Size Of Silver Particles Research Articles

Thermosensitive Behavior and Super-Antibacterial Properties of Cotton Fabrics Modified with a Sercin-NIPAAm-AgNPs Interpenetrating Polymer Network Hydrogel.

Poly(N-isopropylacrylamide) (PNIPAAm), sericin (SS), and silver nitrate were combined to prepare an interpenetrating network (IPN) hydrogel having dual functions of temperature sensitivity and antibacterial properties. The structure and size of AgNPs in such an IPN hydrogel were characterized by the Fourier Transform Infrared spectrum (FT-IR), X-ray powder diffraction (XRD) and Transmission Electron Microscope (TEM), and the thermal properties of the IPN hydrogel were characterized by Differential Scanning Calorimetry (DSC). Based on XRD patterns, Ag+ was successfully reduced to Ag0 by SS. It was observed by TEM that the particle size of silver particles was lower than 100 nm. The glass transition temperature (Tg) of IPN hydrogel was better than that of the PNIPAAm/AgNPs hydrogels, and lower critical solution temperature (LCST) values of the IPN hydrogel were obtained by DSC i.e. 31 °C. The thermal stability of the IPN hydrogel was successfully determined by the TGA. This IPN hydrogel was then used to modify the cotton fabrics by the “impregnation” method using glutaraldehyde (GA) as the cross-linking agent. The structures and properties of IPN hydrogel modified cotton fabric were characterized by scanning electron microscopy (SEM), FT-IR, and the thermogravimetry analysis (TGA). The results show that NIPAAm was successfully polymerized into PNIPAAm, and that there were neglected new groups in the hydrogel IPN. The IPN hydrogel was then successfully grafted onto cotton fabrics. SEM observations showed that the IPN hydrogel formed a membrane structure between the fibers, and improved the compactness of the fibers. At the temperature close to LCST (≈31 °C), the entire system was easily able to absorb water molecules. However, the hydrophilicity tended to decrease when the temperature was higher or lower than the LCST. The antibacterial rates of the modified cotton fabric against S. aureus and E. coli were as high as 99%.

Effective and regenerable Ag/4A zeolite nanocomposite for Hg0 removal from natural gas

The silver loaded adsorbents has been demonstrated to be an exciting approach towards Hg0 removal from natural gas streams, its Hg0 removal efficiency and capacity is closely related to the valence state, particle size and dispersity of silver particles. This study focused on chemical reduction methods in aqueous solutions to synthesize Ag/4A zeolite, and the influences of ultrasonic and protective additives were investigated to reduce the size of silver particles. The characterization results showed that silver particles are loaded on the surface of 4A zeolite with highly dispersed elemental form, ultrasonic and addition of stearic acid as protective additives are the effective ways to produce small nano-scale silver particles close to 15 nm. Meanwhile, the silver particles on the surface of Ag/4A zeolite are the active sites for Hg0 adsorption which can react with Hg0 to form Ag-Hg amalgam alloy. The silver lattices disappeared from the outer boundary to the interior of the particles after Hg0 adsorption, which indicated that the Hg0 firstly reacts with the nano-scale silver on the surfaces and then gradually penetrates into the interior of silver particles. The Hg0 removal efficiency of prepared Ag/4A zeolite adsorbents was higher than 96% after 200 min adsorption at 30 °C, and adsorption capacity reached to 5.985 mg/g. Furthermore, the regeneration and reutilization results indicated that the Hg0 adsorption performance remained stable after 5 reuse cycles.

Sunlight-assisted synthesis of colloidal silver nanoparticles using chitosan as reducing agent

The present study we explore an environmentally friendly colloidal silver nanoparticles preparation using chitosan as reducing agent and stabilizer. It develops a new strategy on preparation of silver nanoparticles through the gel phase using sodium hydroxide (NaOH) as accelerator reagent. Sunlight irradiation was employed to assisted reducing process of silver ions to silver nanoparticles. Localized surface plasmon resonance (LSPR) phenomenon of silver nanoparticles was investigated using UV-Vis spectrophotometer. The shape and size of silver particles were analyzed using TEM. The formation of silver nanoparticles was confirmed by the appearance of LSPR absorption peak at 396.0–412.0 nm. The absorption peak of LSPR were affected by NaOH amount, time of sulight irradiation and concentration of AgNO3. The produced silver nanoparticles were spherical with dominant size range of 5 to 8 nm as shown by TEM images. All colloidals were stable without any aggregation for 30 days after preparation.

