Computer generated holograms for carbon nanotube arrays.

Multiwalled carbon nanotubes are highly diffractive structures in the optical regime. Their metallic character and large scattering cross-section allow their usage as diffractive elements in Fraunhofer holograms. This work elaborates some important features of the far field diffraction patterns produced from periodic arrays of nanotubes. A theoretical approach for the interaction of arrays of nanotubes with light is presented and a computer generated hologram is calculated by means of periodical patterns. Based on the results, fabrication of carbon nanotube arrays (in holographic patterns) was performed. Experimentally measured diffraction patterns were in good agreement with the calculations.

Dry oxidation and vacuum annealing treatments for tuning the wetting properties of carbon nanotube arrays.

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.(1,2) These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.(2) Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.(3-5) The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

Reversible tuning of the wettability of carbon nanotube arrays: the effect of ultraviolet/ozone and vacuum pyrolysis treatments.

Among diverse types of synthetic materials, arrays of vertically aligned carbon nanotubes have attracted the most attention, mainly because of their exceptional mechanical, electrical, optical, and thermal properties. However, their wetting properties are yet to be understood. In this present study, oxygenated surface functional groups have been identified as a vital factor in controlling the wetting properties of carbon nanotube arrays. The results presented herein indeed show that a combination of ultraviolet/ozone and vacuum pyrolysis treatments can be used to vary the surface concentration of these functional groups such that the carbon nanotube array can be repeatedly switched between hydrophilic and hydrophobic.

Effect of dry oxidation on the performance of carbon nanotube arrays electrochemical capacitors

In this study, the effect of dry oxidation on the electrochemical properties of carbon nanotube arrays is investigated. Oxygenated surface functional groups were introduced to the arrays by oxygen plasma treatment, where their surface concentrations were varied by controlling the exposure time. The finding presented herein shows an augmentation of nearly thirty times in term of specific capacitance when the arrays are oxidized. Similar behavior is also observed in the non-aqueous electrolytes where the specific capacitance of the oxidized carbon nanotube arrays is measured more than three times higher than that of the pristine ones. However, overexposure to oxygen plasma treatment reverses this effect. At such high oxidation level, the damage to the graphitic structure becomes more pronounced such that the capacitive behavior of the arrays is overshadowed by their resistive behavior. These findings are important for further development of carbon nanotube based electrochemical capacitors. © 2012 Materials Research Society.

Physicochemical characteristics and droplet impact dynamics of superhydrophobic carbon nanotube arrays.

The physicochemical and droplet impact dynamics of superhydrophobic carbon nanotube arrays are investigated. These superhydrophobic arrays are fabricated simply by exposing the as-grown carbon nanotube arrays to a vacuum annealing treatment at a moderate temperature. This treatment, which allows a significant removal of oxygen adsorbates, leads to a dramatic change in wettability of the arrays, from mildly hydrophobic to superhydrophobic. Such change in wettability is also accompanied by a substantial change in surface charge and electrochemical properties. Here, the droplet impact dynamics are characterized in terms of critical Weber number, coefficient of restitution, spreading factor, and contact time. Based on these characteristics, it is found that superhydrophobic carbon nanotube arrays are among the best water-repellent surfaces ever reported. The results presented herein may pave a way for the utilization of superhydrophobic carbon nanotube arrays in numerous industrial and practical applications, including inkjet printing, direct injection engines, steam turbines, and microelectronic fabrication.

Fabrication and optical properties of gold nanotube arrays

Arrays of gold nanotubes with polypyrrole cores were grown on glass substrates by electrodeposition into thin film porous alumina templates. Measurements of optical transmission revealed strong extinction peaks related to plasmonic resonances, which were sensitive to the polarization state and angle of incidence. On prolonging the electrodeposition of gold, the polypyrrole core became fully encapsulated and this had a dramatic effect on the optical properties of the arrays, which was rationalized by finite element simulation of the local field intensities resulting from plasmon excitation.

