Fabrication of functional layer based on Cu(OH)2 nanoneedle arrays or Pt-decorated MWNT composites

Abstract

Nanostructured copper compounds were grown by electrochemical anodization of copper foil in aqueous NaOH under varying conditions including electrolyte concentration, reaction temperature, and current density. The morphology and atomic composition were investigated by using SEM, EDS, TEM, XPS and XRD. At the optimized conditions ([NaOH] = 1 M, 20�aC, 2 mA cm-2), needle-like orthorhombic Cu(OH)2 nanobundles with an average width of 100 - 300 nm and length of 10 ��m were synthesized with the preferential [100] growth direction by scrolling nanosheets of Cu(OH)2. When the concentration decreased to 0.5 M NaOH, the 1D nanobundle structure became narrower and longer without any change in compositions or crystalline structure. These Cu(OH)2 nanoneedles were further modified by a silane chemical with a low surface energy. A contact angle of the modified nanoneedles was about 165�a for water, showing a superhydrophobic property. Furthermore, the silane-modified surface exhibited a superoleophilic feature with the contact angle of less than 5�a for non-polar solvents. These superhydrophobic and superoleophilic properties were found to maintain over a wide pH range of 0 - 14 and at the high temperature of 250�aC. Pt nanoparticles decorated multiwall carbon nanotube (Pt/MWNT) was synthesized by using a wet chemical reduction method. The resultant Pt/MWNT nanocomposite was probed to have a structure of having a good dispersion of 2 �V 7 nm Pt particles with an fcc crystal structure on MWNT through SEM, TEM and XRD analyses. A gas permeable electrode with sufficient adhesion and nano-sized porosity was readily formed on microporous PTFE membrane through the vacuum filtration of the Pt/MWNT solution. This membrane was evaluated as a gas diffusion sensing electrode for the amperometric hydrogen detection. With optimizing the process parameters such as MWNT content, H2PtCl6 concentration, NaBH4 concentration and a drying temperature, the Pt/MWNT sensor was found to have a maximum sensitivity of 217 �gA ppm-1 and an excellent linear response to H2 concentration in the wide range of 5 - 1000 ppm. Furthermore, this sensor exhibited a better performance in selectively compared with the binary nanoparticle electrodes of Pt-ZnO/MWNT, Pt-Ni/MWNT, Pt-Zn/MWNT and Pt-Pd/MWNT.