Efficient synthesis and structural characterization of silver nanoparticle/ bis(o-phenolpropyl)silicone composites

Silver nanoparticle/bis(o-phenolpropyl)silicone composites have been synthesized by the reduction of silver nitrate with bis(o-phenolpropyl)silicone BPPS [(o-phenolpropyl)2(SiMe2O)n, n = 2, 3, 8, 236]. TEM and FE-SEM data clearly show that the silver nanoparticles with the size of < 20 nm are well dispersed throughout the BPPS matrix in the composites. XRD patterns are consistent with those for multicrystalline silver. The size of silver nanoparticles increased with increasing the relative molar concentration of silver salts added. It was found that in the absence of BPPS, most of the silver nanoparticles undergo macroscopic precipitation by agglomeration, indicating that BPPS is essential to stabilize the silver nanoparticles.     

Synthesis of silver-integrated silica nanostructures using rice hulls and their electrochemical performance for supercapacitor application

We report the synthesis of silver-integrated silica nanostructures using rice hulls and silver chloride through a facile thermal combustion process. The formation of mesoporous silica nanomatrix embedded with silver nanoparticles (SiO₂:Ag 5 wt% and SiO₂:Ag 10 wt%) was confirmed by XRD, FTIR, EDX, BET, and TEM analysis. Also, the obtained results from the above studies revealed that the concentration of silver ions significantly increases the particle size and number of silver nanoparticles formed in the silica matrix. The electrochemical performance was studied using silver-integrated silica nanostructures as a working electrode in KOH electrolyte. The maximum specific capacitance of SiO₂:Ag 5 wt%- and SiO₂:Ag 10 wt%-coated electrode was found to be 517 and 580 F/g at current density of 1 A/g. It was also found that SiO₂:Ag 10 wt% electrode exhibit an excellent stability with the capacitance retention of 94% than SiO₂:Ag 5 wt% (capacitance retention of 85%) after 1000 cycles at a current density of 1 A/g. These results may be attributed to the inherent characteristic of more silver nanoparticles present in the silica nanomatrix in SiO₂:Ag 10 wt%. The intrinsic characteristic of rice hull-derived silica nanostructures such as high surface area and mesoporous structure along with the advantage of silver nanoparticles (conductivity) can facilitate the Faradic redox processes at electrode surface which are responsible for the supercapacitive behavior of the prepared silver-integrated silica nanostructures.

     

Synthesis and characterization of silver nanoparticle composite with poly(p-Br-phenylsilane)

The one-pot synthesis and characterization of silver nanoparticle-poly(p-Br-phenylsilane) composites have been carried out. The conversion of silver(+1) salt to stable silver(0) nanoparticles is promoted by poly(p-Br-phenylsilane), Br-PPS possessing both possible reactive Si-H bonds in the polymer backbone and C-Br bonds in the substituents. The composites were characterized using XRD, TEM, FE-SEM, and solid-state UV-vis analytical techniques. TEM and FE-SEM data show the formation of the composites where large number of silver nanoparticles (less than 30 nm of size) are well dispersed throughout the Br-PPS matrix. XRD patterns are consistent with that for fcc-typed silver. The elemental analysis for Br atom and the polymer solubility confirm that the cleavage of C-Br bond and the Si-Br dative bonding were not occurred appreciably at ambient temperature. Nonetheless, TGA data suggest that some sort of cross-linking was occurred at high temperature. The size and processability of such nanoparticles depend on the ratio of metal to Br-PPS. In the absence of Br-PPS, most of the silver particles undergo macroscopic aggregation, which indicates that the polysilane is necessary for stabilizing the silver nanoparticles.     

Preparation of silver nanoparticles having low melting temperature through a new synthetic process without solvent

This study presents a new synthetic method of silver nanoparticles using a novel polyoxyethylene maleate-based surfactant (PEOM). Unlike conventional process using large amount of a solvent to dissolve silver salts, large amount of silver salts (AgNO3) can be dissolved and stabilized by our surfactant without solvent. Silver salts can be dissociated within PEOM by the formation of charge complex between hydrophilic-COOH segments and Ag+NO3-, resulting in formation of self-assembled microstructures which acting as a nano-reactor and stabilizer. After reduction using NaBH4, uniform sized silver nanoparticles were formed in the hydrophilic domain of PEOM. Silver contents in the colloids were changed by 0.5 approximately 3 wt%. Distribution of silver nanoparticle sizes was investigated by using TEM and XRD. Melting temperature of silver nanoparticles was measured by differential scanning calorimetry, which depends upon the particle size of silver nanoparticles. The lowest melting temperature of 112 degrees was measured from 3.5 nm average-sized silver particles.     

