Cobalt Carbon Nanotubes Research Articles

Selective Electrochemical Determination of L-Cysteine by a Cobalt Carbon Nanotube (CNT)-Modified Glassy Carbon Electrode (GCE)

L-Cysteine is a semi-essential and proteinogenic amino acid, with the formula HO2CCH (NH2) CH2SH. L-cysteine is mostly found in protein-rich foods. In this study, catalysts consisting of cobalt (Co) supported on carbon nanotubes (CNTs) were prepared using the sodium borohydride (NaBH4) reduction method. These catalysts were characterized by means of energy-dispersive x-ray (EDX) with scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and temperature-programmed oxidation (TPO) techniques. Characterization results confirmed the successful preparation of the desired catalyst. After preparing the Co/CNT catalysts, a highly efficient and sensitive electrochemical sensor was developed using a glassy carbon electrode (GCE) modified with the Co/CNT catalysts. The electrochemical behavior of the bare GCE and Co/CNT-modified GCE electrodes was investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) in 0.1 M phosphate buffer solution (PBS) + L-cysteine. Electrochemical results showed that the Co/CNT-modified GCE electrode exhibited high sensitivity and selectivity compared to the bare GCE, with sensitivity of 0.0046 µA/µM, limit of detection of 0.2 µM, and limit of quantification of 0.6 µM. Furthermore, this electrode showed higher sensitivity values than those reported in the literature. Further interference studies were performed using CV and EIS to investigate interfering species in the serum environment, such as D-glucose, uric acid, L-tyrosine, and L-tryptophan. In conclusion, the results suggest that the Co/CNT-modified GCE electrode is a promising catalyst for the sensitive detection of L-cysteine.

Cobalt-Carbon nanotubes supported on V2O3 nanorods as sulfur hosts for High-performance Lithium-Sulfur batteries

Exploring advanced sulfur cathode materials with high catalytic activity to accelerate the slow redox reactions of lithium polysulfides (LiPSs) is of great significance for lithium-sulfur batteries (LSBs). In this study, a coral-like hybrid composed of cobalt nanoparticle-embedded N-doped carbon nanotubes supported by Vanadium (III) oxide (V2O3) nanorods (Co-CNTs/C @V2O3) was designed as an efficient sulfur host using a simple annealing process. Characterization combined with electrochemical analysis confirmed that the V2O3 nanorods exhibited enhanced LiPSs adsorption capacity, and the in situ grown short-length Co-CNTs improved electron/mass transport and enhanced the catalytic activity for conversion to LiPSs. Owing to these merits, the S@Co-CNTs/C@V2O3 cathode exhibits effective capacity and cycle lifetime. Its initial capacity was 864 mAh g−1 at 1.0C and remained at 594 mAh g−1 after 800cycles with a decay rate of 0.039%. Furthermore, even at a high sulfur loading (4.5 mg cm−2), S@Co-CNTs/C@V2O3 also shows acceptable initial capacity of 880 mAh g−1 at 0.5C. This study provides new ideas for preparing long-cycle S-hosting cathodes for LSBs.

Effect of grain boundary constitution on corrosion behaviour in cobalt-carbon nanotube composite coatings

Corrosion behavior and micro-texture of electrodeposited cobalt coatings containing different volume fractions of carbon nanotubes (CNTs) were investigated and correlated. For lower CNT volume fractions, a compact and smoother coating morphology were observed. The morphology however, became coarser for higher CNT volume fractions. Corrosion properties of the coatings were determined using the electrochemical impedance spectroscopy and Tafel polarization techniques. Pristine cobalt coating showed corrosion potential (Ecorr), corrosion current density (icorr), and polarization resistance (Rp) values of -0.574 V, 21.48µA/cm2 and 2071 ohms.cm2 respectively. With the incorporation of CNTs, the coating corrosion resistance increased up to Co-CNT3 coating (produced by 20mg/L of CNT dispersion). Co-CNT3 coating showed Ecorr, icorr and Rp values of -0.521V, 5.33µA/cm2 and 3525 ohms.cm2 respectively. However, for higher volume fractions of CNTs, the coating corrosion resistance dropped to values lower than pristine cobalt coating. For Co-CNT6 coating (produced from 80 mg/L of CNT dispersion) the Ecorr, icorr and Rp values were -0.581V, 23.45µA/cm2 and 1409 ohms.cm2 respectively. Micro-texture analysis was conducted for pristine Co and Co-CNT3 coatings to investigate the correlation between the observed corrosion behavior and coating micro-texture. Both the coatings showed strong {211¯0} texture along the coating growth direction. When compared to printine Co coating, the Co-CNT3 coating showed lesser fraction of high angle grain boundaries as well as higher fraction of low energy special boundaries like STGBs (32°/ [211¯0], 62°/ [211¯0] angle axis pair) leading to better corrosion resistance performance for Co-CNT3 coatings.

