Pt–Ru nanoparticles supported on functionalized carbon as electrocatalysts for the methanol oxidation

Platinum–ruthenium alloy electrocatalysts, for methanol oxidation reaction, were prepared on carbons thermally treated in helium atmosphere or chemically functionalized in H₂O₂, or in HNO₃ + H₂SO₄ or in HNO₃ solutions. The functionalized carbon that is produced using acid solutions contains more surface oxygenated functional groups than carbon treated with H₂O₂ solution or HeTT. The XRD/HR-TEM analysis have showed the existence of a higher alloying degree for Pt–Ru electrocatalysts supported on functionalized carbon, which present superior electrocatalytic performance, assessed by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy, as compared to electrocatalysts on unfunctionalized carbon. It also was found that Pt–Ru alloy electrocatalysts on functionalized carbon improve the reaction rate compared to Pt–Ru on carbons treated with H₂O₂ solution and thermally. A mechanism is discussed, where oxygenated groups generated from acid functionalization of carbon and adsorbed on Pt–Ru electrocatalysts are considered to enhance the electrocatalytic activity of the methanol oxidation reaction.     

Crystallinity of biodegradable polymers reinforced with functionalized carbon nanotubes

Well-dispersed multiwall carbon nanotubes (MWCNTs) were prepared by grafting poly(L-lactide-co-ε-caprolactone) (PLACL) biodegradable copolymer onto the sidewall of hydroxylated MWCNTs using oligomeric L-lactide (LA) and ε-caprolactone (CL). After preparation of MWCNT/PLACL composites, the effect of functionalized MWCNTs on crystallinity of PLACL was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarized light optical microscopy (POM). The surface functionalization effectively improved the dispersion and adhesion of MWCNTs which acted as reinforcing filler in the PLACL polymer matrix and hence improved the physical and thermomechanical properties of the nanocomposites. The glass transition temperature (T _g) and the crystallinity of nanocomposites decreased in comparison with those of neat PLACL when the concentration of functionalized MWCNTs in nanocomposites was 0.5 wt%. With further increment in concentration of functionalized MWCNTs, the T _g of composites increased until the T _g of neat PLACL, and also the crystallinity of composites increased. The functionalized MWCNTs have no significant effect on the melting point of nanocomposites. The MWCNTs acted as heterogeneous nucleation points and increased the lamella size and therefore the crystallinity of PLACL. Furthermore, the larger agglomerated clusters of both kinds of MWCNTs (i.e., MWCNT-grafted-PLACL and pristine MWCNTs) are more effective than small clusters as nucleation points for growing the spherulites.     

Composites based on acrylic polymers and carbon nanotubes as precursors of carbon materials

The effect of carbon nanotubes on the properties of composite fibers and films based on polyacrylonitrile is analyzed. It is shown that the introduction of carbon nanotubes makes it possible to improve the mechanical characteristics of the composite material. Data on the effect of carbon nanotubes on chemical reactions occurring during the thermal stabilization and carbonization of these materials are cited.     

Support effects of nickel on activated carbon as a catalyst for vapor phase methanol carbonylation

Nickel supported on activated carbon can be used for the vapor phase carbonylation of methanol, producing methyl acetate and acetic acid as products. In contrast to previous reports, a strong influence of the support on the performance of the catalyst, in terms of both activity and stability, was observed in the current study. The effect appears to be related to the pore size distribution of the support. Catalysts prepared on large pore activated carbons are less active than catalysts prepared on smaller pore activated carbons but show no deactivation over time on stream. The mechanism of deactivation appears to be consistent with a strong adsorption of methanol and reaction products that plugs the catalyst pores and leads to increasingly strong diffusion limitations with time on stream.     

Rheology of polymers containing carbon black

In order to elucidate the flow behavior of electrophotographic toner systems, shear stress was measured as a function of shear rate in a cone and plate rheometer for polymer melts containing carbon blacks of surface area 24 and 625 m²/g at several concentrations and temperatures. Polymers included high and low molecular weight polystyrene and poly(butyl methacrylate). The addition of carbon black to the polymers caused a large increase in viscosity, especially at low shear rates and shear stresses. As the concentration of carbon black was increased, the viscosity at low shear rates became unbounded below a value of the shear stress designated the yield stress. The absolute magnitude of the yield stress depended primarily on the concentration and surface area of the carbon black and was independent of the polymer and temperature. Apparently, carbon black forms an independent network within the polymer at low shear rates which precludes flow. In some cases, the viscosity of polymers filled with carbon black was lower than that of the pure polymer. This effect was favored for polystyrene compared to poly(butyl methacrylate) and was facilitated by increasing the molecular weight of polystyrene, reducing the surface area and concentration of carbon black, and by increasing the temperature and shear rate.     

