Intercalation of dyes in layered zirconium phosphates.: 1.: Preparation and spectroscopic characterization of α-zirconium phosphate crystal violet compounds

The intercalation of crystal violet (CV+) into the ethanol form of a-zirconium phosphate has been investigated. X-ray powder diffraction patterns of samples with increasing dye loading showed that a pure phase (interlayer distance 2.2 nm) was obtained at a dye loading of 22% of the maximum ion-exchange capacity. Computer models and calculations based on dye dimensions and the structure of the host showed that this phase possesses dye loading and an interlayer distance very near to the maximum values, i.e., about 25% and 2.14 nm, respectively, that can be obtained if the crystal violet is intercalated as a monolayer of dye cations placed perpendicular to the inorganic layers of the host. The decrease of the interlayer distance to 1.8 nm with drying was attributed to a change on the inclination of dye molecules inside the interlayer space after the solvent is eliminated. The absorption spectra measured by diffuse reflectance spectroscopy showed maxima around 430 and 640 nm due to the protonation of the dye by the acidic P-OH groups of alpha-zirconium phosphate, exhibiting pK values in the range from similar to 0 (430 nm) to similar to 1 (640 nm). The dye-dye interaction in the perpendicular orientation caused absorption around 510 nm assigned to stacked (CV+)(n) layers.