Photocatalytic Nitrogen Oxide Removal Activity Improved Step-by-Step through Serial Multistep Cu Modifications

Previous research has evidenced the insufficient efficiency in a one-step modified photocatalyst for NO removal. In this article, a serial multistep modification was explored to improve the NO removal activity of g-C₃N₄. In the experiment, a g-C₃N₄ photocatalyst has been successfully modified by Cu elements three times on one continuous process. Meanwhile, results showed that the serial multistep modifications could improve NO removal activity by g-C₃N₄ step by step. The main active species in the g-C₃N₄ system were h⁺ and ^•O₂^– but they were h⁺ and ^•OH in the three-modified g-C₃N₄ systems. Moreover, different mechanisms of activity improvement caused by the modified Cu in the serial-modified samples were identified. In the first modified sample, Cu²⁺ can decompose H₂O₂ molecules into ^•OH via a Fenton-like reaction. In the second modified sample, the H₂O₂ molecule is activated by Cu⁰ and decomposed into ^•OH by the generated photoelectrons. After the third modification, the synergistic effects of the N vacancy and Cu⁰ were identified, which significantly enhanced the photocatalytic NO removal activity of g-C₃N₄. This study proposed that the serial multistep modification can be a promising method to improve the NO removal activity of g-C₃N₄ stage-by-stage.