Exfoliation of layered yttrium hydroxide by rapid expansion of supercritical suspensions

Rapid expansion of supercritical suspensions was used for the first time to push apart the layers in a layered metal hydroxide structure. Treatment with supercritical CO2 resulted in significant changes in interlayer distances in yttrium hydroxide intercalated with dodecyl sulfate anions. According to XRD, SEM, TEM, nitrogen adsorption and IR-spectroscopy measurements, the structure and composition of the layered material depended substantially on the pressure of supercritical CO2. Low pressure treatment (75-200 atm) resulted in a significant increase (by 20%) in the interlayer distance, while higher pressures did not affect the interlayer distance, but increased the specific surface area of the material (from similar to 10 to 74 m(2)/g). Supercritically treated layered yttrium hydroxide exfoliated readily in toluene under ultrasonication. The re-assembly of exfoliated layers upon solvent evaporation was identified using time-resolved XRD. No effect of supercritical CO2 treatment was observed for layered yttrium hydroxide intercalated with nitrate, oleate and stearate anions. (C) 2019 Elsevier B.V. All rights reserved.