44ª Reunião Anual Virtual da SBQ

Catalysts based on ferrite have shown promising for environmental remediation through photocatalysis [1]. The magnetic property of this class of materials allows easy recovery of the aqueous medium by the simple application of a magnetic field [2]. However, the structural relation and photoactivity of cobalt ferrite are still not clear, since cobalt ferrite can be stabilized in two distinct structures (normal or inverse spinel), remaining with the same stoichiometry [3]. Therefore, this work aims to investigate the photocatalytic property of cobalt ferrites and their correlation with the spinel structure. Cobalt ferrite powders were synthesized by the co-precipitation method, varying the cobalt concentration between 0.4 and 1.2 mol. The morphology of the nanoparticles was analyzed by Scanning Electron Microscopy, which indicated the presence of nanoparticle clusters. Structural characterization, carried out by X-ray diffraction, indicated the formation of single-phase cobalt ferrite powders in a spinel-like structure with cubic symmetry Fd-3m. The structural refinement showed an evolution of the inverse spinel structure to normal one with the increase in the concentration of Co2+. However, the concentration above 1 mol showed that cobalt starts to occupy both the octahedral and tetrahedral sites, favoring the normal spinel structure. The band gap energy, determined by Diffuse Reflectance Spectroscopy in the UV-Visible region, showed value of ca. 1.9 eV. The photoactivity of the powder (0.1 g) was evaluated by photodegradation of the dye rhodamine 6G (10.4 mol L-1) under UV-Visible light. The photocatalytic degradation of the dye rhodamine 6G, with cobalt ferrite nanoparticles, followed the pseudo-first order reaction with a maximum apparent rate constant of 10.23x10-3 for CoFe2O4. The photoactivity of cobalt ferrites showed to be strongly influenced by the tetrahedral and octahedral sites of the spinel structure. The displacement of cobalt from the octahedral site to the tetrahedral site, with increasing cobalt concentration, favors the migration of photogenerated electrons. However, the concentration above 1 mol of cobalt, leads to the occupation of both octahedral and tetrahedral sites by cobalt, decreasing its photocatalytic activity.
References
[1] E. Ferdosi, H. Bahiraei, D. Ghanbari. Sep. Purif. Technol. 211 (2019) 35–39.
[2] Z. Jia, D. Ren, Y. Liang, R. Zhu. Mater. Lett. 65 (2011) 3116–3119.
[3] K. E. Sickafus, J. M. Wills, N. W. Grimes. Journal of the American Ceramic Society 82 (1999) 3279–3292.