Synthesis and Characterization of Ag-Modified V2O5 Photocatalytic Materials

Hindawi Journal of Chemistry Volume 2017, Article ID 5849103, 10 pages https://doi.org/10.1155/2017/5849103 Research Article Synthesis and Characterization of Ag-Modified V2O5 Photocatalytic Materials Dora Alicia Solis-Casados,1 Luis Escobar-Alarcon,2 Antonia Infantes-Molina,3 Tatyana Klimova,4 Lizbeth Serrato-Garcia,1 Enrique Rodriguez-Castellon,3 Susana Hernandez-Lopez,5 and Alejandro Dorazco-Gonzalez1 1 Centro Conjunto de Investigación en Quı́mica Sustentable UAEM-UNAM, Km 14.5 Carretera Toluca-Atlacomulco, Unidad San Cayetano, 50200 Toluca, MEX, Mexico 2 Departamento de Fı́sica, Instituto Nacional de Investigaciones Nucleares, P.O. Box 18-1027, 11801 Mexico City, Mexico 3 Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Malaga, 29071 Malaga, Spain 4 Departamento de Ingenieria Quimica, UNAM, Mexico City, Mexico 5 Facultad de Quı́mica, Universidad Autónoma del Estado de México, Paseo Colon esq Paseo Tollocan Col Nueva la Moderna, 50000 Toluca, MEX, Mexico Correspondence should be addressed to Dora Alicia Solis-Casados; solis Received 6 August 2016; Revised 29 October 2016; Accepted 10 November 2016; Published 14 February 2017 Academic Editor: Julie J. M. Mesa Copyright © 2017 Dora Alicia Solis-Casados et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. V2 O5 powders modified with different theoretical silver contents (1, 5, 10, 15, and 20 wt% as Ag2 O) were obtained with acicular morphologies observed by scanning electron microscopy (SEM). Shcherbinaite crystalline phase is transformed into the Ag0.33 V2 O5 crystalline one with the incorporation and increase in silver content as was suggested by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With further increase in silver contents the Ag2 O phase appears. Catalysts were active in photocatalytic degradation of malachite green dye under simulated solar light, which is one of the most remarkable facts of this work. It was found that V2 O5 -20Ag was the most active catalytic formulation and its activity was attributed to the mixture of coupled semiconductors that promotes the slight decrease in the rate of the electron-hole pair recombination. 1. Introduction In recent years, wastewaters from domestic and industrial uses have contributed to the environmental problem because they arrive to the soil and aquifers mantles polluting clean water. In order to address this issue, the effort of many researchers from several scientific disciplines around the world [1, 2] has been focused on wastewater remediation. Heavy metals such as mercury, iron, cadmium, and chromium are included between the most dangerous pollutants in wastewaters as well as some organic compounds such as the phenols, dyes, pesticides, pharmaceutical, and fertilizers and in some cases solvents. All of them are extremely toxic to the humans and also living organisms, even if they are in a low concentration [3]. Several researchers have proposed solutions to reduce the most dangerous and toxic pollutants contained in wastewaters and also to improve water quality modifying the chemical processes, proposing new absorbent materials and some of the advanced oxidation processes as photocatalysis, which includes developing a photocatalytic material. The remotion of the most resilient organic compounds is among the most important topics concerning wastewater remediation and widely studied nowadays. In so many cases, one of the most extended methods is the photocatalytic degradation, whereby the catalyst is activated by using light. It is noteworthy that degradation of the resilient organic compounds dissolved in water occurs in a natural way by the photolysis process by using the cheapest 2 source energy such as that provided by the sun. The main disadvantage is its very low efficiency since the organic molecules degrade slowly, taking days and even months to achieve the complete mineralization of organic compounds into water and CO2 . The photocatalytic process increases the decomposition rate of organic compounds present in wastewaters. The photocatalyst employed is commonly a semiconductor material with desirable characteristics such as photoactivity, being chemically and biologically inert, photostability, nontoxicity, and low cost [4]. A photocatalyst could be employed in its pure, mixed, or doped form. An example of this is the TiO2 in its anatase crystalline phase with a band gap energy around 3.2 eV and the rutile crystalline phase with a band gap energy of 3.0 eV [5, 6]. It has been reported that mixing different ratios of anatase : rutile results in higher catalytic activities, which can be attributed to the synergistic effect between both phases, as occurs in coupled semiconductors [7]. Titania in its anatase crystalline phase is in disadvantage for generating the electron-hole pair if the excitation source is sunlight [8, 9]. It is the reason to improve the photocatalytic performance of TiO2 by doping and modification with metals and nonmetals [10, 11]. It is well known that, in order to obtain better catalytic performance, it is not enough that the photocatalytic material has a low band gap energy to be active under sunlight. Some unstable materials with reduced band gap energy are Fe2 O3 (2.3 eV), GaP (2.23 eV), and GaAs (1.4 eV) that are not so good as photocatalysts to degrade organic compounds in aqueous solutions [12]. It has been reported before by some researchers that one of the materials with low band gap energy, of around 2.8 eV, and some stability in aqueous solutions is the V2 O5 -based photocatalysts [13], potentially active under irradiation with visible light and investigated in the last years [14–17]. The synthesis of V2 O5 has been reported by using techniques as the hydrothermal synthesis [18], solgel technique [19], thermal decomposition of several precursors as ammonium metavanadate (NH4 VO3 ) [20], flamespray pyrolysis [21, 22] magnetron sputtering, electron-beam evaporation, and pulsed laser deposition [23, 24], obtaining several morphologies as nanobelts [18, 19], nanowires [18], nanoribbons, nanopowders [18, 21], and also thin films [19, 21–23]. Thin films and powders have been obtained with different textural and structural properties related in some cases with their photocatalytic activity [24–26]. It should be considered that the request of doped or coupled a V2 O5 catalyst to another semiconductor to retarding the recombination of the electron-hole pair, improving catalytic activity [27], is due to the disadvantage of short migration distances for excited electron-hole pairs which increases the recombination rate and decreasing the photocatalytic activity. Other researchers to solve this fact in photocatalysts with low band gap energy have reported that adding a small amount of noble metals (such (...truncated)