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

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 degrees 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 degrees C for 6 h) showed the highest activity, with a photocatalytic H-2-evolution rate of 4.46 mu mol 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 H-2-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.