Environmentally Healthy Nanotechnology

By Vijayalakshmi "Viji" Kalyanaraman

Turning Plastic Bags into Carbon Nanotubes

Every time you throw your plastic grocery bag into the garbage, do you feel that you are hurting the environment? Yes, it may be something to consider, as plastic bags are non-biodegradable and their decomposition takes about 1000 years. Although some of them are recycled, many can still end up in the landfills and can also find their ways into waterways, beaches and roads. As plastics are indigestible, they can be dangerous to animals living around the polluted area. If burnt, they release toxic fumes into the air.

Governments in several countries have brought in regulations to reduce the impact of plastics on the environment.  In countries like India, grocers began charging for plastic bags in order to reduce their usage. Many grocery stores such as, Whole Foods Market stopped offering plastic bags entirely and started exclusively using paper bags. Plastic recycling is an excellent method to reduce environmental effects. However, plastic recycling is very expensive and hence only 1% of the waste is recycled.

Recently, Argonne research scientists discovered a recycle method that transforms a plastic garbage bag into carbon nanotubes (see picture), a black nanosized carbon compound that can be used as one of the important components in rechargeable batteries.

Plastic bags are made of polyethylene, a carbon based polymer compound. It is nothing but a long chain of carbon atoms connected by single bonds with each carbon atom attached to two hydrogen atoms (see picture). Argonne Chemist Vilas Pol can turn plastic bags into carbon nanotubes that can be used as anode materials in Li-ion batteries. This process involves heating the plastic to 700oC with a cobalt catalyst and then cooling it down. The bonds in the polyethylene (plastic) completely break down and the decomposed products grow as carbon nanotubes on the cobalt catalyst. The resulting carbon nanotubes are encapsulated with cobalt and can be used as is in Li-ion batteries as an anode material.

“It works fantastically” Pol told the press.

This new method of carbon nanotube production is one of the cheapest known today. It can potentially result in cheaper batteries while also reducing the environmental impact of plastic bags use.

About 100 billion plastic bags are used every year in the US alone. It is worth mentioning that plastic bags are produced from petroleum by-products; as we know, petroleum is a non-renewable source and its supply is diminishing day by day. Conversion of waste plastic bags into carbon nanotubes helps to solve the environmental issue.

Polyethylene
Carbon nanotube: obtained by rolling graphite layers into a tube. The diameter is only a few nanometers (~ 1/50,000th the size of a human hair).

Industrial partners can now buy this formula which can also be applied other type of plastics. Nanotechnlogy has sometimes been considered to be hazardous to health and environment – this is an excellent example where nanotechnology can do wonders to create a healthy environment. May be soon you will be exchanging your plastic grocery bags for mobile phone batteries!

About the Author:

Vijayalakshmi “Viji” Kalyanaraman

Viji has been a postdoctoral research scientist at Argonne National Laboratory for the last two years. Her research includes investigating astrochemical reactions using x-ray photoelectron spectroscopy and optical luminescence techniques, in an effort to understand the origin of life on the earth.  She studied the reaction mechanisms in thin film amino acids, DNA as well as of organic molecules when bombarded with soft x-rays from advanced photon source.  She is now on her way to take up new challenges.