Antimicrobial properties of α-Ag2WO4 rod-like microcrystals synthesized by sonochemistry and sonochemistry followed by hydrothermal conventional method

Tuning the morphology to enhance the catalytic activity of α-Ag2WO4 through V-doping

Here, we present the synthesis of a highly efficient V-doped α-Ag2WO4 catalyst for the oxidation of sulfides to sulfones, exhibiting a high degree of tolerance towards various sensitive functional groups. Remarkably, the catalysts with 0.01% V-doping content exhibited outstanding selectivity towards the oxidation process. Scavenger experiments indicated the direct involvement of electron-hole (e-/h+) pairs, hydroxyl radical (˙OH), and singlet oxygen (1O2) in the catalytic mechanism. Based on the experimental and theoretical results, the higher activity of the V-doped α-Ag2WO4 samples was associated with the preferential formation of the (100) surface in the catalyst morphology.

Ternary V-Scheme Ag2WO4/BaO/NiO Heterojunction Photocatalysts: Very Fast Degradation Process for Congo Red under UV-Light Irradiation

With increasing industrial production, pollutants generated in the process of bleaching or dying disperse to the natural water medium. Therefore, an effective photocatalytic material must be prepared for water treatment quickly. In the present study, a novel and effective V-scheme Ag₂WO₄/BaO/NiO heterostructure photocatalyst with high photocatalytic performance for the degradation of different organic pollutants was designed and formed by a simple precipitation method. Scanning electron microscopy images showed that BaO, NiO, and Ag₂WO₄/BaO/NiO have a nanopipe, spherical, and nanorod morphology, respectively. X-ray diffraction results indicated that cubic phases were obtained with higher crystallite structure and lower crystallite distortion. The optical properties of the samples exhibited UV-absorption regions with about 3.35, 3.38, and 3.28 eV band gaps for BaO, BaO/NiO, and Ag₂WO₄/BaO/NiO, respectively. The photocatalytic activity was investigated by the degradation of Congo red under UV-light irradiation. To investigate the photocatalytic mechanism, the photodegradation performance of the catalyst was analyzed with different scavengers such as isopropyl alcohol, ascorbic acid, and potassium iodide (KI), and it was shown that the main active species were ^•O₂ ^- radicals and that OH^• radicals have a significant contribution toward the degradation process. Compared to bare BaO and BaO/NiO samples, Ag₂WO₄/BaO/NiO showed excellent photocatalytic activity and about 41%, 66 and 99% of Congo red photodegraded under UV light within 30 min. The reason for this is that the Ag₂WO₄/BaO/NiO heterostructure displayed wider contact which promoted more charge-transfer ways to shorten the electron transportation path and increase the inhibition of electron-hole pairs.

Tug-of-War Driven by the Structure of Carboxylic Acids: Tuning the Size, Morphology, and Photocatalytic Activity of α-Ag2WO4

Size and morphology control during the synthesis of materials requires a molecular-level understanding of how the addition of surface ligands regulates nucleation and growth. In this work, this control is achieved by using three carboxylic acids (tartaric, benzoic, and citric) during sonochemical syntheses. The presence of carboxylic acids affects the kinetics of the nucleation process, alters the growth rate, and governs the size and morphology. Samples synthesized with citric acid revealed excellent photocatalytic activity for the degradation process of Rhodamine B, and recyclability experiments demonstrate that it retains 91% of its photocatalytic activity after four recycles. Scavenger experiments indicate that both the hydroxyl radical and the hole are key species for the success of the transformation. A reaction pathway is proposed that involves a series of dissolution-hydration-dehydration and precipitation processes, mediated by the complexation of Ag⁺. We believe these studies contribute to a fundamental understanding of the crystallization process and provide guidance as to how carboxylic acids can influence the synthesis of materials with controlled size and morphology, which is promising for multiple other scientific fields, such as sensor and catalysis fields.

Disclosing the Biocide Activity of α-Ag2−2xCuxWO4 (0 ≤ x ≤ 0.16) Solid Solutions

In this work, α-Ag2−2xCuxWO4 (0 ≤ x ≤ 0.16) solid solutions with enhanced antibacterial (against methicillin-resistant Staphylococcus aureus) and antifungal (against Candida albicans) activities are reported. A plethora of techniques (X-ray diffraction with Rietveld refinements, inductively coupled plasma atomic emission spectrometry, micro-Raman spectroscopy, attenuated total reflectance–Fourier transform infrared spectroscopy, field emission scanning electron microscopy, ultraviolet–visible spectroscopy, photoluminescence emissions, and X-ray photoelectron spectroscopy) were employed to characterize the as-synthetized samples and determine the local coordination geometry of Cu2+ cations at the orthorhombic lattice. To find a correlation between morphology and biocide activity, the experimental results were sustained by first-principles calculations at the density functional theory level to decipher the cluster coordinations and electronic properties of the exposed surfaces. Based on the analysis of the under-coordinated Ag and Cu clusters at the (010) and (101) exposed surfaces, we propose a mechanism to explain the biocide activity of these solid solutions.

Toxicity of α-Ag2WO4 microcrystals to freshwater microalga Raphidocelis subcapitata at cellular and population levels

Silver-based materials have microbicidal action, photocatalytic activity and electronic properties. The increase in manufacturing and consumption of these compounds, given their wide functionality and application, is a source of contamination to freshwater ecosystems and causes toxicity to aquatic biota. Therefore, for the first time, we evaluated the toxicity of the silver tungstate (α-Ag₂WO₄), in different morphologies (cube and rod), for the microalga Raphidocelis subcapitata. To investigate the toxicity, we evaluated the growth rate, cell complexity and size, reactive oxygen species (ROS) production and chlorophyll a (Chl a) fluorescence. The α-Ag₂WO₄ - R (rod) was 1.7 times more toxic than α-Ag₂WO₄-C (cube), with IC₁₀ and IC₅₀ values of, respectively, 8.68 ± 0.91 μg L^-1 and 13.72 ± 1.48 μg L^-1 for α-Ag₂WO₄ - R and 18.60 ± 1.61 μg L^-1 and 23.47 ± 1.16 μg L^-1 for α-Ag₂WO₄-C. The release of silver ions was quantified and indicated that the silver ions dissolution from the α-Ag₂WO₄ - R ranged from 34 to 71%, while the Ag ions from the α-Ag₂WO₄-C varied from 35 to 97%. The α-Ag₂WO₄-C induced, after 24 h exposure, the increase of ROS at the lowest concentrations (8.81 and 19.32 μg L^-1), whereas the α-Ag₂WO₄ - R significantly induced ROS production at 96 h at the highest concentration (31.76 μg L^-1). Both microcrystal shapes significantly altered the cellular complexity and decreased the Chl a fluorescence at all tested concentrations. We conclude that the different morphologies of α-Ag₂WO₄ negatively affect the microalga and are important sources of silver ions leading to harmful consequences to the aquatic ecosystem.

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

Silver tungstate (Ag₂WO₄) 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 Ag₂WO₄ 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-synthesized Ag₂WO₄ polymorphs were investigated by using a combination of X-ray diffraction and Rietveld refinements, X-ray absorption spectroscopy, 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 the 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 Ag₂WO₄ 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.

Multi-dimensional architecture of Ag/α-Ag2WO4 crystals: insights into microstructural, morphological, and photoluminescence properties

Varying the concentration of ethylenediamine resulted in hollow or solid Ag/α-Ag₂WO₄ microflowers that emit light in the red region or in the blue region, respectively.