Multi-walled Carbon Nanotubes Material Research Articles

Efficient sensitive detection of nitrite with Binary Y/Fe-modified multiwalled carbon nanotube nanocomposite by electrochemical approaches

Low-dimensional metal nanoparticles (MNPs) intercalated with three-dimensional multiwalled carbon nanotube (MWCNT) materials may be combined to produce new nanocomposites for enhancing their chemical, structural, and morphological features. These composites have interesting physical and chemical characteristics that can be used in electrochemical sensing systems that work significantly well. This research presents a new method for detecting nitrite using an electrochemical sensor that utilizes a flat-electrode made of GCE fabricated by nanocomposite of MWCNTs intercalated with yttrium oxide (Y2O3) and iron oxide (Fe2O3) as Y/Fe-MWCNT at higher temperature. FT-IR, UV–vis., SEM, powder XRD, EDS, BET, and TEM were significantly used to characterize in detail the nanocomposite after its preparation by the solid-state chemical approach. Using CV, LSV, and EIS techniques, the electrochemical attributes of both the bare and Y/Fe-MWCNT fabricated electrodes (with the help of 5 % Nafion as conducting coating binder) were investigated. In addition, the linear relationship between nitrite concentration and peak current of LSV was seen between 1.0 and 1.6 M, with a lower limit of detection (LOD) of 0.027 M. When compared to modified electrodes with nitrite, the electrocatalytic behavior of the nanocomposite electrode is enhanced significantly. At applied potential window of −0.1 to +1.8 V, the Y/Fe-MWCNT sensor shows good selectivity even when there are a lot of interfering chemicals and metal ions. In addition, different PBS electrolyte solutions with pH values ranging from 6.5 to 8 were used to study the prepared sensor. The standard addition method was employed to detect the unidentified nitrite concentration in various real samples including sea water, industrial wastewater, and well water. It introduced a new route for the development of noble sensor probe with nanocomposite materials by electrochemical approach for the safety of environmental and health care field in a broad scale.

Volatile capacitance of resistor with differential resistance

The differential current dV/dR in a resistor forms a volatile capacitance across itself. When the differential current is less than the Ohm current, V/R, the volatile capacitance is positive. Conversely, when it exceeds the Ohm current, the volatile capacitance becomes negative. If the differential current equals the Ohm current, the volatile capacitance is zero. The transition of this volatile capacitance from positive to negative has been observed in a combination of multi-walled carbon nanotube material and vacuum space. Additionally, we have fabricated a two-dimensional planar inductor without a coil using this negative capacitor.

Ternary (molybdenum disulfide/graphene)/carbon nanotube nanocomposites assembled via a facile colloidal electrostatic path as electrocatalysts for the oxygen reduction reaction: Composition and nitrogen-doping play a key role in their performance

Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS2/GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure–activity relationships. Both the (MoS2/GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N-GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS2/N-GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further.

Environmental safety of energy storing devices using carbon nanotubes: possible impacts of waste in aquatic and terrestrial environments

Electric double layer capacitors (EDLC) are energy storage devices based on the charging and discharging electrode-electrolyte interfaces of high surface area materials such as multi-walled carbon nanotubes (MWCNT) and activated carbon (AC). Despite the broad applicability, the final destination of these components is the environment, mainly water and soil, where they can represent impacts on organisms along different trophic levels. Bioassays with Raphidoceles subcapitata, are widely used to evaluate aquatic totoxicity and oligochaetes are good terrestrial bioindicators. The study aimed to evaluate aquatic and terrestrial toxicity of MWCNT from EDLC-type capacitors using bioindicators, R. subcapitata and Eisenia andrei. The MWCNT material was synthesized by the floating catalyst-based chemical vapor deposition method (FC-CVD) on stainless steel (AISI 304L). The MWCNT concentrations for the assays were 0.1 1.0, 10 and 100 mg.L–1 for the bioindicator R. subcapitata and the concentrations of 1, 10 and 100 mg.Kg–1 for bioindicator E. andrei. MWCNT inhibited the algal biomass in a concentration dependent manner at concentrations higher than 10 mg.L–1. In the soil the presence of MWCNT, at the concentrations tested did not cause mortality in the earthworm, but resulted in a significant mass reduction in the exposed organisms after 14 days. In the cytology analysis, it was not observed the production of micronuclei, but cytoplasmic vacuolization and nuclear atypia in coelomocytes were frequent. In the comet assay, there was a predominance of nucleoids in the stage 1 classification. Thus, no genotoxic effect was demonstrated in these organisms. The concentrations that showed toxic effects are within the range of environmentally expected concentrations. MWCNT are released from EDLC and may pose an occupational and environmental risk.

