Is C 3 N 4 Chemically Stable toward Reactive Oxygen Species in Sunlight-Driven Water Treatment?

Reactive oxygen species (ROS) are key oxidants for the degradation of organic pollutants in sunlight-driven photocatalytic water treatment, but their interaction with the photocatalyst is easily ignored and, hence, is comparatively poorly understood. Here we show that graphitic carbon nitride (C N , a famous visible-light-responsive photocatalyst) is chemically stable toward ozone and superoxide radical; in contrast, hydroxyl radical ( OH) can tear the heptazine unit directly from C N to form cyameluric acid and further release nitrates into the aqueous environment. The ratios of released nitrogen from nanosheet-structured C N and bulk C N that finally exists in the form of NO reach 9.5 and 6.8 mol % in initially ultrapure water, respectively, after 10 h treatment by solar photocatalytic ozonation, which can rapidly generate abundant OH to attack C N . On a positive note, in the presence of organic pollutants which compete against C N for OH, the C N decomposition has been completely or partially blocked; therefore, the stability of C N under practical working conditions has been obviously preserved. This work supplements the missing knowledge of the chemical instability of C N toward OH and calls for attention to the potential deactivation and secondary pollution of catalysts in OH-involved water treatment processes.