Metal-Based Nanoparticle Synthesis from the Rapid Expansion of Carbon Dioxide Solutions

Synthesis of 10 to 500 nm diameter Fe-based nanoparticles is described. Nanometer-sized droplets of iron carbonyl are generated by the rapid expansion of CO₂-based supercritical fluid solutions and are photolyzed in-flight using a UV lamp to remove the carbonyl groups. Solid metal particles are collected electrostatically as coatings or loose particle aggregates on solid surfaces. Upon air oxidation, the iron particles react rapidly to produce an iron oxide phase. Mo-based nanoparticles were similarly produced using a Mo(Co)₆ precursor. FTIR analysis of collected nanoparticles suggests that carbonyl groups are more readily photolyzed from the Fe precursor than from the Mo analog.