SYNTHESIS OF GOLD NANOPARTICLES VIA HYDROGEN PEROXIDE REDUCTION AND THEIR CHARACTERIZATION

SYNTHESIS OF GOLD NANOPARTICLES VIA HYDROGEN PEROXIDE REDUCTION AND THEIR CHARACTERIZATION

MelebaevDaulbay

АННОТАЦИЯ

В этой работе, коллоидные наночастицы золота (НЧЗ) были синтезированы путём химического восстановления кислого раствора золотохлороводородной кислоты () в качестве прекурсора с раствором пероксида водорода (H₂O₂) в качестве восстановителя при комнатной температуре 21. В литературе этот метод известен как метод Зигмонди. Оптическая спектроскопия и метод динамического рассеяния света (ДРС) были использованы для получения спектра поглощения и гидродинамических радиусов приготовленных наночастиц золота вместе с их распределением по размерам. Коллоидная стабильность образцов была получена посредством измерений дзета потенциала ().

ABSTRACT In this work, colloidal gold nanoparticles (GNPs) were synthesized by the chemical reduction of an acid solution of tetrachloroauric acid () as a precursor with a solution of hydrogen peroxide (H₂O₂) as a reducing agent at a room temperature 21. In the literature, this method is known as the Zigmond method. UV-Vis spectrometry and Dynamic Light Scattering (DLS) were used to obtain the absorption spectra and the hydrodynamic radii of the prepared gold nanoparticles with their size distribution. The colloidal stability of the samples was obtained via Zeta potential () measurements.

Ключевые слова: наночастицы золота, золотохлороводородная кислота, метод пероксидного восстановления, размер частицы, дзета потенциал, спектр поглощения.

Keywords: gold nanoparticles, tetrachloroauric acid, peroxide reduction method, particle size, zeta potential, absorption spectra.

1.INTRODUCTION

Research in nanotechnology is increasing and is prioritized in developed countries such as the United States, the United Kingdom and Japan. This technology exploits the unique properties of nanoparticles. These are particles ranging from 1 to 100 nm. Depending on the type of material, nanoparticles can be broadly divided into four classes: metallic, semiconductor, magnetic and others [1]. In this work, we focus on metal and, in particular, gold nanoparticles. Gold nanoparticles have attracted extensive attention due to their applications in various fields, such as medicine, biotechnology, catalysis, and nanoscale electronics, and are thus the most intensively studied nanoparticles [2-5]. Great interest in the study of structures of different chemical composition, structure and morphology is caused by extraordinary physicochemical, electromagnetic, optical, mechanical and other properties of nanomaterials that opens wide prospects of their practical applications [6-9,10]. The small size of nanoparticles in the range from 1 to 100 nm determine the uniqueness of their properties [11]. Certainly, the main impetus for this research is that nanoparticles exhibit size-dependent properties that are very different to the constituent bulk material. Implicit in this, is that actual dimensions of the nanoparticles are critical for their properties, and thus suitability for any application. Therefore, for any potential application, it is of extreme importance that suitable techniques are used to characterize the nanoparticles, in order to understand this structure-property relationship. Although the synthesis of gold nanoparticles started approximately sixty years ago, most chemical methods have the disadvantages to produce gold sols with byproducts due to the used reducing agent.

In this work, we measured the sizes and polydispersityindices (PDI) of resulting gold nanoparticles via dynamic light scattering (DLS) spectroscopy. The nanoparticles were also confirmed by UV–Vis spectroscopy and the stability (- zeta potential) of nanoparticles was measured by electrokinetic sonic amplitude (ESA).

2.EXPERIMENTAL

2.1.Material and reagents

For the synthesis of colloidal gold nanoparticles, we used tetrachloroauric acid (HAuCl₄) as gold precursor and hydrogen peroxide (H₂O₂) as a reducing agent. The concentration of HAuCl₄ aqueous solution was 12 mM. We used freshly prepared hydrogen peroxide. The glassware used was all cleaned in a bath of freshly prepared aqua regia solution, and then rinsed thoroughly with de-ionized water before use.

.Instruments

The UV-vis absorption spectra forcolloidal gold nanoparticles were recorded by using UV-vis spectrophotometer (ОКБСпектр, 130063СФ-2000Спектрофотометр). Size and size distribution ofcolloidal gold nanoparticleswere analyzed by the dynamic light scattering method (PHOTOCOR Mini, 130130). The values of zeta potential of colloid gold nanoparticles were measured using zeta potential analyzer (PA field ESA, 0124F.49, PA Partikel - Analytik - Meßgeräte GmbH). To weigh chemicals and reagents, we used microscale (METTLER TOLEDO, MS204S). For the reactions, we used the chemical glassware (KLIN) and the pipette (Thermo Fisher Scientific) to transport a measured volume of liquids.

