Synthesis of Gold Nanoparticle/Silica Nanostructures
Nano-Scale and Amorphous Materials: Synthesis of Gold Nanoparticle/Silica Nanostructures
Turkevich Method for Gold Nanoparticle Synthesis Revisited ..
In Turkevich's work, the influence of reactant concentration of HAuCl4 from 0.25 mM to decreased values was studied . 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 . 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 ) 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.
In this work, uniform GNPs with low size polydispersity can be synthesized from the chloroauric acid precursor at high concentration (2.5 mM) by the citrate reduction method via combined temperature and pH controls. The addition of a proper amount of sodium hydroxide can produce uniform GNPs with a narrow size distribution. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained at different temperatures in presence of an optimized NaOH dosage. The pH analysis demonstrates that uniform GNPs can be obtained at around neutral conditions. The modified citrate reduction method can produce concentrated gold colloid dispersions and 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 to match the increasing commercial and industrial demands.
Gold nanoparticle delivery-enhanced proteasome …
The sodium citrate first acts as a . Later the negatively-charged citrate ions are onto the gold nanoparticles, introducing the surface charge that repels the particles and prevents them from aggregating.
Recently, the evolution of the spherical gold nanoparticles in the Turkevich reaction has been elucidated. Interestingly, extensive networks of gold nanowires are formed as a transient intermediate. These gold nanowires are responsible for the dark appearance of the reaction solution before it turns ruby-red.
Turkevich method for gold nanoparticle synthesis ..
This method was discovered by Brust and Schiffrin in early 1990s, and can be used to produce gold nanoparticles in that are normally not with water (like ).
The method pioneered by J. Turkevich et al. in 1951 and refined by G. Frens in 1970s, is the simplest one available. Generally, it is used to produce modestly spherical gold nanoparticles suspended in water of around 10–20 nm in diameter. Larger particles can be produced, but this comes at the cost of monodispersity and shape.
"Turkevich Method for Gold Nanoparticle Synthesis …
Colloidal gold - Gold Nanoparticles
Gold nanoparticle - Revolvy
How to Synthesize Gold Nanoparticles in Aqueous Phase
13/02/2016 · Facile synthesis of concentrated gold nanoparticles with low size-distribution ..
Turkevich Method for Gold Nanoparticle Synthesis ..
After initial nanoparticle synthesis, colloidal gold ligands are often ..
Synthesis of gelatin-capped gold nanoparticles with ..
Here, the gold nanoparticles will be around 5–6 nm. NaBH4 is the reducing agent, and TOAB is both the and the stabilizing agent.
Gold nanoparticle (Au NP) synthesis ..
Generally, gold nanoparticles are produced in a liquid ("liquid chemical methods") by of (H[AuCl4]), although more advanced and precise methods do exist. After dissolving H[AuCl4], the solution is rapidly stirred while a is added. This causes Au3+ to be reduced to neutral gold . As more and more of these gold atoms form, the solution becomes , and gold gradually starts to in the form of sub-nanometer particles. The rest of the gold atoms that form stick to the existing particles, and, if the solution is stirred vigorously enough, the particles will be fairly uniform in size.
methods for growing gold nanoparticles, the Turkevich method, ..
It is important to note that TOAB does not bind to the gold nanoparticles particularly strongly, so the solution will aggregate gradually over the course of approximately two weeks. To prevent this, one can add a stronger binding agent, like a (in particular, alkanethiols), which will bind to gold , producing a near-permanent solution. Alkanethiol protected gold nanoparticles can be precipitated and then redissolved. Some of the phase transfer agent may remain bound to the purified nanoparticles, this may affect physical properties such as . In order to remove as much of this agent as possible the nanoparticles must be further purified by .
A Facile pH Controlled Citrate-Based Reduction Method …
This approach, discovered by Perrault and Chan in 2009, uses hydroquinone to reduce HAuCl4 in an aqueous solution that contains gold nanoparticle seeds. This process is similar to that used in photographic film development, in which silver grains within the film grow through addition of reduced silver onto their surface. Similarly, gold nanoparticles can act in conjunction with hydroquinone to catalyze reduction of ionic gold onto their surface. The presence of a stabilizer such as citrate results in controlled particle growth. Typically, the nanoparticle seeds are produced using the citrate method. The hydroquinone method complements that of Frens, as it extends the range of monodispersed spherical particle sizes that can be produced. Whereas the Frens method is ideal for particles of 12-20 nm, the hydroquinone method can produce particles of at least 30-250 nm.
A Facile pH Controlled Citrate-Based Reduction Method for ..
The growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail to explore the parameter space of reaction conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defined size distribution, following the earlier work of Turkevich and Frens. The reaction is initiated thermally or in comparison by UV irradiation, which results in similar final products. The kinetics of the extinction spectra show the multiple steps of primary and secondary clustering leading to polycrystallites.
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