Facile metal organic framework composites as photocatalysts for lone/simultaneous photodegradation of naproxen, ibuprofen and methyl orange

Abstract

Pharmaceuticals and dyes are known to have endocrine disrupting effects in humans and aquatic animals. As a result of inefficient removal of these micropollutants from wastewater, they have been detected in potable water supplies. In this work, photocatalysts were prepared by incorporating TiO 2 and ZnO into the framework of the MOF, MIL-53(Al), and were used in photodegradation studies of single and binary mixtures of naproxen, ibuprofen and methyl orange. The photocatalyst composites, MIL-53(Al)@TiO 2 and MIL-53(Al)@ZnO, were characterized by XRD, FTIR, BET and FE-SEM, which confirmed attachment of TiO 2 and ZnO nanoparticles to MIL-53(Al). DRS revealed direct optical band gaps of MIL-53(Al)@TiO 2 and MIL-53(Al)@ZnO to be 3.34 eV and 3.24 eV, respectively. Uncoated MIL-53(Al) showed greatest photodegradation efficiency for naproxen (89.5%), closely followed by MIL-53(Al)@TiO 2 (80.3%) and MIL-53(Al)@ZnO (76.6%). Uncoated MIL-53(Al) was also efficient at degrading ibuprofen from single and binary micropollutant systems, with MIL-53(Al)@ZnO performing better than MIL-53(Al)@TiO 2 in both systems. MIL-53(Al)@ZnO was the only photocatalyst that was able to degrade methyl orange in both systems. It was established that a 3:1 ratio of naproxen (mg/L) to MIL-53(Al)@TiO 2 (mg) was optimum for photodegradation, while for ibuprofen and methyl orange in single and binary systems, a 2:1 ratio of total micropollutant (mg/L) to MIL-53(Al)@ZnO (mg) gave the best degradation performance. The photodegradations kinetics were investigated and fitted to zero and pseudo-first/second order models. Recyclability of MIL-53(Al)@TiO 2 for three consecutive photodegradation cycles showed a decrease of only 13.6% in photodegradation efficiency. Experiments conducted with scavengers showed that hydroxyl radicals played a major role in the photocatalytic process photodegradation, and it was found that only 1 h of treatment was sufficient to obtain a considerable COD reduction of 58%. This study provides a promising strategy for uniform MOF loading into ZnO and TiO 2 for binary pharmaceutical and dye wastewater photodegradation treatment. • Composites were prepared using MIL-53(Al), TiO 2 and ZnO for photodegradation studies of micropollutants. • Lone and simultaneous photodegradation of ibuprofen and methyl orange were studied. • Experimental data was fitted to adsorption and photodegradation kinetic models. • MIL-53(Al)@TiO 2 was recyclable over three consecutive naproxen photodegradation cycles. • •OH was generated by all photocatalysts to drive photodegradation.