Synthesis and characterization of pH-responsive single-walled carbon nanotubes with a large number of carboxy groups

A new type of pH-responsive single-walled carbon nanotubes (SWNTs) with a large number of carboxy groups was prepared by in situ grafting polymerization. Through exfoliating the SWNT bundles with sodium dodecylbenzene sulfonate (SDBS), individual SWNTs have been obtained. Due to the existence of SDBS, the individual SWNTs could be readily dispersed in water, then forming stable dispersions. Grafting polymerization of acrylonitrile was performed in micelles of SWNTs to produce polyacrylonitrile funtionalized SWNTs (PAN-SWNTs). Experimental results showed that adsorbing acrylonitrile on the SWNT surfaces plays a key role in the grafting process. After hydrolyzing PAN, polyacrylic acid functionalized SWNTs (PAA-SWNTs) were obtained. The amount of PAA grafted could be controlled by changing the feed ratio of initiator to monomer, and the maximum grafting amount could reach 40 wt%. The solubility of PAA-SWNTs in water could be adjusted by pH, with better solubility at higher pH. The large number of carboxy groups on the SWNT surfaces lends the systems convenient for further modification via amidation or esterfication.