Antibacterial activity of silver nanoparticles prepared by a chemical reduction method

Silver nanoparticles were obtained by chemical reduction of silver nitrate in water with sodium borohydride (NaBH₄) in the presence of SDS (sodium dodecyl sulfate) as a stabilizer. The synthesized silver nanoparticles were characterized by UV-vis spectroscopy (UV-vis) and transmission electron microscopy (TEM). The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima at 400 nm by UV-vis. TEM showed the spherical nanoparticles with size in 10–20 nm. The antibacterial activity of silver nanoparticles was tested by using Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coil (E. coli). The silver nanoparticles, whose bacterial activity was dependent on the aggregation degree between particles, exhibited bacterial activity against S. aureus and E. coli.     

Synthesis, characterization, and antibacterial activity of metal nanoparticles embedded into amphiphilic comb-type graft copolymers

The synthesis, spectroscopic characterization, and antimicrobial efficiency of gold and silver nanoparticles embedded in novel amphiphilic comb-type graft copolymers having good film-forming properties have been described. Amphiphilic comb-type graft copolymers were synthesized by the reaction of chlorinated polypropylene (PP) (M _w = 140,000 Da) with polyethylene glycol (PEG) (M _n  = 2,000 Da) at different molar ratios. Metal nanoparticles embedded graft copolymers were prepared by reducing solutions of the salts of silver or gold and the copolymer in tetrahydrofuran. The optical properties of the metal nanoparticle embedded copolymers were determined by using UV–visible spectroscopy. Surface plasmon resonance (SPR) of the gold and silver nanoparticle embedded copolymers in toluene was observed at a maximum wavelength (λ_max) of 428 and 551 nm in the UV–VIS absorption spectra, respectively. The average particle diameters of the gold and silver nanoparticles were found to be 50 nm from the high resolution scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Amphiphilic polymer films containing silver and gold nanoparticles were found to be highly antimicrobial by virtue of their antiseptic properties to Escherichia coli and Staphylococcus aureus.     

Catalytic Activity of Ruthenium Nanoparticles Supported on Carbon Nanotubes for Hydrogenation of Soybean Oil

Ruthenium catalysts supported on multiwalled carbon nanotubes (MCNTs) with different loadings (1% wt, 3% wt, 5% wt) were prepared by reduction with H₂ or NaBH₄ for selective hydrogenation of soybean oil at 338 K and initial pressure of 1.066 MPa. These catalysts were characterized using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), N₂ adsorption–desorption, and H₂-temperature programmed desorption (TPD) techniques. Ru particles were dispersed more homogeneously on the surface of the nanotubes after being reduced with H₂ than with NaBH₄. The catalysts with 3% and 5% Ru loadings had higher hydrogenation activity. The NaBH₄-reduced catalyst had higher cis-isomer selectivity.     

Investigation of Carbon Supported Nanostructured PtAu Alloy as Electrocatalyst for Direct Borohydride Fuel Cell

Carbon supported bimetallic PtAu electrocatalysts for sodium borohydride electrooxidation are prepared by a modified citrate stabilized NaBH₄ reduction process at different pH and temperature values. The physical properties of the materials are characterized by X‐ray diffraction spectroscopy, energy dispersive spectrometry, X‐ray photoelectron spectroscopy and transmission electron microscopy. Nano sized electrocatalysts have narrow size distributions and are uniformly dispersed on the surface of carbon support. Electrochemical performances of catalysts for sodium borohydride electrooxidation are tested with 25 cm² single fuel cell. The highest performance is obtained at a peak power density of 161 mW cm⁻² with 20 wt. % PtAu/C catalyst of 7.03 nm. Impact of the fuel cell operation parameters including concentration of NaBH₄, flow rates of oxidant and fuel, and fuel cell operation temperature are investigated. The best operation parameters are obtained at 1 M NaBH₄ concentration, 3 cm³ min⁻¹ NaBH₄ flow rate, 0.2 dm³ min⁻¹ oxygen flow rate and 65 °C fuel cell temperature.     

Spherical polymer brushes with vinylimidazolium-type poly(ionic liquid) chains as support for metallic nanoparticles

We present here the synthesis of spherical polyelectrolyte brushes by photo-emulsion polymerization with a solid polystyrene core (diameter ～ 100 nm) onto which chains of vinylimidazolium-type poly(ionic liquid)s have been densely grafted. The as-synthesized brush particles were employed as nanoreactors for the generation and immobilization of metal nanoparticles. Transmission electron microscopy characterization shows that Au and Pd nanoparticles with diameter of 2.1 ± 0.2 nm and 2.5 ± 0.3 nm are homogeneously embedded inside the PIL brushes, respectively. The study of swelling behavior of the brush particles before and after metal deposition indicates obviously ion-specific effect. The composite particles exhibit a long-term colloidal stability in aqueous solutions as well as in ionic liquids. Catalytic activity of the as-synthesized metal nanocomposite particles is investigated by using the reduction of 4-nitrophenol with NaBH₄ as a model reaction, which can be compared directly with reported systems. In addition, it is found that the rate constant k_app of PIL-metal nanocatalyst could be modulated by salt concentration.     

Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride

The synthesis of early transition nanocrystals using NaBH₄ and the respective metal oxides at atmospheric pressure was studied at temperatures between 400 and 1000°C. Reaction products were analyzed by x‐ray diffraction, the crystallite size was determined after Rietveld refinement of diffraction patterns, while the morphology was analyzed by scanning and transmission electron microscopy. For all the investigated systems the lowest temperature to complete the synthesis was 700°C and the reaction occurred in three subsequent steps: (i) decomposition of NaBH₄, (ii) formation of crystalline ternary species Na–M–O and Na–B–O, (iii) conversion of intermediary species to MB₂ and NaBO₂. Syntheses carried out at T > 700°C only caused coarsening of the powders. The synthetized boride powders had the morphology of highly agglomerated nanocrystals. TiB₂ had a specific surface area of 33.5 m²/g and crystallite diameter of 12 nm. Both ZrB₂ and HfB₂ had a platelet‐like morphology with crystallite diameter around 45 nm and specific surface area of 25.0 and 36.4 m²/g, respectively. Finally, NbB₂ and TaB₂ powders had a crystallite diameter around 5 nm with specific surface area of 21.1 and 11.4 m²/g, respectively. The goal of this synthesis is the use of cheap raw materials and moderate temperature conditions.     

Pd–Ru/C as the electrocatalyst for hydrogen peroxide reduction

Pd–Ru, Pd and Ru nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl₂ and/or RuCl₃ in aqueous solution using NaBH₄ as the reducing agent. Transmission electron microscopy measurements showed that Pd–Ru particles were uniformly dispersed on carbon. The particle size of Pd–Ru is around 5–9 nm. X-ray diffraction analysis indicated that Ru formed alloy with Pd in Pd–Ru/C catalyst. The electroreduction of hydrogen peroxide on Pd–Ru/C, Pd/C and Ru/C in H₂SO₄ solution was examined by linear sweep voltammetry and chronoamperometry measurements. Results revealed that Pd–Ru/C catalyst exhibited higher electrocatalytic activity for hydrogen peroxide reduction than Pd/C and Ru/C. All the catalysts showed good stability for hydrogen peroxide electroreduction in H₂SO₄ electrolyte.     

Poly(vinyl-pyrrolidone) assisted hydrothermal synthesis of flower-like CdS nanorings

Well-defined CdS nanorings with flower-like morphology were synthesized by a hydrothermal method using poly(vinyl-pyrrolidone) as capping agent. The phase composition, morphology, structure, and optical properties of CdS nanorings were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscopy, and UV–vis absorption spectroscopic techniques. The XRD pattern of the sample can be indexed to the cubic zinc blende phase CdS. According to the quantitative analysis of energy-dispersive spectrum, the Cd:S molar ratio of the sample is about 1:0.96. The possible formation mechanism of the CdS nanorings is proposed which is based on time-resolved experiments. Furthermore, the absorption peak of CdS nanorings is red-shifted to 523 nm in the UV–vis absorption spectrum.     

Plant mediated green synthesis and antibacterial activity of silver nanoparticles using Crataegus douglasii fruit extract

In this study, silver nanoparticles were synthesized using the Crataegus douglasii fruit extract as a reducing agent. The reaction process was monitored by UV–vis spectroscopy. Further characterization was carried out using scanning electron microscopy (SEM). To optimize the biosynthesis of silver nanoparticles, the effect of process variables such as extract concentrations, mixing ratio of the reactants, time and pH were also investigated. The SEM images showed silver nanoparticles with 29.28 nm size and nearly spherical shape at 24 h interaction time. The antibacterial activity of the synthesized silver nanoparticles was confirmed against Staphylococcus aureus and Escherichia coli.     

Use of a nickel-boride–silica nanocomposite catalyst prepared by in-situ reduction for hydrogen production from hydrolysis of sodium borohydride

Hydrogen was produced by hydrolysis of sodium borohydride (NaBH₄) using nickel-boride–silica nanocomposite catalyst. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDX). The Ni-B–silica nanocomposite catalyst was found to consist of amorphous Ni-B nanoparticles attached to the surface of amine-modified silica nanosphere. The kinetics of hydrolysis of NaBH₄ by Ni-B–silica composite catalyst was investigated. The effects of temperature, NaBH₄ concentration, and catalyst concentration on hydrogen generation were also investigated. A rate of hydrogen generation as high as 1916 ml H₂/min/g Ni was achieved by catalytic hydrolysis of NaBH₄. The stability of the composite catalyst was also explored.     

