Impact and nature of open metal sites: a water and carbon monoxide adsorption study on MOF-74 isostructural MOFs

dc.contributor.advisor Walton, Krista S.
dc.contributor.author Flemming, Christine Juliette Jane
dc.contributor.committeeMember Hess, Dennis
dc.contributor.committeeMember Kawajiri, Yoshiaki
dc.contributor.department Chemical Engineering
dc.date.accessioned 2013-09-19T13:03:32Z
dc.date.available 2013-09-19T13:03:32Z
dc.date.issued 2012-07-06
dc.description.abstract In this work the magnesium, zinc, nickel and cobalt MOFs of the MOF-74 isostructural family are used to probe metal-dependent adsorbate interactions with water and with carbon monoxide because of their ability to generate open metal sites upon activation. An isostructural family is used so that the only variable from one MOF to another is the metal incorporated into the framework. For water adsorption isotherms with humidities up to 90%, the observed trend at 298K and 1 bar is Mg-MOF-74 > Zn-MOF-74 > Co-MOF-74 > Ni-MOF-74. This observed trend is due to Lewis acid-base interactions. When the weight effect is removed, differences are still observed, especially below 40% relative humidity, thereby confirming that there is a metal effect. These studies revealed that PXRD alone cannot indicate the level of structural decomposition and that none of the four isostructures fully retain their structural integrity on exposure to humidified air because of microstrain and/or the presence of oxygen; more studies examining the extent of structural decomposition need to be undertaken. For carbon monoxide adsorption the general observed trend for P < 4 bar and temperatures of 298, 313 and 333K is Co-MOF-74 > Ni-MOF-74 > Zn-MOF-74 > Mg-MOF-74. This trend is based on π-backbonding interactions. Here again, differences remain after removal of the weight effect, confirming the metal dependence. Notably, Co-MOF-74 has the highest CO loading at 298K and 1 bar reported so far. Both the Toth and Virial Isotherms were used to fit the CO adsorption data followed by the use of the Clausius-Clapeyron equation to find the isosteric heats of adsorption, qst. The results from the Toth isotherm are more reliable and showed that qst remains constant as loading increases for Mg-MOF-74, decreases for Zn-MOF-74 and increases with loading for Co-MOF-74 and Ni-MOF-74; Ni-MOF-74 had the highest heat of adsorption at all loadings. It appears that using the Clausius-Clapeyron equation to calculate qst is an inappropriate method for Ni-MOF-74 so other methods such as calorimetry are recommended. It is also recommended to model the data of all the MOFs with other isotherm models such as Sips equation and to investigate the possibility of chemisorption for the cobalt and nickel isostructures. Finally, Henry’s constant results reveal that Ni-MOF-74 has the highest affinity for CO at low coverages.
dc.description.degree M.S.
dc.identifier.uri http://hdl.handle.net/1853/48992
dc.language.iso en_US
dc.publisher Georgia Institute of Technology
dc.subject Heat of adsorption
dc.subject DOBDC
dc.subject Adsorption
dc.subject CPO-27
dc.subject Carbon monoxide
dc.subject MOF-74
dc.subject.lcsh Organometallic compounds
dc.subject.lcsh Adsorption
dc.subject.lcsh Carbon monoxide
dc.subject.lcsh Water
dc.title Impact and nature of open metal sites: a water and carbon monoxide adsorption study on MOF-74 isostructural MOFs
dc.type Text
dc.type.genre Thesis
dspace.entity.type Publication
local.contributor.advisor Walton, Krista S.
local.contributor.corporatename School of Chemical and Biomolecular Engineering
local.contributor.corporatename College of Engineering
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relation.isOrgUnitOfPublication 6cfa2dc6-c5bf-4f6b-99a2-57105d8f7a6f
relation.isOrgUnitOfPublication 7c022d60-21d5-497c-b552-95e489a06569
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