F.P. Dousek

Low temperature electrochemical preparation of carbon with a high surface area from polytetrafluoroethylene

A mixture of carbon and lithium fluoride dispersed on a molecular scale was prepared at a temperature of 100°C by corrosion of polytetrafluoroethylene using lithium amalgam. The corrosion mechanism was found to be electrochemical. Very highly dispersed amorphous carbon having a specific surface area of 3.5−4.0 × 103m2/g could be isolated from the mixture by melting the lithium fluoride particles or dissolving them in water. The surface of the carbon particles is hydrophilic. Adsorption of Ar on them obeys an isotherm of the Langmuir type. No capillary condensation occurred during the adsorption.

Some aspects of existence of elementary carbon with sp-hybridized bonds

Abstract The existence of elementary carbon with sp -hybridized bonds was shown to be impossible if its single chains cannot be retained in a sufficient mutual distance. The course of synthesis of the nuclei of a skeleton from carbon macromolecules in sp state is discussed on the basis of experimental data which characterize the products of reduction of poly(tetrafluoroethylene) (PTFE) with Li-amalgam (WAXS, SAXS, Li-content, densities of reduction products, adsorption measurements). Cubic crystallities of LiF, growing during the reduction from Li + and F − ions to the size of 3.3 nm, were shown as structure-determining elements. A novel polymeric compound of carbon with lithium is formed by PTFE reduction. A structural scheme of this compound, based on narrow monolayer ribbons of six-membered rings, is proposed. Lithium atoms bound to the edge-atoms hinder the extension of the ribbons to a graphite-like sheet. Many physico-chemical properties of the carbon skeleton (nongraphitic state, surface area, adsorption capacity, easy oxidability) can be explained on the basis of the proposed mechanism of its synthesis.

Kinetics of electrochemical corrosion of polytetrafluorethylene by alkali metal amalgams

Abstract Alkali metals contained in amalgams react with polytetrafluorethylene at room temperature. An electrochemical mechanism of the reaction was suggested. A theoretical relation (d l /d t = Kl −1 ) was derived and verified by experiment for the rate of penetration of the reaction into the depth of polytetrafluorethylene. The system alkali metal —polytetrafluorethylene forms a typical corrosion galvanic cell with a solid electrolyte. The electrolyte exhibits selective ionic conductivity for Li + .

Reactivity of polymeric carbon chains reduced from poly(tetrafluoroethylene)

Abstract Electrochemical reduction of poly(tetrafluoroethylene) (Teflon), which contains very long linear carbon atom chains, yields in the presence of Li+ a solid mixture of lithium fluoride and polymeric carbon. The latter is probably in the sp state and is very chemically reactive. Its chains begin to bind into a solid carbon skeleton only after separation from the salt sheaths, so that chemical bonds are formed between certain carbon atoms of neighbouring chains. The form of the skeleton is much influenced by physico-chemical conditions during the separation process. The porous carbon layer consisting from sporadically bound carbon chains was found to be plastic as long as the skeleton does not become more rigid by the formation of additional chemical bonds. Three different carbonaceous materials were prepared from the same mixture (C, LiF) by different technologies. Differences between them were studied by elementary chemical analysis, nitrogen adsorption, wide-angle and small-angle X-ray scattering, and electron microscopy. The obtained results enable to discuss the course of formation of the carbon skeleton.

New carbon adsorbent for high-performance liquid chromatography

Abstract A carbon adsorbent prepared by reduction of poly(tetrafluoroethylene) with alkali-metal amalgams can be used as a mechanically stable packing for high-performance liquid chromatography. Physical properties of the material are presented, and the structure of the particles is discussed. The separations of some aliphatic alcohols, aromatic compounds and isomeric carboranes are used to illustrate the performance of the adsorbent.

Some sorption properties of a new type of active carbon

Abstract The soprtion properties of a new type fo active carbon, prepared by decomposition of polytetrafluoroethylene by lithim amalgam, were tested under chromatographic conditions with various types of adsorbates. It was found that aliphatic hydrocarbons penetrate into the carbon skeleton. The high heats of adsorption for these molecules are the result of very close contact between the adsorbent adn adsorbate. Polar substances exhibit a physical adsorption that can be partialy suppresed by the reation product(LiF crytals) present in the carbon skeleton. This adsorbent was classfied as tupe I adsorbent according to Kiselevs classification.

A PTFE-based carbon adsorbent in high-performance liquid chromatography

Abstract A new type of carbon adsorbent, prepared by reduction of PTFE, was studied and modified with the aim of obtaining a material with a relatively homogeneous, non-polar surface for applications in high-performance liquid chromatography. Three types of sorbent differing in the specific surface area, oxygen remainder and porosity were investigated. The chromatographic behaviour of various solutes, both in non-polar (e.g., pentane) and polar (aqueous buffer) media, has been studied. The plots of natural logarithm of the capacity factor vs. the carbon number were reasonably parallel for a homologous series with different functional groups. The influence of the ionization of some amino acids on their retention over the whole pH range has been shown.

Electrochemical corrosion of polytetrafluorethylene contacting lithium amalgam

Abstract The decomposition of polytetrafluorethylene contacting 0·9 at.% Li-amalgam at ambient temperature is described. The reaction has the character of corrosion penetrating into depth; its course is elucidated on the basis of an electrochemical mechanism. The lithium amalgam functions as anode of a galvanic corrosion cell and polytetrafluorethylene as cathodic depolariser. The operation of the cell results in the formation of a solid electrolyte, a molecular dispersion of carbon and lithium fluoride, possessing electronic as well as ionic conductivity at 20°C.

Structural studies of carbon prepared by electrochemical reduction of polytetrafluoroethylene

Abstract The methods of electron microscopy and X-ray scattering were used in the investigation of the structure of carbon JADO, prepared by the electrochemical reduction of polytetrafluoroethylene, and of the intermediate system C-LiF. The carbon JADO was found to be nongraphitc with a typical nodular morphology. The structure parameters as assessed by both methods were in good agreement and suggested that the carbon ordering in polytetrafluoroethylene did not change substantially during the reduction. The obtained results explained also the abnormally high specific surface area of the carbon. The electrochemical reaction allowed to decompose a bulk polymer into lamellae and to make visible its nodular morphology.

XPS study of carbon in electrochemical reduction products of poly(tetrafluoroethylene)

Abstract XPS spectra of reaction products of poly(tetrafluoroethylene) with lithium amalgam were studied. The primary reaction product is a mixture of LiF and elementary carbon in the sp- state in a molar ratio of 2:1. This carbon is very reactive, among others also with respect to air oxidation at room temperature leading to the formation of surface oxides with a well-defined chemical shift of the C 1s photoemission band, which can be attributed to COOH groups. The binding energy of 1s electrons in C atoms of the basic skeleton hidden in LiF is markedly higher than with other known modifications of carbon. The carbonaceous materials formed by the leaching out of LiF with water, or by the removal of LiF by melting, contain, after air oxidation, various types of surface oxides. The binding energy of C 1s photoelectrons in the resulting skeletons is comparable with that of other carbonaceous materials.