Noncovalent functionalization of carbon nanotubes with sodium lignosulfonate and subsequent quantum dot decoration

A novel noncovalent approach is developed for the functionalization of multimalled carbon nanotubes (MWNTs) using a biopolymer obtained in the cellulose industry-sodium lignosulfonate (SLS). Using a simple physical grinding technique, the SLS-functionalized MWNTs can be well-dispersed in water with a MWNTs-equivalent solubility as high as 1.5 mg/mL, and the high stability can be maintained for more than 3 months. The SLS-functionalized MWNTs have been characterized by transmission electron microscopy (TEM), Raman spectra, and zeta-potential measurements. It is proposed that pi-pi stacking and the hydrophobic interactions are dominant mechanisms for the interaction between SLS and MWNTs, and the anionic polymeric nature of SLS imparts the high stability of MWNTs via the electrosteric repulsion. By taking advantage of the diverse anionic groups on the SLS-functionalized MWNTs as anchorage centers, SnO2 and CdS quantum dots with the size of 4-6 nm are controllably and uniformly decorated on the MWNTs surface using an in-situ formation method. These MWNTs/quantum dot hybrid materials are highly dispersible in water, thus opening possibilities for their prospective technological applications.