Effect of oxidation-induced aging on the adsorption and co-adsorption of tetracycline and Cu2+ onto biochar.

The bamboo biochars pyrolyzed at 400 °C and 600 °C (BC400 and BC600) were modified by hydrogen peroxide (H2O2) to obtain the oxidized biochars. Biochar stability and the effect of oxidation treatment on the adsorption and co-adsorption of tetracycline (TC) and Cu2+ onto biochars were investigated. The calculated carbon loss of biochars after oxidation treatment indicated that BC600 presented higher carbon stability than BC400 due to the condensed aromatic structure of biochar. Moreover, oxidation treatment introduced O-containing functional groups on biochar surface, but destructed the aromatic structures of oxidized biochars, which in turn affected the adsorption capacity of biochars for TC and Cu2+. Oxidation treatment obviously enhanced the adsorption of TC and Cu2+ onto BC400 owing to the increase of O-containing functional groups, but significantly decreased TC and Cu2+ adsorption onto BC600 because of the decreased π-π dispersive forces between biochar and adsorbate. The promotion effect of Cu2+ on TC adsorption onto BC400 changed into inhibition effect after chemical oxidation owing to the pore blockage. However, the promotion degree of Cu2+ for TC adsorption onto BC600 was enhanced through oxidation treatment due to electrostatic attraction and complexation. Meanwhile, oxidation treatment reduced the inhibition degrees of TC for Cu2+ adsorption onto biochars, which was attributed to the increased amount of electron-rich groups. The results are helpful for the application of biochars in the soils remediation.