Multi-wall carbon nanotube counter electrodes for dye-sensitized solar cells prepared by electrophoretic deposition

In this study, electrophoretic deposition (EPD) was employed to fabricate multi-wall carbon nanotube (MWCNT) counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Firstly, raw MWCNTs were functionalized by means of an acid mixture solution and then subjected to EPD. The results obtained from Raman spectroscopy, Fourier transform infrared spectroscopy, field-emission scanning electron microscope, and cyclic voltammogram demonstrated that the defects and open ends on the MWCNTs can be obtained via chemical functionalization and thus facilitate the enhancement in the electrocatalytic activity for I₃⁻ reduction of MWCNT CEs. In addition to optimizing chemical functionalization of MWCNTs surface, the optimal thickness of MWCNT CEs prepared by EPD was also investigated. Additionally, consecutive cyclic voltammetric tests demonstrated that the MWCNT CE fabricated by EPD possessed excellent electrochemical stability. In comparison with MWCNT CEs fabricated by tape-casting approach, MWCNT CEs prepared by EPD presented a superior adhesion between MWCNT deposits and conducting glass substrates. Therefore, MWCNT CEs fabricated by EPD can be of great potential for use in low-cost plastic DSSCs.     

三元复合材料PANI／Ag／MWNT的电化学行为和比电容

通过原位聚合的方式在银纳米粒子/多壁碳纳米管（Ag/MWCNT）复合材料的表面成功聚合苯胺单体制备了聚苯胺/银纳米粒子/多壁碳纳米管（PANI/Ag/MWCNT）三元复合材料苯．通过对三元复合材料的结构以及表面形貌进行分析,表明聚苯胺层完全包覆了Ag/MWCNT复合材料,形成了核壳式结构．同时银纳米粒子则以单质晶体的形态存在于多壁碳纳米管与聚苯胺层之间．三元复合材料电极在1 mol/L的KOH溶液中具有极低的阻抗,而与聚苯胺电极相比,这些复合材料电极则表现出更低的电阻、更高的电化学活性和更好的循环稳定性．尤其是当苯胺和Ag：MWCNTs质量比为5：5时,该复合材料电极在0.25 A/g的电流密度下表现出最大的比电容值为160 F/g．     

Surface activation of plasma-patterned carbon nanotube based DNA sensing electrodes

We have studied the effect of treatment of multiwalled carbon nanotubes (MWCNTs) for use in DNA-based biosensors with oxygen plasma. Well-patterned MWCNT electrodes were photolithographically fabricated on glass substrates. Pure oxygen was used for etching and functionalization of the MWCNT film in a lab-made plasma chamber. The resulting electrodes exhibited a dramatic change in the morphology of their surface, the chemical composition, and the electrochemical properties in terms of peak current and peak potential separation. The electrodes also showed increased DNA immobilization efficiency and much higher sensitivity in the detection of target DNA as compared to non-treated MWCNT electrodes. Plasma treatment was optimized and electrodes were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential pulse voltammetry.

Heterogeneous Electron Transfer and Oxygen Reduction Reaction at Nanostructured Iron(II) Phthalocyanine and Its MWCNTs Nanocomposites

Electron transfer and oxygen reduction dynamics at nanostructured iron(II) phthalocyanine/multi‐walled carbon nanotubes composite supported on an edge plane pyrolytic graphite electrode (EPPGE‐MWCNT‐nanoFePc) platform have been reported. All the electrodes showed the category 3 diffusional behaviour according to the Davies–Compton theoretical framework. Both MWCNTs and MWCNT‐nanoFePc showed huge current responses compared to the other electrodes, suggesting the redox processes of trapped redox species within the porous layers of MWCNTs. Electron transfer process is much easier at the EPPGE‐MWCNT and EPPGE‐MWCNT‐nanoFePc compared to the other electrodes. The best response for oxygen reduction reaction was at the EPPGE‐MWCNT‐nanoFePc, yielding a 4‐electron process.     

Facile Synthesis and Enhanced Nonlinear Optical Properties of Porphyrin‐Functionalized Multi‐Walled Carbon Nanotubes

Two multi‐walled carbon nanotube (MWCNT)‐based nanohybrids, MWCNT–ZnTPP and MWCNT–TPP (TPP=5‐[4‐{2‐(4‐formylphenoxy)‐ ethyloxy}phenyl]‐10,15,20‐triphenylporphyrin, ZnTPP=5‐[4‐{(4‐formylphenyl)ethynyl}phenyl]‐10,15,20‐triphenylporphinatozinc(II)), were prepared directly from pristine MWCNTs through 1,3‐dipolar cycloaddition reactions. Covalent attachment of the porphyrins to the surfaces of the MWCNTs was confirmed by Fourier transform infrared spectroscopy, ultraviolet/visible absorption, fluorescence, Raman, and X‐ray photoelectron spectroscopy, elemental analysis, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin moieties to the surface of the MWCNTs significantly improves the solubility and ease of processing of these MWCNT–porphyrin composite materials. Z‐scan studies reveal that these MWCNT–porphyrin nanohybrids exhibit enhanced nonlinear optical properties under both nanosecond and picosecond laser pulses at λ=532 nm in comparison with free MWCNTs and the free porphyrin chromophores, whereas superior optical limiting performance was displayed by MWCNT–porphyrin composite materials rather than MWCNTs/ZnTPP and MWCNTs/TPP blends, which is consistent with a remarkable accumulation effect as a result of the covalent linkage between the porphyrin and the MWCNTs.     

Electrochemical activities of platinum-decorated multi-wall carbon nanotube/chitosan composites for the oxidations of alcohols

Electrooxidation of alcohols including methanol, ethanol, and isopropanol is studied on the modified solid glassy carbon electrodes with various amounts of platinum nanoparticles (PtNPs) immobilized on a composite of functionalized multi-walled carbon nanotubes (MWCNTs) and chitosan in an acidic solution. Here the chitosan is available as a binder to tightly anchor Pt nanoparticles onto the MWCNTs surfaces. MWCNTs/chitosan composite support can significantly improve the activity of the catalyst for alcohol oxidation and reduce the Pt catalyst loading. The calculated electrochemical active surface area is 379.2 m²/g Pt for PtNP–MWCNT/chitosan. Cyclic voltammetry and chronoamperometry techniques are employed for catalytic activity evaluation. The effects of operational parameters including platinum loading, concentration of the corresponding alcohol, concentration of the acid solution, scanning rate, and the final limit of anodic potential on the performance of the electrodes are also investigated.     

Excellent electrocatalytic performance of a Ni<Superscript>2+</Superscript>-loaded multiwalled carbon nanotube composite in glucose oxidation

A new type of Ni²⁺-loaded MWCNT composite was prepared by mixing carboxylated multiwalled carbon nanotubes (MWCNTs) and Ni²⁺ ions and allowing them to interact electrostatically. The resulting composite was subsequently used as an electrocatalyst for glucose (Glu) oxidation. Compared with electrodes modified through the addition of free Ni²⁺ ions or MWCNTs, the Ni²⁺/MWCNT composite electrode showed greatly improved properties such as hydrophilicity. Investigations of the Ni²⁺/MWCNT composite electrode via inductively coupled plasma atomic emission spectroscopy and nitrogen adsorption–desorption isotherms verified that Ni²⁺ ions had been adsorbed onto the surfaces of the MWCNTs in the composite. As expected, a Ni²⁺/MWCNT composite-based sensor showed extraordinary electrocatalytic performance in Glu oxidation. In the concentration range 0–4.3 mM, a good linear relationship between the Glu added and the current generated was observed, with a correlation coefficient (R ²) of 0.9988. The detection limit and sensitivity were calculated to be 0.081 μM and 2285 μA mM^?1 cm^?2, respectively. Finally, the new method was successfully applied to determine the Glu in a human blood sample. Recoveries of >100%, indicative of high reliability, accuracy, and precision, were obtained.     

Facile synthesis of multiwalled carbon nanotube–V2O5 nanocomposites as cathode materials for Li-ion batteries

Multiwalled carbon nanotube (MWCNT)–vanadium pentoxide (V₂O₅) nanocomposites have been fabricated using a facile and environmental friendly hydrothermal method without any pretreatment, surfactants, or chelate agents added. The as-annealed nanocomposites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the results indicate that V₂O₅ nanoparticles grew on MWCNTs. As a cathode material for lithium batteries, it exhibits superior electrochemical performance compare to the pure V₂O₅ powders. A high specific discharge capacity of 253 mA h g^?1 can be obtained for the 15 % MWCNT–V₂O₅ nanocomposite electrodes, which retains 209 mA h g^?1 after 50 cycles. However, the pure V₂O₅ powder electrodes only possess a specific discharge capacity of 157 mA h g^?1 with a capacity retention of 127 mA h g^?1 after 50 cycles. Moreover, the MWCNT–V₂O₅ nanocomposite electrodes show an excellent rate capability with a specific discharge capacity of 180 mA h g^?1 at the current rate of 4 C. The enhanced electrochemical performance of the nanocomposites is attributed to the formation of conductive networks by MWCNTs, and large surface areas of V₂O₅ nanoparticles grew on MWCNTs which stabilizes these nanoparticles against agglomeration.     

