Heterophase structure of ZnSnO3 (rhombohedral and orthorhombic) for efficient dye degradation and N2-to-NH3 conversion via piezocatalysis and piezo-photocatalysis

Abstract

Fabricating heterophase junctions proves to be an efficient strategy for achieving efficient charge separation and enhancing the catalytic activity of photocatalysts. Surprisingly, this approach is rarely utilized in the field of piezocatalysis. In this work, a novel ZnSnO3 heterophase junction catalyst was fabricated by combining rhombohedral (R-ZnSnO3) and orthorhombic (O-ZnSnO3) phases for efficient piezo and piezo-photocatalytic RhB degradation and N2 fixation. The piezocatalytic RhB degradation rates of ZnSnO3 heterophase catalysts are 5.6 and 3.6 times higher than those of O-ZnSnO3 and R-ZnSnO3, respectively, with similar enhancements observed in piezocatalytic N2 fixation. The coupling of R-ZnSnO3 and O-ZnSnO3 does not increase the piezoelectric properties; however, an S-scheme structure formed at the interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and achieve effective spatial separation. This result supports the energy band theory over the induction charge theory, contributing to the ongoing debate in piezocatalytic mechanisms. Electrochemical analyses and piezo-photocatalytic tests further indicate that ZnSnO3 heterophase junctions exhibit a synergistic effect between piezocatalysis and photocatalysis. This synergy can be attributed to the complementary effects of photoinduced carrier generation and piezoelectric field-assisted carrier separation. Hydroxyl radicals, superoxide radicals, and holes serve as the primary active species responsible for piezocatalytic RhB degradation through a mechanism similar to photocatalysis. Theoretical calculations reveal that the Sn site on the surface of O-ZnSnO3 acts as the active site within the ZnSnO3 heterophase junction, providing valuable insights for future catalyst development. This work offers a deeper understanding of the synergistic mechanisms in piezo-photocatalysis, presenting a promising route for efficient environmental and energy applications.