Enhanced light-driven CO₂ reduction on metal-free rich terminal oxygen-defects carbon nitride nanosheets

Exploiting highly-efficient and metal-free photocatalyst for CO₂ conversion into useful chemicals is a promising pathway to solve the energy and environmental crises. In this work, through a facile exfoliation process, an ultra-thin and short-range order g-C₃N₄ nanosheet with rich terminal oxygen defects is successfully constructed, which presents total electron yield of 36.30 μmol g^-1h^-1, 3.05 times higher than that of bulk one. The results affirms that both the van der Waals forces between the C₃N₄ layers and the CN bonds on the periodic heptazine units could be disrupted during the sonication process, thus achieving the ultra-thin and ultra-small g-C₃N₄ nanosheet, which enables the improvement of optical absorption and carrier separation abilities. The π-conjugated triazine rings structure is still remained but the terminal active C radicals tend to transform into oxygen defects which become the sites to bind and activate CO₂. The in-situ DRIFTS provides the direct evidence that the size regulation and oxygen-defects design strategy can effectively promote the CO₂ adsorption and activation process upon the photocatalyst, thus turning out to boost the reactivity toward CO₂.