Page 152 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 8
8.1 Introduction
Due to the well-known bacteria inactivation and good microbial resistance, silver nanoparticles have been widely used as effective antimicrobial agents.1 As demonstrated in Chapter 6 and Chapter 7, in the described experimental configuration, electrons are driven and transported toward the liquid surface to initiate chemical reactions without the usage of reducing agents.2,3 Nanoparticles of controllable properties can be obtained by choosing proper precursors, avoiding toxical chemicals and impurities.4,5 Therefore, this technique can serve as a promising nanofabrication method, especially for bio-application purpose.
The electrochemical production of Ag nanoparticles by means of silver ions reduction at plasma-liquid interphase with dispersants such as fructose and dextran to control the particle size and uniformity was already reported in several works.6,7 A detailed study on the Ag nanoparticles production rate via plasma-assisted process using silver nitrate solution was recently presented by Ghosh et al.8 By means of precise determination of product weight as well as employing simplified reaction model the effects of discharge current value and ionic concentration in liquid on the process kinetics were explained. Yet another important factor, influencing the process characteristics, is the type of the ions participating in electrochemical reaction. This chapter presents the first study of Ag nanoparticles synthesis using Tollens’ reagent as the silver source by the microplasma-assisted method. The advantages of the product obtained from Tollens’ reagent were shown via the investigation on the reaction process and the antibacterial capability.
8.2 Experiment Section
8.2.1 Experimental
Experiments were carried out using the microplasma setup for the liquid-phase nanofabrication (Figure 2.3). A schematical diagram of the reactor is shown in Figure 8.1. In a typical experiment, 10 ml of electrolyte solution (molar concentrations: 0.15-1.5 mM) was filled in the microreactor for plasma treatment and was continuously stirred by a magnetic stirrer at a speed of 200 rpm. Plasma was ignited and sustained by applying 2 kV DC voltage. All experiments were carried out with a constant discharge current of 5.3 mA and operating power of 2.2 W. An argon flow of 50 sccm flow rate was coupled into the capillary tube as the plasma gas. After certain process time (5-30 min), the plasma was switched off. The generated particles were filtered using a 10 kDa centrifugal filter by centrifuging at 3000×g and washed with deionized water for 3 times to remove possible impurities. Finally, the obtained particles were dried under vacuum and quantified using Sartorius BP 211 D electronic scale.
To synthesize Ag nanoparticles, Tollens’ reagent was used as the precursor. Sucrose (C12H22O11, Sigma) was used as the dispersant. The precursor solution containing 0.45 mM silver source without and with 2.25 mM dispersant was treated with plasma for 5 min to produce colloidal Ag nanoparticles. Moreover, AgNO3 solution was carried out in the same reactor arrangement as a reference process. Furthermore, the nanoparticles were purified strictly from residues of silver ions to allow a proper antibacterial test.
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