Facile fabrication of TT-T Nb2O5 heterophase junctions via in situ phase transformation towards enhanced photocatalytic H2-production activity

Abstract

Constructing phase junctions is an effective method to enhance charge separation and transfer in semiconductor photocatalysts, thereby greatly improving the photocatalytic activity. As a well-known candidate, Nb₂O₅ has been widely used in photocatalytic applications. Although Nb₂O₅ has many crystalline phases, the successful preparation of Nb₂O₅ heterophase junctions with improved photocatalytic activity has been rarely reported. In this work, TT-Nb₂O₅/T-Nb₂O₅ (TT-T Nb₂O₅) heterophase junctions were synthesized via a facile in situ phase transformation method using pyrochlore niobic acid (H₄Nb₂O₇) as a precursor. At lower calcination temperatures (400 °C), H₄Nb₂O₇ precursors were first transformed into a hexagonal phase of Nb₂O₅ (TT-Nb₂O₅), and then the hexagonal phase was gradually transformed into an orthorhombic phase of Nb₂O₅ (T-Nb₂O₅) at elevated temperature, resulting in the successful formation of TT-T Nb₂O₅ heterophase junctions. The TT-T Nb₂O₅ heterophase junction obtained under optimized preparation conditions (480 °C for 6 h) showed the highest activity, with a photocatalytic H₂-evolution rate of 4.46 μmol h⁻¹, about 8 times and 60 times higher than those of TT-Nb₂O₅ and T-Nb₂O₅, respectively. The experimental results demonstrated that the formation of heterophase junctions can significantly accelerate the separation and transfer of photogenerated electron–hole pairs caused by the creation of an oriented built-in electric field, thus leading to enhanced photocatalytic H₂-production activity. The rational design of this heterophase junction can be extended to the development of other innovative semiconductor photocatalysts for efficient solar energy conversion.