Silver nanoparticles/montmorillonite composites prepared using nitrating reagent at water and glycerol

Three procedures (P) were applied to prepare silver nanoparticles on natural Ca-montmorillonite (MT). The intercalation of the montmorillonite with silver nitrate in aqueous solution (P1), the intercalation of the montmorillonite with silver nitrate in glycerol (P2) and the successive combination of both P1 and P2 methods resulted to P3 method. X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared (FTIR) spectroscopy and the molecular modeling were employed to characterize silver nanoparticles and montmorillonite nanocomposite. The P1 produced MT-1 composite with 2.3 wt% Ag and the partially collapsed layered structure. Nanoparticles of silver larger than 20 nm with a lot of planar defects were randomly distributed on the MT-1 surface; nanoparticles smaller than 20 nm were oriented to the montmorillonite substrate. The MT-2 composite from P2 contained only 1 wt% of Ag. The molecular simulation model of MT-2 showed the interlayer space with the exchangeable cations and metallic silver atoms arrangement within the glycerol bilayer. The P3 produced composite MT-3 that contained 2.4 wt% Ag. The nanoparticles > 20 nm size had a well-defined geometry, very small nanoparticles were amorphous. The modeled structure showed the exchangeable cations, Ag+ and Ag0 located close to the silicate layers and monolayer of glycerol molecules in the interlayer space.     

Thermal precipitation of silver nanoparticles and thermoluminescence in tellurite glasses

Silver metal and/or oxide precipitation of nanoparticles in thermally treated Ag-doped tellurite glasses was studied by optical absorption (OA) and transmission electron microscopy (TEM). The Lorentzian adjusted silver nanoparticles plasma resonance OA band was compared to the Drude model approach. The silver nanoparticles size distribution on the surface rather than in the bulk was determined by TEM. A model for the metallic silver precipitation is proposed. The characterization of the formation of silver nanoparticles was carried out with differential thermal analysis (DTA) to determine the glass transition temperature (Tg) and of crystallization (Tc). Previously γ-irradiated samples exhibited thermoluminescence (TL) peaks and the defect centers TeOHC, NBOHC and TeEC were identified by electron paramagnetic resonance (EPR), but no Ag⁰ signal was detected. The silver nanoparticles are known to introduce desired third-order optical nonlinearities in the composites, at wavelengths close to the characteristic surface-plasmon resonance of the metal precipitates. An increase of the glass density and refractive index with increasing AgNO₃ content was observed.     

Nanosilver particle formation on a high surface area titanate

Titanium based molecular sieves, such as ETS-10, have the ability to exchange silver ions and subsequently support self assembly of stable silver nanoparticles when heated. We report that a high surface area sodium titanate (resembling ETS-2) displays a similar ability to self template silver nanoparticles on its surface. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show high concentrations of silver nanoparticles on the surface of this sodium titanate, formed by thermal reduction of exchanged silver cations. The nanoparticles range in size from 4 to 12 nm, centered at around 6 nm. In addition to SEM and TEM, XRD and surface area analysis were used to characterize the material. The results indicate that this sodium titanate has a high surface area (>263 m2/g), and high ion exchange capacity for silver (30+ wt%) making it an excellent substrate for the exchange and generation of uniform, high-density silver nanoparticles.     

Broad-spectrum antimicrobial activity of bacterial cellulose silver nanocomposites with sustained release

Bacterial cellulose-based antifouling materials have been produced by incorporation of silver nanoparticles for broad-spectrum antimicrobial activity. Three variations of silver nitrate (AgNO₃) to reducing agent concentrations have been tried to vary the silver nanoparticle dimension. The formation of silver nanoparticles was also evidenced by the X-ray diffraction, and the crystallite size was found to decrease with increase in NaBH₄ concentration. AgBC composites having < 2% (W/W) of silver exhibited 99.9% antimicrobial activity which was sustained up to 72 h against spoiled food derived mixed microbial culture. On the other hand, only 90% activity was observed with colloidal AgNPs due to aggregate formation. Composites displayed superior antimicrobial activity than colloid with equivalent amount of silver. Food stuff was protected from microbial spoilage for 30 days when stored in AgBC nanocomposites, whereas spoilage was noticed within 15 days for food stuff stored in regular polythene bag. Therefore, the AgBC composite having < 2% silver can be used as a lining of regular food packaging material to extend shelf life till 30 days. Toxicity due to high amount of silver can be prevented with these composites and can be safely used in healthcare applications such as food packaging, wound dressing, hospital bed lining and surgical apparels.     

