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求翻译英文文献，化工类的，必有重谢！
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Applications of MOFs a) MOFs as Storage Materials: With the fossil fuels disappearing rapidly, there is an urgent need to identify alternative energy sources which are sustainable. Hydrogen is identified as the fuel of the future as it can be readily made and is the cleanest fuel one can imagine as its combustion product is just water. However, storage and transportation of hydrogen for on-board applications continue to be two major technical problems [7]. The 2010 target for hydrogen storage density is 6.0 wt% and 45 kg H2 per m3. In view of their porous nature with large surface areas MOFs are considered to be promising materials for hydrogen storage. MOFs are easy to synthesize and the scale up of production is facile. MOFs with surface area greater than 1000m2 g–1,which is greater than that demonstrated for zeolites, have been reported in literature. MOF made from Zn2+ and 1,3,5-(4-carboxyphenyl) benzene (Entry 1 in Scheme 6) has a monolayer with equivalent surface area of 4,526m2 g–1. It has a hydrogen uptake capacity of 1.2wt% at 77 K and 1 atm [8]. Hydrogen uptake as high as 3.8 wt % has been reported for MOF synthesized from Al3+ and terephthalic acid (tpa) [Al(OH)(tpa)] at 77 K and 16 bar pressure [9]. Although these results are promising, there are some issues of fundamental nature concerning the thermal and pore dimension stabilities of the MOFs. The pores of MOFs are generally filled with solvent molecules during their synthesis. Removal of these guest molecules can result in the collapse of the porous structure making them useless for any technological applications. MOFs with permanent pores are particularly useful as storage materials. From the available data there is no apparent correlation of hydrogen storage capacity to the surface area or pore volume of MOFs. Recent theoretical investigations [10] indicate that at low pressures of H2, the initial site of hydrogen adsorption is the metal clusters and with increasing pressures, uptake of more hydrogen is observed, occupying the aromatic walls of MOFs. The interaction between the MOF and hydrogen molecule is essentially weak van der Waals interaction. Based on theoretical studies it is suggested that MOFs with lighter metals (Be and Mg instead of Zn) and larger aromatic linkers are good candidates for hydrogen storage. There are nearly 5,000 MOFs with two-dimensional and hree-dimensional structures reported so far, but only a fraction of these have been tested for hydrogen storage application. With the rapid advancements occurring in this area, it is hoped that some useful MOFs will emerge in the near future to meet the 2010 target set for on-board hydrogen storage. Besides hydrogen storage, efforts are underway for the storage of other gaseous and small hydrocarbon molecules (C1 to C4) in MOFs [11]. b) Separation and Catalysis: Zeolites are well known for shape selectivity due to their restrictive pore dimensions [12]. MOFs are also suitable materials for application in separation technology, in particular chiral separation, which has wide applications in chemical and pharmaceutical industries. MOFs bearing homochiral ligands and hence pores with chiral environment are known and have been demonstrated to be useful in chiral separation [13]. For example,MOF synthesized from the ligand shown in Scheme 7 with Zn2+ is homochiral in nature in view of the chirality of the ligand. It has a layered structure with large one-dimensional chiral channels with voids accounting for 47% of the total volume. When racemic [Ru(2,2’-bipy)3]Cl2 is treated with this MOF, it is observed that the color of the MOF changes from white to reddish yellow accompanied by the exchange of 80% of lattice protons with [Ru(2,2’-bipy)3]2+; the exchange happens with 66%enantiomeric excess (ee) in favour of the D form of the ruthenium complex [14]. Scheme 7. Formation of chiral MOF using enantiopure organic building unit, L. The SBU in this case is an oxo-bridged trinuclear metal carboxylate hydrate. RCOO- group in the SBU corresponds to the carboxylate derived from L wherein the two oxygen atoms correspond to the carboxylate oxygen and the amide oxygen forming a six-membered chelate. Lis derived from enantiopure tartaric acid The same chiral MOF is also used to demonstrate enantioselective catalytic activity.Transesterification of 2,4-dinitrophenyl acetate with racemic alcohols (± 1-phenylethanol) proceeded with modest enantioselectivity of 8% ee for either the R isomer or the S isomer depending upon the chirality of the MOF used. This is an example of the kinetic resolution of a racemic alcohol. Although very modest in selectivity, it is noteworthy that asymmetric induction mediated by modular porous materials has never been observed prior to this report. Summary and Outlook Synthesis of MOFs is a contemporary area of research with potential in many technological applications. Creation of MOFs with predetermined architecture, pore size and permanent pores is a challenging problem. A race is on among the players in this field to synthesize a MOF with the largest surface area. Synthesis of chiral MOFs using enantiopure organic linkers and cavity functionalized MOFs to perform specific chemical reactions are currently in progress. Although porous MOFs are unlikely to compete with zeolites and metal oxide based porous materials in their thermal stabilities, these soft materials will nevertheless find use in many applications such as hydrogen storage, asymmetric transformation and separation in the future. The fact that MOFs are easy to assemble from their organic and inorganic building blocks and the ease of scale up makes them attractive candidates for investigation. The kinds of materials that can be produced in this area are limited only by the imagination of those who attempt their synthesis; as one of the leading researchers in the field, Féret put it, ‘The limits are in our imagination’ [3e]. |
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