Dispersed Silver Nanoparticles Research Articles

Inkjet-Assisted Lithography of Templates for the Electroforming of Micromagnets for MEMS Applications

The integration of hard magnetic alloys in the form of patterned layers is one of the most interesting challenges for the manufacturing of energy efficient magnetic microelectromechanical systems (MEMS) [1]. With respect to current state of the art devices, whose working principle mostly relies on the exploitation of Lorentzian forces, MEMS based on permanent magnets can potentially present lower power consumption, larger displacements and stronger actuation forces. However, despite these attractive advantages, it is generally difficult to integrate thick hard magnetic layers with currently employed MEMS fabrication techniques.Electrodeposition is a technique that can be exploited to accomplish this task and that is characterized by many significant advantages: high deposition rates, no necessity of a vacuum system, low cost, possibility to deposit both alloys and composites. In addition, Reverse Pulse Plating (RPP) [2] can be used to mitigate the challenges connected to the deposition of hard magnetic alloys: high residual stress, presence of cracks and inadequate surface finishing. It can also simplify electrolyte formulation, eliminating the need of excessive amounts of additives.Regardless of the material selected, electrodeposition needs a template in order to confer a specific shape to the magnetic layer. Such template is normally manufactured using state-of-the-art technologies like standard lithography. This technique, however, is characterized by the necessity to use photomasks, which are costly and poorly adaptable to geometrical variations. Furthermore, the initial investment for the lithography equipment is typically high. A possible alternative is represented by the use of inkjet printing (IJP). This technology is characterized by low costs, high flexibility and optimal productivity. It can be applied to the micrometric patterning of electroformed layers by following a novel approach described in the present work for the first time: inkjet-assisted lithography (IAL). Briefly, droplets of a dispersion of silver nanoparticles are printed on the surface of a spin coated layer of negative photoresist. Silver is opaque for the UV radiation and it constitutes a mask for the resist. The resist is exposed and developed, forming thus templates usable for electroforming.The present work investigates the application of this approach to the production of thick and crack-free CoNiP micromagnets, which are RPP deposited inside IAL templates. CoNiP was selected due to its low-cost and good magnetic properties (with HC up to 2000 Oe). The alloy is electrodeposited from a chloride based acidic electrolyte [3], using ultra-fast RPP, in micrometric circular pores created via IAL. The diameter of the pores, and consequently the diameter of the finished magnets, can be efficiently tuned by changing the speed of the jetted droplets of silver ink. Conversely, the thickness of the magnets can be tuned by varying the deposition time. The resulting micromagnets, characterized by diameters in the 20-50 µm range and thickness up to 10 µm, are characterized to assess their morphology, phase composition and magnetic properties. The micrometric magnets here described may potentially find application for the realization of powerless MEMS, energy harvesting systems or microelectronic components.[1] N. M. Dempsey, “Hard Magnetic Materials for MEMS Applications” in: Nanoscale Magnetic Materials and Applications, Springer, Boston, MA (2009)[2] S. Pané et al., Electrochim. Acta 56, 8979-8988 (2011)[3] D. Y. Park et al., Electrochim. Acta 47, 2893-2900 (2002)

A Flexible Wearable Strain Sensor Based on Nano-Silver-Modified Laser-Induced Graphene for Monitoring Hand Movements.

The advancement in performance in the domain of flexible wearable strain sensors has become increasingly significant due to extensive research on laser-induced graphene (LIG). An innovative doping modification technique is required owing to the limited progress achieved by adjusting the laser parameters to enhance the LIG's performance. By pre-treating with AgNO3, we successfully manufactured LIG with a uniform dispersion of silver nanoparticles across its surface. The experimental results for the flexible strain sensor exhibit exceptional characteristics, including low resistance (183.4 Ω), high sensitivity (426.8), a response time of approximately 150 ms, and a relaxation time of about 200 ms. Moreover, this sensor demonstrates excellent stability under various tensile strains and remarkable repeatability during cyclic tests lasting up to 8000 s. Additionally, this technique yields favorable results in finger bending and hand back stretching experiments, holding significant reference value for preserving the inherent characteristics of LIG preparation in a single-step and in situ manner.

