CHARACTERIZATION OF THE STRUCTURE AND SURFACE-ACIDITY OF HYDROXYCHROMIUM TAENIOLITES

Hydroxychromium taeniolites were prepared using hydroxychromium soluti ons with a OH/Cr content of about 1 and 2. To study the influence of o xidation on the properties of the synthesized materials, the samples w ere heated in air and, for comparison, in vacuum. Structural character istics were obtained using X-ray diffraction and sorption of nitrogen. The surface chemistry was evaluated using potentiometric titration. T he pK(a) distributions calculated from potentiometric titration data r evealed peaks characteristic of chromium polymers (Cr-III) for the ini tial samples and peaks with a pK(a) corresponding to chromic acid (Cr- VI) for the oxidized samples. In addition, the pK(a) distributions als o provide evidence for inner-sphere complexation of the interlayer Cr with siloxane oxygen. The materials' acidity and structure, obtained f rom X-ray diffraction and sorption of nitrogen, demonstrate that chrom ium species are adsorbed mainly on the external surface of taeniolite and that the properties of the final products depend upon the OH/Cr ra tio of hydroxychromium solutions used in their preparation.