Wesley Wampler

Composites of polypyrrole and carbon black: Part III. Chemical synthesis and characterization

A new class of molecular composites of carbon black and an electronically conducting polymer, namely polypyrrole, has been synthesized by chemically polymerizing pyrrole in an aqueous dispersion of carbon black. The carbon black content of these composites can be varied from ∼5% to ∼85% (by weight). The surface area and density of these composites were compared to corresponding mixtures of carbon black and polypyrrole. The influence of carbon black on the efficiency of polymerization of pyrrole is described. The effect of carbon black content on the electronic conductivity of the composite has been mapped, and compared with the corresponding behavior of a mixture of carbon black and polyvinylchloride. The influence of the parent black characteristics (porosity, void volume, surface area) on the electronic conductivity of the resultant composite has been probed by comparing the behavior of composites derived from six commercial and experimental blacks. The temperature dependence of the composites has been studied as a function of the carbon black content. Finally, the application of these new materials is an environmental remediation scenario is demonstrated for Cr(vi) as a model pollutant.

Redox characterization of furnace carbon black surfaces

Abstract The redox properties of furnace-type carbon blacks were studied by UV–visible spectrophotometry and potentiometry. The carbon black surface was exposed to redox reagents such as Cr(VI), Mn(VII), Fe(III), and sulfite. The ability of the carbon black surface to undergo redox reactions with these reagents was correlated with the morphological attributes of the black such as crystallite size and surface area. The effect of high temperature treatment was also explored. These data show that the ability of carbon black to accept or donate electrons is a sensitive function of the defect site density of the carbon black surface. Thus an initially inert graphitic surface could be rendered redox active by mechanically damaging it. Conversely, high temperature treatment ‘graphitized’ the carbon black and weakened its redox activity. The ‘structure’ of carbon black (as probed by dibutylphthalate absorption) did not appear to influence its redox activity. Laser Raman spectroscopy and cyclic voltammetry provided further insights into the redox activity of the furnace carbon black surface.

Composites of polypyrrole and carbon black: 4. Use in environmental pollution abatement of hexavalent chromium

Abstract Composites of an electronically conducting polymer (polypyrrole) with carbon black were used to reduce Cr(VI) to (the less toxic) Cr(III) in aqueous media. The carbon black content in these composites was varied from ~5 to ~65% (by weight); an increase in the carbon black fraction increased the ability of the composite to reduce Cr(VI). The composite outperformed both its components, namely polypyrrole and carbon black, in its ability to treat Cr(VI). The Cr(VI) conversion obeyed pseudo firstorder kinetics. The mechanistic and practical implications of this new Cr(VI) pollution abatement approach are discussed.

Photocatalytically Generated Bimetallic ( Pt – Au ∕ C – TiO2 ) Electrocatalysts for Polymer Electrolyte Fuel Cell Applications

Heterogeneous photocatalysis was used to prepare bimetallic Pt―Au modified carbon―TiO 2 matrices for use in polymer electrolyte fuel cells. These new generation electrocatalysts were characterized by transmission electron microscopy, energy-dispersive X-ray analyses, X-ray diffraction, and X-ray photoelectron microscopy. The electrocatalytic activity of these materials for the oxygen reduction reaction (ORR) was assessed by rotating disk hydrodynamic voltammetry. Of the three variant scenarios that can be envisioned for photocatalytic deposition of the two metals, i.e., sequential deposition (with Pt first and Au second or Au first and Pt second) or simultaneous deposition of Pt and Au on the C―TiO 2 nanocomposite surface from a single bath, electrocatalyst samples with Pt decorating the initially deposited Au nanoclusters (designated as Pt/Au/C―TiO 2 ) performed the best in terms of ORR kinetic facility, even relative to the monometallic case of Pt supported on C―TiO 2 . The durability of these electrocatalysts (in terms of corrosion) was assessed via galvanostatic polarization tests; once again Pt/Au/C―TiO 2 fared best relative to the other two samples as well as the Pt/C―TiO 2 control case. For all the electrochemical analyses, the total metal loading in the electrocatalysts was kept constant at 20% (by mass) for meaningful comparison.

Electrocomposites of Polypyrrole and Carbon Black

Aqueous dispersions of carbon black were used to electrosynthesize polypyrrole-carbon black composites with the carbon black content ranging from about 10-80 weight percent. These electrocomposites showed enhanced charge storage capacity (relative to pure polypyrrole) and more importantly, retained good electronic conductivity even at potentials wherein the polymer is in the reduced (insulating) state

Structure of carbon black-elastomer composites by small-angle neutron scattering and the method of contrast variation

We have been exploring the use of small-angle neutron scattering and the method of contrast variation to give a new look at very old problem--reinforcement of elastomers by carbon black in durable rubber products. Carbon black has a hierarchy of structures consisting of particles covalently bound into aggregates, which in turn associate by weak interactions into agglomerates. We found that in one carbon black, HSA, the aggregates are rod-like, containing an average of 4-6 particles. The aggregates have another graphitic shell and an inner core of lower density carbon. The core is continuous throughout the carbon black aggregate. Contrast variation of swollen HSA-polyisoprene gels shows that the HSA is completely embedded in polyisoprene and that the agglomerates are formed predominantly by end on associations of the rod-like aggregates. The surface structure of the carbon black appears smooth over length scales above about 10 angstrom. Further studies using production carbon blacks suggest that these structural characteristics are generally present in commercial rubber composites.