Construction of Highly Active and Selective Polydopamine Modified Hollow ZnO/Co3O4 p‑n Heterojunction Catalyst for Photocatalytic CO2 Reduction

The facile synthesis of low-cost, eco-friendly photocatalysts with high charge separation efficiency and CO2 adsorption capacity for efficient photocatalytic CO2 reduction remains a challenge. Herein, a hollow structured p-n heterojunction catalyst, polydopamine (PDA)-ZnO/Co3O4, was successfully synthesized by pyrolyzing bimetallic ZnCo-ZIFs, followed by modification with PDA. Through optimizing the Zn/Co ratio, a high separation efficiency of the photogenerated electron–hole pairs has been achieved. Furthermore, by tuning the content of PDA on the surface of ZnO/Co3O4, the adsorption capacity of CO2 can be maximized. Consequently, PDA15/ZnO/Co3O4 showed a CO production rate of 537.5 μmol/g/h with a CO selectivity of 97.7% without using the photosensitizer and additional sacrificial agent. Band structure based on results of X-ray photoelectron spectroscopy, photoelectrochemical characterization, as well as density functional theory calculation was used to propose a plausible mechanism for photocatalytic CO2 reduction on the PDA15/ZnO/Co3O4. The present study provides an effective approach to fabricate highly efficient photocatalysts based on semiconducting metal oxides for CO2 reduction with remarkable abilities of absorbing lights, separating charge carriers, and adsorbing CO2.