Mechanism of silver nucleation upon the radiation-induced reduction of its ions in polyphosphate-containing aqueous solutions

Long-lived (hours to days) silver clusters, Ag ₄ ²⁺ , Ag ₄ ⁺ , Ag ₈ ²⁺ , etc., are formed upon the radiation-induced reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The efficiency of the cluster formation decreases and the stability of the clusters increase with a rise in the concentration of the polymeric stabilizer. In the course of the aggregation of clusters, their sizes increase, quasi-metallic particles emerge, and the process terminates with the formation of silver nanoparticles. The mechanism of silver nucleation upon the radiation-induced reduction of silver ions in aqueous solutions is discussed.     

Formation of long-lived clusters and silver nucleation in the γ-irradiation of aqueous silver perchlorate solutions containing polyphosphate

It was found that long-lived positively charged and neutral silver clusters were formed by the radiation-chemical reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The nuclearity of the clusters increased with absorbed dose; then, quasi-metal particles were formed. The process culminated in the formation of silver nanoparticles.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 2, 2005, pp. 83–87.Original Russian Text Copyright © 2005 by Ershov, Abkhalimov, Sukhov.This revised version was published online in April 2005 with a corrected cover date.     

Formation of silver clusters by borohydride reduction of AgNO<Subscript>3</Subscript> in polyacrylate aqueous solutions

Chemical synthesis of the compounds of silver clusters and polyacrylate was performed using sodium borohydride as a metal cation reducing agent. The effect of silver cation content on spectral properties and structure of the synthesized metal—polymer systems was studied by optical spectroscopy and transmission electron microscopy.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 79–86.Original Russian Text Copyright © 2005 by B. Sergeev, Lopatina, Prusov, G. Sergeev.     

Formation of silver nanoparticles in aqueous carboxymethyl cellulose solutions and the evolution of their sizes

Size dependences of silver nanoparticles synthesized in aqueous carboxymethyl cellulose solutions and dependences of their ζ-potentials on solution pH are studied by the dynamic light scattering method. Variations in nanoparticle size distributions and ζ-potential of particles with time are monitored. It is revealed that the size of silver nanoparticles decreases linearly with an increase in solution pH. The size of particles noticeably decreases in the aging process of the colloidal solution. The ζ-potential tends to one and the same value with time for all studied hydrosol samples.     

Adsorption preconcentration of pyrene by silver nanoparticles and its determination in aqueous solutions

The reduction of silver nitrate with sodium borohydrate in an aqueous medium in the presence of cetyl trimethylammonium bromide gives a stable sol of silver, which can adsorb nonpolar organic compounds, e.g., polycyclic aromatic hydrocarbons, on the surface of metal nanoparticles. The subsequent luminescent determination demonstrated the effect of sensitized luminescence of silver nanoparticles, which could provide a basis for the determination of traces of polycyclic aromatic compounds in water.     

Reactions of alkyl-radicals with gold and silver nanoparticles in aqueous solutions

Silver and gold nanoparticles are very efficient catalysts for the dimerization of methyl-radicals in aqueous solutions. The rate constants for the reaction of methyl-radicals with the gold and silver nanoparticles were measured and found to be 3.7 x 10(8) M(-1) s(-1) and 1.4 x 10(9) M(-1) s(-1), respectively. The results thus suggest that alkyl-radicals, also not reducing ones, are scavenged by these nanoparticles. This might explain the role, if such a role exists, of these nanoparticles in medical applications.     

Formation of the bimodal ensemble of silver nanoparticles in polymer solutions

Silver nanoparticles synthesized in polymer solutions are studied by spectroscopy (in near ultraviolet, visible, and infrared spectral regions) and high-resolution transmission electron microscopy. It is established that the ensemble with bimodal particle size distribution is formed from initially polydisperse nanoparticle ensemble in methylhydroxy ethyl cellulose solution. In contrast to the classical scheme of the ripening of colloidal dispersions, the number of small particles increases with time in the studied system; moreover, particles with a size of about 2 nm turned out to be stable. The large particles grow with time and their concentration drops.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 87–93. Original Russian Text Copyright © 2005 by Serebryakova, Uryupina, Roldughin.     

Nucleation and growth of silver nanoparticles monitored by titration microcalorimetry

The nucleation and the growth of silver nanoparticles were studied by spectrophotometry and transmission electron microscopy, with simultaneous recording of the concomitant enthalpy changes. Silver nanoparticles were stabilized by sodium citrate and reduction was brought about by the addition of hydroquinone in aqueous medium. It was established that nucleation is an exothermic process and heat effects are basically determined by the ratio of silver ions to hydroquinone. The process of nanoparticle formation was divided to three phases: the nucleation phase is exothermic, the growth phase is endothermic and further addition of the reducing agent results in the aggregation of silver nanoparticles, which produces a second exothermic heat effect.     

Morphology and size-controlled synthesis of silver nanoparticles in aqueous surfactant polymer solutions

We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies. The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter were obtained when 1 wt% aqueous starch solution of AgNO₃ precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized by NaOH reduction of AgNO₃ in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time.     