Cobalt Organic Framework Supported over Carbon-Based Materials as Novel Catalysts in the Hydrolysis of Sodium Borohydride

It is no secret that the global supplies of fossil fuel resources have been steadily dwindling. While there is no consensus on when the reserves will be completely depleted, there has been an effort among scientists to find a new, sustainable energy source for the future. It is generally agreed that such a source needs to not only be abundant, but also avoid the harmful biproducts of current fuel sources. Some proposed energy sources include solar, wind, geothermal and more. While each of these sources have their benefits, they also have their drawbacks and the cost to install and maintain these sources, as well as the environmental damage done during their construction can offset their benefits. One potential new energy source can be found in hydrogen gas. Hydrogen is not only the most abundant element in the universe, but its gaseous form can be burned to produce only energy and water [1-12]. The biggest hurdle a hydrogen economy faces is in the storage of the highly combustible gas. An interesting method of storing hydrogen is via adsorption within the chemical structure of a molecule. Sodium borohydride (NaBH4) for example is a chemical that contains 10.8% hydrogen by weight and steadily releases hydrogen gas when mixed with water.1 In order to efficiently utilize this reaction a catalyst is required. Typical catalysts are often precious metals like platinum, gold, and palladium, which tend to be expensive to use. By forming these metals into nanoparticles, their surface area can be increased, which increases their catalytic potential, however, these nanoparticles have a tendency to agglomerate in solution. Previous work by this team explored the catalytic capability of these metals and notes the use of carbon-based support structures can mitigate this agglomeration.2-4 This study aims to expand on those studies by using cobalt nanoparticles, which is a more cost-effective metal. Two novel Cobalt terephthalate complexes were combined with graphene and multiwalled carbon nanotubes (MWCNT) respectively, then tested for their ability to catalyze the hydrolysis of sodium borohydride. These materials were characterized using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Powdered X-ray diffraction (P-XRD), and Fourier Transform Infrared spectroscopy (FTIR). It was observed that after a single reaction, our materials appeared to be converted into cobalt borohydrides. The hydrogen produced for each material was 73 mL and 76 mL for the graphene and MWCNT materials, respectively. This study provides a possible method for producing cheaper, cleaner energy for a more sustainable future.

Graphene as a Platform in Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) for Amino-TEMPO Electro-Grafting

