Magazine article Science News

Better and Cheaper Porous Carbon Filters

Magazine article Science News

Better and Cheaper Porous Carbon Filters

Article excerpt

Although activated carbon has been used for more than half a century to filter contaminants from air and water, scientists have only now imaged the twisting and turning pores that enable the adsorbent to do its job.

Christian L. Mangun and James Economy of the University of Illinois at Urbana-Champaign and their colleagues at Southern Illinois University at Carbondale used scanning tunneling microscopy to look at cross sections of carbon fibers that had been activated by heat to make them porous. By understanding the microstructure, they can tailor the fibers' properties to filter specific contaminants. "We can not only control pore size and shape but also pore chemistry," Economy says. The group's findings will appear in the October Carbon.

Although low-cost carbon granules, not fibers, are used in most applications, no one has yet sliced granules into thin sections that would show the tiny pores, which are often only a few tenths of a nanometer wide, Mangun says.

That pore size is small enough to filter out contaminants like sulfur dioxide, butane, and trichloroethylene. The researchers have changed the chemistry of the pores by lining them with different compounds, thus improving further the fibers' ability to trap passing molecules. For example, acidic pores remove ammonia gas, and basic pores filter out hydrochloric acid, they find.

The researchers' analysis also showed that conventional wisdom about greater surface area leading to greater adsorption wasn't completely correct, Mangun says. …

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