Specific and non-specific interactions on non-porous carbon black surfaces

Abstract

The interactions which occur between methanol, ethanol or propanol and the surfaces of non-porous carbon blacks with increasin levels of oxygen chemistry have been studied using adsorption isotherm analysis and immersion calorimetry. Surface oxygen has bee controlled by ozone treatment and characterised using X-ray photoelectron spectroscopy, which gives a direct and quantitative measur of surface composition from first-principles, and has not yet been extensively employed in detailed carbon adsorption studies. Nitroge adsorption at 77 K and heat of immersion hi (mJ m ) data for toluene, show that the physical structure of the carbon blacks is no modified by ozone treatment. A systematic shift to higher adsorption values, due to increasing specific hydrogen bonding interaction between the alcohol –OH groups and surface oxygen, is observed in all of the alcohol isotherms as the total oxygen content of the carbo surfaces ([O]T/at.%) increases. This effect is most significant for methanol confirming that the mechanism of adsorption is dominated b hydrogen bonding and therefore dependant on the surface concentration of oxygen sites. It is also observed for ethanol and propanol bu is less marked due to the increasing non-specific, dispersion, interactions of the alkyl chain with the non-polar carbon surface. Th description is in agreement with the data obtained for the specific enthalpies of immersion hi (mJ m ) into the alcohols and into wate or toluene which allow a semi-quantitative assessment off the relative polar and dispersion contributions to the overall interactions a functions of both carbon surface oxygen composition and the molecular structure of the alcohols. An overall correlation is observe between adsorption behaviour, [O]T/at.%, the resulting hi values and the characteristic energy E (kJ mol ) of the DRK equation It is also observed that the values of the affinity coefficient bDRK increase directly as a function of [O]T indicating that this latter param eter may provide a basis for predicting the adsorption isotherms of certain polar vapours on non-porous carbon surfaces. The effects o carbon surface chemistry on the character of adsorption isotherms, which change from Type III for the base N330 (and for a graphitize carbon black N234G) to Type II for the oxidised N330 materials, is discussed and the resulting effects on the surface area parameter SDRK and SBET (m 2 g ) are considered.

9 Figures and Tables

Cite this paper

@inproceedings{Andreu2007SpecificAN, title={Specific and non-specific interactions on non-porous carbon black surfaces}, author={Aja Andreu and H. F. Stoeckli}, year={2007} }