High-throughput computational screening of Cu-MOFs with open metal sites for efficient C_2H_2/C_2H_4 separation

Cost effective separation of acetylene(C_2H_2)and ethylene(C_2H_4)is of key importance to obtain essential chemical raw materials for polymer industry.Due to the low compression limit of C_2H_2,there is an urgent demand to develop suitable materials for efficiently separating the two gases under ambient conditions.In this paper,we provided a high-throughput screening strategy to study porous metal-organic frameworks(MOFs)containing open metal sites(OMS)for C_2H_2/C_2H_4 separation,followed by a rational design of novel MOFs in-silico.A set of accurate force fields was established from ab initio calculations to describe the critical role of OMS towards guest molecules.From a large-scale computational screening of 916 experimental Cu-paddlewheel-based MOFs,three materials were identified with excellent separation performance.The structure-performance relationships revealed that the optimal materials should have the largest cavity diameter around 5-10?and pore volume in-between 0.3-1.0 cm^3 g^(-1).Based on the systematic screening study result,three novel MOFs were further designed with the incorporation of fluorine functional group.The results showed that Cu-OMS and the-F group on the aromatic rings close to Cu sites could generate a synergistic effect on the preferential adsorption of C_2H_2 over C_2H_4,leading to a remarkable improvement of C_2H_2 separation performance of the materials.The findings could provide insight for future experimental design and synthesis of high-performance nanostructured materials for C_2H_2/C_2H_4 separation.

A pillared-layer metal-organic framework for efficient separation of C_(3)H_(8)/C_(2)H_(6)/CH_(4) in natural gas

Metal-organic frameworks(MOFs)have great potentials as adsorbents for natural gas purification.However,the trade-off between selectivity and adsorption capacity remains a challenge.Herein,we report a pillared-layer metal-organic framework Ni(HBTC)(bipy)for efficiently separating the C_(3)H_(8)/C_(2)H_(6)/CH_(4) mixture.The experimental results show that the adsorption capacity of C_(3)H_(8) and C_(2)H_(6) on Ni(HBTC)(bipy)are as high as 6.18 and 5.85 mmol·g^(-1),while only 0.93 mmol·g^(-1) for CH_(4) at 298 K and 100 kPa.Especially,the adsorption capacity of C_(3)H_(8) at 5 kPa can reach an unprecedented 4.52 mmol·g^(-1) and for C_(2)H_(6) it is 1.48 mmol·g^(-1) at 10 kPa.The ideal adsorbed solution theory predicted C_(3)H_(8)/CH_(4) selectivity is as high as 1857.0,superior to most of the reported materials.Breakthrough experiment results indicated that material could completely separate the C_(3)H_(8)/C_(2)H_(6)/CH_(4) mixture.Therefore,Ni(HBTC)(bipy)is a promising material for separation of natural gas.

Screening and design of COF-based mixed-matrix membrane for CH_(4)/N_(2) separation

Membrane separation is a high-efficiency,energy-saving,and environment-friendly separation technology.Covalent organic framework(COF)-based mixed-matrix membranes(MMMs)have broad application prospects in gas separation and are expected to provide new solutions for coal-bed methane purification.Herein,a high-throughput screening method is used to calculate and evaluate COF-based MMMs for CH_(4)/N_(2) separation.General design rules are proposed from thermodynamic and kinetic points of view using the computation-ready,experimental COFs.From our database containing 471,671 generated COFs,5 COF membrane materials were screened with excellent membrane selectivities,which were then used as the filler of MMMs for separation performance evaluation.Among them,BAR-NAP-Benzene_CF_(3) combined with polydimethylsiloxane and styrene-b-butadiene-b-styrene show high CH_(4) permeability of 4.43×10^(-13) mol·m·s^(-1)·Pa^(-1)·m^(-2) and high CH_(4)/N_(2) selectivity of 9.54,respectively.The obtained results may provide reasonable information for the design of COF-based membranes for the efficient separation of CH_(4)/N_(2).

A thiophene-containing covalent triazine-based framework with ultramicropore for CO2 capture

In this work, a 2D covalent triazine-based framework was prepared by using 1,3-dicyanobenzo[c]thiophene（DCBT） as monomer to effectively capture CO. The resulting CTF-DCBT was characterized by FT-IR, XPS, PXRD, elemental analysis, SEM, TEM, and Nadsorption-desorption.The results indicate that CTF-DCBT is partially crystalline and has ultramicropore（6.5 A?） as well as high heteroatom contents（11.24 wt% and 12.61 wt% for N and S, respectively）. In addition, the BET surface area and total pore volume of CTF-DCBT are 500 m/g and 0.26 cm/g, respectively. CTF-DCBT possesses excellent thermal stability（450 °C） and chemical stability towards boiling water, 4 M HCl, and 1 M Na OH.The COadsorption capacity of CTF-DCBT is 37.8 cm/g at 1 bar and 25 °C. After six adsorption-desorption cycles, there is no obvious loss of COuptake observed. Due to the ultramicropore and high heteroatom contents, CTF-DCBT has high isosteric heats of adsorption for COand high selectivities of COover Nand CH. At 25 °C, the CO/Nand CO/CHselectivities are 112.5 and 10.3, respectively, which are higher than those of most POFs. Breakthrough curves indicate that CTF-DCBT could effectively separate CO/Nand CO/CHmixtures.

Large-scale simulations of CO_(2) diffusion in metal-organic frameworks with open Cu sites

Understanding CO_(2) diffusion behavior in functional nanoporous materials is beneficial for improving the CO_(2) adsorption,separation,and conversion performances.However,it is a great challenge for studying the diffusion process in experiments.Herein,CO_(2) diffusion in 962 metal–organic frameworks(MOFs)with open Cu sites was systematically investigated by theoretical methods in the combination of molecular dynamic simulations and density functional theory(DFT)calculations.A specific force field was derived from DFT-D2 method combined with Grimme’s dispersion-corrected(D2)density functional to well describe the interaction energies between Cu and CO_(2).It is observed that the suitable topology is conductive to CO_(2) diffusion,and 2D-MOFs are more flexible in tuning and balancing the CO_(2) adsorption and diffusion behaviors than 3D-MOFs.In addition,analysis of diffusive trajectories and the residence times on different positions indicate that CO_(2) diffusion is mainly along with the frameworks in these MOFs,jumping from one strong adsorption site to another.It is also influenced by the electrostatic interaction of the frameworks.Therefore,the obtained information may provide useful guidance for the rational design and synthesis of MOFs with enhanced CO_(2) diffusion performance for specific applications.

A Fluorescent Zirconium-Based Metal-Organic Framework for Selective Detection of Nitro Explosives and Metal Ions

In this work, a new porous Zrobased metal-organic framework （MOF） with a large Brunner-Emmet-Teller （BET） surface area was prepared by the solvothermal method using 4,4＇-（naphthalene-1,4-diyl）dibenzoic acid （NDDA） as the organic ligand, and the luminescent detection performance was studied systematically. The experiments comb- ing with computations indicate that the as-synthesized material can sensitively and selectively detect nitro explo- sives and metal ions, especially for 2,4,6-trinitrophenol （TNP） and Fe3＋, due to the possible electron transfer from inorganic moieties to organic moieties with naphthalene part. Interestingly, owing to its high porosity and large sur- face area, this Zr-MOF showed quick luminescent response time （in 1 min） for TNP and Fe3＋. The results obtained may provide useful information for the design of MOFs with the large permanent porosity in sensing applications for large molecules in the future.

Nitrogen-rich porphyrinic metal-organic frameworks synthesized by postsynthetic metathesis: from inert material to active catalyst

With the aid of a postsynthetic metathesis method, an inert nitrogen-rich porphyrinic metal-organic framework can exhibit a high catalytic activity in one-pot deacetalization-Knoevenagel condensation reaction.