Structural and Optical Properties of Mn-Incorporated BiVO₄ Nanoparticles Synthesized by Sonochemical Process

Abstract

In this work, Mn-incorporated BiVO4 nanoparticles with different Mn contents (0–5%) were synthesized by one-step sonochemical process. Structural phase of Mn-incorporated BiVO4 nanoparticles was extensively carried out by X-ray diffraction technique. The XRD results show that the structural phase of BiVO4 belongs to the monoclinic principal structure while the secondary phases of MnO, Mn2O3, and Mn3O4 structures are noticed in Mn-loaded samples. Chemical bondings of Mn-incorporated BiVO4 nanoparticles were characterized with Raman spectroscopy. Relevant chemical bondings confirm the existence of VO43− tetrahedron and the V–O band by Raman spectra. Diffuse reflection spectroscopy and FE-SEM were employed to examine their optical and morphological properties, respectively. The results indicate that the incorporation of Mn can induce the red-shift of optical absorption edge in visible range, which can decrease the optical band gap of BiVO4. Morphology of all samples demonstrates the difference in shape of the compounds with the incorporation of Mn contents. Oxidation number and local structure of Mn-incorporated BiVO4 nanoparticles were investigated by X-ray absorption spectroscopy. XAS results demonstrate that oxidation number of all elements correspond to Mn2+/Mn3+, Bi3+, and V5+ ions. The normalized Mn K-edge XANES spectra suggest that Mn atoms would not locate at the local site of Bi or V in BiVO4 crystal because the specific feature of experimental spectra are inconsistent with simulated spectra, which is corresponded to XRD results indicating the formation of Mn-based oxide structures with various oxidation states.