Structural Transformation of Biochar Black Carbon by C Superstructure: Environmental Implications.

Pyrogenic carbon is widespread in soil due to wildfires, soot deposition, and intentional amendment of pyrolyzed waste biomass (biochar). Interactions between engineered carbon nanoparticles and natural pyrogenic carbon (char) are unknown. This study first employed transmission electron microscopy (TEM) and X-ray diffraction (XRD) to interpret the superstructure composing aqueous fullerene C nanoparticles prepared by prolonged stirring of commercial fullerite in water (nC-stir). The nC-stir was a superstructure composed of face-centered cubic (fcc) close-packing of near-spherical C superatoms. The nC-stir superstructure (≈100 nm) reproducibly disintegrated pecan shell biochar pellets (2 mm) made at 700 °C into a stable and homogeneous aqueous colloidal (<100 nm) suspension. The amorphous carbon structure of biochar was preserved after the disintegration, which only occurred above the weight ratio of 30,000 biochar to nC-stir. Favorable hydrophobic surface interactions between nC-stir and 700 °C biochar likely disrupted van der Waals forces holding together the amorphous carbon units of biochar and C packing in the nC superstructure.