Self-assembly steers platinum nanoparticles to form large-pore metallic structures
Mitch Jacoby

CORNELL UNIVERSITY researchers have developed asynthesis for well-ordered metallic materials that feature pores in thepreviously unattainable tens-of-nanometers size range (Science 2008, 320,1748). Known as "mesoporous" metals, these kinds of materials canmediate a substantial flow of molecules through their large pores andmay be useful as fuel-cell electrodes or in other applications such ascatalysis and photonics.
                                                               
Scott C. Warren & Ulrich Wiesner/Cornell
A new synthesis guides platinum nanoparticles to form ordered materials with 10–20-nm-sized pores.
                               
The variety and number of porous materials, including zeolite-typecompounds and metal-organic frameworks, have grown substantially inrecent years due to advances in synthesis methods. Yet thoseprocedures, which often involve organic compounds asstructure-directing agents, have not made it easy to prepare orderedmetals with pores larger than roughly 2 nm.

"The challenge with metals is that their high surface energies cause the particles to cluster," explains Ulrich Wiesner,the Cornell material scientist who led the team. This tendency toaggregate makes it difficult to coax metal particles into lining up inan orderly fashion, which is a critical step in forming orderedmaterials.
Rather than following what Wiesner calls "the traditional 'heat itand beat it' approach" to structuring metals, Wiesner, Scott C. Warren,and their coworkers prepared their materials through self-assembly ofblock copolymers and stabilized platinum nanoparticles.

Specifically, the team used ionic-liquid ligands (methylammoniumchloride compounds) to render the 1.8-nm platinum particles soluble andto prevent their agglomeration. When combined withisoprene-methacrylate block copolymers, the metal particlesself-assemble to form ordered metal-organic hybrid structures. Finally,by applying various heat treatments and etching procedures, theresearchers removed the organic components, leaving a metallic platinummaterial with an orderly array of pores measuring 10–20 nm.

Describing the work as "a significant advance," Edward J. Kramer,a professor of materials and chemical engineering at the University ofCalifornia, Santa Barbara, remarks that the novel material may lead toa host of applications. He notes, for example, that in addition topotential use in battery and fuel-cell electrodes, the new material mayalso be useful for chemical separations and fabrication of mesoporouscrystals for catalysis.