To the average coffee drinker, black specks at the bottom of a mug might look like nothing more than leftovers from a morning cup of joe. But to a University of Calgary researcher, they look like miniature sleuths for detecting toxins in drinking water.

Dr. Seonghwan (Sam) Kim, Canada Research Chair in Nano Sensing Systems and a professor in the university’s Department of Mechanical and Manufacturing Engineering, has developed a new way to detect trace amounts of hexavalent chromium ions (Cr⁶⁺) using coffee grounds. The ions are highly toxic carcinogens found in water near industrial facilities used for steel production, metal coating, dyeing, leather tanning, and petroleum catalyst production. They have been identified as a cause of neurological disorders, organ damage and infertility.

Dr. Kim says Cr⁶⁺ concentrations in water vary significantly depending on local conditions, like proximity to steel plants and refineries, presence of natural organic matter or minerals in water and soil, and a waterway’s flow conditions. Cr⁶⁺ isn’t naturally widespread in most regions of Canada—it’s more often found in China, India, the United States, parts of Africa and Latin America. But it can occur locally in Canada due to industrial activities.

Because coffee is rich in carbon and contains chemical groups such as chlorogenic and amino acids—many of which remain in coffee grounds—coffee waste seemed like the perfect way to develop a test to track Cr⁶⁺, says Dr. Kim.

Along with Dr. Arindam Phani and PhD student Pegah Zandi, Dr. Kim developed a method of using coffee waste to manufacture carbon quantum dots, which are nanoscale carbon particles that have a number of purposes, including fluorescence. The team then synthesized a final product: graphitic carbon nitride sheets decorated with the carbon quantum dots.

Dr. Phani says the resulting material behaves like a fluorescent highlighter, becoming visibly darker when exposed to Cr⁶⁺ in water, even at very low concentrations.

It’s one thing to detect Cr⁶⁺ in water, and quite another to remove it from the water supply. But Dr. Kim says the ions can be adsorbed—held as a thin film on the surface of the water—and reduced to trivalent chromium, or Cr³⁺, a less harmful version.

The team developed a highly selective sensor that allowed them to monitor this reduction process effectively. “The sensor can distinguish between Cr⁶⁺ and Cr³⁺ with high specificity,” says Zandi.

The next phase of the team’s research will look at how much adsorption and conversion happens through their process.

“By further refining the sensing protocol and developing a portable sensing system, this simple method could be widely adopted and used for water safety screening in the field and even at supply stations,” says Dr. Kim.

As for the research itself, he views it as a significant achievement.

“We demonstrated that this simple sensing method could detect hexavalent chromium ions at a concentration that meets the World Health Organization’s recommended standard,” he says.

The team has filed a provisional patent application with Innovate Calgary and may launch a start-up company to commercialize the technology.

Dr. Kim says his team’s findings could go a long way toward providing safer drinking water for communities around the world.

This article was adapted and published with permission from the University of Calgary.