Exfoliation and Restacking of Lepidocrocite-type Layered Titanates Studied by Small-Angle X-ray Scattering

The exfoliation of the lepidocrocite-type layered titanate K-0.8[Ti1.73Li0.27O4] (KLTO) in aqueous solution and the restacking of exfoliated nanosheets was investigated by small-angle X-ray scattering (SAXS). Suspensions with completely exfoliated titania nanosheets of 1 nm thickness were obtained after protonation of KLTO to HTi1.6O3.7 (HTO), followed by addition of tetrabutyl ammonium hydroxide (TBAOH) to a molar ratio TBAOH/HTO = 1. Restocking of nanosheets into small stacks of 2-4 units occurred at TBAOH/HTO ratios of 1.6 or higher. The separation distance between the sheets was found to be reversible and very sensitive to the pH and ionic strength of the solution and increased up to 12 nm. The experimental data indicate that the separation distance between restocked nanosheets scaled with the Debye length of the solution. This suggests that the stacks are organized via electrostatic interactions due to the presence of a diffuse double layer of positively charged ions between the negatively charged nanosheets.