Construction of Bi12O17Cl2/ZnO-CN Z-scheme photocatalyst with ZIF-8 as precursor to remove antibiotics and Cr(VI) under visible light: Optimization, mechanism and degradation path

Abstract

In this work, Bi12O17Cl2 and ZIF-8 were synthesized via a facile in-situ precipitation method, while ZnO-CN was obtained through the pyrolysis of ZIF-8. Then, a novel Bi12O17Cl2/ZnO-CN composite catalyst with Z-scheme heterojunction was prepared by mechanical mixing-low temperature activation method. When the ZnO-CN is pyrolyzed at 550 ℃ and accounts for 10 wt% in the Bi12O17Cl2/ZnO-CN composite, the composite exhibited a significantly higher degradation rate for levofloxacin hydrochloride (LVX) (94.50%) compared to Bi12O17Cl2 (67.30%) and ZnO-CN (36.80%), while also achieving a high removal rate of Cr(VI) under acidic conditions (92.00%). And the toxicity of LVX to wheat decreased significantly after photocatalytic degradation. Meanwhile, the Bi12O17Cl2/ZnO-CN has good universality, salt resistance and reuse stability. The experimental results of sample characterization show that the improved photocatalytic performance of Bi12O17Cl2/ZnO-CN composite can be attributed to the high-efficiency separation of electron-hole pairs (e--h+), enhanced light absorption in the visible region, increased specific surface area and active sites. Both the free radical capture experiment and electron paramagnetic resonance (EPR) test indicate that •O2- and h+ are the primary active species in the process of degrading LVX by Bi12O17Cl2/ZnO-CN. Combined with mechanism exploration experiment and iquid chromatography-mass spectrometry (LC-MS) analysis, a possible direct Z-scheme heterojunction electron transfer mechanism and photocatalytic degradation pathways for LVX was proposed. This work enhances the photocatalytic performance of Bi12O17Cl2 and provides an idea for antibiotic or Cr(VI) wastewater treatment.