Composite with Silver Nanoparticles and Oregano Essential Oil-Loaded Nanoparticles Intended for Wound Healing.

Since wounds are a primary source of infection, it is desirable to have a wound dressing that prevents infectious processes during the tissue regeneration phase. In this regard, silver nanoparticles, oregano essential oil, and chitosan have been utilized due to their antimicrobial activity. This work focused on the preparation of a composite containing these three components, intended to provide protection for wounds, especially by exerting antimicrobial effects. A composite based on chitosan nanoparticles loaded with oregano essential oil (OEO) and silver nanoparticles was fabricated through the casting-solvent evaporation method. The films were prepared from a suspension of chitosan nanoparticles. The nanoparticles were characterized by size and entrapment efficiency. The surface of the films was observed by SEM, and the mechanical resistance, occlusive capacity, and antimicrobial activity against S. aureus, E. coli, and P. aeruginosa were evaluated. The release of OEO from the films was studied using Franz-type cells. A composite was successfully prepared from a dispersion of OEO-loaded chitosan nanoparticles (147.8 nm, PDI = 0.35; entrapment efficiency = 80.9 %; loading capacity = 38 %) and silver nanoparticles (19.6 nm, PDI = 0.4). A film could be formed that made the composite by pouring the chitosan nanoparticle dispersion directly into molds. The composite presented advantageous characteristics, such as being semi-occlusive (occlusion factor ~ 40 % and reduction in TEWL of 18 %), allowing the sustained release of OEO (about 0.2 mgCm-2 h-1 during 8 h), and having antimicrobial activity for the three strains evaluated. The prepared composite can be considered a potential candidate for dressing materials intended to prevent and treat wound infections.

Evaluation of the immunotoxicity potential of nanomaterials using THP-1 cells.

With the expansion of nanomaterials (NMs) usage, concerns about their toxicity are increasing, and the wide variety of NMs makes it difficult to assess their toxicity. Therefore, the development of a high-throughput, accurate, and certified method to evaluate the immunotoxicity of NMs is required. In this study, we assessed the immunotoxicity potential of various NMs, such as nanoparticles of silver, silica, and titanium dioxide, using the human Cell Line Activation Test (h-CLAT) at the cellular level. After exposure to silver nanoparticle dispersions, the expression levels of CD86 and CD54 increased, suggesting the activation of antigen-presenting cells (APCs) by silver nanoparticles. Quantification of silver ions eluted from silver nanoparticles and the activation of APCs by silver ions suggested that it was due to the release of silver ions. Silica nanoparticles also increased the expression of CD86 and/or CD54, and their activation ability correlated with the synthesis methods and hydrodynamic diameters. The ability of titanium dioxide to activate APCs differed depending on the crystal type and hydrodynamic diameter. These results suggest a potential method to evaluate the immunotoxicity potential of various NMs based on their ability to activate APCs using human monocytic THP-1 cells. This method will be valuable in assessing the immunotoxicity potential and elucidating the immunotoxic mechanisms of NMs.

Silver-promoted ceramic conversion treatment of Ti6Al4V alloy and its mechanical performance

In this paper, the Ti6Al4V alloy surface was modified via ceramic conversion treatment (CCT) with or without a pre-deposited silver layer. After characterizing the surface morphologies, microstructure and phase constituents of the ceramic oxide layer formed at 620 °C, we investigated the surface hardness and the cross-sectional nano-hardness profile under the oxide layer. The static load-bearing capacity of the oxide layers was examined by applying discrete loads via a Vickers indenter and observing the indentations. A scratch test was used to evaluate the load-bearing capacity and the adhesion/cohesion of the oxide layers. The wettability of the surface changed due to the incorporation of silver and the change of surface morphology. Reciprocating friction and wear test was used to assess the tribological properties. Small and dispersed silver nanoparticles and clusters were found in the oxide layer of the Ag pre-deposited Ti6Al4V samples, and they had much better tribological properties in terms of reduced coefficient of friction and wear volume. With the assistance of silver, the efficiency of the CCT was significantly improved.