Grafting onto carbon black by the reaction of reactive carbon black having acyl chloride group with several polymers

Summary Acyl chloride group introduced onto carbon black rapidly lost its activity by the moisture in air. However, the decrease of acyl chloride group content in vacuum was negligibly small. By the reaction of the acyl chloride group with several polymers having hydroxyl or amino group, such as polyethylene glycol (PEG), poly(vinyl alcohol)(PVA), and polyethyleneimine (PEI), these polymers were found to be effectively grafted onto carbon black; for instance, the grafting ratio of PEG (Mn=8.2×10³), PVA (Mn=2.2×10⁴), and PEI (Mn=2.0×10⁴) was 18.5%, 32.9%, and 45.8%, respectively. The number of polymer grafted onto carbon black decreased with an increase of its molecular weight.     

Electrical conductivity of polymers containing carbon black

Changes in volume resistivity with temperature of carbon-black-filled polymers and a random copolymer of styrene and butyl methacrylate were measured. For polystyrene containing 20 wt % carbon black, of surface area 24 m²/g, the resistivity changes abruptly from 10¹³ to 10⁶ ohm-cm above 150°C. Poly(butyl methacrylate) did not show well-defined changes in resistivity on heating. The random copolymer containing 16.7 or 28.6 wt % carbon black, of surface area 24 m²/g, showed a resistivity exceeding 10¹³ ohm-cm, that decreased to about 10⁷ ohm-cm on heating above 120°C. This Copolymer containing 16.7 wt % carbon black, of surface area 625 m²/g, shows a resistivity of about 108 ohm-cm that decreases sharply to 10³ ohm-cm by 150°C. Decreases in resistivity on increasing the temperature in the quiescent state are correlated with the observation of a yield stress at low shear rates in rheological studies. It is suggested that carbon black agglomerates at elevated temperature and forms an independent conductive network that prevents flow.     

Multi-wall carbon nanotube networks as potential resistive gas sensors for organic vapor detection

The sensitivity of multi-wall carbon nanotube (MWCNT) networks of randomly entangled pure nanotubes and those oxidized with acidic KMnO₄ to various organic solvent vapors (iso-pentane, diethyl ether, acetone and methanol) has been investigated by resistance measurements. The solvents had different polarities given by Hansen solubility parameters and different volume fractions of saturated vapors defined by the vapor pressure. The results show that the network electrical resistance increases when exposed to organic solvent vapors, and a reversible reaction is observed when the network is removed from the vapors. The reaction with KMnO₄ increases oxygen content on the nanotube surface and causes lower porosity of MWCNT network as well as higher electrical resistance, which improves the network selectivity to polar solvents. The investigated MWCNT networks could be potentially used as sensing elements for sensitive and selective organic vapor switches.     

Polyaniline/carbon black composite as Pt electrocatalyst supports for methanol oxidation: Synthesis and characterization

Core/shell composites of polyaniline (PANI) and Vulcan XC‐72 Carbon (VC), in which the carbon represents the core and PANI forms the shell, were synthesized by in situ chemical oxidation polymerization. Platinum (Pt) particles were then deposited on the PANI/VC composites by chemical reduction method. The highest conductivity is obtained when a mass ratio of PANI/VC equals to 0.28, as proved by Fourier transform infrared spectra. And it is also proved that there are some reactions happened between PANI and VC. Scanning electron microscope, transmission electron microscope, and X‐ray diffraction measurements were performed to analyze their structure and surface morphology. It has been observed that the Pt particles are smaller in size and more uniformly distributed on these composite supports than on pure VC supports, considered as a reference. Methanol oxidation performed on the electrode modified by such a composite catalyst has been measured by cyclic voltammogram focusing on the attenuation of methanol oxidation current after 200 cycles. The attenuation degree for the composite catalyst is only one‐third of the one measured for a simple Pt/VC catalyst. It is proved that the composite catalyst better resist carbon monoxide poisoning in comparison with the Pt/VC catalyst, which may be due to the synergetic effects between the composite support and the Pt catalyst. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dynamic mechanical behavior of polymers containing carbon black

The dynamic mechanical behavior of carbon black filled polymers of styrene and butyl methacrylate was examined at low strain amplitude and frequency in order to minimize destruction of the composite structure and elucidate the basis of yield and plasticization observed in steady shear. For specific filled systems, both G′ and G″ became independent of frequency and temperature at low frequencies, consistent with a yield phenomenon and the formation of a carbon black network. On the other hand, although the high molecular weight polystyrene showed plasticization effects at higher shear rates in steady shear rheology, such, plasticization effects were never observed in dynamic mechanical analysts. Yield behavior was observed most readily for the low molecular weight polystyrene. Limiting moduli for filled polystyrenes were independent of temperature, whereas, for polybutyl methacrylate, were sensitive to temperature. It is suggested that an independent network of carbon black is strongest in the low molecular weight polystyrene and weakest in poly (butyl methacrylate).     

