Mechanism of Nanostructure Growth

The key to developing and exploiting new nanostructured materials lies in an increased understanding of how synthesis conditions affect the properties of nanostructured materials in order to tailor materials to specific needs. A knowledge of the mechanism of nanostructure formation is of particular importance. Since the discovery of the wet chemical method of transformation of raw titania to nanotubular titanates, many attempts have been made to describe this mechanism and to rationalise these...

References

Phys., 1985, 38(1-2), 231. 2. R. Digilov, Langmuir, 2000, 16, 1424. 3. M. Alcoutlabi and G. B. McKenna, J. Phys. Condens. Matter., 2005, 17, R461. 4. R. Ma, T. Sasaki and Y. Bando, Chem. Commun., 2005, 7, 948. 5. D. V. Bavykin, A. A. Lapkin, P. K. Plucinski, J. M. Friedrich and F. C. Walsh, J. Catal, 2005, 235, 10. 6. X. Sun and Y. Li, Chem. Eur. J., 2003, 9, 2229. 7. D. V. Bavykin, V. N. Parmon, A. A. Lapkin and F. C. Walsh, J. Mater. Chem., 2004, 14, 3370. 8. D. V....

Effect of Ionic Charge on Adsorption from Aqueous Solutions

In an aqueous suspension, nanotubular titanates tend to develop a negative zeta potential due to the dissociation of titanic acid (e.g. H2Ti3O7 H1 + HTi3O7 ).41 This phenomenon greatly affects the ability of charged molecules to adsorb onto the surface of nanotubes. The affinity of species in the cationic form is much better than that of anionic species, indicating the major role of electrostatic interactions between the adsorbent and the adsorbate during adsorption from aqueous solution....

Crystallography of Titanate Nanofibres Nanorods and Nanosheets

During alkaline hydrothermal treatment of titanium dioxide the formation of fibrous, rather than tubular, nanostructures can occur. The XRD patterns of these nanofibrous materials usually show a characteristic reflection at small angles, confirming a layered structure of the nanofibre crystals. In current literature, the crystal structure of these nanofibres corresponds to the structure of layered protonated polytitanates H2TinO2n+7, where n 5 (ref. 16,17), 6 (ref. 18) and 8 (ref. 16,19), or...

Methods to Control the Morphology of Nanotubes

For practical purposes, it is important to know what methods exist for adjusting the morphological properties of anodic TiO2 nanotubes, including tube diameter and length, wall thickness and roughness, as well as the degree of ordering of the aligned nanotubes. Control of nanotube diameter. Anodic oxidation of titanium in fluoride-free electrolyte usually leads to the growth of a compact layer of TiO2. The thickness of the layer is linearly proportional to the applied potential to the...

Bottomup approach

Figure 2.1 Top-down and bottom-up approaches for the preparation of nanos-tructured materials. Figure 2.2 The template method for the preparation of nanostructured materials. (ALD atomic layer deposition CVD chemical vapour deposition). Figure 2.2 The template method for the preparation of nanostructured materials. (ALD atomic layer deposition CVD chemical vapour deposition). and temperature, respectively. After successful adhesion of material, the template is removed by various methods,...

Kinetic Characteristics of Ion Exchange

Nanostructured titanates, produced by the alkaline hydrothermal treatment of TiO2, are characterized by an open, mesoporous morphology, which facilitates the transport of ions from a liquid towards the surface of nanotubes. Figure 4.2 shows the dynamics of pH change in an aqueous suspension of nanostructured titanate and titania after the addition of aqueous LiOH. For a blank solution of pure water, the addition of LiOH results in a very rapid increase in pH up to a value of 11.5, with an...

Template Methods

The method of template synthesis of nanostructured materials, being a classical bottom-up method, has become extremely popular during the last decade.1 The method utilises the morphological properties of known and characterised materials (templates) in order to construct materials having a similar morphology by methods including reactive deposition. This method is very general by adjusting the morphology of template material, it is possible to prepare numerous new materials having a regular,...

