Highly efficient removal of <i>o</i> -nitrophenol by a green Ag@ZnFe ₂ O ₄ /BC catalyst <i>via</i> Fenton-like oxidation

Abstract

This investigation focused on engineering a novel sustainable Fenton-like catalyst from lime for the efficient degradation of <i>o</i>-NP. The heterogeneous catalyst consisted of Ag NPs and ZnFe₂O₄ that were prepared using lime juice, while waste lime peels were pyrolyzed at 500 °C to fabricate BC. The Fenton-like Ag@ZnFe₂O₄/BC catalyst was analyzed using SEM to study its morphology, FTIR to assess its chemical composition, XPS to define its elemental composition, zeta potential analysis to evaluate its surface charge, and XRD to reveal its crystal structure. The experimental findings of the Fenton-like degradation of the <i>o</i>-NP compound revealed that the best catalytic parameters were as follows: pH = 3, mass of Ag@ZnFe₂O₄/BC = 0.01 g, concentration of H₂O₂ = 500 mg L^-1, temperature = 25 °C, and concentration of <i>o</i>-NP = 100 mg L^-1. Kinetic assessments showed the suitability of second-order kinetics to model the Fenton-like degradation of <i>o</i>-NP by Ag@ZnFe₂O₄/BC. The mechanistic study suggested the synergistic effect of adsorption and Fenton-like processes, in which several adsorption pathways dominated <i>o</i>-NP adsorption, including pi-pi interactions, electron donor-acceptor interactions, coordination bonds, and hydrogen bonds. The Fenton-like reaction of <i>o</i>-NP proceeded <i>via</i> the free radical Fenton-like mechanism using the active species of Ag@ZnFe₂O₄/BC, comprising Fe²⁺, Ag⁰, and EPFRs-BC for activating H₂O₂ and yielding ˙OH. GC-MS analysis identified the intermediates yielded throughout the degradation of the <i>o</i>-NP compound by the Fenton-like Ag@ZnFe₂O₄/BC catalyst.