Silver-embedded zeolite crystals as substrates for surface-enhanced Raman scattering

This paper reports the preparation of a type of Ag-embedded zeolite crystals as surface-enhanced Raman spectroscopy (SERS) substrates by chemical reduction of Ag⁺-exchanged ZSM-5. Ag⁺ ions were loaded into the zeolite framework by ion exchange. Then the exchanged-Ag⁺ ions were reduced and metallic silver clusters formed inside the zeolite channel. The resulting Ag-embedded zeolite crystals are characterized by using a number of techniques including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy to confirm silver formed inside the crystal channel. The fabricated Ag-embedded ZSM-5 zeolite substrates displayed strong and reproducible SERS activity for different Raman probe molecules such as Tris(2,2′-bipyridyl) ruthenium(II) chloride (RuBpy) and rhodamine 6G (R6G). Since silver embedded into the zeolite channel without changing the crystal surface property, the Ag–ZSM-5 zeolite crystal can be used to prepare different SERS-active substrate (SERS-tags), in which different probe molecules may be detected. Such Ag-embedded zeolite substrate would be useful in chemical and biological sensing and in the development of SERS-based analytical devices.     

PVC silver zeolite composites with antimicrobial properties

Poly(vinyl chloride) (PVC) composites containing increasing amounts (2–20%, w/w) of silver zeolite (SZ) were prepared by melt mixing and characterized by thermal, mechanical and rheological analyses. The addition of large amount of SZ did not influence the processability and the formability of the composites, if compared to neat plasticized PVC. The antibacterial activity of PVC SZ composites was tested on Escherichia coli and Staphylococcus epidermidis and resulted promising both in culture broth and on agar plate and also in sterile urine seeded with these strains, for simulation purposes. In sterile urine, composites induced a significant reduction (4–6 log units) of viability of both strains already at 24 h, inhibiting E. coli growth up to 20 days, whereas their antimicrobial action against S. epidermidis vanished within 5 days. The silver release in sterile urine was determined up to 20 days. It was found that the highest amount of silver ions was released during the first day (0.365 ppm), whilst from days 6 to 20 the silver release decreased, reaching a steady daily mean value of 0.02 ppm.     

Silver, gold and bimetallic nanoparticles production using single-cell protein (Spirulina platensis) Geitler

Interaction of single-cell protein of Spirulina platensis with aqueous AgNO₃ and HAuCl₄ was investigated for the synthesis of Ag, Au and Au core—Ag shell nanoparticles. Biological reduction and extracellular synthesis of nanoparticles were achieved in 120 h at 37 °C at pH 5.6. The nanometallic dispersions were characterized by surface plasmon absorbance measuring at 424 and 530 nm for Ag and Au nanoparticles, respectively. For bimetallic nanoparticles, absorption peak was observed at 509, 486 and 464 nm at 75:25, 50:50 and 25:75 (Au:Ag) mol concentrations, respectively. High-resolution transmission electron microscopy showed formation of nanoparticles in the range of 7–16 (silver), 6–10 (gold) and 17–25 nm (bimetallic 50:50 ratio). XRD analysis of the silver and gold nanoparticles confirmed the formation of metallic silver and gold. Fourier transform infrared spectroscopic measurements revealed the fact that the protein is the possible biomolecule responsible for the reduction and capping of the biosynthesized nanoparticles.     

Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.     

Evaluation of commercial adsorbents and their application for desulfurization of model fuel

The removal of dibenzothiophene from model fuel was carried out by adsorption on commercially available adsorbents including an activated carbon, aluminum oxide, 13X and Y zeolite. Activated carbon was SOLCARB^TM C3 which was grinded from its original particle size 1.0–2.0 mm to the 0.40–0.80 mm, while aluminum oxide Selexsorb CDX, 13X zeolite MSE 13X and Y zeolite HSZ-320NAA were used in their as delivered particle size ranges of 2.7–3.0, 1.6, and 300–600 nm, respectively. Adsorption experiments were carried out in batch mode at 24.5 ± 0.7°C using model fuel comprising cyclo-hexane, n-heptane, n-octane and dibenzothiophene in the concentration range of 0.48–42.91 mg/g. The experimental data was used to compare applied adsorbents and to carry out equilibrium characterization and kinetic analysis of the adsorption process. The evaluation of the tested adsorbents showed that the best adsorptive performance was achieved by the Y zeolite. The analysis of the adsorption equilibrium data and the kinetic analysis showed that of the applied models the best fits to the experimental data were achieved by the Sips and Ritchie models, respectively.     