Studies on the electrical conductivity of carbon black filled polymers

The conductivity mechanism for a carbon black (CB) filled high-density polyethylene (HDPE) compound was investigated in this work. From the experimental results obtained, it can be seen that the relation between electrical current density (J) and applied voltage across the sample (V) coincides with Simmons's equation (i.e., the electrical resistivity of the compound decreases with the applied voltage, especially at the critical voltage). The minimum electrical resistivity occurs near the glass transition temperature (T_g) of HDPE (198 K). It can be concluded that electron tunneling is an important mechanism and a dominant transport process in the HDPE/CB composite. A new model of carbon black dispersion in the matrix was established, and the resistivity was calculated by using percolation and quantum mechanical theories. © 1996 John Wiley & Sons, Inc.     

Using formic acid vapor as reducer to prepare Pt nanoparticles supported on carbon nanofiber mats for methanol electrooxidation

A novel process has been developed to prepare well-dispersed Pt nanoparticles on electrospinning-derived carbon fibrous mats (CFMs), which involved the physical adsorption of H₂PtCl₆ on CFMs and the reduction of H₂PtCl₆ with formic acid vapor. The most important advantage of this method is its simplicity, solvent-saving and benign to the environment. The performance of the prepared Pt-CFMs electrodes for methanol oxidation has been investigated and the results demonstrate that Pt-CFMs exhibit higher electrocatalytic activity and stability towards methanol oxidation and better tolerance towards reaction intermediates than commercial Pt/C supported on CFMs.     

Carbon black/polystyrene composites as candidates for gas sensing materials

Amorphous polymer-based composites consisting of polystyrene and carbon black were developed in the current work as candidates for gas sensing materials. With the help of polymerization filling, i.e., in-situ polymerization of styrene in the presence of carbon black, the composites were provided with low percolation threshold. The experimental results indicated that the composites have selective sensitivity as characterized by high electrical responsivity to the vapors of non-polar and low polar solvents, and low responsivity to high polar solvent vapors as well. Besides conductivity of the composites, absorption characteristics of both the matrix and the fillers exert importance influence on the gas sensitivity of the composites. Therefore, composites’ performance can be tailored by changing filler concentration, molecular weight and molecular weight distribution of matrix polymer, etc. In regard to the fact that most conducting polymer composites as vapor sensing materials are based on crystalline polymer matrices, the approach reported by this paper provides another feasible way to develop new candidates.     

以甲醇为碳源甲烷氧化细菌的高密度培养

分别考察了甲烷和甲醇对甲基弯菌IMV 3011生长的影响,并对甲醇添加方式对菌体生长的影响进行了比较。结果表明:甲醇可以代替甲烷作为碳源;当甲醇的最佳添加量为0.1%(V/V)时,间歇性添加甲醇发酵终止后的细胞密度为1.622g(dry wt).L-1,生长速率相对于甲烷提高到0.043h-1,但细胞生长的延滞期较长,为59.6254h;而相比较通过在线监测自动添加甲醇,发酵终止后的细胞密度为1.772g(dry wt).L-1,生长速率提高至0.056h-1,细胞生长的延滞期为37.1807h。说明在线监测自动添加甲醇缩短了细胞生长的延滞期即减少了发酵时间,促进了细胞的高密度生长。     

Melt processing of composites of PVDF and carbon black modified with conducting polymers

Conductive composites from poly(vinylidene fluoride) (PVDF) and a novel thermally stable conductive additive made via in situ deposition of polyaniline or polypyrrole on carbon black particles were produced by a melting process. Electrical conductivity in the order of 10^?2 S/cm could be achieved with low contents of the conductive filler. Thermogravimetric analysis (TGA) showed that there is no appreciable degradation of the composites at temperatures as high as 300°C. Moreover, the addition of the conducting polymer‐modified carbon black additive is advantageous to the melt processing of the composites, reducing the melt viscosity in comparison to the addition of pure carbon black. Composites containing the β‐phase of PVDF could be obtained via quenching from the melt, as indicated by X‐Ray diffraction analysis. The type and amount of the additive and the quenching rate influence the formation of β‐phase in the PVDF composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 553–557, 2004     

