Alginate hydrogel microbeads incorporated with Ag nanoparticles obtained by electrochemical method

An innovative method was developed for production of alginate hydrogel microbeads incorporated with silver nanoparticles (AgNPs) based on electrochemical synthesis followed by electrostatic extrusion. AgNPs were synthesized galvanostatically at different values of AgNO₃ concentration in the initial solution (0.5–3.9 mM), current density (5–50 mA cm⁻²), and implementation time (0.5–10 min). Increase in all of these parameters increased the concentration of AgNPs in alginate solution and was confirmed by TEM analysis and UV–vis spectroscopy. Cyclic voltammetry studies and Fourier transform infrared spectroscopy proved the alginate to be a good capping agent for the electrochemical synthesis of silver nanoparticles, due to coordination bonding between hydroxyl and ether groups, as well as ring oxygen atoms in uronic acid residues of alginate molecules, and Ag nanoparticles. Ag/alginate colloid solution was used for production of uniform hydrogel microbeads (with diameter of 487.75 ± 16.5 μm) by electrostatic extrusion technique. UV–vis spectroscopy confirmed retention and entrapment of AgNPs in microbeads during the production process. Alginate microbeads incorporated with AgNPs are attractive as biocompatible carriers and/or efficient donors of AgNPs as active components especially for potential biomedical applications, which was demonstrated by the antibacterial activity against Staphylococcus aureus.     

Biosynthesis of silver nanoparticles using leaves of Stevia rebaudiana

The synthesis of silver nanoparticles employing a shadow-dried Stevia rebaudiana leaf extract in AgNO₃ solution is reported. Transmission electron microscopy and X-ray diffraction inspections indicate that nanoparticles are spherical and polydispersed with diameters ranging between 2 and 50 nm with a maximum at 15 nm. Ultraviolet–visible spectra recorded against the reaction time confirms the reduction of silver nanoparticles indicating that the formation and the aggregation of nanoparticles take place shortly after the mixing, as they persist concurrently with characteristic times of 48.5 min and 454.5 min, respectively. Aggregation is found to be the dominant mechanism after the first 73 min. Proton nuclear magnetic resonance spectrum of the silver nanoparticles reveals the existence of aliphatic, alcoholic and olefinic CH₂ and CH₃ groups, as well as some aromatic compounds but no sign of aldehydes or carboxylic acids. Infrared absorption of the silver nanoparticles suggests that the capping reagents of silver and gold nanoparticles reduced in plant extracts/broths are of the same chemical composition of different ratios. Ketones are shown to play a somehow active role for the formation of nanoparticles in plant extracts/broths.     

Silver nanoparticles: Ultrasonic wave assisted synthesis, optical characterization and surface area studies

Silver nanoparticles have been successfully synthesized by the sonochemical route using sodium borohydride and sodium citrate as the reducing agents. The effect of the reducing agents on the particle size and morphology has been studied by carrying out the two reactions at the same ultrasound frequency (20 KHz). The strong reducing agent (NaBH₄) produced spherical silver nanoparticles of sizes 10 nm whereas sodium citrate led to much smaller silver nanoparticles of ~ 3 nm diameter. Powder X-ray diffraction studies reveal a high degree of crystallinity and monophasic silver particles. UV-Visible studies show the presence of a surface plasmon band at 405 nm. However the reflectance spectra give a broad band between 340 and 360 nm which is characteristic for the quasi-spherical silver nanoparticles. The specific surface area was found to be 2.6 and 13.1 m²/g and the pore radius was found to be 15.2 and 12.3 Å for silver nanoparticles obtained by the sodium borohydride and sodium citrate reduction respectively.     

