http://phys.org/news/2012-05-lemons-lem ... oxide.html
Making carbon-based products from CO2 is nothing new, but carbon dioxide molecules are so stable that those reactions usually take up a lot of energy. If that energy were to come from fossil fuels, over time the chemical reactions would ultimately result in more carbon dioxide entering the atmosphere—defeating the purpose of a process that could otherwise help mitigate climate change.
Professor Yun Hang Hu’s research team developed a heat-releasing reaction between carbon dioxide and Li3N that forms two chemicals: amorphous carbon nitride (C3N4), a semiconductor; and lithium cyanamide (Li2CN2), a precursor to fertilizers.
“The reaction converts CO2 to a solid material,” said Hu. “That would be good even if it weren’t useful, but it is.”