ABSTRACT
The overwhelming majority of experimental results that up to the present have been achieved by the NMR method are related to researches into organic substances and water adsorbed on carbon surfaces. Here we can distinguish three main directions of studies: measurements of chemical shifts for adsorbed molecules. determination of their dynamic characteristics (mobility. diffusion coefficient). and investigations of thick layers of a liquid adsorbed on the surface. Each of these directions permits one to characterize certain properties of a material. Thus the chemical shift value makes it possible to evaluate the coordination positions of molecules on carbon surfaces [8-13]. The very first experiments with recording 'H and 19p NMR spectra for toluene and benzene adsorbed on graphitized carbon blacks (Spheron. Graphon. Carbopack) have already shown [8] that such a spectrum may have two signals shifted into a region of strong magnetic fields. The authors of this paper made the assumption that the main causes of the phenomenon observed were the influences of the local magnetic anisotropy of the fused system of benzene rings forming the carbon surface and adsorption on sites of various types. The chemical shift value calculated on the basis of local magnetic field strengths proved to be close to that acquired by experiment. Thus it has been shown that spectral characteristics of signals of adsorbed molecules can be used for identification of the adsorption site structure. These inferences
The present review discusses the results of the I H NMR spectroscopy for a wide range of carbonaceous materials (heat-treated and nongraphitizable activated carbons, carbon blacks, exfoliated and oxidized graphites, porous and amorphous carbonized silicas). This technique made it possible to determine the spectral characteristics of organic molecules with diverse chemical properties, as well as of water molecules adsorbed on the surface. These characteristics are compared with the structural properties of the materials under consideration. The calculations done for the majority of the subjects of inquiry gave the values of their free surface energies in an aqueous medium as well as the characteristics of bound water layers of various types.
