Biochar catalyzed dechlorination – Which biochar properties matter?

Highlights: • Biochar reactivity for catalyzing dechlorination of trichloroethylene (TCE) varies. • The extent of TCE conversion to acetylene is biochar dependent. • Graphite and activated carbon have no catalytic activity. • Graphitic structure and O functional groups are critical. • High surface area and high TCE adsorption to biochar stimulate biochar reactivity. Bone char catalyzed dechlorination of trichloroethylene (TCE) by green rust (iron(II)-iron(III) hydroxide, GR) has introduced a promising new reaction platform for degradation of chlorinated solvents. This study aimed to reveal whether a broader class of biochars are catalytically active for the dechlorination reaction and to identify which biochar properties are the most important for the catalytic activity. Biochars produced by pyrolysis of animal, plant, and sewage waste substrates at 950 °C were prepared for catalytic dechlorination of TCE by GR tested in batch experiments with 0.15 g L⁻¹ biochar, 3.2 g L⁻¹ GR, and ~ 20 µM TCE. The results showed that the biochar substrate significantly affects its catalytic activity, with the highest TCE reduction rate observed for bone and shrimp-based biochars (k ≥ 0.18 h⁻¹), whereas no reactivity was seen for graphite and activated carbon references. Multivariate regression indicated that the biochar catalytic activity is controlled by multiple biochar properties - biochar surface area, TCE sorption, abundance of C–O groups, and pore size are the properties that impact the catalytic activity most. Derivation of biochar reactivity relationship for a broad spectrum of biochars provides a new approach for identifying proper biochar catalysts for pollutant degradation.