Photocatalytic NO removal activity improved step-by-step through serial multistep Cu modifications.

Previous research has evidenced the insufficient efficiency in 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 turn out to be 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.