Effect of high gold salt concentrations on the size and polydispersity of gold nanoparticles prepared by an extended Turkevich–Frens method (original) (raw)
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Size Variation of Gold Nanoparticles Synthesized Using
2013
The size evolution of gold nanoparticles synthesized using tannic acid with initial gold chloride concentrations ranging from 0.2-2 mM at various tannic acid to chloroauric acid molar ratios (ranging from 2:1 to 12:1) has been analysed. Dynamic light scattering spectroscopic and tramission electron microscopic analyses were performed to assess the size of formed gold nanoparticles. Two different patterns of nanoparticle size evolution were obtained; the size evolution trend below 1 mM chloroauric acid concentration was found to be different from the one obtained at gold chloride concentrations higher than or equal to 1 mM. In case of sizes obtained for less than 1 mM gold chloride concentration, a general decrease in particle size was observed with increase in gold salt concentration. On the contrary, for the particles synthesised using chloroauric acid concentrations higher than or equal to 1 mM, with increase in gold salt concentration, a general increase in nanoparticle diameter was seen. For the molarities 0.2 and 0.5 mM, with increase in tannic acid/ chloroauric acid ratios, first the size decreases and then increases and finally reaches saturation. Particles formed at molarities greater than equal to 1 mM do not exhibit plateaux in their size rather initially decrease and then increase in response to increasing tannic acid/chloroauric acid ratios except for 2 mM concentration at which a small saturation is observed. The findings enumerate that higher gold chloride concentrations leave a significant impact on the sizes of gold nanaparticles obtained using tannic acid as a reducing agent of chloroauric acid solution.
The citrate reduction method of synthesis of gold nanoparticles (AuNPs) as introduced by Frens has been standardized to enable one to prepare AuNPs of desired dimension by controlling the composition of the reactants. The standardization has been made through characterization of the nanoparticles by UV-vis spectroscopy and from the transmission electron microscopic (TEM) measurements. Linearity of the plot of the plasmon absorption maximum ( max of the synthesized AuNPs against their diameter as measured from TEM, as well as the plot of max with the fractional concentration of citrate in the reaction mixture provides a convenient and easy route to dictate the size of the synthesized AuNPs from a control on the composition of the reactants. The standardization reveals that a calculated composition of citrate (in terms of fractional concentration) in the reaction mixture produces AuNPs of a desired dimension within the range of 15-60 nm. The diameter of the synthesized gold nanoparticles can be confirmed simply from the UV-vis spectrophotometric technique. This essentially makes the use of costly TEM unnecessary, at least for the primary purposes.
New Insight Into the Size Tuning of Monodispersed Colloidal Gold Obtained by Citrate Method
2013
International audienceWe study the effect of citrate to gold molar ratio (X) on the size of citrated gold nanoparticles (AuNPs). This dependence is still a matter of debate for X ≥ 3 where the polydispersity is yet minimized. Indeed, there is no consensus between experiments proposed so far for comparable experimental conditions. Nonetheless, the sole available theoretical prediction has never been validated experimentally in this range of X. We show unambiguously using 3 techniques (UV-Vis spectroscopy, dynamic light scattering and transmission electronic microscopy), 2 different synthetic approaches (Direct, Inverse) and 10 X values for each approach that AuNPs’ size decay as a monoexponential with X. This result is, for the first time, in agreement with the sole available theoretical prediction by Kumar et al. on the whole studied range of X
pH tunable morphology of the gold nanoparticles produced by citrate reduction
Materials Chemistry and Physics, 2008
The reduction of AuCl 4 − by citrate produces gold nanoparticles with a variety of shapes and sizes depending on the exact conditions used in the preparation. We present results that show that the pH of the reacting mixture has a dramatic effect on the size, polydispersity and morphology of the resulting gold nanoparticles. This occurs by altering the citrate charge controlling its stabilizing effect during the growth of the particles. On one hand, wide size distributions of predominantly polyhedra are obtained at pH lower than 5.0. On the other hand, narrow size distributions of nearly spherical particles are obtained at pH higher than 6. A mixture of ellipsoidal and other shapes with aspect ratio larger than one is formed when the reaction is performed at a pH in the 5-6 range. The mean particle diameters as well as the width of the distributions decrease monotonically as the pH of the solution increases settling to the well-known values for these colloids with a width of ca. 10% of the mean diameter. The variation in the size distribution is controlled mainly by the average charge per citrate molecule.
