Acid-treated Carbon Nanotubes Research Articles

Wear behaviour of copper/carbon nanotubes

PurposeThe purpose of this paper is to study the wear behaviour of copper matrix composites reinforced with carbon nanotubes (CNTs) prepared by powder metallurgy route.Design/methodology/approachThe CNTs were treated by sulphuric acid and nitric acid to deagglomerate the CNTs prior mixing with copper powder. The composites comprised 0 to 4 Vol.% pristine CNTs (PCNTs) and also after acid-treated CNTs (ACNTs). The optimum value (pure Cu, 3 Vol.% PCNTs, 3 Vol.% ACNTs) evaluated by micro-hardness test was selected for wear test analysis.FindingsThe results showed that the enhancement of hardness, weight loss, coefficient of friction, wear depth and surface roughness (Ra) was due to the effect of homogenous distribution of ACNTs in Cu matrix and significant bonding compared to pure Cu and Cu-reinforced PCNTs. The scanning electron microscopy micrograph of worn surfaces and wear depth of the specimens also showed that the addition of ACNTs in Cu resulted in better wear performances.Originality/valueCNTs were treated prior processing to improve hardness and wear properties of Cu/CNTs composites.

The addition of acid treated carbon nanotube on the interfacial adhesion of carbon fiber reinforced UHMWPE composite

Carbon fiber reinforced Ultra High Molecular Weight Polyethylene (CF/UHMWPE) composites have been filled with acid treated carbon nanotube to enhance the adhesion. According to the modification, the interlaminar shear strength (ILSS) of composites has been greatly improved. Dynamic wetting method, XPS and SEM are used to examine the microscopic properties of resultant composites. The enhanced ILSS is attributed to the CNT interlock, which improves the wetting between carbon fibers and resins. Copyright © 2017 John Wiley & Sons, Ltd.

Fabrication of enzyme-based coatings on intact multi-walled carbon nanotubes as highly effective electrodes in biofuel cells

CNTs need to be dispersed in aqueous solution for their successful use, and most methods to disperse CNTs rely on tedious and time-consuming acid-based oxidation. Here, we report the simple dispersion of intact multi-walled carbon nanotubes (CNTs) by adding them directly into an aqueous solution of glucose oxidase (GOx), resulting in simultaneous CNT dispersion and facile enzyme immobilization through sequential enzyme adsorption, precipitation, and crosslinking (EAPC). The EAPC achieved high enzyme loading and stability because of crosslinked enzyme coatings on intact CNTs, while obviating the chemical pretreatment that can seriously damage the electron conductivity of CNTs. EAPC-driven GOx activity was 4.5- and 11-times higher than those of covalently-attached GOx (CA) on acid-treated CNTs and simply-adsorbed GOx (ADS) on intact CNTs, respectively. EAPC showed no decrease of GOx activity for 270 days. EAPC was employed to prepare the enzyme anodes for biofuel cells, and the EAPC anode produced 7.5-times higher power output than the CA anode. Even with a higher amount of bound non-conductive enzymes, the EAPC anode showed 1.7-fold higher electron transfer rate than the CA anode. The EAPC on intact CNTs can improve enzyme loading and stability with key routes of improved electron transfer in various biosensing and bioelectronics devices.

Heterogeneous Cu-Pd binary interface boosts stability and mass activity of atomic Pt clusters in the oxygen reduction reaction.

A ternary metallic CuPdPt nanocatalyst (NC) is synthesized using a wet chemical reduction method, which is sequentially designed, in the presence of acid treated carbon nanotubes. This NC is a nanocrystal with a configuration of a Cu@Pd core and atomic Pt clusters (∼9 wt%) on the top (Cu@Pd/Pt). A residual current of 92.6%, 5.2 times higher than that of commercial Pt catalysts (at 0.85 V vs. RHE), is retained after 40 000 cycles of an accelerated degradation test (ADT). Atomic and electronic structure analyses show that such exclusive stability mainly results from electron localization at Pt clusters in heterogeneous interfaces of the Cu-Pd core. Most importantly, we develop a robust ternary NC, which shows outstanding MA, superior chemical durability, and ∼90 wt% lower Pt loading than commercial Pt NCs in the oxygen reduction reaction.

