Magnetically separable AgI–BiOI/CoFe2O4 hybrid composites for Hg0 removal: characterization, activity and mechanism

Abstract

A series of magnetically separable AgI–BiOI/CoFe₂O₄ hybrid composites were successfully synthesized via a solvothermal and subsequent coprecipitation method. The microstructure and magnetism of the materials were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photocurrent test, electron spin resonance (ESR) and vibrating sample magnetometer (VSM). The photocatalytic performance of AgI–BiOI/CoFe₂O₄ composites on Hg⁰ removal from simulated flue gas was carefully designed and evaluated under fluorescent light (FSL) irradiation. The results showed that AgI–BiOI/CoFe₂O₄ composites displayed superior photocatalytic activities because of the synergistic effects between AgI, BiOI, and CoFe₂O₄ under FSL irradiation. The optimal weight ratio between AgI and the total weight of AgI–BiOI/CoFe₂O₄ photocatalyst was 0.3. The presence of a small amount of SO₂ had a dramatic inhibition on Hg⁰ removal, while the inhibitory effect of NO on Hg⁰ removal could only be observed at a higher NO concentration. The trapping experiments indicated that photoinduced holes (h⁺) and superoxide radicals (˙O₂⁻) were the primary active substances in the AgI–BiOI/CoFe₂O₄ photocatalytic oxidation system. According to the experimental and characterization results, one plausible mechanism for enhanced Hg⁰ removal performance over AgI–BiOI/CoFe₂O₄ composites was proposed.