Selective Annealing Techniques of Multi-Walled Carbon Nanotube Synthesis

Multi-walled carbon nanotubes (MWNTs) offer a variety of industrially important functions, including tensile strength, electrical conductivity, and antimicrobial activity. We have been synthesizing a matrix of 28 O-functionalized MWNT using a nitric acid technique combined with a selective annealing technique.

These functions result from various physical and chemical properties. In order to inform industrially relevant and sustainable design, it is crucial to definitively understand the relationships between MWNT physiochemical properties and these functions, particularly cytotoxicity, which could be desirable or undesirable depending on the application. Nanotube cytotoxicity has been attributed to physical characteristics, chemical characteristics, and production method. It has previously been shown that surface oxygen functional group type plays a critical role in increased MWNT toxicity.  However, it has also been proposed that length or aspect ratio is also an important factor in MWNT toxicity. Single walled carbon nanotubes are currently considered a promising antimicrobial material. However, their high relative cost makes the promise of functionalized MWNTs even more appealing. 

To answer this question, we have been synthesizing a matrix of 28 O-functionalized MWNT. We have been using a nitric acid technique combined with a selective annealing technique for the synthesis. The acid treatment shortens the tubes and adds oxygen surface groups, while annealing under inert conditions selectively removes some of these oxygen groups. This gives us a suite of MWNTs with varying length and oxygen content/group type.

Since completing that synthesis, we have been characterizing the MWNTs through various techniques, including DLS, SLS, a bacterial toxicity assay, TEM, XPS, etc. We will also be looking to perform other tests and collaborate more. 

This research could impact the way we use antimicrobial products, including textiles, polymers and more. This will also offer design principles to CNT manufacturers to make CNTs to meet the needs of their clients, so they can effectively use less material, rather than using a large amount of ineffective material.