(767b) Assembly of 3D Ordered Binary Silica Nanoparticle Superlattices and Multi-Modal Porous Carbons

Multi-modal colloidal crystal assembly employing nanoparticle building blocks of varied size, composition, and function offers a route to diverse ordered mesoporous materials.  Such a bottom-up assembly strategy would provide possible handles for directly tuning material porosity, pore topology, pore coordination, 3D composition, and ordered and distributed function, that could be exploited for applications ranging from size and shape-selective catalysis to molecular sensing of bulky molecules.  Experimentally, binary colloidal crystals have previously been realized at two disparate size scales through assembly of 1) micron- and submicron-scale (100nm-1mm) polymeric particles [1,2] and 2) binary nanoparticle superlattices (BNSL) assembled from metal and/or metal oxide nanoparticles (nanometer scale).[3,4]  The structural diversity realized specifically in the context of BNSLs raises exciting prospects for facile synthesis of tunable but inexpensive silica-based porous inorganic materials and replica structures (e.g., carbons) if the ability to synthesize and assemble size-tunable silica nanoparticles in a similar fashion can be realized.

This talk will discuss proof-of-concept development of a simple strategy to rationally design and synthesize 3D ordered binary silica nanoparticle superlattices (BSNS) through assembly of size-tunable lysine-silica nanoparticles [5,6] with particle sizes ranging from 10 to 50 nm. Evaporative co-assembly of bimodal mixtures of silica nanoparticles with systematically controlled particle size ratios and solution particle stoichiometry results in BSNSs isostructural with NaCl, AlB₂, and NaZn₁₃.  This suggests the partial validity of hard-sphere space-filling principles and entropic predictions [7,8] for assembly within the silica system, and provides the theoretical basis for increasing structural diversity.  2D-SAXS analysis confirms the long-range ordering and high yield of the BSNS structures. The robustness of the assembly mechanism to changing particle size under constant size ratio and large/small particle stoichiometry underscores the versatility of this approach to realizing porous materials of tunable pore size and topology.  We will describe the role of basic amino acids, resulting from particle synthesis, and the tuning of competing time scales for assembly/crystallization and solvent evaporation in improving the yield of 3D ordered structures.  In addition, we will show how BSNSs can be used as a hard sacrificial template for realizing 3D-interconnected bimodal mesoporous carbons with attractive textural properties.  Finally, methods for expanding the compositional and textural diversity of the ordered porous materials and carbon replica structures by tuning particle function and composition will be discussed.

References

[1] Bartlett, Ottewill, Pusey, Phys Rev Lett, 1992, 68, 3801.

[2] Hunt, Jardine, Bartlett, Physical Review E, 2000, 62, 900.

[3] Shevchenko, Talapin, Kotov, O'Brien, Murray, Nature, 2006, 439, 55.

[4] Shevchenko, Talapin, Murray, O'Brien, J. Am Chem Soc, 2006, 128, 3620.

[5] Davis, Snyder, Krohn, Tsapatsis, Chemistry of Materials, 2006, 18, 5814.

[6] Fan, Snyder, Kumar, Lee, Yoo, McCormick, Penn, Stein, Tsapatsis, Nature Materials, 2008, 7, 984.

[7] Cottin, Monson, Journal of Chemical Physics, 1993, 99, 8914.

[8] Eldridge, Madden, Pusey, Bartlett, Mol. Phys., 1995, 84, 395.