Facile size-regulated synthesis of silver nanoparticles by controlled thermolysis of silver alkylcarboxylates in the presence of alkylamines with different chain lengths

Controlled thermolysis of silver alkylcarboxylates with primary alkylamines was investigated as a facile synthetic method of silver nanoparticles. A series of silver alkylcarboxylates, C(7)H(15)COOAg, C(13)H(27)COOAg, and C(17)H(35)COOAg, have been prepared and the thermolysis of those silver alkylcarboxylates in the presence of various alkylamines, C(8)H(17)NH(2), C(12)H(25)NH(2), and C(18)H(37)NH(2), with no use of solvent was conducted at 120 or 180 degrees C for 5 h, providing spherical silver nanoparticles stabilized by alkylcarboxylates and alkylamines. The size and dispersibility of nanoparticles depend on the alkyl chain length of the precursors, alkylcarboxylates and alkylamines.     

Contact probe electrochemical characterization and metal speciation of silver LLDPE nanocomposite films

A contact probe methodology, based on the voltammetry of immobilized microparticle approach, is used for characterizing silver species present in linear low density polyethylene (LLDPE) films with different Ag(I)/Ag(0) ratios and silver nanoparticle features usable as food contact polymers. The films displayed characteristic voltammetric features in contact with aqueous acetate buffer, in particular signals for the stripping oxidation of nanoparticulate Ag systems. Significant differences between the studied films were also observed by means of electrochemical impedance spectroscopy and detected at the nanoscopic scale using electrochemical scanning microscopy. Differences in optical and thermal properties of the studied films are associated with the presence of silver nanoparticles. The silver oxidation state as well as nanoparticle size also had influence on the oxidative resistance of the LLDPE films; indeed, films containing cationic silver showed the lowest oxidation induction time value.     

Mechanism of growth of colloidal silver nanoparticles stabilized by polyvinyl pyrrolidone in gamma-irradiated silver nitrate solution

Silver nanoparticles were prepared by using polyvinyl pyrrolidone (PVP) as a stabilizer and gamma-irradiation. Transmission electron microscopy (TEM) results showed that both the amount and the molecular weight of PVP in the irradiated solution considerably affect the average size of the silver nanoparticles. The average size of the silver nanoparticles decreases with increasing the amount of PVP in the solution, but increases with increasing its molecular weight. Further, TEM showed that the silver nanoparticles become disassembled into smaller nanoparticles after dilution with distilled water and sonication. Since the processes of dilution and sonication are not expected to result in chemical reactions or to split the silver nanoparticles, we conclude that each silver nanoparticle prepared by [Formula: see text] -irradiation consists of several smaller nanoparticles surrounded by PVP. Thus, based on these observations, we propose a three-step mechanism for the growth of the silver nanoparticles under the conditions considered here. In the first step, the silver ions interact with PVP, then in the second step the silver ions that are exposed to gamma-irradiation are reduced to silver atoms; nearby silver atoms then aggregate at close range. These aggregates are the primary nanoparticles. Finally, these primary nanoparticles coalesce with other nearby primary nanoparticles or interact with PVP to form larger aggregates which are the secondary (final) nanoparticles.     

Preparation of size-controlled, highly populated, stable, and nearly monodispersed Ag nanoparticles in an organic medium from a simple interfacial redox process using a conducting polymer

The reducing property of an organically soluble conducting polymer (poly(o-methoxyaniline), POMA) is used to prepare monodisperse, size-controlled, highly populated, and highly stable silver nanoparticles in an organic medium through an interfacial redox process with an aqueous AgNO3 solution. The transition of emeraldine base (EB) to the pernigraniline base (PB) form of POMA occurs during nanoparticle formation, and the nitrogen atoms of POMA(PB) stabilize Ag nanoparticles by coordination to the adsorbed Ag(+) on the nanoparticle surface. The conductivity of the nanocomposite is on the order of 10(-11) S/cm, indicating that no doping of POMA occurs under the preparation conditions. The nanoparticles are free of excess oxidant and external stabilizer particles. The POMA (EB) concentration tailors the size of nanoparticles, and at its higher concentration (0.01% POMA with 0.01 N AgNO3), very dense Ag nanoparticles (6 x 10(15) particles/m(2)) of almost uniform size and shape are produced. The rate constant and Avrami exponent values of the nanoparticle formation are measured from the time-dependent UV-vis spectra using the Avrami equation. The Avrami exponent (n) values are close to 1, indicating 2D athermal nucleation with the circular shape of the nuclei having diffusion-controlled growth. The rate constant values are almost independent of AgNO3 concentration but are strongly dependent on POMA concentration. The higher rate constant with increasing POMA(EB) concentration has been attributed for the lowering of nanoparticle size due to increased nucleation density.     

