Bimetallic FexMny catalysts derived from metal organic frameworks for efficient photocatalytic removal of quinolones without oxidant

Abstract

Quinolones are widely used in the pharmaceutical industry; however, the high residue of these antibiotics has caused serious water quality issues, and their effective removal is still a great challenge. In this work, bimetallic magnetic Fe_xMn_y catalysts are prepared by a facile impregnation method and are efficient for photocatalytic removal of five typical quinolone pollutants without oxidant under simulated light irradiation. The fabricated bimetallic magnetic Fe_xMn_y catalyst with the Fe³⁺/Mn²⁺ ratio of 1 : 1 exhibits a large surface area of 122.5 m² g⁻¹, highly porous structure, rich defects and a covalent metal environment. These fabricated semiconductor catalysts can degrade 98.3% of ciprofloxacin (CIP), 96.0% of ofloxacin (OFL), 91.0% of enrofloxacin (ENR), 92.2% of levofloxacin (LEV), and 93.5% of norfloxacin (NOR) in 30 min without using any oxidant. The magnetic Fe_xMn_y catalysts can be simply recycled using a magnet and maintain high stability, avoiding complex recycling procedures. Even after five cycles, the degradation rate of CIP was still over 92.0%. The degradation performance is far superior to that of most previously reported candidates. The bimetallic Fe_xMn_y catalyst improves the ability to capture sunlight, increases the interface charge transfer rate, and inhibits the recombination of photogenerated electron–hole pairs. In addition, the mechanism and the main intermediates in the photocatalytic degradation of CIP are explored by quenching experiments, electron paramagnetic resonance (EPR) and liquid chromatography-mass spectrometry (LC-MS) analysis. These noble-metal free magnetic Fe_xMn_y catalysts provide a promising opportunity for advanced photocatalytic oxidation technology to treat wastewater.