In-Depth Investigation of the Mechanism of Dehydration-Induced Phase Transformation from Nb3O7(OH) to H-Nb2O5: A Theoretical and Experimental Approach.

ABSTRACT

H-Nb2O5 is a promising energy material, which can be typically obtained from any other polymorph after conducting high temperature calcination (∼1273 K). Recently, a low-temperature dehydration from Nb3O7(OH) was employed to prepare H-Nb2O5 at 723 K for 2 h, and yet the transformation mechanism has remained unclear in the literature. Here, the dehydration kinetic and phase transformation mechanism of the Nb3O7(OH) were investigated for the first time by experiments, density functional theory, and molecular dynamics calculations. After dehydration, the orthorhombic Nb3O7(OH) initially transformed into an intermediate Nb-O compound with dislocations, preserving parent structure, and subsequently transformed into monoclinic H-Nb2O5. The activation energy for the transformation from Nb3O7(OH) to H-Nb2O5 was as low as 1.35 eV, compared to that of T-Nb2O5 to H-Nb2O5 (3.60 eV). Furthermore, the defect-rich H-Nb2O5 obtained from Nb3O7(OH), does not exhibit pristine bound exciton state due to severe recombination of photogenerated carriers, resulting in poor photocatalytic activity.