Solvents-dependent selective fabrication of face-centered cubic and hexagonal close-packed structured ruthenium nanoparticles during liquid-phase laser ablation.

Ruthenium nanoparticles (Ru NPs) with face-centered cubic (fcc) structure possess higher catalytic activity than that with hexagonal close-packed (hcp) structure. However, a high temperature above 1800 K is needed for the formation of the metastable fcc Ru phase. In this study, we present a tunable fabrication strategy of fcc and hcp Ru NPs by laser ablation of Ru target in solvents. In methanol, ethanol or acetone organic solvent, both fcc and hcp Ru NPs encapsulated in carbon layer could be obtained, while in deionized water only pure hcp Ru NPs formed. The extreme conditions, that is, the laser-target interaction induced high temperature and high-pressure plasma plume (4000-5000 K, 10-15 GPa) together with its subsequent quenching process, favored the formation of metastable fcc phase. Significantly, the graphite carbon layers sourced from the thermal decomposition of solvent molecules prevent the further evolution of metastable fcc phase into stable hcp phase. Clarification of the solvents and pulse energy effects promise the tunable fabrication of Ru NPs with desired crystallographic structure during laser ablation in liquids (LAL).