2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) has emerged as an environmentally benign catalyst for the electrochemical oxidation of primary and secondary alcohols to aldehydes and ketones (1). This simple organic free radical reagent possesses high activity, and versatility, and is one of the most promising alternatives to noble metal catalysts that were previously studied. The catalytic activity and reactivity of TEMPO is mostly studied in bulk solutions, for fuel cells, aqueous redox flow batteries and sensors (2, 3). For more practicality, various approaches were developed to immobilize TEMPO on active supports, such as anionic polyelectrolytes, and the electropolymerization of TEMPO-substituted pyrrole or thiophene (4, 5). However, these substrates suffer from instability, loss of catalytic activity, degradation of the polymer film in alkaline environment mostly used for TEMPO regeneration. One other way, is to use carbon-based substrates that are stable in aqueous acid and base environment, as well as non-aqueous solutions and have shown enhanced electrocatalytic behavior (6, 7).In this work, we studied the electro-grafting of amino-TEMPO on graphene using in-situ attenuated total reflection infrared absorption spectroscopy (ATR-IRAS). We observed that TEMPO is attached on the surface through covalent bonding between the amine and the graphene lattice, as previously reported (6, 7). While grafting was successfully demonstrated via the oxidation of the primary amine to a radical cation which reacted with the graphene surface, ATR-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) provided additional spectral feature confirming TEMPO grafting through plasmon induced signal enhancement. Hickey, D. P.; Milton, R. D.; Chen, D.; Sigman, M. S.; Minteer, S. D., TEMPO-Modified Linear Poly(ethylenimine) for Immobilization-Enhanced Electrocatalytic Oxidation of Alcohols. ACS Catalysis 2015, 5 (9), 5519-5524. Mishra, A.; Kim, J.; Zorigt, M.; Romo, A. I. B.; Gaddam, R.; Braun, J. E.; Ziviani, D.; Rodríguez-López, J., Highly Selective TEMPO Catalyzed Bulk Electrooxidation of Isopropanol to Acetone for Application in Electrochemical Heat Pumping. ACS Sustainable Chemistry & Engineering 2023, 11 (16), 6241-6249. Elouarzaki, K.; Mandoc, L.-R. P.; Gorgy, K.; Holzinger, M.; Amarandei, C.-A.; Ungureanu, E.-M.; Cosnier, S., Synthesis and electrochemical characterization of original “TEMPO” functionalized multiwall carbon nanotube materials: Application to iron (II) detection. Electrochemistry Communications 2015, 60, 131-134. Belgsir, E. M.; Schäfer, H. J., Selective oxidation of carbohydrates on Nafion®–TEMPO-modified graphite felt electrodes. Electrochemistry Communications 2001, 3 (1), 32-35. Grimshaw, J.; Perera, S. D., Poly(pyrrole-pyromellitimide) modified electrodes. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1990, 278 (1), 279-286. Barman, K.; Askarova, G.; Jia, R.; Hu, G.; Mirkin, M. V., Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode. Journal of the American Chemical Society 2023, 145 (10), 5786-5794. Yuan, B.; Xu, C.; Zhang, D.; Zhang, R.; Su, H.; Guan, P.; Nie, J.; Fernandez, C., Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications. Electrochemistry Communications 2017, 81, 18-23.

Selectivity enhancement by the presence of HOF + CNT composite membranes investigated by non-equilibrium molecular dynamics

Hydrogen purification through membrane separation offers convenience and suitability for on-site operation, especially in automotive fuel cells that utilize reformed methanol as a hydrogen source. In this study, the molecular dynamics simulation method was employed to investigate the micro-separation mechanism of hydrogen purification using multi-walled carbon nanotubes (MWNTs) and hydrogen-bonded organic frameworks (HOFs) as membrane materials. Novel composite membranes combining different HOF and MWNT materials were designed to enhance the interaction energy with CO2. The results demonstrated that these composite membranes exhibited higher selectivity in the separation of H2/CO2 gas mixtures, achieving higher hydrogen permeability compared with individual HOF and MWNT membranes. Notably, the PhTCz1 + CNT, UPC-H4a + CNT, and TCPP-1,3-DPP + CNT-3 composite membranes demonstrated 100 % CO2 retention and reached a maximum flux hydrogen of 4.782 × 105 GPU, which was higher than traditional membranes by 6 orders of magnitude. Furthermore, the PhTCz1 + CNT-3 composite membrane had a significant ability to simultaneously intercept CO2 and CO. The MD calculation results show that this newly synthesized HOF + CNT composite membrane material can provide high permeability as well as ultrahigh selectivity simultaneously, making it a prospective H2 separation membrane with superior performance.

Construction of multi walled carbon nanotube decorated CoMn2O4 hexagonal nanoplates for high performance aqueous asymmetric supercapacitor

The fabrication of transition metal oxide with carbonaceous material results in hybrid electrode with good charge storage capacity, higher energy density and power density than transition metal oxide electrodes. In this work, hybrid electrode material of CoMn2O4 hexagonal nanoplates and multi-walled carbon nanotubes (MWCNTs) is synthesized by co-precipitation process. The transmission electron microscope (TEM) analysis of prepared material shows that CoMn2O4 nanoplates are uniformly anchored on MWCNTs which helps to keep good electronic channel throughout the electrode material. Further, the MWCNT/CoMn2O4 is widely examined as high-performance electrode material in supercapacitor and, its capacitive faradaic charge storage mechanism is studied. The synergistic interaction between MWCNTs and CoMn2O4 hexagonal nanoplates resulted in the specific capacity of 156.75 mAh g−1 at 1 A g−1 which is higher from the specific capacity of sole CoMn2O4 nanoplates (113.37 mAh g−1 at 1 A g−1). Further, asymmetric supercapacitor is designed and high energy density of 58.41 W h kg−1 is observed at power density of 502.5 W kg−1. Furthermore, four parallel connected yellow color LEDs and a toy motor fan are functionalized by MWCNT/CoMn2O4//AC device.