Electrical property enhancement of carbon nanotube fibers from post treatments

Utilizing the superior properties of individual carbon nanotubes (CNTs), the production of continuous CNT fibers has paved the way for novel CNT macroscale applications. However, it is still a great challenge to create highly electrically-conductive CNT fibers due to the poor transfer of electrical property from nanoscale individual CNTs to macroscale CNT fibers. Here, we report a fast and effective post treatment method consisting of mechanical condensation and acid treatment to enhance the electrical conductivity of the CNT fiber by a factor of 9. Such great enhancement is attributed to the surface modification effects during the post treatments, resulting in the lower contact resistance and stronger inter-CNT interactions. Moreover, the maximum current density of the acid-treated CNT fiber is up to 66000A/cm2, competitive to the conventional copper wires. The promising results in this study enable the CNT fibers novel materials for electrical wiring applications.

High dielectric permittivity and improved mechanical and thermal properties of poly(vinylidene fluoride) composites with low carbon nanotube content: effect of composite processing on phase behavior and dielectric properties

The composite processing technique and nanofiller concentration and its functionalization significantly alter the properties of polymer nanocomposites. To realize this, multi-walled carbon nanotubes (CNT) were dispersed in a poly(vinylidene fluoride) (PVDF) matrix at carefully selected CNT concentrations by two illustrious methods, such as solution-cast and melt-mixing. Notwithstanding the processing method, CNTs induced predominantly the γ-phase in PVDF, instead of the commonly obtained β-phase upon nanofiller incorporation, and imparted significant improvements in dielectric properties. Acid-treatment of CNT improved its dispersion and interfacial adhesion significantly with PVDF, and induced a higher γ-phase content and better dielectric properties in PVDF as compared to pristine CNT. Further, the γ-phase content was found to be higher in solution-cast composites than that in melt-mixed counterparts, most likely due to solvent-induced crystallization in a controlled environment and slow solvent evaporation in the former case. However, interestingly, the melt-mixed composites showed a significantly higher dielectric constant at the onset of the CNT networked-structure as compared to the solution-cast composites. This suggests the possible role of CNT breakage during melt-mixing, which might lead to higher space-charge polarization at the polymer–CNT interface, and in turn an increased number of pseudo-microcapacitors in these composites than the solution-cast counterparts. Notably, PVDF with 0.13 vol% (volume fraction, fc = 0.0013) of acid-treated CNTs, prepared by melt-mixing, displayed the relative permittivity of ∼217 and capacitance of ∼5430 pF, loss tangent of ∼0.4 at 1 kHz and an unprecedented figure of merit of ∼105. We suggest a simple hypothesis for the γ-phase formation and evolution of the high dielectric constant in these composites. Further, the high-dielectric composite film showed marked improvements in mechanical and thermal properties over the neat PVDF film. These composites with exceptional dielectric properties and concomitant improvement in mechanical and thermal properties offer a great promise for use in flexible and mechanically robust charge storage devices.

CNT/TiO2 core-shell structures prepared by atomic layer deposition and characterization of their photocatalytic properties

TiO2 film was coated on acid-treated and pristine multiwall carbon nanotubes (CNTs) with different thicknesses by atomic layer deposition at 100°C to form a CNT/TiO2 core-shell structure. The relationship between oxygen-containing functional groups on the surface of CNTs and growth rate of TiO2 film was studied. The saturation growth rate of TiO2 was 0.55Å/cycle for acid-treated CNTs with sufficient durations of pulse time for the precursors of TiCl4 and H2O. The as-prepared TiO2 film was amorphous, and the anatase and rutile phases of TiO2 were obtained by heating to 300°C and 800°C, respectively. The shell thickness of anatase TiO2 on CNTs was a key factor to determine the efficiency of methylene blue (MB) degradation. The thickness of 22nm exhibited the best efficiency of MB degradation due to lower electron-hole recombination rate and higher amount of hydroxyl group generated on the surface of TiO2 after UV irradiation.

