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.

Tailoring the Bactericidal Activity of Ag Nanoparticles/α-Ag2WO4 Composite Induced by Electron Beam and Femtosecond Laser Irradiation: Integration of Experiment and Computational Modeling.

In nanotechnology research, significant effort is devoted to fabricating patterns of metallic nanoparticles on the surfaces of different semiconductors to find innovative materials with favorable characteristics, such as antimicrobial and photocatalytic properties, for novel applications. We present experimental and computational progress, involving a combined approach, on the antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) of as-synthesized α-Ag2WO4 samples and Ag nanoparticle composites (Ag NPs)/α-Ag2WO4. The former included two morphologies: hexagonal rod-like (α-Ag2WO4-R) and cuboid-like (α-Ag2WO4-C), and the latter included composites formed under electron beam, Ag NPs/α-Ag2WO4-RE and Ag NPs/α-Ag2WO4-CE, and femtosecond (fs) laser irradiation, Ag NPs/α-Ag2WO4-RL and Ag NPs/α-Ag2WO4-CL. Direct observations of the arrangement of Ag NPs on the Ag NPs/α-Ag2WO4 composites irradiated with an electron beam and laser, through transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, and field-emission scanning electron microscopy, allow us to investigate the surface morphology, chemical composition, homogeneity, and crystallinity. Therefore, these experimental factors, and in particular, the facet-dependent response of Ag NPs/α-Ag2WO4 composites were discussed and analyzed from the perspective provided by the results obtained by first-principles calculations. On this basis, α-Ag2WO4-R material proved to be a better bactericidal agent than α-Ag2WO4-C with minimum bactericidal concentration (MBC) values of 128 and 256 µg/mL, respectively. However, the Ag NPs/α-Ag2WO4-CL composite is the most efficient bactericidal agent of all tested samples (MBC = 4 µg/mL). This superior performance can be attributed to the cooperative effects of crystal facets and defect engineering. These results on the synthesis and stability of the Ag NPs/α-Ag2WO4 composites can be used for the development of highly efficient bactericidal agents for use in environmental remediation and the potential extension of methods to produce materials with catalytic applications.