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Long-term photochemical stability of heteroaromatic dye-functionalised g-C3N4 via covalent linkage for efficient photocatalytic hydrogen evolution

Shihang Liu,Xiaodi Chen,Chao Zhang,Xingliang Liu,Shiai Xu

In this study, three typical D–π–A type heteroaromatic organic dyes containing carbazole (CBZ), phenothiazine (PTZ), and phenoxazine (POZ) moiety as electron donor cores and linked to g-C 3 N 4 with amide covalent bonds were synthesized. Thereafter, we studied the long-term photochemical stability and degradation mechanism of the associated dye-sensitised g-C 3 N 4 with covalent linkage or weak interaction. The results revealed that most of the dyes degraded and became unstable after absorption on g-C 3 N 4 under light irradiation. Interestingly, after the target dyes were linked to g-C 3 N 4 with amide covalent bonds, the photostability could be effectively promoted and improved to high levels of stability. For POZ-S dye covalent bond-linked sample g-C 3 N 4 /POZ-S, ∼90.5% percent of the dyes were reserved, whereas only ∼25.3% remained for the physically absorbed dye sample g-C 3 N 4 +POZ-S after 30 min of irradiation aging test. Moreover, the obtained g-C 3 N 4 /POZ-S sample exhibited enhanced H 2 evolution activity with photocatalytic H 2 production rates that were approximately 96- fold of that of pure g-C 3 N 4 . Then, we applied various instrumental analysis and DFT calculation to clarify the mechanism involved with dye photostability and degradation pathway. The typical decarboxylation process was confirmed, and such an unfavourable reaction process could be effectively inhibited if the target dye is linked to g-C 3 N 4 with amide covalent bond instead of the weak interaction. Overall, the existed covalent bond is the key factor for enhancing both the photochemical stability and photocatalytic activity of organic dye-sensitised g-C 3 N 4 for hydrogen evolution .