Formation of Ag Nanoparticles on ß-Ag2WO4 through Electron Beam Irradiation: A Synergetic Computational and Experimental Study.

In the present work, a combined theoretical and experimental study was performed on the structure, optical properties, and growth of Ag nanoparticles in metastable ß-Ag2WO4 microcrystals. This material was synthesized using the precipitation method without the presence of surfactants. The structural behavior was analyzed using X-ray diffraction and Raman and infrared spectroscopy. Field-emission scanning electron microscopy revealed the presence of irregular spherical-like Ag nanoparticles on the ß-Ag2WO4 microcrystals, which were induced by electron beam irradiation under high vacuum conditions. A detailed analysis of the optimized ß-Ag2WO4 geometry and theoretical results enabled interpretation of both the Raman and infrared spectra and provided deeper insight into rationalizing the observed morphology. In addition, first-principles calculations, within the quantum theory of atoms in molecules framework, provided an in-depth understanding of the nucleation and early evolution of Ag nanoparticles. The Ag nucleation and formation is the result of structural and electronic changes of the [AgO6] and [AgO5] clusters as a constituent building block of ß-Ag2WO4, which is consistent with Ag metallic formation.

Synthesis and characterization of metastable ß-Ag2WO4: an experimental and theoretical approach.

Metastable silver tungstate (ß-Ag2WO4) has attracted much attention lately because of its many potential applications. However, the synthesis of metastable phases of inorganic compounds is challenging because of the ease of transformation to the stable phase. We have overcome this challenge and have successfully synthesized ß-Ag2WO4 microcrystals using a dropwise precipitation (DP) method in aqueous media at low temperature. The microcrystals were characterized by X-ray diffraction (XRD), including powder X-ray diffraction structural determination, field-emission scanning electron microscopy (FE-SEM), and micro-Raman/ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy. To complement the experimental data, we present first-principles quantum-mechanical density functional theory (DFT) calculations. Using XRD data, Raman/UV-vis data, and the determined optical band gap, together with geometric optimization calculations, we confirmed the structure of this compound. ß-Ag2WO4 has a hexagonal structure with a P63/m space group. The building blocks of the lattice comprise two types of W-O clusters, [WO4] and [WO5], coordinated to four and five O atoms, respectively, and two types of Ag-O clusters, [AgO6], and [AgO5], linked to six and five O atoms, respectively. This type of fundamental study, combining multiple experimental methods and first-principles calculations, helps to obtain a basic understanding of the local structure and bonding in the material.

Structural and electronic analysis of the atomic scale nucleation of Ag on α-Ag2WO4 induced by electron irradiation.

In this work, we utilise a combination of theory, computation and experiments to understand the early events related to the nucleation of Ag filaments on α-Ag2WO4 crystals, which is driven by an accelerated electron beam from an electron microscope under high vacuum. The growth process and the chemical composition and elemental distribution in these filaments were analysed in depth at the nanoscale level using TEM, HAADF, EDS and XPS; the structural and electronic aspects were systematically studied in using first-principles electronic structure theory within QTAIM framework. The Ag nucleation and formation on α-Ag2WO4 is a result of the order/disorder effects generated in the crystal by the electron-beam irradiation. Both experimental and theoretical results show that this behavior is associated with structural and electronic changes of the [AgO2] and [AgO4] clusters and, to a minor extent, to the [WO6] cluster; these clusters collectively represent the constituent building blocks of α-Ag2WO4.