Nanoscale clean-up operation

Researchers at the University of Michigan have demonstrated that carbon nanotubes can remove dioxins from combustible organic compounds associated with municipal, medical, and hazardous waste incinerators.

Ralph Yang and Richard Long in the University of Michigan’s Chemical Engineering Department built and tested carbon multiwalled nanotubes (MWNTs) to demonstrate that carbon nanotubes remove dioxins far more effectively than the activated carbon that has been used in Europe and Japan since 1991.

The researchers used data from their study to calculate that the interaction of dioxins with MWNTs can yield up to 1034 greater removal, making the approach vastly superior to alternatives like activated carbon, clays, alumina, and zeolites.

According to a statement increased performance can be attributed to hexagonal arrays of carbon atoms in the graphene sheets that surround the tube axis, where the benzene rings of dioxin and the nanotube surface are expected to react strongly.

Modified temperature-programmed desorption is said to have allowed researchers to obtain information about the parts-per-trillion range, which is important because the US Environmental Protection Agency requires dioxins to be removed from combustion waste below 1 ng/m3.

Although activated carbon and nanotubes absorb dioxin, mercury, and other hydrocarbons, Yang is certain that the required amount of carbon nanotubes would be much less than that of activated carbon for the same dioxin removal.

‘We can make nanotubes from methane and low-cost iron- or nickel-containing catalysts, at fast rates and high yields,’ added Yang.

Businesses trying to commercialise nanotubes for applications ranging from electronics to chemical sensors predict that large-scale quantities will be available within the next few years.

Reinette Marek, business manager at Carbon Nanotechnologies, Inc in Texas, projects that brand-name, single-walled nanotubes (SWNTs) will be mass produced by 2005 and predicts that the price for complex process SWNTs will fall from the current $500 per gram to $0.55 per gram by that time.