Comparison of the solar photocatalytic activity of ZnO–Fe2O3 and ZnO–Fe0 on 2,4-D degradation in a CPC reactor

Abstract

In this work a comparative study of the catalytic activity of ZnO–Fe₂O₃ and ZnO–Fe⁰ 0.5 wt% materials was carried out in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) as a commercial formulation Hierbamina®, using a compound parabolic collector (CPC) reactor. The catalysts were synthesized by the sol–gel method and characterized by X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The textural properties of solids were determined from N₂ adsorption isotherms using the Brunauer–Emmett–Teller (BET) method. The incorporation of Fe⁰ onto ZnO was demonstrated by X-ray photoelectron spectroscopy analysis. The photocatalytic tests were performed at pH 7, using 10 mg L⁻¹ of herbicide and 0.5 g L⁻¹ of catalyst loading. The decay in herbicide concentration was followed by reversed-phase chromatography. A complete degradation of 2,4-D was achieved using ZnO–Fe⁰ while 47% of herbicide removal was attained with ZnO–Fe₂O₃ mixed oxide for an accumulated energy Q_UV ≈ 2 kJ L⁻¹. The removal percentage of total organic carbon (TOC) during the solar photocatalytic process was superior using ZnO–Fe⁰, achieving 45% compared to the 15% obtained with the mixed oxide catalyst.