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Über dieses Buch

This book describes a series of contemporary techniques and their combinations used for CNTs solubilization, from physical to chemical and biological, applying inorganic and organic compounds, as well as some metal complexes. In some cases, successive steps can be applied, for instance the use of low and high-weight surfactants, or mineral acid treatment for creation of –OH and –COOH groups and their further interaction with organic molecules. Each discussed method leads to an improvement of CNT solubility, frequently a considerable one. The formed dispersions can be stable for long periods of time, from several weeks to some months, and they sometimes even remain stable after centrifugation. Several special studies have been carried out in the areas of influence of solvent and light on CNTs dispersibility, combinations and abilities of surfactants, CNT cytotoxicity, etc. Applications of solubilized CNTs are discussed in this book as well.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
The carbon nanotubes (CNTs), one of the best novel nanostructures [1] and classic objects in nanotechnology, form bundle-like structures with very complex morphologies with a high number of Van der Waals interactions, causing extremely poor solubility in water or organic solvents. Due to their exceptional combination of mechanical, thermal, chemical, and electronic properties, single-walled (SWNTs or SWCNTs) and multiwalled carbon nanotubes (MWNTs or MWCNTs) are considered as unique materials, with very promising future applications, especially in the field of nanotechnology, nanoelectronics, and composite materials. Additionally, CNTs are becoming highly attractive molecules for applications in medicinal chemistry. At present, potential biological and medical applications [2] of CNTs have been little explored, in particular for drug delivery purposes [3]. The main difficulty to integrate such materials into biological systems derives from their lack of solubility in physiological solutions. Functionalization of CNTs with the assistance of biological molecules remarkably improves the solubility of nanotubes in aqueous or organic environment and, thus, facilitates the development of novel biotechnology, biomedicine, and bioengineering. Many of these applications require an increased “solubility” of CNTs in solvents, first of all in water, especially for biological applications. This could be reached by their functionalization, which is a very actively discussed topic in contemporary literature because the planned modification of CNT properties is believed to open the road toward real nanotechnology applications [4]. It is difficult to prepare an aqueous dispersion of CNTs stable for months; their insolubility has been a limitation for the practical applications of this unique material. Proper dispersion of CNT materials is important to retaining the electronic properties of nanotubes. The redissoluble functional compound/CNT composites are needed for post-processing because CNT dispersions usually easily aggregate and therefore make additional processing very difficult.
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 2. Physical Methods

Abstract
Ultrasonication is often used to disperse nanoparticles in aqueous solution. However, a good dispersion of nanoparticles in aqueous solution is not always achieved, due to the fact that incoming ultrasonic waves in liquid are usually reflected and damped at the gas/liquid interface. For the case of carbon nanotubes, this is a classic debundling method: the MWCNTs can be effectively ultrasonically dispersed in the water solution [1]. Under the ultrasound action, the cavitation process produces the strong shear force, leading to the exfoliation of carbon nanotube bundles, bubble formation, and collapse, providing homogeneity of nanosuspension [2].
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 3. Chemical Methods

Abstract
Ozone can be used alone or with combination with UV light. Thus, chemical functionalization of MWCNTs was carried out [1, 2] by UV/ozone treatment. The presence of oxygen-containing groups (such as carboxylic, quinine, and hydroxyl groups) on the MWCNT surfaces by UV/ozone treatment was confirmed resulting in dispersion stability better than for pristine MWCNTs in polar solvents. Authors predicted the dispersion states of MWCNTs treated with UV/ozone in 32 different solvents in terms of a Hansen solubility parameter sphere, which increased as UV/ozone exposure time increased. The solubility of UV/ozone-treated MWCNTs in polar organic solvents can be increased by as much as 320%, maintaining almost the same thermal stability, compared to raw MWCNTs [3]. The dispersed nanotubes suspension (MWCNTs functionalized by oxygen- and hydrogen-containing groups) can be stable for a few months after treatment [4].
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 4. Biological/Biochemical Methods

Abstract
Soluble CNTs and especially water-soluble ones, functionalized with biomolecules, could get many applications in medicinal chemistry; that is why a host of efforts has been dedicated to CNT treatment with biologically active species, sugars, and their derivatives. Thus, as a first step before incorporation into poly(amide–imide) matrix, MWCNTs were modified with glucose and fructose (reaction scheme 4.1) carbohydrates as biomolecules to obtain Gl-MWCNTs and Fr-MWCNTs, leading to water-soluble and biocompatible products [1].
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 5. Special Studies and Characterization of CNT Dispersions

Abstract
During more than 20-year period of investigations in the field of carbon nanotubes and their dispersions in water and organic solvents, a series of important observations, effects, and conclusions have been made, in particular after the CNT dispersions have been studied within solution. As it will be seen below, influence of solvent and external influence (i.e., UV light or the presence of ions), free radicals, and a row of other factors can improve or affect the CNT dispersibility, which could differ depending on CNT type and their purity.
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 6. Cost and Main Applications of Soluble CNTs

Abstract
In addition to such wide applications of soluble CNTs as biosensors [1–5], electrodes in biofuel cells [6], composites [7–11], advanced polymers [12–15], cements [16], agriculture [17], radar-absorbing materials [18], etc., mentioned throughout the text, we would like to underline the following uses. Soluble CNTs are applied mainly in nanomedicine [19] for different purposes, the most important of which is the drug delivery [20]. Within the family of nanomaterials, CNTs have emerged as a new alternative and efficient tool for transporting and translocating therapeutic molecules. It has become possible after the recent discovery of their capacity to penetrate into the cells. CNT can be loaded with active molecules by forming stable covalent bonds or supramolecular assemblies based on noncovalent interactions.
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 7. Training on CNT Solubilization

Abstract
In this section, we present several selected experimental procedures, directly borrowed from original articles. We hope this material will be very useful as educational material for M.Sc. and Ph.D. students, working in the areas of biochemistry and drug delivery, fabrication of CNT thin films from dispersion, application of CNT composites with polymers, etc.
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Chapter 8. Conclusions and Further Outlook

Abstract
The field of carbon nanotubes continues to be one of the hottest topics in the nanoscience and nanotechnology, so the development of their functionalization and dispersion methods is and will be an important research area, at least for the next 10 years. A series of contemporary techniques are being used for CNT solubilization, from physical (classic ultrasound, plasma treatment, UV light, dielectrophoresis [1, 2], gel electrophoresis [3, 4], density-gradient ultracentrifugation [5, 6], irradiation techniques, and chromatography [7], among others) to chemical and biological, applying inorganic (other carbon allotropes, iodine, bromine, metallic sodium in liquid ammonia, CO2, peroxides, ozone, metal salts, and mineral acids) and organic (acids, salts, polymers, dyes, natural products, in particular diazonium salts [8]; functionalization with porphyrins, amines, pyrene, polymers, sugars, etc.) compounds and biomolecules (DNA, peptides, amino acids, etc.), as well as micelles on their basis and some metal complexes. CNTs can be functionalized by oxidation (peroxy acids; metal oxidants, such as osmium tetroxide, potassium permanganate, chromates; ozone; oxygen; superoxides) or reduction reactions (interactions with thiols, carbenes, dienes, etc.).
Oxana Vasilievna Kharissova, Boris Ildusovich Kharisov

Backmatter

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