Photo-accelerated Co3+/Co2+ transformation on cobalt and phosphorus co-doped g-C3N4 for Fenton-like reaction

Peroxydisulfate (PDS) can be activated by graphitic carbon nitride (g-C3N4) under irradiation, and the generated oxygen reactive species (ROSs) can degrade organic pollutants effectively. However, the photocatalytic activity of pristine g-C3N4 is limited due to its narrow light absorption range and rapid electron-hole recombination. Herein, cobalt and phosphorus co-doped g-C3N4 (Co, P-CN) was synthesized by a facile one-pot pyrolysis method. Co and P co-doping enhances the light absorption and charge separation, thus greatly promoting the photocatalytic activation of PDS. Additionally, the presence of doped Co2+ can chemically activate PDS, with Co2+ transforming into Co3+ simultaneously. Recycling tests reveal that Co2+ in Co, P-CN can maintain a high level attributing to the fast Co3+/Co2+ transformation rate under light irradiation. The density functional theory (DFT) calculations show that the Co-N-x species formed by chemical coordination between Co and g-C3N4 in Co, P-CN could effectively activate PDS. The synergistic effect of photo-catalytic and chemical-catalytic driven PDS activation and a faster Co3+/Co2+ redox cycle result in the enhanced bisphenol A (BPA) degradation with a reaction rate constant (k) of 0.375 min(-1), which is 7 times larger than that of pristine g-C3N4. This work provides an effective method for the in situ regeneration of active low-valent transition metal ions, and reveals the mechanism of synergistic activation of PDS by photo-catalysis and chemical-catalysis for pollutant degradation.

Automated summary

Co and P co-doped g-C3N4 (Co, P-CN) synthesized by a facile one-pot pyrolysis method enhances light absorption and charge separation, promoting the photocatalytic activation of PDS. The chemical activation of doped Co2+ and the synergistic effect of photo-catalysis and chemical-catalysis result in the enhanced degradation of BPA with a reaction rate constant 7 times larger than pristine g-C3N4. This work provides an effective method for in situ regeneration of active low-valent transition metal ions and reveals the mechanism of synergistic activation of PDS for pollutant degradation.