Acid-treated Multi-walled Carbon Nanotubes Research Articles

Effects of Multiwall Carbon Nanotubes on Premature Kidney Aging: Biochemical and Histological Analysis.

Carbon nanotubes (CNTs) have gained much attention due to their superb properties, which make them promising options for the reinforcing composite materials with desirable mechanical properties. However, little is known about the linkage between lung exposure to nanomaterials and kidney disease. In this study, we compared the effects on the kidneys and aging for two different types of multiwall carbon nanotubes (MWCNTs): pristine MWCNTs (PMWCNTs) and acid-treated MWCNTs (TMWCNTs), with TMWCNTs being the preferred form for use as a composite material due to its superior dispersion properties. We used tracheal instillation and maximum tolerated dose (MTD) for both types of CNTs. MTD was determined as a 10% weight loss dose in a 3-month subchronic study, and the appropriate dosage for 1-year exposure was 0.1 mg/mouse. Serum and kidney samples were analyzed using ELISA, Western blot, and immunohistochemistry after 6 months and 1 year of treatment. PMWCNT-administered mice showed the activation of pathways for inflammation, apoptosis, and insufficient autophagy, as well as decreased serum Klotho levels and increased serum levels of DKK-1, FGF-23, and sclerostin, while TMWCNTs did not. Our study suggests that lung exposure to PMWCNTs can induce premature kidney aging and highlights a possible toxic effect of using MWCNTs on the kidneys in the industrial field, further highlighting that dispersibility can affect the toxicity of the nanotubes.

Improvement in the corrosion resistance of electrodeposited Ni-W alloy by MWCNT co-deposition and prevention of metal-carbon interfacial corrosion by carbide formation

Composite plating is an effective method which can enhance the properties of conventional metal plating by co-deposition of composite materials. In this study, multi-walled carbon nanotubes (MWCNTs) were used as a composite material to improve the corrosion resistance of Ni-W alloys, and the effect of the MWCNTs addition on the anti-corrosion properties was discussed. The corrosion current density of the Ni-W/MWCNTs composite decreased approximately 4 times from 16.6 to 4.6 μA·cm-2 in 3 wt% NaCl solution compared to the pristine Ni-W; this showed that the co-deposition of MWCNTs was effective for improvement in the corrosion resistance. However, the interfacial corrosion between the metal matrix and MWCNTs occurred in the high potential region and degraded the passivation properties of plating. This interfacial corrosion is caused by the high O content due to the hydroxyl groups on the acid-treated MWCNTs surface and the difference in W concentration between the interface of MWCNTs and the Ni-W matrix. Heat treatment in Ar atmosphere removes these hydroxyl groups and diffuses Ni and W into MWCNTs to form metal carbide (Ni6W6C), effectively alleviating interfacial corrosion. This study presents interfacial corrosion can be effectively mitigated by forming metal carbides at the interface of carbon materials in metal/carbon composites.

The effect of acid treated multi-walled carbon nanotubes on the properties of cement paste prepared by ultrasonication with polycarboxylate ester

Chemical functionalization of carbon nanotubes by the mix of sulfuric (H2SO4) and nitric (HNO3) acids has been reported to enhance the hydrophilicity of carbon nanotubes, which, in turn, improves its dispersion quality in aqueous solution and within the cement matrix. In this study, multi-walled carbon nanotubes (MWCNT) were treated by a mix of H2SO4 and HNO3, and used for preparation of MWCNT solutions by ultrasonic tip sonication with low amounts of polycarboxylate ester (PCE). The effects of acid functionalization on the dispersion of MWCNT, mechanical performance and hydration of cement paste were studied with respect to changes in MWCNT concentration, ultrasonication time and MWCNT:PCE ratio. According to the experimental results, acid-treated MWCNT contained 13 wt% of carboxyl functional group. The results from Raman spectroscopy showed the increased amount of unadsorbed PCE in solution with acid-treated MWCNT due to the increase in hydrophilicity. Increase in hydrophilicity contributed to a stronger bond between a-MWCNT and cement hydration products, and increased the mechanical strength of cement paste by 55%. The addition of a-MWCNT at 0.1 wt% concentration resulted in the increase of 28-day compressive strength from 40 MPa up to 62 MPa and flexural strength from 4.4 MPa up to 7.6 MPa. Retardation in hydration and increase in porosity were found to be associated with PCE that was not adsorbed on the surface of MWCNT.

