Abstract
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.
Highlights
The last few decades have witnessed the emergence of nanotechnology as a promising field since it deals with nanoparticles displaying unique optical [1], electronic [2], chemical [3], photoelectrochemical [4] or magnetic properties [5] which render them to be applied for diverse functions
In the present study, taking a lead from a recent report on the effect of high gold chloride concentrations on the size of gold nanoparticles (GNPs) prepared by citrate reduction of gold salt [22], we studied the variation in the size of GNPs produced using tannic acid (TA) as the reducing and stabilizing agent with different initial molarities of HAuCl4 solution and taking TA to HAuCl4 molar ratios in the range of 2:1 to 12:1
With increasing concentration of HAuCl4, a general decrease in the size of GNPs is observed whereas the sizes obtained for HAuCl4 molarities greater than 1 mM present a different pattern; as the concentration of chloroauric acid increased, a general increase in the size of as-synthesized GNPs is observed
Summary
The last few decades have witnessed the emergence of nanotechnology as a promising field since it deals with nanoparticles displaying unique optical [1], electronic [2], chemical [3], photoelectrochemical [4] or magnetic properties [5] which render them to be applied for diverse functions. Owing to the diverse properties exhibited by gold nanoparticles (GNPs) [7], they bear applications in various areas such as cosmetics [8], electronics [9], therapeutics [10,11], imaging [12,13], drug delivery [14,15] and pollution remediation [16,17]. Applications in such diverse fields often require GNPs to be of a particular size and be in large numbers or higher concentrations [18,19]. Exploitation of tannic acid (a plant derived polyphenol) as a reductant
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