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Metal-semiconductor piezo-photocatalysts are generally investigated due to their high photocatalytic performances by the coupling effect of piezotronics and localized surface plasmon resonance (LSPR). However, the mechanism is still indistinct, even the charge migration route is disputable. Here, the electron migration from Ag to BaTiO3 has been confirmed by electron spin resonance (ESR) and radical trapping experiments. Furthermore, this work first proposes that piezoelectric field can promote the photocatalytic properties through electrical modulation of plasmon-exciton interaction. To exactly reveal the mechanism, the piezo-photocatalysis process is fully simulated by numerical analysis and finite element method (FEM). The unabridged mechanism of piezotronics boosted photocatalysis of LSPR-BaTiO3 shows that piezoelectric field can modulate LSPR to generate more hot electrons, suppress Schottky barrier for improved hot electron injection from Ag to BaTiO3 and restrain the recombination of electron–hole pairs by spatial separation of opposite charges.

Highlights • ZnO/ZnS nanostructures with type-II heterojunction are successfully synthesized. • Heterojunction nanotube exhibits better sonophotocatalysis than nanorod. • Effect of morphology on piezoelectric is experimentally and simulatively studied. • Morphology engineering can affect sonophotocatalysis through turning piezoelectric., Sonophotocatalysis is one of the most significant outcomes of the exploration of the interaction between piezoelectric field and charge carriers, which exhibits potential applications in dye degradation, water splitting, and sterilization. Although several heterojunction catalysts have been applied to improve the sonophotocatalytic capability, the importance of the morphology on the sonophotocatalytic capability has not been emphasized. In this study, brush-like ZnO nanorod arrays are synthesized on a stainless-steel mesh and subsequently vulcanized into ZnO/ZnS core–shell nanorod arrays to investigate the sonophotocatalytic capability of the heterojunction. The sonophotocatalytic capability increases from 25.1% to 45.4% through vulcanization. Afterward, the ZnO/ZnS nanorods are etched to ZnO/ZnS nanotubes without affecting the crystallography and distribution of the ZnS nanoparticle shell, further improving the capability to 63.3%. The improvement can be ascribed to the coupling effect of the enhanced piezoelectric field and the reduced migration distance, which suppresses the recombination of photoexcited electron–hole pairs while transforming the morphology from nanorod to nanotube, as proven by the electron spin resonance test and numerical simulations. This study explores a novel approach of morphology engineering for enhancing the sonophotocatalytic capability of heterojunction nanoarrays.

The recombination of photogenerated charge carriers hinder the application of photocatalyst. In this study, ternary piezoelectric photocatalyst consisting of ZnO, ZnS and MoS2 nanostructures has been synthesized by a two-step hydrothermal method, which exhibits excellent piezo-photocatalytic efficiency while degrading methylene blue (MB). The piezo-photocatalytic degradation efficiency of MB is ~2.5 times of that without piezoelectricity. Moreover, the ZnO/ZnS/MoS2 nanocomposites exhibit good piezo-photocatalytic stability; after 5 cycles, the efficiency remains at ~80% of the initial value. This mechanism can be attributed to the coupling effect of piezoelectricity, photocatalysis and dual heterojunctions, as verified by ESR and diagrammed by band energy structure.

Direct Z-scheme heterojunction of ZnO/MoS2 nanoarray on Ni foam has been realized by flowing induced piezoelectric field for enhanced sunlight photocatalytic performances. The porous structure of Ni substrate can effectively induce applied deformation on nanorod arrays and generate built-in piezoelectric field by water flowing. Under sunlight irradiation for 50 min, the photocatalytic degradation efficiency of methyl orange is 50.6 %, and the degradation efficiency rapidly increases to 92.7 % under stirring-sunlight irradiation. The degradation rate increases with increasing stirring speed along an S-shaped relationship. In addition, the heterojunction photocatalyst also performs good repeatability in aqueous solution and even in alkaline solution. The role and amount of active radicals are investigated by radical scavenger experiments and electron spin resonance technique, indicating that only the amount of ∙ O H radicals can be significantly increased by flowing induced piezoelectric field. This interesting phenomenon can be attributed to that piezoelectric field converts Ⅱ-type heterojunction into Z-scheme configuration.