Boosting peroxymonosulfate activation with a composite of highly dispersed FeS 2 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 FeS 2 anchored on nitrogen-doped biochar (FeS 2 @NBC) was prepared via a hydrothermal process and used for PMS activation to degrade the pollutant tetracycline (TC). Benefiting from in situ growth of FeS 2 on the NBC surface, FeS 2 @NBC alleviated the side effects caused by FeS 2 agglomeration, and the synergistic catalytic effect of the FeS 2 nanoparticles and N-doped biochar resulted in excellent performance. The optimal FeS 2 @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 ( 1 O 2 ) and hydroxyl radical ( center dot OH) were the dominant reactive oxygen species (ROS), the sulfate radical (SO 4 center dot- ) 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, FeS 2 @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.