An "upcycling" method of converting waste plastic bags into nanotubes has been developed at the Argonne National Laboratory in Illinois. In this path breaking method, 1 gm pieces of high or low-density polyethylene (HDPE and LDPE) were cooked at high temperatures (700 degrees C) which broke down the chemical bonds of plastic and cause carbon nanotubes to grow on pieces of the cobalt acetate catalyst. Though a lot of catalyst (about a fifth of the weight of the plastic being converted) is needed to get good results, this is still one of the cheapest and environmentally friendly ways yet found to grow nanotubes. Individual pieces of the catalyst become trapped inside forests of newly grown nanotubes. But the research has shown the nanotubes can be used as is without further processing to cut them free. "I have used the as-prepared cobalt-encapsulated nanotubes as an anode material for lithium-ion batteries and they work fantastically," says Pol. "The specific capacity of my carbon nanotubes is higher than commercial nanotubes." The cobalt impurities also make the nanotubes suitable for use in lithium-air batteries, because the cobalt is converted to cobalt oxides that perform as catalysts to help the reactions of ions in the battery that let current flow, he says. He has patented the use of the cobalt-containing nanotubes in both lithium-ion and lithium-air batteries. Nanotubes could also become self-repair tools for electronic circuits in our smart phones and laptops.