Synthesis and intercalation of silver nanoparticles in kaolinite/DMSO complexes

Ag nanoparticles were synthesized in the interlamellar space of a layered kaolinite. Disaggregation of the lamellae of the nonswelling kaolinite was achieved by the intercalation of dimethyl sulfoxide (DMSO). The kaolinite was suspended in aqueous AgNO₃ solution and the adsorbed Ag⁺ ions were reduced on the surface of kaolinite lamellae with NaBH₄ or UV light irradiation. The silver nanoparticles formed were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). We studied the effects of the two reduction methods on the size and the size distribution of Ag nanoparticles and how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. Photoreduction of silver led to the formation of relatively large Ag nanoparticles (diameter 8–14 nm).     

Temperature-dependent transport properties of micro and nano-sized zinc cobalt oxide (ZnCo2O4) and zinc manganese oxide (ZnMn2O4) particles synthesized by a hydrothermal route

In the present work, a hydrothermal method has been adopted to synthesize micro (~150 nm), and nano (~20 nm) particles of Zinc based, cobalt, and manganese oxide structures, i.e., ZnCo₂O₄ (ZCO) and ZnMn₂O₄ (ZMO). These structures have been examined by X-ray diffraction, Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The effect of different reducing agents and solvents have been ascertained on the morphological and the crystalline nature of the samples. The highly crystalline and micron-sized particle formation has been observed with the usage of NaBH₄ as the reductant in the water solution, and a polycrystalline structure with nanosized particle formation has been found with NaOH as the reductant in the water and DMF solution. The electrical properties have been investigated between 100 Hz and 1 MHz by varying the temperature from 303 K to 513 K. The micro and nano sized particles of ZCO and ZMO have shown frequency dependence, thermally activated and relaxation-type dielectric behavior confirming the semiconducting nature. The variation of ac conductivity with frequency at different temperatures is according to Jonscher's power law for micro and nano sized particles of the ZCO and ZMO but supporting different conduction mechanisms. The conduction mechanism in microparticles and nano-particles is according to an overlapping-large polaron tunneling (OLPT) model, and the Non-overlapping small polaron tunneling (NSPT) model, respectively.     

Preparation of colloidal silver nanoparticles by chemical reduction method

Colloidal silver nanoparticles were obtained by chemical reduction of silver nitrate in water with sodium borohydride (NaBH₄) in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The obtained nanoparticles were characterized by their UV-vis absorption spectra and transmission electron micrograph (TEM) images. The UV-vis absorption spectra showed that NaBH₄ served not only as a reducing agent but also as a stabilizer, which protects the aggregation of silver nanoparticles. The TEM images showed that the particles were dispersed better with increasing the NaBH₄ concentration.     

Ionic liquid-mediated synthesis of crystalline CeO2 mesoporous films and their application in aerobic oxidation of benzyl alcohol

In this work, mesoporous CeO₂ crystalline film was prepared via calcining the solution of Ce(NO₃)₃ in ionic liquid (1-allyl-3-methylimidazolium chloride) containing cellulose. The as-prepared CeO₂ film was characterized by means of different techniques including X-ray diffraction, transmission electron microscopy equipped with energy dispersive X-ray spectroscopy, scanning electron microscopy and nitrogen sorption analysis. It was indicated that the as-prepared CeO₂ film was composed of numerous CeO₂ crystals with size of ～9 nm, which assembled with each other to form interconnected channels within the film. The BET specific surface area and the pore volume of the CeO₂ film were estimated to be 62 m²/g and 0.15 cm³/g, respectively, based on the N₂ sorption isotherms. Being used as a support, the CeO₂ film was loaded with Au nanoparticles of ～5 nm in size via the reduction of HAuCl₄ with NaBH₄ in aqueous solution. The as-synthesized Au/CeO₂ nanocomposite demonstrated a good catalytic activity for aerobic oxidation of benzyl alcohol.     

Ultrahigh Active Pd Nanocatalyst Supported on Core-Sheath Conducting Polymer/Metal Oxide Composite Nanorods

Abstract  

A facile and aqueous-phase method based on the electron transfer reduction process for fabricating core-sheath structured polyaniline (PANI)/SnO₂ composite nanorods supported Pd nanocatalyst has been demonstrated. The Pd nanoparticles synthesized by this strategy have a small size of smaller than 3.0 nm. The well dispersed Pd nanoparticles with small sizes supported on core-sheath PANI/SnO₂ composite nanorods exhibited an ultrahigh catalytic activity during the catalytic reduction of p-nitrophenol into p-aminophenol by NaBH₄ in aqueous solution. The kinetic apparent rate constant (k_app) reach to be about 26.9 × 10⁻³ s⁻¹. It is believed that this method could be extended to cover many kinds of other functional composite nanomaterials where the active component is expected to bring in new features and applications.     

