Despite considerable progress in the field of porous solids, major challenges remain in the synthesis of ordered mesostructured materials with high metal content from the coassembly of macromolecular surfactants and inorganic species. The ability to control the structure of metals at the mesoscale (2 to 50 nm) helps to promote the development of improved fuel cell electrodes and may also assist in the miniaturization of optical and electronic materials for data transmission, storage, and computation (A. Haryono, W. H. Binder, Small 2, 600 (2006); A. C. Balazs, T. Emrick, T. P. Russell, Science 314, 1107 (2006)).
An early route to preparing mesoporous metals involves the dealloying of a less noble metal from a bimetallic alloy; this has been used for the preparation of Raney nickel and other metals (M. Raney, U.S. Pat. No. 1,628,190 (1927)). Dealloying processes provide limited control over structural parameters such as pore geometry and order. In contrast, block copolymer self-assembly or templating with metal species provides access to highly ordered structures. Synthetic routes to such structures have included adsorbing and then reducing metal ions within a preassembled block copolymer scaffold (Y. N. C. Chan, R. R. Schrock, R. E. Cohen, Chem. Mater. 4, 24 (1992)) and coassembling ligand-stabilized nanoparticles (NPs) with block copolymers (D. E. Fogg, L. H. Radzilowski, R. Blanski, R. R. Schrock, E. L. Thomas, Macromolecules 30, 417 (1997)). More recently, polymer-coated NPs that behave like surfactants have been isolated at the interface of block copolymer domains, which can create a bicontinuous morphology at higher loadings (B. J. Kim, G. H. Fredrickson, C. J. Hawker, E. J. Kramer, Langmuir 23, 7804 (2007)).
Despite this progress, the conversion of metal polymer hybrids into porous mesostructured materials with ordered and large pores (≧5 nm) has not been accomplished, in part because of the low volume fraction of metals in most hybrids and the widespread use of gold, which has a high diffusion coefficient and therefore retains its mesostructure only at low temperatures (P. Buffat, J.-P. Borel, Phys. Rev. A 13, 2287 (1976); R. Li, K. Sieradzki, Phys. Rev. Lett. 68, 1168 (1992); J. Erlebacher, M. J. Aziz, A. Karma, N. Dimitrov, K. Sieradzki, Nature 410, 450 (2001)). Although a protective organic layer can be added to metal NPs to prevent uncontrolled aggregation, even a thin organic layer represents a considerable volume of the overall material: For example, a 1-nm-diameter metal NP with a relatively thin 1-nm organic shell is just 4% metal by volume. As a result, the typical metal content in most block copolymer-metal NP hybrids is only a few volume %, and the prospects for converting the hybrid into an ordered porous mesostructured material, in which the metal would have a volume fraction between 60 and 75% for an inverse hexagonal structure, are poor. Mesoporous metals have been synthesized at a smaller length scale, with 2- to 4-nm pores, through the coassembly of metal ions with small-molecule surfactants followed by reduction (G. S. Attard et al., Science 278, 838 (1997); G. S. Attard, C. G. Göltner, J. M. Corker, S. Henke, R. H. Templer, Angew. Chem. Int. Ed. Engl. 36, 1315 (1997); Y. Yamauchi, T. Yokoshima, T. Momma, T. Osaka, K. Kuroda, J. Mater. Chem. 14, 2935 (2004); J. Jiang, A. Kucernak, Chem. Mater. 16, 1362 (2004)). The small pore size, however, limits the flow of liquids through the material, which is essential for many applications (D. Y. Zhao et al., Science 279, 548 (1998); M. E. Davis, Nature 417, 813 (2002)). Metals have also been deposited onto (W. A. Lopes, H. M. Jaeger, Nature 414, 735 (2001)) or into (J. Chai, D. Wang, X. Fan, J. M. Buriak, Nat. Nanotechnol. 2, 500 (2007)) thin films of block copolymers to create metal wires, but the surface dependent nature of the metal deposition most likely limits these processes to two-dimensional materials.
There is therefore a need in the art for mesostructured metal NP-block copolymer hybrids with exceptionally high NP loadings and tunable phase-separated morphologies with feature sizes>10 nm. There is also a need in the art for metal-rich mesostructures with ordered and large (≧5 nm) uniform pores.
Citation or identification of any reference in Section 2, or in any other section of this application, shall not be considered an admission that such reference is available as prior art to the present invention.