Effect of controlling nano-sized copper by silver in copper-based catalyst on catalytic oxidation of toluene

Catalytic oxidation of VOC (toluene) over a copper based catalyst was carried out to assess its properties and performance. The Brunauer Emmett Teller (BET) method, X-ray diffraction (XRD), temperature programmed reduction (TPR), N2O pulse titration and energy dispersive spectroscopy (EDS) were used to characterize a series of 5 wt% Cu/gamma-Al2O3 catalysts modified with silver. The experimental results revealed that the addition of silver to 5 wt% Cu/gamma-Al2O3 catalyst highly enhanced its catalytic activity. With increasing addition amount of silver, the light-off curve for complete oxidation of toluene shifted to lower temperature. In addition, the increase of the addition amount of silver caused the copper particle size of 5 wt% Cu/gamma-Al2O3 catalyst to gradually increase. Subsequently, it demonstrated that the increase in the copper particle size is closely associated with the increase in catalytic activity.     

Bio-mechanochemical synthesis of silver nanoparticles with antibacterial activity

By using a bio-mechanochemical approach combining mechanochemistry (ball milling) and green synthesis for the first time, silver nanoparticles (Ag NPs) with antibacterial activity were successfully synthesized. Concretely, eggshell membrane (ESM) or Origanum vulgare L. plant (ORE) and silver nitrate were used as environmentally friendly reducing agent and Ag precursor, respectively. The whole synthesis took 30?min in the former and 45?min in the latter case. The photon cross-correlation measurements have shown finer character of the product in the case of milling with Origanum. UV–Vis measurements have shown the formation of spherical NPs in both samples. TEM study has revealed that both samples are composites of nanosized silver nanoparticles homogenously dispersed within the organic matrices. It has shown that the size and size distribution of the silver nanoparticles is smaller and more uniform in the case of eggshell membrane matrix implying lower silver mobility within this matrix. The antibacterial activity was higher for the silver nanoparticles synthesized with co-milling with Origanum plant than in the case of milling with eggshell membrane.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

Synthesis of Yb nanoparticles by laser ablation of ytterbium target in sodium bis(2-ethylhexyl)sulfosuccinate reverse micellar solution

Surfactant-coated ytterbium nanoparticles were produced by Nd:YAG laser ablation of a Yb bulk target immersed in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane micellar solution. In our experimental conditions, as highlighted by IR spectroscopy, AOT molecules are not decomposed by the intense laser pulses but play a pivotal role in the stabilisation of Yb nanoparticles. The formation of Yb nanoparticles in the liquid phase was monitored by UV-Vis spectroscopy whereas the Yb/AOT composites obtained by evaporation of the organic solvent were characterised by XPS and TEM. Data analysis consistently shows the presence of surfactant-coated, nearly spherical and non-interacting Yb nanoparticles of mean diameter of 3 nm.Moreover, the presence of bigger polycrystalline nanoparticles (about 30%) in coexistence with smaller mono crystalline ones indicates that, after the rapid formation of the pristine Yb nanoparticles from plume condensation, two processes effectively compete for their size distribution: nanoparticle agglomeration and surfactant adsorption.     

In-situ preparation of epoxy/silver nanocomposites by thermal decomposition of silver–imidazole complex

A novel method for the preparation of epoxy/silver nanocomposites was developed by in-situ formation of silver nanoparticles within the epoxy matrix. The silver–imidazole complex was synthesized by silver acetate and 2-ethyl-4-methylimidazole (2E4MZ). During the cure of epoxy resin, silver nanoparticles were in-situ generated through thermal decomposition of the silver–imidazole complex which was capable of reducing Ag⁺ to Ag⁰ by itself. The simultaneously released imidazole could cure the epoxy. In addition, the in-situ generated silver nanoparticles could be stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed silver nanoparticles of size of around 11.6 nm were in-situ generated in epoxy matrix.     

