Size-dependent antimicrobial properties of sugar-encapsulated gold nanoparticles synthesized by a green method

The antimicrobial properties of dextrose-encapsulated gold nanoparticles (dGNPs) with average diameters of 25, 60, and 120 nm (± 5) and synthesized by green chemistry principles were investigated against both Gram-negative and Gram-positive bacteria. Studies were performed involving the effect of dGNPs on the growth, morphology, and ultrastructural properties of bacteria. dGNPs were found to have significant dose-dependent antibacterial activity which was also proportional to their size. Experiments revealed the dGNPs to be bacteriostatic as well as bactericidal. The dGNPs exhibited their bactericidal action by disrupting the bacterial cell membrane which leads to the leakage of cytoplasmic content. The overall outcome of this study suggests that green-synthesized dGNPs hold promise as a potent antibacterial agent against a wide range of disease-causing bacteria by preventing and controlling possible infections or diseases.     

Preparation and characterization of polyurethane–gold nanocomposites prepared using encapsulated gold nanoparticles

Gold nanoparticles (GNPs) have been widely studied due to their unique properties. Although many research groups have developed the synthesis of GNPs using various polymers as stabilizing or reducing agents, the effects of GNPs on the structures and properties of polymer matrices have been less reported. We propose a new design for the preparation of polyurethane–gold (PU–Au) nanocomposites. 11‐Mercapto‐1‐undecanol‐coated GNPs acted as the chain extenders and reacted with isocyanates to form covalent bonds between PU and GNPs. PU–Au nanocomposites were successfully synthesized, and the effects of multifunctional GNPs on the structures, morphology and properties of poly(ester urethane) were investigated. Scanning electron microscopy images suggested the GNPs can be dispersed uniformly in the PU matrix. Maltese‐cross of spherical crystals was observed in the PU–Au nanocomposites, and the size of the crystals decreased with an increase in gold content. As the gold content increased, the thermal decomposition temperature and the temperature of the maximum decomposition rate increased. The glass transition temperature, crystal melting temperature and melting enthalpy of the soft segment also increased progressively. The results showed that multifunctional GNPs concentrated hard segments and resulted in an increase of heterogeneous nucleation, phase separation and elasticity. Copyright © 2010 Society of Chemical Industry     

Plant mediated green biosynthesis of silver nanoparticles using Vitex negundo L. extract

In the present study silver nanoparticles (Ag-NPs) were synthesized from aqueous silver nitrate through a biosynthetic route using water extract of Vitex negundo L. extract which acted as a reductant and stabilizer agents, simultaneously. Formations of Ag/V. negundo were determined by UV–vis spectroscopy where surface plasmon absorption maxima can be observed at 423–432 nm. The XRD analysis shows that the Ag-NPs are of face centered cubic structure. TEM images show the well dispersed of Ag-NPs with average particle size less than 20 nm. The FT-IR spectrum indicates the presence of V. negundo in capping with silver nanoparticles.     

A novel one-pot biosynthesis of pure alpha aluminum oxide nanoparticles using the macroalgae Sargassum ilicifolium: A green marine approach

A novel biological method is proposed for producing ceramic alpha aluminum oxide nanoparticles using an extract of the algae Sargassum ilicifolium. The algal extract functions as a bioreducing as well as a stabilizer agent. The presence of an absorption peak at 227?nm, confirmed the formation of the aluminum oxide nanoparticles using a UV–visible spectroscopy. FTIR analysis indicated that bioreduction of aluminum ions and nanoparticle stabilization probably occurred by interactions between aluminum and the biofunctional groups of algal extract. The XRD pattern revealed that after calcination at ~ 1200?°C, the Al₂O₃ nanoparticles were alpha crystalline in nature with a diameter of 35?nm and had a rhombohedral structure. TEM indicated that the alumina nanoparticles were well-dispersed and spherical in shape with an average size of 20?±?2.1?nm. EDX spectroscopy revealed that the sample contained only aluminum (46.31%) and oxygen (53.69%), confirming the high purity of the alumina nanopowder. The results demonstrated that alpha alumina NPs has an optical band gap of 5.46?eV.     

