Gentle, Spontaneous Delamination of Layered Titanate Yielding New Types of Lithium Titanate Nanosheets

Abstract

Lepidocrocite-type layered titanate (K 0.8 Ti 1.73 Li 0.27 O 4 ) typically is delaminated in a two-step process, where first K + is exchanged for protons (H 1.07 Ti 1.73 O 4 •H 2 O) followed by deprotonation of the solid acid by tetraalkylammonium hydroxide upon which delamination sets in producing titanate nanosheets. Unfortunately, the harsh acidic conditions during proton exchange concomitantly leach all structural lithium and the obtained nanosheets (Ti 0.87 O 2 0.52− ) suffer from substantial structural defects. Here, we propose a one-step delamination of the pristine K-titanate, where the K + is directly exchanged by a bulky, hydrophilic organocation (N-methyl-D-glucammonium, Meg + ) that spontaneously delaminates in deionized water into titanate nanosheets without any significant loss of structural lithium. The new procedure not only saves one conversion step but also preserves the structural lithium, and moreover, the delamination itself seems to be gentler as indicated by larger aspect ratios of the resulting nanosheets obtained. Starting with the same pristine K-titanate, the established two-step delamination applying tetrabutylammonium hydroxide gave a d 50 diameter of 3 μm, while direct delamination applying Meg + yielded a substantially higher d 50 diameter of 19 μm. The Meg + delamination thus yields lithium titanate nanosheets of high aspect ratio of ≈20,000 in a high yield of ≈99% establishing the suggested procedure to be a highly attractive alternative to the established protocol, while giving access to hitherto unknown types of titanate nanosheets, in which pristine structural lithium ions are preserved.