How to make carbon nanotubes
at room temperature

Made at 180°C
(a record low, not long ago)

As I noted in a recent post on self-assembled nanoelectronics (“Carbon Nanotube Transistors through DNA Origami”), carbon nanotubes (CNTs) hold promise for self-assembled nanomechanical systems, too: They are orders of magnitude stiffer than biomolecules, and can serve not only as rigid components, but also as low-friction linear and rotary bearings to support moving parts.

Recent research has shown that self-assembled, biopolymer-based structures can incorporate CNTs as components, but could they also be used to help make them — for example by serving as templates of some sort? If so, then techniques based on self-assembly might provide tools for making CNT and graphene nanostructures of unprecedented complexity and precision.

Unfortunately, the most common methods for synthesizing CNTs operate at temperatures (e.g., 700°C) that would toast organic macromolecular structures in an instant.

Fortunately, however, a recently-issued patent explains how to synthesize CNTs in a process catalyzed and templated by organic macromolecular structures at room temperature. I think this deserves some creative attention from experimentalists.

Here’s a patent excerpt with a recipe:

United States Patent No.:	7,556,789 B2
Date of Patent:	July 7, 2009

Low temperature synthesis of carbon nanotubes

Abstract: Low temperature methods for synthesizing carbon nanotubes (CNTs) comprise decomposing a halogenated hydrocarbon in a fluid in the presence of a catalyst where the catalyst catalyzes the formation of a carbon phase comprising nanotubes…. In preferred embodiments, the catalyst comprises a metal encapsulated dendrimer molecule.
[...]

Example 1

Synthesis of 16:1, Iron Encapsulated Dendrimer

Generation “4” PPI dendrimer, 0.4156 g (commercial product of Sigma-Aldrich) is dissolved in 20 mL of water. A separate solution is made by adding FeCl₃ .6H₂ O, 0.5123 g to 20 mL of water. The two solutions are combined and mixed for one hour. The solution becomes dark brown to red. A third solution is made by dissolving sodium borohydride, 0.3303 g in 15 mL of water. The sodium borohydride solution is added dropwise to the combined dendrimer/iron chloride solution. The solution turns brown to black, a noticeable solid forms, and gas evolves. The combined solutions are mixed one hour after the addition of the sodium borohydride. The reaction mixture is centrifuged and the solvent is decanted. The reaction product is black. The material is dried for 48 hours.
[...]

Example 4

Iron PPI Dendrimer CNT Growth (Room Temperature)

In a round bottom flask, 0.062 g of the iron dendrimer catalyst of Example 1, 12 mL benzene, 2.7 mL tetrachloroethylene, and 0.99 g potassium are combined in an inert atmosphere. Potassium is trimmed with a razor blade prior to combining with the other ingredients in the round bottom flask in order to remove surface oxides. The mixture is stirred for one week in the round bottom flask in an inert atmosphere at room temperature. Afterward, the flask is removed from the inert atmospheric conditions. The potassium is removed and cleaned in a series of washes with t-butyl alcohol, methanol, and water. The reaction product is isolated by centrifugation and decantation of the liquid. Transmission electron microscopy shows the presence of CNTs in the reaction products, with observable diameters on the order of 15-20 nm. Raman spectroscopy shows graphitic peaks corresponding to MWNT growth.

Chemistry with chlorinated hydrocarbons in benzene… Could biopolymeric systems work under such conditions? This might seem doubtful, since there is a mythology that says water is necessary for everything that smells of biology. Nonetheless, a number of natural enzymes function in organic solvents (including benzene and chlorinated hydrocarbons). Even more enzymes work, or work better, after some engineering adjustment.

Together, these results suggest that advances in biomolecular and biomimetic systems engineering are building a technology platform strong enough to support more than one might expect.

• Carbon Nanotube Transistors through DNA Origami
• Modular Molecular Composite Nanosystems
• From Self-Assembly to Mechanosynthesis

Tagged as: bionanotechnology, carbon nanotubes, graphene, nanosystems