Adsorption of Methylene Blue Dye onto Carbon Nanotubes:  A Route to an Electrochemically Functional Nanostructure and Its Layer-by-Layer Assembled Nanocomposite

This paper describes the adsorption of electroactive methylene blue (MB) dye onto single-walled carbon nanotubes (SWNTs) to form an electrochemically functional nanostructure and its layered nanocomposite. UV−visible and FT-IR spectroscopy and electrochemistry used for characterization of the MB adsorption onto SWNTs reveal that MB essentially interacts with SWNTs through charge-transfer and hydrophobic interactions, leading to the formation of a MB−SWNT adsorptive nanostructure which exhibits distinct electrochemical properties from those of MB adsorbed onto a glassy carbon (GC) electrode. The interactions between MB and the SWNTs are demonstrated to closely associate with the structural properties of the SWNTs by comparing the electrochemical properties of MB adsorbed onto different substrates, i.e., glassy carbon, SWNTs, and SWNTs intentionally sidewall functionalized with hydroxyl groups (SWNT-OHs). The stable adsorption of water-soluble and positively charged MB molecules onto the SWNTs is further demonstrated to be able to solubilize the formed nanostructure in water quite well and to fabricate a functional nanocomposite by layer-by-layer assembling of the formed nanostructure on a solid substrate.