Silver nanoparticles: Large scale solvothermal synthesis and optical properties

Silver nanoparticles have been successfully synthesized by a simple and modified solvothermal method at large scale using ethanol as the refluxing solvent and NaBH₄ as reducing agent. The nanopowder was investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-visible and BET surface area studies. XRD studies reveal the monophasic nature of these highly crystalline silver nanoparticles. Transmission electron microscopic studies show the monodisperse and highly uniform nanoparticles of silver of the particle size of 5 nm, however, the size is found to be 7 nm using dynamic light scattering which is in good agreement with the TEM and X-ray line broadening studies. The surface area was found to be 34.5 m²/g. UV-visible studies show the absorption band at ∼425 nm due to surface plasmon resonance. The percentage yield of silver nanoparticles was found to be as high as 98.5%.     

Green synthesis of silver nanoparticles using marine polysaccharide: Study of in-vitro antibacterial activity

The present contribution deals with one pot method for synthesis of silver nanoparticles through green route using sulfated polysaccharide isolated from marine red algae (Porphyra vietnamensis). The obtained silver nanoparticles showed surface plasmon resonance centered at 404 nm with average particle size measured to be 13 ± 3 nm. FTIR spectra revealed the involvement of sulfate moiety of polysaccharide for reduction of silver nitrate. The capping of anionic polysaccharide on the surface of nanoparticles was confirmed by zeta potential measurement (−35.05 mV) and is responsible for the electrostatic stability. The silver nanoparticles were highly stable at wide range of pH (2-10) and electrolyte concentration (up to 10⁻² M of NaCl). The dose dependent effect of synthesized silver nanoparticles revealed strong antibacterial activity against gram negative bacteria as compared to gram positive bacteria.     

Preparation of highly concentrated and stable suspensions of silver nanoparticles by an organic base catalyzed reduction reaction

Highly concentrated and stable suspensions of silver nanoparticles have been synthesized by chemical reduction from silver nitrate in a formaldehyde reductant using an organic base, triethylamine, as the reaction promoter. In this reaction, a low molecular weight organic compound, thiosalicylic acid (TSA), was used as the protecting agent. The average size of the silver nanoparticles prepared from this method was less than 10 nm, which allowed low-temperature sintering of the metal. The suspensions were further stabilized by the addition of excessive triethylamine, which forms an amine salt with TSA. A 50 wt%, stable suspension has been prepared. The suspensions of silver nanoparticles prepared by this method are free from any metal ion contamination, and are suitable for use in semiconductor industries.     

Black tea leaf extract derived Ag nanoparticle-PVA composite film: Structural and dielectric properties

Biosynthesized metal (Ag) nanoparticles have been used to prepare high dielectric polymer composite film of technological importance. Different amounts of the tea leaf extract (E) (mother leaker prepared by soaking 2 g tea leaf in 100 ml boiled water for 3 min) were used to synthesize silver nanoparticles from 10⁻³ M AgNO₃ solution. Such a resultant solution containing Ag nanoparticles was mixed with 20 ml PVA solution (5 g PVA in 100 ml water) was used to make anhydrous Ag/PVA composite film where spherical silver nanoparticles (AgNPs) of average diameter 10 nm are well dispersed in the composite. The Ag particle size in the composite was found to enhance with the increase of E content in PVA. XRD, SEM, TEM, FT-IR, UV–vis, TGA and DSC studies are made to characterize the nanoparticles. Detailed frequency and E concentration dependent electrical and dielectric properties of the nanocomposites have been made showing low loss (∼0.14) and high dielectric property of these films. Maximum value of dielectric permittivity (∼900 which is almost 170 times higher than that of pure PVA ∼ 5.2) have been observed for 15 ml E-AgNPs/PVA nanocomposite film at 1 kHz and room temperature. Present study establishes the importance of the biosynthesized metal nanoparticles for industrial applications as in capacitors.     