Dense aqueous colloidal gold nanoparticles prepared from highly concentrated precursor solution

Gold nanoparticles were fabricated by reduction of highly concentrated Au(III) ions (200 mM) with casein proteins from milk. The gold nanoparticles were converted to nanoparticle-powders after washing and subsequent vacuum drying without aggregation. The nanoparticle-powders completely re-dispersed in aqueous solution, and stable colloidal gold nanoparticles were obtained. UV-vis extinction spectra and dynamic light scattering (DLS) measurements revealed that large assemblies (size, ca. 3 μm) and subaggregates (size, <0.5 μm) composed of gold nanoparticle-casein protein chain-Au(III) ion were dynamically formed and disintegrated over the course of the growth of the gold nanoparticles. Fourier transform infrared (FT-IR) spectra indicated conformational changes of casein proteins induced by the interaction of casein protein-Au(III) ion and -gold nanoparticle. Finally, rapid, one-pot, and highly concentrated synthetic procedures of gold and silver nanoparticle powders protected by casein (mean diameters below 10 nm) were successfully developed using 3-amino-1-propanol aqueous solutions as reaction media. Dense colloidal gold (40 g L(-1)) and silver (22 g L(-1)) nanoparticle aqueous solutions were obtained by re-dispersing the metal nanoparticle powders.     

Structural transformations in silver nanoparticles

A molecular dynamics simulation was performed for silver clusters of 147, 309, and 561 atoms with the initial cuboctahedral habit in the temperature range 0–1000 K with an embedded atom potential for silver. Structural transitions of the silver clusters to complex twins (icosahedral habit) with coherent (111)/(111) boundaries over all edges of icosahedra were found, which started at temperatures of 50 K, 350 K, and 700 K, respectively. To analyze the structural transformations in nanoparticles, an algorithm is proposed based on a simplicial Delaunay decomposition (Delaunay triangulation). It was found that after the transition of silver nanoparticles to complex twins, the atomic motion becomes vibrational; the atoms vibrate around the sites that correspond to the vertices of the regular polyhedra. In the case of the 147-atom silver nanoparticle, the polyhedra are arranged in the following sequence, starting from the center of mass: icosahedron (12 atoms), icosododecahedron (30 atoms), icosahedron (12 atoms), dodecahedron (20 atoms), truncated icosahedron (60 atoms, isostructural with fullerene C₆₀), icosahedron (12 atoms), and one atom at the center of mass.     

Adsorption of silver on cellobiose and cellulose studied with MIES, UPS, XPS and AFM

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy as well as atomic force microscopy were employed to study the adsorption of silver on cellulose as well as its precursor cellobiose. The formation of silver nanoparticles encapsulated by the organic film previously found for the monomer glucose is well reproduced for the dimer cellobiose. For the polymer cellulose on the other hand, no nanoparticle formation is found even though the surface is covered with silver atoms. No significant chemical interaction is found in any of these cases.     

In situ-preparation and characterization of silver-HEMA/PEGDA hydrogel matrix nanocomposites: Silver inclusion studies into hydrogel matrix

Poly(ethylene glycol) diacrylate (PEGDA) of different molecular weights (Mn = 575 and 700) was used as crosslinking agent for the photopolymerization of 2-hydroxyethyl methacrylate (HEMA) in order to obtain HEMA/PEGDA-based hydrogels. Composites were synthesized in situ employing a new methodology that implies the addition of different quantities of silver nitrate aqueous solution to the monomer mixture with the finality to obtain hydrogels with different silver nanoparticles’ spatial density and distribution. Samples were characterized by thermal, optical, spectroscopic and structural/morphological methods. Thermal studies showed that the increase of PEGDA molecular weight and the AgNO₃ concentration in the reaction mixture enhance the glass transition temperature and the thermal stability of the composites. This behavior could be related to the silver coordination with the polymer network. Infrared spectroscopy with Fourier transform and Raman analyses were realized in order to corroborate the sample chemical structure by the identification of specific functional groups. Surface hydrogel morphology was visualized with scanning electron microscopy analysis, detecting a homogeneous micro-porous surface for the samples obtained from high molecular weight PEGDA. Presence of silver nanoparticles was established by X-ray fluorescence spectroscopy and UV/Vis methods. In this last case, the characteristic silver nanoparticle plasmon was observed. Using Transmission Electron Microscopy it was possible to visualize a homogeneous spatial distribution of spherical silver nanoparticles with very narrow diameter distribution that rounds about 14–21 ± 5 nm. In general, the silver nanoparticle presence in the compounds enhances considerably their thermal/morphological characteristics.     

