Synergistic Enhancement of Photocatalytic Cr(VI) Reduction Using NH₂-UiO-66/Fe-BiOX (X = Cl/I) Nanocomposites under Visible Light

This study investigates the synergistic photocatalytic activity of mixed bismuth oxyhalides (BiOI and BiOCl) and the critical role of iron doping in enhancing the Cr(VI) reduction. By employing FeCl₃ as both a chloride source and iron dopant precursor, we achieved in situ Fe³⁺ incorporation into bismuth oxyhalides (BiOX; X = Cl/I) during a one-pot coprecipitation synthesis at room temperature. The resulting iron-doped BiOX formed flower-like particles integrated with NH₂-UiO-66, a zirconium-based metal-organic framework (MOF), creating a Z-scheme heterojunction composite. The NH₂-UiO-66/Fe-BiOX composite exhibited exceptional visible-light-driven Cr(VI) reduction, achieving 98% efficiency within 30 min (pH 2, 100 W LED). This performance surpasses that of the NH₂-UiO-66/BiOI reference system (82% efficiency), highlighting the dual role of iron doping and mixed oxyhalide phases in promoting charge separation and suppressing recombination. Mechanistic studies revealed that photogenerated electrons and superoxide radicals (^•O₂^-) act as primary reductants, with the Fe³⁺/Fe²⁺ redox cycle enhancing ^•O₂^- generation via efficient electron transfer.