Kinetics Of Nanoparticle Formation Research Articles

Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies.

Herein, using in situ generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.

Kinetics of Nanoparticles Formation Under UV, VIS and IR Nanosecond Laser Irradiation of a Silver-Ions-Enriched Glass

Kinetics of Nanoparticles Formation Under UV, VIS and IR Nanosecond Laser Irradiation of a Silver-Ions-Enriched Glass

Nanoparticle Formation Kinetics, Mechanisms, and Accurate Rate Constants: Examination of a Second-Generation Ir(0)n Particle Formation System by Five Monitoring Methods Plus Initial Mechanism-Enabled Population Balance Modeling

Nanoparticle Formation Kinetics, Mechanisms, and Accurate Rate Constants: Examination of a Second-Generation Ir(0)_<i>n</i> Particle Formation System by Five Monitoring Methods Plus Initial Mechanism-Enabled Population Balance Modeling

Laser-scribed ultrasmall nanoparticles with unary and binary phases

• Laser-scribing enables rapid synthesis of ultrasmall nanoparticles@carbon out of MOFs. • The method can precisely tune the particle size, uniformity and phase composition. • The kinetics is controlled by the reducibility of metal ions and the cooling rate. • The Ni nanoparticles@carbon showed excellent HER activities in various electrolytes. Ultrasmall nanoparticles embedded in conductive support have immense potential in catalytic and energy-related applications, yet developing a fast and proper synthesis method remains a challenge. Herein, we demonstrate that, via simple laser scribing, isostructural metal–organic frameworks can be readily transformed into ultrasmall nanoparticles (5–14 nm) with different elemental compositions embedded in conductive carbon support. We found that the formation kinetics of nanoparticles is controlled by the thermodynamic reducibility of metal ions in the metal-organic framework as well as the cooling rate. This method allowed us to precisely tune the particle size and uniformity as well as the composition. As a potential application of the produced nanoparticles, we evaluated the electrocatalytic behavior of the Ni nanoparticles embedded in carbon support. It exhibited excellent performance and stability for the hydrogen evolution reaction in both acid and alkaline electrolytes.

Response to “Particle Size Is a Primary Determinant for Sigmoidal Kinetics of Nanoparticle Formation: A “Disproof” of the Finke–Watzky (F-W) Nanoparticle Nucleation and Growth Mechanism”

Response to “Particle Size Is a Primary Determinant for Sigmoidal Kinetics of Nanoparticle Formation: A “Disproof” of the Finke–Watzky (F-W) Nanoparticle Nucleation and Growth Mechanism”

Particle Size Is a Primary Determinant for Sigmoidal Kinetics of Nanoparticle Formation: A “Disproof” of the Finke–Watzky (F-W) Nanoparticle Nucleation and Growth Mechanism

Particle Size Is a Primary Determinant for Sigmoidal Kinetics of Nanoparticle Formation: A “Disproof” of the Finke–Watzky (F-W) Nanoparticle Nucleation and Growth Mechanism

Mesoscale Modeling and Experimental Study of Quercetin Organization as Nanoparticles in the Poly-lactic-co-glycolic Acid/Water System under Different Conditions

To understand the nanoparticle formation of quercetin in the poly-lactic-co-glycolic acid/water system, a multiscale approach combining experimental, molecular, and mesoscale modelings was carried out. The evolution of interactions occurring between compounds mixed at different ratios was evaluated by the order parameter, calculated using MesoDyn simulations. The obtained results indicated that the studied systems allowed to produce spherical nanoparticles well distributed in the continuous medium (water). The fast kinetics of nanoparticle formation is reached with 10 g L–1 of poly-lactic-co-glycolic acid, 0.5 g L–1 of quercetin, and 0.5% of polyvinyl alcohol. The corresponding order parameter of water (Pwater) was equal to 0.018. The increase of poly-lactic-co-glycolic acid and quercetin concentrations and the lactic acid content in poly-lactic-co-glycolic acid favor the formation of nanoparticles with a large size. The formed nanoparticles were composed of quercetin in the center of the system, poly-lactic-co-glycolic acid, as the second layer, and polyvinyl alcohol as the third layer. The water is the continuous phase. The shape, the size, and the order organization of nanoparticles were checked experimentally using transmission electron microscopy and dynamic light scattering. The obtained results indicated that experimental investigations are in good agreement with the simulated ones. Therefore, computational mesoscopic modeling can be used as a successful tool to predict the behavior of quercetin/poly-lactic-co-glycolic acid/water systems under different operating conditions.

