The solution to pollution is mimicking evolution

Among the many threats corals face is pollution: the structure and chemical makeup of their skeletons make them so good at capturing, or adsorbing, toxins from the water that even very low levels of pollution can be fatal to the animals.

But a team of engineers from Anhui Jianzhu University in China is turning that weakness into a strength, taking inspiration from the architecture of corals to develop a new technology for cleaning up polluted water. They have manufactured synthetic coral that adsorbs heavy metals like lead, arsenic, and mercury to remove these toxins from the water column.

Real coral skeletons are composed of calcium carbonate, while the synthetic version is made of aluminum oxide. Microscopic aluminum oxide beads are already used to clean up polluted water, but they don’t work as well as originally hoped. That’s because they tend to stick to each other, reducing the surface area available to stick to pollutants. The nano-sized particles are also difficult to filter out of the water once cleanup is done.

Mimicking the hierarchical, branching architecture of corals solves both of these problems, the researchers report in the new issue of the Journal of Colloid and Interface Science. Their synthetic coral consists of small pieces of aluminum oxide about 1.5 micrometers across that are covered with tiny cups – each a mere 2.5 nanometers in diameter – that are just perfect for catching and holding heavy metal ions.

The key to getting the material to self-assemble, or spontaneously form these nanoscale cups, is using a 4:1 ratio of ethylene glycol to water during the manufacturing process, the researchers have discovered. The ethylene glycol molecules stick to the aluminum oxide molecules, and also stick to each other. This causes the aluminum oxide, a material that normally prefers to form flat sheets, to curl up into the cup-like shapes that resemble the microarchitecture of many corals.

The resulting synthetic corals remove 2.5 times more mercury from water compared to standard aluminum oxide nanoparticles, the researchers found. Because they are larger than the nanoparticles, they are also easier to remove from the water, they say.

The idea of synthetic coral self-assembly is pretty mind-boggling. But the principle behind the approach is almost alchemical in itself: The very life forms most threatened by water pollution may inspire the technologies that end up saving them. – Sarah DeWeerdt | 4 August 2015

Source: Wang X. et al. 2015 Self-curled coral-like γ-Al2O3 nanoplates for use as an adsorbent. Journal of Colloid and Interface Science DOI: 10.1016/j.jcis.2015.03.065

Header image: Coral reef at Palmyra Atoll National Wildlife Refuge. Credit: USFWS/Jim Maragos via Flickr.