Nanoparticle preparation methods are broadly categorized into chemical, physical, and biological approaches, each with distinct advantages and limitations:
Chemical Methods:
- Co-precipitation
- Simple mixing of metal salt solutions with precipitating agents
- Fast, scalable, cost-effective
- Used for: Metal oxide nanoparticles (iron oxide, zinc oxide)
- Challenge: Wide size distributions without precise control
- Sol-Gel Process
- Chemical solution (sol) transforms into integrated network (gel)
- Excellent compositional control and purity
- Used for: Metal oxides, ceramics, composite materials
- Requires: Careful control of hydrolysis and condensation rates
- Hydrothermal/Solvothermal Synthesis
- Reactions in sealed autoclaves at high temperature/pressure
- Produces highly crystalline, uniform nanoparticles
- Used for: Complex oxides, quantum dots, ceramic nanoparticles
- Limitation: Batch processing, long reaction times
- Microemulsion (Reverse Micelle)
- Surfactant-stabilized water droplets in oil act as nanoreactors
- Narrow size distributions possible
- Used for: Metal and metal oxide nanoparticles
- Drawback: Large volumes of surfactants, complex separation
- Chemical Vapor Deposition (CVD)
- Vapor-phase precursors decompose on substrates
- High purity, conformal coatings
- Used for: Carbon nanotubes, thin films, quantum dots
- Requires: Specialized equipment, high temperatures
- Electrochemical Synthesis
- Electric current drives nanoparticle formation
- Good size control, room temperature operation
- Used for: Metal nanoparticles, conducting polymers
- Limited scalability for some applications