Pore structure of soot deposits from several combustion sources

Soot was harvested from five combustion sources: a dodecane flame, marine and bus diesel engines, a wood stove, and an oil furnace. The soots ranged from 20% to 90% carbon by weight and molar C/H ratios from 1 to 7, the latter suggesting a highly condensed aromatic structure. Total surface areas (by nitrogen adsorption using the Brunauer Emmett Teller, BET method) ranged from 1 to 85 m² g^-1. Comparison of the surface area and mesa-pore (pores 2-50 nm) surface area predicted by density functional theory (DFT) suggested that the soot was highly porous. Total mesa-pore volume and surface area ranged from 0.004-0.08 cm³ g^-1 and from 0.33-6.9 m² g^-1, respectively, accounting for up 33% of the BET surface area. The micro-pore volume (pores < 2 nm) calculated from CO₂ adsorption data (by DFT) ranged from 0.0009 to 0.013 cm³ g^-1 and micro-pore surface area was 3.1-41 m² g^-1, accounting for 10-20% of the total intra-particle (mesa-plus micro-pores) pore volume and 70-90% of the total intra-particle surface area. Higher pore volume and surface area values were computed using the Dubinin Radushkevich plot technique; ranging from 0.004-0.04 cm³ g^-1 to 11-102 m² g^-1 for micro- pore volume and surface area, respectively. Comparison of the C/H ratio and the micro-pore structure showed a strong correlation, suggesting a relationship between the condensation of the skeletal structure and micro- porosity of the soot. These data contradict literature reports that soot particles are non-porous and are consistent with recent literature reports that soil organic matter has large micro-pore surface areas. (C) 2000 Elsevier Science Ltd.