Band gap values and structural changes on MoO3 obtained by ion-exchange method

In this work we present a study of a new synthesis for molybdenum oxide (MoO₃) produced by an ion-exchange method in the sol-gel route as well as its structural characterization. Subsequently, the influences of this new synthesis under the structure and, consequently, its optical properties have been examined. Different pH and concentration values were used: pH = 2, 4 and 5; and concentrations: 0.05, 0.10, 0.20, 0.30, 0.40 and 0.50 mol L⁻¹. From the X-ray diffraction profiles, the presence of two polymorphic phases of MoO₃ were observed: the stable phase α-MoO₃ in its orthorhombic form and the metastable phase h-MoO₃ which corresponds to its hexagonal structure. In the spectroscopic investigation, by adopting Tauc's plot, the optical band gap energies of MoO₃ are estimated. The band gap widening from 2.58 to 3.99 eV, which were useful in the energetic evaluation of electron transfer between the conduction and valence bands between oxygen and molybdenum, also confirms the effect of structure variation, further confirming the effect of the structural variations induced by the new synthesis method in different conditions.