To do so, they prepared a slurry of coffee grounds, water and zinc chloride, a chemical "activator." The team then dried and baked the mixture at temperatures of up to 800 degrees Celsius. The process of activation fills the carbon with scores of minute holes about 10-30 angstroms in diameter, roughly equivalent to 10-30 hydrogen atom-widths across. These densely packed pores are blanketed with nitrogen, perfect to capture hydrogen sulfide molecules passing through.
Hydrogen sulfide gas (H2S) isn't just a smelly nuisance for sewage plant neighbors; it can be deadly. Human noses are so sensitive to the rotten-egg scent of this toxin that it can overwhelm the sense of smell, Professor Bandosz explained. "When someone is exposed to high concentrations of H2S, the nose will stop detecting it," she said. "There have been cases in which workers died of H2S exposure in sewer systems." Professor Bandosz suspects that the coffee-based carbon could also separate out other pollutants from the air and water.
With the ubiquitous motto to "Reduce, Reuse, Recycle," and coffee-ground carbon's special affinity for a toxic gas, Professor Bandosz hopes coffee grounds can be commercially developed into the next green waste filter. For now, however, she recycles them on her own: "I put them outside under the plants in my garden, especially those that like acidic soil," she said. They are a great fertilizer, of course, packed as they are with nitrogen-rich caffeine.
|Contact: Jessa Netting|
City College of New York