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

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.