Defects controlled by acid-modulators and water molecules enabled UiO-67 for exceptional toluene uptakes: An experimental and theoretical study

Abstract A facile defect-engineering approach enabled by introducing monocarboxylic acid modulators (acetic acid, formic acid and benzoic acid) was conducted in this paper. The greatest toluene uptake (480 mg g−1) was obtained on defective UiO-67 synthesized with benzoic acid due to highest missing linker defects and higher compensating linker defects. It is worth mentioning that water molecule exhibited creative promoting effect on the adsorption behavior of defective UiO-67. The original structure of defective UiO-67 was inevitably destroyed under water-containing environment due to the coordination between water molecule and metal cluster. 1H NMR analysis demonstrated that slight loss of BPDC linkers and benzoate linkers due to occupied binding sites, more extra adsorption sites were generated in this process. Furthermore, adsorption mechanisms were studied via density functional theory (DFT) calculations. The synergic effects between π-π, OH-CH3 and OH-π hydrogen bonding strength obviously enforced toluene adsorption, and OH-π exhibited strongest interaction. Moreover, under the circumstance of structural changes due to water molecules, abundant μ3-OH groups were exposed and hydrogen bond interaction was strengthened, which greatly promoted toluene adsorption. Finally, experimental results as well as computational studies forecasted the potentials of defect-tunable MOFs as promising materials in gas adsorption.