EPR spectra of aerosol particles formed by pyrolysis of C₃H₈ plus Ar and C₃H₈ plus Fe(CO)₅ plus Ar mixtures in a flow reactor

Abstract

The paper is devoted to electron paramagnetic resonance investigation of nanoparticles and aggregates of nanoparticles formed by pyrolysis of propane as well as a mixture of propane and iron pentacarbonyl. The measurement showed that the pyrolysis of the C₃H₈ plus Ar mixture results in the formation of a carbonaceous phase (phase I), which is quite different from that formed by the C₃H₈ plus Fe(CO)₅ plus Ar mixture (phase II). In phase I there is a strong oxygen effect for as-prepared samples; 75% of spins are accessible to the environmental gas via the interconnected system of microvoids and microchannels. In phase II there was a weak oxygen effect for the as-prepared samples. However, after exposition of phase II to air for 160 h, the properties of phase II have become about the same as that of phase I. A strong oxygen effect was observed for the air-exposed phase II. The line width for phase II increases monotonically with the iron content in the sample. This increase is probably related to the dipole-dipole interactions between the radical centers and the iron atoms distributed throughout the carbon matrix.