Combinational Synthetic Approaches for Isoreticular and Polymorphic Metal-Organic Frameworks with Tuned Pore Geometries and Surface Properties

Isoreticular and polymorphic 3-D MOFs were prepared via the combination of direct solvothermal reactions, postsynthetic ligand exchanges of the MOFs prepared via the direct solvothermal reactions, and postsynthetic ligand insertions into a 2-D MOF. The appropriate pore dimensions, surface areas, and adsorption enthalpies of the MOFs combined well to produce the largest working CO2 capture capacities via the pressure swing adsorption process.close4

Hybrid bimetallic metal-organic frameworks: Modulation of the framework stability and ultralarge CO2 uptake capacity

A series of isostructural hybrid bimetallic metal-organic frameworks (MOFs), NixM1-x-ITHDs [M = Zn(II), Co(II)], have been prepared via a conventional solvothermal reaction in the presence of varying mole ratios of Ni(II)/Zn(II) or Ni(II)/Co(II) mixed metal ions. While a critical amount of the doped Ni(II) ion (more than ≈0.2 mol fraction) is needed to have any enhancement of the framework stability of the hybrid bimetallic Ni xZn1-x-ITHDs, even a very small amount of the doped Ni(II) ion (≈0.1 mol fraction) produced a full enhancement of the framework stability of the hybrid bimetallic NixCo1-x-ITHDs. The highly porous and rigid NixCo1-x-ITHDs activated via a conventional vacuum drying process shows a Brunauer-Emmett-Teller specific surface area of 5370 m2 g-1, which is comparable to that of pure Ni-ITHD. The CO2 uptake capacities of Ni-ITHD and Ni 0.11Co0.89-ITHD (2.79 and 2.71 g g-1, respectively) at 1 bar and 195 K are larger than those of any other reported MOFs under similar conditions and the excess CO2 uptake capacity at 40 bar and 295 K (≈1.50 g g-1) is comparable to those of other MOFs, which are activated via the supercritical carbon dioxide drying process, with similar pore volumes.close4

Molecular simulation of CO2 adsorption in the presence of water in single-walled carbon nanotubes

The adsorption of carbon dioxide in the presence of water in single-walled carbon nanotubes is studied using Monte Carlo simulation, at 300, 325, and 350 K. We also investigate the influence of the diameter and chirality of the nanotubes on the adsorption isotherms of CO2. It is observed that increasing the nanotube diameter from 1.36 nm (10, 10) to 2.03 nm (15, 15) leads to enhanced CO2 capacity, while change in chirality has little effect on the adsorption capacity of carbon nanotubes. Our results show that the influence of preadsorbed water on CO2 adsorption is dependent on both the effects of excluded volume and H2O-CO2 interactions. The maximum adsorbed amount of CO2 decreases linearly with the loading of water, and drops more rapidly in narrower nanotubes. The structure of water in hydrophobic nanopores is in the form of hydrogen-bonded clusters, and its adsorption does not affect the arrangement and orientation of CO2 molecules (i.e., it does not affect the mechanism of CO2 adsorption). The average size of water clusters coexisting with CO2 depends strongly on the adsorbed amount of CO2; however, it is shown that splitting large water clusters into smaller ones can lead to significant enhancement of CO2 adsorption, due to the resulting stronger water-CO2 interaction. The maximum percentage increase in the excess adsorption of CO2 is as high as 53.4% when a single cluster is split into multiple smaller clusters. This finding demonstrates that the efficiency of CO2 capture from flue gas can be significantly improved by controlling the structure of coexisting water in carbon nanotubes