Mannitol-assisted Fe-O clusters@ZIF-L for Cr(VI) photocatalytic reduction under neutral conditions inspired by Fe-based MOFs photocatalysts

Abstract

Photocatalytic reduction of Cr(VI) in non-acidic circumstances has been an essential problem in the recent research of wastewater treatment. In this study, unique xFe-O@ZIF-L photocatalysts were synthesized with the assistance of mannitol. Fe-O clusters were in-situ encapsulated into the cavities of ZIF-L via this method. The morphology, optical response, electrochemical properties, and Cr(VI) degradability of as-synthesized photocatalysts were investigated. Several experiments demonstrated that the addition of Fe-O clusters considerably expanded the photo-response range while also enhanced photogenerated electron usage through the redox cycling of Fe sites. The micro-mesoporous structure in hybrid samples provides better conditions for mass transfer and exposure of reaction sites. Benefiting from the incorporation of Fe-O clusters, the hybrid material showed improved photocatalytic Cr(VI) reduction ability. After 90 min illumination, the optimum sample with a dosage of 0.5 mg/mL achieved an 86.6% degradation rate of 30 mg/L K2Cr2O7 solution even under neutral conditions. The reaction rate constant of the optimum sample (0.0210 min−1) can be up to 105 times that of the original ZIF-L (0.0002 min−1). This innovative hybrid xFe-O@ZIF-L photocatalysts offer a fresh strategy for the photocatalytic treatment of non-acidic Cr(VI)-containing wastewater.