ADSORPTION OF PYRIDINE ON SILICA-GELS

Raman spectra of pyridine adsorbed at silica surface are reported as a function of surface coverage, ranging from a fraction of a monolayer to completely filled pores. It is observed that pyridine is preferentially adsorbed by silica, and it is suggested that the process results in bilayer structure of the interface. The increased concentration of pyridine in silica pores in comparison with the concentration of pyridine in binary mixtures in the reservoir outside of the sample is reported for mixtures with CCl4, CH3NO2, and, to a lesser extent, (CH3)2CO and CHCl3. For mixtures of pyridine with CH3CN, silica preferentially adsorbs acetonitrile, and the final concentration of pyridine is less than that in the reservoir in contact with the sample. This effect is also attributed to the bilayer structure of the interface. The diffusion rate is determined, and it is shown that pyridine diffusion is slower in mixtures with CS2, an inert solvent, and faster in mixtures with acetonitrile, a polar solvent.