A new and interesting method of combating heavy metal pollution presents itself in the form of...air. It is a novel aerogel that is made mostly of thin air, trapped in large spaces between the gel molecules. With an incredibly low density, it can soak up vast amounts of heavy metals in run-off water from polluted industrial sites.

Aerogels are low-density gel-like solids, where the liquid component of the gel has been replaced with gas. Consequently, they become remarkable materials, semi-transparent, ultra-light and very good heat insulators.

Usually, they are made of 90-99.8% air, with densities ranging from 1.9 to around 150 mg/cm³ and constructed from silicon dioxide or other organic polymers. They are mostly used in radiation detectors and thermal insulators.

This one prefers heavy metals and it is able to filter nearly all of the heavy metals, like mercury, a potent neurotoxin like lead and cadmium, allowing other metals like zinc and magnesium to pass through.

"We have a material that presents a very high surface area and the surface itself is made out of something with different reactivities than oxides," says chemist Mercouri Kanatzidis of Northwestern University and Argonne National Laboratory, whose team discovered the gels. "That gives rise to properties that oxides don't have."

The gel is made in solution from chalcogens (the column of elements on the periodic table that begins with oxygen) and platinum. The scientists observed that contaminated water - with mercury - that was run through a sulfur-germanium chalcogel, was greatly purified, meaning that the mercury concentration dropped from 645 parts-per-million to just 0.04 ppm.

"These heavy elements love to bind to sulfur atoms," Kanatzidis says. The metal-bearing water passes through the "torturous, porous network" of the chalcogel and "sooner or later, these heavy elements will encounter sulfur. It's sticky to them."

Although the mechanism behind the stickiness is yet unknown, it is bound to find useful practical applications in the shortest time.