Synthesis and anti-bacterial activity of Cu, Ag and Cu-Ag alloy nanoparticles: A green approach

Metallic and bimetallic nanoparticles of copper and silver in various proportions were prepared by microwave assisted chemical reduction in aqueous medium using the biopolymer, starch as a stabilizing agent. Ascorbic acid was used as the reducing agent. The silver and copper nanoparticles exhibited surface plasmon absorption resonance maxima (SPR) at 416 and 584 nm, respectively; while SPR for the Cu-Ag alloys appeared in between depending on the alloy composition. The SPR maxima for bimetallic nanoparticles changes linearly with increasing copper content in the alloy. Transmission electron micrograph (TEM) showed monodispersed particles in the range of 20 ± 5 nm size. Both silver and copper nanoparticles exhibited emission band at 485 and 645 nm, respectively. The starch-stabilized nanoparticles exhibited interesting antibacterial activity with both gram positive and gram negative bacteria at micromolar concentrations.     

Extracellular synthesis of silver nanoparticles using the leaf extract of Coleus amboinicus Lour.

In the present investigation, Coleus amboinicus Lour. leaf extract-mediated green chemistry approach for the synthesis of silver nanoparticles was described. The nanoparticles were characterized by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The influence of leaf extract on the control of size and shape of silver nanoparticles is reported. Upon an increase in the concentration of leaf extract, there was a shift in the shape of nanoparticles from anisotrophic nanostructures like triangle, decahedral and hexagonal to isotrophic spherical nanoparticles. Crystalline nature of fcc structured nanoparticles was confirmed by XRD spectrum with peaks corresponding to (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes and bright circular spots in the selected-area electron diffraction (SAED). Such environment friendly and sustainable methods are non-toxic, cheap and alternative to hazardous chemical procedures.     

A facile and novel way for the synthesis of nearly monodisperse silver nanoparticles

A facile and novel way was reported for the preparation of nearly monodisperse silver nanoparticles with controlled hydrophilic or hydrophobic surface, using trioctylphosphine as the surfactant and stabilizer. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and UV-vis spectroscopy. The monodisperse silver nanoparticles showed a strong surface plasmon resonance band at 402 nm from the UV-vis spectrum.     

IR-sintering of ink-jet printed metal-nanoparticles on paper

Sintering of printed metal nanoparticles can be made not only by conventional heating, but also by, e.g., electrical, microwave, plasma, laser and flash lamp annealing. We demonstrate sintering by using low-cost incandescent lamps as an effective way of obtaining highly conductive contacts of two types of ink-jet printed metal-nanoparticle inks on paper; both alkanethiol protected gold nanoparticles and a commercially available silver nanoparticle ink. This low-cost roll-to-roll compatible sintering process is especially suitable on paper substrates because of the high diffuse reflectance, relatively high thermal stability and low thermal conductivity of paper. A volume resistivity of around 10 μΩ cm was achieved of the inkjetted silver nanoparticles within 15 s of exposure to an IR lamp, which corresponds to a conductivity of 10-20% of that of bulk silver. Too long exposure time and too high intensity, however, lead to darkening of the paper fibers. Both the crack formation and the coffee ring effect of the inkjet printed gold nanoparticles were, furthermore, found to be reduced on paper as compared to glass or plastic substrates.     

Biocide activity of diatom-silver nanocomposite

Diatom-nAg composites containing 1 wt.% of metallic silver nanoparticles (≤ 20 nm) have been obtained by a colloidal route and chemical reduction. This nanostructured powder has proved to be a selective green inorganic biocide which reduces the starting concentrations of Escherichia coli and Micrococcus luteus cultures by at least 5 orders of magnitude, while completely inactive against yeast. Diatom-nAg can be considered as a selective inorganic biocide particularly suitable for the food and pharmacological sectors. The silver nanoparticles are released from the diatom surface to the liquid media in a controlled manner, reaching a concentration (< 11 ppm) far below the toxicity limit for human cells.     