Three-dimensional network structure Co/CNT derived from bimetal MOFs toward efficient electromagnetic wave absorber

The development of radar stealth technology and the innovation of modern communication technology have put forward new requirements for microwave absorbing materials. Herein, the novel cobalt/carbon nanotube (Co/CNT) material with a three-dimensional (3D) network structure was prepared through the pyrolysis of nanosized bimetallic CoZn-ZIF precursor. The material exhibits excellent performance under the synergistic effect of multiple loss mechanisms. The minimum reflection loss (RLmin) value reaches −43 dB with 3.3 mm at a filled ratio of 20 wt%. In addition, its effective absorption bandwidth (EAB) can reach 4.2 GHz with a thickness of 3 mm. Furthermore, based on the systematic analysis of the absorption mechanism, an MA fabric with EAB covering the entire X band was successfully constructed with polyimide (PI) fabric as the substrate. The interconnected graphite network provides strong conduction loss and polarization loss, and the existence of Co nanoparticles not only provides magnetic loss but also effectively adjusts impedance matching performance. Overall, this research provides a new perspective for the design and application of high-performance microwave absorbing materials.

Green synthesis of 1,4-dihydropyridines using cobalt carbon nanotubes as recyclable catalysts

Heterocyclic compounds occur widely in nature and in drug molecules. The activity of many nitrogen-containing heterocyclic compounds is unique. For example, 1,4-dihydropyridines display good antitumor and antibacterial effects and can be commercially used as calcium channel blocker agents in the treatment of cardiovascular diseases. To reduce the use of toxic catalysts in the synthesis of 1,4-dihydropyridines, here we designed cobalt carbon nanotubes as a heterogeneous catalyst. We report the efficient synthesis of 1,4-dihydropyridines under mild conditions, which allows to access a wide array of 1,4-dihydropyridines from aromatic aldehyde in high yields, up to 96%. Advantages include the use of ethanol as solvent, low catalyst loading of 6% mol, short reaction time of 5–15 min, easy preparation and recyclable catalyst.

Enhanced removal of methylparaben mediated by cobalt/carbon nanotubes (Co/CNTs) activated peroxymonosulfate in chloride-containing water: Reaction kinetics, mechanisms and pathways

Chloride ion (Cl−) widely presents in natural water and wastewater, which can significantly affect the performance of sulfate radical-based advanced oxidation processes (SR-AOPs). However, few studies are available now on the generation of chlorinated by-products in the peroxymonosulfate (PMS) based systems. Here a novel catalyst (cobalt/carbon nanotubes, Co/CNTs) was synthesized and used as a PMS activator to remove methylparaben (MeP) with and without Cl−. The morphology and chemical composition of the fresh and used Co/CNTs were characterized by TEM, SEM, XRD, BET, and XPS. Results revealed that Co/CNTs exhibited significant catalytic activity toward MeP removal, and the removal efficiency increased with the augment of reaction temperature and concentrations of Co/CNTs and PMS. In the absence of Cl−, 83.2% of 10 μM MeP was degraded within 60 min by using 2 mg/L Co/CNTs and 100 μM PMS at 25 °C with pH 7.0. However, complete removal of MeP was achieved within 20 min in the presence of 100 mM Cl−, which enhanced the apparent rate constant by a factor of 4.3. Consequently, TOC removal was enhanced from 8.1% to 19.2% within 60 min. Through the quenching experiments, both SO4− and OH were found responsible for MeP degradation without Cl−, while Cl2− was the main reactive oxygen species (ROS) with 100 mM Cl−. Based on the intermediates identified via TOF-LC-MS, four potential reaction pathways were proposed, including hydrogen abstraction coupling reaction, hydroxylation, OH attack, and Cl2− attack. The intermediates also exhibited decreased toxicity compared to the parent compound based on the ecotoxicity evaluation. In addition, Co/CNTs + PMS system achieved over 60% MeP removal from real wastewater with elevated PMS concentration, indicating the process applicability. These findings provide valuable information of SR-AOPs to facilitate organic contaminants removal in Cl−-containing water.

Effect of “cobalt–carbon nanotubes” catalysts on anthracene coking

Coking of anthracene at 400–600°C in the presence or in the absence of a cobalt catalyst supported on carbon nanotubes (CNTs) was studied for the first time. The coking products were examined by X-ray diffraction and electron microscopy. The CoO-CNTs catalyst considerably (by 50°C) decreased the temperature of the onset of coking and accelerated the coke formation. The presence of CoO-CNTs changed the coke morphology. Whereas coking of pure anthracene affords ~1 micron spherical particles of poorly crystallized carbon, in the presence of the catalyst, a carbon “coating” covering the CNT surface is formed.