Effects of Synthesis Method on Catalytic Activities of Ag/TiO2 Catalyst in CO Oxidation Reaction

Supported silver catalysts on titanium dioxide have been synthesized by three different methods to compare catalytic activity in CO oxidation. The catalysts were prepared by the wet impregnation method with 10 mole% of silver. In the first method, the silver catalysts were impregnated on the titanium dioxide nanoparticles (Ag/TNP), while in the second method, the silver catalysts were impregnated on the titanium dioxide nanotubes (Ag/TNT). The third method, the silver catalysts were impregnated on the titanium dioxide nanoparticles before the nanotube process (Ag/TNP-TNT). The Ag/TNP and Ag/TNT catalysts showed highly dispersed silver nanoparticles with an average particle size of less than 5 nm on the surface of titanium dioxide, whereas the Ag/TNP-TNT catalyst exhibited much lower dispersion of silver nanoparticles. The highly dispersed silver on the titanium dioxide resulted in a large number of surface active sites (Ag0). The catalytic activity test found that the Ag/TNT catalysts with the highest number of active sites (2.20 × 1020 atom/g-catalyst) exhibited higher CO oxidation activity than the Ag/TNP and Ag/TNT catalysts with 100% CO conversion at 125°C.

Silver nanoparticles induced enhanced stability, dielectric anisotropy, and electro-optical parameters of a nematic liquid crystalline material 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzene

Nanocomposites of 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzene nematic liquid crystals and silver nanoparticles have been prepared. UV absorption spectroscopy, Fourier transform infrared and Raman spectroscopies were used to characterize the morphology of silver nanoparticles (Ag-NPs). Thermodynamic, optical, and dielectric studies have been done to explore the change in the physical parameters of the composites with respect to the pure sample. Due to dispersion of silver nanoparticles, transition temperature, associated enthalpy and order parameters of the nanocomposites have increased. Dielectric study shows enhanced dielectric anisotropy for Ag-NPs dispersed nanocomposites. The relaxation frequency of an observed mode has shifted towards high frequency region for the nanocomposites. Optical band gap for pure and nanocomposites samples has been estimated from UV absorption peaks and it is found that optical properties of the nanocomposites are almost invariant. Threshold (switching) voltage, rotational viscosity and splay elastic constant for pure and dispersed samples have also been obtained from electro-optical studies.

Optimized framework numerical solution for swirling hybrid nanofluid flow with silver/gold nanoparticles on a stretching cylinder with heat source/sink and reactive agents

Abstract The heat and mass transportation for nanofluid across a swirling cylinder under the actions of magnetic effects and Cattaneo–Christov heat flux is reported in the current analysis. The objective of this study is to examine the energy and mass transmissions through hybrid nanofluid under the influence of heat source/sink and reactive species. The hybrid nanoliquid has been prepared by the dispersion of silver (Ag) and gold (Au) nanoparticles (NPs) in the base fluid ethylene glycol (C2H6O2). The flow phenomena are expressed in the form of nonlinear partial differential equations and are converted to a nondimensional form, by employing the similarity substitution. For the computational estimation of the problem, the parametric continuation method is employed. The demonstration of velocity, mass, and energy outlines versus distinct physical factors is exposed in the form of figures. It has been perceived that the axial and swirling velocity outline drops with the influence of the Reynolds number, magnetic effect, and the insertion of Au and Ag NPs in C2H6O2. Furthermore, the hybrid nanofluid energy curve declines with the effect of the Reynolds number, thermal relaxation factor, and the volume friction of NPs.

