Stable cuprous active sites in Cu⁺-graphitic carbon nitride: Structure analysis and performance in Fenton-like...

Cu⁺-based catalysts have great potential in Fenton reactions under neutral pH conditions. However, cuprous (Cu⁺) materials are instable in the aqueous environment. Herein, using the cheap precursors, a Cu⁺-graphitic carbon nitride complex with an efficient Fenton-like activity as well as relative stability was prepared. 99.2% removal of Rhodamine B with an initial concentration of 50 mg/L could be attained in 1 h. Several experimental techniques are employed to study the structure of this catalyst. Results show that after the addition of Cu, the graphitic carbon nitride (g-C₃N₄) network is partially destroyed and the reduced Cu is therefore firmly embedded in the fragmentary g-C₃N₄ sheet. The X-ray adsorption fine spectra illustrates the chemical state and the local structure of the bonded Cu. Due to the strong orbital hybridization, Cu⁺ could be stabilized through the coordination with pyridinic N. A two-coordinate structure with a bond length of 1.90 Å is confirmed and this structure is not changed even after the Fenton-like reaction. Singlet oxygen (¹O₂) and hydroxyl radicals (HO•) are produced by the rapid interaction of bonded Cu⁺ with H₂O₂ and the resulting Cu²⁺ can be easily reduced to its cuprous state due to its structure stability, leading to its high activity in the Fenton-like reaction.