Effect of “Cobalt–Carbon Nanotubes” Catalysts on Anthracene Coking

Effect of “Cobalt–Carbon Nanotubes” Catalysts on Anthracene Coking

Fabrication and Characterization of Aligned Carbon Nanotubes Cluster Reinforced Magnesium Composite Based On Ultrasound/Magnetic Compound Field

Abstract Carbon nanotubes (CNTs)-based materials have been the focus of intense research since their discovery because of their superior mechanical properties, good electrical conductivity and unique nano-effect of unique one dimensional nanostructures. Control and manipulation of the alignment of CNTs in the matrix can effectively affect the electrical, optical and mechanical properties of the composites. At present, there are many researches on the magnetic-field induced the alignment of CNTs in the polymer matrix, but less research on magnetic- field induced the alignment of CNTs in the metal matrix. In order to realize the alignment of CNTs in metal matrix, CNTs were firstly magnetically modified by electroless plating, and a uniform layer of cobalt nanoparticles was successfully plated on the surface of carbon nanotubes. For facilitating the macro-analysis of the different factors on the cobalt-carbon nanotubes directional effect, three kinds of matrixes (distilled water, vegetable oil and high viscosity glue) were used to simulate the magnesium alloy melt. The effects of ultrasonic, magnetic field and temperature on the Co coated CNTs dispersion and alignment in three kinds of matrix were studied by orthogonal test. It was found that the dispersion of CNTs was significantly affected by ultrasound and the alignment of CNTs affected by the magnetic field intensity. In this paper, the CNTs / Mg composites were prepared by liquid-state method and the wettability between CNTs and Mg alloy was improved by the modification of carbon nanotubes. Under the compound effect of ultrasonic and magnetic field, the alignment of the carbon nanotubes cluster in magnesium matrix composites was quantitatively characterized by Image J software. It is found that the Cobalt particles coated CNTs can respond well to magnetic field (typically 0.3–0.8T). With the increase of magnetic field strength, CNTs show higher relative frequencies along the magnetic field direction. When the magnetic field strength was 0.8T, the relative frequencies within 20-50° was 0.7. This indicated that Co-CNTs can achieve obviously alignment in AZ91D alloy under a low magnetic field. In addition, the compressive specimens were prepared according to the optimum process parameters determined by the orthogonal test. The compressive properties of the composites parallel to and perpendicular to the direction of the magnetic field were studied. The results shown that the compressive strength of the Co-CNTs/Mg composites was obviously higher than that of the magnesium matrix and exhibited anisotropy due to directional aligned carbon nanotube.

Hydrothermal synthesis and electrochemical properties of cobalt–carbon nanotubes nanocomposite

Cobalt–carbon nanotubes composite (Co–CNTs) is synthesized through a facile hydrothermal route. SEM and TEM characterizations reveal that the Co–CNTs composite contains abundance of carbon nanotubes connected by cobalt spheres and some of the CNTs are filled with metallic nanoparticles or nanorods. A series of electrochemical measurements show that the adding CNTs can remarkably enhance the electrochemical activity of the Co, leading to a notable improvement of the discharge capacity and the cycle performance. The practical maximum discharge capacity of the active Co is 495 mAh g −1 after deducting the weight contribution of CNTs, which is about 280 mAh g −1 higher than that of pure Co. The electrochemical reaction mechanism can be attributed to the dissolution–precipitation mechanism of Co in alkaline solution. And the functions of the CNTs are to improve dispersion of Co particles, increase contact area between Co and alkaline solution and promote the charge-transfer reaction.

Structure and electrochemical properties of ball-milled Co-carbon nanotube composites as negative electrode material of alkaline rechargeable batteries

A series of cobalt-carbon nanotube (CNT) composites is synthesized by direct ball-milling of Co and CNT powders with different Co/CNT weight ratios. The microstructure, morphology and chemical state of the ball-milled Co-CNT composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is found that metallic Co nanoparticles of 50–100 nm in size are highly dispersed on the inactive CNT matrix after ball-milling. The electrochemical performance of Co-CNT composites as negative electrode material of alkaline rechargeable batteries is investigated by galvanostatic charge–discharge, linear polarization and cyclic voltammetry (CV) techniques. The results show that the Co-CNT composite (weight ratio 5/1, BM 10 h) displays the optimized electrochemical performance, including discharge capacity and cycle stability. The reversible faradaic reaction between Co and Co(OH) 2 is dominant for ball-milled Co-CNT composites.