Thermodynamic Control of Metal Loading and Composition of Carbon Aerogel Supported Pt-Cu Alloy Nanoparticles by Supercritical Deposition

Carbon aerogel (CA) supported Pt-Cu bimetallic nanoparticles were synthesized via simultaneous adsorption of bis(1,1,1,3,5,5,6,6,6-nonafluorohexane-2,4-diiminate)copper (CuDI6) and dimethyl(1,5-cyclooctadiene)platinum(II) (Pt-(cod)me(2)) onto CM in the presence of supercritical carbon dioxide (scCO(2)) and subsequent thermal conversion at ambient pressure. Binary adsorption isotherms of metal precursors on CM in scCO(2) were measured at 35 degrees C and 10.6 MPa by analyzing the fluid phase concentrations in a batch system and could be predicted from pure component adsorption isotherms using ideal adsorbed solution theory (IAST). Homogeneously dispersed Pt-Cu nanoparticles were formed on the surface of the CM via the thermal conversion of the precursors at 400 degrees C. As the Pt/Cu ratio decreased from 97:3 to 21:79, both the mean and the standard deviation of the particle size increased from 2.9 to 7.2 nm and from 1.3 to 3.7 nm, respectively. The alloying of Pt and Cu within the nanoparticles was confirmed via XRD peak shifts, and XPS data indicated that the surfaces of these Pt-Cu alloy nanoparticles were enriched in Pt.