Direct Synthesis of Mesoporous Carbon Microwires and Nanowires

Martin Steinhart (CNMS Visiting Scholar)
Chengdu Liang, Michelle D. Pawel, and Sheng Dai (CNMS Staff)

Achievement
We have reported a direct and solvent-free approach to the synthesis of mesoporous carbon nanowires and microwires with high aspect ratios and low defect density. Porous alumina membranes were used as hard templates to control the 1-D morphology of the resulting mesoporous carbon while block copolymers were employed as soft templates to generate mesopores. The self-assembly synthesis of carbon precursors was conducted in 1-D channels of porous alumina membranes with space confinements. Mesoporous carbon nanowires and microwires were successfully released from the hard templates via chemical etching of the porous alumina membranes. Released mesoporous carbon microwires and nanowires may be used as lightweight functional filler material that allows tuning of the mechanical and electrical properties of nanocomposites.

Significance
The essence of our reported preparation of carbon nanowires and microwires lies in the combination of hard-template synthesis with soft-template synthesis. Ordered mesoporous materials combine a large specific surface area with well-defined pore geometry and have been used in energy storage, energy conversion, and catalysis. Their synthesis is based on the self-assembly of block copolymers and surfactants. Whereas the mesopore arrays thus formed may show a well-developed local order, the control over shape and arrangement of the mesoporous entities on a macroscopic scale remains a challenge. A strategy that addresses these problems involves the synthesis of mesoporous silica nanowires inside the pores of porous alumina, thus adapting an established method for the preparation of one-dimensional nanostructures based on the use of porous templates. It is highly desirable to apply this concept to amorphous mesoporous carbon, which exhibits superior resistance to acids and bases, excellent heat resistance, and high intrinsic electrical conductivity compared to mesoporous silica. Such materials may be promising components for miniaturized devices or nanocomposites.

Publications
M. Steinhart, C. Liang, G. W. Lynn, U. Gosele, and S. Dai, “Direct Synthesis of Mesoporous Carbon Microwires and Nanowires,” S. Chem. Mater., 19(10), 2383-2385 (2007).

This research was conducted in the Nanocatalyst & Building Block Theme at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. Department of Energy.

Mesoporous carbon microwires with a diameter of 400 nm. (a) SEM image of the surface of porous alumina containing microwires (scale bar 1 µm); (b) SEM image of released microwires at low magnification (scale bar 20 µm); (c) SE image showing a microwire segment; (d) DFTEM image of the area shown in (c); (e) SE image of a fractured mesoporous carbon microwire; (f) DF-TEM image of a detail of a microwire segment at high magnification.