Intrinsic defects enhanced biochar/peroxydisulfate oxidation capacity through electron-transfer regime

• Content of intrinsic defects in graphitic biochar was regulated by thermal annealing. • Annealed BC exhibited superior efficiency for PDS activation than the pristine one. • Intrinsic defects were identified as the main active site by correlation analysis. • Radicals and singlet oxygen played minor role in the degradation of TC. • Intrinsic defects promoted non-radical oxidation of TC through electron transfer. Enhanced oxidation process via non-radical pathway in biochar (BC)/persulfate system is an important technology in environmental remediation because of its selectivity toward electron-rich organic compounds. The current methods are focused on heteroatom doping to improve the catalytic performance of BC, while the role of intrinsic defects remains unclear. Herein, graphitic biochar (GBC) was firstly prepared and then post annealed to tailor the degree of intrinsic defects. The annealed GBC exhibited a superior activity in the activation of peroxydisulfate (PDS) for tetracycline (TC) degradation than the pristine one. In particular, product derived at 1000 °C (GBC-1000) exhibited the highest catalytic efficiency and degradation rate, which was 2.6-fold of the pristine GBC. The contribution of free radicals ( SO 4 •− , HO•) and singlet oxygen ( 1 O 2 ) to the oxidation process were excluded by electron paramagnetic resonance and quenching test. A positive linear correlation between the pseudo first order rate constants ( k obs ) and carbon defects (I D /I G ) was established, implying the crucial role of intrinsic defects in PDS activation. The analysis of in situ Raman and linear sweep voltammetry (LSV) experiments indicated that intrinsic defects act as active sites by combining PDS molecules to form metastable surface-confined reactive species (BC-PDS*), which involved in the nonradical oxidation path. Together with chronoamperometry tests and electrochemical impedance spectroscopy, it was revealed that the catalytic mechanism of intrinsic defects in PDS activation was a BC-PDS* meditated electron transfer pathway. This study provides a new alternative method for regulating the electron transfer pathway of biochar/peroxydisulfate system.