Enhanced 2, 6-dimethylpyrazine removal by catalytic ozonation with legumes biochar: The roles of oxygen- and nitrogen-containing functional groups

Designing efficient and environmentally friendly catalysts is essential to activating ozonation for wastewater remediation. This study prepared soybean biochar (SB), adzuki beans biochar (AB), and mung beans biochar (MB) catalysts using moldy legumes as precursors. The biochars were characterized to investigate the surface characters' effect on ozone activation toward 2, 6-dimethylpyrazine (2,6-DMP) degradation. All prepared samples drastically facilitated the degradation more than with sole ozonation. It was found that at pH 7 with 10 mg L-1 catalysts, the removal rates of 5 mu M 2,6-DMP were 88.3 %, 90.7 %, and 87.3 % by SB, MB, and AB at 30 min, respectively. The surface-area-normalized reaction rate constants (k(obs)/S-BET) showed that AB exhibited the best catalytic activity with the rate of 1.5 x 10(-2) mg center dot m(2)center dot min(-1), which is 2.3- and 23.1-fold higher than that of SB and MB, respectively. Further characterization confirmed that oxygen- (C-O/C = O and -OH) and nitrogen-containing groups (pyridine N and pyrrole N) were crucial to the catalytic degradation, as electron transfer was promoted to form more ROS. In addition, the quenching test and electron paramagnetic resonance (EPR) revealed OH, O-2(-), and O-1(2) as the main reactive oxygen species (ROS) during the heterogeneous catalytic ozonation (HCO), indicating that 2,6-DMP degradation followed the radical and non-radical oxidation pathways. Overall, this study helped to understand the relationship between surface functional groups and intrinsic activity. It also provided a new direction for utilizing agricultural waste.