Catalytic ozonation of 2,4-dichlorophenoxyacetic acid over novel Fe–Ni/AC

Abstract

Iron and nickel based bimetallic loaded activated carbon (Fe–Ni/AC) prepared by an impregnation method was employed as a heterogeneous catalyst for the ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The Fe–Ni/AC was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption–desorption, and atomic absorption spectrometry (AAS). The results indicated that the degradation and mineralization efficiencies of 2,4-D were considerably improved in the presence of Fe–Ni/AC. During the ozonation (50 mg h⁻¹ ozone flow rate) of 2,4-D aqueous solution (10 mg L⁻¹, pH = 4.18) in the presence of Fe–Ni/AC, the TOC removal rate reached 72% at 60 min reaction time, while the rate was 60% with Fe/AC, 62% with Ni/AC, 50% with activated carbon (AC), and only 34% by ozonation alone. The 2,4-D removal process followed the pseudo first order reaction model well, its degradation rate constant with Fe–Ni/AC/O₃ was 1.6 times higher than that with AC/O₃, and 1.9 times than that by O₃ alone. The Fe–Ni/AC showed much better catalytic activity and stability based on the seven times repetition of the ozonation of 2,4-D. In addition, the effects of 2,4-D initial concentration, pH value and reaction temperature on catalytic ozonation of 2,4-D over Fe–Ni/AC were also investigated. The addition of tert-butanol (TBA) strongly inhibited the catalytic degradation of 2,4-D, which suggests that the degradation reaction follows the mechanism of hydroxyl radical (HO˙) oxidation.