Fe/Fe cycling promoted by Ta3N5 under visible irradiation in Fenton degradation of organic pollutants

Ta₃N₅ was synthesized by nitridation of Ta₂O₅ under NH₃ flow at 700 °C. The catalyst was pure Ta₃N₅ according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m²/g. When Ta₃N₅ was added to Fe³⁺/H₂O₂ solution (known as Fenton-like system), most Fe³⁺ were adsorbed on the Ta₃N₅ surface and could not react with H₂O₂ in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe³⁺ ions were reduced to Fe²⁺ rapidly and Fe²⁺ were reoxidized by H₂O₂ on the Ta₃N₅ surface, thus a fast Fe³⁺/Fe²⁺ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta₃N₅/Fe³⁺/H₂O₂ system could efficiently decompose H₂O₂ to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N,N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results.