Papers by Keyword: Silver

Abstract: This work revealed the ability of silver,silicon co-substituted apatite (Ag,Si-HA) to inhibit the growth of Staphylococcus aureus (S. aureus), with a 7-log reduction of adherent bacteria on Ag,Si-HA as compared to HA. Furthermore, it demonstrated that surface-bound Ag⁺ ions was responsible for the antibacterial action since there was not much Ag⁺ ions being released.

Abstract: Hydroxyapatite [Ca₅(PO₄)₃(OH)] is a form of calcium phosphate inorganic compound of great importance in the health area because of its presence in bone as in teeth where it provides structural rigidity to the matrix. Hydroxyapatite is often used in the biomaterial area as a primary material for implants that help regenerate tissues. The addition of doping agents may improve the degree of crystallization providing new characteristics to the material without losing its biocompatibility. The present study shows characterization results for a hydroxyapatite biomaterial doped with silver and/or fluorine prepared through combustion method. The mineralogy was determined using X-Ray diffraction identifying the following phases: Ca₅(PO₄)₃OH, Ca₂P₂O₇, Ag₃PO₄, Ca₅(PO₄)₃F and CaF₂; the oxidation state of elements was determined by X-ray photoelectron spectroscopy; the morphological structure was studied by scanning electron microscopy and atomic force microscopy. Biocompatibility tests through intramuscular and subcutaneous implantation were performed in rodents to evaluate inflammatory response at 7, 14 and 30 days.

Abstract: A novel method was used to make palygorskite supported nano-silver powder at room temperature. XRD result showed the presence of silver in the final product. TEM investigation revealed that nano-sliver particles of 6-10 nm in diameter were successfully attached on surface of palygorskite fiber. FTIR was also used to clarify the formation mechanism of our method. The antibacterial effect of palygorskite supported nano-silver powder was investigated. Palygorskite supported nano-silver powder had good antibacterial activity on standard Escherichia coli and Staphylococcus aureus.

Abstract: For achieving high-temperature resistance and a broadband of microwave transmission, ceramic metamaterials consisting of fused silica ceramic substrates and electrically conductive networks/ arrays are desirable. A new strategy of fabricating the fused silica metamaterials is to combine the low temperature co-fired ceramic (LTCC) technique with a method of ceramic joining via green tapes. The important part of the new strategy lies in the preparation of suitable green tapes that are co-firable with a conductive silver-based film/strip and have a strong affinity to the fused silica substrates. Therefore, in this paper, three green tape materials were prepared and intensively characterised using scanning electron microscopy, x-ray diffraction, dilatometry, dielectric measurement, etc. It was found that the tape materials were based on dielectric glasses and crystalline phases of major eulytite and minor cristobalite, leading to rather low levels of dielectric constant (<6) and loss tangent (in the order of 10^-3). The three tape materials also had different levels of thermal expansion coefficients, co-firability with a conductive silver-based paste, and bondability to the fused silica substrates. These findings suggest that one can achieve desirable ceramic matematerials with well-controlled shapes and dimensions of the condutive networks/arrays after properly laminating the green tapes between the fused silica substrates.

Abstract: This work describes the formation of silver-coated gold nanoparticles (Ag-AuNPs) using the seeding-growth method. 15 nm AuNPs seeds were synthesized using the citrate reduction method. In the growth stage, the adding sequence of seeds, ascorbic acid (AA), gold chloride (HAuCl₄) and silver nitrate (AgNO₃) was explored. The effect AgNO₃ volume (20 mM) was varied at 0.10, 0.25, 0.50, 1.00, 1.25 and 1.50 ml. Morphology of Ag-AuNPs was observed using a Transmission Electron Microscope (TEM) while UV-Vis Spectrophotometer was used to study the concentration and absorption spectra of colloidal Ag-AuNPs. Zeta-sizer analysis was used to study the particle size distribution of Ag-AuNPs in colloidal form. In the growth stage, the optimum adding sequence was found by adding AA as a reducing agent into AuNPs seeds followed by the addition of HAuCl₄ and AgNO₃. This reshuffle sequence is chosen due to the presence of two absorbance peaks at 398 nm and 501 nm compared to others. From TEM images, increasing concentration of silver ions affected the optical properties, end size of Ag-AuNPs as well as raises the concentration of the colloids suspension. The biological properties of samples Ag-AuNPs (0.1 ml to 0.5 ml AgNO₃) were studied by performing the conjugation process between samples and antibody; goat anti-human IgA (GaHIgA). An additional washing process was required to perform conjugation for Ag-AuNPs in order to remove by-product or unreacted chemical produced during synthesis process. The Ag-AuNPs was successfully conjugated with GaHIgA and required a minimum concentration of antibody (9µg/ml) after washing process. In addition, the washed Ag-AuNPs also improved its binding capability with GaHIgA by giving higher intense signal when tested with lined Human IgA on the lateral flow immunoassay (LFI) compared to un-washed Ag-AuNPs.

