Construction of hollow binary oxide heterostructures by Ostwald ripening for superior photoelectrochemical removal of reactive brilliant blue KNR dye

Abstract

Although the Ostwald ripening approach is often utilized to manufacture single hollow metal oxide, constructing hollow binary oxide heterostructures as potent photoelectrochemical (PEC) catalysts is still obscure and challenging. Herein, we reveal a general strategy for fabricating hollow binary oxides heterostructures (Co₃O₄-δ-MnO₂ and Co₃O₄–SnO₂) utilizing Ostwald ripening. Hollow Co₃O₄-δ-MnO₂ nano-network with the structure evolution process was systematically explored through experimental and theoretical tools, identifying the origin of hollow binary oxides due to the interfaces acting as landing sites for their growth. In addition, the structural evolution, from hollow Co₃O₄-δ-MnO₂ to Co₃O₄-α-MnO₂, can be observed when the time of secondary hydrothermal reaches 96 ​h due to the topotactic layer-to-tunnel transition process. Notably, optimized Co₃O₄-δ-MnO₂-48 exhibits a superior PEC degradation efficiency of 96.42% and excellent durability (20,000 ​min) under harsh acid conditions, attributed to the massive hollow structures' vast surface area for high intently active species. Furthermore, density functional theory simulations elucidated the Co₃O₄-δ-MnO₂’ electron-deficient surface and high d-band center (Co₃O₄-δ-MnO₂, -1.06; Co₃O₄-α-MnO_2, -1.49), strengthening the interaction between the catalyst's surface and active species and prolonging the lifetime of active species of •O₂⁻ and ¹O₂. This work not only demonstrates superior PEC degradation efficiency of hollow Co₃O₄-δ-MnO₂ for practical use but also lays the cornerstone for constructing hollow binary oxides heterostructures through Ostwald ripening.