Marcelo Assis

Mechanism of Antibacterial Activity via Morphology Change of α-AgVO3: Theoretical and Experimental Insights

The electronic configuration, morphology, optical features, and antibacterial activity of metastable α-AgVO3 crystals have been discussed by a conciliation and association of the results acquired by experimental procedures and first-principles calculations. The α-AgVO3 powders were synthesized using a coprecipitation method at 10, 20, and 30 °C. By using a Wulff construction for all relevant low-index surfaces [(100), (010), (001), (110), (011), (101), and (111)], the fine-tuning of the desired morphologies can be achieved by controlling the values of the surface energies, thereby lending a microscopic understanding to the experimental results. The as-synthesized α-AgVO3 crystals display a high antibacterial activity against methicillin-resistant Staphylococcus aureus. The results obtained from the experimental and theoretical techniques allow us to propose a mechanism for understanding the relationship between the morphological changes and antimicrobial performance of α-AgVO3.

Disclosing the electronic structure and optical properties of Ag4V2O7 crystals: experimental and theoretical insights

This work combines experimental and computational techniques to exploit the best of both methodologies and thus provide a tool for understanding the geometry, cluster coordination, electronic structure, and optical properties of Ag4V2O7 crystals. This tool has been developed to create structural models and enable a much more complete and rapid refinement of 3D (three dimensional) structures from limited data, aiding the determination of structure–property relationships and providing critical input for materials simulations. Ag4V2O7 crystals were synthesized by a simple precipitation method from an aqueous solution at 30 °C for 10 min. The obtained crystals were characterized by X-ray diffraction (XRD) and Rietveld refinement, and micro-Raman spectroscopy. The crystal morphology was determined by field emission scanning electron microscopy (FESEM), and the optical properties were investigated by ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) measurements. The geometric and electronic structures of Ag4V2O7 crystals were investigated by first-principles quantum-mechanical calculations based on the density functional theory. The theoretical results agree with the experimental data to confirm that Ag4V2O7 crystals have an orthorhombic structure, and that the building blocks of the lattice comprise two types of V clusters, [VO4] and [VO5], and two types of Ag clusters, [AgO5] and [AgO6]. This type of fundamental studies, which combine multiple experimental methods and first-principles calculations, have been proved valuable in obtaining a basic understanding of the local structure, bonding, band gap, and electronic and optical properties of Ag4V2O7 crystals.

Towards the scale-up of the formation of nanoparticles on α-Ag 2 WO 4 with bactericidal properties by femtosecond laser irradiation

In recent years, complex nanocomposites formed by Ag nanoparticles coupled to an α-Ag2WO4 semiconductor network have emerged as promising bactericides, where the semiconductor attracts bacterial agents and Ag nanoparticles neutralize them. However, the production rate of such materials has been limited to transmission electron microscope processing, making it difficult to cross the barrier from basic research to real applications. The interaction between pulsed laser radiation and α-Ag2WO4 has revealed a new processing alternative to scale up the production of the nanocomposite resulting in a 32-fold improvement of bactericidal performance, and at the same time obtaining a new class of spherical AgxWyOz nanoparticles.

Experimental and theoretical study of the energetic, morphological, and photoluminescence properties of CaZrO3:Eu3+

In this study, we present a combined experimental and theoretical study of the geometry, electronic structure, morphology, and photoluminescence properties of CaZrO3:Eu3+ materials. The polymeric precursor method was employed to synthesize CaZrO3:Eu3+ crystals, while density functional theory calculations were performed to determine the geometrical and electronic properties of CaZrO3:Eu3+ in its ground and excited electronic states (singlet and triplet). The results were combined with X-ray diffraction (XRD) measurements to elucidate the local structural changes induced by the introduction of Eu3+ in the crystal lattice. This process results in the formation of intermediate levels in the band-gap (Egap) region, narrowing its width. The PL emissions were rationalized by characterizing the electronic structure of the excited singlet and triplet electronic states, which provided deep insight into the main structural and electronic fingerprints associated with [CaO8], [EuO8], and [ZrO6] clusters. In addition, the Wulff construction, obtained from the first-principles calculations, was used to clarify the experimental morphologies. These results extend our fundamental understanding of the atomic processes that underpin the Eu doping of CaZrO3.

From Complex Inorganic Oxides to Ag–Bi Nanoalloy: Synthesis by Femtosecond Laser Irradiation

Bimetallic nanoalloys with a wide variety of structures and compositions have been fabricated through many diverse techniques. Generally, various steps and chemicals are involved in their fabrication. In this study, the synthesis of Ag–Bi nanoalloys by femtosecond laser irradiation of an inorganic oxide Ag2WO4/NaBiO3 target without any chemicals like reducing agents or solvent is presented. The interaction between these materials and the ultrashort pulse of light allows the migration of Ag and Bi atoms from the crystal lattice to the particles surfaces and then to the plasma plume, where the reduction of the positively charged Ag and Bi species in their respective metallic species takes place. Subsequently, the controlled nucleation and growth of the Ag–Bi alloyed nanoparticles occurs in situ during the irradiation process in air. Although at the bulk level, these elements are highly immiscible, it was experimentally demonstrated that at nanoscale, the Ag–Bi nanoalloy can assume a randomly mixed structure with up to 6 ± 1 atom % of Bi solubilized into the face-centered cubic structure of Ag. Furthermore, the Ag–Bi binary system possesses high antibacterial activity against Staphylococcus aureus (methicillin-resistant and methicilin-susceptible), which is interesting for potential antimicrobial applications, consequently increasing their range of applicability. The present results provide potential insights into the structures formed by the Ag–Bi systems at the nanoscale and reveal a new processing method where complex inorganic oxides can be used as precursors for the controlled synthesis of alloyed bimetallic nanoparticles.