Radiolytically induced formation and optical absorption spectra of colloidal silver nanoparticles in supercritical ethane

Colloidal silver nanoparticles were synthesized in supercritical ethane at 80 degreesC and 80-120 bar, with methanol as cosolvent. Solvated electrons, produced by a pulse of 20 MeV electrons, reduced the silver ions. The time -resolved technique of pulse radiolysis was employed to characterize the re duction products and colloidal metallic particles. The absorption spectra o f small silver clusters (Ag-2(+), Ag-3(+), Ag-4(2+), etc.) were detected at short times after the pulse. Colloidal metallic silver particles were iden tified by their characteristic plasmon absorption at 1-10 s after the pulse . Colloidal particles are stable for hours in supercritical ethane. The par ticles are less than 10 nm in diameter. Their size was determined using tra nsmission electron microscope after precipitation from the solution.