Efeitos estruturais e suas influências nas propriedades fotocatalíticas se SnO2 sintetizado pelo método dos precursores poliméricos

Abstract

Tin dioxide, SnO2, in its pure and doped form have been extensively investigated and applied in several applications, such as gas sensors, photovoltaic cells, light-emitting diodes and heterogeneous photocatalysts for environmental remediation, among others. Thus, this work aimed to evaluate the influence of structural parameters the SnO2 in the discoloration and degradation process of anionic and cationic dyes. The oxide samples were obtained by the polymeric precursor method, crystallized at 700°C for different calcination times (2, 4 and 6 hours), and characterized by X-ray diffraction (XRD), Raman and absorption spectroscopy in the region infrared (IR) and ultraviolet-visible (UV-vis). The photocatalytic efficiency of SnO2 was evaluated in the degradation of the cationic dye, crystal violet (CV), and anionic dye, orange G (OG), using a photochemical reactor equipped with a 30 W UVC lamp (λ = 254 nm ≈ 4.9 eV), varying the catalyst mass (0.1 to 0.5 g) and dye concentrations (5 ppm to 20 ppm). The structural results by XRD of the SnO2 samples confirmed the formation of a tetragonal crystalline phase of the rutile type mean crystallite size (DC) performed from the XRD standards of the samples showed a decrease in FWHM and an increase in DC as a function of the increase in the calcination time of the materials, indicating a greater long-range structural organization for samples treated longer. The Raman spectra of all samples confirmed the presence of vibrational modes and translational and longitudinal acoustic modes present in SnO2, it was also observed that the increase in SnO2 calcination time decreases the FWHM values in regarding to the classic modes A1g and B2g, suggesting a greater degree of symmetry in the distorted octahedra environment. Regarding the photocatalytic properties of the materials, the sample treated at 700 °C for 2 hours showed the best result with maximum efficiency of 91.27% in CV decolorization and 65.13% in OG decolorization after 6 h of exposure to UVC light. Additionally, the influence of catalyst mass and dye concentration was studied, and it was found that the best result was 0.1 g and 0.5 g of catalyst for CV and OG dyes, respectively. As for dye concentration, the increase promoted a decrease in photocatalytic efficiency, related to the difficulty of interaction of light with the catalyst due to excess dye in the reaction médium.