Spin probe study of acidity of inorganic materials

• Published in: Colloid journal of the Russian Academy of Sciences 2007-12, Vol.69 (6), p.769-776
• Main Authors: Molochnikov, L. S., Kovaleva, E. G., Golovkina, E. L., Kirilyuk, I. A., Grigor’ev, I. A.
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Functional groups; Hydrogels; Inorganic materials; Nanostructure; Silica gel; Silicon dioxide; Sorbents; Titanium dioxide; Transitional aluminas
• ISSN: 1061-933X; 1608-3067
• DOI: 10.1134/S1061933X07060130

Acidic characteristics of various inorganic materials, such as silica gel, aluminum, and titanium(IV) oxides, original and modified with F− and SO42− 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 (pHintr) differ from the pH of external solutions by 0.5–1.1 units. In the pores of original γ-Al2O3, the pHintr values are higher, while, in pores of γ-Al2O3 samples modified with F− и SO42−, as well as nonmodified α-Al2O3, SiO2 gel, and TiO2 hydrogels, pHintr are lower compared to the pH of the external solution. It is found that pHintr decreases, as the content of Cu2+ ions in the TiO2 phase grows, and, beginning with a certain moment, it coincides with pH of an equilibrium solution. The pKa 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.