Treated Carbon Nanotubes Research Articles

Metallic nanoparticles on plasma treated carbon nanotubes: Nano 2hybrids

Multi-wall carbon nanotubes (MWCNTs) were decorated with metal clusters by thermal evaporation. Transmission electron microscopy (TEM) shows that the nature and extent of metal coverage can be varied by plasma treating the MWCNT surface. The metal clusters on oxygen plasma treated arc-discharge MWCNTs have a more dense distribution than the clusters evaporated on as-synthesized arc-discharge MWCNTs. In contrast, the plasma treatment did not affect the cluster distribution on CVD MWCNTs. Analyses of the valence band and the core levels by X-ray photoelectron spectroscopy suggest poor charge transfer between gold clusters and MWCNTs; on the contrary suggest good charge transfer between Ni clusters and MWCNTs.

Improvement of field emission from screen-printed carbon nanotubes by He∕(N2,Ar) atmospheric pressure plasma treatment

A screen-printed carbon nanotube (CNT) paste for applications to field emission emitters was treated with He, He∕Ar, and He∕N2 atmospheric pressure plasmas. The effect of the different plasma treatments on the field emission characteristics of the screen-printed CNTs was investigated. The atmospheric pressure plasma applied to the screen-printed CNT paste for 10s resulted in a reduction in the turn-on electric field. In particular, the application of a He∕N2 plasma treatment decreased the turn-on electric field from 3.13to1.29V∕μm and increased the field enhancement factor from 737 to 2775 after the treatment. These results suggest that an adequate atmospheric pressure plasma treatment of screen-printed CNTs can be effective in enhancing the field emission properties.

Carbon nanotubes show no sign of acute toxicity but induce intracellular reactive oxygen species in dependence on contaminants

Today nanosciences are experiencing massive investment worldwide although research on toxicological aspects of these nano-sized particles has just begun and to date, no clear guidelines exist to quantify the effects. In the present study, we focus on carbon nanotubes (CNTs), which represent one of the most widely investigated carbon nanoparticles. The present data indicate that CNTs are able to cross the cell membrane of rat macrophages (NR8383) and, therefore, might have an influence on cell physiology and function. NR8383 and human A549 lung cells were incubated with commercial single-walled (NT-1) and multi-walled (NT-2, NT-3) CNTs, carbon black and quartz as reference particles as well as an acid-treated single-walled CNT preparation (SWCNT a.t.) with reduced metal catalyst content. We did not observe any acute toxicity on cell viability (WST-1, PI-staining) upon incubation with all CNT products. None of the CNTs induced the inflammatory mediators NO, TNF-α and IL-8. A rising tendency of TNF-α release from LPS-primed cells due to CNT treatment could be observed. We detected however, a dose- and time-dependent increase of intracellular reactive oxygen species and a decrease of the mitochondrial membrane potential with the commercial CNTs in both cell types after particle treatment whereas incubation with the purified CNTs (SWCNT a.t.) had no effect. This leads us to the conclusion that metal traces associated with the commercial nanotubes are responsible for the biological effects.

Physical and electrochemical characterization of platinum and platinum–ruthenium treated carbon nanotubes directly grown on carbon cloth

Dense carbon nanotubes (CNTs) were grown via a thermal chemical vapor deposition process on titanium treated carbon cloths. The catalysts in the form of either platinum (Pt) or platinum–ruthenium (Pt–Ru) nano-sized particles were then deposited on the CNT surface by potentiostatic electrodeposition. After the deposition process, the surface morphology of prepared specimens was examined by scanning electron microscopy and transmission electron microscopy, and the electrochemical characteristics of the specimens were also investigated by cyclic voltammetry in nitrogen saturated sulfuric acid aqueous solutions and in mixed sulfuric acid and methanol aqueous solutions. Well dispersed catalysts, Pt alone or Pt–Ru, were observed on the surfaces of the CNTs directly grown on carbon cloths. It was found that the electrochemical behavior of the specimen with Pt–Ru deposits was distinctly different from that of those with only Pt deposits. It was also observed that a more negative electrodeposition potential led to a better performance of the catalysts in terms of methanol oxidation efficiency and the suppression of carbon monoxide poisoning.

Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900°C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of π* features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl (CO), π*(CO), and ether C–O–C, σ*(CO), functionalities were present. Upon heating in a vacuum to 900°C the π*(CO) resonances disappeared while the σ*(CO) resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the π* feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.

Platinum Catalysts Prepared with Functional Carbon Nanotube Defects and Its Improved Catalytic Performance for Methanol Oxidation

Carbon nanotube (CNT) supported Pt nanoparticle catalysts have been prepared by spontaneous reduction of PtCl6(2-) ion as a result of direct redox reactions between PtCl6(2-) and oxygen-containing functional groups at defect sites of CNTs, which were introduced by chemical and electrochemical oxidation treatment of CNTs. The electrocatalytic properties of as-prepared Pt-CNT catalysts for methanol oxidation were investigated by chronopotentiometry and cyclic voltammetry. Compared with Pt catalysts prepared by hydrogen reduction and electrochemical deposition methods, Pt catalysts synthesized by functional CNT defects show excellent antipoisoning ability and long-term cycle stability.

Hydrogen storage properties of CNTs treated at different temperature in vacuum

The effect of multi-wall nanotubes (MWNTs) treated at different temperature in vacuum on the electrochemical hydrogen storage properties were investigated. The MWNTs were synthesized by chemical vapor deposition. The CNTs(carbon nanotubes)-LaNi5 electrodes were prepared by mixing MWNTs and LaNi5 alloy in a weight ratio of 1∶10. Three-electrode system was introduced. The CNTs-LaNi5 electrodes were used as the working electrode. Ni(OH)2/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode. 6mol/L KOH solution acted as the electrolyte. Results showed that the CNTs-LaNi5 electrodes with CNTs treated at 850℃ in vacuum has the best electrochemical hydrogen storage capacity with a maximum discharging capacity of 503.6mAh/g and a corresponding discharging plateau voltage of 1.18V under the same testing condition. From 500℃ to 850℃, the higher the temperature of heating, the better the electrochemical hydrogen storage property of WMNTs. However, CNTs-LaNi5 electrodes with CNTs treated at 950℃ in vacuum has lower discharging capacity under the same testing condition. This shows that the temperature of CNTs treatment in vacuum is an important factor that influences its electrochemical hydrogen storage performance.

Synthesis and characterization of water-soluble carbon nanotubes from mustard soot

Carbon nanotubes (CNT) has been synthesized by pyrolysing mustard oil using an oil lamp. It was made water-soluble (wsCNT) through oxidative treatment by dilute nitric acid and was characterized by SEM, AFM, XRD, Raman and FTIR spectroscopy. The synthesized wsCNT showed the presence of several junctions and defects in it. The presence of curved graphene structure (sp2) with frequent sp3 hybridized carbon is found to be responsible for the observed defects. These defects along with the presence of di- and tri-podal junctions showed interesting magnetic properties of carbon radicals formed by spin frustration. This trapped carbon radical showed ESR signal in aqueous solution and was very stable even under drastic treatment by strong oxidizing or reducing agents. Oxidative acid treatment of CNT introduced several carboxylic acid group functionalities in wsCNT along with the nicking of the CNT at different lengths with varied molecular weight. To evaluate molecular weights of these wsCNTs, an innovative method like gel electrophoresis using high molecular weight DNA as marker was introduced.