Preparation and properties of a novel electrically conductive adhesive using a composite of silver nanorods, silver nanoparticles, and modified epoxy resin

A novel preparation method for a high-performance electrically conductive adhesive (ECA) which consisted of silver nanorods, silver nanoparticles and modified epoxy resin was developed. Silver nanorods (100 nm in diameter and 5 μm in length) were synthesized by reduction of silver nitrate with ethylene glycol in the presence of Pd seeds and poly (vinyl pyrrolidone) (PVP). Silver nanoparticles (50~60 nm) were synthesized using N, N′-Dimethylformanide as the reducing agent and PVP as the stabilizer. The nanorods and nanoparticles were dispersed well and no agglomerate in the matrix. The volume electrical resistivity tests showed the volume electrical resistivity of the ECA was closely related with the various sintering temperatures and time, and the ECA could achieve the volume electrical resistivity of (3–4) × 10⁻⁵ Ω cm after sintering at 160 °C for 20 min. Moreover, the results showed the as-prepared ECA was able to achieve low-temperature sintering and possessed excellent electrical, thermal, and mechanical properties.     

Synthesis and characterization of silicalite powders and membranes with micro–meso bimodal pores

Silicalite sols containing silicalite agglomerates of 150–380 nm in size were synthesized by hydrothermal synthesis for 0.5–3 days. Silicalite powders and supported silicalite membranes containing micro-meso bimodal pores were prepared by the sol–gel method using these silicalite sols. The silicalite powders contain intracrystalline zeolitic pores (0.54 nm) and intercrystalline mesopores of about 3–4 nm in diameter. For the silicalite powders the mesopore size decreases and mesopore surface area increases with increasing silicalite agglomerate size as a result of a change of the shape of silicalite agglomerates from round to more faceted one. Continuous silicalite thin films of thicknesses ranging from 3 μm to 12 μm were made on α-alumina by the sol–gel dip-coating method. The supported silicalite membranes also contain both zeolitic pores and mesoporous intercrystalline pores. The single gas He permeance of the 3 μm thick α-alumina supported silicalite membrane was found to be from 2.7 × 10⁻⁶ to 3.3 × 10⁻⁶ mol/m² s Pa. These bimodal pore zeolite powders offer the potential as catalysts and sorbents with improved efficiency. The bimodal pore zeolite membrane can be used as support for zeolite and other membranes and as compact packed-bed reactor for chemical reaction.     

Particle size-dependent electrical properties of nanocrystalline NiO

Nickel oxide nanoparticles are formed by chemical precipitation and subsequent drying and calcinations at temperatures ≥523 K. Samples are characterized using X-ray diffraction and BET surface area measurements indicating the formation of a single NiO phase whose crystallite size increases with increasing calcination temperature. The electrical properties are examined by measuring DC and AC conductivities and dielectric properties as functions of temperature. Electrical conductivities first slightly increases with increasing particle size up to 7–10 nm and are about 8 orders of magnitude higher than that of NiO single crystals. Further increasing the particle size above 10 nm, leads to a monotonic decrease of conductivity. The data are discussed in view of variations of grain boundary as well as triple junction volume fractions as the particle size varies. At temperatures above θ_D/2 (θ_D is the Debye temperature), the conductivity is ascribed to a band-like conduction due to the large polaron. The activation energy of conduction was found to be minimal for the highly conducting samples of 7–10 nm, and gradually increases to ~0.5 eV with increasing the particle size above 10 nm. For T < θ_D/2, the conductivity is best described by variable–range–hopping models. Model parameters are thus estimated and presented as functions of particle size. Frequency as well as temperature dependencies of the AC conductivity and dielectric constant exhibit trends usually observed in carrier dominated dielectrics.     

