Microwave-assisted hydrothermal synthesis of Ag2Mo1-xWxO4 (x=0, 0.25, 0.50, 0.75 and 1 mol%) heterostructures for enhanced photocatalytic degradation of organic dyes

摘要

In this work, Ag2Mo1-xWxO4 (x = 0, 0.25, 0.50, 0.75 and 1 mol%) heterostructures were synthesized by a microwave-assisted hydrothermal (MAH) method under 140 degrees C. The powders are characterized by X-ray diffractogram (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and spectroscopy in the ultraviolet-visible region (UV-Vis). The photocatalytic degradations are investigated by methylene blue (cationic) and methyl orange (anionic) dyes and the mechanisms acting in the photocatalysis are estimated by a scavenger's methodology. The diffractograms indicate that the MAH method provides powders with high crystallinity and without secondary phases. SEM micrographs indicate that the Ag2MoO4 phase is formed by micrometric particles with a coarse aspect and the Ag2WO4 phase is formed by micrometric rods with a square cross-section. The direct Egap varied from 3.46 to 3.23 eV for the Ag2MoO4 and Ag2WO4 phases, respectively. The adsorptive and photocatalytic tests showed that the Ag2WO4 phase has a better performance against both dyes than the Ag2MoO4 phase, being the best performance against the MB dye (complete discoloration after 20 min). The scavenger's tests showed that the positive charges (h(+)) are the main mechanism acting in the photocatalysis for the Ag2MoO4 phase, while the h(+) and hydroxyl radicals (center dot OH) have a similar influence in the Ag2WO4 phase. Photocatalytic tests of reuse indicated that the samples have a good photocatalytic capacity even in the third consecutive cycle. (C) 2020 Elsevier B.V. All rights reserved.