An in situ-fabricated p-Co3O4@n-ZnO surface heterojunction photocatalyst for solar-to-fuel conversion of CO2

Abstract

The development of commercially promising ZnO-based photocatalysts for CO₂ reduction without photosensitizers and scavengers has encountered bottlenecks due to low photon utilization and easy recombination of photoexcited electron–hole pairs. Herein, a p-Co₃O₄@n-ZnO surface heterojunction photocatalyst (simplified as Co₃O₄@ZnO), composed of ZnO nanorods surface-synergized with Co₃O₄ nanosheets, has been constructed for efficient CO₂ photoreduction using a facile in situ solution-fabricated approach. The resulting Co₃O₄@ZnO demonstrates a dramatic 36-fold higher catalytic activity (89.26 μmol g⁻¹ h⁻¹) than pristine ZnO (2.44 μmol g⁻¹ h⁻¹) under simulated sunlight, with a long-term durability of 30 h. Various characterizations and finite difference time domain simulations reveal that the formed Co₃O₄@ZnO surface p–n heterojunctions expand the light absorption range, promote the separation of photocarriers, and accelerate the charge transport, thereby benefiting the photocatalytic efficiency and stability. In addition, on the surface of heterojunctions, the accumulated electrons and adsorbed protons further encourage the evolution of CH₄ products, which makes the CH₄ selectivity of Co₃O₄@ZnO (70.5%) far exceed that of pristine ZnO (12.4%). This work provides guidance in the fabrication of efficient and convenient heterojunction photocatalysts for CO₂ conversion into carbon fuels, and is anticipated to promote the popularization and application of ZnO-based photocatalysts.