Stabilisation of FeCoNiCuPt high-entropy alloy nanoparticles by surface capping.

High-entropy alloys (HEA) are a distinct class of materials made up of multiple principal components (≥5) in near-equimolar ratios, resulting in extraordinary properties, including high catalytic activity, corrosion and oxidation resistance, and tunable magnetic properties. In nanoparticle form, these alloys are highly promising for a variety of advanced applications, such as catalysis, magnetic storage, and biomedical technology [Zoubi et al., Nano Energy, 2023, 110, 108362]. This study used an isolating-medium-assisted solid-state reaction to synthesise FeCoNiCuPt HEA nanoparticles with ultrafine NaCl particles as the isolating medium [Meng et al., Mater. Adv., 2024, 5, 719]. The nanoparticles were stabilised with a range of hydrophobic and hydrophilic capping agents, such as polyethylenimine, polyvinylpyrrolidone, stearic acid, octadecylamine, etc., introduced before or after the removal of the isolating medium. The formation of single-phase nanoparticles and the chemical composition of FeCoNiCuPt was validated using X-ray diffraction and energy-dispersive X-ray spectroscopy. Transmission electron microscopy and dynamic light scattering were used to determine particle sizes, effective capping agent thickness, and particle stability. The results highlight the successful synthesis of the FeCoNiCuPt nanoparticles, the effect of capping agents on the control of particle size, and the stability of capped-nanoparticle suspensions in water and organic solvents. The study emphasises the importance of selecting the appropriate capping agent to maintain nanoparticle stability and prevent agglomeration.