Highly efficient photocatalytic conversion of CO(2) into solid CO using H(2) O as a reductant over Ag-modified ZnGa(2)O(4)

Abstract

Highly crystalline spinel phase ZnGa(2)O(4) modified with a Ag cocatalyst exhibited high activity and selectivity toward CO evolution in the photocatalytic conversion of CO(2) using H(2)O as a reductant under UV light irradiation. The stoichiometric evolution of CO, H(2), and O(2) clearly indicated that H(2)O worked as an electron donor for the photoreduction of CO(2). Highly crystalline ZnGa(2)O(4) was synthesized by a solid-state reaction method at a calcination temperature as low as 973 K. Upon optimizing the fabrication conditions, such as calcination temperature and duration, the photocatalytic activity of ZnGa(2)O(4) was maximized because of the optimum balance between crystallinity and surface area in the catalyst material. Furthermore, the formation of metallic Ag particles with different sizes and dispersions on the surface of ZnGa(2)O(4) influenced the evolution of CO. When Ag nanoparticles were loaded onto the ZnGa(2)O(4) calcined at 1123 K for 40 h using a chemical reduction method, the highest formation rates of CO, H(2), and O(2) (155, 8.5, and 74.3 μmol h[−1], respectively) were obtained, and the selectivity toward CO evolution reached 95.0%. An isotope-labeling experiment using [13]CO(2) confirmed that the origin of the evolved CO was not from organic contamination but from the CO(2) gas introduced during the reaction process.