16 February 2012
After your cup of coffee has perked you up, you can use the leftover grounds to fertilize your garden. A new study has found another possible use for them: eliminating the smell of toxic gases from the air.
Researcher at the City College of New York took regular coffee grounds and turned them into a charcoal-like substance capable of sopping up gases such as hydrogen sulfide, which give sewers their rotten-egg scent and put sewer workers at risk.
The inspiration came to Teresa Bandosz, a professor of chemistry and chemical engineering, because she drank a lot of coffee and knew the caffeine in it contains nitrogen – which is key for scrubbing gases. Everything from coal to wood to coconut shells is used today to make carbon filters, but nitrogen has to be added during the process, which adds to the cost.
Bandosz, lead study author, said she and her team first tried baking the coffee grounds dry. The results weren’t quite what they were looking for, so they added water and a chemical activator, zinc chloride, to the grounds to produce a slurry, then baked it at 800 degree Celsius (1,472 degrees Fahrenheit).
The finished product had densely packed pores covered with nitrogen. “What is important in the material is the nitrogen on the surface should be very well distributed,” Bandosz told Innovation News Daily.
Technically, there are no large hurdles to commercializing the use of coffee grounds as charcoal filters, but considering the tons of activated carbons used in industrial scrubbers, it would take an incredible amount of leftover coffee grounds to replace even a portion of them, Bandosz said.
The team at CCNY is looking into other possible applications for their baked slurry: energy storage and gas sensing.
For the do-it-yourself crowd seeking a small air freshener, they might be better off relying on the smell of a freshly brewed pot of coffee to waft through their home and cover up other scents. Bandosz doesn’t recommend trying to carbonize the coffee grounds in a kitchen oven at 400 or even 500 degrees Fahrenheit. “If you heated it in the oven,” she said, “you’d probably just burn it and not carbonize it.”
The study appeared in the Jan. 30 issue of the Journal of Hazardous Materials.