Synthesis of platinum embedded in amorphous carbon by micro-gap discharge in heptane

•We synthesized platinum nanoparticles in a carbon matrix by discharges in heptane.•Three size distributions of platinum nanoparticles are found.•Each distribution is associated to a specific growth mechanism.•The carbon matrix exhibit a short-range order.

Micro-gap discharges created in heptane between two platinum pin-electrodes produce platinum particles embedded in an amorphous carbon matrix which exhibits a short-range order. The platinum particles can be sorted by size. The largest ones (>100 nm in diameter) are created by emission of droplets from the liquid pool formed when the discharge hits the electrode surface. They are submitted to high stress levels by fast thermal quenching. The smallest ones (<5 nm) are synthesized in the plasma. Nanoparticles with diameters ranging from 10 to 20 nm have structure defects and are synthesized in post-discharge where huge temperature gradients exist. The short-range order observed in carbon extends typically over 3 nm, and it is observed by high-resolution transmission electron microscopy. This ordered structure of carbon (and a fortiori sp3 bonds which are identified by FTIR analyses) is clearly visible around the smallest nanoparticles and it is likely formed at the same location, i.e. in the plasma.