Plasmochemical preparation of silver nanoparticles: thermodynamics and kinetics analysis of the process

The thermodynamics and kinetics analysis of the plasmochemical formation of silver nanoparticles is performed. The thermodynamics analysis is made on the basis of calculation of the Gibbs free energy of formation of silver nanoparticles in an aqueous medium by various methods. It was found that the Gibbs free energy in aqueous solutions increases with decreasing size of silver particles. Based on experimental data, it was determined that the average size of plasmochemically prepared particles depends on the initial concentration of silver ions in the solution and equals 36.5–60.1 nm for 0.25–3.0 mmol/l. The kinetics of chemical conversion in aqueous solutions of silver nitrate under plasma treatment conditions in a gas-liquid plasmochemical batch reactor is investigated. The curves of Ag + dependence on duration of plasmochemical treatment of solutions and initial concentration of silver ions are given. It is found that the process of plasmochemical formation of silver nanoparticles is the second-order reaction. The rate constant of formation of silver nanoparticles is k=0.07–1.53 mol -1 ∙dm 3 ∙min -1 depending on the initial concentration of silver ions. It is shown that the formation of silver nanodispersions under plasma discharge impact is characterized by the presence of the peak λ max =400–440 nm.

Influence of the sintering temperature on morphology and particle size of silver synthesized by spark discharge

The morphology and particle size of silver were investigated depending on the sintering temperature in the range from 25 to 1000 °C. Silver nanoparticles synthesized by the multi-spark discharge generator and then sintered in a tube furnace. It is found that the particle size decreases irregularly with increasing sintering temperature, according to TEM and aerosol measurements. Individual spherical nanoparticles are formed at the sintering temperature more than 200 °C. The size of the particles is almost constant of about 45 nm in the temperature range of sintering of 200-900 °C. However, the particle size is significantly reduced to 7 nm at a sintering temperature of about 1000 °C. Thus, it was found that the variation in sintering temperature makes it possible to significantly change the morphology and size of synthesized nanoparticles, which is relevant for a number of applications in optics and medicine.

Thermal and photo-thermal PROX reaction over Ag/SiO2 catalysts

The effect of plasmonic excitation of Ag/SiO2 catalysts was studied in the preferential CO oxidation in presence of H2 (PROX) at low temperature. Catalysts with 5 wt% silver loading were prepared by wet impregnation in aqueous and basic media. TEM analysis indicates the presence of Ag nanoparticles with a broad particle size distribution which can achieve both, good PROX activity at low temperature and plasmonic interaction with visible light. Photo-assisted reaction at 35 °C enhance CO and O2 conversions; however, the greater improvement was found for O2 conversion. The selectivity towards CO2 decrease when reaction took place under photo-thermal conditions. Occurrence of different silver species and particle size changed after reaction as evidenced by DRS-UV–vis and TEM.

Control of the Size of Silver Nanoparticles and Release of Silver in Heat Treated SiO₂-Ag Composite Powders.

The growth of silver nanoparticles, the activation energy for silver particle growth, and the release of silver species in heat treated -Ag composite powders are investigated. The silver particle growth is controlled by heat treatment for 75 min of the as-synthesized -Ag composite powder at 300–800 °C. During heat treatment the mean size of the Ag particles increases from 10 nm up to 61 nm with increasing temperature, however, the particle size distribution widens and the mean size increases with increasing heat treatment temperature. Based on X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies, silver particles are crystalline and in a metallic state after annealing in all -Ag composite powders. The growth of Ag particles is suggested to take place via diffusion and Ostwald ripening. The activation energy for particle growth was determined as 0.14 eV. The dissolution of silver in aqueous solutions from the -Ag composites heat treated, at 300 °C, 600 °C, and 700 °C, was investigated by varying pH and temperature. The dissolution was reduced in all conditions with increasing silver particle size, i.e., when the total surface area of Ag particles is reduced. It is suggested that the dissolution of silver from the composite powders can conveniently be adjusted by controlling the Ag particle size by the heat treatment of the composite powder.