Dust Effects on Ir(0)n Nanoparticle Formation Nucleation and Growth Kinetics and Particle Size-Distributions: Analysis by and Insights from Mechanism-Enabled Population Balance Modeling.

The effects of microfiltration removal of filterable dust on nanoparticle formation kinetics and particle-size distribution, in a polyoxometalate polyanion (P2W15Nb3O629-)-stabilized Ir(0)n nanoparticle formation system, are analyzed by the newly developed method of Mechanism-Enabled Population Balance Modeling (ME-PBM). The [(Bu4N)5Na3(1,5-COD)Ir·P2W15Nb3O62] precatalyst system produces on average Ir(0)∼200 nanoparticles of 1.74 ± 0.33 nm and hence a particle-size distribution (PSD) of ±19% dispersion when the precatalyst is reduced under H2 in unfiltered propylene carbonate solvent. But if the precatalyst is reduced in microfiltered solvent and microfiltered reagent solutions (where the filtered solvent is then also used to rinse dust from the glassware), then larger Ir(0)∼300 1.96 ± 0.16 nm nanoparticles are produced with a remarkable, 2.4-fold lowered ±8% dispersion. The results and effects of the microfiltration reduction of dust are analyzed by the newly developed method of ME-PBM. More specifically, the studies reported herein address eight outstanding questions that are listed in the Introduction. Those questions include: how easy or difficult it is to fit PSD data? What is the ability of the recently discovered alternative termolecular nucleation and two size-dependent growth steps mechanism to account for the effects of dust on the PSD? What types and amount of PSD kinetics data are needed to deconvolute the PSD into the parameters of the ME-PBM? What is the reliability of the resulting rate constants? Additional questions addressed include: if the ME-PBM results offer insights into the remarkable 2.4-fold narrowing of the PSD post simple microfiltration lowering of the dust, and if the results are likely to be more general? The Summary and Conclusions section lists nine specific insights that include comments on needed future studies.

Experimental probes of silver metal nanoparticle formation kinetics: Comparing indirect versus more direct methods

AbstractThe kinetics of noble metal nanoparticle formation in bottom‐up syntheses are important for controlling and optimizing these methods. Hence, experimental probes that are easily accessible to most laboratories are also of interest. We collected kinetic curves for the formation of silver nanoparticles in a modified Turkevich method with citrate acting as the reducing and stabilizing agent by (i) measuring the change in silver nanoparticle surface plasmon resonance by UV‐visible spectroscopy, a somewhat indirect method, and then also by (ii) measuring the change in silver ion concentration by ion‐selective electrode potentiometry and/or atomic absorption spectroscopy, two more direct methods. The resulting sigmoidal kinetic curves were curvefitted with the Finke‐Watzky two‐step kinetic model of slow, continuous nucleation and fast autocatalytic growth to extract average rate constants. We found that the kinetic curves obtained by following the change in silver ion concentration were apparent mirror images of those constructed by following the change in nanoparticle surface plasmon resonance, and that their respective curvefits displayed the same sigmoidal characteristics. The resultant values of the rate constants for nucleation and growth overlapped within experimental error between the methods and showed similar trends over the range of citrate concentrations studied. The use of multiple probes in this work to follow the kinetics of nanoparticle formation helps fill a need for the comparison and evaluation of different methods available to scientists, particularly those considered easily accessible.

Two Growth Mechanisms of Thiol-Capped Gold Nanoparticles Controlled by Ligand Chemistry.

Thiols play an important role in the synthesis of well-defined nanoparticles (NPs) with tailored properties, but their effects on the formation kinetics of NPs are still under investigation. Here, we used in situ small-angle X-ray scattering (SAXS)/UV-vis spectroscopy and time-dependent transmission electron microscopy (TEM) to elucidate the role of thiols in the formation process of gold NPs (AuNPs) by changing the adding sequence between thiol ligand and reducing agent. Through quantitative analysis of in situ SAXS/UV-vis and TEM, detailed information on size, size distribution, the number of particles, optical properties, and the size evolution was obtained. Two different growth mechanisms of monodisperse AuNPs controlled by thiol ligand are exhibited: (i) thiol plays a dual role as a digestive ripening etchant and as a stabilizing ligand in the presence of a weak phosphine ligand. The digestive ripening mechanism involving the dissolution of bigger particles and subsequent deposition of monomers onto existing small NPs is responsible for producing narrowly dispersed NPs. (ii) Thiol acts as a strong stabilizing agent; in this case, the formation rate constant is quite slow, thus limiting the growth rate of NPs. Therefore, diffusion-limited growth mechanism is proposed for obtaining narrowly dispersed NPs with a diameter of 5.6 nm (12%). Our findings demonstrate that the formation of nearly monodisperse AuNPs with controllable size distribution could be realized by different growth mechanisms in the presence of thiol ligand.

