Available online 26 November 2010.
Many chemists want to speed things up, faster reactions can produce higher yields. But Brookhaven National Laboratory chemist James Wishart would rather slow some reactions down. He studies syrupy materials known as ionic liquids, liquids composed entirely of positive and negative ions. Unlike solutions of ions (e.g., sodium and chloride) dissolved in some other liquid, ionic liquids are more like melted salts, with higher viscosity than ordinary solvents. Molecules and electrons move more slowly through them, and they react to the movement of charge more slowly. That gives Wishart a chance to “see” reactions as they happen and allows new reactions to take place.
In a special issue of the Journal of Physical Chemistry Letters, Wishart will examine whether syrupy solvents do indeed provide the key to unlocking a new world of reaction.
The chemistry that Wishart studies may be applied to more efficiently convert solar energy into fuels or electricity, or improve the efficiency and storage capacity of batteries. And some of great personal interest to Wishart could be useful in recycling spent nuclear fuel to minimize waste.
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Energetic transients in ionic liquids show unusual reactivity patterns – courtesy, James Wishart.
“The spent-fuel treatment systems we have in place now were designed during the Cold War with the idea of recovering only what could be used to make nuclear weapons,” Wishart said. “Separating other useful elements out of the waste stream was neglected. With an advanced separation system making use of the unique properties of ionic liquids, we could take spent fuel — composed of uranium, plutonium, and other highly radioactive elements and fission products, and direct each component either to be burned up in reactors, used for industrial purposes, or assigned as waste. That would make better use of scarce resources and add greater certainty and security to waste disposal because the volume of waste would be reduced and what's left would be radioactive for a much shorter period of time.”
Because ionic liquids have low flammability and low volatility, they are particularly attractive for this kind of hazardous waste treatment. Additionally, boron (10B), which captures atom-splitting neutrons, can be included in the ionic liquid to prevent a nuclear chain reaction from occurring during the processing of fissile materials.
“We want to make these ionic separation systems ‘self-healing,’ resulting in as much recombination of electrons and holes as possible, that way the separation system does not become chemically degraded and inefficient, so it can be used over and over again”.