New insight on interfacial charge transfer at graphitic carbon nitride/sodium niobate heterojunction under piezoelectric effect for the generation of reactive oxygen species

Piezocatalytic removal of metronidazole (MET) using graphitic carbon nitride (g-C₃N₄, GCN)/sodium niobate (NaNbO₃) heterojunction was investigated under ultrasonication. Herein, optimized GCN(50)/NaNbO₃ heterojunction achieved 87.2% MET removal within 160 min (k = 0.0138 min^-1). A new pathway for the generation of reactive oxygen species (ROS) via GCN(50)/NaNbO₃ piezocatalytic heterojunction was identified. The type-II heterojunction formulated using optimized GCN(50)/NaNbO₃ was found to generate hydroxyl radical (^.OH); however, it was thermodynamically not feasible. The main reasons are; (i) piezopotential generated converted type-II to S-scheme heterojunction and resulted in the participation of high oxidizing potential holes in valence band (VB) of NaNbO₃, and (ii) formation of depletion region at the GCN-water interface and subsequent improvement in the redox potential of holes, and (iii) piezopotential generated at NaNbO₃ provided bias to GCN and established a piezo-electrocatalytic system. The higher screening of piezopotential in presence of external ions was found to reduce the generation of ^.OH. Overall, self-powered NaNbO₃ has great ability to improve interfacial charge transfer at GCN(50)/NaNbO₃ to form ROS.