Exfoliated HNb3O8 nanosheets of enhanced acidity prepared by efficient contact of K2CO3 with Nb2O5

Abstract

Although exfoliated HNb3O8 nanosheet (e-HNb3O8) is known to be a powerful catalyst in acid-catalyzed reactions, the preparation technique has limitations in its high-yield production. We herein report the enhanced exfoliation efficiency and recovery of e-HNb3O8 by contacting Nb2O5 solid with a diluted K2CO3 solution before ball milling (mechanochemical activation). The so-obtained e-HNb3O8 showed a larger specific surface area, a higher density of total acid sites and an improved catalytic performance in the dehydration of 2-heptanol and formic acid, compared to the corresponding sample prepared by the conventional solid-state mixing. The ball-milled K2CO3–Nb2O5 mixtures, layered KNb3O8, ion-exchanged HNb3O8 and exfoliated HNb3O8 samples were characterized by PXRD, TEM-EDS, TGA-MS and SEM-EDS. The characterization results revealed more intercalated K+ ions in KNb3O8 particles as well as more homogeneous K2CO3–Nb2O5 mixture when the employed preparation technique was used. This is achieved by more infiltration of K2CO3 into Nb2O5 lattice before ball milling, thereby resulting in the above positive findings. Therefore, our approach has great potential to be extended to other niobate-containing nanosheet-type materials.