Surface characterization of diesel engine soot inferred from physico-chemical methods

This paper presents some basic physicochemical characteristics of diesel-exhaust particles. Elementary chemical analysis, particles size distribution, specific surface area and enthalpy of immersional wetting of soot particles in different liquids are evidenced. The resulting data show that soot is a very heterogeneous divided solid from a surface chemical and physical point of view, with a strong dependence on the chemical treatment. The main feature is an unusual strong surface activity or surface energy suggesting that this dusty material may also be biologically dangerous. Moreover, adsorption of non-ionic, ionic and zwitterionic surfactants onto washed soot particles has been investigated so as to provide valuable characteristics of the soot surfaces. The adsorption isotherms and the corresponding electrokinetics data allowed some conclusions to be drawn. This soot surface shows an hydrophilic-hydrophobic partition and is weakly negatively charged in aqueous solution. The negative charge of the surface can be altered by the adsorption of cationic and amphoteric surfactants while adsorption of anionic surfactant increases the negative charge of the surface. sorption of non-ionic surfactants does not influence the charge of the surface.