The role of bio-inspired ZnO nanoparticles in the modification of MIL101(Cr) properties for visible light degradation of phenanthrene

MIL-101(Cr) metal-organic frameworks and novel zinc oxide-MIL101(Cr) metal organic frameworks (ZnO-MIL101(Cr)) were prepared by hydrothermal technique at 160 °C and 220 °C for photodegradation of phenanthrene (PHE) in visible light. X-ray diffraction (XRD) analysis indicated a reduction in crystallite sizes of ZnO-MIL101(Cr) when compared to MIL101(Cr). However, incorporation of zinc oxide (ZnO) did not disrupt the MIL101(Cr) structure. ZnO-MIL101(Cr) exhibited high BET surface area (>1000 m²/g) when compared to MIL-101(Cr). These composites have lower bandgaps of ∼3.20 eV, than MIL-101(Cr) (3.5 eV). Optical studies reveal that incorporation of ZnO into MIL101(Cr) delays recombination of electron-hole pairs. These factors lead to ZnO-MIL101(Cr) having similar PHE degradation (98%), however within a shorter time when compared to MIL101(Cr). Catalysts followed the pseudo first-order kinetic model with ZnO-MIL101@220 °C having a rate constant of 2.83 × 10⁻² min⁻¹. This is 2.3× and 1.1× higher than ZnO and the respective MIL101(Cr), correspondingly. Scavenging tests reveal that the hydroxyl radical (•OH) is the primary reactive species for PHE degradation. A degradation mechanism is proposed based on this finding.