Silver nanoparticles (AgNPs) are synthesized through chemical reduction of silver salts, typically silver nitrate (AgNO₃), using various reducing agents:
Common Synthesis Methods:
Chemical Reduction: The most widely used approach involves:
- Dissolving silver nitrate in water or organic solvents
- Adding a reducing agent (sodium borohydride, ascorbic acid, citrate, or glucose)
- Controlling pH, temperature, and reagent concentrations
- Using stabilizing agents (PVP, citrate, or surfactants) to prevent aggregation
Green Synthesis: Environmentally friendly methods using:
- Plant extracts containing natural reducing compounds
- Biological organisms (bacteria, fungi, or algae)
- Natural polymers as both reducing and stabilizing agents
Critical Parameters for Quality:
- Size control: Achieved by adjusting reagent ratios, temperature, and reduction kinetics
- Morphology: Spherical, cubic, triangular, or rod-shaped particles obtained by controlling growth conditions
- Surface properties: Stabilizing agents determine dispersion stability and functionality
- Purity: Removing unreacted reagents and byproducts is essential for most applications
Manufacturing Considerations: Traditional batch synthesis of silver nanoparticles faces challenges with:
- Inconsistent particle size distributions
- Poor reproducibility between batches
- Aggregation during scale-up
- Limited control over particle morphology
Advanced continuous flow reactors address these limitations by maintaining uniform reaction conditions, enabling production of high-quality silver nanoparticles with consistent properties from laboratory to manufacturing scale. The precise control over mixing, temperature, and residence time in flow systems produces AgNPs with narrow size distributions and reproducible performance characteristics.