EPFL’s Wendy Queen holding vials containing the hexavalent chromium-adsorbing MOFs. Photo: Alain Herzog/EPFL.
EPFL’s Wendy Queen holding vials containing the hexavalent chromium-adsorbing MOFs. Photo: Alain Herzog/EPFL.

Hexavalent chromium continues to contaminate water sources around the world, with one US company fined in February this year for having put employees at risk. Hexavalent chromium is considered to be extremely toxic, especially when inhaled or ingested, and its use is regulated in Europe and in many countries around the world. It is thought to be genotoxic, leading to DNA damage and the formation of cancerous tumors.

Now, chemists at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland are developing energy efficient processes for removing contaminants such as hexavalent chromium from water. They report their latest results in a paper in the Journal of Materials Chemistry A.

"Providing access to clean water is one of the most important challenges of our time," says lead author Wendy Queen of EPFL's Laboratory of Functional Materials. "The development of energy efficient processes able to rapidly remove water contaminants play an important role in our effort to globally improve human health and environmental well-being."

Queen and her colleagues are developing sponge-like materials that can collect specific substances from solution. Their materials are actually crystals called metal-organic frameworks (MOF), which the scientists are tailoring to capture particular substances.

These materials are extremely porous, such that the contact surface area contained in 1g of MOFs can be as large as that of a football field. The target substance enters these pores and sticks to the internal surface area of the MOF in a process called adsorption.

The scientists have previously shown that MOFs can be tailored to efficiently adsorb various substances dissolved in solution, like gold, mercury and lead. For instance, 1 gram of MOF can adsorb almost 1 gram of gold. In collaboration with EPFL scientist Berend Smit and EPFL PhD student Bardiya Valizadeh, Queen has now developed MOFs that can extract hexavalent chromium from water.

Hexavalent chromium is a relatively light substance, and so these MOFs can extract approximately 208mg per gram of MOF. In addition, if light is shone onto the MOF, it can transform the highly toxic hexavalent chromium into relatively nontoxic trivalent chromium.

Further developments are required in order to implement this technology for decontaminating water outside of the laboratory. "The great thing about our sponges is they are relatively easy and cheap to make," explains Queen. "The next step is to test our sponges at larger scales." The scientists expect 1kg of MOFs to cost roughly 15 Swiss Francs to make, whereas 1kg of gold is worth roughly 55,000 Swiss Francs.

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.