Virtual High Throughput Screening Confirmed Experimentally: Porous Coordination Polymer Hydration

Abstract

Hydrothermal stability is a pertinent issue to address for many industrial applications where percent levels of water can be present at temperatures ranging from subambient to several hundred degrees. Our objective is to understand relative stabilities of MOF materials through experimental testing combined with molecular modeling. This will enable the ultimate design of materials with improved hydrothermal stability, while maintaining the properties of interest. The tools that we have employed for these studies include quantum mechanical calculations based upon cluster models and combinatorial steaming methods whereby a steam stability map was formulated according to the relative stability of different materials. The experimental steaming method allows for high throughput screening of materials stability over a broad range of steam levels as well as in-depth investigation of structural transformations under more highly resolved conditions, while the cluster model presented here yields the correct trends in hydrothermal stability. Good agreement was observed between predicted relative stabilities of materials by molecular modeling and experimental results. Fundamental information from these studies has provided insight into how metal composition and coordination, chemical functionality of organic linker, framework dimensionality, and interpenetration affect the relative stabilities of PCP materials. This work suggests that the strength of the bond between the metal oxide cluster and the bridging linker is important in determining the hydrothermal stability of the PCP. Although the flexibility of the framework plays a role, it is not as important as the metal-linker bond strength. This demonstration of alignment between experimental and calculated observations has proven the validity of the method, and the insight derived herein insight facilitates direction in designing ideal MOF materials with improved hydrothermal stability for desired applications.

Stability and Hydrolyzation of Metal Organic Frameworks with Paddle-Wheel SBUs upon Hydration

“…Low et al used a quantum mechanical to model the hydrolysis reaction of water with metal oxide clusters, showing that it involved the breaking and reforming of bonds in different types of metal organic frameworks depending on the specific secondary building units (SBUs). 18 The proton of water molecules can attack the oxygen of metal oxide cluster when the carboxylate opens up a coordination site on the metal for the water molecules. Later, Han used a reactive force field (ReaxFF) approach to perform a detailed study of hydrolysis of MOF-5 and found a direct water interaction with ZnO 4 tetrahedron in framework induces cleavage of Zn-O bonds and dissociation of H 2 O molecules of into OH and H. The resulting OH forms a chemical bond with Zn, and the proton is attached to the oxygen of the bdc moiety.…”

“…15,16 The stability of MOFs under water vapor atmosphere has so far been mainly evaluated by X-ray Diffraction. [17][18][19] Some widely investigated MOFs including MOF-5, MOF-177, though exhibiting excellent performance in H 2 and CO 2 storage in porous materials, are not stable in the presence of small amount of water. [20][21][22] Greathouse and Allendorf used empirical force fields and molecular dynamics to simulate the interaction of water with MOF-5.…”

Zeolite membranes – a review and comparison with MOFs

“…280,281 In a previous pioneering paper by Low, a good overview of the steam stability of MOFs as a function of temperature is given. 282 In many studies on steam stability of MOF membranes, the tests have been carried out only for short periods of time (1-2 days) and it is hard to make conclusions on the long-term stability. 283,284 12.…”

Designed amyloid fibers as materials for selective carbon dioxide capture

“…To overcome the high energy consumption for MEA regeneration, solid adsorbents such as zeolites, activated carbons, and metal-organic frameworks have been extensively exploited (4,(6)(7)(8)(9)(10). These classes of porous materials generally have high capacity and low energy cost for regeneration, but lose their efficiency when exposed to water vapor, as is the case in combustion gases (11,12). To combine the high affinity of MEA and energy-efficient regeneration of a dry system, new materials with amines implanted in the pores of solid materials are being investigated and show some promise for improved performance (13)(14)(15).…”