Remarkably enhanced catalytic performance in CoO/BiTiO heterostructures for methyl orange degradation via piezocatalysis and piezo-photocatalysis.

A novel heterojunction composite of CoO/BiTiO was synthesized through a combination of molten salt and photodeposition methods. The optimal sample exhibited superior performance in the piezocatalytic degradation of methyl orange (MO) dye with a degradation rate of 1.09 h, which was 2.4 times higher than that of pristine BiTiO. Various characterizations were conducted to reveal the fundamental nature accountable for the outstanding piezocatalytic performance of CoO/BiTiO. The investigation of the band structure indicated that the CoO/BiTiO composite formed a type-I p-n heterojunction structure, with CoO acting as a hole trapper to effectively separate and transfer piezogenerated carriers. Significantly, the MO degradation rate of the best CoO/BiTiO sample further increased to 2.96 h under combined ultrasonic vibration and simulated sunlight. The synergy between piezocatalysis and photocatalysis can be ascribed to the following factors. The photoexcitation process ensures the sufficient generation of charge carriers in the CoO/BiTiO, while the piezoelectric field within BiTiO promotes the separation of electron-hole pairs in the bulk phase. Furthermore, the heterojunction structure between BiTiO and CoO significantly facilitates the surface separation of charge carriers. This increased involvement of free electrons and holes in the reaction leads to a remarkable enhancement in catalytic MO degradation. This work contributes to the understanding of the coupling mechanism between the piezoelectric effect and photocatalysis, and also provides a promising strategy for the development of efficient catalysts for wastewater treatment.