G. Nansé

XPS study of the halogenation of carbon black—Part 2. Chlorination

Abstract Three furnace carbon blacks, a thermal black, and an electrically conductive sample were submitted as received to chlorination, at 450 °C, with a mix of chlorine and carbon tetrachloride vapors. The treated samples were examined using chemical and spectroscopic (XPS) methods. The interpretation of the XPS spectra is facilitated by comparison with spectra of reference materials. XPS detects various types of carbon-chloride bonds formed essentially by addition or hydrogen substitution processes. The amount of fixed chlorine is dependent on the origin of the blacks, and there is no direct relationship between specific surface area and chlorine uptake. It is shown that chlorination is not limited to the external surface, nor is it to a sub-superficial layer. In fact, it proceeds inside the carbon black particles to a depth depending on their origin.

Fluorination of carbon blacks: An X-ray photoelectron spectroscopy study: I. A literature review of XPS studies of fluorinated carbons. XPS investigation of some reference compounds

Abstract A critical review of the literature relative to the chemical characterisation of fluorinated carbon compounds by X-ray photoelectron spectroscopy is proposed. Guidelines for identification and assignation of the different components which are individualized by fitting of the C 1s and F 1s peaks are given. It is suggested that in fluorocarbons, the chemical shifts of the C and F core levels depend not only on the nature of the CF bond (ionic, semi-ionic or covalent), the number of F atoms linked to the C atom and the chemical environment of the CF group (β effect), but also on the structure and conformation of the C atom skeleton in the fluorinated material. The types of fluorinated structural unit that are formed vary as a function of the conditions of fluorination (temperature, eventual presence of traces of HF or fluoride acting as catalysts) and of the structure and graphitic character on the starting material. Since the experimental values of the binding energy of the different types of CF bonds proposed by the authors differ to a slight extent, some fluorinated polymers and fluorographites of known composition have been analysed by XPS. The binding energies of the components of the C 1s and F 1s peaks, the energy separation ΔCiCr of the former relative to the component (Cr) corresponding to hydrocarbon contamination and the energy separation ΔCiFi between the corresponding components of the C 1s and F 1s peak have been determined and correlated to the nature of the chemical and structural environment of the involved atom.

The characterization of nitrogen-enriched activated carbons by IR, XPS and LSER methods

The aim of this work is to study the efficiency of the nitrogen enrichment by urea of lignites and the induced changes of the adsorptive properties towards volatile organic compounds (VOCs) of the activated carbons derived from these modified precursors. The study is made using infrared and X-ray photoelectrons spectroscopies and the LSER (linear solvation energy relationship) modeling. Four activated lignites derived from the same raw material, original or enriched with nitrogen, are characterized in this way. The effect of the chemical treatment by urea and of the burn-off amount are investigated in term of evolution of the chemistry of the studied materials. The influence of these parameters on the selective behavior of the activated lignites towards two pairs of VOCs is also discussed in terms of molecular interactions using the LSER approach. The results show that the chemical treatment of the raw material is successful, leading to significant enrichment with nitrogen under pyridinic form at the surface of the activated carbons. Moreover, they reveal some selective properties well explained by the LSER analysis and spectroscopic measurements. The selective character of the studied materials is modulated by the duration of the activation step.

Fluorination of carbon blacks: an X-ray photoelectron spectroscopy study: IV. Reactivity of different carbon blacks in CF4 radiofrequency plasma