EuMnO3/EuMn2O5/MWCNT nanocomposites: Insights into synthesis and application as potential materials for development of hydrogen storage capacity

Although, hydrogen as a novel clean-burning fuel is the most promising option for energy production/consumption systems, the relative low volumetric energy density value has limited success in sorption abilities at ambient conditions. In response to the energy crisis, numerous studies on the rational construction of high-capacity electrode materials have been aimed to address the growing complications. Herein, a novel energetic solid composite based on nano-sized EuMnO3/EuMn2O5 incorporated with multiwalled carbon nanotube (EM/EMM/MWCNT) materials was fabricated via efficient synthesis protocols. An in-situ combustion route was proposed for interfacial architecture design of binary EM/EMM nanocomposites by manipulating the fuel concentration. The fundamental impacts of the Schiff-base ligand tris(2-(2-hydroxyacetophenylidene)ethyl)amine as both fuel and nucleation center on the crystalline phase structure and morphology features of binary EM/EMM products were investigated, for the first time. Correspondingly, the incorporation of MWCNT at varying concentrations was explored for preferable electrochemical hydrogen storage of composite texture in terms of the redox reactivity and improved electronic conductivity. When the MWCNT concentration was 3.0%, the structural advantages of the EM/EMM/MWCNT nanocomposites delivered maximum discharge capacity of 382.50 mAhg−1 after 15 cycles in 2.0 M KOH medium, which was 7.30 times higher than that yield by binary EM/EMM nanocomposites. It can be emphasized that this report suggests freestanding pathways for developing manganite-based electrode materials with highly efficient discharge capacity.

Detection of hydrogen peroxide vapor using flexible gas sensor based on SnO2 nanoparticles decorated with multi-walled carbon nanotubes

In this work, a high-sensitive flexible sensor based on the SnO2 nanoparticles decorated with the multi-walled carbon nanotubes (MWCNTs) was fabricated by a simple and cost-effective centrifugation method for hydrogen peroxide vapour (HPV) detection. Morphological, composition, structural, and HPV sensing studies of the film were thoroughly conducted. Scanning electron microscopy (SEM) revealed the presence of MWCNTs in the SnO2 material and energy dispersive x-ray (EDX) elementary analysis determined the actual concentration of carbon elements (24.47 wt%) in the SnO2:MWCNTs material with pronounced peaks of C, O, and Sn. Elemental mapping analysis showed the nearly homogeneous distribution of the elements while x-ray diffraction analysis (XRD) confirmed the diffraction peaks of tin oxide and carbon. The HPV sensing behaviour of the flexible SnO2:MWCNTs sensor was investigated in the temperature range of 25 °C–150 °C towards 1.5–56 ppm HPV under ultraviolet (UV) irradiation. The flexible sensor had a fairly high response (44) to 1.5 ppm of HPV concentration at room temperature (RT). The fabricated SnO2:MWCNTs based sensor was capable of detecting extremely low concentrations of HPV, thus being a potential candidate for use in real environments.

PVK-grafted multiwalled carbon nanotube materials with enhanced mobility for electronic devices

Carbon nanotubes are unique due to their exceptional optical, electrical, thermal, and mechanical capabilities. This research included enhancing the electrical conductivity of a poly (9-vinyl carbazole) (PVK)-based organic semiconductor by combining it with a multi-walled carbon nanotube (MWCNT). The electrical conductivity was calculated utilizing composites of PVK-doped CNTs. In an organic medium, the composites were synthesized via in situ chemical polymerization. The immobility of PVK in the form of oxidation, high conductivity, and permitting electrochemical behavior of the materials for application in electronics was investigated. The study involved composites that alter electrical conductivity and different structure that shows stable dispersion in the PVK polymer of various molecular weights. It is an effective nanotube dispersion at low PVK concentration. X-ray powder diffraction (XRD), ultraviolet-visible spectroscopy, Thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) were used to validate the generation of composites from synthesized CNTs and composites. The morphological structures were examined using field emission scanning electron microscopy (FESEM). The electrical conductivity was evaluated, and the movement of charge between polymers and CNTs was discussed.

