Soluções sólidas α-Ag2-xCuxWO4 (0 ≤ x ≤ 0,1) obtidas por síntese hidrotermal: uma abordagem acerca das propriedades estruturais, morfológicas e fotocatalíticas

Abstract

In recent decades, the drinking water supply in the world has become a restricted and worrying source due to the scarcity of this valuable resource, mainly due to population growth and inappropriate effluents disposal with distinct carcinogenic, toxic and bioaccumulative capabilities. In these circumstances, this dissertation is based on development and integration of new technologies able to provide quick decontamination of persistent organic compounds within visible light region provided by blue LEDs irradiation. Therefore, solid solutions α Ag2 xCuxWO4 (x = 0; 0.01; 0.02, 0.06 and 0.1 mol) were synthesized through lattice substitutional of silver by copper atoms in pristine α-Ag2WO4 by conventional hydrothermal method at 140 ºC for 24 h. Subsequently, the evaluation of copper doping effect in the framework was performed by several analytical techniques and tested its photocatalytic efficiency against RhB dye. XRD results shows high purity, crystallinity, order at long-range while all samples were indexed to the orthorhombic phase, with conspicuous absence of secondary phases and impurities. Through Rietveld refinement it was clearly seen the favored substitution of copper atoms preferably in a lattice coordinate orientation, especially replacing the angular and tetrahedral silver clusters, arising [CuOy], y = 2, 4 and 6 clusters. Thus, FTIR and Raman spectra evidently shows the active modes of the orthorhombic structure of α Ag2WO4 carried out with bonding lengths changes as the copper content increases in solid solutions, therefore both greater resolution and new intense modes appearance evidence the formation of solid solutions. The optical results observed through reflectance UV-Vis confirms the copper insertion in the framework with red shift and significant decrease in Egap value, obtaining 3.12 eV for x = 0 mol and, 3.07 eV, 3.00 eV, 3.08 eV and, 3.04 eV for x = 0.01 mol; 0.02 mol; 0.06 mol and 0.1 mol, respectively, corroborating the visual color appearance in colorimetry experiments also changing the powder appearance from light beige to yellowish green. SEM images describe that the replacement takes high amount of superficial stress, that is, transformation of rod-like with hexagonal faces into faceted cuboid-like microcrystals within smaller crystals growing on bigger microcrystals surfaces. According to DLS results, as the doping content of copper increases greater is the dispersion and the distribution size of particles on the micro and sub-micro scale range in accordance to ZP behavior revealing anionic aspect of all samples and increasing stability to copper content. Accordingly, to the photocatalytic activities, all solid solutions were capable to achieve superior efficiency compared to pristine Ag2WO4, standing out the one x = 0.02 mol, which revealed activity in a wide pH range maintaining its efficiency above 80% thus PZC confirms that this catalyst has pH-dependent surface regions. Ultimately, the catalytic performance of the solid solution x = 0.02 mol is inherently higher compared to pristine silver tungstate and photolysis, with degradation and reaction constants rates 10.61 higher and 37.77 times more efficient.