Synergistic Function between Phosphorus-Containing Flame Retardant and Multi-Walled Carbon Nanotubes towards Fire Safe Polystyrene Composites with Enhanced Electromagnetic Interference Shielding.

As a universal polymer material, polystyrene (PS) is widely applied in electrical devices and construction. Thus, it is necessary to improve the flame retardancy and electromagnetic shielding properties of PS material. In this work, PS/silicon-wrapped ammonium polyphosphate/Inorganic acid-treated multi-walled carbon nanotubes composites (PS/SiAPP/aMWCNT, abbreviated as PAC) were prepared via methods of filtration-induced assembly and hot-pressing. Morphology and structure characterization demonstrated that SiAPP and aMWCNT had good dispersion in PS and excellent compatibility with the PS matrix. Thermogravimetric analysis revealed that the addition of aMWCNT to PS improved its thermal stability and carbon-forming characteristics. The peak heat release rate, the peak carbon monoxide production rate, and the peak smoke production rate of the PAC10 composite decreased by 53.7%, 41.9%, and 45.5%, respectively, while its electromagnetic shielding effectiveness reached 12 dB. These enhancements were attributed to the reason that SiAPP and aMWCNT synergistically catalyzed the char generation and SiAPP produced free radical scavengers and numbers of incombustible gases, which could decrease the oxygen concentration and retard the combustion reaction. Therefore, the assembled PS/SiAPP/aMWCNT system provides a new pathway to improve the flame retardant and electromagnetic shielding properties of PS.

Pseudocapacitive Effects of Multi-Walled Carbon Nanotubes-Functionalised Spinel Copper Manganese Oxide.

Spinel copper manganese oxide nanoparticles combined with acid-treated multi-walled carbon nanotubes (CuMn2O4/MWCNTs) were used in the development of electrodes for pseudocapacitor applications. The CuMn2O4/MWCNTs preparation involved initial synthesis of Mn3O4 and CuMn2O4 precursors followed by an energy efficient reflux growth method for the CuMn2O4/MWCNTs. The CuMn2O4/MWCNTs in a three-electrode cell assembly and in 3 M LiOH aqueous electrolyte exhibited a specific capacitance of 1652.91 F g−1 at 0.5 A g−1 current load. Similar investigation in 3 M KOH aqueous electrolyte delivered a specific capacitance of 653.41 F g−1 at 0.5 A g−1 current load. Stability studies showed that after 6000 cycles, the CuMn2O4/MWCNTs electrode exhibited a higher capacitance retention (88%) in LiOH than in KOH (64%). The higher capacitance retention and cycling stability with a Coulombic efficiency of 99.6% observed in the LiOH is an indication of a better charge storage behaviour in this electrolyte than in the KOH electrolyte with a Coulombic efficiency of 97.3%. This superior performance in the LiOH electrolyte than in the KOH electrolyte is attributed to an intercalation/de-intercalation mechanism which occurs more easily in the LiOH electrolyte than in the KOH electrolyte.

Ultra-sensitive flexible strain sensors based on hybrid conductive networks for monitoring human activities

Flexible strain sensors have aroused great interest because of their prospective applications in motion detection, healthcare, and wearable electronics. However, the construction of strain sensing materials with both ultra-high sensitivity and excellent stretchability via a facile and scalable strategy remains a challenge. Here, an ultra-sensitive and highly stretchable strain sensor with a unique hybrid conductive network was fabricated based on reduced graphene oxide (RGO)/multi-walled carbon nanotubes (MWCNT) hybrid fillers, carbonized woven fabric, and natural rubber (NR). The RGO/MWCNT/carbonized woven fabric (GMWF) composite was obtained by fast reduction of graphene oxide (GO)/acid-treated MWCNT (MWCNT-COOH) hybrid fillers and pyrolysis of woven fabric in an alcohol flame synchronously. The resulting GMWF/NR strain sensor exhibited a laudable trade-off between sensitivity and detection range (gauge factor of 1451, 3587, and 8225 within 0 ~ 32%, 32 ~ 49%, and 49 ~ 67% strain, respectively), fast response (200 ms), low detection limit (0.5%), and outstanding durability (1000 cycles). It could detect full-range (vigorous and subtle) human activities in real time. This integration of synergistic conductive fillers and facile template method to construct the hybrid conductive network demonstrates an effective strategy for fabricating high-performance strain sensors for wearable electronic devices.

