A facile synthesis of polypyrrole nanotubes using a template-mediated vapor deposition polymerization and the conversion to carbon nanotubes
Polypyrrole (PPy) nanotubes with highly uniform surface and tunable wall thickness were fabricated by one-step vapor deposition polymerization (VDP) using anodic aluminium oxide (AAO) template membranes, and transformed into carbon nanotubes through a carbonization process. Conducting polymer nanotubes have been attracting considerable attention because of their potential applications as nano-sized transistors, displays, sensors, and molecular wires. 1 To date, the fabrication of conducting
... mer nanotubes has been largely conducted with solution-based approaches using inorganic or organic templates. 2 In a solution-based approach, it is relatively difficult to tune the wall thickness due to the possible capillary condensation and the strong interfacial tension between monomer and template. Recently, our group reported that a vapor deposition technique allows powerful control of the shell thickness of inorganic-polymer core-shell nanostructures, and creates a smoother and more uniform surface by consecutive polymerization of vaporized monomer under vacuum onto the desired surface. 3 In addition, it provides experimental simplicity and accessability such as solvent-free system and no recovering process. So far, the vapor phase polymerization of conducting polymers has been mainly performed to fabricate conductive thin films 4 and filled composite materials, 5 whereas considerably less attention has been paid to the preparation of tubular nanostructures. Herein, we report on the facile synthesis of polypyrrole (PPy) nanotubes using a templatemediated VDP and the conversion into carbon nanotubes through the carbonization process. In a typical synthesis of PPy nanotubes, AAO template membranes having a thickness of 60 mm and pore diameters of 20 and 100 nm were soaked in ferric chloride aqueous solution (0.21 M). After wetting the template thoroughly, residual ferric chloride on the top and bottom surfaces of the AAO membrane was removed to reduce the possible closing and interconnection of the nanotubular edges. The dried AAO membranes were moved into a reaction vessel (100 mL) equipped with a sealing apparatus and a monomer loading reservoir. The reaction chamber was evacuated at room temperature until the pressure inside reached about 10 21 Torr. Then, a variable amount of pyrrole monomer was injected into the closed reservoir. The monomers were partially vaporized as soon as they were injected inside the reactor at room temperature. The monomer reservoir valve was open and the monomers were completely vaporized by heating the reactor at 70 °C. As the vaporized pyrrole monomer was polymerized into the channels of the AAO membrane, the color of the AAO membrane was changed from white to black. After 12 h of chemical vapor polymerization, the AAO templates were dissolved in NaOH aqueous solution (3 M). Excess water was added to dilute the solution, and the PPy nanotubes were precipitated. The upper solution containing the AAO salts and residual oxidants was discarded, the PPy nanotube precipitates were dried in a vacuum oven at room temperature. In the carbonization procedure, the collected PPy nanotubes were placed in an alumina tube, and heated to carbonization temperature at a heating rate of 3 °C min 21 under Ar gas flow (0.2 L min 21 ). The AAO membrane containing PPy nanotubes could also be used for carbonization directly. After 3 h of carbonization, the quartz tube was naturally cooled to room temperature.