Improving the blood compatibility of polyurethane using carbon nanotubes as fillers and its implications to cardiovascular surgery

Blood compatibility has been an occlusion for biomaterials used in the cardiovascular system. In this work, a multiwalled carbon nanotubes-polyurethane composite (MWNT-PU) was prepared through a controlled co-precipitation. The surface chemical composition of treated carbon nanotubes was analyzed with XPS and the thermal behaviors of composite were characterized by DSC. The platelet adhesion and activation caused by the composite were evaluated by using SEM and flow cytometric analysis, respectively, and the disruption of red blood cells was analyzed through measuring the absorbance of free hemoglobin. The experimental results demonstrated that: (1) Multiwalled carbon nanotubes (MWNTs) with oxygen-containing functional groups could be well dispersed in polyurethane matrix through a controlled coprecipitation; (2) the composite surface displayed a significantly improved anticoagulant function, which can be indicative of the promising potentials of carbon nanotube-based materials in the implants and medical devices applied in blood-contacting environments.

Synthesis and Electrochemical Characterization of Uniformly-Dispersed High Loading Pt Nanoparticles on Sonochemically-Treated Carbon Nanotubes

A sonochemical process was developed to treat carbon nanotubes in nitric and sulfuric acids to create surface functional groups for metal nanoparticle deposition. Carbon nanotubes treated in the sonochemical process are shown to lead to the deposition of uniformly dispersed high loading Pt nanoparticles, which have not been achieved with carbon nanotubes treated in reflux processes. Pt nanoparticles of a size less than 5 nm and loading up to 30 wt % with little aggregation were synthesized on the sonochemically treated carbon nanotubes. Cyclic voltammetry measurements in 1.0 M H2SO4 showed that the Pt nanoparticles on carbon nanotubes are more than 100% active in the electrochemical adsorption and desorption of hydrogen than the Pt nanoparticles supported on carbon black. This enhancement of electrochemical activity is attributed to the unique structures of carbon nanotubes and the interactions between the Pt nanoparticles and the carbon nanotube support. The ability to synthesize high loading Pt on carbo...

A study of the electrical properties of carbon nanotube-NiFe 2O 4 composites: Effect of the surface treatment of the carbon nanotubes

Novel carbon nanotube-NiFe 2O 4 composite materials have been prepared for the first time by in situ chemical precipitation of metal hydroxides in ethanol in the presence of carbon nanotubes (CNTs) and followed by hydrothermal processing. The obtained composite powders were characterized using XRD, TEM and EDS. The effect of surface oxidation treatment of CNTs on their properties was investigated by FTIR, zeta potential and hydrodynamic radius distribution characterization. Electrical conductivity measurements show that surface oxidation treatment of CNTs can improve the electrical conductivity of the composites more pronouncedly than pristine CNTs do. With 10 wt.% addition of surface treated CNTs, the electrical conductivity is increased by 5 orders of magnitude. The surface oxidized CNTs are crucial for this significant increase in electrical conductivity, which provides strong adhesion between the nanotubes and the matrix to give a homogeneous carbon nanotube-NiFe 2O 4 composite.

Nondestructive Damage Sensitivity and Reinforcing Effect of Functionalized Carbon Nanotube and Nanofiber/Epoxy Composites Using Electro-Micromechanical Techniques

ABSTRACTNondestructive damage sensing and load transfer mechanisms of thermal treated carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites were investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison. Electro-micromechanical techniques were applied to obtain the fiber damage and stress transferring effect of carbon nanocomposites with their contents. Thermal treatment and temperature affected on apparent modulus and electrical properties on nanocomposites due to enhanced inherent properties of each CNMs. Coefficient of variation (COV) of volumetric electrical resistance can be used to obtain the dispersion degree indirectly for various CNMs. Dispersion and surface modification are very important parameters to obtain improved mechanical and electrical properties of CNMs for multifunctional applications. Further optimized functionalization and dispersion conditions will be investigated for the following work continuously.

Fabrication of nanowires with polymer shells using treated carbon nanotube bundles as macro-initiators

Nanowires with polymer shells were produced via radical grafting polymerization of methyl methacrylate using treated carbon nanotube bundles as macro-initiators, thereby providing an efficient way to produce high grafting ratio nanocomposites.

