Tungstate Microcrystals Research Articles

Silver tungstate microcrystals and their performance over several clinical multidrug resistant microorganisms

In this paper, we report the screening antimicrobial properties against several pathogenic microorganisms of silver tungstate microcrystals synthesized by the hydrothermal method at 120 °C for 12 h. These microcrystals were structurally characterized using the X-ray diffraction (XRD) and Rietveld refinement, where the orthorhombic structure (α-Ag2WO4) with space group and point group of Pn2n and C2v10, respectively. In according, the Raman spectrum and infrared spectrum are characteristic of pure alpha phase of silver tungstate exhibiting the main characteristic bands of orthorhombic structure. Thorough UV–vis by diffuse reflectance employing the Tauc’s method the obtained optical band gap (Egap) was 3.02(3) eV. While, the survey spectrum and high resolution Ag3d, O1s and W4f by X-ray photoelectron spectroscopy (XPS) are shown all biding energy peaks of characteristic elements of silver tungstate as well as, confirming the presence of Ag0 for silver nanoparticles. Several rod-like microcrystals were archived by field emission scanning electron microscopy (FE-SEM), all these, exhibiting high definition and grown of silver nanoparticles with the increase of exposure time by electrons gun. Finally, the screening antimicrobial properties of α-Ag2WO4 confirm the high antimicrobial activity for main gram-positive and gram-positive bacteria with minimum inhibitory concentration (MIC) less than positive control (TIENAM). Therefore, the α-Ag2WO4 microcrystals synthesized have been exhibited promissory properties in biomedical applications, particularly, in the multi-drugs gram-positive and gram-negative stains control.

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

In this study we report the synthesis of silver tungstate microcrystals (α-Ag2WO4) by sonochemistry method (SC) at 65 °C and sonochemistry followed by conventional hydrothermal (SC + HC) for 1, 6 and 12 h, at 140 °C. The structural characterization by XRD confirms the alpha phase of the orthorhombic structure and the space group Pn2n, for all synthesized microcrystals. All the actives modes identified at the Raman spectroscopy were characteristic of alpha phase. The optical band gap by UV-Vis spectroscopy using the diffuse reflectance were 2.98, 3.0, 2.99 and 2.96 eV, for the microcrystals SC, SC + HC-1 h, SC + HC-6 h and SC + HC-12 h, respectively. FE-SEM images show the rod-like microcrystals, however, exhibiting the plane surface (1 0 1) only for the synthesized microcrystals with the assistance of the hydrothermal method (SC + HC-1 h, SC + HC- 6 h and SC + HC-12 h). The antimicrobial potential was confirmed for all α-Ag2WO4 microcrystals synthesized. However, the SC + HC-12 h microcrystals were more susceptible in the bacterial and fungal inhibition, with MIC values for microorganisms C. albicans, T. rubrum, MRSA e EHEC, 0.2-0.5, 4-9, 250 and 31.25 μg mL-1, respectively.

Promising effects of silver tungstate microcrystals on fibroblast human cells and three dimensional collagen matrix models: A novel non-cytotoxic material to fight oral disease

Silver tungstate (α-Ag2WO4) microcrystals have shown encouraging results regarding their antimicrobial activity. However, in addition to the promising outcomes in fighting oral disease, cytotoxic tests are mandatory for screening new materials for biological applications. Here, we developed a better understanding of the effects of microcrystals on the behavior of both human gingival fibroblast (HGF) cells and three-dimensional (3D) collagen matrices. To perform these experiments, the lowest concentration of α-Ag2WO4 capable of preventing the visible growth of Candida albicans (C. albicans) planktonic cells was defined as the test concentration, and it ranged from 0.781 (C1) to 7.81 (C2) to 78.1 (C3) μg/mL. Complete medium and lysis buffer (LB) served as negative (C-) and positive (C+) controls, respectively. The effect of the microcrystal concentration on the morphology, remodeling and proliferation of HGF cells was evaluated by different approaches. Quantitative and qualitative assessments demonstrated that α-Ag2WO4 did not affect the mitochondrial enzymatic activity of HGF cells cultured in a monolayer or the cell viability within 3D collagen matrices. These experiments showed that α-Ag2WO4 at the C2 concentration did not damage the genomic DNA. The development of new materials is attractive for the possible treatment of diseases and for avoiding indiscriminate prescribing of antibiotics. These findings provide information on the effect of α-Ag2WO4 on cell behavior and reveal that these microcrystals are non-cytotoxic against human gingival cells over a sufficient period to measure the hazard potential.

Enhancement of symmetry-induced photoluminescence in bismuth tungstate microcrystals

Bi2WO6 (BWO) powders synthesized via hydrothermal processes were studied in order to determine the effect of structure on photoluminescence (PL). BWO samples were characterized using X-Ray Powder Diffraction, UV–vis diffuse reflectance, field emission scanning electron microscopy, and PL intensity measurements. Orthorhombic structures were observed in all samples. A change in crystal microstructure and optical band gap was observed. The PL intensity obtained with different samples varied, with the highest intensity obtained with BWO fabricated with polyvinylpyrrolidone (PVP). Using Raman spectroscopy, a change in the microcrystal symmetry from P21ab to B2cb was observed and found to be responsible for the increase in photoluminescence.

