Síntese e caracterização de óxidos de vanádio (V2O5.n_H2O) dopados com átomos de cobalto

Abstract

This work aimed to synthesize and characterize vanadium oxides gels (V2O5) doped with cobalt (Co) ions. These materials comprise a special class of vanadium oxides, and has been studied with emphasis on device engineering applications or as active element in industrial catalysis process. The gels of vanadium oxide were synthesized by sol gel technique. In this route, the sol (colloidal solution formed by the molecular precursors) evolve to a gel state throw hydrolysis and condensation reactions of molecular precursors. The gels were produced from an aqueous solution containing H2O2 and V2O5, at room temperature. The doping of the material occurred by the addition of the CoSO4 salt to the solution. The gels were deposited by impregnation onto p-type crystalline silicon oriented along [100] direction. The deposits formed on silicon were characterized before and after annealing at 350 ° C by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy and X-ray diffraction (XRD). The SEM analysis showed that the surface morphology of the deposits is dependent on the doping concentration. The surface of undoped gel was characterized in terms of interconnected chains of V2O5, while samples doped at higher concentrations present a surface formed by fibers, circular agglomerates and pores. The deposits present a relative stability during annealing. Significant changes in the surface morphology were observed only for sample doped with a higher Co concentration. The rate between the atomic concentration of vanadium and oxygen atoms as determined by the EDS analysis indicate that the oxide preset a stoichiometry close to the V2O5 oxide. Additionally, the presence of Co atoms in the deposits was confirmed. The Raman analysis points for a synthesized gel with local order characteristic of layered materials. For the present work, layers of V2O5. The layered structure lead to the intercalation of water molecules. The intercalation occurs during the synthesis. Our data demonstrated a inverse relation between the degree of hydration of the gels and the dopant concentration. The layered monoclinic structure of gels was determined by XRD measurements. The layers are formed by the (00l) atomic planes stacking along the crystallographic direction c. Was observed a dependence between the interplanar spacing of layers and dopant concentration, being smaller for higher concentration of Co. Both techniques XRD and Raman spectroscopy indicate that the annealing of samples lead to the structural transformation from monoclinic to orthorhombic one, characteristic of crystalline V2O5. However higher concentration of dopant lead to the reduction of long range order of oxide.