| As a kind of important one-dimensional nanomaterial. carbon nanotubes (CNTs) have drawn many researchers'interest due to their unique electrical, optical, and mechanical properties since their discovery. However, it is very difficult to dissolve CNTs in aqueous solution and other organic solvents because of their poor solubility and strong van der Waals force between tubes, which limits greatly their applications in liquid. To solve this problem, many approaches have been attempted, such as surfactants, polymers and other organic compounds. As "green solvents" ionic liquids (ILs) have been widely used to disperse CNTs. Surface active ionic liquids is a new type of ILs, which combine the properties of ILs and surfactants, and can disperse CNTs better than traditional surfactants. Carbon nanotubes have been widely used as a supporting material of noble metal nanoparticles (NPs) due to their high surface area, electric conductivity and chemical stability. CNTs and noble metal composite combine the advantages of two kinds of materials, and have many potential applications in sensors, optical electronics and electrocatalysis. How to prepare CNTs and noble metal composite with good performance has recently become one of the focuses of research. Many compounds have been used as linkers of CNTs and noble metal. As an excellent electrolyte, ILs have been widely used as a linker and protecting agent for preparing CNTs and noble metal composite. We used two different types of surface active ILs containing imidazole and pyrrole to disperse multi-walled carbon nanotubes (MWCNTs), respectively, and investigated the capacity and stability of ILs for dispersing MWCNTs. Then we used surface active ILs as linker to prepare composite containing MWCNTs and Au NPs.(1) Dispersion MWCNTs in aqueous solution by surface active ILs.Various types of compounds have been used to disperse MWCNTs. Surface active Ils, butyl-a,(3-bis(dodecylimidazolium bromide) ([C12-C4-C12im]Br2) and N-dodecyl-N-methyl pyrrolidinium bromide (C12MPB) can all disperse MWCNTs very well. The capacity and stability of ILs for dispersing MWCNTs were investigated by visual observation, UV-vis-NIR and transmissions electron microscope (TEM). The dispersed amount of MWCNTs first increased and then decreased with the increasing concentration of ILs, which may be caused by micelles formation of surface active ILs when their concentration reached critical micelle concentration (cmc). Compared with single chain ionic liquids, Gemini imidazolium type ionic liquids has stronger ability of dispersing MWCNTs, and the ability of dispersing MWCNTs increases with increasing hydrocarbon chain length, which is also explained by the structure of ILs. The possible dispersion mechanism was proposed byζ-potential measurement. Adding MWCNTs to C12MPB aqueous solution can affect the aggregation behavior of ILs, and experiment indicated the cmc of ILs containing MWCNTs became bigger than that of aqueous solution, which can be ascribed to the adsorption of ILs on the surface of MWCNTs.(2) Preparing MWCNTs-Au composite by surface acitive ILs.Synthesis of carbon nanotubes-Au composite using ILs as linkers is a research focus. Surface active ILs,1-hexadecyl-3-methyl imidazolium bromide (C16mimBr), can disperse MWCNTs very well. As a dispersant and protecting agent, C16mimBr was used to prepare MWCNTs-Au composite. Due to adsorption of C16mim+, MWCNTs became positive charge, and Au NPs with negative charged which protected by trisodium citrate were attached on the surfaces of MWCNTs due to the electrostatic attraction. Both X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicated that as-prepared MWCNTs-Au composite contained high-purity Au NPs. The amount of Au NPs adsorbed on MWCNTs can be adjusted by the ratio of MWCNTs suspension and Au NPs added in the mixture. A simple and feasible approach to prepare MWCNTs and noble metal composite has been proposed, and the composite is expected to be applied to electrochemistry and other fields. |
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