Metal Oxide Nanotubes
Aluminium oxide nanotubes. The anodic oxidation of aluminium in acidic electrolytes, resulting in the formation of a porous film of anodic aluminium oxide AAO consisting of nanotubes, was discovered in a pre-nanoscience era.28 In a typical method, pure aluminium is anodised in the presence of oxalic acid 0.3 mol dm-3 , at a constant cell voltage of 40 V. A long period of ano-disation can improve the regularity of the tube arrangement, towards a hexagonal array of nanotubes.29 AAO films are...
Techniques and Instruments Used to Study Nanomaterials
The current boom in nanoscience and nanotechnology is to some extent a result of the recent advances in the methods of investigating and manipulating small objects. Such developments were mostly driven by the improvement in the resolution, reliability and availability of electron microscopy, including scanning SEM and transmittance TEM modes. The recent invention of scanning tunnelling STM and atomic force AFM microscopy, first appearing in 1982 and 1986, respectively,1 also provided additional...
O. P. Ferreira A. G. S. Filho J. M. Filho O. L. Alves And J. Braz Chem. Soc.
1. T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino and K. Niihara, Langmuir, 1998, 14, 3160. 2. B. Poudel, W. Z. Wang, C. Dames, J. Y. Huang, S. Kunwar, D. Z. Wang, D. Banerjee, G. Chen and Z. F. Ren, Nanotechnology, 2005, 16, 1935. 3. G. H. Du, Q. Chen, R. C. Che, Z. Y. Yuan and L. -M. Peng, Appl. Phys. Lett., 2001, 79, 3702. 4. Q. Chen, G. H. Du, S. Zhang and L. M. Peng, Acta Crystallogr, Sect B Struct. Sci., 2002, 58, 587. 5. D. Wu, J. Liu, X. Zhao, A. Li, Y. Chen and N. Ming, Chem. Mater.,...
Thermal Stability
A knowledge of the thermal stability of titanate nanotubes is important, since some applications or manipulations including catalyst supports or the curing of composite films require an increased operating temperature. At elevated temperatures there are at least three processes occurring with protonated titanate nanotubes, namely dehydration, crystal structure transformation and a modification in morphology. All three processes occur simultaneously, and each has a characteristic range of...
Catalysis Electrocatalysis and Photocatalysis 521 Reaction Catalysis
Elongated nanostructured titanates are characterised by a relatively high specific surface area, which is typically in the range of 200 to 300m2g_1 for nanotubes, and 20 to 50m2g_1 for nanofibres or nanorods. These values contrast with lt 20m2g_1 for TiO2 nanotubular arrays produced by anodisa-tion. The range of pore sizes from 2 to 10 nm ranks these materials as mesoporous such structures are widely used in as a support in heterogeneous catalytic processes. The high surface area of the support...
Electronic Structure of Titanate Nanotubes
The electronic structure of titanium dioxide has been thoroughly studied in recent years due to its potential use in several applications,43 including pho-tocatalysis, photovoltaic cells, sensors and electronic devices. Generally, TiO2 is a wide-band gap semiconductor EG 3.2 eV with indirect interband electron transitions.44 Titanium dioxide spheroidal nanoparticles show a relatively small apparent bandgap blue shift45,46 lt 0.1-0.2 eV , caused by quantum size effects for particles sizes down...
Solar Cells
Elongated titanates and TiO2 nanostructures have been examined for use as an electrode for dye-sensitized solar cells DSSC . Figure 5.1a shows the principle of DSSC utilising nanotubular titanates. The photoexcited molecule of dye adsorbed onto the surface of nanotubes injects an electron to the semiconductor, which then diffuses towards the electron sink. The oxidised form of the dye is reduced by iodide ions in the electrolyte solution, and the iodine released is further reduced on the...
Surface Area of Nanotubes
The specific surface area of some structures e.g. nanotubular structures can be estimated by the calculation of the geometrical surface area see Figure 3.4 . The specific surface area of a nanotube S can be calculated as a sum of the external Sext and internal Sint surface areas divided by the mass of the nanotube using the formula where p and Vtube are the density and the volume of the nanotube, respectively. For a cylindrical geometry, it is possible to express surface area and volume using...
Magnetic Materials
The recent interest in room-temperature ferromagnetic semiconductors and magnetic nanosized materials having a high aspect ratio motivated by possible applications in spin-base semiconductor devices , has stimulated research into the synthesis and characterisation of elongated titanates and TiO2 magnetic materials. The pure titanate nanotubes have paramagnetic properties 137 doping nanotubes with Co21 results in ferromagnetic properties with a coercivity of approximately 40 Oe.138 Several...
Crystallography of Anodized and TemplateAssisted TiO2
The crystal structure of titanium oxide films produced by electrochemical oxidation of titanium can be amorphous or crystalline, depending on the parameters of preparation including the applied potential, the time of anodising and the composition of the electrolyte. As far as TiO2 nanotube arrays are concerned, as produced, they are usually characterised by an amorphous structure, which can be transformed to anatase at temperatures as low as 300 C in air.24,25 A further increase in temperature...
Surface Chemistry and Functionalization of Nanostructured Titanates
The surface chemistry of nanostructured titanates is more versatile compared to the relatively inert chemistry of carbon nanotubes. The latter requires special treatment under aggressive conditions in order to activate their surface, using carboxylic groups to provide a flexible route for further functionalization. However, even in this case the surface density of carboxylic groups is relatively low. By contrast, nanotubular titanates are abundant with surface -OH groups, which are...