A low-cost solvent-free method to synthesize α-FeO nanoparticles with applications to degrade methyl orange in photo-fenton system.

Hematite nanoparticles (α-FeO NPs) were successfully synthesized by a low-cost solvent-free reaction using Ferrous sulfate waste (FeSO·7HO) and pyrite (FeS) as raw materials and employed for the decolorization of Methyl Orange by the photo-Fenton system. The properties of α-FeO NPs before and after photo-Fenton reaction were characterized by X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR) spectrum and X-ray photoelectron spectroscopy (XPS), and the optical properties of α-FeO NPs were analyzed by UV-vis diffuse reflectance spectra (UV-vis DRS) and Photoluminescence (PL) spectra. The analytic results showed that the as-formed samples having an average diameter of ~50 nm exhibit pure phase hematite with sphere structure. Besides, little differences were found by comparing the characterization data of the particles before and after the photo-Fenton reaction, indicating that the photo-Fenton reaction was carried out in solution rather than on the surface of α-FeO NPs. A 2 central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model (P-value<0.0001, R = 0.9664) was derived using an analysis of variance (ANOVA), which was adequate to perform the process variables optimization. The optimal process conditions were performed to be 395 nm of the light wavelength, pH 3.0, 5 mmol/L HO and 1 g/L α-FeO, and the decolorization efficiency of methyl orange was 99.55% at 4 min.