Probing of chemically modified silica surfaces by solvatochromic pyridinium N-phenolate betaine indicators

The state of betaine indicators, 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate and 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate, on the surfaces of aminosilicas, silica modified with aminodiphosphonic acid, and unmodified silica gel is studied with diffuse reflectance spectroscopy. The normalized polarity parameters are calculated for the surface layers of the sorbents. It is revealed that regions with substantially different polarity and acidity are present on the surface of chemically modified silicas.