Boosting high-rate-partial-state-of-charge performance of lead-acid batteries by incorporating trace amount of sodium dodecyl sulfate modified multi-walled carbon nanotubes into negative active materials

In this work, trace amount of sodium dodecyl sulfate modified multi-walled carbon nanotubes acid-treated multi-walled carbon nanotubes (SDS-MWCNTs) is incorporated into the negative active materials (NAMs) of lead acid battery by simply blending the SDS-MWCNTs aqueous dispersion with the dry mixture of lead oxide powder, expanders and carbon black for lead paste preparation. As the sulfate groups on SDS can combine with Pb2+ ions to make PbSO4 to generate 3PbO·PbSO4·H2O (3BS), the cured NAMs incorporated with SDS-MWCNTs exhibit an improved 3BS percentage as well as an increased 3BS crystal size. The 3BS percentage reaches 22.47% in the cured NAMs with 100 ppm SDS-MWCNTs, more than 5.4% higher than that in the NAMs without SDS-MWCNTs. After formation, the NAMs containing SDS-MWCNTs presents a morphology of the interconnected Pb rods, which accelerates the kinetics for the electrochemical reactions between Pb and PbSO4 and thus retards PbSO4 accumulation. Simulated cells are assembled, and the cell constructed by the negative plate containing 100 ppm SDS-MWCNTs can achieve a high-rate partial-state-of-charge (HRPSoC) cycle-life of 45,692 cycles, more than 2.1 times as long as that of the cell assembled with the negative plate without SDS-MWCNTs. Our method is of great convenience and low-cost, it is supposed to have a great feasibility in lead-acid battery industry.

High oxygen reduction reaction activity and durability of Pt catalyst photo-deposited on SnO2-coated and uncoated multi-walled carbon nanotubes

• Acid-treated CNTs were coated with SnO 2 by chemical method. • Platinum was photo-deposited on CNTs and SnO 2 -CNT supports. • Surface morphology was investigated by SEM and HAADF-STEM. • Pt/CNT and Pt/SnO 2 -CNT showed high oxygen reduction activity in acid media. Platinum nanoparticles were photo-deposited on acid-treated multi-walled carbon nanotubes (CNTs) and SnO 2 -coated CNTs. The SnO 2 -CNT nanocomposite was synthesised by a chemical method. Scanning and scanning transmission electron microscopy results indicated that the CNTs surface is partially covered by the SnO 2 layer. The surface morphology of the Pt catalyst depends on the nature of the support material. For instance, porous Pt aggregates of various sizes are formed at specific nucleation sites on the CNT surface, while a selective deposition of Pt was observed on the metal oxide part of the SnO 2 -CNT. Cyclic voltammetry and CO stripping investigations in 0.1 M HClO 4 solution confirmed different surface electrochemistry of the Pt catalysts. It is revealed that photo-deposition induces the formation of Pt-Sn nanoalloys due to increased interaction at the oxide interfaces. Both Pt/CNT and Pt/SnO 2 -CNT catalysts showed remarkable activity towards the electroreduction of oxygen in acid media. Durability measurement showed that photo-deposited Pt nanoparticles are more resistant to degradation. The corrosion-resistant nature of the SnO 2 -CNT support further improves the catalysts stability. Pt/CNT and Pt/SnO 2 -CNT catalysts retained 86% and 88% of the initial surface area respectively, after 10,000 potential cycles between 0.6 and 1.2 V RHE .

Multi-Walled Carbon Nanotubes Decorated with Guanidinylated Dendritic Molecular Transporters: An Efficient Platform for the Selective Anticancer Activity of Doxorubicin.

