Glowing crystals detect and trap contaminants in drinking water

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A view of the crystal structure of an organic framework that traps heavy metals(Credit: Rutgers University)

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Researchers have developed tiny, glowing crystals that can both detect and trap toxic heavy metals at the same time. Similar research has been done on structures to either detect or remove such nasty substances, but this appears to be the first capable of doing both. The hope is that the structure could be a tool for cleaning up contaminated drinking water in places like Flint, Michigan.

A team led by researchers from Rutgers University created the crystals to function like miniature traps for toxins such as lead and mercury. As part of the testing and experimentation process, they used intense x-rays at the Berkeley Lab in California to get a detailed look at their engineered crystals, which are known as luminescent metal-organic frameworks, or LMOFs.

"Knowing the crystal structures is one of the most important aspects of our research," explains Rutgers chemistry professor Jing Li. "You need those in order to perform subsequent characterizations and to understand the properties of these materials."

When examined using the x-rays, the team observed their LMOF structure is like a 3D grid of carbon, hydrogen, oxygen, nitrogen, and zinc atoms creating large open channels that allow heavy metals to pass into the holes and then bind to the surrounding framework of the crystal. This is similar to other metal-organic frameworks that have been found to be promising for carbon capture and numerous other potential uses.

The LMOFs created by the Rutgers-led team were also engineered to glow thanks to a fluorescent chemical component that "lights up" when it is first attached the MOF. Then, as the structure takes up more of the heavy metals, the glow begins to turn off through a process the researchers refer to as "quenching," which has to do with the chemical reactions between the toxins and the fluorescent components.

The result is a means of simultaneously detecting and capturing heavy metals. The more the glow of the crystals dims, the more toxins they've trapped, theoretically. The LMOFs the researchers tested bind more strongly to mercury and lead than to lighter, safer metals like magnesium and calcium that are also present in drinking water supplies.

"We need to have a MOF that is selective and will only take the harmful (metals)," Li emphasized.

The researchers found the crystals can be cleaned and reused up to three times, but Li says further research could lead to the development of more durable LMOFs that could potentially be integrated into water filters.

"These filters could be used for capture on a larger scale," she said, adding that a key next step would be to test the LMOFs' performance on actual contaminated water sources. "These are promising results, but we have a long way to go."

The study was published in the journal Applied Materials and Interfaces.

Source: Berkeley Lab

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