Understanding the oxygen-containing functional groups on multiwall carbon nanotubes toward supercapacitors

Typical functionalization treatment by strong acid is used to introduce functional groups into/onto the multiwall carbon nanotubes (MWCNTs), to enhance the desired redox activity for electrochemical applications. The influence of various functional groups on the redox of MWCNT has been studied in recent years. Different functional groups on MWCNT can be removed selectively using different thermal annealing temperatures. By this method, it is recognized that carboxyl, anhydride, and phenol groups play essential roles in the redox reaction. A designed carboxyl/anhydride-rich defective MWCNT is fabricated with a superior specific areal capacitance of 34.55 mF/cm². These results provide more information for the study of the MWCNTs' electrochemical applications toward supercapacitors and batteries.     

Sensitive voltammetric determination of paracetamol by poly (4-vinylpyridine)/multiwalled carbon nanotubes modified glassy carbon electrode

A novel glassy carbon electrode (GCE) modified with a composite film of poly (4-vinylpyridine) (P4VP) and multiwalled carbon nanotubes (P4VP/MWCNT GCE) was used for the voltammetric determination of paracetamol (PCT). This novel electrode displayed a combined effect of P4VP and MWCNT on the electro-oxidation of PCT in a solution of phosphate buffer at pH 7. Hence, conducting properties of P4VP along with the remarkable physical properties of MWCNTs might have combined effects in enhancing the kinetics of PCT oxidation. The P4VP/MWCNT GCE has also demonstrated excellent electrochemical activity toward PCT oxidation compared to that with bare GCE and MWCNT GCE. The anodic peak currents of PCT on the P4VP/MWCNT GCE were about 300 fold higher than that of the non-modified electrodes. By applying differential pulse voltammetry technique under optimized experimental conditions, a good linear ratio of oxidation peak currents and concentrations of PCT over the range of 0.02–450 μM with a limit of detection of 1.69 nM were achieved. This novel electrode was stable for more than 60 days and reproducible responses were obtained at 99% of the initial current of PCT without any influence of physiologically common interferences such as ascorbic acid and uric acid. The application of this electrode to determine PCT in tablets and urine samples was proposed.     

Poly(vinyltriethoxysilane) modified MWCNT/polyimide nanocomposites—Preparation,morphological, mechanical,and electrical properties

Multi‐walled carbon nanotube (MWCNT) modified by vinyltriethoxysilane (VTES) via free radical reaction has been prepared (poly (vinyltriethoxysilane) modified MWCNTs, PVTES‐MWCNT). Precursor of polyimide, polyamic acid has been synthesized by reacting 4,4′‐oxydianiline with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride. PVTES‐MWCNT were then mixed with polyamic acid and heated to 300 °C to form CNT/polyimide composite. During the imidization processes, the silanes on CNT surface reacted with each other and may be connected together by covalent bond (Si? O? Si). The PVTES‐MWCNT was analyzed by Fourier transform infrared and X‐ray photoelectron spectroscopy. The PVTES‐MWCNT/polyimide composites were analyzed by CP/MAS solid state ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. Morphological properties of the PVTES‐MWCNT/polyimide composites were investigated by scanning electron microscope and transmission electron microscope. Electrical conductivity increased dramatically comparing to the unmodified MWCNT/polyimide composites. Mechanical properties of nanocomposite were enhanced significantly by PVTES‐MWCNT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 803–816, 2008     

Effect of scale and surface chemistry on the mechanical properties of carbon nanotubes‐based composites

