α-MoO3 nanoestruturado: obtenção, caracterização e estudo das propriedades

Abstract

This work describes an original simple and low-cost route to synthesize the molybdenum trioxide, -MoO3, using MoS2 as a precursor, which was patented. As well as the study of the potential applications of this material. This synthetic route consists of refluxing the precursor in oxidant media (HNO3/H2SO4 aqueous solution) leading to -MoO3 (called MoO3_Cz) with reduced size particles, high purity and strongly-preferred crystallographic orientation. -MoO3 was also synthesized by calcination of MoS2, for a comparative study of the oxide properties. -MoO3 was characterized by X-ray diffractometry, transmission and scanning electron microscopy in high-resolution mode (HRTEM and HRSEM), atomic force microscopy (AFM), infrared (FTIR), ultraviolet and near infrared (UV-VIS-NIR) and Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). The results show that -MoO3 was obtained with high purity and preferential growth, with particles in nanobelt forms, presenting two dimensions in nanometric scale. Based on these techniques, it was possible to demonstrate that MoO3_Cz presented structural defects, due to the Mo5+ species in its structure. Due to these characteristics, MoO3_Cz was applied as a hole carrier in inverted organic solar cells, showing superior outdoor efficiency and stability when compared to PEDOT: PSS, traditional hole carrier for these devices, because molybdenum trioxide acts also as a protective layer for the active layer of the solar cell, so it can be called a multifunctional material. MoO3_Cz was also applied as a photocatalyst for degradation of organic dye rhodamine B, used as a standard molecule, being about 80% more effective than the commercial oxide and also occurring in a pseudo first order kinetics with a half-life of 11.74 minutes. The photolysis and adsorption processes were also evaluated, but without significant results. The electrochemical study of MoO3_Cz showed the easy intercalation of H+ and Li+ ions. The tests showed that there was evolution of hydrogen. Thus, the Tafel curve in acidic medium showed that MoO3_Cz has specific activity in the potential of 0.0 V, which was about 3.4 times greater than the commercial oxide. Tafel inclination was 68 mV/dec, indicating that the hydrogen evolution occurs via Volmer-Tafel mechanism, a faster kinetic mechanism than described in the literature for MoO3.