Effects of different treatment atmospheres on CeO2/g-C3N4 photocatalytic CO2 reduction: good or bad?

Abstract

Atmospheric treatment of a photocatalyst is of great significance to the activity. In this work, oxidizing, inert and reducing atmospheres were employed to treat CeO₂/g-C₃N₄ photocatalysts, denoted as CeCN, CeCN-N₂, and CeCN-H₂. Interestingly, after N₂ treatment, CeCN-N₂ showed the best photoreduction CO₂ performance, while the poorest activity was observed on CeCN-H₂. The obvious reversal of activities was explored. The H₂ treatment with stronger reducibility resulted in too many defects, and then bulk defects led to the charge recombination and poor CO₂ activation. On the other hand, moderately inert N₂ treatment introduced both the surface oxygen defects of CeO₂ and amino groups in CN heterocycles, which synergistically enhanced the photoinduced electron–hole separating efficiency and medium base sites for the CO₂ activation. Furthermore, a Z-scheme photocatalytic system instead of type II (CeCN) was formed on CeCN-N₂, which was provided with stronger redox, and the generated overpotential was beneficial for CO₂ photoreduction.