Radical-Driven Decomposition Of Graphitic Carbon Nitride Nanosheets: Light Exposure Matters

Understanding the transformation of graphitic carbon nitride (g-C3N4) is essential to assess nanomaterial robustness and environmental risks. Using an integrated experimental and simulation approach, our work has demonstrated that the photoinduced hole (h(+)) on g-C3N4 nanosheets significantly enhances nanomaterial decomposition under (OH)-O-center dot attack. Two g-C3N4 nanosheet samples D and M2 were synthesized, among which M2 had more pores, defects, and edges, and they were subjected to treatments with (OH)-O-center dot alone and both (OH)-O-center dot and h+. Both D and M2 were oxidized and released nitrate and soluble organic fragments, and M2 was more susceptible to oxidation. Particularly, h(+) increased the nitrate release rate by 3.37-6.33 times even though the steady-state concentration of (OH)-O-center dot was similar. Molecular simulations highlighted that (OH)-O-center dot only attacked a limited number of edge-site heptazines on g-C3N4 nanosheets and resulted in peripheral etching and slow degradation, whereas h(+) decreased the activation energy barrier of C-N bond breaking between heptazines, shifted the degradation pathway to bulk fragmentation, and thus led to much faster degradation. This discovery not only sheds light on the unique environmental transformation of emerging photoreactive nanomaterials but also provides guidelines for designing robust nanomaterials for engineering applications.