Photo-transformation of graphitic carbon nitride synthesized from different precursors: Influence on environmental fate and photocatalytic water disinfection

Photo-stability and environmental impacts of photocatalysts are critical issues for large-scale applications. Herein, photo-transformation properties of graphitic carbon nitride (CNs) as water disinfection photocatalysts synthesized from precursors of urea (UCN), thiourea (TCN) and melamine (MCN) were studied for the first time. Results demonstrated that all the CNs were unstable under photoaging, with photo-stability following the order of TCN < UCN < MCN. This was associated to the highest H2O2 production ability of TCN, indicating the non-radical species were also important to determine the photo-stability of CNs. Photocatalytic disinfection performances were in the order of UCN > TCN > MCN, which was due to the differences in specific surface area and band structures. The disinfection activities were all decreased after photoaging, attributing to the partial decomposition of CNs. In addition, bacterial inactivation efficiencies of CNs aqueous filtrates (CN-FTs) after photoaging was firstly studied. Interestingly, it was unexpected to find that the CN-FTs possessed considerable photocatalytic disinfection activities with TCN-FT being the highest, probably due to the release of carbon dots-like substances. The water stability of TCN was also the highest due to its most negative Zeta potential leading to the lowest sedimentation rate, which indicates TCN and its photo-transformation products might cause persistent adverse environmental effects when releasing into water bodies. This work highlighted that CNs from different precursors have distinct influence on photocatalytic water disinfection activity and environmental fate, which should be concerned for their real applications.