Destruction and formation of a conductive carbon nanotube network in polymer melts: In-line experiments

Investigations on electric conductivity and dielectric permittivity have been performed during melt processing of polycarbonate (PC) and polyamide 6 (PA6) containing different amounts of multi-walled carbon nanotubes (MWNT). For the experiments a measurement slit die containing two electrodes in capacitor geometry was flanged to the outlet of a twin-screw extruder. AC conductivity and the related complex permittivity were measured in the frequency range from 21.5 to 10⁶ Hz for different processing conditions (melt temperature and throughput) and after stopping the extruder. It was found that the conductivity dropped down to values typical for the matrix polymer when the extrusion started. After the extruder was stopped the conductivity shows an increase of up to eight orders of magnitude with time. This conductivity recovery in the rest time after mechanical deformation was found to be faster for increasing melt temperature or samples with higher CNT concentration. The increase of the conductivity in the quiescent melt is explained by reorganization of the conductive network-like filler structure, which was - at least partially - destroyed under mechanical deformation. The reformation kinetics of the conductive network after mechanical deformation is considered to be an agglomeration process, which can be approximated by a combination of cluster aggregation and percolation theory.     

Ag seeds mediated growth of Au nanoparticles within PVA matrix: An eco-friendly catalyst for degradation of 4-nitrophenol

The integration of highly monodispersed gold (Au) nanoparticles into polyvinyl alcohol (PVA) film is developed through a new seeded-growth pathway. Silver (Ag) nanoparticles are used during the synthesis as the reactive seeds to induce the reduction of Au under the UV-irradiation. The narrow surface plasmon resonance confirms the success of preparing gold nanoparticles with narrow size and shape distribution. The as-prepared PVA/Au nanocomposite films show sturdy cohesion between the PVA chains and/or between PVA network and gold nanoparticles. This has led to interest in their use as brand-new product in catalytic reduction of 4-nitrophenol with NaBH₄.     

Swelling measurement of polymers in high pressure carbon dioxide using a spectroscopic reflectometer

We developed an in situ thickness monitor using a spectroscopic reflectometer to measure the swelling behaviors of polymer thin films in carbon dioxide up to 30 MPa. Because the change in thickness was measured under high-pressure CO₂, the measurement was performed through a sapphire window with a relatively high refractive index. We found that the window effect on the reflectivity can be successfully eliminated. To confirm the accuracy of the analysis, we measured the swelling behaviors of four polymers (poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(n-butyl methacrylate) (PBMA), and poly(dimethylsiloxane) (PDMS)), and compared the swelling measurements with reported data. The swelling ratios of the polymers were in reasonable agreement with literature data. Notably, anomalous swelling was observed for PBMA and PDMS, although anomalous swelling has been observed in films much thinner than those of our samples, probably due to the low glass transition temperatures and high swelling ratios of PBMA and PDMS.     

Highly sensitive electrochemical determination of nitric oxide using fused spherical gold nanoparticles modified ITO electrode

This paper describes the highly sensitive electrochemical determination of nitric oxide (NO) using the fused spherical gold nanoparticles (FAuNPs) modified ITO electrode. The FAuNPs were self-assembled on a (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film, which was preassembled on ITO electrode. The attachment of FAuNPs on MPTS sol-gel film was confirmed by UV-vis absorption spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV). The AFM image shows that the AuNPs retain their fused morphology after immobilized on MPTS sol-gel film. The FAuNPs modified ITO electrode shows an excellent electrocatalytic activity towards the oxidation of NO. Using FAuNPs modified electrode, the detection of 12 nM NO was achieved for the first time by amperometry method. Further, the current response was increased linearly with increasing NO concentration in the range of 1.2 × 10⁻⁸ to 7 × 10⁻⁴ M and the detection limit was found to be 3.1 × 10⁻¹⁰ M (S/N = 3). The FAuNPs modified ITO electrode displays an excellent selectivity towards the determination of 12 nM NO even in the presence of 1000-fold excess common interfering agents.     

Photochemically reduced polyoxometalate assisted generation of silver and gold nanoparticles in composite films: a single step route

A simple method to embed noble metal (Ag, Au) nanoparticles in organic–inorganic nanocomposite films by single step method is described. This is accomplished by the assistance of Keggin ions present in the composite film. The photochemically reduced composite film has served both as a reducing agent and host for the metal nanoparticles in a single process. The embedded metal nanoparticles in composites film have been characterized by UV–Visible, TEM, EDAX, XPS techniques. Particles of less than 20 nm were readily embedded using the described approach, and monodisperse nanoparticles were obtained under optimized conditions. The fluorescence experiments showed that embedded Ag and Au nanoparticles are responsible for fluorescence emissions. The described method is facile and simple, and provides a simple potential route to fabricate self-standing noble metal embedded composite films.     

