Fast and slow adsorption of carbamazepine on biochar as affected by carbon structure and mineral composition.

The influence of carbon structure and mineral composition of biochar on fast adsorption and slow adsorption of ionic organic contaminants (IOCs) is still unclear. This study used carbamazepine (CBZ) as adsorbate, peanut-shell-derived biochars produced at different charred temperatures, and the corresponding acid-washed biochars as adsorbents, to investigate the adsorption kinetics as affected by carbon structure and mineral composition of biochar. The adsorption of CBZ on amorphous (loose) carbon was lower than aromatic (condensed) carbon, but the former mainly contributed to the fast adsorption of CBZ. The hydrophobic and π-π interactions were likely the predominant adsorption mechanisms of CBZ on biochar. The ratio of CBZ fast and slow adsorption fractions (ffast/fslow) significantly reduced after acid-wash treatment of the biochars. The X-ray diffraction and Fourier transform infrared spectra indicated that minerals, including CaCO3, KAlO2, and quartz, were likely responsible for the fast adsorption of CBZ by the hydrogen bonds between CBZ and -OH on the surface of minerals. These results are useful for better understanding of the environmental behavior and prediction of the environmental risks of IOCs in biochar-amended soils.