Thermal oxidation activation of hydrochar for tetracycline adsorption: the role of oxygen concentration and temperature

Poplar hydrochar (RHC) was activated by thermal oxidation (TA-O) in air at 300 degrees C (O300) and in air + N-2 (0.5% O-2) at 500 and 700 degrees C (O500 and O700), respectively, and in N-2 at 300-700 degrees C (N300-N700) as control. Samples characterized by various methods were used to analyze their effect on tetracycline adsorption. The results showed that TA-O greatly increased adsorption capacity q(e), 100 (mg.g(-1), C-0 = 100 mg.L-1) from 6.29 for RHC to 33.32, 96.23 and 60.90 for O300, O500 and O700, respectively. The O300 increased carboxyl and aromaticity whereas little influenced on porosity. The O500, with the highest S-BET and S-micro, enhanced adsorption probably by micropore filling and pi-pi interactions. The O700 fused micropore into mesopore but decreased the S-BET, S-micro and q(e), 100. Thus, thermal oxidation at 500 degrees C and 0.5% O-2 is recommended for hydrochar activation to absorb tetracycline.