Partly Graphitized AC

Samples of SCA 2000 treated in vacnnm at 2273 K were used in the experiments. The specific surface area of this adsorbent was 360 m /g, and pore volume amounted to 0.56 cmVg. The measurements were carried ont nnder liqnid phase freezing conditions. At T 273 K, water (SAW) in intergrannlar space and in the most large pores froze, and in the H NMR spectrum it was possible to detect signals only for the water molecules bound to the surface. 

It was shown that the appearance of signal 3 depended on the thermal treatment of the material, i.e., on the extent of its local graphitization, rather than on the presence of molecularly adsorbed and chemisorbed oxygen in the adsorbent (Turov et al. 1990). This led to a conclusion that signal 3 was caused by water adsorbed on graphitized areas of the surface. A similar type of the temperature dependence was also found for the following organic compounds frozen in pores of SCA 2000 acetonitrile and 1,2-dichloroethane (Kolychev et al. 1992, Turov et al. 1992). 

To ascertain the relationship between a pore size and a chemical shift of an adsorbate, the following approach was used. Benzene vapors were adsorbed at a low relative pressure p/po=0.1. 

Nuclear Magnetic Resonance Studies of Interfacial Phenomena 

FIGURE 3.55 Temperature-dependent variations of the shape of H NMR spectra for (a) water, (b) acetonitrile, and (c) benzene adsorbed onto partly graphitized activated carbon SCA 2000. 

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