Adsorption and catalytic degradation of organic contaminants by biochar: Overlooked role of biochar's particle size.

Biochar (BC) is considered as a promising adsorbent and/or catalyst for the removal of organic contaminants. However, the relationship between the particle size of BC and its adsorption/catalysis performance is largely unclear. We therefore investigated the influence of particle size on the performance of BC pyrolyzed at 300-900 °C in trichloroethylene (TCE) adsorption and persulfate (PS) activation for sulfamethazine (SMT) degradation. The results showed that high-temperature pyrolyzed BC (BC900) presented superior adsorption capacity for TCE and excellent catalytic activity for PS activation to degrade SMT. Compared to 150-250 µm, 75-150 µm and pristine BC900, 0-75 µm BC900 showed the highest TCE adsorption efficiency, which increased by 19.5-62.3%. Similarly, SMT removal by BC900/PS systems also increased from 24.2% to 98.3% with decreasing BC particle size. However, the catalytic activity of BC after grinding was not significantly improved as expected, indicating the properties of biochar was not only controlled by size effect. Characterization measurements proved that small-sized BC tended to have larger specific surface area, more micropores, higher conductivity, rich graphitic domains and surface redox-active functional groups, thus resulting in an enhanced adsorption and catalytic ability of BC.