Effect of the pH of the preparation medium on the microstructure and electrocatalytic activity of carbon nanotubes decorated with PtSn nanoparticles for use in methanol oxidation

Carbon nanotubes (CNTs) decorated with PtSn nanoparticles (PtSn/CNT) were prepared by the microwave-assisted ethylene glycol reduction method and characterized by atomic adsorption spectroscopy, X-ray diffraction and transmission electron microscopy. Results indicated that the loading efficiency of the metal catalyst, and the degree of alloying and morphology of the PtSn nanoparticles were significantly affected by the solution pH value of the metallic ions in the ethylene glycol. The required composition of the PtSn/CNT catalysts could be obtained by adjusting the pH value to about 5, which is almost the isoelectric point of the acid-treated CNTs. The size of the PtSn nanoparticles decreased with the pH value in the range 2 to 7, but they became large and agglomerated when the pH value was greater than 7. Electrocatalytic activity tests indicated that the PtSn/CNTs prepared at pH 5 had the best catalytic performance towards methanol oxidation. The improvement in catalytic activity was mainly attributed to a high loading efficiency and control of particle shape and size distribution.

Investigation of the H2S poisoning process for sensing composite material based on carbon nanotubes and metal oxides

The poisoning of H2S sensing material based on the mixture of acid-treated carbon nanotubes, CuO and SnO2 was investigated by exposing the material to high doses of H2S (1% in volume) and following the changes spectroscopically. The presence of metal sulfides (CuS and SnS2), sulfates and thiols was confirmed on the surface of this material as the result of H2S poisoning. Further study revealed that leaving this material in air for extended period of time led to reoxidation of metal sulfides back to metal oxides. The formation of thiols and sulfates directly on carbon nanotubes is not reversible under these conditions; however, the extent of the overall surface reaction in this case is substantially lower than that for the composite material.

Polyelectrolyte-free layer by layer self-assembled multilayer films of cationic phthalocyanine cobalt(II) and carbon nanotube for the efficient detection of 4-nitrophenol

4-Nitrophenol (4-NP) sensors with high sensitivity and reproducibility are desirable for biosafety and environmental monitoring. Herein, cationic tetra-β-(N,N,N-trimethylaminoethoxy) phthalocyanine cobalt(II)/acid-treated carbon nanotubes multilayer films, marked as (tmaePcCo/CNT)n films (n represents the bilayer number), were successfully constructed on glassy carbon electrode (GCE) by a facile, effective layer by layer (LBL) electrostatic assembly method without the assistant of polyelectrolyte. Because CNTs within the multilayer films are beneficial to collect and transfer charges, and polyelectrolyte-free assembly ensures active sites exposing, the obtained (tmaePcCo/CNT)10/GCE exhibits excellent 4-NP electrocatalytic performance with good reproducibility and acceptable stability, a wide linear calibration range over 3 orders of magnitude of 4-NP concentrations (1μM–1.8mM) and a low detection limit of 0.2μM (S/N=3), and it can be applied to the quantification analysis of 4-NP under optimum conditions. This work shows that the LBL multilayer films fabricated without polyelectrolyte can provide a valid way to improve the sensitivity and reproducibility of 4-NP sensors.

Effects of amino group on the properties of carbon nanotubes

ABSTRACTThe surfaces of multi-walled carbon nanotubes were grafted with amino functional groups by reacting acyl-chloride-functionalized carbon nanotubes (CNTs) with hexamethylene diamine, which improves the surfactivity of CNTs. The dispersity, surface morphology, and thermogravimetry of acid-treated and amino-functionalized CNTs were investigated. Amino-functionalized CNTs were added into epoxy resin to analyze the effects of amino functional groups on the properties of resin composites. It was found that the properties of CNTs, such as morphology and scale, were not affected by amino functional groups, but the dispersity in water was highly improved. Amino-functionalized CNTs are better dispersed in resin matrix, and the mechanical properties of composites are improved significantly, whereas the conductivity of composites is not enhanced as expected.

