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Facile synthesis of concentrated gold nanoparticles with low size-distribution in water: temperature and pH controls.

Li C, Li D, Wan G, Xu J, Hou W - Nanoscale Res Lett (2011)

Bottom Line: It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained.The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations.The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory Base of Eco-Chemical Engineering, Lab of Colloids and Interfaces, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China. lidx@iccas.ac.cn.

ABSTRACT
The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

No MeSH data available.


Related in: MedlinePlus

Optical photos of the obtained gold colloids, the diluted samples and their corresponding UV-vis spectra. (A) Photos of gold colloids prepared from a solution of 0.25 mM to 2.0 mM HAuCl4 3H2O (corresponding to 0.1 mg/ml to 0.8 mg/ml, respectively) and their diluted samples at a content of 0.25 mM Au. (B) The corresponding UV-vis spectra of the diluted samples. (Baseline was adjusted artificially).
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Figure 1: Optical photos of the obtained gold colloids, the diluted samples and their corresponding UV-vis spectra. (A) Photos of gold colloids prepared from a solution of 0.25 mM to 2.0 mM HAuCl4 3H2O (corresponding to 0.1 mg/ml to 0.8 mg/ml, respectively) and their diluted samples at a content of 0.25 mM Au. (B) The corresponding UV-vis spectra of the diluted samples. (Baseline was adjusted artificially).

Mentions: In Turkevich's work, the influence of reactant concentration of HAuCl4 from 0.25 mM to decreased values was studied [25]. Herein, our first effort was taken to prepare GNPs through gradual increase of reactant concentration by the classical citrate method. Aqueous chloroauric acid solution from 0.25 to 2.5 mM was heated to boiling and the four times molar amount of sodium citrate was added, followed by continuously heating for a certain period to get the ruby-red colloids. It was found that the reaction rate was greatly enhanced at high reactant concentration. The optical photos of the obtained samples and diluted samples, as well as the corresponding UV-vis spectra, are shown in Figure 1. The color and the surface plasmon resonance (SPR) peaks of these colloids do not show obvious differences, and no obvious difference is found in the full width at half maximum of these peak profiles. However, TEM images of these GNPs (Figure 2) show that the size polydispersity remarkably varies with the reactant concentration increase although the particle average sizes are all located in a range of 10 to 20 nm. The large size distribution of GNPs at high reactant concentration will limit further applications such as size-related bioassays and well-defined nanoassembly. Moreover, the as-obtained gold colloids from 2.5 mM HAuCl4 are not stable and become black precipitates after hours; this is partially ascribed to the colloidal instability at high ionic strength.


Facile synthesis of concentrated gold nanoparticles with low size-distribution in water: temperature and pH controls.

Li C, Li D, Wan G, Xu J, Hou W - Nanoscale Res Lett (2011)

Optical photos of the obtained gold colloids, the diluted samples and their corresponding UV-vis spectra. (A) Photos of gold colloids prepared from a solution of 0.25 mM to 2.0 mM HAuCl4 3H2O (corresponding to 0.1 mg/ml to 0.8 mg/ml, respectively) and their diluted samples at a content of 0.25 mM Au. (B) The corresponding UV-vis spectra of the diluted samples. (Baseline was adjusted artificially).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211859&req=5

Figure 1: Optical photos of the obtained gold colloids, the diluted samples and their corresponding UV-vis spectra. (A) Photos of gold colloids prepared from a solution of 0.25 mM to 2.0 mM HAuCl4 3H2O (corresponding to 0.1 mg/ml to 0.8 mg/ml, respectively) and their diluted samples at a content of 0.25 mM Au. (B) The corresponding UV-vis spectra of the diluted samples. (Baseline was adjusted artificially).
Mentions: In Turkevich's work, the influence of reactant concentration of HAuCl4 from 0.25 mM to decreased values was studied [25]. Herein, our first effort was taken to prepare GNPs through gradual increase of reactant concentration by the classical citrate method. Aqueous chloroauric acid solution from 0.25 to 2.5 mM was heated to boiling and the four times molar amount of sodium citrate was added, followed by continuously heating for a certain period to get the ruby-red colloids. It was found that the reaction rate was greatly enhanced at high reactant concentration. The optical photos of the obtained samples and diluted samples, as well as the corresponding UV-vis spectra, are shown in Figure 1. The color and the surface plasmon resonance (SPR) peaks of these colloids do not show obvious differences, and no obvious difference is found in the full width at half maximum of these peak profiles. However, TEM images of these GNPs (Figure 2) show that the size polydispersity remarkably varies with the reactant concentration increase although the particle average sizes are all located in a range of 10 to 20 nm. The large size distribution of GNPs at high reactant concentration will limit further applications such as size-related bioassays and well-defined nanoassembly. Moreover, the as-obtained gold colloids from 2.5 mM HAuCl4 are not stable and become black precipitates after hours; this is partially ascribed to the colloidal instability at high ionic strength.

Bottom Line: It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained.The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations.The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory Base of Eco-Chemical Engineering, Lab of Colloids and Interfaces, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China. lidx@iccas.ac.cn.

ABSTRACT
The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

No MeSH data available.


Related in: MedlinePlus