Selective Synthesis of α-, β-, and γ-Ag₂WO₄ Polymorphs: Promising Platforms for Photocatalytic and Antibacterial Materials

Abstract

Silver tungstate (Ag 2 WO 4 ) shows structural polymorphism with different crystalline phases, namely orthorhombic, hexagonal, and cubic structures that are commonly known as α, β, and γ, respectively. In this work, these Ag 2 WO 4 polymorphs were selectively and successfully synthesized through a simple precipitation route at ambient temperature. The polymorph-controlled synthesis was conducted by means of the volumetric ratios of the silver nitrate/tungstate sodium dehydrate precursors in solution. The structural and electronic properties of the as-synthetized Ag 2 WO 4 polymorphs were investigated by using a combination of X-ray diffraction and Rietveld refinements, X-ray absorption spectroscopies, X-ray absorption near edge structure spectroscopy, field emission-scanning electron microscopy images, and photoluminescence. To complement and rationalize the experimental results, first-principles calculations, at density functional theory level, were carried out, leading to an unprecedented glimpse into the atomic-level properties of the morphology and the exposed surfaces of Ag 2 WO 4 polymorphs. Following the analysis of the local coordination of Ag and W cations (clusters) at each exposed surface of the three polymorphs, the structure-property relationship between the morphology and the photocatalytic and antibacterial activities against Amiloride degradation under ultraviolet light irradiation and methicillin-resistant Staphylococcus aureus, respectively, was investigated. A possible mechanism of the photocatalytic and antibacterial activity as well the formation process and growth of the polymorphs is also explored and proposed.

Interface matters: Design of an efficient α-Ag2WO4/Ag3PO4 photocatalyst

“…The Ag3PO4 and α-Ag2WO4 were synthesized by the coprecipitation method previously reported (Trench, Machado et al 2018, Roman Alvarez-Roca 2021. The heterojunctions containing 12, 24, and 36 wt% of α-Ag2WO4 in relation to Ag3PO4 were synthesized as shown in Figure 1, and were denoted as AWP 1, AWP 2 and AWP 3, respectively.…”

Ag2WO4 as a multifunctional material: Fundamentals and progress of an extraordinarily versatile semiconductor

“…Our research group also attained these microcrystals in 2013 in a rapid stoichiometric CP reaction at 90 C without external agents and via MAH in 2014 and another study with PVP surfactant, but this time, the morphologies were accompanied by other shapes, such as cubic and triangular crystals [12,17,19]. In recent article, we report the selective synthesis of each a-, b-, g-Ag 2 WO 4 polymorphs through a simple precipitation route at ambient temperature by controlling the volumetric ratios of the AgNO 3 /Na 2 WO 4 •2H 2 O precursors in solution [101]. This selective synthesis allows us to control the formation of the desired polymorph.…”

Zinc tungstate: a review on its application as heterogeneous photocatalyst

“…Its physical and chemical properties, in terms of molecular and electronic versatility, reactivity, and stability, make ZnWO 4 a promising candidate in photocatalysis for the photodegradation of chemical contaminants [37][38][39][40]. At room temperature, ZnWO 4 has a wolframite-type structure, characterized by a monoclinic symmetry with space group P2/c or C 4 2h and no evidence of polymorphism has been reported in the literature yet for ZnWO 4 as it occurs in SrWO 4 [41], Ag 2 WO 4 [42] and Fe 2 WO 6 [43]. In this structure, Zn and W cations are in octahedral symmetry forming a tridimensional lattice of distorted ZnO 6 and WO 6 octahedra in alternating layers as shown in Fig.…”