COMPARATIVE ELECTRON-MICROSCOPIC AND MICROBIOLOGICAL INVESTIGATION OF SILVER PROTEINATE PREPARATIONS

The purpose of this work was a comparative study of the particle sizes of commercial preparations of colloidal silver by the method of electron microscopy, in connection with the characteristics of specific antimicrobial activity of the preparations under the same conditions. Four commercial preparations of colloidal silver were investigated: Vitargol Forte (manufactured by NPC «Elusan»), Protalor (manufactured by OOO «Esko-Farm», Armenia), Sialor (manufactured by PFK «Obnovlenie»). Protargol (prescription drugstore) served as the drug of comparison. Material and methods. The silver particle sizes in the preparations were determined by high-resolution transmission electron microscopy using a JEM 2010 electron microscope (JEOL, Japan) with a resolution of 0.14 nm at an accelerating voltage of 200 kV. The antimicrobial activity of the silver protein preparations was studied by a standard serial dilution method in liquid nutrient media and diffusion method using bacterial cultures of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Results and discussion. Vitargol Forte, manufactured using advanced technology, is the most fine-dispersed and monodisperse preparation. The preparation of standard classical Protargol, prepared in pharmacy conditions, was the most coarsely dispersed and polydispersed. The conclusion. The dependence of antimicrobial activity of the preparation on the size of its silver particles was shown. Of the four investigated preparations of silver proteinate, the smallest particle size was in the Vitargol Fort preparation. The same drug showed the highest bactericidal and bacteriostatic activity.

Characterization of engineered nanoparticles in commercially available spray disinfectant products advertised to contain colloidal silver

Given the potential for human exposure to silver nanoparticles from spray disinfectants and dietary supplements, we characterized the silver-containing nanoparticles in 22 commercial products that advertised the use of silver or colloidal silver as the active ingredient. Characterization parameters included: total silver, fractionated silver (particulate and dissolved), primary particle size distribution, hydrodynamic diameter, particle number, and plasmon resonance absorbance. A high degree of variability between claimed and measured values for total silver was observed. Only 7 of the products showed total silver concentrations within 20% of their nominally reported values. In addition, significant variations in the relative percentages of particulate vs. soluble silver were also measured in many of these products reporting to be colloidal. Primary silver particle size distributions by transmission electron microscopy (TEM) showed two populations of particles - smaller particles (<5nm) and larger particles between 20 and 40nm. Hydrodynamic diameter measurements using nanoparticle tracking analysis (NTA) correlated well with TEM analysis for the larger particles. Z-average (Z-Avg) values measured using dynamic light scattering (DLS); however, were typically larger than both NTA or TEM particle diameters. Plasmon resonance absorbance signatures (peak absorbance at around 400nm indicative of metallic silver nanoparticles) were only noted in 4 of the 9 yellow-brown colored suspensions. Although the total silver concentrations were variable among products, ranging from 0.54mg/L to 960mg/L, silver containing nanoparticles were identified in all of the product suspensions by TEM.

Effect of PVP Addition in the Preparation of Polyethersulfone (PES)–AgNO3 Antibacterial Membrane

Association of antibacterial agent into polymer–based material is an interesting, recent extension in membrane technologies research area. Asymmetric polyethersulfone–silver nitrate (PES–AgNO3) nanocomposite membranes were synthesized by wet phase inversion with polyvinylpyrrolidone (PVP) as additive. Three different molecular weights (MW) of PVP in the range of 10 K to 360 K were tested for their ability to stabilize and disperse silver in the polymer solution. Results showed that PVP 360 K plays a significant role in altering silver particle size with better dispersion compared to the membranes prepared without addition of PVP and with the addition of lower MW of PVP. Results agreed with the leaching detected by ICP–MS where silver loss during membrane fabrication for PES–Ag–P360 is only 0.4636 ppm (0.0093%). The antibacterial activity for the resultant membranes was tested using inhibition zone method. Results indicated that PES–AgNO3 and PES–AgNO3–PVP (loaded with only 0.5 wt% silver) were antibacterial to Escherichia coli and Staphylococcus aureus. The improvement of antibacterial properties of the prepared membranes could be primarily attributed to the PVP addition as well as the surface morphology and permeation properties.

Preparation and particle size effects of Ag/α-Al2O3 catalysts for ethylene epoxidation

Currently, for the industrial ethylene epoxidation α-alumina supported silver catalysts are the only catalyst of choice. We demonstrate a novel method to produce these catalysts with different silver particle sizes, but without changing other key parameters that may affect the catalytic performance such as support specific surface area or metal precursor. α-Alumina was impregnated with a silver oxalate solution, and was subsequently dried and treated in different gas atmospheres and at different temperatures to tune the silver particle sizes in the range of 20–500 nm. Particles of 20 nm exhibited a lower turnover frequency than particles of 70 nm and larger, which exhibit a constant turnover frequency, in accordance with results in literature. However, the selectivity, when measured at constant conversion, was particle size independent. This is the first time that the effect of the particle size on the selectivity of ethylene epoxidation is reported at constant conversion. This was made possible by a new method of producing supported silver catalysts, which we expect that is also applicable for silver catalysts with other supports and for the preparation of other supported metal catalysts.

