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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.

Graphite carbon nitride (g-C3N4) has been proven to have photocatalytic activity for NO-removal under visible-light irradiation. However, the competitive adsorption between NO and O2 during the process may decrease the...

Highly efficient and stable photocatalysts were synthesized at room temperature by modifying MIL-125(Ti) with N-doped carbon quantum dots (N/CM(Ti)). The N/ CM(Ti) with 2.5 vol % N doped carbon quantum dots (N/CQDs) had the best light absorption and visible-light photocatalytic nitrogen oxide (NO) removal efficiency (approximately 49%). It was found through X-ray photoelectron spectroscopy analysis that a N−Ti−O bond was formed in the 2.5 vol % N/CM(Ti), which is more conducive to charge transfer. Photocurrent and electrochemical impedance data also showed that the carrier separation efficiency of 2.5 vol % N/CM(Ti) was significantly superior to that of . In addition, the Ti III −Ti IV of MIL-125(Ti) acts as the active center for photocatalytic removal of NO. Two possible electron migration paths were proposed: electron transfer from N/ CQDs to Ti III −Ti IV center of MIL-125(Ti) due to the photoinduced electron transfer property of N/CQDs, and absorption of UV light generated from the N/CQDs by the terephthalic acid ligand followed by electron transfer to metal active sites for photocatalytic removal of NO.