The History of Nanomaterials

The term ''nanostructured materials'' refers to solids which have an internal or surface structure at the nanoscale. Based on the nanometre (nm), the nanoscale, exists specifically between 1 and 100 nm''.1 Although the concept of nanomaterials is relatively new, such materials have been unwittingly used for centuries. One example is colloidal gold nanoparticles dispersed in the soda glass of the famous Lycurgus Cup2 which dates back to the fifth century and is currently displayed in the British...

Mechanism of Nanotube Growth

For better control over the morphology and the degree of ordering in nano-tubes, it is vital to understand the underlying principles and mechanism for the formation of aligned nanotubes under anodic conditions. The growth of nanotubes by anodising titanium can be described as a selective etching, and the method can be related to a top down approach. In the simplest approach, such nanotube growth can be described in terms of a competition between several electrochemical and chemical reactions,...

Photocatalysis in Elongated Titanates and TiO2

During the last three decades, titanium dioxide has been comprehensively studied as a wide band gap photocatalyst for the oxidation of organic compounds.90 The best TiO2-based catalysts are usually characterised by a highly crystalline structure (which can reduce the recombination of photogenerated carriers) a high specific surface area (for acceleration of the interfacial reaction rate) and an abundance of surface -OH groups (which are required for the generation of OH radicals during...

Electrochemical Anodic Oxidation

Following the discovery of the hexagonal-packed porous aluminium oxide obtained by anodising aluminium,63 many attempts have been made to understand the mechanism of ordered pore formation and the methods for controlling the porous structure and morphology of porous films, by tailoring the electrochemical conditions and the composition of electrolyte. In addition, attempts to translate this method to other valve metals have also been the subject of many investigations. This section describes...

Physical Properties of TiO2 Nanotube Arrays

Physico-chemical properties of TiO2 nanotube arrays are very close to the properties of TiO2 nanoparticles, due to chemical and structural similarities. However, some unusual behaviour of nanotube arrays is observed, resulting from the specific nanotubular morphology of materials, and is considered in this section. Figure 3.18 shows the typical transmittance spectra of a 400 nm thick TiO2 nanotube array film on glass substrate.83 The optical behaviour of the TiO2 nanotube array is quite similar...

Metal Chalcogenide Nanotubes

Chalcogenides of transition metals having a multi-walled nanotubular morphology have been actively studied during recent decades. The methods of nanotube preparation include arc discharge laser ablation sublimation gasphase reduction with H2S or H2Se pyrolysis of (NH4)2MX4 (where M Mo or W X S or Se) and hydrothermal reactions.51 Although gas-phase redox synthesis is the most prominent technique used, in this book we mainly review hydrothermal methods. During hydrothermal sulfurisation, the...

Spectroscopy of Titanate Nanotubes Uvvis Pl Esr Xps Nmr Raman and FTIR

The electronic structure of titanate nanotubes has been studied using a variety of different experimental techniques. Figure 3.10 shows the optical absorption spectra of a colloidal solution of titanate nanotubes of different average internal diameters.53 The absorption spectra are very broad with several features at 250 and 285 nm. The threshold of the spectra suggests that the Figure 3.10 Visible absorption spectra of colloidal titanate nanotubes of differing mean internal diameter 1) 2.5 nm,...

Drug Delivery and Bio Applications

Recent active areas of research which involve the use of nanostructured inorganic materials in biological applications include controlled drug delivery, the labelling of biological objects, and the building of artificial tissues from nanostructured material composites.144,145 Due to their high surface area and affinity towards positively charged ions in aqueous solution, elongated nanostructured titanates have recently been studied as a possible element in amperometric bio-sensors. It has been...

Crystallography of Titanate Nanotubes

Tio6 Octahedral

In an early study, Kasuga et al.1 characterized their product as anatase. In a recent paper, the crystal structure of nanotubular titanates was still been RSC Nanoscience amp Nanotechnology No. 12 Titanate and Titania Nanotubes Synthesis, Properties and Applications By Dmitry V. Bavykin and Frank C. Walsh Dmitry V. Bavykin and Frank C. Walsh 2010 Published by the Royal Society of Chemistry, www.rsc.org interpreted as anatase,2 despite the fact that the crystal structure of these nanotubes is...

Metal 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. 2006 17 2 393.

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 Template Assisted 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

Titanate Periodic Table

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...