Ozonation of dimethyl phthalate catalyzed by highly active Cu_xO-Fe₃O₄ nanoparticles prepared with zero-valent iron as the innovative precursor

Heterogeneous catalytic ozonation provides a promising alternative in the degradation of recalcitrant contaminants. Cu_xO-Fe₃O₄ nanoparticles (Cu_xFeO NPs, both Cu(I) and Cu(II) were contained, about 70 nm) were creatively synthesized using Fe(0) as the precursor and subsequently employed as the ozonation catalyst for dimethyl phthalate (DMP) degradation. Results showed that DMP degradation by O₃/Cu_xFeO was significantly faster than those ozonation catalyzed by CuO, Fe₃O₄, or mixture of CuO and Fe₃O₄ (1:1 M ratio), which was ascribed to the unique Cu_xFeO NPs that composed of abundant structural Cu(I) (≡Cu(I)). It was among the first revealing the synergistic effect between ≡Cu(I) and surface lattice oxygen (O^2-) in HO· generation, resulting in rapid DMP degradation kinetics and high mineralization efficiency. Besides the generation of ≡Cu(I), galvanic corrosion between Fe(0) and Cu(II) also generated structural Fe(II), which could reduce the ≡Cu(II) back to ≡Cu(I), thus compensating the electron loss of ≡Cu(I) and finally obtaining a high-efficiency cycling between ≡Cu(II) and ≡Cu(I). The DMP degradation pathway was introduced based on the intermediates detected. By regulating the (re)-generation of low-valent metal (≡Cu(I)), this study provides an innovative strategy to significantly promote the generation of HO· in catalytic ozonation, which might be promising for advanced wastewater treatment.