Improving the thermal and mechanical properties of silicone polymer by incorporating functionalized graphene oxide

Functionalized graphene oxide (FGO) was produced by reacting graphene oxide nanosheets with vinyl trimethoxy silane (VTMS). The results confirmed the attachment of VTMS molecules to the surface of GO sheets by Si–O–C bonding. The introduction of VTMS molecules led to an excellent dispersibility in tetrahydrofuran and to the complete exfoliation of FGO with a thickness of about 1.19 nm. Meanwhile, FGO/silicone polymer composites were prepared by solution blending method. The incorporation of 0.5 wt% of FGO in silicone polymer improved remarkably the thermal stability, tensile strength, and thermal conductivity of the silicone polymer composite, due to the homogeneous dispersion of FGO in the composites as well as to the strong interfacial adhesion with silicone polymer matrix. Tensile strength and thermal conductivity of the FGO/silicone polymer composite were increased by 95.6 and 78.3 %, respectively, with the addition of 0.5 wt% FGO. The 5 % weight loss temperature of the composite at 0.5 wt% FGO loading was detected 26.1 °C higher than that of silicone polymer.     

碳包钴纳米颗粒/聚二甲基硅氧烷复合热界面材料的制备和性能

为了制备具有良好的热导率、热稳定性、导电性和柔顺性的纳米颗粒填充硅树脂复合材料,首先以乙基封端聚二甲基硅氧烷(PDMS)为基体材料,以碳包钴纳米颗粒(C@Co)为填料,采用研磨共混法制备了C@Co/PDMS复合热界面材料。然后,运用TEM、XRD、Raman和SEM分别对C@Co的微观结构、物相、石墨化程度和分散性进行了研究。最后,研究了C@Co含量对复合热界面材料的热导率、热稳定性、导电性和柔顺性的影响。结果表明:该复合热界面材料的热导率随着C@Co含量的增加而增大,当C@Co的含量为24wt%时,复合材料的热导率达到最大值1.64 W/(m·K),比纯PDMS的提高了10.7倍;TG分析表明,添加24wt%的C@Co后,复合材料的起始分解温度和最终分解温度比纯PDMS的分别提高了约70℃和80℃,说明C@Co能提高复合材料的热稳定性;随着C@Co含量的增加,复合热界面材料的电导率非线性增大,拟合试差计算的逾渗阀值为10wt%,即C@Co含量小于10wt%时复合材料的绝缘性良好,而填充24wt%的C@Co时复合材料的电导率为9.38×10-3 S·m-1;复合材料的硬度适中,处于17.6~26.8HA范围内,表明该复合材料的柔顺性较好。因此,24wt%C@Co/PDMS复合材料不仅能满足热界面材料电性能的基本要求,且具有良好的热导率、热稳定性和柔顺性。     

An Investigation of Y<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18</Subscript> Doping with Ag Nanoparticles and Its Application as Superconductor

Y₃Ba₅Cu₈O₁₈ superconductors were prepared through a standard solid-state reaction and the structural properties of the samples were studied through XRD and the Rietveld refinement method. The effect of silver nanoparticles doping on the Y₃Ba₅Cu₈O₁₈ superconductors was studied as well. It is known that the size of nanoparticles is increased during aging. Therefore, two batches of samples with 1 and 2 wt% of Ag nanoparticles and the size range of 30, 200, 500, 700, 800, and 1000 nm were prepared. After preparing the samples and observing the Meissner effect, the crystallography, critical current density, critical temperature, magnetic susceptibility, SEM, and EDX experiments of the samples were carried out. The results of the critical current density measurements showed that the sample with 2 wt% Ag nanoparticles and the size of 700 nm has the maximum current density. In both batches of samples, increasing the nanoparticle size to 700 nm led to an increase in the critical current density. The crystallography studies showed that silver nanoparticles do not insert into the superconductor’s frame. Actually, they are placed in the samples as a distinct phase.     

Preparation of Au-loaded niobate nanosheets and their plasmon-driven photochemical reaction

Niobate nanosheets prepared by exfoliation of layered hexaniobate K₄Nb₆O₁₇ were sequentially decorated with two noble metal nanoparticles, gold and silver, through two-step photochemical reactions. First, cationic bis(ethylenediamine)gold(III) ions were electrostatically adsorbed on the anionic niobate nanosheets, and reduced to gold nanoparticles by UV excitation of the photocatalytically active niobate nanosheets. Then, the surface plasmon band of the photodeposited gold nanoparticles was excited with visible light, by which the silver cations introduced to the system together with citrate anions were reduced to silver nanoparticles. Spectroscopic and transmission electron microscopic observations indicated the formation of morphologically different silver nanoparticles, for example nanorods and core-shell particles.     