Abstract: Natural clinoptilolite (Cli) and chabazite (Cha) were used as the carrier for two types of antibacterial agents: cetylpyridinium chloride (CPC) and silver cations (Ag). CPC-zeolites, Ag-zeolites and CPC-Ag-zeolites were characterized by Energy Dispersive X-ray (EDX) analyzer and Fourier Transform Infrared (FTIR) spectroscopy and proved the attachment of CPC molecules on Ag-zeolite in CPC-Ag-zeolite samples. The determination of Minimum Inhibition Concentration (MIC) against P. aeruginosa and B. subtilis in saline solution and distilled water was performed to observe the effect of chloride ions on the antibacterial activity of the studied samples. From the MIC values, a new modified zeolite with CPC and Ag (CPC-Ag-zeolites) showed better antibacterial activity compared to that of CPC-zeolites and Ag-zeolites and performed well in both saline solution and distilled water.

Abstract: Semiconductor-mediated photocatalytic oxidation is an interesting method for water decontamination and a specially modified TiO₂ is said to be a promising material. This study verified that the synthesis of 1wt%Ag modified-Sc_0.01Ti_0.99O_1.995 powder samples prepared by Polymeric Precursor Method is capable of forming a mixture of anatase-rutile phase with high photocatalytic performance. This kind of material is found to have a lower bandgap compared to the TiO₂-anatase commercial powders, which can be associated to an innovative hybrid modification. The simultaneous insertion of scandium in order to generate a p-type semiconductor and a metallic silver nanophase acting as an electron trapper demonstrated being capable of enhancing the degradation of rhodamine B compared to the commercial TiO₂. In spite of the different thermal treatments or phase amounts, the hybrid modified powder samples showed higher photocatalytic activity than the commercial ones.

Abstract: This paper shows the results obtained from the synthesis of silver particles (nanoparticles and submicroparticles) on microfiltration membranes, evaluating the influence of surfactants impregnated in the membranes. Sub-micro particles and nanoparticles were obtained by the use of ascorbic acid as a reductant in a microfiltration system. Different shapes and sizes of the deposited silver particles on the membrane were obtained depending on the nature and concentration of the surfactant. The particles deposited over the membranes were characterized by scanning electron microscopy and energy- dispersive X-ray analysis.

Abstract: The objectives of this study were to produce ZrO₂-based nanoparticles doped with silver, using the polymeric precursor method (Pechini), and to verify their bactericidal activity against Escherichia coli and Staphylococcus aureus. Zirconium and silver oxides were chosen due to their bactericidal activity. The oxides were characterized by X-ray diffraction and field emission gun-scanning electron microscopy. The support for the oxides was a porous surface used in gravity filters. The method was not effective against the bacterium Escherichia coli in the sample subjected to UV light for 45 min, since it did not eliminate the bacterium, and did not inhibit colony growth and formation. However, the bactericidal activity test proved effective against Staphylococcus aureus, eliminating the bacterium when the sample was subjected to UV light for 45 min, thus preventing colony growth and formation.

Abstract: Ag/ZnO powders were synthesized through hydrolysis of Zn²⁺ in an alkaline solution at various mole ratios of Zn²⁺:OH^- without any stabilizer. At a mole ratio of Zn²⁺:OH^- = 1:1.5, the ZnO particles showed as bi-hexagonal prisms. At higher OH^- concentrations, the shape became spherical and then finally transformed to an agglomeration of platelet like-shapes at mole ratios of Zn²⁺:OH^- = 1:5. The photocatalytic activity was investigated through degradation of a methylene blue solution. Under irradiation from blacklight fluorescence tubes, ZnO prepared from Zn²⁺:OH^- = 1:1.5 was the best photocatalyst compared with those prepared from different mole ratios of Zn²⁺:OH^-. This could be due to a high area of hexagonal facets as represented by the (0002) plane. By varying the amount of added Ag between 1-5 mol%, the ZnO prepared from 3 mol% of Ag showed the highest efficiency for photocatalytic degradation of methylene blue and its activity was also better than for pure ZnO.