Abstract The effect of CF 4 -plasma enhanced fluorination on the surface modification of carbon blacks has been examined using XPS. Three different types of carbon blacks have been studied: a thermal black, a furnace black and a high electrical conducting black. The analysis of the XPS spectra of fluorinated carbon black samples indicates that all fluorine atoms, fixed at the surface and in a subsuperficial zone of the particles, are covalently linked to carbon atoms. The influence of the physicochemical properties and morphology of these three types of carbon blacks on the fluorination reaction has also been investigated. The proportion of different types of fluorinated carbon atoms, i.e. on one hand CF x surface and border groups of graphitic bulk domains for which the planar configuration of the graphene layers is preserved together with the sp 2 character of C, i.e. structures of type I, on the other hand polyalicyclic perfluorinated structures in which sp 3 C form puckered layers similar to those of covalent fluorographites, i.e. structures of type II, and also the F/C ratio of the fluorinated groups are related to the surface morphology and depend on the microstructural organization of particles. When the microstructure ordering and graphitic character of the carbon increase, the size of the ordered graphitic domain also increases. At the same time the density, the size of defects and proportion of protonated sp 3 C entities bridging the graphene layers decrease. As a consequence, the proportion of carbon atoms, potentially able to form perfluorinated CF 2 and CF 3 groups, decreases. The relative contribution of those groups is appreciably higher in fluorinated compounds which are derived from carbon blacks with a lower structural order.

Fluorination of carbon blacks: An X-ray photoelectron spectroscopy study: III. Fluorination of different carbon blacks with gaseous fluorine at temperatures below 100 °C influence of the morphology, structure and physico-chemical characteristics of the carbon black on the fluorine fixation

Abstract Furnace, thermal and a high electrical conductive blacks were submitted to fluorination at room temperature using a gaseous mix of fluorine and nitrogen. The weight uptake of the samples and their elemental composition were determined and compared to the composition of the outer surface and subsuperficial zone of the particles as determined by XPS. Analysis of the XPS spectra indicates that F is merrily fixed at the surface and in a subsuperficial layer of limited thickness and covalently bonded to C. In the furnace blacks, a minor amount of F2 is trapped in micropores. When the blacks are activated (air oxidation at 450 °C), the amount of fluorine fixed by the furnace and thermal blacks increases due to a slight increase of the density of reactive sites consecutively to the development of porosity. The high conductive black, made of empty carbon shells shows a peculiar behavior as the activation does not lead to an augmentation of the F fixation.

Fluorinated carbon blacks: influence of the morphology of the starting material on the fluorination mechanism

Abstract The effect of fluorination, using CF4 r.f. plasmas, has been studied on three different types of carbon blacks: a thermal black, a furnace black and a high electrical conducting black. The influences of the morphology and structure of the three blacks on the fluorination mechanism have been investigated. In particular, the ratio Type I/Type II structures (i.e., surface (CF) and border groups of graphitic domains with sp2C/polyalicyclic perfluorinated structures with sp3C), has been correlated to the microstructural organisation. The transformation into Type II structures is more easily achieved in highly accessible XE2 blacks, whereas in materials with lower crystallinity (MT), the presence of numerous defects leads preferentially to surface (CFx) perfluorinated groups.

Adsorption of poly(methylmethacrylate) on an α alumina: evidence of formation of surface carboxylate bonds

Abstract Irreversible fixation of poly(methylmethacrylate) (PMMA) on the surface of non-porous alumina was examined by FTIR, XPS and NMR spectroscopies. The hydrolysis of side ester groups of PMMA is evidenced: PMMA bonds strongly to the alumina surface through ionic carboxylate groups.

Characterization of surface properties of nitrogen-enriched activated lignites by spectroscopic and chromatographic coupled with LSER modelling measurements

One investigated way to prepare selective adsorbents towards mixtures of volatile organic compounds (VOCs) is to modify lignite by nitrogen-enrichment. These chemically modified coals are prepared by condensation of urea with the lignite before the carbonization/activation steps. This study describes a set of analytical tools able to explain in term of surface composition and of quantitative molecular interaction parameters the evolution of the selective behavior of three adsorbents. For this purpose, the evolution of the surface chemistry and the selectivity with three percentage of burn-off of a nitrogen-enriched lignite is followed by infrared and X-ray photoelectron spectroscopies and gas chromatography (GC)/linear solvation energy relationship (LSER) method. Then, the selectivity of these materials towards two test-pairs of VOCs is discussed. This QSBR investigation reveals the complementarity of these methods linking composition data of the active carbons and their selective properties.