Carbon nanotubes, some smeared. Outside diameters average 13-16 nm, inside is 4 nm. (via University of Missouri)
Graphene is a super-strong material (has a breaking strength of 200 times greater than steel) made from 1-atom thick sheets of pure carbon. It can be produced by using a myriad of techniques and methods (heating silicon carbide, epitaxial growth on a metal substrate and graphite oxide reduction to name a few) and can be formed into various allotropes (substance variant that exhibits new properties over the original), such as carbon nanotubes. Like most every super material these graphene allotropes, carbon nanotubes (CNTs) in particular, have a dark side and a joint research team from the University of Missouri and the USGS (United States Geological Survey) have released a study that deems the material toxic to aquatic life. CNTs are tiny nano-scaled cylinders, that can be hundreds of times longer than they are wide (up to 132,000,000:1), have incredible thermal and electrical properties. They can be integrated into everything from solar cells to batteries. Current manufacturing methods of CNTs, such as arc discharge, laser ablation and chemical vapor deposition typically result in leaving metal (nickel, chromium etc.) impurities in the resulting material. The research team, led by Professor Christopher Ingersoll, found that the metal impurities as well as the nanotubes themselves can stymie the growth rate and even kill some species of aquatic life. The group came to their findings in tests conducted with mussels, worms, small flies’ larvae and crustaceans (unknown as to which).
Other studies undertaken from researchers, like those from the University of Cambridge back in 2007, have concluded that under certain conditions CNTs have the ability to pass through membrane barriers and into human cells and accumulate in the cytoplasm and cause the death of the cell. Studies conducted on rodents have shown that, regardless of the manufacturing techniques and the amount of metal residue, CNTs were capable of producing inflammation, fibrosis and toxicological changes in the rodent’s lungs. The shape of CNTs closely resembles that of asbestos fibers, which suggests human inhalation may lead to pleural mesothelioma or cancerous lesions in the lining of the lungs. The manufacturing of graphene itself is also widely considered as extremely toxic to humans.
One of the more notable manufacturing processes is graphene oxide reduction, which is created by dispersing oxidized and chemically processed graphite particles in a water solution. Researchers from Singapore’s A*STAR (Agency for Science, Technology and Research) found that this specific manufacturing process has the ability to kill bacteria. The team tested their theory using graphite, graphite oxide, graphene oxide and reduced graphene oxide that was introduced to the bacteria ‘Escherichia coli’ (or E. coli). They found that the two graphene-based materials were substantially more lethal than that of the graphite-based (graphene oxide was the most lethal of the four). The researchers stated that a considerable amount of the E. coli bacteria were ‘wrapped’ by the graphene oxide, which effects the cells overall health while the cells tend to imbed themselves onto the larger graphite particles leading to a less-lethal effect. The goal of the researchers is to raise awareness and educate manufacturers on safe handling techniques, as well as waste management to reduce or limit CNTs and graphene's effects on the environment. They also state that more study of the composite materials break-down (decay) in nature to gain insight and control of the long-term effects/risks of the super-material.
I knew these super materials had to have a dark side.