Tuning the Trade-Off between Ethane/Ethylene Selectivity and Adsorption Capacity within Isoreticular Microporous Metal-Organic Frameworks by Linker Fine-Fluorination.

The pore dimension and surface property directly dictate the transport of guests, endowing diverse gas selective adsorptions to porous materials. It is highly relevant to construct metal-organic frameworks (MOFs) with designable functional groups that can achieve feasible pore regulation to improve their separation performances. However, the role of functionalization in different positions or degrees within framework on the separation of light hydrocarbon has rarely been emphasized. In this context, four isoreticular MOFs (TKL-104-107) bearing dissimilar fluorination are rationally screened out and afforded intriguing differences in the adsorption behavior of C2 H6 and C2 H4 . Ortho-fluoridation of carboxyl allows TKL-105-107 to exhibit enhanced structural stabilities, impressive C2 H6 adsorption capacities (>125 cm3 g-1 ) and desirable inverse selectivities (C2 H6 over C2 H4 ). The more modified ortho-fluorine group and meta-fluorine group of carboxyl have improved the C2 H6 /C2 H4 selectivity and adsorption capacity, respectively, and the C2 H6 /C2 H4 separation potential can be well optimized via linker fine-fluorination. Meanwhile, dynamic breakthrough experiments proved that TKL-105-107 can be used as highly efficient C2 H6 -selective adsorbents for C2 H4 purification. This work highlights that the purposeful functionalization of pore surfaces facilitates the assembly of highly efficient MOF adsorbents for specific gas separation.

Modulation of Hierarchical Pores in Metal-Organic Frameworks for Improved Dye Adsorption and Electrocatalytic Performance.

The hierarchical porous metal-organic framework (HP-MOF) has emerged as a hot topic in porous materials in consideration of their advantages in storage capacity and catalysis performance. Herein, we report the construction and property investigation of a series of HP-MOFs. A series of isoreticular microporous MOFs featuring the pacs topology network based on 2,4,6-tris(4-pyridyl)-1,3,5-triazine and different carboxylic acid ligands are found to be potential precursors to construct HP-MOFs. Through the decarboxylation of carboxylate ligands at high temperatures, a hierarchical porous structure could be obtained with the reservation of a crystalline framework. The formation of hierarchical pores is highly dependent on the structural and component nature (carboxylate ligands and metal centers) of the pristine MOF and the pyrolysis conditions (temperature and treatment time), indicating the highly tunable hierarchical pore characteristic of the HP-MOFs. By taking advantage of the increased pore volume and more exposed activation sites, the HP-MOFs reveal enhanced anionic dye adsorption capacity (800 mg·g-1 for Congo red and 140 mg·g-1 for methyl blue) and catalytic activity toward electrocatalytic oxygen reduction reaction (overpotential of 0.302 V at a current density of 10 mA·cm-2, 51 mV lower than that of the pristine MOF).

Manipulating spatial alignment of donor and acceptor in host-guest MOF for TADF.

Thermally activated delayed fluorescence (TADF) was achieved when electron-rich triphenylene (Tpl) donors were confined to a cage-based porous metal-organic framework (MOF) host (NKU-111) composed of electron-deficient 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (Tpt) acceptor as the ligand. The spatially separated donor and acceptor molecules in a face-to-face stacking pattern generated strong through-space charge transfer (CT) interactions with a small energy splitting between the singlet and triplet excited states (∼0.1 eV), which enabled TADF. The resulting Tpl@NKU-111 exhibited an uncommon enhanced emission intensity as the temperature increased. Extensive steady-state and time-resolved spectroscopic measurements and first-principles simulations revealed the chemical and electronic structure of this compound in both the ground and low-lying excited states. A double-channel (T1, T2) intersystem crossing mechanism with S1 was found and explained as single-directional CT from the degenerate HOMO-1/HOMO of the guest donor to the LUMO+1 of one of the nearest acceptors. The rigid skeleton of the compound and effective through-space CT enhanced the photoluminescence quantum yield (PLQY). A maximum PLQY of 57.36% was achieved by optimizing the Tpl loading ratio in the host framework. These results indicate the potential of the MOFs for the targeted construction and optimization of TADF materials.

Two porous Ni-MOFs based on 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine showing solvent determined structures and distinctive sorption properties toward CO2 and alkanes.

By regulating the solvent used for synthesis, two porous Ni-MOFs, namely {[Ni3(BTC)2(TPT)2/3(H2O)4.08(MeOH)0.92]·2DMF·0.5H2O·0.5MeOH}n (1) and {[Ni3(BTC)2(TPT)2(H2O)6]·6DMF}n (2) (H3BTC = 1,3,5-benzenetricarboxylic acid, TPT = 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine, DMF = N,N-dimethylformamide, and MeOH = methanol) were obtained. Compound 1 reveals a rigid 3D framework, while compound 2 shows a flexible 3-fold interpenetrated framework. Compound 1 exhibits a selective adsorption of CO2 due to the sieving effect of the rigid framework containing two types of cages with small apertures. Noteworthily, the flexible compound 2 displays an obviously guest-induced structural transformation. The desolvated compound 2 reveals a much higher capacity toward CO2 and n-C4H10 than those of N2 CH4, C2H6 and C3H8.