Magnetic-Fluorescent Nanocomposites Fe3O4@SiO2@ZnSe: Preparation and Characterization

Fe₃O₄@SiO₂@ZnSe composite nanoparticles with superparamagnetism and luminescence have been prepared by a facile chemical method. Nontoxic fluorescent ZnSe quantum dots were assembled around the Fe₃O₄-silica core–shell nanocomposite via chemical bonds formed between –COOH and –NH₂. Transmission electron microscopy images show that the nanocomposites are approximately spherical and between 50 nm and 80 nm in size. The bifunctional nanocomposites exhibit superparamagnetic behavior and good fluorescence intensity. Magnetic attraction test, vibrating sample magnetometer at 300 K, UV–visible absorption and fluorescence emission spectroscopy were applied to characterize the magnetic/fluorescent properties of the nanocomposites.     

Combustion Based Synthesis of AlN Nanoparticles Using a Solid Nitrogen Promotion Reaction

Combustion based synthesis of AlN nanoparticles using the “solid nitrogen” promotion reaction was investigated in Al₂O₃ + 3Mg system in nitrogen atmosphere. A controlled amount of Mg + 0.5NH₄Cl mixture as a solid source of nitrogen was blended with the Al₂O₃ + 3Mg starting system and the synthesis reaction of AlN nanoparticles was conducted using the exothermic heat of the entire reaction system. The resulting AlN nanoparticles were characterized by X‐ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR), PL spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller surface area techniques. The analysis results confirmed that single phase and crystalline AlN nanoparticles with an average size of 50–500 nm were obtained from the developed approach. Photoluminescence spectra of AlN nanopowders under the excitation of 230–270 nm UV light revealed that AlN emits yellow‐red light having a wavelength near to 590 nm. The chemistry of the combustion process is discussed and the basic reactions that led to the formation of AlN are presented.     

Preparation of Ag–Cu bimetallic dendritic nanostructures and their hydrogen peroxide electroreduction property

In this work, dendritic silver–copper (Ag–Cu) nanostructures were synthesised on a copper foil by electrodeposition and subsequently galvanic displacement reaction without any surfactant. The crystalline nature of the nanostructures was examined by X-ray diffraction, and the morphology of the material was investigated by field-emission scanning electron microscopy. The applied potential, displacement reaction time, and silver nitrate solution concentration exerted different effects on the nanoparticle shape. And a possible growth mechanism of the Ag–Cu dendrites was proposed based on the experimental results. The electrochemical properties of the Ag–Cu dendrite-modified electrode were characterised by linear sweep voltammetry. The reduction peak potential of hydrogen peroxide (H₂O₂) was about ?0.25 V (vs. a saturated calomel electrode), which indicated that the as-synthesised Ag–Cu dendrites had favourable electroreduction activity towards hydrogen peroxide. At the same time, we found that the solution pH also affected the electrocatalytic ability of the dendrites for H₂O₂ reduction, which was important for the design of a NaBH₄–H₂O₂ battery.     

Tuning mesoporous molecular sieve SBA-15 for the immobilization of α-amylase

The present work describes the immobilization of α-amylase over well ordered mesoporous molecular sieve SBA-15 with different pore diameters synthesized by post synthesis treatment (PST) hydrothermally after reaction at 40°C. The materials were characterized by N₂ adsorption–desorption studies, small angle X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. Since α-amylase obtained from Bacillus subtilis has dimensions of 35 × 40 × 70 Å it is expected that the protein have access to the pore of SBA-15 (PST-120°C) with diameter 74 Å. The pore dimension is appropriate to prevent considerable leaching. The rate of adsorption of the enzyme on silica of various pore sizes revealed the influence of morphology, pore diameter, pore volume and pH.     

Surfactant-free hydrothermal synthesis and characterization of single-crystal K2V8O21 nanobelts

Single-crystal K₂V₈O₂₁ nanobelts were prepared from the reaction between V₂O₅ and KHSO₄ under hydrothermal condition using no surfactant or template. The synthesized nanobelts were characterized by X-ray diffraction, X-ray photon-electron spectrometry, scanning electron microscopy, and transmission electron microscopy. The nanobelts are single-crystalline in nature, and have typical width of 100–500 nm, thickness of less than 100 nm and length up to a few tens of microns. The effects of solution concentration, reaction temperature and molar ratio of K and V on the morphology and phase component of the obtained products have been investigated. The possible formation mechanism was also discussed.