In this article, Multi‐Walled Carbon Nanotubes (MWCNTs) of varying diameters, both untreated and polycarboxylated, were dispersed at constant weight percentage in an epoxy matrix, and resulting fracture toughnesses (K_Ic) were measured in each case. We show that changing the MWCNT diameter has two effects on the composite fracture toughness: (i) a small MWCNT diameter enables larger interfacial surface for adhesion maximization, which increases toughness; (ii) at the same time, it limits the available pull‐out energy and reduces the MWCNT ability to homogeneously disperse in the matrix due to this same large active surface: this decreases toughness. Most commercially available MWCNTs have a length range of several μm, thus an optimal diameter exists which depends on MWCNT wall thickness and surface treatment. Such optimal diameter maximizes pull‐out energy and thus composite fracture toughness. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Functionalization of tungsten oxide into MWCNT and its application for sunlight-induced degradation of rhodamine B

A composite of multi-walled carbon nanotube/tungsten oxide (MWCNT/WO(3)) has been successfully synthesized. The prepared composite was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The catalytic activity was investigated by rhodamine B degradation under solar irradiation. The influence of various degradation parameters such as solar illumination time, initial dye concentration, dosage and pH was investigated. It was found that the composite exhibits an enhanced photocatalytic activity as compared with WO(3) and a mechanical mixture of MWCNTs and WO(3). The enhancement in photocatalytic performance of the MWCNT/WO(3) composite has been explained based on adsorption ability and electron transportation as a result of a strong interaction between WO(3) and MWCNTs. Besides, MWCNTs acts as dispersing agent preventing WO(3) from agglomerating during the catalytic process, providing a high active surface area of the catalyst. A reasonable mechanism for the enhanced reactivity was proposed.     

Complementary effects of multiwalled carbon nanotubes and conductive carbon black on polyamide 6

This article introduces a newly innovative idea for preparation of superconductive ternary polymeric composites of polyamide 6 (PA6), conductive carbon black (CCB), and multiwalled carbon nanotubes (MWCNTs) with different weight ratios by a melt‐mixing technique. The complementary effects of CCB and MWCNTs at different compositions on rheological, physical, morphological, thermal, and dynamic mechanical and electrical properties of the ternary composites have been examined systematically. We have used a novel formulation to produce high‐weight fraction ternary polymer composites that show extremely higher conductivity when compared with their corresponding binary polymer composites at the same carbon loading. For example, with an addition of 10 wt % MWCNTs into the CCB/PA6 composite preloaded with 10 wt % CCB, the electrical conductivity of these ternary composites was about 5 S/m, which was 10 times that of the CCB/PA6 binary composite (0.5 S/m) and 125 times that of the MWCNT/PA6 binary composite (0.04 S/m) at 20 wt % carbon loading. The incorporation of the MWCNTs effectively enhanced the thermal stability and crystallization of the PA6 matrix in the CCB/PA6 composites through heterogeneous nucleation. The MWCNTs appeared to significantly affect the mechanical and rheological properties of the PA6 in the CCB/PA6 composites, a way notably dependent on the MWCNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1203–1212, 2010     

Adsorptive Stripping Differential Pulse Voltammetric Determination of Risperidone with a Multi‐Walled Carbon Nanotube‐Ionic Liquid Paste Modified Glassy Carbon Electrode

A new composite electrode has been fabricated based on coating multi‐walled carbon nanotubes (MWCNTs) and n‐octylpyridinum hexafluorophosphate (OPPF₆) ionic liquid composite on a glassy carbon (GC) electrode (OPPF₆‐MWCNTs/GCE). This electrode shows very attractive electrochemical performances for electrooxidation of risperidone (RIS) compared to conventional electrodes using carbon and mineral oil, notably improved sensitivity and stability. The oxidation peak potentials in cyclic voltammogram of RIS on the OPPF₆‐MWCNTs/GCE was occurred around 230 mV vs. SCE at Britton–Robinson (B–R) buffer (pH 4.0) at scan rate of 100 mV s^?1. The electrochemical parameters such as diffusion coefficient (D), charge transfer coefficient (α) and the electron transfer rate constant (k/_s) were determined using cyclic voltammetry. Under the optimized conditions, the peak current was linear to risperidone concentration over the concentration range of 10–200 nM with sensitivity of 0.016 μA/nM^?1 using differential pulse voltammetry. The detection limit was 6.54 nM (S/N = 3). The electrode also displayed good selectivity and repeatability. In the presence of clozapine (CLZ) the response of RIS kept almost unchanged. Thus this electrode could find application in the determination of RIS in some real samples. The analytical performance of the OPPF₆‐MWCNTs/GCE was demonstrated for the determination of RIS in human serum and pharmaceutical samples.     