Formation of surface layers on silver nanoparticles in aqueous and water-organic media

Synthetic aspects of silver nanoparticle preparation in one-and two-phase aqueous and water-organic media and the influence of experimental factors on particle size and surface hydrophilicity/hydrophobicity are studied. It is shown that silver nanoparticles with controlled mean size and surface hydrophilic-hydrophobic properties can be obtained through direct synthesis or successive transformations.     

Preparation of silver nanoparticles in aqueous solutions in the presence of carbonate ions as stabilizers

Silver nanoparticles are prepared by reducing Ag⁺ ions with sodium borohydride in aqueous solutions containing carbonate ions (5 × 10⁻⁵−1 × 10⁻² mol l⁻¹). It is established that carbonate ions represent an efficient stabilizer that provides nanoparticles with electrostatic protection via the formation of an electrical double layer. The maximum stability of a silver dispersion is observed at a carbonate ion concentration of 1 × 10⁻³ mol l⁻¹. The average size of silver nanoparticles is 10.0 ± 2.5 nm. The formation kinetics of silver nanoparticles is described by an equation for a first-order reaction with a rate constant of 2.3 × 10⁻³ s⁻¹ (±20%).     

Formation of palladium hydride complexes upon the reduction of Pd(II) by hydrogen

Conclusions The reduction of palladium(II) acetate by hydrogen in the presence of 1,10-phenanthroline or 2,2-dipyridyl gives palladium hydride clusters containing a massive metal-like nucleus with interstitial hydrogen atoms. The ligands are found to be peripheral palladium atoms, while the acetate groups are found in the external sphere.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2384, October, 1985.The authors express their gratitude to S. G. Ellert for measuring the magnetic susceptibility and to A. L. Chuvilin for the electron microscopic data.     

The influence of Ag+ ions on transformations of silver clusters in polyacrylate aqueous solutions

It is shown that transformations of unstable clusters, intermediates of the borohydride reduction of silver cations, in weakly alkaline polyacrylate aqueous solutions are governed by the competition between the processes of their oxidation, coalescence into larger particles, and reduction of silver cations. Moreover, these processes depend on the loading of a polyanion with cations and can be controlled by the addition of Ag⁺ ions.     

Formation of silver clusters in nozzle expansions

The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m^?2s^?1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.     

Nucleation and growth kinetics of silver nanoparticles prepared by glutamic acid in micellar media

The title reaction in the presence of cetyltrimethylammonium bromide (CTAB) has been followed spectrophotometrically at 325 nm. In the process of reduction, characteristic surface resonance plasmon absorption peaks appear for the silver nanoparticles (NP) and the intensities increase with reaction time. UV–visible spectra suggest that [CTAB] and glutamic acid influence the morphology of the silver NP and act as shape‐directing agents, whereas [Ag⁺] has no effect. The effects of the total [glutamic acid], [CTAB], and [Ag⁺] on the apparent rate constants of silver NP formation are determined. The sigmoidal curve of absorbance versus reaction time indicates an autocatalytic path involved in the growth process. The α‐amino and ? COOH groups undergo chemical transformation (oxidative deamination and decarboxylation). The particles are spherical in shape with average diameters ranging between 12 and 25 nm, and their size distribution is wide. A plausible mechanism has been proposed with the following rate law: (d[silver sol])/dt = k[Ag⁺][Glutamic acid]_T. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 680–691, 2012     

Formation of gold nanoparticles in aqueous solutions of cellulose derivatives and a study of the properties of these nanoparticles

It was demonstrated that gold nanoparticles can be obtained by using cellulose ethers, methyl hydroxyethyl cellulose and carboxymethylcellulose as reducing agents and also as nanoparticle stabilizers. IR spectral studies revealed a difference between the mechanisms of reduction and nanoparticle stabilization by these cellulose derivatives. A scanning tunnel microscope was used to examine composite films formed from nanoparticle dispersions on the surface of polycrystalline gold films. It was demonstrated that, in the case of gold nanoparticles, densely packed globular structures are formed in a carboxymethyl cellulose solution. A fibril-like structure of layers is formed in the Au+(methyl hydroxyethyl cellulose) system.     

Preparation and characterization of silver nanoparticles by chemical reduction method

Silver nanoparticles were prepared by the reduction of AgNO(3) with aniline in dilute aqueous solutions containing cetyltrimethlyammonium bromide, CTAB. Nanoparticles growth was assessed by UV-vis spectroscopy and the average particle size and the size distribution were determined from transmission electron microscopy, TEM. As the reaction proceeds, a typical plasmon absorption band at 390-450nm appears for the silver nanoparticles and the intensities increase with the time. Effects of [aniline], [CTAB] and [Ag(+)] on the particle formation rate were analyzed. The apparent rate constants for the formation of silver nanoparticles first increased until it reached a maximum then decreased with [aniline]. TEM photographs indicate that the silver sol consist of well dispersed agglomerates of spherical shape nanoparticles with particle size range from 10 to 30nm. Aniline concentrations have no significant effect on the shape, size and the size distribution of Ag-nanoparticles. Aniline acts as a reducing as well as adsorbing agent in the preparation of roughly spherical, agglomerated and face-centered-cubic silver nanoparticles.