Synthesis of Gold Nanospheres and Nanotriangles by the Turkevich Approach (original) (raw)
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Role of Halide Ions and Temperature on the Morphology of Biologically Synthesized Gold Nanotriangles
Langmuir, 2006
In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disklike structures as compared to other halide ions. The study also suggests that the presence of Clions during the synthesis promotes the growth of nanotriangles, whereas the presence of Iions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.
Turkevich in New Robes: Key Questions Answered for the Most Common Gold Nanoparticle Synthesis
ACS Nano, 2015
This contribution provides a comprehensive mechanistic picture of the gold nanoparticle synthesis by citrate reduction of HAuCl 4 , known as Turkevich method, by addressing five key questions. The synthesis leads to monodisperse final particles as a result of a seed-mediated growth mechanism. In the initial phase of the synthesis, seed particles are formed onto which the residual gold is distributed during the course of reaction. It is shown that this mechanism is a fortunate coincidence created by a favorable interplay of several chemical and physicochemical processes which initiate but also terminate the formation of seed particles and prevent the formation of further particles at later stages of reaction. Since no further particles are formed after seed particle formation, the number of seeds defines the final total particle number and therefore the final size. The gained understanding allows illustrating the influence of reaction conditions on the growth process and thus the final size distribution.
Nanoscale research letters, 2016
The synthesis of gold nanoparticles using citrate reduction process has been revisited. A simplified room temperature approach to standard Turkevich synthesis is employed to obtain fairly monodisperse gold nanoparticles. The role of initial pH alongside the concentration ratio of reactants is explored for the size control of Au nanoparticles. The particle size distribution has been investigated using UV-vis spectroscopy and transmission electron microscope (TEM). At optimal pH of 5, gold nanoparticles obtained are highly monodisperse and spherical in shape and have narrower size distribution (sharp surface plasmon at 520 nm). For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift in plasmon peak due to aggregation and large particle size distribution. The room temperature approach results in highly stable "colloidal" suspension of gold nanoparticles. The stability test through absorption spectroscopy indicates no sign of aggregation for a ...
Biological synthesis of triangular gold nanoprisms
Nature Materials, 2004
The optoelectronic and physicochemical properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chemical methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the extract from the lemongrass plant, when reacted with aqueous chloroaurate ions, yields a high percentage of thin, flat, single-crystalline gold nanotriangles. The nanotriangles seem to grow by a process involving rapid reduction, assembly and room-temperature sintering of 'liquid-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-infrared absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.
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.
The Effect of Gold Salt Concentration in the Production of Gold Nanospheres
Journal of Applied Mathematics and Physics, 2020
The optical, electrical and chemical properties of the gold nanospheres synthesized by different gold concentrations in deionized water through a simple chemical reduction method (Turkevich method) were studied. They were dependent on the variation of the gold salt concentration. The peaks of the surface Plasmon resonance (SPR) absorption band and their wavelengths were detected by a UV-visible spectrophotometer. The diameters of the spherical gold nanoparticles were measured theoretically using UV-visible absorption spectrum analysis of the synthesized gold nanoparticles in colloidal form by calculating the ratio of the absorbance at the surface Plasmon resonance (SPR) peak to the absorbance at the lowest peak closed to SPR peak. The values of the gold nanoparticles diameters were (23 nm) and decreased to (13 nm) as the function of molarity changed in the range (0.1-0.3 mM). They were compared with the results of the transmission electron microscopy (TEM), which was about (15-20 nm) measured by the reference images of Sigma-Aldrich values. The conductivity measurements showed increasing the conductivity with molarity increased. The total dissolved solids (TDS) exhibited increase by linear relation with molarity increasing. The pH-value of the gold nanoparticles solutions varied with the molarity and recorded a bowing value of pH-value at (0.2 mM).
2012
The Turkevich-Frens synthesis starting conditions are expanded, ranging the gold salt concentrations up to 2 mM and citrate/gold(III) molar ratios up to 18:1. For each concentration of the initial gold salt solution, the citrate/gold(III) molar ratios are systematically varied from 2:1 to 18:1 and both the size and size distribution of the resulting gold nanoparticles are compared. This study reveals a different nanoparticle size evolution for gold salt solutions ranging below 0.8 mM compared to the case of gold salt solutions above 0.8 mM. In the case of [Au 3+ ]<0.8 mM, both the size and size distribution vary substantially with the citrate/gold(III) ratio, both displaying plateaux that evolve inversely to [Au 3+ ] at larger ratios. Conversely, for [Au 3+ ]≥0.8 mM, the size and size distribution of the synthesized gold nanoparticles continuously rise as the citrate/gold(III) ratio is increased. A starting gold salt concentration of 0.6 mM leads to the formation of the most monodisperse gold nanoparticles (polydispersity index< 0.1) for a wide range of citrate/gold(III) molar ratios (from 4:1 to 18:1). Via a model for the formation of gold nanoparticles by the citrate method, the experimental trends in size could be qualitatively predicted: the simulations showed that the destabilizing effect of increased electrolyte concentration at high initial [Au 3+ ] is compensated by a slight increase in zeta potential of gold nanoparticles to produce concentrated dispersion of gold nanoparticles of small sizes.
Little Adjustments Significantly Improve the Turkevich Synthesis of Gold Nanoparticles
Langmuir, 2014
In this report, we show how the classical and widely used Turkevich synthesis can be improved significantly by simple adjustments. The gold nanoparticles (AuNPs) produced with the optimized protocol have a much narrower size distribution (5−8% standard deviation), and their diameters can be reproduced with unrivaled little variation (<3%). Moreover, large volumes of these particles can be produced in one synthesis; we routinely synthesize 1000 mL of ∼3.5 nM AuNPs. The key features of the improved protocol are the control of the pH by using a citrate buffer instead of a citrate solution as the reducing agent or stabilizer and optimized mixing of reagents. Further, the shape uniformity of the particles can be improved by addition of 0.02 mM EDTA. While the proposed protocol is as straightforward as the original Turkevich protocol, it is more tolerant against variations in precursor concentration.