Change of surface morphology and field emission property of carbon nanotube films treated using a hydrogen plasma

Large-scaled homogeneous multi-wall carbon nanotube (MWNT) films have been obtained at room temperature by a transfer technique. The surface morphology and microstructure features of the films before and after hydrogen plasma (HP) treatment were investigated by scanning electron microscopy, high-resolution transmission electron microscopy, and micro-Raman spectra. The electrical resistance in the temperature range 5–296 K and field emission in diode structure for the MWNT films were examined. Electron microscopy results demonstrated that the surface of treated nanotubes had become open palpus-like graphite layers or were covered by the onion-like carbon nanoparticles. The temperature dependence on electric resistance for MWNT films, which was fitted by three-dimensional variable range hopping conduction, was observed; and the slope and scope of the temperature dependence for the treated film were larger than that of the untreated one. The field emission tests indicated that the turn-on field (at 0.1 μA/cm 2) decreases from 3.9 to 1.5 V/μm after the sample is treated with hydrogen plasma for 30 min. High emission spot density of about 1.5×10 4 cm −2 is achieved at an applied electric field 5.2 V/μm. The conversion mechanism of the treated carbon nanotubes(CNTs) microstructure and the reason for the change of electronic properties and field emission of MWNT films were discussed.

Electronic properties and field emission of carbon nanotube films treated by hydrogen plasma

Large-scale and very even multi-wall carbon nanotube (MWNT) films have been obtained at room temperature by an electrophoresis deposition technique. The characterization, by means of scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and micro-Raman spectroscopy, shows that the MWNTs with hydrogen-plasma (HP) treatment are covered by onion-like nanolumps, and three-dimensional multiple-way-connected nanotube webs are formed. The electronic property of the treated MWNT film is converted from semiconducting to metallic. The field-emission test indicates that the HP-treated MWNT film has a low threshold of 1.1 V/μm (at 0.1 μA/cm2), a high emission light spot density of about 105 cm-2, and a stable and suitable emission current. The conversion mechanism of the treated carbon nanotube structure and the reason for the change of the electronic and field-emission characteristics of the MWNT films are discussed.

A study on the effect of surface treatment of carbon nanotubes for liquid crystalline epoxide–carbon nanotube composites

Chemical surface oxidation of carbon nanotubes was employed to modify the interfaces between liquid crystalline epoxide (LCE) molecules and carbon nanotubes (CNs). Polar functional groups are formed on the surfaces of the carbon nanotubes as a result of the treatment. The thermotropic behavior of the nematic liquid crystalline (LC) phase in liquid crystalline epoxide–carbon nanotube (LCE–CN) composites has been examined using polarized optical microscopy. The LC phase in the LCE–surface oxidized CN composite evolves at a lower temperature compared to that for LCE–CN, due to polar interactions. The mechanical properties of LCE–CN composites tend to increase with increasing CN content. The electrical conductivity of LCE–CN composites was found to increases dramatically compared to that of pristine LCE resin, up to 5 wt% CN loading, and then increase linearly with increasing CN content at high CN loadings. An investigation of the thermal properties of LCE–CNs in relation to the surface treatment of CNs was also undertaken. Surface oxidation of CNs was found to improve the mechanical durability and thermal stability of LCE–CN composites.

Preparation and Characterization of Platinum-Based Electrocatalysts on Multiwalled Carbon Nanotubes for Proton Exchange Membrane Fuel Cells

A higher yield of functionalized carbon nanotubes (CNTs) was obtained by treatment of CNTs in HNO3 or H2SO4−K2Cr2O7. The deposition of platinum nanoparticles and nanoclusters on these functionalized multiwalled carbon nanotubes by electroless plating was facilitated by a two-step sensitization-activation pretreatment. The deposition was sensitive to the aging time of the sensitizing solution and the pH of the plating solution. The resulting electrocatalysts were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. XPS analysis showed that the Pt/CNT electrocatalysts contained 67.3% of Pt(0) and 32.7% of Pt(IV). Test runs on a single stack polymer electrolyte membrane fuel cell showed that these electrocatalysts are very promising for fuel cell applications.