Effect of biochar-derived dissolved organic matter on tetracycline sorption by KMnO4-modified biochar

The effect of biochar-derived dissolved organic matters (BDOM) release and metal oxide loading on adsorption and immobilization of tetracycline (TC) by KMnO4 modified biochar remains unclear. To clarify this issue, the experiments of TC adsorption/desorption performances by pristine (BC), KMnO4-modified (MBC), and BDOM-removed residual biochars (RBC and RMBC) were conducted, and the mechanism was further explored by FTIR, XPS and EEMs. The results implied that, the qmax of TC on MBC (262.392 mg/g) increased by over 7 times than that on BC (36.222 mg/g), mainly by improving the micropore structure, O-containing groups and MnOx loading. However, the EEMs results also indicated that MBC had clearly higher production and release of BDOM than BC. Interestingly, after the removal of BDOM, the adsorption of TC on RBC and RMBC exhibited completely different results. The qmax of TC on RBC (34.996 mg/g) decreased by 3.38% compared with that of BC (36.222 mg/g), which was due to the weakened negative charge-assisted H-bond [(–)CAHB] between RBC and TC; while the qmax of TC on RMBC (328.030 mg/g) sharply raised by 25.01% compared with that of MBC (262.392 mg/g), which was mainly due to the enhanced TC complexation with RMBC. Moreover, the surface and internal complexation jointly led to more significant desorption hysteresis of RMBC (release ratio ≤ 18.93%) than that of MBC (release ratio ≤ 22.17%), indicating that RMBC not only shows remarkable adsorption capacity for TC, but also has good adsorption stability. In short, this work took more consideration of the effect of BDOM loss on the adsorption of pollutants during biochar application, which exhibited critical reference value for the practical application of KMnO4 modified biochar.