An efficient doxorubicin (DOX) drug delivery system with specificity against tumor cells was developed, based on multi-walled carbon nanotubes (MWCNTs) functionalized with guanidinylated dendritic molecular transporters. Acid-treated MWCNTs (oxCNTs) interacted both electrostatically and through hydrogen bonding and van der Waals attraction forces with guanidinylated derivatives of 5000 and 25,000 Da molecular weight hyperbranched polyethyleneimine (GPEI5K and GPEI25K). Chemical characterization of these GPEI-functionalized oxCNTs revealed successful decoration with GPEIs all over the oxCNTs sidewalls, which, due to the presence of guanidinium groups, gave them aqueous compatibility and, thus, exceptional colloidal stability. These GPEI-functionalized CNTs were subsequently loaded with DOX for selective anticancer activity, yielding systems of high DOX loading, up to 99.5% encapsulation efficiency, while the DOX-loaded systems exhibited pH-triggered release and higher therapeutic efficacy compared to that of free DOX. Most importantly, the oxCNTs@GPEI5K-DOX system caused high and selective toxicity against cancer cells in a non-apoptotic, fast and catastrophic manner that cancer cells cannot recover from. Therefore, the oxCNTs@GPEI5K nanocarrier was found to be a potent and efficient nanoscale DOX delivery system, exhibiting high selectivity against cancerous cells, thus constituting a promising candidate for cancer therapy.

Improved CO2 adsorption capacity and fluidization behavior of silica-coated amine-functionalized multi-walled carbon nanotubes

The adsorption capacity and fluidization behavior of silica-coated amine-functionalized multi-walled carbon nanotubes (MWCNTs) were studied in this work. The coupling of both studies is fundamental for the practical application of CO2 sorbents in fluidized beds. Sorbents were prepared by hydrolysis of tetraethylorthosilicate (TEOS) onto acid-treated multi-walled carbon nanotubes followed by impregnation with monoethanolamine (MEA). The effects of different loading amounts of MEA and TEOS on CO2 uptake were investigated using thermogravimetric analysis under a simulated flue gas composed of 15%CO2/85% N2. At the optimal loadings of TEOS (30 ml) and MEA (30 wt%) on MWCNTs, 2.67 wt% of CO2 was captured at 25 °C, while the adsorption capacity of the pristine MWCNTs before any modification was negligible. Adsorption/desorption tests repeated 25 times also showed that the prepared sorbent has excellent stability during the cyclic operation; 9.42% reduction of the uptake was reported. Fluidizability of the most promising sorbent was also assessed when adding hydrophobic silica nanoparticles (NPs). Maximum bed expansion of 3.9 was achieved in the presence of 7.5 wt% silica NPs which was comparable by the amount of 2.24 belonged to raw MWCNTs. Enhancement of fluidity may be attributed to the decreased van der Waals attraction forces between the particles of sorbent. Besides, the CO2 adsorption capacity of the sorbent mixed with 5 wt% silica NPs was surprisingly increased by approximately 8%, reaching ~3 wt% of CO2.

Multifunctional flower-like WS2 hybrids with carbon nanotube veins and WS2 petals: Its sodium ion storage and hydrogen evolution properties

Abstract A hierarchical flower-like hybrid with tungsten disulfide (WS2) nano-sheet petals and multi-walled carbon nanotube (MWCNT) veins is prepared via a facile solvothermal method. High concentration functional groups and defects on the acid-treated MWCNTs bundles initiated the growth of WS2 nano-flowers with an average diameter of 500 nm, inducing strong interface interaction between WS2 and MWCNTs. Furthermore, the MWCNTs are adopted as viens to improve the electron transportation and as interconnected 3D network to alleviate the structural change and restacking of WS2 petals. Meanwhile, the WS2 nano-flowers with abundant edge tungsten atoms are beneficial for sodium ion storage and hydrogen evolution reaction. As a result, the hybrid exhibits excellent electrochemical performances: a specific capacity of 250 mAh g−1 at 0.5 A g−1 after 45 cycles is retained as anode for sodium ion battery; an 80 mV dec−1 Tafel slope and an overpotential of −0.25 V (vs. RHE) are delivered with excellent stability in acidic condition.