2.3. Preparation of gold nanoparticles via hydrogen peroxide method

Colloidal gold nanoparticles were synthesized by the Zigmond method. Briefly, tetrachloroauric acid (HAuCl₄) was reduced with hydrogen peroxide. C=12 mM and V=1 mL of the HAuCl₄ aqueous solution and C=1.34 mM and V=1 mL of the H₂O₂ aqueous solution was added at room temperature (T=21⁰C).

3.RESULTS AND DISCUSSION

3.1. Particle size measurements of colloidal gold nanoparticles by dynamic light scattering (DLS)

Dynamic light scattering (DLS) provides a lot of possibilities to obtain information about such properties as size of nanoparticles and diffusion coefficient. The sizes of colloidal gold nanoparticles were measured using a PHOTOCOR Mini 130130 equipped with a 25 mW temperature stabilized diode laser (654 nm) and operating at an angle of 90⁰ and a room temperature. A sample volume 2 ml was used in 10-mm-diameter cuvettes.

The mean hydrodynamic radii of the particles, R_h, were computed from the intensity of the scattered light using the Photocor software package by multiple mode analysis, based on the theory of Brownian motion and the Stokes–Einstein equation:

(1)

Where D is the diffusion coefficient (the primary parameter obtained from DLS measurements), k the Boltzmann constant, T the temperature, and  the solvent viscosity.

The measurement was carried out at room temperature (T=21⁰C) with Photocor software package. Then we used DynaLS software package to analyze the data. The DLS intensity size distribution of synthesized colloidal gold nanoparticles is shown in Figure 1. The size (radius) and polydispersity of synthesized colloidal gold nanoparticles are 93.76 nm and 0.201.

Figure 1. DLS Intensity % vs. Size graph for synthesized colloidal gold nanoparticles

3.2 Absorption spectra of colloidal gold nanoparticles by UV-vis spectroscopy

The crystal lattice of gold, as other metals, is arranged in such a way that valence electrons are able to move throughout the volume of matter; as a result of this, metals have a high electrical conductivity. An alternating electric field of a light beam shifts the conduction electrons and an electric dipole forms on the surface of a nanoparticle, which oscillates with the field frequency of the incident light. This dipole oscillating near the surface of a nanoparticle is called the surface plasmon. A surface plasmon appears if a nanoparticle is much smaller than the length of the incident light.

The coincidence of the oscillation frequency of the surface plasmon and the oscillation frequency of the incident light causes a resonant absorption and scattering of light, which is called the surface plasmon resonance (SPR).

The absorption of light by a substance is calculated according to the Lambert-Behr law:

(2)

Here,J₀and J are the intensities of the light before and after passing through a layer of thickness d(cm) with a concentration С (mol/l). The ratio and the value ε are called the extinction and the molar extinction coefficient, respectively.

Thus, a specific absorption band of the solution arises in the visible region due to the small particle size. A plasmon absorption band arises if the particle size becomes less than the mean free path of electrons in a bulk metal. Only for three metals (Au, Ag, and Cu) the plasmon frequency of the nanoparticles is shifted from the UV to the visible region of the spectrum; for all others, it is shifted to the UV region [12].

UV-vis absorption spectrum of synthesized colloidal gold nanoparticles is shown in Figure 2. UV-vis absorption spectrum was recorded from 200 nm to 900 nm using a СФ-2000Спектрофотометр with an interval of 0.1 nm with a quartz glass 10 mm cuvette. The values of resonant plasmon absorption and Lambda max (λ_max) in the UV-vis spectrum are 1.07 and 642.4 nm.

Figure 2. Absorption spectrum of synthesized colloidal gold nanoparticles

3.3 Zeta potential measurements of colloidal gold nanoparticles by electrokinetic sonic amplitude (ESA)

The effective charge or zeta potential of particles is classically measured as the speed at which they move in an external electric field (electrophoresis) by applying a direct current. In this case, the particles start moving towards one of the electrodes. The actual parameter that is measured is their dynamic mobility. The PA device employs alternating current to force the charged particles to move. In this case, they oscillate with the frequency of the external electric field. The oscillation of matter at frequencies of 200 KHz to 2 MHz produces sound waves with a net impulse transfer as long as there is sufficient density difference between the particles and the surrounding solvent. The amplitude of this wave or the electrokinetic sonic amplitude (ESA) is proportional through proven theory to the dynamic mobility and thus to the zeta potential of the particles in the dispersion [12]. The zeta potential value of synthesized colloidal gold nanoparticles is -8.4 mV.

4.CONCLUSION

At nanoscale, gold exhibits remarkably unusual physical, chemical and biological properties. In this research, we have applied the hydrogen peroxide reduction of tetratetracloroauric acid in an aqueous medium to obtain colloidal gold nanoparticles. To determine the size and thepolydispersity of the nanoparticles we have used dynamic light scattering method, while to measure the zeta potential we have utilized the electrokitenic sonic amplitude method. The absorption spectrum of the prepared sample was obtained using the UV-visible spectrophotometer. The sample showed a surface plasmon resonance peak, which proves the formation of GNPs.

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