Use of compatible blends to fabricate carbon black composite vapor detectors

The aim of this work was the development of materials to be used in the field of gas sensing for the detection of organic vapors. Conductive sensors were prepared with carbon black filled blends of poly(vinyl chloride) and diol‐terminated poly(?‐caprolactone), an oligomeric plasticizer. For comparison, blends with di(2‐ethylhexyl)phthalate, a traditional low‐molecular‐weight plasticizer, were also prepared. All sensors were tested upon exposure to different organic vapors. In general, the plasticizer content affected the response rates of the sensors, and a linear variation of the relative resistance with the analyte concentration was observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1816–1821, 2004     

p-Hexafluoroisopropanol phenyl covalently functionalized single-walled carbon nanotubes for detection of nerve agents

Novel p-hexafluoroisopropanol phenyl (HFIPPH) covalently functionalized single-walled carbon nanotubes (SWCNTs) have been prepared through in situ diazonium reaction between SWCNTs and p-hexafluoroisopropanol aniline; moreover, the hybridized material can be characterized by ultraviolet vision near infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectrometry, field-emission scanning electron microscopy and high resolution transmission electron microscopy. The results reveal that the one-dimensional electronic structures of the functionalized tubes could be basically maintained without damaging their electronic properties. Considered that strong hydrogen-bonding can be formed between hexafluoroisopropanol groups and dimethyl methylphosphonate (DMMP) (simulant of nerve agent sarin), the SWCNT-HFIPPH sensing devices have been fabricated and employed to detect DMMP. Excellent sensitivity and selectivity of the hybridized SWCNT-HFIPPH devices suggest that it has great capability of detecting explosives and chemical warfare agents.     

Single-walled carbon nanotubes functionalized with polydiphenylamine as active materials for applications in the supercapacitors field

Composites based on polydiphenylamine (PDPA) doped with heteropolyanions of H₃PW₁₂O₄₀ and single-walled carbon nanotubes (SWNTs) were prepared by electrochemical polymerization of diphenylamine (DPA) on carbon nanotube films deposited onto Pt electrodes. HRTEM studies reveal that the electrochemical polymerization leads to the filling the spaces between tubes which compose the bundles, creating a monolithic film on the Pt electrode. The resulting composites were tested as active materials in supercapacitors. Resonant Raman scattering studies showed that the electropolymerization of DPA in the presence of H₃PW₁₂O₄₀ and SWNTs leads to the covalent functionalization of SWNTs with doped PDPA. The covalent functionalization of SWNTs with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions was revealed by FTIR spectroscopy, based on the changes in the vibrational features of PDPA and H₃PW₁₂O₄₀. These changes included i) a down-shift of the PDPA IR bands, which was attributed to the C–H bending vibrational mode of benzene (B), C_aromatic–N, C–C stretching (B) + C–H bending (B) and C–C stretching vibrations of the B ring, from 1174, 1321, 1495 and 1603 cm^− 1 to 1165, 1313, 1487 and 1599 cm^− 1, respectively; ii) a change in the peak positions of IR bands associated with the W = O and P-O-W vibration modes of H₃PW₁₂O₄₀; and iii) a down-shift of the IR band situated in the spectral range 650–725 cm^− 1, which was assigned to the inter-ring deformation vibration mode.The characterization of symmetric solid-state supercapacitors was performed for electrodes prepared from i) SWNTs functionalized with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions, ii) SWNTs electrochemically decorated with H₃PW₁₂O₄₀ heteropolyanions, and iii) PDPA doped with H₃PW₁₂O₄₀ heteropolyanions. Preliminary results indicate high discharge capacitance values of up to 157.2 mF/cm² for SWNTs functionalized with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions. The discharge capacitance of this material is superior to those recorded for SWNTs electrochemically decorated with H₃PW₁₂O₄₀ heteropolyanions (~ 18.2 mF/cm²) and PDPA doped with H₃PW₁₂O₄₀ heteropolyanions (~ 62.1 mF/cm²).     

Synthesis and evaluation of hexafluorodimethylcarbinol functionalized polymers as microsensor coatings

Polystyrenes, polyacrylates, and poly(3,4-isoprenes) incorporating the hexafluorodimethylcarbinol functionality have been synthesized, characterized, and tested as microsensor coatings on a surface acoustic wave (SAW) device for dimethyl methylphosphonate (DMMP) vapor absorption sensitivity. The syntheses involved monomer functionalization and polymerization or hexafluoroacetone reaction with preformed polymer. All fluoroalcohol functionalized polymer coatings displayed sub parts per million level sensitivity with the slope of the absorption isotherm steepest at low DMMP concentrations. The order of sensitivity for the isomeric polystyrene fluoroalcohols (meta > para ? ortho) paralleled that of the relative free hydroxyl to hydrogen-bonded hydroxyl content. Strong hydrogen bonding between the fluoroalcohol polymers and DMMP vapor was observed by IR spectroscopy. Acylation of the fluoroalcohol group markedly reduced the DMMP sensitivity.