Pristine, carboxylated, and hybrid multi-walled carbon nanotubes exert potent antioxidant activities in in vitro-cell free systems

Multi-walled carbon nanotubes (MWCNTs) are tubular-shaped carbon allotropes, composed of multiple concentric graphene cylinders. The extended systems of conjugated double bonds, that MWCNTs are constituted by, provide them with high electron affinities, enabling them to act as electron donors or acceptors. Consequently, their potential biomedical applications, as synthetic antioxidant agents, are of particular interest. Based on the above, the purpose of the present study was to evaluate the intrinsic antioxidant properties of pristine and carboxylated MWCNTs, as well as of novel hybrid nanocomposites of MWCNTs and inorganic nanoparticles. To this end, after the synthesis and characterization of MWCNTs, their antiradical, reducing, and antigenotoxic properties were assessed in cell-free assays, using a methodological approach that has been recently proposed by our research group. According to our results, most of the tested MWCNTs exhibited strong antioxidant activities. More elaborately, the hybrid material of MWCNTs and ferrous oxide nanoparticles, i.e., CNTs@Fe3O4, showed robust scavenging capacities in all free-radical scavenging assays examined. As regards reducing properties, the pristine MWCNTs, i.e., CNTs-Ref, exhibited the greater electron donating capacity. Finally, in terms of antigenotoxic properties, the hybrid material of MWCNTs and silicon carbide nanoparticles, i.e., CNTs@SiC, exhibited potent ability to inhibit the formation of peroxyl radicals, thus preventing from the oxidative DNA damage. Conclusively, our findings suggest that the MWCNTs of the study could be considered as promising broad-spectrum antioxidants, however, further investigations are required to evaluate their toxicological profile in cell-based and in vivo systems.

Dual-Amplifying Electrochemiluminescence Sensor Based on CdS QDs@HKUST-1/MWCNTs Composite for Sensitive Catechol Assay

Herein, a novel electrochemiluminescence (ECL) sensor was developed using a dual signal amplification mechanism based on a typical HKUST-1 metal-organic framework, [Cu3(BTC)2(H2O)3, BTC=1,3,5-benzene tricarboxylate], CdS quantum dots (QDs) and multi-walled carbon nanotubes (MWCNTs) for ultrasensitive determination of catechol. HKUST-1 not only has a dispersion effect to carry more CdS QDs for enhancing stability, but also acts as effective catalyzer to accelerate the transformation of persulfate ion (S2O8 2−) for generating more sulfate radical anions (SO4 •−), therefore amplifying the signal of the ECL sensor. Meanwhile, the introduction of MWCNTs to the ECL process could promote the electron transfer rate and accelerate the kinetics of the electro-catalytic reaction attributing to its stronger conductivity, achieving dual-amplifying effect, which could obviously increase the sensitivity of the ECL sensor. The proposed sensor displayed a wide linear range of 1 × 10−7 − 1 × 10−3 M and a low detection limit of 3.8 × 10−8 M with excellent stability, high repeatability and outstanding anti-interference ability under the optimal conditions. Impressively, the sensor possessed commendable feedback when detecting catechol in real samples. Therefore, this research provided a new strategy combining the advantages of MOFs, QDs and MWCNTs materials for phenolic pollutants detection.

Effect of Carbon Nanotubes on the performance of Perovskite Solar Cells

Perovskite solar cells (PSCs) made with metal halide are affordable and can give better efficiency values than older versions but their low efficiency values is still a concern. Two Perovskite solar cells were fabricated and one had Multi wall Carbon nanotube (MWCNT) in its design. The effect of the Multi-wall Carbon nanotube (MWCNT) on their performance and power conversion were studied. MWCNT and m-TiO2 materials were characterised using UV-vis spectroscopy and their optical energy band gap values were obtained. The TiO2 showed a prominent peak at 319 nm with absorbance 0.5 and its optical energy bandgap of 2.59 eV falls in the visible region showing it is a clean energy source with implications for solar energy conversion. The MWCNT has 2.19 eV and showed multiple peaks. A prominent peak at 329 nm with absorbance 0.6 which was blue shifted and a peak at 517 nm with absorbance 0.3 was red-shifted. The PSC with the MWCNT in the light had a fill factor of 0.53 but 0.47 was obtained for the PSC without the MWCNT. The PSC with MWCNT had power conversion efficiency (PCE) of 40.1 % in the dark, a value which was 2.7 % higher than the PCE of 37.4 % obtained for the same cell in light. Furthermore, the PSC without the MWCNT in the dark had a fill factor of 0.87 while the PSC with MWCNT in the dark had a fill factor was 0.51. The PSC with MWCNT had better power conversion efficiency when in the dark than in light.