Synthesis of Ag@Fe2O3 nanocomposite based on O-carboxymethylchitosan with antimicrobial activity

In this paper, nano-hybrid particles of Ag@Fe2O3 based on O-carboxymethylchitosan were successfully synthesized using different reducing agents (NaBH4, sucrose) and without reducing agent. The smallest silver nanoparticles were those prepared without reducing agent (∼5±3nm). The average size of silver particles prepared with NaBH4 is around 5–15nm, and for samples prepared with sucrose, the average particle size is 10–25nm. The magnetization curves are roughly reversible, indicating that γ-Fe2O3 nanoparticles transit to a superparamagnetic state. Nanocomposites subjected to antimicrobial tests showed great antimicrobial activity against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria, and good activity against the yeast Candida albicans and resistant strains of Staphylococcus aureus. The antibacterial behavior as a function of time was investigated in microbial growth kinetics, and the best nanocomposite was the one without reducing agent, which completely inhibited microbial growth for 48h.

Size‐Selective Silver‐Induced Evolution of Mn3O4−Ag Nanocomposites for Effective Ethanol Sensing

AbstractTrimanganese tetraoxide (Mn3O4)−silver (Ag) nanocomposites have been synthesized by seed‐mediated growth of manganese oxide by alkaline hydrolysis of manganese precursor on preformed silver nanoparticles at water/n‐heptane interface. The morphology of the nanocomposites has been varied by individual addition of five size‐selective silver nanoparticles for the evolution of the manganese components. Varieties of spectroscopic and microscopic techniques have been used to characterize these materials. Now, the efficacy of these as‐synthesized nanocomposites has been demonstrated towards the sensing of various hazardous volatile organic compounds, exhibiting high sensitivity to ethanol compared to other components. Moreover, the structure‐function relationship of the Mn3O4−Ag nanocomposites upon variation of the size of silver particles towards the sensory activity of ethanol has been elucidated.

Preparation of Silver Nanoparticles in Poly(N-vinylpyrrolidone)/Ethanol Solutions

Silver nanoparticles have been synthesized from Poly(N-vinylpyrrolidone) (PVP)/ethanol solutions, and six different PVP to silver nitrate weight ratios (PVP:AgNO3) are studied in reduction of silver nitrate in ethanol with the presence of PVP as a stabilizer. The produced silver nanoparticles showed strong plasmon resonance peak centered at around 405[Formula: see text]nm in UV-Vis spectra. The particle morphologies were also examined and compared under secondary electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersion X-ray spectroscopy (EDX) was utilized to determine the formation of silver nanoparticles. We found that the particle size and morphology were strongly dependent on the PVP:AgNO3 weight ratio. The average size of silver particles decreased from 19.25[Formula: see text]nm to 10.03[Formula: see text]nm as the weight ratio of PVP:AgNO3 increased from 1:1 to 20:1.

Novel olygomeric C-3 esters of betulin derivatives

ABSTRACTNovel copolymers of C-3 esters of betulin derivatives (3-hydroxy-1-cyano-2,3-seco-2-nor-19β,28-epoxyoleane 3-O-vinylbenzoate (I), 3-hydroxy-1-cyano-2,3-seco-2-nor-19β,28-epoxyoleane 3-O-vinylacetate (II), methyl 3-hydroxy-1-cyano-2,3-seco-2-norlup-20(29)-en-28-oate 3-O-vinylbenzoate (III)) with N-vinylpyrrolidone and acrylonitrile have been prepared by free radical copolymerization. Kinetic regularities of the process were investigated. New water-soluble silver nanocomposites based on (III) copolymer with N-vinylpyrrolidone [poly((III)-VP)] have been developed. The average silver particle size ranged from 40 to 52 nm, with the corresponding UV–vis absorption peak position at 400 nm. The nanocomposite obtained has a significant cytotoxic activity toward melanoma cell line and may be considered for the development of new materials for medical applications.

Effects of Silver Microparticles and Nanoparticles on Thermal and Electrical Characteristics of Electrically Conductive Adhesives

The effects of different volume fractions of silver (Ag) particles of different size (microsize, 2 μm to 3.5 μm diameter; nanosize, 80 nm diameter) on the thermal and electrical characteristics of epoxy–Ag electrically conductive adhesive (ECA) have been evaluated, as well as hybrid ECAs with both particle sizes at different ratios. Improved thermal and electrical conductivity resulted from the interaction between the particles, as evaluated by analysis of sample morphology. The interaction was altered to improve the conductivity. For both particle sizes, the electrical resistivity showed a transition from insulation to conduction at 6 vol.% Ag. In the hybrid system, the thermal conductivity decreased with increasing microparticle filler ratio. The electrical conductivity of the hybrid composite increased at 50:50 weight ratio.

