun Poly(vinyl alcohol)/Carbon Nanotube Mats into Dense Films for Alcohol Dehydration

Pervaporation is a green process that consumes low energy and does not require solvents for separation. In this work, interfacial engineering of poly(vinyl alcohol) (PVA)/carbon nanotube (CNT) electrospun fibers was attempted to fabricate dense membranes for pervaporation. Ethanol and water were used as nonsolvent and solvent, respectively, to alter the nanoscopic configuration of the fibers through interfacial solvent interactions. PVA and PVA/CNT mats with micron-sized pores (>100 μm) were prepared by optimizing electrospinning conditions. The mats were compacted via immersion in ethanol. They exhibited asymmetric close-packed top and bottom layers and porous intermediate layers. Further consolidation was achieved using water to fuse the fibers. The mats with more than 1.5 wt % CNT loading were stable against water owing to the cross-linking between CNTs and PVA. Because of the uniform dispersion of CNTs into the PVA matrix, the PVA/CNT dense films exhibited higher water/ethanol selectivity and water flux than those exhibited by similar films prepared by solution-casting. Thus, simple interfacial engineering of electrospun mats presented in this work successfully generates high-performance PVA/CNT membranes. A high alcohol dehydration performance and time-efficient membrane fabrication are achieved.