Preparation and stability of gold nanoparticles
In the present study a prechosen size of gold nanoparticles prepared by chemical reduction method and has been found to be highly stable under a range of different experimental conditions explored. The gold nanoparticles have been characterized by UV–vis spectroscopy and transmission electron microscopy. The stability of citrate stabilized gold nanoparticles has been investigated as a function of pH by UV–visible absorption spectroscopy and Zeta-potentiometer and has shown good stability over the experimental methods adopted.
Growth kinetics and controlled auto-assembly of gold nanoparticles
Nanoparticles superlattices can be prepared by self-assembly of hybrid nanoparticles composed of a metallic core surrounded by an organic passivating layer. These superlattices are promising materials for applications in various fields such as recording media, light-emitting devices, biological tags, catalysts, solar cells, and sensors. The self-assembly is only possible when the nanoparticles display a narrow size distribution. The citrate reduction of gold(III) in water is one of the most commonly used synthetic pathways for the preparation of gold colloids [1]. The nucleation and growth mechanisms remain however unclear and are the subject of intense research. We have investigated the synthesis of gold nanoparticles under different experimental conditions and using different experimental techniques in order to gain insight into their formation mechanism.
Gold nanoparticles a renaissance in gold chemistry
Gold Bulletin, 1996
Vapour synthesis techniques have been used to prepare nanoparticulate dispersions of gold and other precious metals in non-aqueous solvents. The dimensions of these solvent-stabilised particles, which can be controlled within the 1-3nm size regime, effectively encompass the areas of molecular chemistry (as typified by high-nuclearity metal clusters) and the smaller colloidal metals. Gold nanoparticles differ from those of the other metals in exhibiting unusual time-and concentration-dependent behaviour. A regime of preparative conditions under which 1-3nm size gold particles, which are stable with respect to aggregation as a function of time, is defined. Some implications for these new developments are indicated.
Size-Controlled Synthesis of Gold Nanoparticles via High-Temperature Reduction
Langmuir, 2004
Gold nanoparticles having prechosen size ranging from 5 to 110 nm have been prepared in two steps. Firstly, small spherical particles (seed) of average diameters between 5 and 20 nm were prepared by varying the ratio of gold ion concentration to stabilizer/reductant, TX-100 concentration and using UV irradiation. Secondly, 20-110 nm particles were formed by a non-iterative seed-mediated growth where small particles produced by the above irradiation technique were exploited as seeds and fresh Au(III) ions were reduced onto the surface on the seed particles by ascorbic acid. The kinetics of particle formation has also been reported. These methods were fast and showed improved monodispersity sphericity and excellent reproducibility.
pH Dependence of Size Control in Gold Nanoparticles Synthesized at Room Temperature
Oriental Journal of Chemistry, 2018
We have developed the spherical gold nanoparticles (AuNPs) with different size at room temperature using L-ascorbic acid as a reducing agent. Controlling pH of L-ascorbic acid from 2.0 to 10.0 caused the decreasing of AuNPs size when measured using particle size analyzer. The alkaline condition leads to increase the reactivity of L-ascorbic acid even at room temperature. The homogeneous AuNPs were achieved even the synthesis was conducted at different pH of L-ascorbic acid (pH 2.0 to 12.0). The investigation using Transmission Electron Microscopy (TEM) confirmed that AuNPs performed a spherical shape. SEM-EDX measurement performed a strong characteristic peak of Au appeared at 2.0 keV. This research could be used to control of AuNPs size when synthesized at room temperature. The AuNPs obtained at optimum condition was stable up to 3 months.
Controlling the size and size distribution of gold nanoparticles: A design of experiment study
International Journal of Nanoscience, 2012
The Turkevich method is the oldest and most widely employed protocol for the production of colloidal gold. Gold nanoparticles are non toxic in nature and have potential applications in various biomedical fields including drug delivery and bioimaging. These metallic nanoparticles can be functionalized with drugs, targeting ligands such as tumor necrosis factor and groups (e.g. Poly ethylene glycol) to provide shielding from undesired immune responses. In this study we investigate the influence of process variables on the synthesis of nanoparticles by the reduction of chloroauric acid (HAuCl4) solution with sodium citrate. A Design of Experiment (DoE) approach was used to investigate the influence of production volume, temperature, stirring rate and sodium citrate concentration on the physical properties of nanoparticle namely size, size distribution, zeta potential and UV-Vis characteristics. The study showed that the relative amount of sodium citrate added (Au/citrate mole ratio) had a significant effect on the size, Poly Dispersity Index (PDI), the number of peaks in the size distribution and the position of Lambda max in the UV-Vis spectra. By varying the Au/Citrate ratio it is possible to synthesise particles with average diameters from 20 to 80 nm. However, the use of low amounts of sodium citrate in order to produce particles larger than ~35 nm tends to result in a wide bimodal size distribution.""