Structural and photocatalytic properties and X-ray absorption spectroscopic study of BiVO4 nanoparticles incorporated with Fe synthesized by sonochemical method

Abstract

In this work, Fe-incorporated BiVO4 nanoparticles with different Fe-loading contents (0–4%) were synthesized via one-step sonochemical process. Crystal structure of all samples was investigated by X-ray diffraction technique (XRD). XRD patterns obviously show the main structure of monoclinic BiVO4 structure. The secondary phase is found in the form of Fe-based oxide as a hematite Fe2O3 phase at for Fe-loading contents ≥ 2%. Relevant chemical bonding of as-synthesized samples was carried out by Raman spectroscopy indicating the fundamental vibration with various vibration modes of VO43− tetrahedron and V–O band, respectively. Morphological structure of pure BiVO4 shows rod-like structure while 1–4%Fe-incorporated BiVO4 display different morphologies. The chemical compositions and oxidation numbers of all elements of the samples were carried out via X-ray photoelectron spectroscopy (XPS). XPS spectra indicate the existence of all elements on their surface and the oxidation states of all elements are clearly scrutinized. Local structure of all samples was investigated to interrogate the local atomic site of Fe atoms by X-ray absorption spectroscopy (XAS). The normalized Fe K-edge XANES spectra of all samples indicate that the local atomic site of Fe atoms would not replace in local sites of either Bi or V sites in BiVO4 crystal verified by simulated XANES spectra. However, the specific features of measured XANES spectra of all samples corresponds to the Fe K-edge XANES spectra of Fe2O3 and BiFeO3 structure suggesting that local structure of all samples are formed to Fe-based oxide between Fe2O3 and BiFeO3 structure. Fitting EXAFS spectra of 1–4%Fe-incorporated were practically conducted by artemis program with Fe2O3 and BiFeO3 used as structural models to identify local atomic environment of Fe atoms. Results show agreeable fitting with their structural models and reveal pertinent information of localization of Fe atoms. Optical properties of the samples were analyzed by UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). DRS results exhibit the absorption edge in visible range of all samples. Meanwhile, influence of Fe loading contents into pure BiVO4 displays to confirm the red-shift on the absorption edge in visible range to higher wavelength, which suggests the lower optical band gap of pure BiVO4. The optimized photocatalytic degradation of RhB was performed by 4%Fe–BiVO4 with 82% decolorization under visible-light irradiation within 10 min and exhibited rate constant at 0.150 min−1.