Green synthesis of tea Ag nanocomposite hydrogels via mint leaf extraction for effective antibacterial activity

In this report, we investigated the swelling behavior and antibacterial property of nanosilver composite hydrogels made from tea with polyacrylamide via a free-radical polymerization and green process technique. This is probably for the first time; tea-based nano silver composite hydrogels were developed. The composite hydrogels comprise embedded nano silver particles in the tea hydrogel matrix via a green process with mint leaf extract. The size of the nano silver particles in the hydrogel matrix was found to be < 10 nm. The nano silver composite hydrogels formed and their blank hydrogels from the mint leaf were characterized by using ultraviolet-visible spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy, thermogravimetric analysis and X-ray diffraction studies. The nano silver composite hydrogels developed exhibit eminent antibacterial activity against Escherichia coli and Staphylococcus aureus. This clearly indicates that the nano silver composite hydrogels are potential candidates for antimicrobial applications.

Growth of Hierarchically 3D Silver–Silica Hybrid Nanostructures by Metastable State Assisted Atomic Layer Deposition (MS‐ALD)

A novel fabrication strategy is introduced for the synthesis of 3D silver–silica hybrid nanostructures by employing the plasma‐enhanced atomic layer deposition (PE‐ALD) on the templated substrates with enzymatically generated silver nanoparticles (EGNPs). Comparing with the conventional PE‐ALD process for the silica deposition (by using the precursors of tri‐dimethyl‐amino‐silane (TDMAS) and oxygen plasma), here the EGNPs play a key role for the formation of 3D hierarchical structures. During the oxygen plasma step, a metastable silver oxide surface is formed, and then thermally decomposes and releases excess oxygen during the next TDMAS step. A side reaction for the deposition of silica occurs with the excess released oxygen. The formation of the metastable silver oxide and its decomposition repeat cyclically during the PE‐ALD process, thereby, the side reaction is going on progressively, and finally, the 3D silver–silica hybrid nanostructures are formed with this novel strategy of metastable state assisted atomic layer deposition. Various 3D silver–silica composite nanostructures, such as nanosponges and nanoflowers, can be fabricated easily by tuning the PE‐ALD parameters. With each additional ALD cycle, the silver particle size decreases which also further reduces side reactions. The observed growth‐effect thus seems to be limited by the amount of silver used.

Tuning the properties of a black TiO2-Ag visible light photocatalyst produced by a rapid one-pot chemical reduction

A highly efficient black TiO2-Ag photocatalytic nanocomposite, active under both UV and visible light illumination, was synthesized by decorating the surface of 25 nm TiO2 particles with Ag nanoparticles. The material was obtained via a rapid, one-pot, simple (surfactant and complexing agent free) chemical reduction method using silver nitrate and formaldehyde as a metal salt and reducing agent, respectively. The nanocomposite shows an increase of over 800% in the rate of photocatalytic methylene blue dye degradation, compared to commercial unmodified TiO2, under UV-VIS illumination. Unlike pure TiO2, the nanocomposite exhibits visible light activation, with a corresponding drop in optical reflectance from 100% to less than 10%. The photocatalytic properties were shown to be strongly enhanced by post-reduction annealing heat treatments in air, which were observed to decrease, rather than coarsen, silver particle size, and increase particle distribution. This, accompanied by a variation in the silver surface oxidation states, appear to dramatically affect the photocatalytic efficiency under both UV and visible light. This highly active photocatalyst could have wide ranging applications in water and air pollution remediation and solar fuel production.

Biosynthesis of silver nanoparticles using dried fruit extract of Ficus carica - Screening for its anticancer activity and toxicity in animal models

There is an increasing commercial demand for various nanoparticles due to their extensive applicability in various areas such as electronics, catalysis, chemistry, energy and medicine. Metallic nanoparticles are traditionally synthesized by wet chemical techniques, where the chemicals used are quite often toxic and flammable. Fig has been a typical fruit component of the health-promoting Mediterranean diet for a very long time. In the present study, we describe a cost effective and eco-friendly technique for green synthesis of silver nanoparticles from 1 mM AgNO3 solution through the extract of dried fig (Ficus carica L.) fruit as reducing as well as capping agent. Nanoparticles were characterized using UV absorption spectroscopy and SEM. The sizes of the spherical silver particles were found to be in the range of 54–89 nm. The biologically synthesized nanoparticles also exhibited a significant cytotoxic effect on MCF7cell lines and further animal acute toxicity results state that the above AgNPs are toxicologically safe by oral administration.