Characterization of particles collected from combustion systems by water-based sampling

In this paper, sampling of carbon particles based on water interaction is described. The water-sampling allows to selectively collect the fraction of carbonaceous particles having the highest affinity with water. Chemico-physical characterization of the material collected from premixed hydrocarbon flames as water suspension has been performed by optical methods, like light absorption and Laser Induced Fluorescence (LIF), together with Fourier Transform Infrared (FTIR), and Surface Enhanced Raman Spectroscopy (SERS). All of these analysis methods indicate that the material collected in water samples is composed of aromatic-aliphatic linked functionalities and possibly also oxygen atoms. Particle sizes have been investigated by using different methods, each method gives a relevant piece of information even suffering for some limitations due to the very small size of the species to analyze. Dynamic Light Scattering and electrospray-Differential Mobility Analyser furnished the particle size distribution from the measurement of particle diffusivity in water and mobility in an electric field. Time Resolved Fluorescence Polarization Anisotropy, TRFPA, and Fluorescence Correlation Spectroscopy, FCS, have confirmed the size determination by E-DMA and DLS and they have further demonstrated that the laser induced fluorescence detected in water-sample and in flames by in-situ measurements is emitted by particles with mean sizes of about 2 nm.