Synthesis of silver nanoparticles using surfactin: A biosurfactant as stabilizing agent

Surfactin, a lipopeptide biosurfactant, was used to stabilize the formation of silver nanoparticles. Synthesis of silver nanoparticles using a borohydrate reduction was performed at three pH levels (pH 5, 7 and 9) and two different temperatures in the presence of surfactin. The nanomaterials were characterized by UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy. The nanoparticles were synthesized at different pH conditions and temperature and remained stable for 2 months. The UV-vis spectra showed a surface plasmon resonance vibration band at 428 nm for all samples. TEM micrographs revealed that the mean nanoparticle size decreased with increase of pH from 5 to 9 (i.e. 17.8 ± 9.8, 6.9 ± 1.5 and 4.3 ± 1.1 nm) at 4 °C. However, at room temperature, size increased with pH (4.9 ± 1.4, 6.5 ± 1.6, 9.7 ± 4.3 nm at pH 5, 7 and 9 respectively). This report describes the use of a renewable, environmentally compatible, biodegradable surfactant as a stabilizing agent for the synthesis of silver nanoparticles.     

Silica/potassium ferrite nanocomposite: Structural,morphological, magnetic,thermal and in vitro cytotoxicity analysis

The coating of silica on potassium ferrite (KFeO₂) nanoparticles has been reported in the present study. The X-ray diffraction pattern revealed the formation of orthorhombic structure of bare potassium ferrite nanoparticles, which was also retained after the silica coating, along with a broad band near 2θ ∼ 20–25° pertaining to the presence of amorphous silica. The size of bare and coated potassium ferrite nanoparticles was found to be 4–8 nm and 10–22 nm, respectively, as observed from transmission electron microscope. The presence of silica was also revealed by the Fourier transform infrared spectrum and high resolution transmission electron microscope. In vibrating sample magnetometer analysis, both bare as well as coated potassium ferrite nanoparticles exhibited superparamagnetic behaviour with magnetic saturation values, 49.01 and 21.17 emu/g, respectively. Dose-dependent cellular toxicity was observed in the in vitro MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) – assay study on Jurkat cells, where both bare as well as silica coated nanoparticles exhibited non-toxicity below 250 μg/ml. An augmentation of cell viability was observed in case of silica coated potassium ferrite nanoparticles. The nanosize, superparamagnetic behaviour and enhanced cell viability make silica coated potassium ferrite nanoparticles a potential claimant for biomedical applications.     

Intensified biosynthesis of silver nanoparticles using a native extremophilic Ureibacillus thermosphaericus strain

The microflora of Ramsar geothermal hot springs located in Mazandaran province, Iran was screened for native thermophilic bacteria that are capable of biosynthesis of silver nanoparticles. One isolate identified as “Ureibacillus thermosphaericus” showed high potential for silver nanoparticle biosynthesis with extracellular mechanism and selected for the biosynthesis optimization. Biosynthesis reactions were conducted using the culture supernatant at different temperatures (60-80 °C) and silver ion concentrations (0.001-0.1 M). The results obtained showed that pure spherical nanoparticles in the range of 10-100 nm were produced, and the maximum nanoparticle production was achieved using 0.01 M Ag-NO₃ at 80 °C. In conclusion, the findings of this study confirmed the great biocatalyzing potential of the extremophilic U. thermosphaericus supernatant for intensified biosynthesis of silver nanoparticle at elevated temperatures and high silver ion concentrations.     

Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

The fungus, Aspergillus flavus when challenged with silver nitrate solution accumulated silver nanoparticles on the surface of its cell wall in 72 h. These nanoparticles dislodged by ultrasonication showed an absorption peak at 420 nm in UV-visible spectrum corresponding to the plasmon resonance of silver nanoparticles. The transmission electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodisperse silver nanoparticles (average particle size: 8.92 ± 1.61 nm) by the fungus. X-ray diffraction spectrum of the nanoparticles confirmed the formation of metallic silver. The Fourier transform infrared spectroscopy confirmed the presence of protein as the stabilizing agent surrounding the silver nanoparticles. These protein-stabilized silver nanoparticles produced a characteristic emission peak at 553 nm when excited at 420 nm in photoluminescence spectrum. The use of fungus for silver nanoparticles synthesis offers the benefits of eco-friendliness and amenability for large-scale production.     

