The recent discovery of lead in drinking water in Flint, Michigan, and Newark, New Jersey, are sobering reminders that contaminated drinking water is not an environmental health hazard restricted to developing countries. The cases underscored the importance of having technologies in place that can detect low levels of heavy metals and that can remove these pollutants from water. A group of researchers recently developed a compound that has the potential do both these jobs. What’s more, it’s cheap and recyclable.
The new material is a luminescent metal-organic framework that has the patterned form of a crystal. Scientists recently described how they developed and tested it in a recent paper in the journal Applied Materials and Interfaces.
For the study, the researchers first developed three similar luminescent, metal organic frameworks, or LMOFs. The glowing material wanes in intensity in the presence of heavy metals. They are also highly porous and able to trap metals. (One gram has so many pores that if its surface area was laid flat it would cover 2,000 square meters, says co-author Jing Li.) The researchers then analyzed their structure with powerful X-rays. Finally, they tested how the materials reacted in water with different heavy and light metals in terms of detection, capture, and selectivity.
They found that one of these LMOFs could detect lead at 19.7 ppb—among the lowest concentrations of any LMOF studied to date—and mercury at 3.3 ppb. In terms of cleaning the water, experiments revealed that this same LMOF performed best with mercury, removing 99 percent of the mercury in a water solution in 30 minutes. It performed slightly less well for lead, but was still highly effective, Li said. The compound was selective for these two heavy metals in mixtures that contained light metals calcium and magnesium, which are non-toxic and even beneficial.
Ideally, Li says, this compound could be placed in a polymer to trap heavy metals as they flow over it. Further research and development is needed to make the technology both cheaper and more durable. If it works, we can look forward to not just crystal clear water, but water that is crystal-cleaned, too.