Two-dimensional MoS2/Mn-MOF/multi-walled carbon nanotubes composite material for high-performance supercapacitors

A series of MoS2 and Mn metal organic frameworks (Mn-MOF) were synthesized by hydrothermal method, and then MoS2, Mn-MOF and multi-walled carbon nanotubes (MWCNT) were mixed in different mass ratios and applied for supercapacitor. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) are used to investigate the electrochemical performance of MoS2/Mn-MOF/MWCNT materials with different mass ratios. The experimental results show that when the mass ratio of m(MoS2): m(Mn-MOF): m(MWCNT) is 1:4:1, the electrochemical performance of the MoS2/Mn-MOF/MWCNT composite is the best. The specific capacitance of optimal MoS2/Mn-MOF/MWCNT (1:4:1) reaches 862.73F g−1, which is noticeable higher than that of MoS2 (42.29F g−1), Mn-MOF (70.23F g−1) and MWCNT (347.27F g−1) materials. Moreover, the EIS test manifests that the MoS2/Mn-MOF/MWCNT (1:4:1) composite has a lower Rct value (2.566 Ω). Therefore, MoS2/Mn-MOF/MWCNT (1:4:1) has the best electrochemical performance among the all as-fabricated supercapacitor materials. This research provides an effective method for the development of Mn-based supercapacitor materials and improves the capacitance performance of MOFs materials.

Voltammetric Amitriptyline Determination Using a Metal-Free Electrode Based on Phosphorus-Doped Multi-Walled Carbon Nanotubes

A new electrode material of phosphorus-doped multi-walled carbon nanotubes (P-MWCNTs) was developed as an electrochemical sensing element for amitriptyline (AMT). P-MWCNTs were hydrothermally synthesized and drop casted on a glassy carbon electrode (P-MWCNTs/GCE). The P-MWCNTs were morphologically, chemically and structurally characterized. The electrochemical characteristics of the P-MWCNTs/GCE were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and adsorptive stripping voltammetry (AdSV). The P-MWCNTs increased electron transfer at the GCE and the electrochemical conductivity of the electrode. Electrocatalytic activity toward the oxidation of AMT was excellent. In the optimal voltammetric condition, the P-MWCNTs/GCE produced linear ranges of 0.50 to 10 μg ml−1 and 10 to 40 μg ml−1. The limit of detection (LOD) and limit of quantification (LOQ) were 0.15 μg ml−1 and 0.52 μg ml−1, respectively. The developed sensor displayed good repeatability, reproducibility and specificity. The sensor successfully quantified AMT in pharmaceutical tablets, giving results consistent with spectrophotometric analysis. The sensor achieved recoveries from 98 ± 2% to 101 ± 5% from spiked urine samples. The proposed sensor could be applied to determine AMT in pharmaceutical and urine samples for forensic toxicology.

Solid-phase microextraction of eleven organochlorine pesticides from fruit and vegetable samples by a coated fiber with boron nitride modified multiwalled carbon nanotubes

A boron nitride modified multiwalled carbon nanotube material (BN@MWCNTs) was synthesized, and the synthesis conditions were optimized. The BN@MWCNTs was then used as the SPME fiber coating adsorbent for the extraction of eleven organochlorine pesticides (OCPs) from fruit and vegetable samples. Under the optimal conditions, the SPME coupled with the detection by GC-ECD had a linear response for the determination of the target analytes in the range of 0.03 to 200 ng g−1 with the coefficients of determination (r2) ≥ 0.9977. Based on the signal-to-noise ratios of 3 and 10, the limits of detection and the limits of quantification were measured to be 0.01–0.20 ng g−1 and 0.03–0.67 ng g−1, respectively. The relative recoveries of the analytes for spiked samples under three concentration levels (1.0, 10.0 and 100 ng g−1) were between 83.7% and 124% with the relative standard deviations ≤ 10.9%. The established method was successfully applied to the determination of OCPs in real fruit and vegetable samples.