Low-grade heat recycling of vertical thermoelectric cells based on thermal-induced electric double layer

Employing electric double-layer (EDL) capacitors to harvest low-grade heat (LGH) is a novel technique in the high-efficiency energy absorption field. This work reports the fabrication of a vertical thermoelectric cell, based on a nanoporous graphene electrode immersed in low-concentration saline solution, for use as thermo-charging supercapacitors to convert LGH to electricity via thermally induced voltage. Because of a large specific area and a large number of micropores of nanoporous graphene films, the effective thermoelectric coefficient of the thermoelectric cell containing 0.01 M KCl solution can reach as high as 4.73 mV/°C. However, many factors, such as electrode materials, electrolyte solutions, and energy conversion device components, determine the efficiency of a thermoelectric conversion device. In summary, the device has a lower internal resistance and higher output voltage when the concentration of KCl solution is 0.05 M, and demonstrates higher thermoelectric conversion efficiency. Moreover, improving the conductivity of the electrolyte solution without affecting the device output voltage is also a way to reduce the internal power consumption of the device. The specific power and thermoelectric conversion efficiency of the device are increased by several orders of magnitude when uniformly dispersed silver nanoparticles are added to the potassium chloride solution to enhance the conductivity of the solution. The specific power underwent an increase from 0.50 mW g−1 to 42.37 mW g−1, and the thermoelectric conversion efficiency also increased from 0.0022% to 0.1358%.

Blended Copper and Nano-Silver Screen-Printed Circuits on FTO-Coated Glass

Using a mixture of micro-copper and nano-silver in the production of screen-printed circuits has the potential to reduce material costs and cost variability. The fundamental premise of this study involved dispersing silver nanoparticles among the larger copper microparticles at selected ratios and subsequently sintering in order to establish their resultant electrical and physical performance. Commercial materials were mixed, printed, and sintered at two thermal regimes on fluorine-doped tin oxide (FTO)-coated glass substrate. The inclusion of 25% silver provided an appreciable reduction in electrical resistance from 4.21 Ω to 0.93 Ω, with further silver additions having less impact. The thermal regime used for sintering had a secondary impact on the final electrical performance. The addition of silver reduced the adhesion to the FTO substrate, with reduced film integrity. The results show that blending inks offers the advantage of enhancing material conductivity while simultaneously reducing costs, making it a compelling area for exploration and advancement in the field of electronics manufacturing.

Antibacterial, antibiofilm, and anticancer activity of silver-nanoparticles synthesized from the cell-filtrate of Streptomyces enissocaesilis

Silver nanoparticles (Ag-NPs) have a unique mode of action as antibacterial agents in addition to their anticancer and antioxidant properties. In this study, microbial nanotechnology is employed to synthesize Ag-NPs using the cell filtrate of Streptomyces enissocaesilis BS1. The synthesized Ag-NPs are confirmed by ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Also, the effects of different factors on Ag-NPs synthesis were evaluated to set the optimum synthesis conditions. Also, the antibacterial, antibiofilm, and anticancer activity of Ag-NPs was assessed. The X-ray diffraction (XRD) analysis confirmed the crystalline nature of the sample and validated that the crystal structure under consideration is a face-centered cubic (FCC) pattern. The TEM examination displayed the spherical particles of the Ag-NPs and their average size, which is 32.2 nm. Fourier transform infrared spectroscopy (FTIR) revealed significant changes in functionality after silver nanoparticle dispersion, which could be attributed to the potency of the cell filtrate of Streptomyces enissocaesilis BS1 to act as both a reducing agent and a capping agent. The bioactivity tests showed that our synthesized Ag-NPs exhibited remarkable antibacterial activity against different pathogenic strains. Also, when the preformed biofilms of Pseudomonas aeruginosa ATCC 9027, Salmonella typhi ATCC 12023, Escherichia coli ATCC 8739, and Staphylococcus aureus ATCC 6598 were exposed to Ag NPs 50 mg/ml for 24 hours, the biofilm biomass was reduced by 10.7, 34.6, 34.75, and 39.08%, respectively. Furthermore, the Ag-NPs showed in vitro cancer-specific sensitivity against human breast cancer MCF-7 cell lines and colon cancer cell line Caco-2, and the IC50 was 0.160 mg/mL and 0.156 mg/mL, respectively. The results of this study prove the ease and efficiency of the synthesis of Ag-NPs using actinomycetes and demonstrate the significant potential of these Ag-NPs as anticancer and antibacterial agents.

