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Stirring-promoted piezo-photocatalysis based on a three-dimensional foam architecture has great potential applications in wastewater treatment and water splitting. However, the detailed mechanism of stirring-promoted piezo-photocatalysis has not been quantitatively studied, and the utilization of visible light needs to be further improved. In this work, the high solar-driven piezo-photocatalytic ability of graphite carbon nitride (g-C

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.

Constructing heterojunction is a promising approach to enhance the piezo-photocatalytic performance of ZnO nanostructures. In this study, ZnO/ZnS heterojunction nanoarrays have been synthesized by facile vulcanizing surface of wurtzite ZnO nanorods into blende ZnS nanoparticles through hydrothermal method. Both the synthesized wurtzite ZnO nanorods and blende ZnS nanoparticles are piezoelectric semiconductors with wide band gaps. For degrading methyl blue solution under UV irradiation and ultrasonic sonication, it is found that both the piezocatalytic, photocatalytic and piezo-photocatalytic performances of ZnO/ZnS nanoarrays are much higher than those of pure ZnO. In addition, the piezo-photocatalytic degradation rate of ZnO/ZnS nanoarrays can be further increased by improving the ultrasonic power. The mechanism can be attributed to the synergetic effect of piezoelectric effect and heterojunction photocatalysis.

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.