Cotton wool proves effective in separating single-wall carbon nanotubes

Cotton wool proves effective in separating single-wall carbon nanotubes
Credit: Kazan Federal University

Carbon nanotubes (CNT) are a family of 1D nanostructures with numerous verified applications, made possible due to their excellent mechanical, optical and conductive properties. However, application of CNTs is hampered by the presence of species with various structures in the raw production mixture, which obscures unique properties of individual species.

There are various methods for separating CNTs, but they are difficult to scale up mainly because of the high cost of the reagents involved. Notably, most of these methods were originally developed for sorting proteins, and were only recently adopted for separating CNTs.

In this paper, the authors propose a new, cost effective separation method, suitable for the industrial scale processing of CNTs. The method of separation is based on passing the CNTs' surfactant solution through a column filled with chemically modified wool.

One of the existing methods of separation, referred to as selective gel permeation, in its essence is a basic column chromatography. Namely, the CNTs surfactant solution is passed through a column, filled with beaded gels of agarose and/or dextran with the trade names Sepharose and Sephacryl. Both agarose and dextran are polysaccharides made from the glucose or glucose-like building units. Cellulose is a natural polysaccharide consisting of the same structural units. This is why the team decided to try this material as a column filler for selective permeation.

Cotton is natural cellulose, possessing due to the fibrous structure. Co-author Timur Khamidullin, a Ph.D. student in Ayrat Dimiev's group (Laboratory of Advanced Carbon Nanomaterials, Kazan Federal University) made the first try with natural cotton wool purchased at a local pharmacy. Despite low sorting efficiency, there was some registered separation, i.e. cotton worked as a column filler. Inspired by the result, Ayrat Dimiev decided to chemically modify the cotton wool to change the chemical nature of its surface. Results were even higher that the expectations: this gave much better separating efficiency from the first very trial. It took another year and half of the collective group efforts to fine-tune both chemical modification of cotton, and the surfactants' ratio in dispersing and eluting solutions.

The use of modified cotton wool allowed the achievement of a level of separation which was never reported for tubal CNTs before. In addition, modified cotton wool is about 200 times cheaper than the agarose-and dextran-based hydrogels, currently employed in the selective gel permeation separation method. The method's scalability is limited only by the diameter of the separation column.

The main contribution to the work was made by group leader Ayrat Dimiev, Ph.D. student Timur Khamidullin, and postdocs Shamil Galyaltdinov and Artur Khannanov.

In the raw production mixture, CNTs of different structures and properties obscure each other's value. Industrial demand for separated CNTs will appear and grow in the coming years. CNTs with metallic type conductivity can be used in flexible transparent conductive films and even potentially replace metals in wiring. Semiconducting CNTs can be used as transistors and as platforms for imaging and targeted drug delivery due to their distinct and unique emission in the IR region. Thus, efficient methods for separating raw CNT production mixtures would raise application of CNTs on a new scientific and technological level. Moreover, the availability of ready-made separated nanotubes will spur the search for new directions of their application.

The main area of future work is to further increase the efficiency of separation by fine-tuning the separation process parameters and the structure of the modified cotton wool. The optimal structure of the modified cotton wool and the conditions for its production are still not fully understood; this question needs to be fully resolved. After this is achieved, the process should be scaled to industrial quantities, and separated nanotubes with various types of conductivity should be tested for practical solutions.

The paper has been made available online and is set to appear in print in June 2021.

Explore further

Process to produce well-aligned CNT arrays on a 10-centimeter silicon wafer

More information: Timur Khamidullin et al, Simple, cost-efficient and high throughput method for separating single-wall carbon nanotubes with modified cotton, Carbon (2021). DOI: 10.1016/j.carbon.2021.03.003
Journal information: Carbon

Citation: Cotton wool proves effective in separating single-wall carbon nanotubes (2021, April 19) retrieved 6 May 2021 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments