Defect-engineered indium-organic framework displays the higher CO₂ adsorption and more excellent catalytic...

In order to achieve the high adsorption and catalytic performance of CO₂, the direct self-assembly of robust defect-engineered MOFs is a scarcely reported and challenging proposition. Herein, a highly robust nanoporous indium(III)-organic framework of {[In₂(CPPDA)(H₂O)₃](NO₃)·2DMF·3H₂O}_n (NUC-107) consisting of two kinds of inorganic units of chain-shaped [In(COO)₂(H₂O)]_n and watery binuclear [In₂(COO)₄(H₂O)₈] was generated by regulating the growth environment. It is worth mentioning that [In₂(COO)₄(H₂O)₈] is very rare in terms of its richer associated water molecules, implying that defect-enriched metal ions in the activated host framework can serve as strong Lewis acid. Compared to reported skeleton of [In₄(CPPDA)₂(μ₃-OH)₂(DMF)(H₂O)₂]_n (NUC-66) with tetranuclear clusters of [In₄(μ₃-OH)₂(COO)₁₀(DMF)(H₂O)₂] as nodes, the void volume of NUC-107 (50.7%) is slightly lower than the one of NUC-66 (52.8%). However, each In³⁺ ion in NUC-107 has an average of 1.5 coordinated small molecules (H₂O), which far exceeds the average of 0.75 in NUC-66 (H₂O and DMF). After thermal activation, NUC-107a characterizes the merits of unsaturated In³⁺ sites, free pyridine moieties, solvent-free nanochannels (10.2 × 15.7 Ų). Adsorption tests prove that the host framework of NUC-107a has a higher CO₂ adsorption (113.2 cm³/g at 273 K and 64.8 cm³/g at 298 K) than NUC-66 (91.2 cm³/g at 273 K and 53.0 cm³/g at 298 K). Catalytic experiments confirmed that activated NUC-107a with the aid of n-Bu₄NBr was capable of efficiently catalyzing the cycloaddition of CO₂ with epoxides into corresponding cyclic carbonates under the mild conditions. Under the similar conditions of 0.10 mol% MOFs, 0.5 mol% n-Bu₄NBr, 0.5 MP CO₂, 60 °C and 3 h, compared with NUC-66a, the conversion of SO to SC catalyzed by NUC-107a increased by 21%. Hence, this work offers a valuable perspective that the in situ creation of robust defect-engineered MOFs can be realized by regulating the growth environment.