Functionalized carbon nanotubes as sensitive materials for electrochemical detection of ultra-trace 2,4,6-trinitrotoluene

This report demonstrates a novel electrochemical method for fast and sensitive detection of ultra-trace 2,4,6-trinitrotoluene (TNT) based on modified electrodes by functionalized MWCNTs. To fabricate new kind of functionalized MWCNTs material sensitive to TNT, our work first theoretically investigated the interaction between triphenylene (TP) and TNT by calculating their electrostatic potentials, and secondly characterized this interaction by the fluorescence spectra. The functionalized MWCNTs of TP-MWCNTs were thoroughly characterized by fluorescence and UV-visible spectra, and by analysing these results, the interaction between TP and MWCNTs was also examined. Electrochemical experiment suggests, compared to MWCNTs- and TP- modified electrodes, TP-MWCNTs-modified electrodes result in both fast response and enhanced sensitivity to TNT detection. These results show the attachment of TP on MWCNTs leads to better sensing unit with more receptor site to TNT, associated with the coordinative recognition of TP and MWCNTs to TNT, finally result in the improvement of response and sensitivity. And this improved recognition process is attributed to the geometric and electrostatic complementarity between TP and TNT. The present study demonstrates TP-MWCNTs-modified electrode holds promising and important implications for the detection of ultra-trace TNT.     

Thermal and electrical properties of poly(l-lactide)-graft-multiwalled carbon nanotube composites

The dispersion of the nanometer-sized carbon nanotubes in a polymer matrix leads to a marked improvement in the properties of the polymer. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(l-lactide) (PLLA), which has received a great deal of attention due to environmental concerns. In this study, PLLA was melt compounded with multiwalled carbon nanotubes (MWCNTs). A high degree of dispersion of the MWCNTs in the composites was obtained by grafting PLLA onto the MWCNTs (PLLA-g-MWCNTs). After oxidizing the MWCNTs by treating them with strong acids, they were reacted with l-lactide to produce the PLLA-g-MWCNTs. The morphology of the composite was observed with scanning electron microscopy. The mechanical properties of the PLLA/PLLA-g-MWCNT composite were higher than those of the PLLA/MWCNT composite. The thermal stability of the composites was studied using thermogravimetric analysis and their activation energy during thermal degradation was determined using the Kissinger and Flynn-Wall-Ozawa methods. The activation energy of PLLA/PLLA-g-MWCNT was higher than that of PLLA/MWCNT, which indicates that the composite made with the PLLA-g-MWCNTs was more thermally stable than the composite made with the MWCNTs.     

Fabrication of multiwalled carbon nanotube-wrapped magnetic carbonyl iron microspheres and their magnetorheology

Magnetorheological (MR) properties and dispersion stability of magnetic carbonyl iron (CI) microspheres were examined and found to be enhanced by fabricating a dense nest composed of multiwalled carbon nanotubes (MWCNTs) on the surface of CI particles in this study. The coating process is achieved by using 4-aminobenzoic acid as a grafting agent via self-assembly mechanism under sonication in which the MWCNTs were adopted as the coating material because MWCNTs possess similar density with polymer but better magnetic properties due to the iron catalyst originally included within the walls. The coating thickness and morphology of the MWCNTs nest were found to be related with the sonication duration. The influence of the coating layers on the magnetic properties and MR performance (yield stress behavior, shear viscosity) were examined using a vibrating sample magnetometer and rotational rheometer. Sedimentation rates of the fabricated MWCNT/CI suspension and pure CI suspension were also investigated.     

Orientation and mechanical properties of laser‐induced photothermally drawn fibers composed of multiwalled carbon nanotubes and poly(ethylene terephthalate)

This study presents a novel photothermal drawing of poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) fibers. The photothermal drawing was carried out using the near infrared laser‐induced photothermal properties of MWCNTs. An uniform fiber surface was obtained from a continuous necking deformation of the undrawn fibers, particularly at a draw ratio of 4 and higher. The breaking stress and modulus of the photothermally drawn PET/MWCNT fibers were significantly enhanced, in comparison to those of hot drawn fibers at the same draw ratio. The enhanced mechanical properties were ascribed to the increased orientation of PET chains and MWCNTs as well as PET crystallinity due to photothermal drawing. In particular, a significantly higher degree of orientation of the MWCNTs along the fiber axis was obtained from photothermal drawing, as shown in polarized Raman spectra measurements. The photothermal drawing in this study has the potential to enhance the mechanical properties of fibers containing MWCNTs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 603–609