Nanoparticle Formation Kinetics and Mechanistic Studies Important to Mechanism-Based Particle-Size Control: Evidence for Ligand-Based Slowing of the Autocatalytic Surface Growth Step Plus Postulated Mechanisms

Ligands are known to affect the formation, stabilization, size, and size-dispersion control of transition-metal and other nanoparticles, yet the kinetic and mechanistic basis for such ligand effects remains to be elucidated and then coupled to predictions for improved particle size and narrower particle size distribution syntheses. Toward this broad goal, the effect of the added excess ligand (L) and the stabilizer, L = POM9– (= the polyoxometalate, P2W15Nb3O629–) is studied for the formation of POM9–-stabilized Ir(0)n nanoparticles, {Ir(0)n·(POM9–)m}9m−, synthesized from an atomically characterized precatalyst (COD)Ir·POM8– under H2. First, the balanced reaction stoichiometry and characterization of the nanoparticle products are established. Next, the kinetics of nanoparticle formation is analyzed initially by the FW 2-step minimum mechanism consisting of slow, continuous nucleation, A → B (rate constant k1obs), and autocatalytic surface growth, A + B → 2B (rate constant k2obs), where A is nominally (COD...

Selective Hydrogenation of Levulinic Acid Using Ru/C Catalysts Prepared by Sol-Immobilisation

A 1% Ru/C catalyst prepared by the sol immobilization method showed a high yield of γ-valerolactone from levulinic acid. We performed an optimization of the catalyst by varying the preparation variables involved in the sol immobilization method and detremined that the ratio of PVA, NaBH4 to Ru and heat treatment conditions play a crucial role in the synthesis of active and selective catalysts. By varying these parameters we have identified the optimum conditions for catalyst preparation by providing well dispersed nanoparticles of RuOx on the carbon support that are reducible under low reaction temperature and in turn gave an enhanced catalytic activity. In contrast to a catalyst prepared without using a PVA stabiliser, the use of a small amount PVA (PVA/Ru = 0.1) provided active nanoparticles, by controlling the steric size of the Ru nanoparticles. An optimum amount of NaBH4 was required in order to provide the reducible Ru species on the surface of catalyst and further increase in NaBH4 was found to cause a decline in activity that was related to the kinetics of nanoparticle formation during catalyst preparation. A variation of heat treatment temperature showed a corresponding decrease in catalytic activity linked with the sintering and an increase in particle size.Graphical

Gold Nanoparticle Formation Kinetics and Mechanism: A Critical Analysis of the "Redox Crystallization" Mechanism.

A 2013 paper proposed a “redox crystallization” (R-C) mechanism for the formation of Au0n nanoparticles from the reduction of a AuCl4– precursor. That study used an unconventional analysis of the valuable, expertly obtained kinetics data reported, and came up with multiple claims and insights collected under the putatively new R-C mechanism. If confirmed, those claims and the R-C mechanism provide a valuable addition to the knowledge of gold nanoparticle formation kinetics and mechanisms. On the other hand, if the methodology used to support the R-C mechanism is flawed so that its resultant conclusions are incorrect, then the R-C mechanism needs to be discarded until compelling evidence for it can be gathered, evidence that would have to include the disproof of the other dominant mechanism(s) of nanoparticle formation. The present work provides a critical analysis of the evidence previously offered for the R-C mechanism, efforts that are of interest to the areas of Au0n nanoparticles, the kinetics and mechanisms of nanoparticle formation and, as it turns out, more generally to those interested in kinetic and mechanistic studies.