Abrasive Wear Behavior of CNT-Filled Unidirectional Kenaf–Epoxy Composites

Kenaf (Hibiscus Cannabinus) fibers have received significant attention for replacing the usage of synthetic fibers, especially glass fiber, in the fabrication of fiber-reinforced polymer (FRP) composites. The aim of this research was to study the change in wear behavior of kenaf-epoxy fiber composites by filling them with multiwall carbon nanotubes (MWCNT). In particular, the effect of untreated MWCNT (PMWCNT), acid-treated MWCNT (AMWCNT), and silane-treated MWCNT (SMWCNT) was studied, using three different MWCNT loadings, i.e., 0.5, 0.75, and 1 wt.%. The abrasive wear test was conducted to measure the wear properties of the composites. A thermal infrared camera was also used to measure the punctual contact temperature during the abrasive wear test, while the abraded surfaces were analyzed using the stereomicroscope. Starting from the considerable reduction of wear rate with the introduction of kenaf fibers, it was observed that PMWCNT provided some further, yet modest, reduction of wear rate only at the higher loadings. In contrast, the inclusion of AMWCNT proved to increase the specific wear rate of the epoxy-kenaf composites, an effect worsened at higher loadings. This may be due to the weakened interfacial bonding between the AMWCNT and epoxy. On the other hand, the presence of SMWCNT improved the interfacial bonding between CNT and epoxy, as shown by an increase in contact temperature. However, the increase in bonding strength was stipulated to have caused the rougher worn debris, thus inducing a three-body abrasive wear effect.

Acid-treated multi-walled carbon nanotubes as additives for negative active materials to improve high-rate-partial-state-of-charge cycle-life of lead-acid batteries.

In this work, a trace amount of acid-treated multi-walled carbon nanotubes (a-MWCNTs) is introduced into the negative active materials (NAMs) of a lead acid battery (LAB) by simply dispersing a-MWCNTs in the water, which is then added into the dry mixture of lead oxide powder, expanders and carbon black for lead paste preparation. The abundant oxygen-containing groups on the a-MWCNTs show significant influence on the chemical reactions happening during the curing process, leading to the improved properties of NAMs. Specifically, after formation, the NAMs containing 100 ppm a-MWCNTs display a spongy-like structure comprised of interconnected domino-like Pb slices, giving favorable porosity and electroactive surface area of the NAMs. Moreover, the quasi-rod structure of Pb slices provides the channels for fast electron transfer. These two features greatly accelerate the electrochemical reaction between Pb and PbSO4, and hence hinder the accumulation of PbSO4 crystals. As a result, the high-rate partial-state-of-charge (HRPSoC) cycle-life of the simulated cell constructed from the a-MWCNTs-containing negative plate achieves a HRPSoC cycle-life more than 1.5 times longer than the cell constructed when the negative plate contains only carbon black. Since our method is of great convenience and low-cost, it is expected to have a great feasibility in the LAB industry.

Effect of MWCNT Surface Functionalisation and Distribution on Compressive Properties of Kenaf and Hybrid Kenaf/Glass Fibres Reinforced Polymer Composites.

The aim of this study is to evaluate the effect of surface treated multi wall carbon nanotubes (MWCNTs) on compressive properties of the unidirectional (UD) kenaf and hybrid woven glass/UD kenaf fibre reinforced polymer composites. The MWCNTs were first treated using concentrated acid (a mix of H2SO4 and HNO3) and silane (three-aminoprophyltriethoxysilane) in order to improve the dispersion within the epoxy matrix using a high shear roll milling technique. In this study, nanomodified epoxies were prepared using 0.5, 0.75 and 1.0 wt % of pristine MWCNT (PCNT), acid treated MWCNT (ACNT) and silane treated MWCNT (SCNT). These nanomodified epoxies were then used for the fabrication of kenaf and hybrid composites using combination of filament winding and resin impregnation. The uniaxial compression test was conducted using a universal testing machine according to the ASTM D3410 standard. The morphology of fractured samples was observed and analysed using scanning electron microscopy (SEM) in order to evaluate the failure behaviour and mechanisms involved during compression. It was found that the addition of treated MWCNT (ACNT and SCNT) improved the compressive properties of kenaf and hybrid composites as compared to those of untreated-MWCNT (PCNT). The addition of 1.0 wt % of SCNT exhibited good compressive properties in both kenaf and hybrid composite systems. The compressive modulus and strength increased by 73.25% and 20.15%, respectively, for composites made of 1.0 wt % SCNT and Kenaf (1.0SCNT/K). For the hybrid composites, the compressive modulus and strength increased by 21.18% and 7.73% for composites made of 1.0 wt % SCNT filled G/K composites (1.0SCNT/G/K).

Enhanced Electrochemical Properties of Catalyst by Phosphorous Addition for Direct Urea Fuel Cell.