Biological synthesis of very small silver nanoparticles by culture supernatant of Klebsiella pneumonia: The effects of visible-light irradiation and the liquid mixing process

This study has investigated different visible-light irradiation's effect on the formation of silver nanoparticles from silver nitrate using the culture supernatant of Klebsiella pneumonia. Our study shows that visible-light emission can significantly prompt the synthesis of silver nanoparticles. Also, the study experimentally investigated the liquid mixing process effect on silver nanoparticle synthesis by visible-light irradiation. This study successfully synthesized uniformly dispersed silver nanoparticles with a uniform size and shape in the range of 1-6 nm with an average size of 3 nm. Furthermore, the study investigated the mechanism of the reduction of silver ions by culture supernatant of K. pneumonia, and used X-ray diffraction to characterize silver chloride as an intermediate compound. Silver chloride was prepared synthetically and used as a substrate for the synthesis of silver nanoparticles by culture supernatant of K. pneumonia. The silver nanoparticles have been prepared from silver chloride during this investigation for the first time.     

Microwave absorption performance of magnetic Fe–Ni–P nanoparticles electrolessly plated on hollow glass microspheres

Magnetic Fe–Ni–P nanoparticles have been successfully fabricated on hollow glass microspheres via electroless plating for the application of lightweight microwave absorbers. The resultant materials were characterized by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. The results show that compact and uniform Fe–Ni–P nanoparticles with the average diameter of about 150 nm have been successfully plated on the hollow glass microspheres. The plated microspheres exhibit excellent soft magnetic characteristics with high saturation magnetization and low coercivity, and the soft magnetic characteristic behaves better with the increasing of iron content in the coatings. Microwave absorption performance shows the maximum reflection loss of the composite powder reaches −49.2 dB at the frequency of 7.7 GHz with the thickness of 5 mm, and the bandwidth with the reflection loss less than −20 dB exceeds 2.2 GHz.     

Physicochemical characterization of Fe3O4/SiO2/Au multilayer nanostructure

The purpose of this research was to synthesize and characterize gold-coated Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetite nanoparticles (NPs) were prepared using co-precipitation method. Smaller particles were synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g⁻¹. For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of 80–100 emu g⁻¹ and coercivity of 80–120 Oe for particles between 35 and 96 nm, respectively. The magnetic NPs were modified with a thin layer of silica using Stober method. Small gold colloids (1–3 nm) were synthesized using Duff method and covered the amino functionalized particle surface. Magnetic and optical properties of gold nanoshells were assessed using Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis spectrophotometer, atomic and magnetic force microscope (AFM, MFM), and transmission electron microscope (TEM). Based on the X-ray diffraction (XRD) results, three main peaks of Au (1 1 1), (2 0 0) and (2 2 0) were identified. The formation of each layer of a nanoshell is also demonstrated by Fourier transform infrared (FTIR) results. The Fe₃O₄/SiO₂/Au nanostructures, with 85 nm as particle size, exhibited an absorption peak at ∼550 nm with a magnetization value of 1.3 emu g⁻¹ with a specific surface area of 71 m² g⁻¹.     

Chemical solution deposited lanthanum zirconium oxide thin films: Synthesis and chemistry

Pyrochlore lanthanum zirconium oxide (LZO) thin films textured along 〈4 0 0〉 are synthesized using lanthanum acetate hydrate, zirconium propoxide, propionic acid, acetic acid glacial, and methanol as precursors. The materials growth and chemistry are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). The formation of inkjet printed LZO films on Ni-5%W tape is found to be based on the decomposition of the LZO precursor solution. In the annealing process, Zr metal–oxides bonds are first eliminated between 150 and 250 °C, while carboxylates from precursors remain in LZO after the annealing carried out at 900 °C for an hour. Annealed LZO films have dense and smooth structure that are composed of nanoparticles sizing 10–15 nm and some pinholes sizing 25–35 nm accounted for less than 0.1% of the area are observed.