Carboxymethyl-chitosan-modified carbon nanotubes have sensitive CO2-responsive dispersion in water

In this study, we grafted carboxymethyl chitosan (CMC) onto carbon nanotubes (CNTs), demonstrating that the CMC-grafted CNTs (CNT-g-CMCs) can disperse or aggregate in water in response to the bubbling of CO2. The CO2-switchable dispersion and aggregation of CNT-g-CMCs depend on the relative amounts of COOH to NH2 in CMC. With similar amounts of COOH and NH2 in CMC, the CNT-g-CMCs are well dispersed in water at pH 10 and exhibit no phase changes in response to the bubbling of CO2. With a higher amount of COOH than NH2 in CMC, the CNT-g-CMC dispersion in water at pH 10 becomes sensitively aggregated in response to 1 min of CO2 bubbling, but reverts to good dispersion with bubbling of N2 after 10 min. This newly developed CNT-g-CMC system with a novel CO2-responsive amphiphilic feature provides an environmentally friendly way of dispersing or aggregating CNTs in an aqueous solution without using acids and bases.