Surface-dependent properties of α-Ag2WO4: a joint experimental and theoretical investigation

Alpha-silver tungstate (α-Ag2WO4) has attracted much attention in recent years due to its unique crystal and electronic structures, which are suitable for a wide range of applications. This work presents a more realistic study, based on frst-principles calculations and experimental results, of the potential of α-Ag2WO4 for antibacterial and photocatalytic activity. α-Ag2WO4 material has been successfully synthesized by a coprecipitation method and subjected to microwave irradiation for diferent times. The as-synthesized microcrystals were structurally characterized by X-ray difraction, while the morphological aspects were investigated by feld emission scanning electron microscopy. The experimental studies and theoretical simulations of α-Ag2WO4, based on density functional theory calculations, have highlighted several key parameters (surface dependent) that determine the antibacterial (against Staphylococcus aureus) and photocatalytic activity (for the degradation of rhodamine B) and provided some general principles for material design. We believe that our results ofer new insights regarding the local coordination of superfcial Ag and W atoms (i.e. clusters) on each exposed surface of the corresponding morphology, that dictate the antibacterial and photocatalytic activities of α-Ag2WO4, a feld that has so far remained unexplored

Zinc-substituted Ag2CrO4: A material with enhanced photocatalytic and biological activity

In the past years, new environmentally-friendly photocatalysts have been reported, but the realization of efficient visible-light driven photocatalyst with highly active bactericidal and fungicidal activity is still challenging. This work is a joint experimental and theoretical study on the structural, electronic, and optical properties of Ag2CrO4:Zn2+ (ACOxZn, x = 1%, 2%, and 4%) solid solutions for photocatalytic, bactericidal, and fungicidal activity. For the first time, synthesis of these innovative and multifunctional materials were performed through the cation exchange of zinc and silver using a simple, fast, and cheap co-precipitation method. Powder X-ray diffraction measurements revealed the long range order of the materials. X-ray photoelectron spectroscopy provided information about the surface of the samples demonstrating that they were pure. The materials showed short-range order as verified by FT-Raman spectroscopy. Additionally, ultraviolet-visible diffuse reflectance spectra and photoluminescence spectroscopy were used to examine the electronic properties which corroborated with the increasing photocatalytic activity for the degradation of Rhodamine B and bactericidal activity against Staphylococcus aureus and Candida albicans. Field emission scanning electron microscopy images showed different types of particles with different facets and sizes. Theoretical results based on density functional theory calculations complement the experimental results to rationalize the effects of the incorporation of Zn cations in the ACO host lattice

Towards the scale-up of the formation of nanoparticles on α-Ag2WO4 with bactericidal properties by femtosecond laser irradiation

Abstract 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

Synthesis, antifungal evaluation and optical properties of silver molybdate microcrystals in different solvents: a combined experimental and theoretical study

International audienceIn this study, we investigate the structure, antifungal activity, and optical properties of beta-Ag2MoO4 using experimental and theoretical approaches. beta-Ag2MoO4 samples were prepared by a co-precipitation method using different solvents (water, ethanol and ammonia), and their antifungal activity against Candida albicans was investigated. The samples were characterized by X-ray diffraction, micro-Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy with energy dispersive spectroscopy. The optical properties were investigated by UV-Vis spectroscopy and photoluminescence measurements at room temperature. The thermodynamic equilibrium shape of the beta-Ag2MoO4 crystals was determined based on the surface energies calculated using Wulff construction. The (011) orientation was the predominant surface in the morphology. The experimental morphology was obtained by varying the surface energy ratio for each facet. A large decrease in surface energy for the (111) surface provided the experimental morphology for crystals synthesized using water and ethanol as solvents; when the surface energies for both (011) and (001) surfaces increased, the crystal morphology obtained using ammonia as a solvent was reproduced. A correlation between the exposed surfaces and antifungal activity was revealed, and an explanation to this behavior that arises from different morphologies and structural data was provided. Theoretical calculations confirm the rationality of the experimental scheme and elucidate the underlying reason for the fungistatic and fungicidal activity against Candida albicans

