Simultaneous photo-degradation of multi persistent herbicide pollutants using MIL-88A under UV or visible light irradiation

A major risk for global water security is the accumulation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) and its degradation product 4-chloro-2-methylphenol (CMP) in water bodies. MIL-88A, an iron-based metal organic framework, has been previously utilized in pilot scale water treatment for single antibiotic degradation, however, a comparative assessment to a benchmark or commercial material is yet to be done. Here we report for the first time a comparison of MIL-88A, for the simultaneous photodegradation of MCPA and CMP with commercial UV active TiO₂ (P25) and ZnO photocatalysts as well as common visible light active lab-pilot scale photocatalysts α-Fe₂O₃ and g-C₃N₄. MIL-88A outperformed commercial UV active TiO₂ (P25) and ZnO photocatalysts and common visible light active α-Fe₂O₃ and g-C₃N₄, demonstrating at least 3 times greater degradation rates than those achieved for each of these conventional photocatalysts. The OH radical generation rate of MIL-88A was over 5 times greater than that observed for TiO₂ (P25), ZnO, α-Fe₂O₃ and g-C₃N₄ under UV and visible light. Furthermore, for the first time an investigation of the degradation of a series of MCPA/CMP solutions of differing relative concentrations in simulated river water has been carried out. Under different pH conditions and in the presence of common ions typically detected in natural water bodies, remarkably MIL-88A was found to degrade 99 % of MCPA/CMP solutions after 120 min under visible light. Conventional catalysts have not been reported for their activity in degradation of pollutant solutions. In these regards, MIL-88A has been demonstrated to be a highly active visible light photocatalyst for the simultaneous degradation of MCPA and CMP in water with clear advantages over conventional commercial photocatalysts.