Morphological studies on single crystals and nanofibers of poly(heptamethylene terephthalate)

Poly(heptamethylene terephthalate) (poly(7GT)) was synthesized, and its lamellar single-crystals were grown isothermally at 70 °C from a dilute solution in 1-octanol. Poly(7GT) nanofibers were prepared via electrospinning of its solution in 1,1,1,3,3,3-hexafluoro-2-propanol. Morphology of the single crystals and that of as-spun and annealed nanofibers were investigated by transmission electron microscopy. Selected-area electron diffraction (SAED) of the crystals gave a well-defined N-pattern consisting of spot-like hk0 reflections, and that of bundles of the annealed nanofibers indicated a highly oriented fiber pattern. From the analysis of SAED diagrams for single crystals and nanofibers, it can be assumed that poly(7GT) takes an orthorhombic crystal system and its unit cell parameters estimated are as follows: a = 1.409 nm, b = 1.480 nm, c (chain axis) = 3.392 nm, and α = β = γ = 90°.     

Synthesis and characterization of gold–polypyrrole film composite

Polypyrrole (PPy) coatings have potential applications in batteries, fuel cells, sensors, anti-corrosion coatings, and drug delivery systems. In this article, PPy film coating on the electrode of quartz crystal microbalance (QCM) was exposed to acidic aqueous HAuCl₄ solution. The reduction for gold ions took place and gold particles were produced at the film surface. The gold content at the PPy film was monitored by using QCM. The concentration of gold uptake increases as the original concentration of HAuCl₄ solution increases. The morphology of the film before and after the deposition of the gold particles was studied by the scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The gold particles are of undefined shape and have diameters around 200–600 nm. However, the image of the composite powder shows that gold particles of sizes 100–120 nm are distributed over the surface of the polymer particles with some aggregation. Infrared spectroscopy and X-ray diffraction were used to characterize the composite.     

Preparation of pH-responsive silver nanoparticles by RAFT polymerization

Silver nanoparticles were prepared by chemical reduction of AgNO₃ in the presence of the PDMAEMA-b-PPA, which was synthesized by the reversible addition-fragmentation transfer technique. The formation of the silver nanoparticles was determined by the transmission electron microscopy (TEM) images and UV–Vis absorption spectra. The average size of the silver nanoparticles was shown to 11.4 nm. Particularly, the pH-responsive property of the silver nanoparticle was further observed. It was characterized by the zate potential, the UV–Vis spectra, and TEM images. The results show that the pH-responsive property is attributed to the aggregate of the silver nanoparticles as a function of pH. The characteristic is expected to apply in the nanoscale optical biosensor and biomaterials.     

High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Conductive polymer preparation under extreme or non-classical conditions

Polyaniline (PANI) emeraldine salt form and PANI/silver composites have been synthesized by sonochemical and ionizing radiation methods. These composite materials were obtained through sonication and γ irradiation of an aqueous solution of aniline and silver nitrate, in room temperature, respectively. The mechanisms suggested to explain the formation of these products are based on the fact that both methods produce hydroxyl radical ^•OH and hydrogen radical ^•H, where hydroxyl radical ^•OH acts as an oxidizing agent in the polymerization process of aniline monomer; and hydrogen radical ^•H, as a reducing agent for silver ions. Spectroscopic, X-ray, and SEM measures show that PANI and silver nano particles of 40 nm average diameter are produced with ultrasonic methods, whereas silver nano particles of 60 nm average, and fibrillar, highly network morphology for PANI with 60 nm fibrillar diameter average are obtained using γ radiation).     

