Insights into Photochemical Stability of Graphitic Carbon Nitride-Based Photocatalysts in Water Treatment

Chemical stability is a critical issue and prerequisite for realizing intended engineering applications of materials and is closely correlated to practical implementation efficiency, operation cost, and environmental impact. Herein, we demonstrate that the intrinsic characters of graphitic carbon nitride (CN)-based photocatalysts lead to a varying degree of photoinduced decomposition of CN. Elevated photochemical instability was shown as a synergistic consequence of a downshifting of the valence band potential and an enlarged surface area in CN. CN self-decomposition pathways involving superoxide (O2•‒) radicals and holes (h+) have been explored. A greater deterioration in the photocatalytic degradation efficiency of the target pollutant, diclofenac (DCF), was found in CN samples with inferior photostability, wherein sp2 C–NC nitrogen atoms in CN deteriorated during usage. Additionally, the presence of aromatic-rich humic acid slows down both the photoinduced self-decomposition of CN and the degradation of DCF by CN. The compiled results identified factors affecting the photodurability of CN, which inform a guiding framework for advancing the material design of CN-based materials toward boosting its long-term catalytic performance in water treatment, and the need of considering stability in the ongoing effort of improving CN’s photocatalytic efficiency is highlighted.