Supercritical N,N-dimethylformamide exfoliation of the layered bulk titanate material into titania nanosheets

Titania nanosheets with {0 0 1} facets were produced by the supercritical N,N-dimethylformamide (SC-DMF) fluid exfoliation of the layered bulk titanate material. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) showed the starting titanate crystals with layered structure; SEM, atomic force microscopy (AFM) and transmission electron micrographs (TEM) demonstrated the obtained two-dimensional nanosheets with a thickness of 1.3 nm around and lateral dimensions of several microns; ultraviolet–visible (UV–vis) spectroscopy characterized the optic properties of the nanosheets with uniformity and the disassembly of layered structure. Absorbance peak is centered at 301 nm and the molar extinction coefficient is 1.01 × 102 mol−1 dm3 cm−1; thermogravimetric analysis (TGA) of the sediments revealed that the weight loss in the case of ice-cold water cooling was the least. The course of the SCF exfoliation was explained to be rapid intercalation and swollen exfoliation by thermal stress. Restacking of exfoliated nanosheets was shown by the in situ XRD technique, and ratios of the obtained single layers in the working conditions of furnace cooling, air cooling and ice-cold water cooling are increased up to 7.8%.