Structure and electrophysical properties of self-organized composite layers based on peptide and silver nanoparticles

Atomic force microscopy, scanning tunnel microscopy, and IR spectroscopy are employed to study composite films formed from dispersions of silver nanoparticles in an aqueous solution of Asp-Glu-Val-Asp-Trp-Phe-Asp peptide on different substrates at room temperature. It is established that pure peptide crystallizes on substrates to yield different structures, the character of which essentially depends on the chemical nature of a substrate, method of its pretreatment, and solution pH. When films are formed from dispersions containing both silver nanoparticles and peptide, globular structures are formed, in which individual nanoparticles are included into a peptide matrix. It is established that, during the reduction of silver ions and stabilization of resulting nanoparticles, peptide bonds are partly ruptured and another isomeric form (cisconfiguration) of peptide molecules is realized in the silver nanoparticle dispersion in its solution. Distributions of the surface potential and local tunnel voltage-current characteristics are measured for the composite layers. The voltage-current characteristics of all examined composite layers are essentially nonlinear. It is established that the charge transfer in the composite and pure peptide layers is carried out via the Poole-Frenkel mechanism and the Schottky overbarrier emission, respectively.     

A SERS-active system based on silver nanoparticles tethered to a deposited silver film

A series of SERS-active nanostructures were produced by exposing a freshly deposited silver film (fabricated to be as free from roughness as practicable) to a solution containing a mixture of 1-decanethiol (m) and 1,9-nonanedithiol (d) of varying concentrations of m to d, then allowing colloidal silver nanoparticles to interact with the surface. Silver nanoparticles were found to bind exclusively to films which were prepared from solutions with a nonzero concentration of the dithiol implying that the nanoparticles were tethered to the silver surface by the dithiol with one of the thiolate groups bound to the nanoparticle and the other to the silver film. Intense SERS spectra were observed even from samples in which the m/d concentration ratio was so large that the adsorbed molecules in the vicinity of only approximately 8 +/- 3 nanoparticles were illuminated by the diffraction-limited focused laser beam. At such high dilution, the molecules (numbering at most approximately 330) residing in the SERS "hot spots" associated with the approximately 8 nanoparticles consisted primarily of m (although, of course, for each nanoparticle, at least one molecule in the hot spot had to be d to serve as the linker). This was corroborated by the SERS spectra. An analysis is presented, which accounts for the fact that as the concentration ratio of m/d increases, the SERS intensity associated with bands belonging to m first increases to a maximum then decreases. The nanoparticle-metal film system presented here is a simple embodiment of a more general range of SERS-active sensing platforms in which a molecular tether is used to create a SERS hot spot that (although nanosized) is large enough to accommodate analyte molecules that cannot themselves function as linkers, which are subsequently detected by SERS at the few-molecule level.     

Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth

We report on the use of Neem (Azadirachta indica) leaf broth in the extracellular synthesis of pure metallic silver and gold nanoparticles and bimetallic Au/Ag nanoparticles. On treatment of aqueous solutions of silver nitrate and chloroauric acid with Neem leaf extract, the rapid formation of stable silver and gold nanoparticles at high concentrations is observed to occur. The silver and gold nanoparticles are polydisperse, with a large percentage of gold particles exhibiting an interesting flat, platelike morphology. Competitive reduction of Au3+ and Ag+ ions present simultaneously in solution during exposure to Neem leaf extract leads to the synthesis of bimetallic Au core-Ag shell nanoparticles in solution. Transmission electron microscopy revealed that the silver nanoparticles are adsorbed onto the gold nanoparticles, forming a core-shell structure. The rates of reduction of the metal ions by Neem leaf extract are much faster than those observed by us in our earlier studies using microorganisms such as fungi, highlighting the possibility that nanoparticle biological synthesis methodologies will achieve rates of synthesis comparable to those of chemical methods.     