Silver nanoparticles decorated polydopamine-coated pure silica zeolite as an efficient nanocatalyst for organic pollutants removal

An efficient catalyst, composed of silver-decorated polydopamine coatings on pure silicon zeolite (PSZN/PDA/Ag), capable of removing organic pollutants in water effectively, was synthesized using an economical in-situ reduction approach. The polydopamine (PDA) coating facilitates the stable dispersion of silver (Ag) nanoparticles and offers numerous catalytic active sites. This can be attributed to the ability of PDA in acting as a redox medium, via the interchange between its catechol group and the benzoquinone structure, thereby decreasing impediments to electron transfer among reactants, and consequently promoting the catalytic reaction. The porous structure of PSZN aids in embedding the PDA elements inside the pores, preventing the coating from peeling off and providing additional adsorption to transport reactants to the catalytic center for cooperative catalysis. Leveraging these properties, it demonstrates excellent efficiency and reusability in the catalytic reduction of waste methylene blue (MB) and 4-nitrophenol (4-NP), achieving reaction rates of 41.23 × 10-2 min−1 across five cycles respectively, with a minimum average conversion rate of 96 %. Moreover, the impressive performance is primarily due to the significant load (wt = 30.7 %) and small size (11.85 nm) of Ag nanoparticles, which boast a large number of reaction centers.

Experimental study on the preparation of monodisperse nano-silver by hydrothermal synthesis

As a new material with wide application prospect, nano-silver is getting high attention. Hydrothermal synthesis has the advantages of green, easy operation and low cost, and is a promising technology for the preparation of nano-silver. In this paper, the effects of reaction time, reaction temperature, precursor concentration, PVP concentration and modifier addition on the particle size distribution and surface morphology of nano-silver during the subcritical hydrothermal reaction were optimized by comparing the supercritical and subcritical hydrothermal methods. Then, the important role and reaction mechanism of PVP as a modifier and the formation mechanism of spherical nano-silver particles were analyzed. The experimental results showed that the average particle size of 23.68 nm can be obtained by using NaHCO3 and PVP as reducing and dispersing agents, the reaction time is 5 h, the reaction temperature is 180 °C, and the concentrations of AgNO3 and PVP are 0.1 M and 0.3 M, respectively, to obtain the more uniformly dispersed silver nanoparticles. The results provide an important reference for future research on the preparation of conductive pastes.

Synthesis of silver nanoparticles

The article presents information about plant protection products, methods for the synthesis of silver nanoparticles, stabilization of the resulting solutions, and the morphology of the resulting colloidal solution. The chemical synthesis of silver nanoparticles was carried out in the presence of reducing agents and stabilizers. Silver nitrate was used as a source of silver, and glucose, sodium citrate and hydrazine were used as reducing agents; water-soluble polymers were used as stabilizers - polyvinylprolidone, polyvinyl alcohol and polyvinyl acetate. Under optimal conditions, stable silver nanoparticles with different color solutions were obtained. An increase in the color intensity of solutions is associated with the dispersion of silver nanoparticles. The shape and size of silver nanoparticles are directly dependent on the concentration of solutions, the nature of stabilizers, reducing agents and temperature. By controlling the reaction conditions, it is possible to synthesize silver nanoparticles of various shapes and sizes. The relationship between the shapes and sizes of nanoparticles, the concentration of silver salt, temperature and the nature of the stabilizer is indicated. The resulting nanosilver is recommended for use in agriculture.

