In situ-generated H2O2 with NCQDs/MIL-101(Fe) by activating O2: A dual effect of photocatalysis and photo-Fenton for efficient removal of tetracyline at natural pH

Herein, a novel composite of MIL-101(Fe) loaded with nitrogen doped carbon quantum dots (NCQDs/MIL-101(Fe), denoted as NQML), which can construct dual effect of photocatalysis and photo-Fenton for organic pollutants removal, was prepared by solvent impregnation method. Characterization methods proved that NQML had been synthesized successfully. Additionally, the adding volume of NCQDs could effectively influence the photocatalytic activities of NQML-x composites (x represents the adding volume of NCQDs) for tetracycline (TC) degradation, and NQML-8 exhibited the optimum photocatalytic performance among the studied catalysts upon visible light illumination under natural pH, which can completely degrade TC within 180 min. By comparison, the TC degradation kinetic constant in the system with NQML-8 was as 15.85 and 8.24 folds of that in the NCQDs and MIL-101(Fe) systems, respectively. The mechanism study proved that the enhanced photocatalytic performance of NQML was resulted from the visible light up-conversion property, electron-hole separation and transfer capacity of NCQDs. Meanwhile, NQML could not only produce h + but also lead to in-situ generation of O 2 - and H 2 O 2 by activation of O 2 under visible light. The generated H 2 O 2 could react with Fe(II) in MIL-101(Fe) to produce OH so as to construct a dual effect of photocatalysis and photo-Fenton in TC removal.