Green Synthesis of Silver Nanoparticles

Nanoparticles are structures with dimensions of approximately 1–100 nm. The general advantage of nanoparticles lies in their increased effect mechanism due to the large surface area provided by their small size small. Silver is a free electron system containing an equal number of positive ions and conduction electrons. Silver nanoparticles exhibit characteristic properties such as high electrical conductivity, chemical stability, antibacterial, antifungal and antiviral activity like, and biocompatibility in therapeutic environments row. The nano-scale size of the particles also enhances the penetration potential of silver particles, thereby facilitating better utilization of their properties. AgNPs have a wide range of applications including antimicrobial uses, biosensor materials, composite fibers, cryogenic superconducting materials, cosmetic products and electronic components.

Nanoparticle Synthesis Methods

Physical and chemical production techniques are employed in nanoparticle production. Two approaches are used for synthesis: top-down ‘Down’ and bottom-up ‘Bottom Up’. In top-down approaches, mechanical grinding via various techniques is used to obtain nanoscale materials. In bottom-up approaches, atomic or molecular structures are assembled to reach nanoscale dimensions chemical reactions.

Chemical reduction using various organic and inorganic reducing agents, ultrasonic radiation, laser ablation, sol-gel, and thermal decomposition are commonly used for the synthesis of AgNPs. However issues such as stability, aggregation, morphology, size and size distribution arise with silver nanoparticles produced by these methods. Additionally, these methods require high pressure, temperature, energy and the use of toxic chemicals. Moreover, nanoparticles synthesized chemically are less biocompatible, which limits their applications in biomedical fields. Such problems have created a need for non-chemical, environment friendly methods in nanoparticle production. The Green synthesis approach addresses these issues by enabling low-cost synthesis, simple processing, absence of chemicals, lower energy requirements and environmental friendliness solution.

Green Synthesis

Green synthesis is a bottom-up approach to metal nanoparticle production in which reduction/oxidation reactions are mediated by biological agents place.

The three key components involved in preparing nanoparticles using biological methods are a solvent medium, an eco-friendly reducing agent and a non-toxic stabilizing agent. In green synthesis, bacteria, fungi and plants are used as reducing agents.

Principles of Green Synthesis

1. The solvent used in green synthesis must be biocompatible and non-toxic.
2. An environmentally friendly reducing agent must be used.
3. Stable nanoparticle synthesis must be achieved using non-toxic materials.

Goals of Green Synthesis

• Prevent waste generation
• Limit the use of toxic chemicals
• Maximize energy efficiency
• Ensure the use of renewable raw materials
• Produce final products using environmentally friendly components

Bacteria in Silver Synthesis

The first example of silver production using bacteria was achieved using the Pseudomonas stutzeri AG259 strain. The most widely accepted mechanism of silver biosynthesis involves the presence of nitrate reductase enzyme. Enzyme converts nitrate to nitrite. Electrons are then transferred to silver ions, thereby reducing silver ions to metallic silver (Ag+ to Ag0). It has been reported that Bacillus licheniformis, known to secrete NADPH-dependent enzymes such as nitrate reductase that effectively convert Ag+ to Ag0, exhibits this behavior. There are also cases where silver nanoparticles are biosynthesized without enzymes. Dried Lactobacillus sp. A09 can reduce silver ions through interaction with functional groups on the microbial cell wall.

Fungi in Silver Synthesis

Production of silver nanoparticles using fungi occurs through adsorption of Ag+ ions onto the fungal cell surface followed by reduction of silver ions by enzymes present in fungi. Extracellular enzymes such as naphthoquinones and anthraquinones are believed to be active in the reduction process. Compared to bacterial use, fungi can produce larger quantities of nanoparticles due to their ability to secrete significantly higher amounts of protein, resulting in higher nanoparticle yields. Compared to Plant use, silver production via fungi occurs in a much slower process. This situation time represents a significant disadvantage.

Plants in Silver Synthesis

The use of plant extracts in silver nanoparticle production offers advantages such as easy availability, safety, non-toxicity, the presence of various metabolites capable of reducing silver ions, and the ability to facilitate synthesis at fast. Production occurs through the reduction of silver ions by plant phytochemicals. The main relevant phytochemicals are terpenoids, flavonoids, ketones, aldehydes, amides and carboxylic acids. Although the mechanism varies depending on the phytochemicals involved in each plant, the primary mechanism is always the reduction of ions.