An anode bimetallic catalyst comprising Ni-Pd alloy nanoparticles was loaded on acid-treated multi-walled carbon nanotubes (MWCNTs) for application in a direct urea fuel cell. The bimetallic catalyst and MWCNTs were synthesized by a hydrothermal method at 160°C for 5 h. To reduce the catalyst particle size, alkaline resistance, and facilitate their uniform distribution on the surface of the MWCNTs, phosphorus (P) was added to the Ni-Pd/MWCNT catalyst. The effects of P on the distribution and reduction in size of catalyst particles were investigated by Brunauer–Emmett–Teller analysis, transmission electron microscopy, and X-ray diffraction analysis. The enhanced catalytic activity and durability of the P-containing catalyst was confirmed by the high current density [1897.76 mA/cm2 (vs. Ag/AgCl)] obtained at 0.45 V in a 3 M KOH/1.0 M urea alkaline aqueous solution compared with that of the catalyst without P [604.87 mA/cm2 (vs. Ag/AgCl)], as determined by cyclic voltammetry and chronoamperometry. A Urea–O2 fuel cell assembled with a membrane electrode assembly comprising the Ni-Pd(P)/MWCNT catalyst delivered peak power densities of 0.756 and 3.825 mW/cm2 at 25 and 60°C, respectively, in a 3 M KOH/1 M urea solution.

Screen-Printed High-Performance Flexible Electrothermal Films Based on Three-Dimensional Intercalation Graphene Nanosheets/MWCNT/Carbon Black Composite.

A liquid-phase stripping method was used to strip the graphite under the action of mechanical shear force to prepare graphene nanosheets (GNSs) on a large scale. Given the multicomponent composite conductive particles formed by GNSs with acid-treated MWCNTs (f-MWCNTs) and carbon black (CB), the three-dimensional (3D) intercalation electrothermal composite of GNSs/MWCNTs/CB with excellent conductivity and mechanical properties was prepared with water-based acrylic resin as a connector. Carbon particles (16.97 wt %) are found in the composite and the sheet resistance (Rs) is only 4 Ω sq-1 as f-MWCNTs and CB intercalations form a more stable 3D conducting medium between the GNSs. The flexible electrothermal film (2.5 cm × 2.5 cm) printed with the 3D intercalation GNSs/MWCNTs/CB composite had a saturation temperature (Ts) of 175 °C with an input of 3 V and lower power consumption (249.87 cm2 W-1). It only takes 10 s to reach Ts and the electrical performance is still intact under the pressure of 1 × 105 kPa. After being bent 2500 times (bending radius is 5 mm), the electrothermal performance of the flexible electrothermal film remained stable.

Mechanical and thermal properties and crystallization behavior of PA66 composites reinforced with MWCNTs-coated milled glass fiber

Constructing a hierarchical structure of nanomaterials on the surface of reinforcing fibers is the best strategy to obtain other desired functions while improving the mechanical properties of polymers. In this article, acid-treated multiwall carbon nanotubes (MWCNTs) were introduced to the surface of milled glass fiber (MGF) under the combined action of tetraethyl orthosilicate and 3-aminopropyltriethyloxysilane to prepare a hierarchical fiber (MWCNTs-GF). The surface morphology and microstructure of this hierarchical fiber were characterized by field-emission scanning electron microscope and transmission electron microscope, and a composite coating with MWCNTs as the main component was observed on each fiber surface. Fourier transform infrared and Raman spectroscopy revealed the presence of the specific interactions between MWCNTs and MGF. Polyamide 66 (PA66) composites with different content of MWCNTs-GF were fabricated by melt blending. The resulting composites exhibited improved mechanical properties relative to pure PA66, in which the tensile strength and notched impact strength of the composite filled with 3 wt% MWCNTs-GF increased by 23.3% and 69.0%, respectively. Subsequently, by analyzing fracture morphology and interfacial adhesion of the composites, the strengthening and toughening mechanisms of MWCNTs-GF were elaborated in detail. In addition, the results of thermogravimetric analysis and differential scanning calorimetry showed that MWCNTs-GF possessed strong heterogeneous nucleation ability, and its addition could refine the grain size of PA66 and significantly increase the crystallization temperature and thermal stability of the corresponding composites. Compared to PA66 composites reinforced with neat MGF, it was found that the unique surface structure of MWCNTs-GF was likely responsible for improved thermal properties of this hierarchical fiber-reinforced PA66 composites.

