Electrochemistry as a Complementary Technique for Revealing the Influence of Reducing Agent Concentration on AgNPs.

Nanomaterials appear to have a vital role in materials science, chemistry, physics and medicine, already finding applications in several fields, including therapeutic, diagnostic and sensors. According to research, the preparation of nanoparticles depends on many experimental conditions, including the choice of reducing agent. Understanding the reasons for the aggregation, shape, surface, and change of size of the nanoparticles after integration into a target application is critical for optimizing performance. Among metallic nanoparticles, silver nanoparticles (AgNPs) are the most studied nanomaterials because of attractive interest due to versatility in synthesis, easy processing, and fast kinetic reaction rate, high thermal and chemical stability.  In addition to this, AgNPs often used have general dispersibility and wide size distribution, which may inevitably generate imprecise results.

Countless procedures have been used for the preparation of AgNPs. However, wet chemical reduction process is one of the most simple and advantageous methods with a better yield compared to physical procedures. Wet chemical methods timeously use three main components, which are metal precursors, reducing agents, and stabilizing/capping agents. In most of the synthesis methods, reducing agents are used in excess with regards to stoichiometric quantities. This makes complications to the process. It is important to mention that the current tendency is to find reaction conditions where the reducing is also in charge of directing the structure and being a stabilizer of the final product. 

Many methods have been used to optimize the synthesis parameters of AgNPs, especially to reduce the size and improve their physico-chemical properties. However, although there are well-established techniques for the monitoring of experimental factors in the synthesis of nanoparticles, it is necessary to investigate simple electrochemical methods that require short reaction times and low cost. Electrochemical methods offer detailed information on the surface structure of shape-controlled metal nanoparticles based on many nanoparticles that are available on the electrode surface. However, scientific research is lacking data on electrochemical methods for investigating the size and aggregation of AgNPs.

Synthesis of Ag nanoparticles in a controlled manner is still difficult challenge because of the lack of design principles that allow accessing the desired structures in a predictive manner. Several reducing agents play a major role in the formation of metal salts into metal nanoparticles which are important parameter selections in shape and size of nanoparticles. Also, the potential application of any nanoparticles is strongly dependent on their stability against aggregation. In most cases, the application of AgNPs is to a certain extent limited by the common problem of dispersion instability against aggregation. This process ended up in the formation of large aggregates that decrease the active surface area and therefore result in a significant decrease in their unique properties. This encouraged our group to investigate electrochemical methods for monitoring AgNPs at different reducing agent concentrations and compare them with other traditional methods. With this point of view, we address the issue of transitions that may occur on the synthesis of Ag nanoparticles and how these methods can be effectively combined and how they can complement each other.  One of the most relevant aspects in the production of AgNPs is that their resultant colour presents high dependence on their size and shape.

In this work, tri-sodium citrate (TSC) was used as a reducing agent in ratios of AgNO3: TSC (1: 5); (1: 10); (1: 50), and (1: 100) to observe the effect of the concentration. The results of different methods for characterization of AgNPs at TSC concentration were compared. The correlation of these methods was reported by studying optical (UV-VIS), electrochemical (CV and DPV) and, microscopic (SEM) properties. The similarities and differences of each method are discussed, especially with respect to the size and the ability to distinguish their degrees of aggregation. While CV and DPV are unable to quantify the size but they can give an idea about how big or small the nanoparticle is. A scanning electron microscope (SEM) is able to give quantitative information on particle sizes. It is shown that it is possible to use voltammetry to get some of the information that is vital and needed on size and aggregation. An experimental setup is investigated to determine optimal synthesis conditions in order to produce small well-dispersed AgNPs of uniform sizes in a simple and cost‐effective way. As the results, the optimal synthesis conditions have been obtained. Since AgNPs are important in various applications, in this work, a correlation to the results obtained was found and with those coming from optical and microscopic methods.

The study did not require ethics clearence.