Ag Nanoparticles/AgX (X=Cl, Br and I) Composites with Enhanced Photocatalytic Activity and Low Toxicological Effects

This is the pre-peer reviewed version of the following article: M. Assis, F. C. Groppo Filho, D. S. Pimentel, T. Robeldo, A. F. Gouveia, T. F. D. Castro, H. C. S. Fukushima, C. C. de Foggi, J. P. C. da Costa, R. C. Borra, J. Andrés, E. Longo. Ag Nanoparticles/AgX (X=Cl, Br and I) Composites with Enhanced Photocatalytic Activity and Low Toxicological Effects, which has been published in final form at https://doi.org/10.1002/slct.202000502. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Periodic structures induced by electron irradiation are a unique phenomenon when electron beams irradiate on the surface of some materials. These periodic structures have potential for technological applications. However, the fuzzy nature of the electron‐induced structuring hinders its further exploration in such applications. In this paper, novel Ag nanoparticle/AgX (X=Cl, Br and I) composites, with enhanced photocatalytic activity and low toxicological effects, were prepared, for the first time, using electron beam irradiation. The remarkable advantage of this approach is that the Ag nanoparticles/AgX composites can be easily prepared in one‐step without the need for high‐pressure conditions, surfactants, ionic liquids, or reducing agents. Furthermore, our method does not involve any toxic substances, which makes the as‐synthesized samples highly applicable for technological applications. The structure, morphology and physicochemical properties of the Ag nanoparticles/AgX composites were studied using various characterization techniques. Using first‐principles calculations based on density functional theory and the quantum theory of atoms in molecules, we reveal how the concentration of excess electrons in the AgX materials induces the formation of the Ag nanoparticles under electron beam irradiation. These results extend the fundamental understanding of the atomic process underlying the mechanism of Ag−X bond rupture observed during the transformation induced via electron irradiation of the AgX crystals by increasing the total number of electrons in the bulk structure. Thus, our findings provide viable guidance for the realization of new materials for the degradation of contaminated wastewater with low toxicity

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

Rational Design of W-Doped Ag3PO4 as an Efficient Antibacterial Agent and Photocatalyst for Organic Pollutant Degradation

International audienceBacterial and organic pollutants are major problems with potential adverse impacts on human health and the environment. A promising strategy to alleviate these impacts consists in designing innovative photocatalysts with a wider spectrum of application. In this paper, we report the improved photocatalytic and antibacterial activities of chemically precipitated Ag3PO4 microcrystals by the incorporation of W at doping levels 0.5, 1, and 2 mol %. The presence of W directly influences the crystallization of Ag3PO4, affecting the morphology, particle size, and surface area of the microcrystals. Also, the characterization via experimental and theoretical approaches evidenced a high density of disordered [AgO4], [PO4], and [WO4] structural clusters due to the substitution of P5+ by W6+ into the Ag3PO4 lattice. This leads to new defect-related energy states, which decreases the band gap energy of the materials (from 2.27 to 2.04 eV) and delays the recombination of e'-h(center dot) pairs, leading to an enhanced degradation process. As a result of such behaviors, W-doped Ag3PO4 (Ag3PO4:W) is a better visible-light photocatalyst than Ag3PO4, demonstrated here by the photodegradation of potential environmental pollutants. The degradation of rhodamine B dye was 100% in 4 min for Ag3PO4:W 1%, and for Ag3PO4, the obtained result was 90% of degradation in 15 min of reaction. Ag3PO4:W 1% allowed the total degradation of cephalexin antibiotic in only 4 min, whereas pure Ag3PO4 took 20 min to achieve the same result. For the degradation of imidacloprid insecticide, Ag3PO4:W 1% allowed 90% of degradation, whereas Ag3PO4 allowed 40%, both in 20 min of reaction. Moreover, the presence of W-dopant results in a 16-fold improvement of bactericidal performance against methicillin-resistant Staphylococcus aureus. The outstanding results using the Ag3PO4:W material demonstrated its potential multifunctionality for the control of organic pollutants and bacteria in environmental applications