Effective degradation of phenol via Fenton reaction over CuNiFe layered double hydroxides

A series of CuNiFe layered double hydroxides (LDHs) with various Cu/Ni molar ratios were synthesized as catalysts for Fenton degradation of phenol. It is found that Cu⁺, Cu²⁺, Ni²⁺, Ni³⁺ and Fe³⁺ are present on LDHs, owing to an electron transfer from Ni²⁺ to Cu²⁺ via metal-oxo-metal bridges. At lower Cu/Ni ratios, the highly dispersed MO₆ octahedra and the electron donation effect of Ni facilitate such electron transfer and thus increase the percentage of Cu⁺. The catalytic activity increases with the decrease in Cu/Ni ratio. The most active Cu_0.5Ni_2.5Fe LDH can mineralize 98.9% phenol at ambient pH and less excessive H₂O₂ dosage ( [Formula: see text] /M_phenol = 37). Even at the H₂O₂ dosage close to the theoretical value, around 90% phenol can be mineralized. The structure-activity correlation indicates Cu⁺ which can readily react with H₂O₂ to produce hydroxyl radicals may dominate the reaction. The regeneration of Cu⁺ could be achieved by the electron transfer between Cu²⁺ and Ni²⁺ in LDHs. Moreover, Fe³⁺ can also act as Fenton-like active sites. The special structure of CuNiFe LDHs could offer surface-enriched and easily regenerated Cu⁺ species, leading to the complete mineralization of phenol and the efficient use of H₂O₂.