Silica And Ice Template Creates Holey Microfibers

With a "brick and mortar" assembly approach, researchers have made porous, hollow carbon/metal oxide microfibers with well-controlled pore structures (J. Am. Chem. Soc., DOI: 10.1021/ja800376t). Such composites of carbon and metal oxide are useful for catalysis, electrochemistry, and electrooptical applications. Although existing techniques produce uniform pore structures in carbon fibers, materials researchers say precise control over the formation of uniform pores in carbon/metal oxide fibers has remained challenging. In the new study, Galen D. Stucky and Qihui Shi at the University of California, Santa Barbara, and colleagues created "bricks" by coating silica spheres first with an oxide of zirconium or of titanium and then with polyacrylonitrile. The spheres were dispersed into an aqueous polyvinyl alcohol (PVA) solution and frozen. With PVA left behind to act as "mortar," the spheres formed fibers when the ice was sublimed away by freeze-drying. The researchers then pyrolyzed the resulting fibers. Dissolving the silica cores with a basic solution finally produced porous, hollow composite fibers (shown). Stucky says this clean, economic, and versatile method is suitable for assembling different core/shell-structured particles into a single fiber, giving the fiber multiple functionalities, among them catalytic or magnetic properties.