Packaging Vertically Aligned Carbon Nanotubes into a Heat Shrink Tubing for Efficient Removal of Phenolic Pollutants

Abstract

Having extremely high surface-to-volume ratio, carbon nanotubes (CNTs) are excellent adsorbents for the removal of organic pollutants. Majority of studies utilizing CNTs for such purpose disperse CNTs in a batch-type reactor filled with a solution of pollutants. However, retrieval or collection of CNTs after the adsorption can often be more demanding than the removal of pollutants. In this study, we address the challenge by packaging vertically aligned CNTs into a PTFE heat shrink tubing. Insertion of CNTs into the tubing and its thermal shrinkage densified the CNTs radially by 35%, which also reduced wrinkles in the nanotubes as confirmed by scanning electron microscopy (SEM). The CNT-based adsorption tube with a circular cross-section enabled facile connection to a source of polluted water, which we demonstrated by connecting the tubular platform to a syringe filled with solution of phenolic compounds. We passed the solution through the adsorption tube and analysed the filtrate in gas chromatography, which gave adsorption capacity of 72, 85, and 66 mg/g for phenol, m-cresol, 2-chlorophenol, respectively. Another advantage of our platform is that CNTs can be easily functionalized by flowing reactants through the tubing. Functionalization of CNTs with carboxyl groups, by flowing solution of nitric acid, enhanced the corresponding adsorption capacity to 115, 124, and 81 mg/g. We attribute the high adsorption capacity of our platform to efficient adsorbate-CNT interaction within the narrow interstitial channels between the aligned nanotubes. The CNT-based adsorption tubes can be of great significance for the simple and efficient removal of phenolic and other types of organic pollutants.