Preparation and Characterization of Concentric-tubular Composite Microstructures Using the Template Synthesis Method
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dried under vacuum at 1500 C for 24 hours to remove H20. Ethylene carbonate (Aldrich) and and diethyl carbonate (Aldrich) were distilled prior to electrochemical use. The Powder XRD was obtained using a Enraf Nordas FR552 camera with a Cu KQ anode using 2-0 representation. The TiO2 composites were annealed using a Thermacraft model 2214 furnace. Fabrication of the Au/polyphenylene oxide/polypyrrole composite microstructures. Polyester track-etch membranes (pore dia. = 3 ym) were used to prepare these composites. The outer Au tubule was deposited using an electroless plating method described previously 16, 7J. This method yields a Au microtubule within each pore; in addition, Au surface layers form on both faces of the membrane. One surface layer was removed from the Au plated membrane, and the exposed Au tubules were used as anodes for electropolymerization of inner tubules of poly(2,6-dimethylphenol) (PPO) [8J. The Au membrane was clamped between a glass o-ring joint and a glass slide to form an electrochemical cell. A Ag/AgCI reference electrode (BAS RE-5) and a spiral Pt wire electrode were also placed in this one compartment cell. The electropolymerization of the inner PPO tubules was accomplished using cyclic voltammetry by scanning between the limits of - 0.2 V and + 0.8 V 181. To determine that the inner PPO tubules had formed, cyclic voltammetric experiments were conducted at the Au tubule electrodes before and after PPO deposition. K3Fe(CN)6 (2 mM in 0.2 M NaO2CCF3) was used as the voltammetric probe. Oyama et. al. have shown that the PPO films are impermeable to this anion [81; formation of the inner PPO tubules could, therefore, be ascertained by the disappearance of the Fe(CN)6 3 -/4- voltammetric wave. The final step was to deposit polypyrrole (PPy) microwires down the center of the inner PPO tubules. After PPO deposition, the Au/PPO-tubule-containing membrane was removed from the electrochemical cell. Both surfaces were cleaned, and a new Au film was sputtered onto the bottom of the membrane. This Au film was used as the working electrode to electropolymerize the PPy microwires within the PPO tubules. The electrochemical cell described above was used; PPy was deposited into the PPO inner tubules using a constant current density of 0.14 mA cm- 2 . The polymerization solution consisted of 0.1M pyrrole and 0.025 M NalO4 in 1:2 (v/v) methanol/H20. The completed Au/PPO/PPy composite microstructures within the pores of the template membranes were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Fabrication of TiO2/Au composite microstructures. The polyester membrane with 1 mdia. pores was used to prepare these composites. The outer Au tubules were electrolessly deposited inside the pores of the membrane 16, 71. One of the surface Au layers was removed, and the Au/polyester composite was placed (remaining surface layer down) on Al foil. The polyester was dissolved using HFIP. The exposed Au tubules, protruding from the Al foil surface, were immersed in a 2% solution
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