Adsorptive removal of fluoride using polymer-modified ceria nanoparticles: determination of equilibrium,kinetic and thermodynamic parameters

ABSTRACT

Polyaniline/Ceria nanocomposite is prepared in two steps: CeO₂ by gel combustion method and it’s polymer nanocomposite by in situ polymerization. The as-synthesized nanocomposite is characterized by X-Ray Diffractometer, Scanning Electron Microscopy, Brunauer–Emmett–Teller technique, etc. Its efficacy in adsorptive removal of fluoride in water is investigated by the batch method under various experimental conditions including contact time, pH, initial concentration, temperature, etc. The maximum adsorption capacity is obtained at neutral pH within 1 h. The adsorption kinetics data is well fitted into the pseudo-second order model and Langmuir model. The results of the adsorption thermodynamic study evidenced a spontaneous, exothermic and entropy-driving adsorption process.     

Multilayer thin films of colloidal gold and silica nanoparticles: Effect of polyelectrolyte coating

The use of oppositely charged colloidal nanoparticles to build multilayered structures is an approach in thin film science. In this work, uniform spherical nano‐dispersions of gold (ca. 20 nm) and silica (ca. 30 nm) were synthesised with specific volume concentration to achieve colloidal stability. Exploiting the use of self‐assembly, multilayers of these oppositely charged nanoparticles were built using alternate coating with chitosan. Gold nanoparticles have strong optical absorption in visible region of electromagnetic spectrum resulting from its surface plasmon resonance. Silica nanoparticles have low refractive index and absorb light mostly in the ultraviolet (UV) region. The optical absorption band of the fabricated thin films extends from UV to visible region of the electromagnetic spectrum. The spectral characteristics of these thin‐film assemblies are a combination of thickness and the order of the layers in a stack. These films have potential applications as optical elements and in optoelectronics. © 2011 Canadian Society for Chemical Engineering     

Hydrothermal synthesis of pseudocubic BaTiO3 nanoparticles using TiO2 nanofibers: Study on photocatalytic and dielectric properties

In this study, TiO₂ nanofibers were fabricated via the electrospinning method followed by air annealing. Then, Ti-requirement in the conventional hydrothermal synthesis of BaTiO₃ stoichiometry was supplied by using these nanofibers. The microstructural and compositional properties of BaTiO₃ nanoparticles were studied using SEM, TEM, XRD, XPS, and Raman spectroscopy. The structural analysis showed that the cubic symmetry was the dominant one in the BaTiO₃ nanoparticles, whereas Raman spectroscopy indicated the coexistence of cubic symmetry with the tetragonal polymorph. The nanoparticles displayed higher photocatalytic reactivity under UV-A light compared to visible irradiation during decomposition of methylene blue dye and reached 24.2% and 18.8% degradation, respectively, after 1 hour. Furthermore, the dielectric properties were investigated using sintered compacts of these nanoparticles. Among the employed temperatures for sintering, the highest relative density (90%) and dielectric constant (2165 at 1 MHz) were obtained at 1250°C and 5 hours. This study revealed that the electrospun TiO₂ nanofiber precursor can successfully be used for the production of nanoscale barium titanate particles suitable for various applications.     

Formation of nanotubes in poly (vinylidene fluoride): Application as solid polymer electrolyte in DSC fabricated using carbon counter electrode

In the present work, we report the incorporation of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) in poly(vinylidene fluoride) (PVDF) along with the redox couple (I⁻/I₃⁻). When ABTS, a π-electron donor, is used to dope PVDF, the polymer composite forms brush-like nanotubes and has been successfully used as a solid polymer electrolyte in dye-sensitized solar cells. Under the given conditions, the electrolyte composition forms nanotubes while it is doped with ABTS, a π-electron donor. With this new electrolyte, a dye-sensitized solar cell was fabricated using N3 dye adsorbed over TiO₂ nanoparticles as the photoanode and conducting carbon cement coated FTO as counter electrode.     