油酸囊泡层状液晶作为模板电化学合成银纳米颗粒

在油酸囊泡的层状液晶中利用电化学沉积法成功地制备了银纳米颗粒。并用扫描隧道显微镜(STM)和透射电子显微镜(TEM)对银纳米颗粒进行了表征，发现银纳米颗粒能够均匀地分散在油酸囊泡中，并且油酸囊泡能够有效地阻止产生的银纳米颗粒发生聚集反应。此外，我们还提出了银纳米颗粒形成的机理。     

Butylphenyl-functionalized Pt nanoparticles as CO-resistant electrocatalysts for formic acid oxidation

Butylphenyl-functionalized Pt nanoparticles (Pt-BP) with an average core diameter of 2.93 ± 0.49 nm were synthesized by the co-reduction of butylphenyl diazonium salt and H(2)PtCl(4). Cyclic voltammetric studies of the Pt-BP nanoparticles showed a much less pronounced hysteresis between the oxidation currents of formic acid in the forward and reverse scans, as compared to that on naked Pt surfaces. Electrochemical in situ FTIR studies confirmed that no adsorbed CO, a poisoning intermediate, was generated on the Pt-BP nanoparticle surface. These results suggest that functionalization of the Pt nanoparticles by butylphenyl fragments effectively blocked the CO poisoning pathway, most probably through third-body effects, and hence led to an apparent improvement of the electrocatalytic activity in formic acid oxidation.     

以葡聚糖-乙二胺聚合物为载体制备纳米银

以葡聚糖-乙二胺聚合物为载体制备纳米银.首先合成葡聚糖-乙二胺聚合物,并用紫外光谱红外光谱对聚合物进行表征;该聚合物与硝酸银反应生成葡聚糖-乙二胺聚合物-银配合物,再通过化学还原或光化学还原法使配合物中的银离子转变成单质银纳米粒,以透射电子显微镜激光纳米测定仪对制备的纳米银进行测定.结果表明制备出了粒径为23.1nm的纳米单质银.以葡聚糖-乙二胺聚合物为载体制备纳米银的方法是可行的.     

Preparation and Storage of Silver Nanoparticles in Aqueons Polymers

以水溶性聚合物为保护剂,采用化学还原法制备了银纳米粒子,分别利用透射电子显微镜、紫外可见光谱、同步光散射光谱等手段对其进行了表征,并探索了制备银纳米粒子的最佳实验条件。通过将银纳米粒子-聚合物溶液进行脱水,得到含有银纳米粒子的固态聚合物膜。将固态聚合物膜重新溶解于水,其水溶液的紫外可见光谱与脱水前的溶液进行了比较,发现两者性质并无明显差异。因此,将银纳米粒子分散固定在聚合物膜中是一种崭新而有效的银纳米粒子制备和存储方法。     

Electrochemical determination of chromium(VI) using metallic nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPEs) modified with metal nanoparticles present an interesting alternative in the determination of chromium(VI) by differential pulse voltammetry (DPV).Metallic silver and gold nanoparticle deposits have been obtained by electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized silver and gold nanoparticles are deposited in aggregated form.The detection limit for the analytical procedures developed in this work were 8.5 × 10⁻⁷ and 4.0 × 10⁻⁷ M for silver and gold nanoparticle-modifed CSPE, respectively.In terms of reproducibility, the precision of the above-mentioned method was calculated at 6.7% in %R.S.D. values for silver and 3.21% for gold nanoparticle CSPE.     

Preparation of airborne Ag/CNT hybrid nanoparticles using an aerosol process and their application to antimicrobial air filtration