Cytotoxic effects of silver tungstate microcrystals on fibroblast human cells

Cytotoxic effects of silver tungstate microcrystals on fibroblast human cells

Influence of surfactant on morphology of CaWO4 nano- and microcrystals

Calcium tungstate nanocrystals and spherical microcrystals were prepared, using a calcium tungstate muddy solution by precipitation with natrium tungstate and calcium acetate as starting materials, and adding different surfactants (PEG200 and CTAB). The samples were characterised by X-ray diffraction and transmission electron microscopy. The results indicate that the crystallites of the calcium tungstate samples are excellent, and the particles are well dispersed and not aggregated. PEG200 is essential for the preparation of dispersing calcium tungstate nanocrystals. Cetyltrimethyl ammonium bromide plays an important role in the formation of spherical calcium tungstate microcrystals. When excited at 265 nm, the luminescence of calcium tungstate exhibits the luminous peak in the blue band. The spherical calcium tungstate microcrystals have the maximum luminescent intensity.

Effect of annealing on structural and optical properties of lead tungstate microcrystals

Shuttle-like lead tungstate (PbWO4) microcrystals are synthesized at room temperature using the precipitation method with the cetyltrimethyl ammonium bromide. Results from both the X-ray diffraction and the scanning electron microscopy show that the lattice distortions of the PbWO4 microcrystals are reduced significantly when the annealing temperature is increased to 873 K. The result from the ultraviolet-visible diffuse reflectance spectroscopy shows that the exciton absorption appears in the sample annealed at 673 K. The self-trapped exciton luminescence due to the Jahn-Teller effect is also observed in the blue band. The interstitial oxygen ions in the WO42− groups are mainly resposible for the enhancement effect of the green luminescence of the annealed samples. The above results are supported by the spectrum analysis of the as-grown and the post-annealed samples using the X-ray photoelectron spectroscopy.

Fabrication of lead tungstate microcrystals on a lead surface at room temperature

A new strategy has been successfully designed to synthesize lead tungstate (PbWO 4) microcrystals on a lead surface by employing a novel solution-phase approach at room temperature. This method consists of a liquid–solid reaction between Na 2WO 4 solution and lead substrate itself in the assistance of glycine, l-glutamic acid, sodium citrate, or sodium adipic acid, respectively. The existence of these organic molecules plays an important role in the current synthetic process (serves as a growth promoter and organic structure-directing agent). This approach provides a facile strategy to produce PbWO 4 microcrystals on a lead substrate, which may be applicable to the synthesis of other inorganic materials on other metal substrates with various potential applications.

Reply to the ‘Comment on ‘Molten salt synthesis of barium molybdate and tungstate microcrystals’’

Reply to the ‘Comment on ‘Molten salt synthesis of barium molybdate and tungstate microcrystals’’

Fast synthesis and morphology control of lead tungstate microcrystals via a microwave-assisted method

Lead tungstate (PbWO 4) microcrystals with different morphologies, such as tetragonal flowerlike, amygdaloidal, and multiple-lamellar, have been successfully synthesized via a simple microwave-assisted method. Various factors, such as the pH value and the concentration of the cetyltrimethylammonium bromide (CTAB), play an important role in the morphological control of PbWO 4 microcrystals. The products were characterized by the techniques of powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The possible formation mechanisms of PbWO 4 samples of various morphologies were discussed. The luminescence properties of the final products were investigated and the as-prepared PbWO 4 microcrystals showed special room-temperature photoluminescence intensity compared to the solid structures.

Microwave-assisted synthesis and characterization of luminescent lead tungstate microcrystals

Lead tungstate (PbWO 4) microcrystals with different morphologies, such as tetragonal sheet-like, multiwall-like, quasi octahedron-like, and flower-like, have been successfully synthesized for the first time via a facile microwave-assisted method. The concentration of cetyltrimethylammonium and the reaction time were found to play an important role in the morphological control of resulting PbWO 4 microcrystals. The products were characterized by the techniques of powder X-ray diffraction pattern and field-emission scanning electron microscopy. A possible process contributed to the formation of the well-fined PbWO 4 microcrystals was discussed. The PbWO 4 microcrystals were found to display a strong room temperature luminescence with intensity depending on their shape.

Morphology control of stolzite microcrystals with high hierarchy in solution.

Crystal gazing: A mild solution route has been designed for the controlled synthesis of lead tungstate microcrystals with high crystal symmetry, in which the cationic surfactant, pH value, and temperature play key roles. Helix- (see TEM image), spindle-, chainlike, and dendritic structures can be produced by varying the reaction conditions.