Enhanced Fe/Fe cycle by a novel 2D/2D FeS/ACN composite for rapid photo-Fenton degradation of tetracycline-based wastewater.

Fe-based photo-Fenton process is widely used to remove antibiotic in wastewater, however, the synthesis of efficient and stable catalysts to solve the problems of Fe/Fe ions cycling and iron sludge formation of FeS-based catalysts is challenging. Herein, a strategy combining mechanical activation and pyrolysis was proposed to construct a novel FeS/amorphous carbon nitride (2D/2D FeS/ACN) composite with a two-dimensional (2D) stacked structure, where the FeS and ACN connected by Fe-N bonds. The removal rates of oxytetracycline, tetracycline, and chlorotetracycline over 2D/2D FeS/ACN both surpassed 96.0 % within 30 min in the photo-Fenton system, and the photo-Fenton system exhibited a much higher total organic carbon (TOC) removal than the Fenton and photo systems, giving an improvement of rate constant to 3.0 and 6.5 times, respectively. The excellent performance attributed to the fact that the photogenerated electrons were trapped by the sulfur vacancy and directed to the Fe active site for Fe/Fe cycling via a highly-efficient charge transfer channel (Fe-N), resulting in efficiently circulating Fe to Fe. Moreover, due to the involvement of photogenerated electrons in the reduction of Fe to decrease the consumption of S (S and S), 2D/2D FeS/ACN showed superior stability after five cycles, inhibiting the formation of iron sludge. This work provides a new route for the acceleration of Fe/Fe cycling in Fe-based photo-Fenton process for the efficient treatment of tetracycline-based wastewater.