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 meso-pore (pores 2–50 nm) surface area predicted by density functional theory (DFT) suggested that the soot was highly porous. Total meso-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 (meso-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.