Adsorption of [Al(Urea)(6)](3+) and [Cr(Urea)(6)](3+) complexes in the vermiculite interlayer

This work investigates the interaction between vermiculite and urea metal complexes {[Cr(Urea)(6)](3+) and [AI(Urea)(6)](3+)} via several techniques, including: i) chemical analyses; ii) X-ray diffraction at controlled temperature; iii) microdiffraction on selected crystal areas; iv) thermal analyses and mass spectrometry of evolved species during heating; v) atomic force microscopy; vi) micro-FTIR. Organo-clay complexes were prepared both at room (25 C) and 60 degrees C temperature. Vermiculite treated with [Al(Urea)(6)](3+) showed a complete adsorption of the complex at room temperature, unlike vermiculite treated with [Cr(Urea)(6)](3+) where only a partial exchange was observed. The X-ray investigation evidenced disordered sequences in the layer stacking as common in vermiculite treated with [Al(Urea)6](3+) and [Cr(Urea)(6)](3+) at 60 degrees C. Stacking disorder is present also at room temperature when complexed with [Cr(Urea)(6)](3+) solutions. Microdiffraction investigation identified several domains in vermiculite treated at 60 degrees C. This evidence is also reinforced by FTIR spectroscopy data, which revealed the presence of ammonium isocyanate.