The controlled fabrication and geometry tunable optics of gold nanotube arrays

Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15–30 nm, wall thicknesses of 5–15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600–900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

Structural Effects of Nanotubes, Nanowires, and Nanoporous Ti/TiO2 Electrodes on Photoelectrocatalytic Oxidation of 4,4-Oxydianiline

The present work illustrates the effect of electrolyte composition on the self-organized TiO2 nanotube arrays electrode preparation. The influence of structural and surface morphology of the TiO2 nanotube-like anode on their photoactivity and photoelectrocatalytic performance was also investigated. TiO2 nanotubular array electrodes are grown by anodization of Ti foil in 0.25wt % NH4F/glycerol/water, but nanowires can be obtained in 4% HF-DMSO as supporting electrolyte, even when both are subjected to electrochemical anodization at 30V during 50 h. The morphological characteristics are analyzed by X-ray diffraction (XRD) and field emission scanning electron microscope (FEG-SEM). The electrodes were successfully applied in photoelectrocatalytic oxidation of 4,4'-oxydianiline (ODAN) in aqueous solution, as a model of a harmful pollutant. Complete removal of the aromatic amine was obtained after 3 hours of photoelectrocatalytic treatment on nanotubular arrays electrodes.

Reduced in vitro immune response on titania nanotube arrays compared to titanium surface

Material surfaces that provide biomimetic cues, such as nanoscale architectures, have been shown to alter cell/biomaterial interactions. Recent studies have identified titania nanotube arrays as strong candidates for use in interfaces on implantable devices due to their ability to elicit improved cellular functionality. However, limited information exists regarding the immune response of nanotube arrays. Thus, in this study, we have investigated the short- and long-term immune cell reaction of titania nanotube arrays. Whole blood lysate (containing leukocytes, thrombocytes and trace amounts of erythrocytes), isolated from human blood, were cultured on titania nanotube arrays and biomedical grade titanium (as a control) for 2 hours and 2 and 7 days. In order to determine the in vitro immune response on titania nanotube arrays, immune cell functionality was evaluated by cellular viability, adhesion, proliferation, morphology, cytokine/chemokine expression, with and without lipopolysaccharide (LPS), and nitric oxide release. The results presented in this study indicate a decrease in short- and long-term monocyte, macrophage and neutrophil functionality on titania nanotube arrays as compared to the control substrate. This work shows a reduced stimulation of the immune response on titania nanotube arrays, identifying this specific nanoarchitecture as a potentially optimal interface for implantable biomedical devices. © 2013 The Royal Society of Chemistry.

Decoration of Ti/TiO2 Nanotubes with Pt Nanoparticles for Enhanced UV-Vis Light Absorption in Photoelectrocatalytic Process

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efficient Photoelectrochemical Reduction of Nitrite to Ammonium and Nitrogen Containing Gaseous Species Using Ti/TiO2 Nanotube Electrodes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photoelectrochemical Hydrogen Generation and Concomitant Organic Dye Oxidation under TiO2 Nanotube

The present work describes the photoelectrochemical hydrogen generation during a photodegradation of an organic compound. For this, it was chosen the reactive black 5 dye as a model of organic pollutant and its oxidation under TiO2 nanotube in a two compartment cell. The photoelectrocatalysis is conducted in 0.1 mol L-1 Na2SO4 pH 6 medium under photoanode biased at +1.0 V (SCE) and activated by UV and visible light using 150W Xe-Arc lamp (Oriel) and 125 W Hg lamp (Osram). The concomitant hydrogen production was monitored at cathodic compartment using a Pt cathode. Using optimized condition of Na2SO4 0.1 mol L-1 pH 6 as supporting electrolyte, applied potential of +1.0V it was verified 100% of discoloration and 72% of TOC removal of 1.0 x 10(-5) mol L-1 Reactive Black 5 dye after 120 min of treatment (rate constant of 10.6 x10(-2) min(-1)). The concomitant hydrogen generation was 44% in this condition.

Enhanced photoabsorption properties of composites of Ti/TiO2 nanotubes decorated by Sb2S3 and improvement of degradation of hair dye

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Packing-dependent pore structure in single-walled carbon nanotube arrays

Based on a self-similar array model of single-walled carbon nanotubes (SWNTs), the pore structure of SWNT bundles is analyzed and compared with that obtained from the conventional triangular model and adsorption experimental results. In addition to the well known cylindrical endo-cavities and interstitial pores, two types of newly defined pores with diameters of 2-10 and 8-100 nm are proposed, inter-bundle pores and inter-array pores. In particular, the relationship between the packing configuration of SWNTs and their pore structures is systematically investigated. (c) 2005 American Institute of Physics.