Self and Transport Diffusivity of CO 2 in the MetalOrganic Framework MIL- 47(V) Explored by Quasi-elastic Neutron Scattering Experiments and Molecular Dynamics Simulations Fabrice Salles, † Herve ´ Jobic, ‡, * Thomas Devic, § Philip L. Llewellyn,  Christian Serre, § Ge ´ rard Fe ´ rey, § and Guillaume Maurin †, * † Institut Charles Gerhardt Montpellier, UMR CNRS 5253, UM2, ENSCM, Universite ´ Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France, ‡ Institut de Recherches sur la Catalyse et l’Environnement de Lyon, Universite ´ de Lyon CNRS, 2 Avenue A. Einstein, F-69626 Villeurbanne, France, § Institut Lavoisier, UMR CNRS 8180, Universite ´ Versailles-Saint-Quentin-en-Yvelines, 78035 Versailles, France, and  Laboratoire Chimie Provence, Universite ´ Aix-Marseille I, II, and III-CNRS-UMR 6264, Centre de Saint-Je ´ro ˆme, 13397 Marseille, France T he economically viable capture of carbon dioxide appears clearly as a priority to reduce global warming caused by the emission of greenhouse gases and to favor the emergence of the fu- ture world economy based on hydrogen as an energy vector. 1,2 Advances in reducing CO 2 emissions may thus lead to a number of potential benefits in different fields re- lated to both energy development and en- vironmental protection. Such environmen- tal and economical problems that society faces today have galvanized the research for novel competitive nanoporous materi- als able to efficiently adsorb CO 2 . 1,3 To that purpose, the metal-organic framework (MOF) materials appear as promising alter- native candidates to zeolites and activated carbons, currently used as adsorbents in PSA-based systems. 4-6 Indeed, MOFs ex- hibit very attractive features for the adsorp- tion of various gases including H 2 , 7-12 CH 4 , and CO 2 . 7,13-16 For instance, a very high CO 2 adsorption uptake has been highlighted for the MIL-101 solid. 17 Further, some MOFs are able to breathe in the presence of spe- cific probe molecules which can open up an interesting way to efficiently control selec- tive gas adsorption. 3,18-21 Experimental and theoretical studies have generally focused on the adsorption/diffusion of H 2 in differ- ent MOFs. 11,22-25 In contrast, fewer experi- mental explorations have been dedicated to CO 2 adsorption properties of these materials. 5,17,26-31 Nevertheless, several studies have been devoted to the MIL- series (MIL-53(Cr), MIL-47(V), MIL-100 (Cr), and MIL-101 (Cr)), 17,27 MOF-508b 30 as well as to other MOFs systems recently synthe- sized such as Zn 2 (NDC) 2 (DPNI) (where NDC = 2,6-naphthalenedicarboxylate, DPNI = N,N=-di-(4-pyridil-1,4,5,8-naphthalen tetra- carboxydiimide) 26 and CPO-27 or Ni 2 (dhtp) (where H 4 dhtp = 2,5-dihydroxyterephthalic acid; CPO = coordination polymer from Os- lo) 29 solids. They were completed by molec- ular simulations at different levels of theory including thermodynamics models. 32 Using the quantum chemical approach, the geo- metric and energetic nature of the CO 2 / MOF framework interactions were deduced. 32,33 Classical simulations based *Address correspondence to gmaurin@lpmc.univ-montp2.fr, herve.jobic@ircelyon.univ-lyon1.fr. Received for review September 1, 2009 and accepted November 27, 2009. Published online December 3, 2009. 10.1021/nn901132k © 2010 American Chemical Society ABSTRACT Quasi-elastic neutron scattering measurements are combined with molecular dynamics simulations to determine the self-diffusivity, corrected diffusivity, and transport diffusivity of CO 2 in the metalorganic framework MIL-47(V) (MIL  Materials Institut Lavoisier) over a wide range of loading. The force field used for describing the host/guest interactions is first validated on the thermodynamics of the MIL-47(V)/CO 2 system, prior to being transferred to the investigations of the dynamics. A decreasing profile is then deduced for D s and D o whereas D t presents a non monotonous evolution with a slight decrease at low loading followed by a sharp increase at higher loading. Such decrease of D t which has never been evidenced in any microporous systems comes from the atypical evolution of the thermodynamic correction factor that reaches values below 1 at low loading. This implies that, due to intermolecular interactions, the CO 2 molecules in MIL-47(V) do not behave like an ideal gas. Further, molecular simulations enabled us to elucidate unambiguously a 3D diffusion mechanism within the pores of MIL-47(V). KEYWORDS: metalorganic framework · self-diffusivity · corrected diffusivity · transport diffusivity · QENS · molecular dynamics · CO 2 ARTICLE www.acsnano.org VOL. 4 ▪ NO. 1 ▪ 143–152 ▪ 2010 143