MIL-53(Al)/ZnO coated plates with high photocatalytic activity for extended degradation of trimethoprim via novel photocatalytic reactor

Metal organic frameworks (MOFs) have been recently utilized in many environmental applications including photocatalysis. Herein, we report a developed photocatalytic reactor to exploit a novel composite of MIL-53(Al)/ZnO for the degradation of trimethoprim. Zn-free MIL53(Al) was synthesized and employed as a reactive template to obtain MIL-53(Al)/ZnO nanoparticles by hydrothermal method. The analyses by XRD, Raman spectroscopy, XPS, TEM, and EDX affirmed the growth of the desired composite. MIL-53(Al)/ZnO was coated on glass plates using polysiloxane; thereafter, the plates were placed in the photocatalytic reactor. The optimization of the operating parameters was performed by the response surface methodology (RSM) coupled with a central composite design (CCD), yielding optimum pH, flow rate, and initial trimethoprim concentration of 8.4, 5.3 mL/min, and 6.9 mg/L, respectively. The extended operation of the MIL-53(Al)/ZnO plates for five continuous cycles corroborated the stable photocatalytic activity and the prospect of effective reuse. The contributions of different reactive oxidant species (ROS) were elucidated by employing different radical scavengers. Furthermore, The degradation pathway was proposed via the identification of transformation products by liquid chromatography/tandem mass spectrometry (LC-MS/MS). Our present findings emphasize on the merits of employing the photocatalysts in a retained form, which can be an avenue for practical application of photocatalysis.