Boosting peroxymonosulfate activation with a composite of highly dispersed FeS2 nanoparticles anchored on N-doped biochar for efficient tetracycline degradation

The rational design of inexpensive peroxymonosulfate (PMS) activators with high efficiencies is still in high demand. Herein, a composite with highly dispersed FeS2 anchored on nitrogen-doped biochar (FeS2@NBC) was prepared via a hydrothermal process and used for PMS activation to degrade the pollutant tetracycline (TC). Benefiting from in situ growth of FeS2 on the NBC surface, FeS2@NBC alleviated the side effects caused by FeS2 agglomeration, and the synergistic catalytic effect of the FeS2 nanoparticles and N-doped biochar resulted in excellent performance. The optimal FeS2@NBC/PMS system could degrade 87.6 % of TC within 10 min, and it exhibited adaptability to pH changes and the presence of common inorganic anions. A comprehensive study involving radical scavenging experiments, electron paramagnetic resonance (EPR) spectroscopy, electrochemical tests and XPS analyses revealed that the singlet oxygen (1O2) and hydroxyl radical (•OH) were the dominant reactive oxygen species (ROS), the sulfate radical (SO4•−) and electron transfer were involved in the TC degradation process. Moreover, three degradation pathways were indicated by LC−MS detection, and the toxicities of the degradation intermediates were predicted and evaluated. Finally, FeS2@NBC showed excellent reusability and stability after five cycles of TC degradation. This work provides a reference for designing efficient catalysts that can be combined with metal sulfides and biochar for efficient PMS activation.