Dispersant-dependent Exfoliation Behavior of Pristine HLaNb2O7·xH2O Layered Perovskite and Its n-Propoxy Derivative in Aspects of Polarity and Hydrolysis Phenomena.

Abstract

The exfoliation efficiency of pristine HLaNb2O7·xH2O (HLN) layered perovskite and its n-propoxy derivative (Pro-LN) by ultrasonication was thoroughly investigated by utilizing H2O and 2-butanone as dispersants. Exfoliation efficiencies of 52 and 33% were achieved for Pro-LN in H2O and 2-butanone, respectively. In contrast, HLN showed an exfoliation efficiency of 18% in H2O, while no exfoliation occurred in 2-butanone. Pro-LN demonstrated a higher exfoliation efficiency than HLN in H2O, exhibiting a decrease in organic loading from 0.958 to 0.601 per [LaNb2O7] unit during exfoliation. This indicates that Pro-LN underwent a hydrolysis process to generate nanosheets with a sufficient number of hydroxyl groups joining the remaining n-propoxy groups, unlike nanosheets obtained from HLN bearing hydroxyl groups only. Since 2-butanone exhibits a lower polarity, it interacted effectively with the hydrophobic nanosheet surfaces bearing n-propoxy groups, while nanosheets possessing hydroxyl groups formed hydrogen bonds with H2O during exfoliation. H2O was found to achieve higher exfoliation efficiency compared to low-polarity 2-butanone for both materials. This study elucidates the crucial importance of the surface chemistry and interactions with dispersants for improving exfoliation efficiency of layered perovskites. In addition, it provides a novel approach to obtaining nanosheets bearing M-OH groups from layered perovskites by hydrolyzing grafted n-alkoxy groups.