Characterisation of CNTs/TiO<SUB align="right">2 nano composites and investigation of composite's photo reactivity

Titanium dioxide (TiO2) nanoparticles have been successfully deposited onto acid treated carbon nanotubes via a simple chemical route. It was demonstrated that the CNTs were coated by well-dispersed TiO2 nanoparticles. The CNTs-TiO2 nano composites were characterised by XRD, FTIR, SEM, EDAX and TEM. The photo catalytic activity of the prepared nano composites was tested under UV irradiation using the results of phenol degradation. Different composites were used as catalyst to investigate the effect of CNTs type and TiO2/CNT mass ratio on phenol removal. UV-vis spectroscopy was used to measure phenol adsorption.

Acid-treated carbon nanotubes and their effects on mortar strength

In the present study, multi-walled carbon nanotubes (MWCNTs) were treated in an acidic mixture solution, made with nitric and sulfuric acids in a ratio of 3:1 by volume. The durations of the treatment were 100 and 180 min. The defects of these treated MWCNTs were examined using Raman spectroscopy. The attachment of hydroxyl functional groups to the walls of the MWCNTs were verified using FTIR spectroscopy. The dispersion of CNTs with acid treatment is assessed using UV-Vis spectroscopy and Scanning Electron Microscopy (SEM). The results indicate that the duration of the acid treatment has significant effect on both the degree of defects and functionality of the MWCNT. The compressive strength of mortar increased with the addition of the acid-treated MWCNTs; however, no appreciable difference was noted for the two treatment durations under this study.

Enhanced electrical and mass transfer characteristics of acid-treated carbon nanotubes for capacitive deionization

Capacitive deionization (CDI) has attracted significant attention for the next generation water treatment due to its low energy consumption and environment friendly properties in comparison to widely established methods. For CDI technology to move forward, however, the development of carbon electrodes having superb electrosorption behavior is essential. In this study, we demonstrate the functionalization of carbon nanotubes (CNTs) via acid treatment shows enhanced electrochemical characteristics and effectively improves the wettability of the acid-treated CNTs (a-CNTs) via the addition of oxygen functional groups, leading to a higher electric double layer capacitance. Furthermore, defect formation in a-CNTs increases the conductivity and decreases the mass transfer resistance during CDI operation. CDI measurements confirmed a 270% increase in performance of a-CNTs in contrast to pristine CNTs (p-CNTs), attributable to the improved characteristics outlined above.

Investigation on the modification to solvent-containing two-component polyurethane coating by carbon nanotubes

Purpose – The purpose of this paper is to investigate the effects of carbon nanotubes (CNTs) on the mechanical, thermal and colour properties of solvent-containing two-component polyurethane (PU) coating. Design/methodology/approach – Fourier transform infrared spectroscopy and observation of dispersion stability were used to assess the effects of acid treatment on CNTs. The CNTs and PU composite coating was synthesised by in situ polymerisation and bending polymerisation, and the mechanical, thermal and colour appearance properties of coating were characterised. Findings – It was found that desirable modifications to CNTs occurred after acid treatment; thus, mainly carboxylic acid groups were introduced onto the surface of CNTs. And the acid-treated CNTs could improve the mechanical and thermal properties of PU coating, and the properties of composite coating was improved more successfully by in situ polymerisation than by blending polymerisation. Practical implications – The investigation established a method to synthesise CNTs and PU composite coating. The mechanical and thermal properties of PU coating could be improved by the inclusion of CNTs. Originality/value – This study established a method to synthesise CNTs and PU composite coating by in situ polymerisation and blending polymerisation; the effects of CNTs on modifying mechanical, thermal and colour properties of PU coating were investigated and compared in detail.

Electro-oxidation of perfluorooctanoic acid by carbon nanotube sponge anode and the mechanism

