Facile synthesis of Z-scheme g-C3N4@MIL-100 (Fe) and the efficient photocatalytic degradation on doxycycline and disinfection by-products by coupling with persulfate: Mechanism and pathway

In this work, g-C3N4@MIL-100 (Fe) composite was prepared in a facile way. The as-prepared photocatalysts were respectively combined with H2O2 and persulfate for the first time to investigate the degradation efficiency on doxycycline (DOX) under visible light. The detection results of XRD and TEM proved that the materials were successfully synthesized. XPS and FTIR measurements revealed that there was a strong interaction between g-C3N4 and MIL-100 (Fe) in the composite. Degradation experiments showed that g-C3N4@MIL-100 (Fe) coupled with persulfate exhibited higher degradation efficiency (82.8%) for DOX than that combined with H2O2 (69.2%) in 30 min. Through LC-MS analysis of the intermediate products, the degradation pathway of DOX is proposed. DOX was degraded through benzene ring-opening and nucleophilic substitution. Furthermore, the proposed g-C3N4@MIL-100 (Fe) + persulfate system demonstrated efficient degradation efficiency from 61.5% to 69.1%, and satisfactory mineralization efficiency from 55.3% to 65.8% for three disinfection by-products (DBPs). Z-scheme electron transfer path and Fenton-like mechanism were proposed through the experiments of PL detection and active species capturing experiments. Z-scheme electron transfer path is conducive to the accumulation of electrons on the conduction band and holes on the valence band which promotes the separation of photogenerated carriers and makes full use of photogenerated electrons. The activation of persulfate and the production of multiple active species including sulfate radicals promote the catalytic oxidation performance of the system. The results showed that this system is promising in efficiently eliminating antibiotics and DBPs in wastewater.