Visible-light-driven N and Fe co-doped carbon dots for peroxymonosulfate activation and highly efficient aminopyrine photodegradation

Low solar energy utilization, instability of Fe ions and Fe(III)/Fe(II) cycle difficulty are three main factors, limiting the photocatalytic activity of the Fe/peroxymonosulfate (PMS) system. Herein, based on the N and Fe co-doped carbon dots (N, Fe-CDs) synthesized by a facile one-pot hydrothermal method, a new Fe(III)/Fe(II) cycle system for PMS activation under visible light irradiation was proposed. The characterization experiments showed that Fe has been successfully doped to the sp2 graphitic structure and mainly existed as Fe-N and Fe-OH complexes, which played an important role in harvesting visible light, enhancing the stability of Fe ions and acting as active sites to accelerate electron transfer. Under visible light irradiation, the photogenerated electrons of N, Fe-CDs could be directly transferred to Fe (III) for Fe (II) formation via the ligand-to-mental charge transfer process, thus accelerating the Fe(III)/Fe(II) cycle. When N, Fe-CDs were used for activating PMS under visible light irradiation, aminopyrine could be efficiently degraded and mineralized to CO2 via the cleavage of pyrazole ring, demethylation, hydroxylation, decarbonylation and the cleavage of benzene ring. The produced O2− and 1O2 played the main roles in the whole photocatalytic reaction. The above results revealed that the novel N, Fe-CDs could effectively activate PMS under visible light irradiation for the degradation of pharmaceuticals in the polluted water.