As an emerging persistent organic pollutant (POPs), perfluorooctanoic acid (PFOA) exists widely in natural environment. It is of particular significance to develop efficient techniques to remove low-concentration PFOA from the contaminated waters. In this work, we adopted a new material, carbon nanotube (CNT) sponge, as electrode to enhance electro-oxidation and achieve high removal efficiency of low-concentration (100μgL−1) PFOA from water. CNT sponge was pretreated by mixed acids to improve the surface morphology, hydrophilicity and the content of carbonyl groups on the surface. The highest removal efficiencies for low-concentration PFOA electrolyzed by acid-treated CNT sponge anode proved higher than 90%. The electro-oxidation mechanism of PFOA on CNT sponge anode was also discussed. PFOA is adsorbed on the CNT sponge rapidly increasing the concentration of PFOA on anode surface. When the potential on the anode is adjusted to more than 3.5V, the adsorbed PFOA undergoes electrochemically oxidation and hydrolysis to produce shorter-chain perfluorocarboxylic acids with less CF2 unit. The efficient electro-oxidation of PFOA by CNT sponge anode is due to the combined effect of adsorption and electrochemical oxidation. These findings provide an efficient method to remove actual concentration PFOA from water.

Chemical Oxidation of Multi-Walled Carbon Nanotube by Sodium Hypochlorite for Production of Graphene Oxide Nanosheets

Carbon nanotubes (CNTs) were chemically oxidized to produce graphene oxide (GO) nanosheets via a simple method. Pristine CNTs were treated with sulfuric acid and acid-treated CNTs were oxidized with sodium hypochlorite (NaOCl) to obtain peeled CNTs and consequently GO nanosheets. Transmission electron microscopy and atomic force microscopy were used to determine the morphology of synthesized GO nanosheets and peeled CNTs, respectively. UV-vis spectroscopy, Raman spectroscopy, Fourier transform infrared, and thermal gravimetric analysis were used to characterize the product structure. The UV-vis spectroscopy revealed peak absorption at 245 nm, which is similar to what is seen on CNT unzipping in producing GO nano-ribbons.

Stearic-acid/carbon-nanotube composites with tailored shape-stabilized phase transitions and light–heat conversion for thermal energy storage

The development of functional materials with both light–heat conversion and thermal energy storage properties is of crucial importance for efficient utilization of sunlight to meet the growing demand for sustainable energy. In this work, the shape-stabilized phase change composites were designed and prepared by integration of stearic acid (SA) and acid-treated carbon nanotubes (a-CNTs). The a-CNTs not only acted as a flexible matrix but also endowed the composites high light–heat conversion ability. The reversible phase transitions shifted from high temperatures (Tm=74°C, Tf=57°C) of pure SA to near room temperature (Tm=∼30°C, Tf=∼22°C) of SA/a-CNTs composites, probably resulting from the strong interface confinement effect. The phase change enthalpy of the SA/a-CNTs composite could also be tailored by changing the mass ratio of SA and a-CNTs. The composites containing SA of 54.2wt.%, 67.8wt.% and 79.5wt.% presented the melting enthalpy of 76.3J/g, 98.8J/g and 111.8J/g, respectively. Moreover, the phase transition of SA/a-CNTs composite could be driven by sunlight for the energy storage/release. Therefore, this research provides a new platform for improving solar utilization, and understanding the phase transition behaviors of organic PCMs in dimensionally confined environments as well.

Cadmium ion sorption from aqueous solutions by high surface area ethylenediaminetetraacetic acid- and diethylene triamine pentaacetic acid-treated carbon nanotubes

Friedel–Crafts acylation under microwave irradiation has been utilized for realizing functionalization of CNT with EDTA and DTPA. Significant increases in the specific surface area and sequestering metal ions are the most important advantages.

Outstanding adsorption performance of graphene–carbon nanotube aerogels for continuous oil removal

We report a green approach for synthesis of graphene–carbon nanotube aerogels with three dimensional (3D) interconnected networks prepared from natural graphite rocks. A one-step reaction under the synergic effects of the reduction of graphene oxide (GO) sheets and acid treated carbon nanotubes (CNTs) by ferrous ion is employed eliminating the use of harsh chemicals for the reduction of GO. CNTs are incorporated into the network to increase the robustness and hydrophobicity of aerogels with excellent porosity and oleophilic properties. The prepared aerogels exhibit outstanding adsorption performance for the removal of petroleum products, fats and organic solvents especially under continuous vacuum regime showing adsorption capacity of 28L of oil per gram of aerogel. The proposed synthetic method is simple and economical for the scalable production of highly porous 3D graphene–carbon nanotube aerogels, which can be successfully used for efficient and cost-effective oil spill clean-up and water purification.