Synchronous detection of cadmium and lead in honey, cocos nucifera and egg white samples using multiwalled carbon nanotube/hyaluronic acid/amino acids nanocomposites

Electrochemical Synchronous detection of cadmium (Cd(II)) and lead (Pb(II)) was obtained by acid treated multiwalled carbon nanotube (A-MWCNT) functionalized with hyaluronic acid (Hyalu) and this mixture was separately further modified with l-cysteine (l-Cys) and l-serine (l-Ser). Under the optimized circumstance best voltammetric responses were produced by A-MWCNT/Hyalu/l-Cys and A-MWCNT/Hyalu/l-Ser modified electrodes. The peak current was linearly dependent on the Cd(II) and Pb(II) concentrations in the range from 0.4 to 4 µg L−1. The sensitivities were calculated as 0.7 µA/nM (Cd(II)) and 3.5 µA/nM (Pb(II)) for A-MWCNT/Hyalu/l-Cys/GCE and 0.6 µA/nM (Cd(II)) and 2.6 µA/nM (Pb(II)) for A-MWCNT/Hyalu/l-Ser/GCE. From the calibration plot LODs were calculated to be 0.032 µg L−1 (Cd(II)) and 0.015 µg L−1 (Pb(II)) for A-MWCNT/Hyalu/l-Cys/GCE and 0.057 µg L−1 (Cd(II)) and 0.034 µg L−1 (Pb(II)) for A-MWCNT/Hyalu/l-Ser/GCE. Moreover, the proposed electrodes were subjected to the real sample application in honey, cocos nucifera and egg white.

On the stability of polyaniline/carbon nanotube composites as binder-free positive electrodes for electrochemical energy storage

Poor stability restricts the use of polyaniline as a transition-metal-free, high-capacity electrode material for electrochemical energy storage. To improve the durability, methods such as adding a carbonaceous support and thermal treatments have been suggested. Here, we combine both of these approaches and study their effects on the degradation of a composite of polyaniline and acid-treated multi-walled carbon nanotubes (PANI/a-MWNT) when used as a positive electrode in a lithium-ion cell. The composite is prepared through facile ultrasonic-assisted mixing of aqueous colloids, processed into binder-free electrodes and heat treated under vacuum (120–180 °C). PANI without the carbon support presents a poor cycling stability due to a decreasing conductivity and changes in the particle morphology. The a-MWNTs are shown to inhibit these changes and to enhance the electrochemical accessibility of PANI in the composite. The heat treatment, in turn, improves the stability of the composite during open circuit conditions, which is ascribed to cross-linking of the polymer. However, with prolonged cycling, the stabilizing effect is lost. Analysis of the electrodes after the cycling reveals that both the pristine and the heat-treated composite undergo dedoping and side reactions with the electrolyte. The extent of the changes is larger for the pristine composite.

Relative humidity sensing properties of doped polyaniline-encased multiwall carbon nanotubes: wearable and flexible human respiration monitoring application

Relative humidity (RH) sensors have been fabricated with polyaniline-encased multiwall carbon nanotube (MWCNT) matrix. MWCNT matrices were grown on oxidized Si substrates by catalytic chemical vapour deposition technique. The MWCNT matrices were made hydrophilic by acid treatment. The sensing properties of MWCNTs were improved by encasing the acid-treated MWCNT matrix with PANI. PANI was synthesized via in situ chemical oxidation technique using three acid dopants, named as 5-sulfosalicylic acid, 4-nitrobenzoic acid and hydrochloric acid (HCl). A growth time variation of the PANI was also performed from 1.5 to 2.5 h. The time-varying sensor resistance was recorded with RH change, and RH sensing properties of the corresponding sensors were investigated with the measured data. Doping variation exhibited that CNT–PANI sensor, fabricated with HCl dopant, showed the highest response (42.6% at 90% RH). Synthesis time variation of PANI from 1.5 to 2.5 h exhibited that with an increase in synthesis time, the sensor responsivities degraded from 42.6 to 19.5% at 90% RH. Excellent repeatability, linear response behaviour (R2 = 0.992), low hysteresis loss (± 2.68%) were exhibited by the fabricated RH sensing devices. A facile transfer technology was developed in order to transfer the MWCNT on PET substrate for fabrication of flexible RH sensor. A practical application on human respiration monitoring was demonstrated with the wearable and flexible RH sensors. The humidity sensing mechanism and electron transfer process were schematically explained with the aid of energy band diagram.