Preparation and antimicrobial activity of silver nanoparticles impregnated with halloysite clay

In the present work, nanotubular halloysite clay was ultrasonically treated and impregnated with silver nanoparticles. The citrate surface-stabilized silver nanoparticles dispersion was prepared using an effective method of electrochemical synthesis. The elemental and phase composition, and the structure of the obtained AgNPs-impregnated and pristine halloysite were investigated by various methods such as X-ray fluorescence (XRF), powder X-ray diffraction analyses and Fourier-transform infrared spectroscopy. The Ag-loaded halloysite sample with 0.454 wt.% silver content was confirmed by the XRF analysis. The antimicrobial activity of the pristine and the AgNPs-impregnated halloysite clay was tested against Escherichia coli ATCC 25922 (Gram-negative) and Bacillus subtilis ATCC 6633 (Gram-positive) strains. The results show that pure halloysite does not exhibit antibacterial activity. The AgNPs-impregnated halloysite demonstrates antibacterial activity against Escherichia coli and Bacillus subtilis with only bacteriostatic effect.

Enhanced thermoluminescence, radioluminescence, and optically stimulated luminescence from lithium fluoride and silver nanoparticles composites

Plasmonic properties of metals can increase the sensitivity of ionizing radiation dosimeters. In this work, we study the plasmon resonance of silver nanoparticles (AgNp) to increase the optically stimulated luminescence (OSL) intensity of lithium fluoride (LiF) polycrystals. We produced LiF/Ag nanocomposites with different volumes of a silver nanoparticle dispersion and investigated their OSL response. We also investigated their thermoluminescence (TL) and radioluminescence/scintillation (RL) responses. X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectroscopy characterized the synthesized materials. XRD results clearly show the characteristic peaks of LiF and AgNps. TEM images revealed silver nanoparticles with diameters between 80 and 120 nm and LiF crystals with sizes between 1 and 5 μm. Reflectance spectroscopy showed a band around 420 nm, attributed to the plasmon resonance of silver nanoparticles. The responses of the OSL curves to X-ray irradiation were analyzed, showing higher OSL sensitivity with 14 mL AgNp, attributed to the AgNp plasmon resonance. A significant increase in TL and RL intensity could be observed for the LiF/Ag nanocomposites. TL, RL, and OSL results support that addition of AgNps do not lead to the creation of more and new traps or luminescent centers. The increase of TL and RL intensities is therefore related to the coupling of the luminescent centers with the AgNPs plasmons, in an energy-transfer mechanism (plasmon-coupled emission), whereas the enhanced OSL intensity directly correlates with the increased photoionization cross-section of the electronic traps under plasmon resonance conditions (plasmon-coupled excitation). Therefore, these results indicate that AgNp are potential candidates to increase the OSL, TL, and RL intensity from LiF dosimeters.

Facile gamma-ray induced synthesis of reduced graphene oxide decorated with silver nanoparticles: a green approach for symmetric supercapacitor applications

This study presents a green, novel, one-pot, and single-step method for synthesizing reduced graphene oxide/silver nanocomposites (RGO/Ags) with different Ag ratios using Roselle extract and 80kGy of γ-ray for symmetric supercapacitor applications. As a natural antioxidant, Roselle extract served as a scavenger of oxidative free radicals to inhibit the oxidation of graphene oxide/silver nitrate suspensions (GO/AgO3), which were undergoing radiolysis under γ irradiation. An additional sample of GO/AgO3 was irradiated with the same dose in the absence of Roselle for comparability. The efficient reduction of GO/AgO3 has been assessed by several analytical techniques, including XRD, FTIR, TEM, and Raman spectroscopy. The presence of Roselle hindered the formation of the AgO phase while concurrently promoting the construction of the Ag phase. Furthermore, using Roselle extract results in a more homogeneous dispersion of spherical silver nanoparticles on reduced graphene oxide (RGO) sheets. Symmetric supercapacitor has been assembled from arbitrary samples amongst RGO/Ags, which showed good performance like low internal resistance and suitable specific capacitance (96 F/g at current density 0.2 A/g). The findings point to the merit of RGO/Ag nanocomposites prepared by the synergetic effect of γ-ray and Roselle extract as an efficient supercapacitor material.

