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Assembling Functional Mesoporous Architectures

Mesoporous films of ITiO and TiO2 were formed from spherical and rod-shaped nanocrystals by templating with block copolymers. Below, schematic of block copolymer supramolecules with nanocrystals congregated on the periphery.

Molecular Foundry researchers headed by Brett Helms and Delia Milliron have unveiled a powerful new technique to form mesoporous materials with precisely controlled structure by mating specialized block copolymers with ligand-stripped nanocrystals. Their approach opens new possibilities for making mesoporous architectures from diverse compositions of materials to achieve new properties.

Nanocrystal assembly is ordinarily dictated by interactions with organic ligands on their surfaces. Forming ordered mesoporous structures out of nanocrystals has proved difficult in the past because their native ligands interact only weakly with templating molecules, allowing limited control.

Here the researchers stripped the nanocrystals of their native ligands, leaving open coordination sites on their naked surfaces. They coordinate the open sites with specialized block copolymers that form spherical assemblies with the tethered nanocrystals congregating on the periphery. After assembly, the researchers drove out the polymer template, leaving a freestanding porous structure of fused nanocrystals.

The team implemented the new technique with a variety of oxides, fluorides and metals, demonstrating unprecedented compositional and structural control, which will help researchers optimize mesoporous materials for energy storage and other technologies.

"Assembly of Ligand-Stripped Nanocrystals into Precisely Controlled Mesoporous Architectures," R. Buonsanti, T. E. Pick, N. Krins, T. J. Richardson, B. A. Helms, and D. J. Milliron, Nano Letters 12, 3872 (2012). DOI: 10.1021/nl302206s