Síntese, caracterização e atividade fotocatalítica de tungstatos de prata obtidos via síntese hidrotérmica assistido por sonificação química

Abstract

In this work was obtained silver tungstates (Ag2WO4) using the hydrothermal (HC) method assisted by sonochemistry (SQ) at a constant temperature of 140 °C for 1 (SQ + HC-1h), 6 (SQ + HC-6h), 12 (SQ + HC-12h) and 24 h (SQ + HC-24h) of synthesis, comparing them with the sonochemistry (SQ) and hydrothermal method at the same time of synthesis (HC-1h, HC-6h , HC-12h and HC-24h) and temperature. The results obtained by X-ray diffraction (XRD) and structural refinement by the Rietveld method confirm a phase mixing for SQ, and SQ + HC-1h samples. For the other samples, was identified the α-Ag2WO4, as a single present in the composition. Infrared spectroscopy performed in the infrared region and Raman, confirmed the active modes corresponding to the α-Ag2WO4, great agreement with XRD analysis. The diffuse reflectance by UV-vis were obtained the energy (Egap) of the synthesized samples, obtaining the lowest value for the sample HC-1h (Egap = 3.04 eV), derived from distortions of the clusters [WO6] and [AgOy], y = 2, 4, 6 and 7, present. The result for the composition of the metals (Ag and W) present by X-ray fluorescence was confirmed the silver (Ag) atoms deficiency in the composition, approaching the theoretical value (Ag2WO4) of the samples SQ + HC-12h (Ag1,96W1,02O4) and HC-1h (Ag1,96W1,02O4). The catalytic study was carried monitoring of degrading the Rhodamine B (RhB) dye molecule in aqueous solution in the presence of UVC radiation, revealed to the adsorption equilibrium using the magnetic stirring the best performance for the sample SQ+HC-12h, checking percentage of degradation, apparent velocity constant (kapp) and half-life time (t1/2) of 48.23 %, 55.1  10-4 min-1 and 125.8 min, respectively. When the catalytic tests were carried out by chemical sonification, the HC-6h sample performed the best catalytic performance, degrading 80.3 % of the dye concentration, obtaining the apparent velocity constant (kapp) and half-life time (t1/2) of 112.1  10-4 min-1 and 61.8 min, respectively