Room‐temperature electrosynthesis of carbonaceous fibers

Abstract

Communications self-assembled thin films were fabricated by an electrostatic deposition technique similar to that described by Decher[2]; Rubner [3], and others [9]. The polymer films consist of alternating layers of a cationic poly(p-pyridiniuin vinylene) (PHPyV or Bu-PHPyV) and anionic sulfonated polyaniline (SPANI) or poly(4-styrene sulfonate) (PSS). Films are grown by first initiating ITO-coated glass substrates with positive charges. This initiation is carried out by treating the ITO-coated glass with (3-aminopropyl)triethoxysilane[7] or by depositing a thin film of polypyrrole or polyaniline directly on the substrate[3b]. In the latter case, the thickiicss of the conducting polymer film was limited to keep the total optical density of the resulting substrate below 0.1 in the visible part of the spectrum. The assembly ofthe multilayer polymer film on the cationicsubstrate was carried out by sequentially dipping the substrate into each polymer solution (alternating between anionic and cationic). Dipping time in each solution was 30 minutes. After each dip, the film was rinsed with water (for PSS or SPANI) or THF-acetone (for Bu-PHPyV) or m-cresol-acetonitrile (for PHPyV) and dried under nitrogen flow before the next deposition.The LEDs were fiiiishcd by vacuum depositing an aluminum electrode on top of the organic film. The base pressure of the chamber was mbar and the evaporating pressure was 10-' mbar The thickness of the electrode was ca.1000 a and the area of the electrode was 1 mm2. The I-Vcharacteristics of the devices were measured on an H P 414BB analyzer and the electroluminescent spectra were collected using ail EG & G nionochromator and Electriin 1000 TE CCD camera. The light intensity was detected by a calibrated broad-area silicon photodiode. ahose photocurrent was measured by H P picoampere meters.The electronic absorption spectra weremeasured on an AVIV Spectrophotometer model 14DS (modified Cary-14) and the photoluminescence spectra were taken with a Perkin-Elmer LS-50 Luminescence Spectrometer. The excitation wavelengths used were thc maximum absorption wavelengths in the electronic absorption spectra. PSS is tiansparent at both the excitation and emission wavelengths, while polypyrrole, polyaniline and SPANI have very low optical densities at these wavelengths in the samples prepared here. Photoluminescence quantum yields of Bu-PPyV and Bu-PHPyV were measured in degassed T H F solutions. typically M (based on the monomer repeat unit). The Bu-PH-PyV was made by adding stoichiometric amount methane sulfonic acid to the Bu-PPyV solution. Rhodamine B in ethanol was used as a reference (u, = 1) [11].The excitation wavelengths for the polymer solutions and Rhodamine B were 420 nm and 530 nm. respectively. The photoluminescent quantum yield of Bu-PPyV is greater than 0.9, and the quantum yield of Bu-PHPyV is ca. 0.8. M R 9357415. The authors wish to thank Victor Gruol for assistmce with the XPS measurements, and Andrew Gewirth (University of Illinois) for generous donation of the HOPG substrate. ...

Electrochemical Carbon

“…105 Analogously, photoreduction of CCl 4 on illuminated TiO 2 yields carbene, :CCl 2 , and • CCl 3 radical, which may be further hydrolyzed to CO, CO 2 , and HCl. 120 Sailor et al 42 have reported reduction of CCl 4 to "carbonaceous fibers" at Ni, Cu, Ag, Pt, and Fe cathodes in acetonitrile or dichloromethane solutions of NBu 4 BF 4 (Bu ) n-butyl) or bis(triphenylphosphoranylidene)ammonium chloride. The product was not pure elemental carbon; it contained residual chlorine and encapsulated solvent molecules.…”

“…Incomplete carbonization, impurities (adsorbed solvents), and n-doping (NR 4 + insertion) are also detectable. 34,35,39,42,64,65,225 Alternatively, surface oxides and impurities are observed by XPS. 46,47,65,177,179,[205][206][207]209,244,257,273 Problems with impurities and incomplete carbonization are avoided in the Raman spectra of C-MF (M ) Li, Na, K), studied in situ by Kuzmany et al 44,45,309 The spectral assignment in the region of the carbon skeleton is difficult, except for the characteristic CtC stretching vibration 29,34,35,64,65,225 at 2000-2200 cm -1 .…”

“…However, the redox carbonizations are often slow and complicated by side reactions. Many important processes are based on reductive carbonizations, in which typical precursors are perhalogenated hydrocarbons. , Table surveys some examples of electrochemical carbonization processes ,− which will be further discussed in detail below. This paper updates a previous review of electrochemical carbonization of fluoropolymers, while a special attention is paid to other carbon precursors, and papers published during 1991 to mid-1997.…”

Selective Synthesis of Graphitic Carbon and Polyacetylene by Electrochemical Reduction of Halogenated Carbons in Ionic Liquid at Room Temperature

“…For example, Herrick and co-workers reported that carbonaceous fibers can be synthesized in high yield by the galvanostatic deposition of CCl 4 in acetonitrile onto a metal substrate at room temperature [15]. The reduction of other halogenated carbon molecules, such as poly(tetrafluoroethylene), hexachlorobuta-1,3-diene and diiodoacetylene, has also resulted in the production of graphitic carbon films [16,17].…”

Room-Temperature Growth of Carbon Nanofibers

“…[4] For the latter technique, temperature regimes on the order of 600-1000 °C are most common, with a few recent reports citing lower temperatures using halogenated precursors, [5,6,7] or through alkali-metal catalyzed transformation of bulk carbon allotropes. [8,9] Sailor et al have reported the first growth of non-amorphous carbon deposits at room temperature. [10] However, their electrochemical synthesis did not produce nanostructural carbon; due to the absence of nanosized catalytic seeds, the diameters of their fibers were > 5µm, and contained copious amounts of Cl, H, N, and O impurities.…”