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Pure anatase titania (TiO2) nanoparticles were anchored on the surface of functionalized multi-walled carbon nanotubes (MWCNTs) using a solution-based synthetic method at room temperature. X-ray diffraction and Raman patterns were used to analyze the structural and phase composition of these nanocomposites, highlighting the formation of anatase TiO2 nanoparticles with MWCNTs up to 0.5 wt.%. The non-spherical particles of TiO2 in the order of 7–12 nm, were confirmed through transmission electron microscopy analysis and these particles were well dispersed on the MWCNTs. The optical absorption spectra of these structures were studied by diffuse reflectance UV–visible spectroscopy. The optical energy band gap of the various nanocomposites was observed from 3.2 to 2.6 eV with an increasing amount of MWCNTs, up to 0.5 wt.%. The generation of OH species in nanocomposites in the presence of visible light irradiation was investigated by photoluminescence spectroscopy. Photoelectrochemical cell performance of TiO2-MWCNTs for 0.5 wt.% content of MWCNTs under light intensity 100 mW/cm2 showed a significant improvement of short-circuit current density from 1.23 to 12.1 mA/cm2 and a cell efficiency (0.090–3.46%) that is better than many reported anatase-based compositions without sensitizer.

Nanoparticle embedded carbon nanotube papers can produce flexible functional films, whose function is based on the electronic coupling of the nanoparticles with the network of carbon nanotubes. Here we report on the expansion of a synergistic light-free catalyst system that requires both the molecular wire capability of multi-walled carbon nanotubes and the piezoelectric properties of ZnO nanoparticles. The electron–hole pairs can be induced by the piezoelectric effect of ZnO nanoparticles under the effect of pressure. The strong oxidizing radicals interact with the electron–hole pairs and aqueous solution to induce the degradation of methylene blue without the requirement of light. This study highlights the use of nanoparticles for the piezoelectric – light free catalyst system and the limitations of increased nanoparticle loading on the catalytic degradation of methylene blue.

Carbon nanotube papers have many potential applications from actuators to electrodes. Cross-linked papers with embedded nanoparticles are now being investigated for use in these applications. Here we report on the development of piezoelectric multi-walled carbon nanotube paper. The piezoelectric effect of the paper was enhanced by four orders of magnitude by embedding zinc oxide nanoparticles into the carbon nanotube network, resulting in a simple method for producing flexible piezoelectric carbon nanotube paper.

High content carbon nanotubes mats have been produced to a range of thicknesses and diameters by covalent bonded cross-linking of thiolated multi-walled carbon nanotubes. The Michael addition pathway was used to cross-link benzoquinone to thiol groups attached to the surface of the nanotubes. The mats were characterized by a variety of techniques including X-ray photoelectron spectroscopy, tensile strength as well as qualitative structural analysis by scanning electron microscopy. It was found that the optimum ratio by weight for cross-linking benzoquinone to thiolated carbon nanotubes was ca. 5:1. This work provided a simple route to the production of mats without high pressure processing or irradiation techniques generally used to produce Buckypaper which can require pressure control chambers, argon and hydrogen ion beams and high temperatures. The mat surface can be further functionalized with nanoparticles to form advanced carbon composite materials.

Here we report on the construction and operation of a cross-linked aminated multi-walled carbon nanotube paper as a hydrogen sensor. The incorporation of palladium onto the surface of the paper resulted in p-type conduction as the resistance of the paper was measured, under exposure to hydrogen gas. When palladium nanocrystals were embedded into the cross-linked paper, n-type conduction was observed during hydrogen sensing. This investigation highlights the next stage in the development of functional nanotube paper.

With careful removal of acid-oxidative lattice fragments and use of acid–base titrations, the covalent reactivity of covalently bound carboxylic groups on multi-walled carbon nanotube surfaces has been directly confirmed, including intermediate states, for carbodiimide promoted amidation reactions.

Understanding the compatibility between spider silk and conducting materials is essential to advance the use of spider silk in electronic applications. Spider silk is tough, but becomes soft when exposed to water. Here we report a strong affinity of amine-functionalised multi-walled carbon nanotubes for spider silk, with coating assisted by a water and mechanical shear method. The nanotubes adhere uniformly and bond to the silk fibre surface to produce tough, custom-shaped, flexible and electrically conducting fibres after drying and contraction. The conductivity of coated silk fibres is reversibly sensitive to strain and humidity, leading to proof-of-concept sensor and actuator demonstrations., The use of spider silk in electronic devices is dependent on its compatibility with electrically conductive materials. Here the authors modify spider silk with carbon nanotubes to produce a strong, flexible and electrically conductive thread.

Concerns about depleting natural resources have been circulating for decades with alarming predictions that have turned out to be less than accurate. What has become clear, however, is the need for a decrease in the utility of a fossil based economy and a focus on a more sus‐ tainable one. This chapter reviews some of the recent progress made in the use of intercon‐ nected carbon nanotubes (CNTs) in the hydrogen, photovoltaics and thermoelectric alternative energy based economies.

Since the inception of the research field on carbon nanotubes (CNTs), there has been an enormous effort to understand how the tubes form and how to best garner their unique electronic and mechanical properties. It soon became apparent that in order to develop the next generation of functional materials, a way to modify the surface of the tubes and connect them was required. The development of the oxidation process with acids was the first revolution in the field of CNTs, potentially opening the door to an extensive library of modifications. Research progressed by integrating the nanotubes into composites at low concentrations with some success, but the goal of producing high nanotube component covalently cross-linked materials was still problematic. Two decades after the report by Sumio Ijima on their discovery, cross-linked CNT materials are still difficult to produce, and this has shifted the field towards a back-to-basics approach to try and solve the problem. One key problem identified was the presence of lattice fragments immobilized on the surface of the CNTs (Fig. 1.). The current methods of characterization such as X-ray photoelectron, Infrared and Raman spectroscopy are indirect and generally fail to distinguish between the surface attached functional groups and oxidized lattice fragments. A CNT washing technique has been developed to remove these fragments and any electrostatically attached products to allow pure covalent interactions with the surface of the nanotube (Wang et al., 2010). With an industry now thriving on the production of cheap functionalized carbon vapor deposition (CVD) CNTs, priced according to the percentage surface functionalization, and the decline in published materials on arc-produced CNTs, the need for effective characterization and quality control increases. It is the intention of this chapter to review some of the successful approaches used to crosslink CNTs with a focus on the importance of the chemistry and techniques involved, and highlight two areas of research we are currently investigating at Florida State University.

An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4'-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs.