Computational model for the formation of uniform silver spheres by aggregation of nanosize precursors (original) (raw)
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Synthesis of Silver Colloids: Experiment and Computational Model
2009
We summarize our recent results [1] that model the formation of uniform spherical silver colloids prepared by mixing iso-ascorbic acid and silver-amine complex solutions in the absence of dispersants. We found that the experimental results [2] can be modeled effectively by the two-stage formation mechanism used previously to model the preparation of colloidal gold spheres . The equilibrium concentration of silver atoms and the surface tension of silver precursor nanocrystals are both treated as free parameters, and the experimental reaction time scale is fit by a narrow region of this two-parameter space. The kinetic parameter required to match the final particle size is found to be very close to that used previously in modeling the formation of uniform gold particles, suggesting that similar kinetics governs the aggregation process. The model also reproduces semi-quantitatively the effects of temperature and solvent viscosity on particle synthesis.
The Journal of Physical Chemistry C, 2018
The nucleation and growth of silver nanoparticles are modeled and simulated based on first-principles calculations. The formation energy of single-crystal and multiply-twinned particles are calculated to elucidate the thermodynamic properties of particles and modeled as a function of geometric parameters. Based on the calculated formation energy and the molecular collision theory, Kinetic Monte Carlo simulations are performed to trace the formation process of silver nanoparticles. In particular, the temporal change of size distribution and morphology are obtained and used to elucidate the governing mechanism in each stage of the formation process. It is demonstrated that the formation process is separated into four phases depending on the power-law time dependence of the particle formation and they are characterized by the size-difference between coalescent particles. The temperature-dependence of size distribution and morphology are also studied to elucidate the underlying mechanisms. The findings are compared with classical theories quantitatively and a strategy to control the morphology of silver nanoparticles is discussed.
ACS Nano, 2012
The formation mechanisms of silver nanoparticles using aqueous silver perchlorate solutions as precursors and sodium borohydride as reducing agent were investigated based on timeresolved in situ experiments. This contribution addresses two important issues in colloidal science: (i) differences and analogies between growth processes of different metals such as gold and silver and (ii) the influence of a steric stabilizing agent on the growth process. The results reveal that a growth due to coalescence is a fundamental growth principle if the monomer-supplying chemical reaction is faster than the actual particle formation.
Mechanism of Formation of Monodispersed Colloids by Aggregation of Nanosize Precursors
1998
It has been experimentally established in numerous cases that precipitation of monodispersed colloids from homogeneous solutions is a complex process. Specifically, it was found that in many systems nuclei, produced rapidly in a supersaturated solution, grow to nanosize primary particles (singlets), which then coagulate to form much larger final colloids in a process dominated by irreversible capture of these singlets. This paper describes a kinetic model that explains the formation of dispersions of narrow size distribution in such systems. Numerical simulations of the kinetic equations, with experimental model parameter values, are reported. The model was tested for a system involving formation of uniform spherical gold particles by reduction of auric chloride in aqueous solutions. The calculated average size, the width of the particle size distribution, and the time scale of the process, agreed reasonably well with the experimental values.
Journal of Colloid and Interface Science, 2005
Uniform, well-dispersed silver particles of various morphologies have been prepared by reducing highly acidic silver nitrate solutions with ascorbic acid in the presence of a sodium naphthalene sulfonate-formaldehyde copolymer as dispersing agent. By varying the temperature of the reaction, the free acid content, the addition rate of the reductant, and the aging time, both isometric and anisotropic silver particles could be obtained. It was found that the latter were formed by aggregation of nanosize subunits, which were identified by electron microscopy and X-ray diffractometry.
Kinetic Study of Silver Nanoparticle Formation
2019
With the increased use of silver nanoparticles in modern day applications, kinetic information on the mechanism of their formation is useful for further studies on its reactivity in a biological environment. Silver nanoparticles were synthesized using a modified Turkevich method. The synthesized nanoparticles were characterized using UV-Visible spectroscopy. The data obtained were plotted as a function of time, and rate constants for the nucleation (k1) and autocatalytic surface growth (k2) were extracted. Comparing the k1 (~10) and k2 (~10) values supports a two-step mechanism of slow nucleation and fast autocatalytic surface growth.
Kinetics of Primary Nanoparticle Agglomeration in Precipitation of Silver
Chemical Engineering & Technology, 2009
The precipitation kinetics of silver was studied using a lab-scale batch crystallizer with special attention to characterization of agglomeration of primary nanoparticles. The vessel was operated at different feed concentrations, molar ratios, and stirrer speed. Nucleation, volume average crystal growth rates, and agglomeration kernels were determined. Empirical relations were obtained between the rates of the different crystallization steps with supersaturation, magma density, and energy dissipation rate. The results show that larger crystals will be obtained at high supersaturation due to dominance of agglomeration, because the rate of agglomeration also increases with supersaturation, thereby suppressing the primary nucleation rate and enhancing the observed average volume growth rate.
The impact of stabilization mechanism on the aggregation kinetics of silver nanoparticles
Science of The Total Environment, 2012
The use of silver nanoparticles (AgNPs) for various applications is growing drastically. The increase in use will eventually lead to their release into the environment. The tendency of AgNPs to aggregate and the kinetics of aggregation are major factors that govern their fate in the environment. Dynamic light scattering (DLS) was utilized to investigate the electrolyte-induced aggregation kinetics (NaNO 3 , NaCl and Ca(NO 3 ) 2 ) of coated and uncoated AgNPs which are electrostatically (H 2 -AgNPs and Citrate-AgNPs), sterically (polyvinylpyrrolidone (PVP)-AgNPs) and electrosterically (branched polyethyleneimine (BPEI)-AgNPs) stabilized. The aggregation kinetics of the electrostatically stabilized AgNPs was in agreement with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and the AgNPs exhibited both reaction-limited and diffusion-limited regimes. The H 2 -AgNPs had critical coagulation concentrations (CCC) of 25, 30 and 3 mM in the presence of NaNO 3 , NaCl and Ca(NO 3 ) 2 salts, respectively. The Citrate-AgNPs had CCC of 70, 70 and 5 mM in the presence of NaNO 3 , NaCl and Ca(NO 3 ) 2 salts, respectively. The values of the Hamaker constant for the electrostatically stabilized AgNPs were also determined and the values were in agreement with the reported values for metallic particles. The aggregation kinetics for both the sterically and electrosterically stabilized AgNPs (PVP-AgNPs and BPEI-AgNPs) was not in agreement with the DLVO theory and the particles were resistant to aggregation even at high ionic strength and electrolyte valence. The PVP-AgNPs and the BPEI-AgNPs had no critical aggregation concentration value at the investigated ionic strength values.
ChemInform Abstract: Formation Mechanisms of Uniform Colloid Particles
ChemInform, 2008
The relationship of the shape and structure of uniform colloidal particles to different mechanisms of formation by precipitation in homogeneous solutions is reviewed. Specifically, conditions leading to (a) amorphous spheres, (b) nonspherical crystals of different shapes, and (c) polycrystalline particles of different morphologies including spheres are distinguished. The last case is observed when larger particles are formed by aggregation of nanosized precursors. It is now recognized that the latter process is more common than previously understood. A model explaining the size selection of monodispersed spheres by aggregation is illustrated in the case of silver particles. It was also demonstrated that uniform polycrystalline particles of other shapes are generated by the aggregation process. Challenges faced in the effort to develop at least a semi-quantitative explanation of the shape factor in the latter case are outlined.