Efeito de diferentes rotas de síntese sobre a morfologia, propriedades ópticas, colorimétricas e fotocatalíticas do β−Ag2MoO4

Abstract

This dissertation describes four synthesis methods: controlled precipitation (CP), sonochemistry, injection of ions in a hot solution with rapid cooling and conventional hydrothermal, used to obtain crystals of silver beta-molybdate (β−Ag2MoO4). The effect of these different synthetic methods on the morphology and the optical, colourimetric and photocatalytic properties were evaluated by different characterization techniques. X−ray diffraction patterns, Rietveld refinement data, and Raman spectroscopies in the infrared region with Fourier transform indicated for all β−Ag2MoO4 crystals a spinel-like cubic structure, with Fdm space group and symmetry point group 𝑂7ℎ. Field emission scanning electron microscopy images found that the different synthesis routes enabled the formation of β−Ag2MoO4 crystals with different shapes and sizes. Spectroscopy measurements in the ultraviolet-visible (UV−Vis) region showed three main absorptions in the UV region (280, 310 and 340 nm). In comparison, the UV−Vis analysis in diffuse reflectance mode noticed an energy absorption tail in the UV range varying between 3.25 eV and 3.3 eV. The quantitative data obtained in the colourimetric analysis indicate that the β−Ag2MoO4 crystals have a desirable characteristic for developing inorganic pigments with colours ranging from beige to brown. They performed photocatalytic tests with UV−C, UV−B, UV−A, and visible light lamps. The β−Ag2MoO4 crystals prepared by the CP method showed a higher rate of degradation, approximately 85.12% of the rhodamine B dye solution under exposure to UV−C light for 240 min.