Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Hydrogen Storage and Release Mechanisms in MOF-5M. MANI-BISWAS 1 , T. CAGIN 1,21 Materials Science and Engineering, Texas A&M University, College Station, TX 77843, USA2 Department of Chemical Engineering, Texas A&M University, Texas, TX 77843-3122, USAAbstract- Metal organic framework MOF-5 is a hybrid porous crystalline material. It has high porosity and largesurface area and hence potential application in gas storage, catalysis, drug delivery, etc. For applications as a gasstorage material, it is important to find out a suitable gas delivery mechanism. Here we propose such amechanism by taking advantage of near shear instability of MOF-5. Using molecular simulation we show that athigh pressure MOF-5 gets deformed to 55% of its original volume. We also show that during this deformationprocess; MOF-5 passes through certain stages from where, by decreasing the pressure, 100% reversibility can beachieved. Based on this behavior, a purely mechanical process is proposed for gas (H 2 ) storage and release.Keywords: Hydrogen storage, Metal organic frameworks, Molecular Dynamics, sorption simulation, mechanical instability.Metal organic frameworks (MOF) are hybridporous crystalline materials. They have the highestpore size, low density and large surface area of anycrystalline material 1-4 . In general, MOFs are madeup of metal oxide clusters positioned at the verticesand connected by organic linkers. For example, thesimplest structure MOF-5 (IRMOF-1) is made upof Zn 4 O clusters are positioned at the corners of thecubic cell and connected by benzene dicarboxylate(BDC) linkers. The framework molecules take uponly a small fraction of the available space in thecrystal and about 80 % of the volume is free toaccommodate any guest molecule 1 . MOFs can beeasily prepared in the laboratory and have goodthermal stability (till 300-400 0 C) 3 . All theseproperties make MOFs suitable for applicationssuch as gas storage/separation, catalysis, molecularrecognition, etc. 5, 6 MOFs have potential to adsorbgases like H 2 , CH 4 , CO 2 , N 2 , Ar, etc. and theadsorption capacity may be improved by changingthe functionality of the linker and thus increasingMOF-guest interaction energy, incorporating openmetal sites, catenation of framework, etc 4 . MOFfilled containers have demonstrated enhancedstorage capacity (44% more hydrogen, 4 timesmore Xenon and 3 times more propane) comparedto empty containers 5 , further strengthening thepotential of MOFs as gas storage medium.Studies on the mechanical property have revealedthat MOF-5 is a soft material and it is nearlyunstable 7-8 , implying that the crystal is flexibleenough to transform to a new structure in thepresence of an external stimulus. Single-crystal-tosingle-crystaltransformations by exchange of guestmolecule or by varying temperature condition havebeen reported for some MOFs 9 and thesetransformations have been implicated in controlleddelivery of the guest molecules. Here we show bytheoretical methods, that at high pressure MOF-5undergoes reversible structural transformation i,evolume compression/decompression stages whichmay be continued for number of cycles. Takingadvantage of the cyclic nature of MOF-5deformation under pressure, a purely mechanicalgas storage and delivery system has been proposed.We considered hydrogen as a representative gasand performed simulations with hydrogen filledMOF-5. Given the pore size of MOF-5 (availablevolume ~ 11267 Å 3 ), at 100 MPa and at roomtemperature, ~167 molecules of hydrogen can beentrapped inside the crystal (considering density ofhydrogen at this condition is 49.25 kg/m 3 ). Thisamounts to 7wt % H 2 per gm of MOF-5. Underpressure as the crystal deforms the entrapped gaswill be released, which may be used further. In theproposed process, using pressure inducedmechanical gas delivery system, efficiency as highas 90% may be achieved.*Corresponding author: cagin@che.tamu.eduREFERENCES[1] Li, H.; Eddaoudi, M.; O.Keeffe, M.; Yaghi, O.M. Nature, 1999, 402, 276-279.[2] Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.;O'Keeffe, M.; Yaghi, O. M. Science, 2002, 295,469-472.[3] Rosi, N.; Eckert J., Eddaoudi M.; Vodat D.T.;Kim J.; O'Keeffe, M.; Yaghi, O. M Science, 2003,300, 1127-1129.[4] Rowsell, J. L.C. Yaghi, O. M. Angew. ChemInt. Ed. 2005, 44, 4670-4679.[5] Mueller, U. Schubert M.; Teich F.; Puetter H.;Schierle-Arndt K.; Pastre J. J. Mater. Chem., 2006,16, 626-636.[6] Ferey, G. Chem. Soc. Rev. 2007, 37, 191-214.[7] Han, S. S. and Goddard III, W. A. J. Phys.Chem. C, 2007, 111 (42), 15185 -15191.[8] Mattesini, M.; Soler, J. M.; Yndurain, F. Phys.Rev. B 2006, 73, 094111 1-8.[9] Wu, C-D.; Lin, W. Angew. Chem. Int. Ed.2005, 44, 1958-1961.6th Nanoscience and Nanotechnology Conference, zmir, 2010 765