UiO(Zr)-based MOF catalysts for light-driven aqueous pollutant degradation†

Abstract

Zirconium-carboxylate metal–organic frameworks (MOFs) of isoreticular crystal morphologies and contrasting pore sizes are examined to understand the relative influence of linker size (UiO-67 vs. UiO-68) and secondary metal incorporation in photocatalytic aqueous pollutant degradation. Here, iron (Fe) is chosen given its prevalence in wastewater treatment literature and applications, resulting from its low toxicity and ability to activate benign oxidants. UiO-67 with Fe incorporated (Fe-UiO-67) via incipient wetness impregnation demonstrates reduced band gap energy relative to the UiO-67 parent and higher apparent photocatalytic degradation under UV light toward methylene blue dye using hydrogen peroxide (H₂O₂), with catalyst mass-normalized pseudo-first order rate constants of 6.8 ± 0.5 g⁻¹ ks⁻¹ and 2.0 ± 0.3 g⁻¹ ks⁻¹, respectively. While structural characterization via X-ray diffraction remains unperturbed for Fe-UiO-67 before and after reaction, some Fe leaching is evident, as indicated by recharge experiments in the filtrate. Synthesized UiO-68, which possesses increased pore size, also has reduced band gap energy resulting in higher UV-light activation than UiO-67 (pseudo-first order rate constant of 3.5 ± 0.4 g⁻¹ ks⁻¹). Further, UiO-68 demonstrates high stability and exhibits a higher productive H₂O₂ utilization fraction than either of the UiO-67 catalysts. Together, this work clarifies the relative influence of linker modulation and active metal incorporation in UiO-MOFs for pollutant degradation and aqueous applications broadly.