Carbon nanotubes (CNTs) have been widely used in a variety of applications because of their unique structure and excellent mechanical and electrical properties. Additionally, silver (Ag) nanoparticles exhibit broad-spectrum biocidal activity toward many different bacteria, fungi, and viruses. In this study, we prepared Ag-coated CNT hybrid nanoparticles (Ag/CNTs) using aerosol nebulization and thermal evaporation/condensation processes and tested their usefulness for antimicrobial air filtration. Droplets were generated from a CNT suspension using a six-jet collison nebulizer, passed through a diffusion dryer to remove moisture, and entered a thermal tube furnace where silver nanoparticles were generated by thermal evaporation/condensation at ～980 °C in a nitrogen atmosphere. The CNT and Ag nanoparticle aerosols mixed together and attached to each other, forming Ag/CNTs. For physicochemical characterization, the Ag/CNTs were introduced into a scanning mobility particle sizer (SMPS) for size distribution measurements and were sampled by the nanoparticle sampler for morphological and elemental analyses. For antimicrobial air filtration applications, the airborne Ag/CNT particles generated were deposited continuously onto an air filter medium. Physical characteristics (fiber morphology, pressure drop, and filtration efficiency) and biological characteristics (antimicrobial tests against Staphylococcus epidermidis and Escherichia coli bioaerosols) were evaluated. Real-time SMPS and transmission electron microscopy (TEM) data showed that Ag nanoparticles that were <20 nm in diameter were homogeneously dispersed and adhered strongly to the CNT surfaces. Because of the attachment of Ag nanoparticles onto the CNT surfaces, the total particle surface area concentration measured by a nanoparticle surface area monitor (NSAM) was lower than the summation of each Ag nanoparticle and CNT generated. When Ag/CNTs were deposited on the surface of an air filter medium, the antimicrobial activity against test bacterial bioaerosols was enhanced, compared with the deposition of CNTs or Ag nanoparticles alone, whereas the filter pressure drop and bioaerosol filtration efficiency were similar to those of CNT deposition only. At a residence time of 2 h, the relative microbial viabilities of gram-positive S. epidermidis were ～32, 13, 5, and 0.9% on the control, CNT-, Ag nanoparticle-, and Ag/CNT-deposited filters, respectively, and those of gram-negative E. coli were 13, 2.1, 0.4, and 0.1% on the control, CNTs, Ag nanoparticles, and Ag/CNTs, respectively. These Ag/CNT hybrid nanoparticles may be useful for applications in biomedical devices and antibacterial control systems.     

Magnetoelectrochemistry of gold nanoparticle quantized capacitance charging

Magnetoelectrochemical studies of gold nanoparticle quantized capacitance charging were carried out at ambient conditions. The single electron transfer responses were found to be sensitive to external magnetic fields, reflected in the enhancement of voltammetric peak currents and shifts of peak formal potentials with increasing magnetic field intensities. Additionally, splittings of voltammetric peaks were also observed upon the application of an external magnetic field. These phenomena might be partly attributed to the paramagnetic characters (electron parity) of nanosized gold particles which are contingent upon their charge states. These novel observations suggest that the nanoparticle electronic energy structures can be varied by magnetic fields, leading to molecular manipulations of the nanoscale charge-transfer chemistry.     

Voltammetric monitoring of gold nanoparticle formation facilitated by glycyl-L-tyrosine: relation to electronic spectra and transmission electron microscopy images

Voltammetric techniques have been introduced to monitor the formation of gold nanoparticles produced via the reaction of the amino acid glycyl-L-tyrosine with Au(III) (bromoaurate) in 0.05 M KOH conditions. The alkaline conditions facilitate amino acid binding to Au(III), inhibit the rate of reduction to Au(0), and provide an excellent supporting electrolyte for voltammetric studies. Data obtained revealed that a range of time-dependent gold solution species are involved in gold nanoparticle formation and that the order in which reagents are mixed is critical to the outcome. Concomitantly with voltammetric measurements, the properties of gold nanoparticles formed are probed by examination of electronic spectra in order to understand how the solution environment present during nanoparticle growth affects the final distribution of the nanoparticles. Images obtained by the ex situ transmission electron microscopy (TEM) technique enable the physical properties of the nanoparticles isolated in the solid state to be assessed. Use of this combination of in situ and ex situ techniques provides a versatile framework for elucidating the details of nanoparticle formation.     

Development and thermal behaviour of ternary PLA matrix composites

Biodegradable PLA composites were prepared using microcrystalline cellulose (MCC) and silver (Ag) nanoparticles. The main objective of the present study is to develop new biopolymer composites with good mechanical properties, thermal stability, maintaining the optical transparency and also providing antimicrobial properties through silver nanoparticle introduction. Composites were prepared with 1%wt of Ag nanoparticles and 5%wt of MCC using a twin-screw microextruder; film parameters were optimized in order to obtain a thickness range between 20 and 60 μm.PLA composites maintained optical transparency properties of the matrix, while MCC was able to reduce polymer permeability. Thermal analysis revealed that MCC increased PLA crystallinity and the mechanical properties of the composites demonstrated that tensile modulus was improved by microcrystalline cellulose.