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

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, [Zn-4((4)-O)(Ir-A)(2(1-x))(Ir-B)(2x)] (ZnIr-MOF-d(x)), were synthesized by doping heterostructured linker Ir-BH3 into the parent [Zn-4((4)-O)(Ir-A)(2)] (ZnIr-MOF), in which Ir-AH(3) represents [Ir(ppy-COOH)(3)] (ppyCOOH=3-(pyridin-2-yl)benzoic acid) and Ir-BH3 is [Ir(ppy-COOH)(2)(2-pyPO(3)H)] (2-pyPO(3)H(2)=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 (N-2, CO2) or vapor (H2O, 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 2.40eV), corresponding to semiconductors. ZnIr-MOF-d(0.3) exhibits dramatically increased photocatalytic efficiency for dye degradation.