Gold also figures highly in a research project at Rice University’s CBEN. The work centers on improving the remediation treatment of trichloroethene (TCE), one of the most pervasive and troublesome groundwater pollutants in the country. “The advantages of palladium-based catalytic remediation of TCE are well-documented,” says lead researcher Michael Wong, assistant professor of chemical engineering and chemistry, “but so is the cost. Using nanotechnology, we were able to maximize the number of palladium atoms that come into contact with TCE molecules and improve efficiency by several orders of magnitude over bulk palladium catalysts.” The team found that in bulk palladium less than 4% of the palladium atoms were on the surface of the particle; pure palladium nanoparticles boosted that to 24%; but Pd/Au nanoparticles have 100% of the palladium atoms accessible for reaction.
Work still needs to be done to develop the proper catalyst reactor system for performing downstream remediation, says Wong, but progress is being made. “We’ve improved upon our catalyst by making smaller particles, which turn out to be more active than our ‘Version 1’ catalysts. And we’ve found that our ‘Version 2’ Pd/Au catalysts are not slowed down or poisoned by chloride ions and that they are less affected by sulfide contaminants than pure Pd catalysts,” he notes. “We can mount the Pd/Au nanoparticles onto powders that can be trapped inside a flow reactor, so we don’t lose Pd/Au nanoparticles during the reaction,” adds Wong.
Most catalysts are expensive, of course, which makes recently reported research at the Georgia Institute of Technology, Atlanta, Ga., particularly interesting. Using the special properties of new magnetic nanoparticles, researchers in the School of Chemical and Biomolecular Engineering have managed to separate for reuse two different catalysts from a multi-step chemical reaction carried out in a single vessel (Figure 3). “By doing the reactions in a single vessel, we can cut out two or three separation steps to provide both an economic advantage and an environmentally benign process,” explains Christopher Jones, associate professor. The magnetic nanoparticles work well as catalyst supports because of their size and high surface area, but because they are superparamagnetic — so small at 5 nm to 20 nm that they don’t exhibit a net magnetic attraction to each other — they remain suspended in the reaction vessel and don’t clump together until a magnetic source is brought near.
Magnetic or not, the attractions of nanotechnology are clearly booming. From his perspective as a designer and builder of nanotechnology facilities, CH2M Hill’s O’Halloran is well placed to see the whole picture. “The pace of change is unbelievable,” he says. “The tools we have developed are accelerating the pace, and as the pace accelerates, the tools get better and the pace gets faster.”
Figure 3. Georgia Tech researchers Nam Phan (left) and Christopher Gill study the separation of magnetic nanoparticle catalysts from polymeric resin catalysts.