Biological synthesis of gold and silver nanoparticles mediated by the bacteria Bacillus subtilis

Biological synthesis of gold and silver nanoparticles was carried out using the bacteria Bacillus subtilis. The reduction processes of chloroaurate and silver ions by B. subtilis were found to be different. Gold nanoparticles were synthesized both intra- and extracellularly, while silver nanoparticles were exclusively formed extracellularly. The gold nanoparticles were formed after 1 day of addition of chloroaurate ions, while the silver nanoparticles were formed after 7 days. The nanoparticles were characterized by X-ray diffraction, UV-vis spectra and transmission electron spectroscopy. X-ray diffraction revealed the formation of face-centered cubic (fcc) crystalline gold nanoparticles in the supernatant, broth solution and bacterial pellet. Silver nanoparticles also exhibited diffraction peaks corresponding to fcc metallic silver. UV-vis spectra showed surface plasmon vibrations for gold and silver nanoparticles centered at 530 and 456 nm, respectively. TEM micrographs depicted the formation of gold nanoparticles intra- and extracellularly, which had an average size of 7.6 +/- 1.8 and 7.3 +/- 2.3 nm, respectively, while silver nanoparticles were exclusively formed extracellularly, with an average size of 6.1 +/- 1.6 nm. The bacterial proteins were analyzed by sodium dodecyl sulfonate-polyacrylamide electrophoresis (SDS-PAGE) before and after the addition of metal ion solutions. We believe that proteins of a molecular weight between 25 and 66 kDa could be responsible for chloroaurate ions reduction, while the formation of silver nanoparticles can be attributed to proteins of a molecular weight between 66 and 116 kDa. We also believe that the nanoparticles were stabilized by the surface-active molecules i.e., surfactin or other biomolecules released into the solution by B. subtilis.     

Structural characterization and catalytic activity of Pt dendrimer encapsulated nanoparticles supported over Al2O3 for SCR of NOx

Pt/Al2O3 and Pt-Mg/Al2O3 nano composites were successfully prepared by dendrimer templated synthesis route. The obtained dendritic nanoparticles were dispersed in alumina support and they were evaluated for SCR of NOx using methane as reductant. Thermal analysis results of uncalcined samples revealed that the oxygen can accelerate the rate of dendrimer shell decomposition. X-ray diffractograms of 500 degrees C calcined samples disclosed the amorphous nature of materials, whereas 1000 degrees C air calcined samples showed enhanced crystallinity as well as diffraction pattern corresponding to Pt and PtO. HRTEM images of Pt40-G4OH dendritic nanoparticles showed uniform particulate distribution with average particle size of 2.4 nm. The STEM results of 0.5 Pt/Al2O3 sample calcined at 500 degrees C exhibited a wide range of particles between 2 and 20 nm. This indicates the huge segregation of platinum metal particles during impregnation and subsequent calcination. Among the synthesized materials 0.5 wt% Pt/Al2O3 sample showed excellent conversion and selectivity for SCR of NOx.     

Conducting polymer coated graphene oxide reinforced C–epoxy composites for enhanced electrical conduction

Enhanced electrical conductivities were achieved in C–epoxy composites by integrating them with conducting polymers (CPs), namely poly pyrrole (PPY), poly(3,4-ethylene dioxythiophene) (PEDOT) and graphene oxide (GO) enwrapped by CPs. By in-situ polymerization of pyrrole or 3,4-ethylenedioxythiophene (EDOT) in the presence of the GO (template), sodium bis(2-ethylhexyl) sulfosuccinate (structure directing agent), ferric chloride (oxidant), the electrically conductive sheets of GO enwrapped CPs were obtained. The formation of CP coating on GO was confirmed by Raman spectroscopy, scanning electron microscopy and thermo gravimetric analysis studies. Different wt% of CP and CP coated GO were added to the epoxy resin and this resin was used to prepare the 2D laminated C–epoxy composites by hand layup method. DC electrical conductivity of the prepared C–epoxy composites were analyzed using current–voltage (I–V) characteristics and impedance measurements. Typical results showed that CP coated GO, at 0.5 wt% addition to epoxy imparted highest DC electrical conductivity for C–epoxy composite.