Green Synthesis and Characterization of Silver Nanoparticles Using Ginkgo Biloba Laf Extract

A facile, effective and green method using Ginkgo Biloba leaf extract was applied and optimized for the preparation of well dispersed silver nanoparticles. In the method, Ginkgo Biloba leaf extract was employed as both stabilizing and reducing agent without the addition of a toxic agent. 0.1 % silver nitrate solution (w/v) was used silver source. The synthesized silver nanoparticles were investigated and examined by UV-vis absorption spectroscopy (UV-vis), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and Dynamic light scattering (DLS). The formation of silver nanoparticles was found by a change of color from light yellow to red, which was further proved by absorbance peak at 456 nm in UV-vis spectroscopy. The prepared nanoparticles are global in shape, highly crystalline in nature with a narrow distribution from 10 nm to 40 nm. The silver nanoparticles were capped with extracts, which prevented them from agglomeration and oxidation. Different parameters affecting the generation performance of silver nanoparticles, such as time, amount of silver nitrate and extract were investigated. The results demonstrate that these reaction parameters play important roles in the synthesis of silver nanoparticles.

Silver-impregnated zeolitized tuffs for environmental degradation of ozone

The natural zeolites were ultrasonically treated and impregnated with silver nanoparticles. The surface stabilized silver nanoparticles dispersion was obtained using an effective electrochemical reduction method. The phase and elemental composition, structure of the Ag-impregnated zeolites (clinoptilolite and mordenite) was studied by various methods such as powder X-ray diffraction, X-ray fluorescence analyses and Fourier-transform infrared spectroscopy. The Ag-impregnated clinoptilolite and mordenite natural zeolite materials with 1.20 wt %, 0.97 wt %, 0.83 wt % and 1.18 wt % silver content were established by XRF analysis. As initial materials were used three types clinoptilolite from Beli Plast, Most, Golobradovo (Kardzhali, Bulgaria) deposits and mordenite from Lyaskovets deposit in Eastern Rhodopes, Bulgaria. The catalytic ability of Ag-mordenite and Ag-clinoptilolites was investigated in the ecologically important reaction of ozone decomposition. The Ag-loaded mordenite demonstrates the higher conversion degree of ozone more than 40% in comparison with Ag-clinoptilolite materials at room temperature.

Formation Kinetics and Antimicrobial Activity of Silver Nanoparticle Dispersions Based on N-Reacetylated Oligochitosan Solutions for Biomedical Applications.

The paper presents the results of the synthesis, a detailed kinetics study, and an investigation of the biological activity of silver nanoparticles (AgNPs) in aqueous solutions of N-reacetylated oligochitosan hydrochloride. UV-visible spectrophotometry and dynamic light scattering were employed to control silver ion reduction. The process was observed to follow a pseudo-first-order law. Transmission and scanning electron microscopy demonstrated that AgNPs ranging in size from 10 to 25 nm formed aggregates measuring 60 to 90 nm, with the aggregate surface coated by a 2-4 nm chitosan shell. X-ray microanalysis and powder X-ray diffractometry were used to study the phase composition, identifying two crystalline phases, nanocrystalline silver and AgCl, present in the dispersions. The antibacterial effect was assessed using the serial dilution method for dispersions with varying degrees of Ag+ conversion. Nanodispersions exhibited significant activity against Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, and Staphylococcus aureus. Interestingly, the activity did not appear to be heavily influenced by the presence of the AgCl phase or the concentration of Ag+ ions. These synthesized dispersions hold promise for the development of materials tailored for biomedical applications.