Bimetallic nanoparticles synthesized in microemulsions: A computer simulation study on relationship between kinetics and metal segregation

Computer simulations were carried out to study the origin of the different metal segregation showed by bimetallic nanoparticles synthesized in microemulsions. Our hypothesis is that the kinetics of nanoparticle formation in microemulsions has to be considered on terms of two potentially limiting factors, chemical reaction itself and the rate of reactants exchange between micelles. From the kinetic study it is deduced that chemical reduction in microemulsions is a pseudo first-order process, but not from the beginning. At the initial stage of the synthesis, redistribution of reactants between micelles is controlled by the intermicellar exchange rate, meanwhile the core and middle layers are being built. This exchange control has a different impact depending on the reduction rate of the particular metal in relation to the intermicellar exchange rate. For the case of Au/Pt nanoparticles, the kinetic constant of Au (fast reduction) is strongly dependent on intermicellar exchange rate and reactant concentration. On the contrary, the kinetic constant of Pt (slower reduction) remains constant. Therefore, the fact that the reaction takes place in a microemulsion affects more or less depending on the reduction rate of the metals. As a consequence, the final nanostructure not only depends on difference between the reduction rates of both metals, but also on the reduction rate of each metal in relation to the intermicellar exchange rate.

Nanoalumina-supported rhodium(0) nanoparticles as catalyst in hydrogen generation from the methanolysis of ammonia borane

Rhodium(0) nanoparticles were in situ formed from the reduction of rhodium(II) octanoate and supported on the surface of nanoalumina yielding Rh(0)/nanoAl2O3 which is highly active catalyst in hydrogen generation from the methanolysis of ammonia borane at room temperature. The kinetics of nanoparticle formation can be followed just by monitoring the volume of hydrogen gas evolved from the methanolysis of ammonia borane. The evaluation of the kinetic data gives valuable insights to the slow, continuous nucleation and autocatalytic surface growth steps of the formation of rhodium(0) nanoparticles. Rh(0)/nanoAl2O3 could be isolated and characterized by a combination of advanced analytical techniques including ATR-IR, PXRD, TEM, XPS, SEM, SEM-EDX and ICP-OES. The results reveal that rhodium(0) nanoparticles are highly dispersed on the surface of nanoalumina. The particle size of Rh(0)/nanoAl2O3 increases with the initial rhodium loading of nanoalumina. Rh(0)/nanoAl2O3 is highly active catalyst in hydrogen generation from the methanolysis of AB providing an exceptional initial turnover frequency of TOF=218min−1 at 25.0±0.5°C, which is the highest value ever reported for rhodium catalysts in hydrogen generation from the methanolysis of ammonia borane.

Synthesis of Silicon Nanoparticles in Nonthermal Capacitively-Coupled Flowing Plasmas: Processes and Transport

Control of the size and material properties of silicon nanoparticles plays a critical role in optimizing applications using those nanoparticles, such as photovoltaics and biomedical devices. While synthesis of silicon nanoparticles in low temperature plasmas has many attractive features, the basic mechanisms leading to formation of nanoparticles in these plasmas are poorly understood. A two-dimensional numerical model for synthesis of silicon nanoparticles (<5 nm in diameter) in radio frequency (RF) discharges was developed and used to investigate mechanisms for particle growth for Ar/He/SiH4 gas mixtures. Algorithms for the kinetics of nanoparticle formation were self-consistently embedded into a plasma hydrodynamics simulation to account for nucleation, growth, charging, and transport of nanoparticles. We found that with RF excitation in narrow tubes at pressures of a few Torr, the electric field does not fully confine charged nanoparticles in the axial direction, which then results in a finite residence time of particles in the plasma. We found that because of the high neutral nanoparticle density, coagulation plays a significant role in growth. The model predicts the possibility of synthesizing crystalline silicon nanoparticles under these conditions. Trends in the growth of nanoparticles as a function of power are discussed.

Rhodium(0) nanoparticles supported on nanosilica: Highly active and long lived catalyst in hydrogen generation from the methanolysis of ammonia borane

