- Elevated temperature and activation increased aromaticity and condensed carbons.
- Activation effects on mildly-treated biochars (<350 °C) were more substantial.
- Activated 350 °C-biochar removed phenanthrene fast and effectively.
- Activated 700 °C-biochar showed stronger binding with phenanthrene.
- Possibility for designing specialized biomass-based adsorbents was proposed
The relationship between physicochemical properties of biochar-based activated carbons and its adsorption was investigated using an aromatic model compound, phenanthrene. Solid-state 13C NMR analysis indicated more condensed aromatic structures when pyrolysis temperature increased or after activation process induced. The increasing aromaticity and non-protonated carbon fraction of the activated biochar treated at 300 °C amounted to 14.7% and 24.0%, respectively, compared to 7.4% and 4.4% for biochar treated at 700 °C. The surface area and pore volume were reduced with the increase in pyrolysis temperature, but increased after activation.
Surface characteristics correlated with the initial sorption rate and equilibrium concentration of phenanthrene, but not with the aromaticity. Solid-state 2H NMR for phenanthrene-d10 saturated activated biochars, however, showed substantial difference in molecular mobility, which might be due to the high aromaticity of the activated biochars. Overall, these results provide an opportunity to manipulate the characteristics of biomass-based adsorbents based on the application needs.