Preparation and Electrochemical Performance of V2O5 @N-CNT/S Composite Cathode Materials

Lithium–sulfur battery hasreceived widespread attention because of its high energy density, low cost, environmental friendliness, and nontoxicity. However, the insulating properties of elemental sulfur, huge volume changes, and dissolution of polysulfides in electrolytes that result in the shuttle effect, low sulfur utilization, and low rate performance seriously hinder the commercialization of lithium–sulfur batteries. In this work, a composite material of nitrogen-doped multiwalled carbon nanotubes and V2O5 was designed and fabricated to serve as the positive electrode of lithium–sulfur battery via the hydrothermal method. The positive electrode of the V2O5@N-CNTs composite material could reach an initial discharge specific capacity of 1,453 mAh g−1at a rate of 0.1C. Moreover, the composite material could maintain a discharge ratio of 538 mAh g−1 at a rate of 0.5C even after 200 charge and discharge cycles. After 400 cycles, the composite had a specific discharge capacity of 439 mAh g−1 at a rate of 1.0C. The excellent electrochemical performance of the V2O5@N-CNT/S composite cathode material was due to the fact that V2O5 contains oxygen ions and has a strong polarized surface. Furthermore, nitrogen doping changed the hybrid structure of carbon atoms and provided additional active sites, thereby improving the conductivity of the material itself and effectively inhibiting the dissolution and diffusion of polysulfides.

Improved CO2 adsorption properties through amine functionalization of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNT) with different functionalities (standard–; OH–; and COOH– functionalized) are chemically modified with N1-(3-trimethoxysilylpropyl)diethylenetriamine (DETASi) aiming to enhance their CO2 adsorption/separation properties. The grafting of the DETASi groups to the surface of the MWCNT samples is studied by X-ray photoelectron spectroscopy (XPS), operando thermogravimetric analysis - infrared spectroscopy (TGA-IR), –196 °C N2-sorption isotherms, and scanning electron microscopy (SEM). A comprehensive overview of the reaction mechanism and samples structure/composition is provided. It was found that the aforementioned functionalities highly influence the physical–chemical and the textural properties of the DETASi modified-MWCNT materials, impacting in the DETASi functionalization degree and its distribution on the sample. Amount (by TGA-IR) and homogeneity (by SEM) of the organosilicon group in the functionalized samples increases with the increase of the functionalities in the parent MWCNT materials. Standard-MWCNT and OH– functionalized MWCNT showed to be unable to adsorb CO2, while COOH– modified MWCNT adsorbed just 0.1% at 1 bar and 30 °C. At the same adsorption conditions, DETASi modification of the MWCNT materials enhanced the CO2 adsorption capacity, with the maximum CO2 uptake (2.11%) for COOH-MWCNT functionalized with DETASi. The selectivity for CO2/N2 separation was also improved after DETASi grafting reaction, with the highest value (1.89%) observed for the standard-MWCNT material modified with DETASi. In general, the increase of the DETASi amount and of the microporosity in the functionalized MWCNT sorbents is accompanied by an improvement of the CO2 adsorption-separation properties. The water vapor adsorption indicated that the standard-MWCNT sample modified with DETASi is resistant to the presence of water and its presence (water vapor of ~3.2 kPa) can improve the CO2 uptake.

Spatially isolated redox processes enabled by ambipolar charge transport in multi-walled carbon nanotube mats.

This work demonstrates a simple dual-well device which enables spatially isolated solutions to undergo complementary redox reactions. The device functions by the ambipolar transport of charge carriers between two spatially isolated poly(dimethylsiloxane) (PDMS) microwells through an underlying multi-walled carbon nanotube (MWCNT) mat. This MWCNT mat enables charge carriers, produced from the decomposition of an analyte in one solution, to drive a redox reaction in a spatially isolated second colorimetric read-out solution via a potential difference between the wells. As proof-of-concept a visible colorimetric read-out was shown using an enzyme, cytochrome c (reduced in 16 h), and the visualizing reagent 3,3',5,5'-tetramethylbenzidine (TMB) (oxidized in 2.5 h) for the detection of dithionite and hydrogen peroxide, respectively, without any external energy input. We discuss the origin of this phenomenon and highlight the ability of MWCNTs to accept and transport both electrons and holes efficiently between spatially isolated solutions giving rise to a highly versatile sensor suitable for use in simple, low-cost point-of-care diagnostics.