Ammonia sensing by hydrochloric acid doped poly(<Emphasis Type="Italic">m</Emphasis>-aminophenol)–silver nanocomposite

Processable poly(m-aminophenol) (PmAP) was synthesized using ammonium persulfate oxidant in 0.6 M sodium hydroxide solution at room temperature. Then, in situ PmAP–silver nanocomposite film was obtained by casting PmAP film from dimethyl sulfoxide with silver hydroxide ammonia mixture at 140 °C. The nanocomposite film was doped with hydrochloric acid (HCl) by general solution doping technique. The undoped and HCl-doped films were characterized by ultraviolet visible spectroscopy, Fourier transformed Infrared spectroscopy, transmittance electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction analysis. Spectroscopic characterizations confirmed that the PmAP was doped by silver nanoparticles and it was further doped by HCl used. So, the synthesized PmAP–silver nanocomposite showed a conductivity of 1.01 × 10⁻⁶ S/cm, which was increased to 3.27 × 10⁻⁴ S/cm after HCl doping. The well dispersed silver nanoparticles with average size 130–150 nm was observed by SEM and TEM analysis. Unlike conventional ammonia sensor here, the resistivity of the nanocomposite film was decreased on exposure to ammonia gas and the sensing properties of the HCl-doped nanocomposite films were also reproducible. It can be seen that the % response of doped nanocomposite was unchanged while, the response time was decreased with increasing ammonia vapor concentrations in air. The ammonia-sensing characteristics of the HCl-doped nanocomposite film was explained on the basis of a proposed mechanism.     

In situ preparation of self-bonded zeolite MCM-22 bodies by vapor-phase transport method

Self-bonded bodies of zeolite MCM-22 were prepared by vapor-phase transport method. The resultant materials were characterized by means of X-ray diffraction, scanning electron microscope, mercury porosimetry, and nitrogen porosimetry. Self-bonded MCM-22 bodies were in situ prepared at pH 10.0 with the molar composition of 0.05Na₂O:SiO₂:0.033Al₂O₃. It was found that the bodies, prepared by aluminosilicate gel, had been transformed into zeolite MCM-22. The MCM-22 bodies of which the mechanical resistance was 126 N/cm avoided binder accession. By adding auxiliary chemical–PEG20000 to the aluminosilicate gel, the pore size distributions of MCM-22 bodies could be adjusted. The average pore radius of MCM-22 bodies reached in the 149.41–653.64 nm range when AC/SiO₂ ratio was 1.5 × 10⁻⁴–9.0 × 10⁻⁴.     

Fabricating of silver and copper nano/microtubes using nano-scale glass fibers as templates

In this paper, large-scale uniform silver and copper nano/microtubes with high length diameter ratios have been successfully synthesized by a facile approach, using low-cost nano-scale glass fibers as templates. The tubular structures can be obtained by reducing of Ag and Cu ions on the surface of the fibers, along with removing the templates. The samples are characterized by SEM and XRD. Results show the tubular structures are very uniform and the tubular walls are composed of densely coalesced crystalline nanoparticles of 30–50 nm.     

Structure–property correlations in the SiO<Subscript>2</Subscript>–PbO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

SiO₂–PbO–Bi₂O₃ glasses having the composition of 35SiO₂–xPbO–(65−x)Bi₂O₃ (where x = 5, 10, 15, 20, 25, 35, 45; in mol%) have been prepared using the conventional melting and annealing method. Density, molar volume and Vickers microhardness of the prepared glasses were measured. Infrared (IR) and UV–visible spectroscopic techniques were used for structural studies of these glasses. Density as well as the microhardness increase systematically and, conversely, the molar volume decreases with increasing the lead oxide content. This behavior can be explained by the correlation with the glass structure. Increasing the lead oxide content (≥20 mol%) increases the network former PbO₄ groups which can play an important role in increasing the connectivity and compactness of the glass matrix via increasing the cross-linking with the other constituent silicate and bismuthate structural units. The increased compactness may explain, in turn, the increase of the density and microhardness. IR spectra reinforce the idea that bismuth participates in the glassy network predominantly as BiO₆ octahedral structural units. UV–VIS optical absorption spectra revealed UV-charge transfer absorption bands related to the contribution of Pb²⁺ ions in the region 350–385 nm; in addition to the extrinsic absorption of trace iron impurities in the range 220–290 nm. In the visible region, three optical bands in the ranges 415–435, 605–650 and 880–890 nm were correlated with the contribution of electronic transitions in Bi³⁺ ions. Calculation of the optical mobility gap and the width of the energy tail of glass from the UV–VIS absorption indicated a slight increase followed by a decrease in their values. The behavior change occurred at the glass in which PbO content is 20 mol% where lead oxide starts to participate into the glassy matrix as a network former. The combination of analytical FTIR and UV–visible spectroscopy provided a consistent picture of structure–property relations in this glass system.     

