Laser ablation in liquids is a well-established technique for nanoparticle synthesis, offering control over size, composition, and crystallinity. When ionic liquids are used as the medium instead of conventional solvents, unique advantages emerge due to their distinctive physicochemical properties. Ionic liquids are molten salts at or near room temperature, composed entirely of ions, with negligible vapor pressure, high thermal stability, and tunable solvation properties. These characteristics make them ideal for laser ablation processes, where they influence nucleation, growth, and stabilization of nanoparticles in ways that water or organic solvents cannot.

The properties of ionic liquids play a critical role in determining nanoparticle formation dynamics. Their high ionic strength and viscosity significantly alter the cavitation bubble dynamics and plasma plume confinement during laser ablation. The reduced mobility of species in viscous ionic liquids slows nanoparticle growth, leading to smaller and more uniform particle sizes compared to ablation in water. Additionally, the absence of volatile components prevents rapid bubble collapse, which can otherwise cause particle aggregation. The ionic liquid’s polarizability and coordination ability further stabilize nascent nanoparticles by forming protective electrostatic or steric layers around them. For example, imidazolium-based ionic liquids interact with metal nanoparticles through cation-π and van der Waals interactions, preventing agglomeration without the need for additional surfactants.

Surface chemistry of nanoparticles synthesized in ionic liquids is distinct due to the ionic liquid’s ability to form stabilizing layers. Unlike conventional solvents, ionic liquids do not merely act as passive media but actively participate in surface passivation. The anions and cations of the ionic liquid adsorb onto nanoparticle surfaces, creating a charged double layer that prevents coalescence. This results in nanoparticles with surfaces that are partially functionalized by the ionic liquid’s ions, which can be leveraged for further chemical modifications. For instance, gold nanoparticles produced in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide exhibit enhanced stability and reduced oxidation due to the protective bis(trifluoromethylsulfonyl)imide anion layer. Such surface modifications can also influence catalytic activity by altering electronic properties or providing reactive sites.

One of the most significant advantages of using ionic liquids is the suppression of oxidation during and after nanoparticle synthesis. Many metals, such as silver and copper, are prone to oxidation when ablated in water or exposed to air. Ionic liquids, being non-aerobic and non-volatile, create an oxygen-free environment that preserves the metallic state of the nanoparticles. This is particularly important for catalytic applications where oxide layers can degrade performance. For example, copper nanoparticles synthesized in 1-ethyl-3-methylimidazolium acetate remain oxide-free and exhibit higher catalytic activity in CO2 reduction compared to those produced in aqueous media.

Dispersion stability is another key benefit of ionic liquid-mediated laser ablation. Nanoparticles produced in conventional solvents often require additional stabilizing agents to prevent sedimentation or aggregation. In contrast, ionic liquids inherently stabilize nanoparticles through electrostatic and steric mechanisms, eliminating the need for external surfactants. This results in long-term colloidal stability, which is crucial for applications such as catalysis, sensing, and nanofluids. Studies have shown that platinum nanoparticles dispersed in ionic liquids remain stable for months without noticeable aggregation, whereas those in water require continuous agitation or chemical stabilizers.

Catalytic nanoparticles synthesized via laser ablation in ionic liquids demonstrate enhanced performance due to their clean surfaces, controlled size, and unique interfacial chemistry. Palladium nanoparticles produced in 1-butyl-3-methylimidazolium hexafluorophosphate exhibit superior activity in hydrogenation reactions compared to chemically synthesized counterparts. The absence of capping agents allows for greater accessibility of active sites, while the ionic liquid layer can modulate electronic effects that influence catalytic selectivity. Similarly, bimetallic nanoparticles, such as Pt-Au systems, show improved catalytic durability in fuel cell reactions when synthesized in ionic liquids, attributed to the prevention of particle coalescence during operation.

The versatility of ionic liquids allows for customization of nanoparticle properties by selecting different cation-anion combinations. For instance, using ionic liquids with fluorinated anions can enhance the hydrophobicity of nanoparticles, making them suitable for non-polar catalytic reactions. Conversely, hydroxyl-functionalized ionic liquids can produce hydrophilic nanoparticles for aqueous-phase applications. This tunability extends to the synthesis of alloy and core-shell nanoparticles, where the ionic liquid’s reducing and stabilizing properties can be fine-tuned to control composition and morphology.

In summary, laser ablation in ionic liquids offers a robust and flexible route for synthesizing high-quality nanoparticles with tailored properties. The unique physicochemical characteristics of ionic liquids influence particle formation, stabilization, and surface chemistry in ways that conventional solvents cannot match. The resulting nanoparticles exhibit reduced oxidation, improved dispersion stability, and enhanced catalytic performance, making them valuable for a wide range of applications. As research progresses, further exploration of ionic liquid structural variations and their interactions with different metals will expand the possibilities for advanced nanomaterial design.