“Green” Synthesis of Metallic Nanoparticles by Sonoelectrochemical and Sonogalvanic Replacement Methods

The main features of the “green” synthesis of metallic nanoparticles (MNPs) by the sonoelectrochemical methods are manufacturability, environmental friendliness, and the possibility of controlling the geometry of the forming particles. The electrochemical reduction technique allows efficiently designing the metal nanoparticles and provides the control of the content of components of bimetallic nanoparticles, as well as minimizing the number of precursors in working solutions. Due to the generation of turbulence, microjets, and shock waves, ultrasound increases mass transfer and formation of radicals in aqueous solutions and, accordingly, accelerates the processes of nucleation and growth of MNPs. Therefore, this hybrid method, which combines electrolysis and ultrasound, has attracted the interest of researchers in the last two decades as one of the most promising techniques. The present work presents a short analysis of the reference literature on sonoelectrochemical synthesis of metallic and bimetallic nanoparticles. The main factors influencing the geometry of nanoparticles and their size distribution are analyzed. The use of pulsed ultrasound and pulsed current supply during sonoelectrochemical synthesis is especially effective in designing MNPs. Emphasis is placed on the role of surfactants in the formation of MNPs and sacrificial anodes in providing the algorithm: “anodic dissolution-electrochemical reduction of metal-nucleation and formation of МNPs.” It is noted that ultrasound allows synthesizing the MNPs and M1M2NPs during the galvanic replacement, and an analogy of the formation of nanoparticles by sonogalvanic replacement and sonoelectrochemical method is shown.

Sonoelectrochemical Synthesis of Antibacterial Active Silver Nanoparticles in Rhamnolipid Solution

The results of studies of the synthesis of AgNPs colloidal solutions by cyclic voltammetry (E from +1.0 to −1.0 V) in rhamnolipid (RL) solutions and the use of soluble anodes in the ultrasound field (22 kHz) are presented. It is shown that the algorithm of anodic dissolution—reduction of Ag(I)—nucleation, and formation of AgNPs makes it possible to obtain nanoparticles with the size from 1 nm to 3 nm. It was found that with an increase in the RL concentration from 1 g/L to 4 g/L, the anodic and cathodic currents increase as well as the rate of AgNPs formation, respectively. The rate of nanoparticles formation also increases with an increase in temperature from 20°C to 60°C, and it corresponds to the diffusion-kinetic range of action of this factor. Moreover, the size of AgNPs depends little on the temperature. The character of the UV-Vis pattern of AgNPs colloidal solutions in RL (with an absorption maximum of 415 nm) is the same over a wide range of nanoparticle concentrations. The curves practically do not change in time, which indicate the stability of anodic and cathodic processes during prolonged sonoelectrochemical synthesis. The cyclic voltammetry curves practically do not change in time, which indicate the stability of anodic and cathodic processes during prolonged sonoelectrochemical synthesis. The antimicrobial activity of synthesized AgNPs solutions to strains of Escherichia coli, Candida albicans, and Staphylococcus aureus was established.

Sonoelectrochemical synthesis of silver nanoparticles in polyvinylpyrrolidone solutions

The results of investigations of the influence of main parameters (surfactant concentration and temperature) on the synthesis of silver nanoparticles (AgNPs) by the sonoelectrochemical method in polyvinylpyrrolidone (PVP) solutions by cyclic voltammetry (CVA) are presented. It is shown that the ultrasonic field (22 kHz) leads to an increase in the anodic and cathodic currents by ~30 %. A scheme of the AgNPs formation has been proposed, which includes the following main processes: 1) dissolution of sacrificial silver anodes at E = 0.2...1.0 V with the formation of [AgPVP]+ complex ions; 2) cathodic and sonochemical reduction of the latter to Ag(0); 3) formation of AgNPs. It has been established that with an increase in PVP concentration from 1 to 4 g·L-1, the anodic and cathodic currents decrease by 40–60 %. The formation rate of AgNPs also decreases. The growth of anodic and cathodic currents and the formation rate of nanoparticles in the range of 20…60 °C corresponds to the diffusion-kinetic action of the temperature factor. The CVA curves practically do not change in time, which indicates the stability of anodic and cathodic processes at prolonged sonoelectrochemical synthesis. The character of the UV-Vis spectra of AgNPs colloidal solutions in PVP with the 405…410 nm absorption maximum is the same in a wide range of nanoparticle concentrations.

Sonoelectrochemical Synthesis of Silver Nanoparticles in Sodium Polyacrylate Solution

The paper shows the effectiveness of a “green” synthesis of silver nanoparticles (AgNPs) in sodium polyacrylate (NaPA) solutions by sonoelectrochemical method using silver sacrificial anodes. Using the cyclic voltammetry in the ultrasonic field in the range of E from 1.0 to -1.0 V, the temperature and NaPA concentration are the main parameters influencing the rate of synthesis and the size of AgNPs. As these parameters increase, the rate of nanoparticle synthesis increases. According to TEM studies, with increasing temperature and decreasing NaPA concentration, there is a tendency to increase the size of AgNPs. However, in all of the cases, the size of AgNPs does not exceed 30 nm. Using the UV–Vis spectroscopy, it was found that the position of the absorption peak at c.a. 500 nm, corresponding to the silver nanoparticles, is practically not shifted during numerous cycles. This fact may indicate the stability of sonoelectrochemical synthesis of AgNPs in time. Synthesized AgNPs revealed high antibacterial activity against gram-positive and gram-negative strains of typical pathogens of nosocomial infections, demonstrating the prospect of using sonoelectrochemical technique for obtaining silver colloids as a component of bactericidal drugs.