Synthesis of uniform silver nanoparticles with a controllable size

A new method for the synthesis of uniform silver nanoparticles using a single silver reduction step is presented. Fine control over the nanoparticle's size is achieved by varying the concentration of tannic acid, one of the reducing agents, resulting in uniform nanoparticles in the range of 18 nm to 30 nm in diameter with a standard deviation of less than 15%. Changes in the optical properties of the nanoparticles are correlated with their diameter. As the diameter increases the absorption peak is red-shifted. Specifically, for six different sizes of nanoparticles, ranging from 18 nm to 30 nm in diameter, a red-shift from 401 nm to 410 nm in the absorption peaks is measured. In addition, the extinction coefficient increases as the third power of the nanoparticle radius. Rhodamine 123 adsorbed to 30 nm silver nanoparticles exhibits characteristic Raman spectrum suggesting that these nanoparticles are efficient substrate for surface-enhanced Raman spectroscopy.     

Silver Diffusion and Clustering in Oxyfluoride Glasses Investigated by Molecular Dynamics Simulations

Glasses with compositions (97 – x)[PbF₂:GeO₂]–3Al₂O₃–xAg₂O, with the PbF₂:GeO₂ ratio equals to 1.5 and x varying from 0 to 3%, form silver surface films after thermal treatment near the glass transition temperature. The NPT molecular dynamics simulations of a glass composition 56.4PbF₂–37.6GeO₂–3Al₂O₃–3Ag₂O have been performed, where 0, 20, 40, 60, and 100% of the Ag⁺ ions were reduced to Ag by the fluoride ions. The simulations showed that the silver atoms aggregate into clusters of increasing numbers and sizes as the silver atoms content increases. In addition, the silver atoms diffusion coefficients are at least one order of magnitude larger than the fastest ion in the matrix. These results are consistent with the rapid formation of the metallic surface film observed experimentally.     

Production of cellulose nanocrystals using hydrobromic acid and click reactions on their surface

Cellulose nanocrystals (CNCs) were prepared by acidic hydrolysis of cotton fibers (Whatman #1 filter paper). In our efforts to select conditions in which the hydrolysis media does not install labile protons on the cellulose crystals, a mineral acid other than sulfuric acid (H₂SO₄) was used. Furthermore, in our attempts to increase the yields of nanocrystals ultrasonic energy was applied during the hydrolysis reaction. The primary objective was to develop hydrolysis reaction conditions for the optimum and reproducible CNC production. As such, the use of hydrobromic acid (HBr) with the application of sonication as a function of concentration (1.5–4.0 M), temperature (80–100 °C), and time (1–4 h) was examined. Applying sonic energy during the reaction was found to have significant positive effects as far as reproducible high yields are concerned. Overall, the combination of 2.5 M HBr, 100 °C, and 3 h associated with the sonication during the reaction generated the highest nanocrystal yields. In addition to the optimization study three types of surface modifications including TEMPO-mediated oxidation, alkynation, and azidation were used to prepare surface-activated, reactive CNCs. Subsequently, click chemistry was employed for bringing together the modified nanocrystalline materials in a unique regularly packed arrangement demonstrating a degree of molecular control for creating these structures at the nano level.