Nanosilica stabilized rhodium(0) nanoparticles (Rh(0)/nanoSiO2), in situ formed from the reduction of rhodium(II) octanoate impregnated on the surface of nanosilica, are active catalyst in hydrogen generation from the methanolysis of ammonia borane at room temperature. Monitoring the hydrogen evolution enables us to follow the kinetics of nanoparticles formation. The resulting sigmoidal kinetic curves are analyzed by using the 2-step mechanism of the slow, continuous nucleation and autocatalytic surface growth. By using the temperature dependent kinetic data, we could calculate the activation energy for the nucleation and autocatalytic surface growth of rhodium(0) nanoparticles as well as for the catalytic methanolysis of ammonia borane. Rh(0)/nanoSiO2 could be isolated and characterized by a combination of advanced analytical techniques including XRD, TEM, EDX, XPS, and N2 adsorption–desorption. The results reveal that rhodium(0) nanoparticles are highly dispersed on nanosilica surface and have tunable particle size depending on the initial metal concentration. An increase in the mean particle size of rhodium(0) nanoparticles is observed when the initial metal concentration increases. Rh(0)/nanoSiO2 are highly active and long lived catalyst in hydrogen generation from the methanolysis providing an exceptional initial turnover frequency of TOF=168min−1 (504min−1 corrected for the surface atoms) at 25.0±0.5°C, which is the highest value ever reported for rhodium catalysts. An inverse dependence of TOF on the initial rhodium concentration is observed and ascribed to the increasing size of rhodium(0) nanoparticles. Carbon disulfide poisoning and filtration experiments unequivocally demonstrate that rhodium(0) nanoparticles are the true heterogeneous catalyst in hydrogen generation from the methanolysis of ammonia borane.

Parallel synthesis of poly(amino ether)-templated plasmonic nanoparticles for transgene delivery.

Plasmonic nanoparticles have been increasingly investigated for numerous applications in medicine, sensing, and catalysis. In particular, gold nanoparticles have been investigated for separations, sensing, drug/nucleic acid delivery, and bioimaging. In addition, silver nanoparticles demonstrate antibacterial activity, resulting in potential application in treatments against microbial infections, burns, diabetic skin ulcers, and medical devices. Here, we describe the facile, parallel synthesis of both gold and silver nanoparticles using a small set of poly(amino ethers), or PAEs, derived from linear polyamines, under ambient conditions and in absence of additional reagents. The kinetics of nanoparticle formation were dependent on PAE concentration and chemical composition. In addition, yields were significantly greater in case of PAEs when compared to 25 kDa poly(ethylene imine), which was used as a standard catonic polymer. Ultraviolet radiation enhanced the kinetics and the yield of both gold and silver nanoparticles, likely by means of a coreduction effect. PAE-templated gold nanoparticles demonstrated the ability to deliver plasmid DNA, resulting in transgene expression, in 22Rv1 human prostate cancer and MB49 murine bladder cancer cell lines. Taken together, our results indicate that chemically diverse poly(amino ethers) can be employed for rapidly templating the formation of metal nanoparticles under ambient conditions. The simplicity of synthesis and chemical diversity make PAE-templated nanoparticles useful tools for several applications in biotechnology, including nucleic acid delivery.

Formation kinetics of nanoparticles as the basis for simulating the generation mechanism of Liesegang rings in gels

An approach has been proposed for determining the space-time parameters of the formation process of Liesegang rings. This approach relates the processes of the formation of nanoparticles and dense periodic precipitates from them. Dynamic light scattering is employed to reveal periodic variations in the intensity of light scattered by nanoparticles with different sizes, from which Liesegang rings are formed. A relationship between the periods of the variations in the intensity of light scattered by nanoparticles (microscopic process) and the times of the formation of Liesegang rings as a whole (macroscopic process) has been found.

Optimization of process parameters of polymer solution mediated growth of calcium carbonate nanoparticles

With the advent of nanotechnology, many methods of synthesis of nanoparticles have come into practice and the ‘polymer mediated growth’ technique is among them. In this route, ions of one of the reactants are allowed to diffuse from an external solution into a polymer matrix where the other reactant is complexed and bound. The exact role of ionic diffusion in the formation of nanoparticles was investigated in the current study by studying the patterns of kinetics of nanoparticle formation using UV vis spectroscopy. Typically, calcium carbonate nanoparticles were formed by the aforementioned technique using polyethylene glycol solution. The particle size was calculated using Scherrer’s formula on x-ray diffraction plots and was reconfirmed with field emission scanning electron microscope and transmission electron microscope images. Energy-dispersive x-ray analysis was used to study the composition and purity of the nanoparticles formed. The reactant to polymer ratio, reaction temperature and molecular weight of polyethylene glycol affected the size of the particles formed. Through this knowledge we optimized these parameters to obtain particles as small as 20 nm and confirmed that this technique can be used to control the size of nanoparticles.