Xinyu Chen,Jinhai Leng,Fengying Ma,Jianqing Wu,Yi Jin,Miao Yu,Haomin Huang,Shanshan Shang,Daiqi Ye
Excessive CO 2 emissions significantly contribute to global warming, promoting the advancement of carbon capture and storage (CCS) technologies. Metal-organic frameworks (MOFs) are promising candidates for selective CO 2 adsorption; however, their effectiveness is often compromised in humid environments, such as flue gas streams. To overcome this limitation, this study synthesizes six isostructural DABCO-pillared MOFs (DMOFs) by finely tuning metal nodes (from Zn to Ni) and integrating methyl (-CH 3 ) functional groups on the organic ligand to enhance CO 2 adsorption performance, especially under humid conditions. Single gas adsorption isotherms reveal that the Ni-TM DMOF achieves the highest CO 2 adsorption capacity of 5.0 mmol g −1 and maintains 100 % regenerability after five cycles. Binary CO 2 /N 2 dynamic breakthrough experiments further demonstrate that the Ni-TM DMOF excels in both CO 2 uptake and CO 2 /N 2 separation performance under both dry and humid conditions (80 % relative humidity). Mechanistic insights from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations elucidate the molecular interactions between CO 2 and the DMOF structure, revealing that CO 2 adsorption predominantly occurs via physisorption, enhanced by C-H·O interaction from the -CH 3 groups. This work provides a strategic approach for enhancing the stability and efficiency of MOFs in industrial CO 2 sequestration applications.
Cai He,Bingfeng Guo,Tong Li,Xiaoxia Jia,Yong Wang,Zhiyun Xiao
A rigid–flexible Zn-DMOF was developed for selective C 2 H 2 /CO 2 separation. • Activation-induced pore contraction enabled dynamic recognition of C 2 H 2 . • Zn-chdc-DABCO retained high C 2 H 2 uptake but greatly improved C 2 H 2 /CO 2 selectivity. • Efficient breakthrough separation was maintained under varying flow rates and humidity. Separating C 2 H 2 from CO 2 is challenging because of their similar sizes and physicochemical properties. Adsorption-based separation using metal–organic frameworks (MOFs) offer a promising alternative. Here, a rigid–flexible framework strategy is used to introduce guest-discriminating dynamic recognition into a 1,4-diazabicyclo[2.2.2]octane (DABCO)-based MOF (DMOF) platform by replacing rigid 1,4-benzenedicarboxylate with flexible trans-1,4-cyclohexanedicarboxylate, affording Zn-trans-1,4-cyclohexanedicarboxylic acid (chdc)-DABCO. Activation induces pore contraction and generates a confined environment that selectively strengthens C 2 H 2 binding while leaving CO 2 largely unaffected. As a result, Zn-chdc-DABCO preserves a C 2 H 2 uptake comparable to that of Zn-DMOF at 298 K and 100 kPa, yet displays markedly enhanced affinity toward C 2 H 2 , a distinct gate-opening response to C 2 H 2 , and little framework response toward CO 2 . The zero-coverage isosteric heat of adsorption reaches 43.9 kJ·mol –1 for C 2 H 2 , substantially higher than that for CO 2 (29.3 kJ·mol –1 ), and the equimolar C 2 H 2 /CO 2 ideal adsorbed solution theory selectivity reaches 8.2, more than four times that of Zn-DMOF. Dynamic breakthrough experiments further confirm efficient separation under mixed-gas, variable-flow, and humid conditions. This work shows that rigid–flexible cooperative design offers an effective route to overcoming the capacity/selectivity trade-off in difficult gas separations. A rigid–flexible Zn-DMOF was engineered to enable activation-induced pore contraction and guest-discriminating dynamic recognition, thereby achieving enhanced selective C 2 H 2 /CO 2 separation with efficient C 2 H 2 recovery. Download: Download high-res image (204KB) Download: Download full-size image
Tong Li,Xiaoxia Jia,Hui Chen,Zeyu Chang,Libo Li,Yong Wang,Jinping Li
Adsorption separation technology using adsorbents is promising as an alternative to the energy-demanding cryogenic distillation of natural gas (CH4/N2) separation. Although a few adsorbents, such as metal–organic frameworks (MOFs), with high performance for CH4/N2 separation, have been reported, it is still challenging to target the desired adsorbents for the actual CH4/N2 separation under humid conditions because the adsorption capacity and selectivity of the adsorbents might be mainly dampened by water vapor. Except for the high CH4 uptake and CH4/N2 selectivity, the adsorption material should simultaneously have excellent stability against moisture and relatively low-water absorption affinity. Here, we tuned the ligands and metal sites of reticular MOFs, Zn-benzene-1,4-dicarboxylic acid–1,4-diazabicyclo[2.2.2]octane (Zn-BDC–DABCO) (DMOF), affording a series of isostructural MOFs (DMOF-N, DMOF-A1, DMOF-A2, and DMOF-A3). Because of the finely engineered pore size and introduced aromatic rings in the functional DMOF, gas sorption results reveal that the materials show improved performance with a benchmark CH4 uptake of 37 cm3/g and a high CH4/N2 adsorption selectivity of 7.2 for DMOF-A2 at 298 K and 1.0 bar. Moisture stability experiments show that DMOF-A2 is a robust MOF with low water vapor capacity even at ∼40% relative humidity (RH) because of the presence of more hydrophobic aromatic rings. Breakthrough experiments verify the excellent CH4/N2 separation performances of DMOF-A2 under high humidity.
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