Defective Metal–Organic Frameworks Incorporating Iridium‐Based Metalloligands: Sorption and Dye Degradation Properties

Abstract

Artificial control and engineering of metal-organic framework (MOF) crystals with defects can endow them with suitable properties for applications in gas storage, separation, and catalysis. A series of defective iridium-containing MOFs, [Zn₄ (μ₄ -O)(Ir-A)_2(1-x) (Ir-B)_2x ] (ZnIr-MOF-d_x ), were synthesized by doping heterostructured linker Ir-BH₃ into the parent [Zn₄ (μ₄ -O)(Ir-A)₂ ] (ZnIr-MOF), in which Ir-AH₃ represents [Ir(ppy-COOH)₃ ] (ppyCOOH=3-(pyridin-2-yl)benzoic acid) and Ir-BH₃ is [Ir(ppy-COOH)₂ (2-pyPO₃ H)] (2-pyPO₃ H₂ =2-pyridylphosphonic acid). Samples with different degrees of defects were characterized by SEM, IR and NMR spectroscopy, powder XRD measurements, and thermal and elemental analyses. ZnIr-MOF-d_0.3 was selected as a representative for gas (N₂ , CO₂ ) or vapor (H₂ O, alcohol) sorption studies. The results demonstrate that defective ZnIr-MOF-d_0.3 possesses multiple pore size distributions, ranging from micro- to mesopores, unlike the parent material, which shows a uniform micropore distribution. The hydrophilicity of the interior surface is also increased after defect engineering. As a result, ZnIr-MOF-d_0.3 shows an enhanced adsorption capability toward n-butanol, relative to that of the parent compound. Optical studies reveal that both ZnIr-MOF and ZnIr-MOF-d_0.3 have low band gaps (2.35 and 2.40 eV), corresponding to semiconductors. ZnIr-MOF-d_0.3 exhibits dramatically increased photocatalytic efficiency for dye degradation.