Enhanced solar-driven carbon dioxide conversion by defect-engineered double p-n heterojunction dodecahedrons with controllable internal structure.

The enhancement of CO2 photoreduction performance is greatly limited by the inefficient separation and inadequate directional transport of photogenerated charge carriers. The traditional binary heterojunctions can to some extent address the aforementioned issues, but there is still room for improvement and further demand. Herein, this study employs zeolitic imidazolate framework-8 (ZIF-8) as a precursor to fabricate double p-n heterojunction ZnO@ZnWO4-CoWO4 dodecahedrons via the sequential steps of surface coating with zeolitic imidazolate framework-67 (ZIF-67) WO42- etching, and final calcination. The internal structure of ZnO@ZnWO4-CoWO4 dodecahedrons can optionally be a double-shell hollow structure or a single-shell hollow structure by changing WO42- etching time. The generated Zn-vacancy-associated defect-engineered double p-n heterojunction configuration generates multiple built-in electric fields at the heterointerfaces, thereby driving the effective spatial charge separation and directed migration of photoexcited carriers more effectively and improving charge transport efficiency. The unique double-shell hollow mesoporous dodecahedrons with Zn-vacancies provide abundant sites for CO2 capture and conversion, while also boosting light harvesting. As expected, the optimized ZnO@ZnWO4-CoWO4 double-shell hollow dodecahedrons exhibit markedly higher CO and CH4 production rates compared with control materials. In situ diffuse reflectance infrared Fourier transform spectroscopy further identifies the reaction intermediates, indicating the easier generation of carbon-based intermediates during CO2 photoreduction process. This finding aligns with the experimental observation that CO is the dominant product. Our work provides an effective, and scalable strategy for designing multi-component heterostructure photocatalysts derived from metal-organic frameworks.