g-C3N4 Enhanced Fe3+/ Fe2+ Cycling to Activate PMS for Pharmaceuticals Degradation Under Solar Irradiation

Abstract

Since Peroxymonosulfate (PMS) is readily available and can produce sulfate radicals with a stronger oxidation capacity, the Fenton-like system Fe²⁺/PMS has gradually replaced Fe²⁺/H₂O₂ system in organic pollutants degradation. However, the Fe³⁺/PMS system has almost no degradation effects, with the conversion of Fe²⁺ to Fe³⁺ being the rate-limiting step in the Fe³⁺/PMS system. In this paper, graphite-like phase carbon nitride (g-C₃N₄) was employed to activate PMS using trace amounts of Fe³⁺ for the treatment of water pollution under sunlight, and the Fe³⁺/g-C₃N₄/PMS system demonstrated the ability to rapidly degrade a wide range of difficult-to-degrade organic pollutants. The Fe³⁺/g-C₃N₄/PMS system was able to completely degrade carbamazepine (CBZ) within 30 min under sunlight. The fundings indicated that this system effectively improved the stringent limitations typically associated with Fenton process regarding the feed ratio of metal ions to oxidants, and could efficiently degrade CBZ across a broad pH range. In addition, the Fe³⁺ concentration of 6.17 × 10⁻⁶ M was used in the experiments to avoid the generation of large amounts of “iron sludge”. The trap burst experiments, DMSO oxidation experiments and electron paramagnetic resonance spectroscopy experiments indicated that O₂·⁻ and ¹O₂ exerted the major effectiveness in the photocatalytic degradation reaction of CBZ, and SO₄·⁻ and ·OH jointly promoted the CBZ degradation.

Graphical Abstract