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 [Al(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 °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 °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 °C. This evidence is also reinforced by FTIR spectroscopy data, which revealed the presence of ammonium isocyanate.