Non-thermal plasma synthesis has emerged as a versatile and efficient method for producing metal nanoparticles, including gold (Au), silver (Ag), and platinum (Pt). Unlike thermal plasma techniques, which rely on high temperatures, non-thermal plasma operates at near-ambient conditions, enabling precise control over particle size and morphology while minimizing aggregation. This method leverages the unique properties of plasma—a partially ionized gas containing electrons, ions, and reactive species—to facilitate nanoparticle formation without the need for solvents or high-temperature processing.

The synthesis process begins with the introduction of a metal precursor, often a volatile compound such as gold chloride (AuCl3) or silver nitrate (AgNO3), into a low-temperature plasma reactor. The plasma environment generates energetic electrons that dissociate the precursor molecules, releasing metal atoms. These atoms then undergo nucleation, forming small clusters that serve as seeds for subsequent nanoparticle growth. The absence of high temperatures prevents excessive agglomeration, while the reactive species in the plasma help stabilize the nanoparticles by passivating their surfaces.

One of the key advantages of non-thermal plasma is its ability to control nanoparticle size with high precision. This is achieved by adjusting parameters such as plasma power, precursor concentration, and residence time. For example, increasing the plasma power enhances the dissociation rate of the precursor, leading to a higher concentration of metal atoms and smaller nanoparticles due to increased nucleation sites. Conversely, lower power settings result in slower nucleation and larger particles. The carrier gas, typically argon or helium, also plays a critical role by influencing the plasma chemistry and transport of reactive species. Inert gases like argon provide a stable environment, while reactive gases such as hydrogen can modify surface chemistry and reduce oxidation.

The nucleation and growth mechanisms in non-thermal plasma synthesis differ significantly from conventional methods. In the plasma phase, nucleation occurs rapidly due to the high density of energetic electrons and ions. The charged species in the plasma interact with the nascent nanoparticles, imparting electrostatic stabilization that prevents uncontrolled aggregation. Growth proceeds through the addition of metal atoms or clusters to existing nuclei, with the plasma environment ensuring uniform distribution of reactants. The absence of solvents eliminates the need for surfactants or capping agents, yielding nanoparticles with clean surfaces that are ideal for catalytic applications.

Applications of plasma-synthesized metal nanoparticles span catalysis and biomedicine. In catalysis, the high surface area and defect-rich surfaces of plasma-derived nanoparticles enhance their activity. For instance, platinum nanoparticles produced via non-thermal plasma exhibit superior performance in fuel cell reactions due to their small size and lack of organic contaminants. Similarly, gold nanoparticles synthesized in plasma environments demonstrate exceptional catalytic activity in oxidation reactions. The clean surface chemistry of these nanoparticles allows for direct integration into catalytic systems without post-synthesis treatments.

In biomedicine, the biocompatibility and tunable surface properties of plasma-synthesized nanoparticles make them attractive for therapeutic and diagnostic applications. Silver nanoparticles produced by non-thermal plasma exhibit potent antimicrobial activity, with studies showing effective inhibition of bacterial growth at low concentrations. The absence of chemical stabilizers reduces cytotoxicity, making these nanoparticles suitable for medical devices and wound dressings. Gold nanoparticles, on the other hand, are utilized in biosensing and imaging due to their plasmonic properties and ease of functionalization.

The scalability of non-thermal plasma synthesis further enhances its industrial relevance. Continuous-flow reactors can produce nanoparticles at gram-scale quantities while maintaining tight control over size and composition. This scalability, combined with the method’s environmental benefits—such as reduced chemical waste and energy consumption—positions non-thermal plasma as a sustainable alternative to traditional nanoparticle synthesis techniques.

In summary, non-thermal plasma offers a robust and controllable route for synthesizing metal nanoparticles with applications in catalysis and biomedicine. By leveraging the unique properties of plasma, this method achieves precise size control, minimizes aggregation, and produces nanoparticles with clean surfaces. The absence of solvents and high temperatures simplifies post-processing and enhances the functional performance of the nanoparticles. As research advances, further optimization of plasma parameters and reactor designs will expand the scope of this technique, enabling the production of next-generation nanomaterials with tailored properties.