Solvent retention in solution-cast films of PMMA: study by dielectric spectroscopy

Conventional PMMA was dissolved in two different solvents (chloroform and toluene). Solid polymeric films were formed after casting of the solutions on a substrate (aluminium) and evaporation of the solvent at room temperature during several days. The dielectric properties of the solid films were studied by dielectric spectroscopy. The evolution of the loss tangent (tanδ) versus temperature was analysed. The results show that the tanδ peak, corresponding to the -transition (glass transition), is shifted towards the lower temperatures, as compared with the bulk polymer obtained by heating press, without any solvent. The magnitude of the shift depends on the type of solvent. These results indicate that, in all cases, solvent molecules are retained and cannot be completely evaporated at room temperature, even after a long period. Solvent molecules are still trapped inside the PMMA films, but their effect on the polymer chains mobility differs in function of the nature of the solvent. Explanations based on acid–base interactions are proposed to try to understand this phenomenon. This work illustrates the interest of dielectric spectroscopy for studying in situ the properties of thin cast polymer films.     

Synthesis of high efficiency Zn2SiO4:Mn green phosphors using nano-particles

In this study, Zn₂SiO₄:Mn²⁺ luminescent phosphors were prepared by mixing nano-scale ZnO, SiO₂, and MnO₂ particles at the compositions corresponding to 2ZnO + SiO₂ + X mol% MnO₂ (Zn₂SiO₄–X-MnO₂, 0.02 ≤ X ≤ 0.05). The mixing powders were calcined from 900 °C to 1300 °C in air and in N₂ atmosphere. No matter calcined in air or in N₂ atmosphere, Zn₂SiO₄ was the mainly crystalline phase in particles calcined at 900 °C and was the only phase in particles calcined at 1000 °C and higher. The influences of MnO₂ concentration and calcining atmosphere and temperature on wavelength of luminescence peak and the emission intensity were further intensively investigated. We would show that the calcining atmosphere had no apparent influences on the physical and photoluminescence (PL) characteristics of Zn₂SiO₄:Mn²⁺ phosphors. The MnO₂ content and the calcining temperature were the main reasons to influence the physical and PL characteristics of Zn₂SiO₄:Mn²⁺ phosphors.     

Cross‐metathesis of methyl 10‐undecenoate with diethyl maleate: Formation of an α,ω‐diester via a metathesis reaction network

The cross‐metathesis of methyl 10‐undecenoate 1 derived from castor oil as a renewable raw material with diethyl maleate 2 was investigated. These reactions were carried out with several phosphine and N‐heterocyclic carbene ruthenium catalysts. The reaction conditions were optimised for high conversions in combination with high cross‐metathesis selectivity. This single‐step and atom‐economic synthetic method illustrates an efficient and selective preparation procedure of linear α,ω‐dicarboxylic acid esters starting from renewable resources and comparatively inexpensive base chemicals. Further by‐products are hardly obtained due to their consumption in secondary metathesis reactions. Hence, a sustainable alternative for polyamide and polyester monomers is presented.     

Photoelectro-Fenton combined with photocatalytic process for degradation of an azo dye using supported TiO2 nanoparticles and carbon nanotube cathode: Neural network modeling

In this work, treatment of an azo dye solution containing C.I. Basic Red 46 (BR46) by photoelectro-Fenton (PEF) combined with photocatalytic process was studied. Carbon nanotube-polytetrafluoroethylene (CNT-PTFE) electrode was used as cathode. The investigated photocatalyst was TiO₂ nanoparticles (Degussa P25) having 80% anatase and 20% rutile, specific surface area (BET) 50 m²/g, and particle size 21 nm immobilized on glass plates. A comparison of electro-Fenton (EF), UV/TiO₂, PEF and PEF/TiO₂ processes for decolorization of BR46 solution was performed. Results showed that color removal follows the decreasing order: PEF/TiO₂ > PEF > EF > UV/TiO₂. The influence of the basic operational parameters such as initial pH of the solution, initial dye concentration, the size of anode, applied current, kind of ultraviolet (UV) light and initial Fe³⁺ concentration on the degradation efficiency of BR46 was studied. The mineralization of the dye was investigated by total organic carbon (TOC) measurements that showed 98.8% mineralization of 20 mg/l dye at 6 h using PEF/TiO₂ process. An artificial neural network (ANN) model was developed to predict the decolorization of BR46 solution. The findings indicated that artificial neural network provided reasonable predictive performance (R² = 0.986).