Spin Probe Study of Acidity of Inorganic Materials

L. S. Molochnikov^a, E. G. Kovaleva^a, E. L. Golovkina^a, I. A. Kirilyuk^b, and I. A. Grigor’ev^b

^a Ural State Forest Technical University, Sibirskii trakt 37, Yekaterinburg, 620100 Russia

^b Vorozhtsov Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. akademika Lavrent’eva 9, Novosibirsk, 630090 Russia

Received August 25, 2006

Abstract—Acidic characteristics of various inorganic materials, such as silica gel, aluminum, and titanium(IV)
oxides, original and modified with F and ions, in the form of hydrogels and nanostructured powders
doped by copper(II) ions, are studied. It is shown that pH values inside pores of the studied sorbents (pH_intr)
differ from the pH of external solutions by 0.5–1.1 units. In the pores of original -Al₂O₃, the pH_intr values are
higher, while, in pores of -Al₂O₃ samples modified with F , as well as nonmodified -Al₂O₃, SiO₂
gel, and TiO₂ hydrogels, pH_intr are lower compared to the pH of the external solution. It is found that pH_intr
decreases, as the content of Cu²⁺ ions in the TiO₂ phase grows, and, beginning with a certain moment, it coin-
cides with pH of an equilibrium solution. The pK_a values of functional group dissociation in some materials are
determined. It is shown that, using spin probes, that is, pH-sensitive nitroxyl radicals, the electrostatic potential
of the surface of nanostructured TiO₂ can be estimated.

DOI: 10.1134/S1061933X07060130

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