Among the myriad consequences of climate change and general industrial pollution, one is perhaps the most terrifying: lack of clean drinking water. If you live with access to drinkable tap water, you should realize just how lucky you are. According to the World Health Organization (WHO) an estimated 1 billion people do not have access to clean drinking water.
The new material described in the report is a so-called Metal Organic Framework (MOF) Polydopamine Composite. It’s an organic chemical metal structure known to pull things like water and gases from air. However, this also proves to be a promising material to remove heavy metals selectively from water. Extract from the report:
Drinking water contamination with heavy metals, particularly lead, is a persistent problem worldwide with grave public health consequences. Existing purification methods often cannot address this problem quickly and economically. Here we report a cheap, water stable metal–organic framework/polymer composite, Fe-BTC/PDA, that exhibits rapid, selective removal of large quantities of heavy metals, such as Pb2+ [lead] and Hg2+ [mercury], from real world water samples. In this work, Fe-BTC is treated with dopamine, which undergoes a spontaneous polymerization to polydopamine (PDA) within its pores via the Fe3+ [iron] open metal sites. The PDA, pinned on the internal MOF surface, gains extrinsic porosity, resulting in a composite that binds up to 1634 mg of Hg2+ and 394 mg of Pb2+ per gram of composite and removes more than 99.8% of these ions from a 1 ppm solution, yielding drinkable levels in seconds. Further, the composite properties are well-maintained in river and seawater samples spiked with only trace amounts of lead, illustrating unprecedented selectivity. Remarkably, no significant uptake of competing metal ions is observed even when interferents, such as Na+ [sodium], are present at concentrations up to 14 000 times that of Pb2+. The material is further shown to be resistant to fouling when tested in high concentrations of common organic interferents, like humic acid, and is fully regenerable over many cycles.
In short: this metal-polymer sponge-like material can sweep up lead and mercury pollutants from any source of water with extreme efficiency, and can even be cleaned and reused over and over again.
To put that “1 parts per million in seconds” into context, consider the current US Environmental Protection Agency limit of lead in drinking water of 2 parts per billion (2 ppb being 500 times less than 1 ppm) — this material does the job!
But didn’t we stop using leaded gasoline long ago? Yes, but lead is difficult to get rid of, and it still originates from paints, ceramic glazes, jewelry, toys and in pipes etc. And the mercury coming from coal-burning power plants and other sources is very persistent.
Heavy metals such as lead and mercury are known to damage the nervous system, and the body is not able to excrete it, so concentrations add up. Solutions like these new materials are crucial to clean up the mess.