The role of single copper atoms in enhancing the photocatalytic activity of carbon nitride for selective oxidation†

Photocatalytic reactions are driven by excited charge carriers; therefore, their performance inherently depends on photocarrier behavior. In this study, we examine the relationship between photocarrier behavior and the photocatalytic activity of g-C₃N₄ loaded with single Cu atoms for the selective oxidation in water. As probed with transient microwave conductivity, the introduction of single Cu atoms enhances photoconductivity by increasing the mobility and extending the lifetimes of photoexcited electrons. This enhancement results in a greater population of mobile electrons. While pristine g-C₃N₄ exhibits no measurable photoconductivity, it is still capable of driving photocatalytic reactions. This suggests that in g-C₃N₄, photoexcited electrons are predominantly trapped rather than recombined, yet they are sufficiently reactive. The product of photoconductivity and electron lifetime shows a linear correlation with photocatalytic activity, demonstrating its potential as a promising descriptor for catalyst design. In terms of performance, our photocatalysts achieve a yield-to-power ratio of up to 1.1 mmol g⁻¹ h⁻¹ W⁻¹ for benzaldehyde production from benzyl alcohol under 455 nm irradiation with 100% selectivity and aromatic balance and an apparent quantum yield of 0.82%. The reaction proceeds under ambient conditions without the need for additives or external oxidants. Equally important, H₂O₂ is also produced at a rate as high as 0.26 mmol g⁻¹ h⁻¹.