Sol–gel nanocoating on commercial TiO<Subscript>2</Subscript> nanopowder using ultrasound

The surface of commercial titania particles was coated by a layer of silica by a two-step process which involved a power ultrasound initiated sol–gel reaction. In the first step of this solution process, aminosilane, i.e. organosilane with amino functional group, was used to modify the surface of pristine nanoparticles. Subsequent silica nanocoating was initiated and sustained under power ultrasound agitation in a mixture of surface modified particles and epoxysilane. As a result, a homogenous coverage of silica on the nanoparticles’ surface, with thickness controllable from one to several nanometers, was obtained. Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and particle surface zeta potential measurements were employed to follow steps in the process and to confirm the reaction mechanism.     

Isolation and characterization of fluorescent nanoparticles from pristine and oxidized electric arc-produced single-walled carbon nanotubes

Fluorescent nanoparticles were isolated from both pristine and nitric acid-oxidized commercially available carbon nanotubes that had been produced by an electric arc method. The pristine and oxidized carbon nanotube-derived fluorescent nanoparticles exhibited a molecular-weight-dependent photoluminescence in the violet-blue and blue to yellowish-green ranges, respectively. The molecular weight dependency of the photoluminescence was strongly related to the specific supplier. We analyzed the composition and morphology of the fluorescent nanoparticles derived from pristine and oxidized nanotubes from one supplier. We found that the isolated fluorescent materials were mainly composed of calcium and zinc. Moreover, the pristine carbon nanotube-derived fluorescent nanoparticles were hydrophobic and had a narrow distribution of maximal lateral dimension. In contrast, the oxidized carbon nanotube-derived fluorescent nanoparticles were superficially oxidized and/or coated by a thin carbon layer, had the ability to aggregate when dispersed in water, and exhibited a broader distribution of maximal lateral dimension.     

Aqueous dispersion, surface thiolation, and direct self-assembly of carbon nanotubes on gold

We report the efficient aqueous dispersion of pristine HiPco single-walled carbon nanotubes (SWNTs) with ionic liquid (IL)-based surfactants 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), the thiolation of nanotube sidewalls with 2, and the controlled self-assembly of positively charged SWNT-1,2 composites on gold. Optical absorption spectra and resonance Raman (RR) data of obtained aqueous SWNT-1,2 dispersions are consistent with debundled and noncovalently functionalized nanotubes whose electronic properties have not been disturbed. Additionally, the dispersion of pristine nanotube material with surfactants 1 and 2 leads to a high degree of purification from carbonaceous particles. The chiralities of the 14 smallest semiconducting HiPco SWNTs in resonance with Raman excitation at 1064 nm (1.165 eV) were determined in SWNT-2 aqueous dispersion using UV-vis-NIR and RR spectra. X-ray photoelectron spectroscopy (XPS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopy of SWNT-2 submonolayers on gold verified the encapsulation of individualized SWNTs with IL surfactants, the cleavage of S-S disulfide bonds formed in aqueous SWNT-2 suspensions, and the direct chemisorption of the SWNT-2 composite on bare gold via the Au-S bond. Aqueous dispersions of SWNTs with IL-based surfactants add biofunctionality to carbon nanotubes by imparting the positive surface charge necessary for interactions with cell membranes. Our technique, which purifies pristine nanotube material and produces water-soluble, positively charged nanotubes with pendent surface-active thiol groups, may also be translated to other carbon nanotubes and carbon nanostructures. Self-assembled, positively charged submonolayers of SWNTs can be further used for applications in cell biology and sensor technology.     

Tailored interfaces in nanocomposites

Different kinds of clays based on sodium montmorillonite have been modified i) by cationic exchange of alkylammonium ions and ii) by covalent grafting of organosilane. We have prepared organophilic clays with different gallery heights (due to alkylammonium ions with alkyl chain length varying from 8 to 18 carbon atoms) and with a specific functionalisation (due to the organosilane). We have generated organoclays with different kind of organic layer properties: ionically bonded or physically adsorbed alkylammonium ions and covalently grafted organosilane. These different organoclays have shown various specific behaviours when dispersed in monomers or in a reactive mixture, proving the influence of the surfactant on the nanocomposite final properties.     

Preparation of Fluorescent Thiol Group‐Functionalized Silica Microspheres for the Detection and Removal of Silver Ions in Aqueous Solutions

We demonstrate that silica microspheres can act as a sensitive fluorescent sensor and adsorbent of Ag⁺ in aqueous media. These thiol‐functionalized silica microspheres are doped with quantum dots (QDs) using organosilane chemistry in a one‐step preparation. Ligand exchange takes place between the thiolated organosilane and acid‐capped QDs, making the doping easy. Ag⁺ adsorption by the silica microspheres causes the decrease of fluorescence intensity of the QDs. The detection limit for Ag⁺ is found to be 10 μmol/L. The abundance of thiol groups on the surface of the microspheres could effectively remove Ag⁺ through strong interaction. When microspheres with a diameter of 1.1 μm are used as the adsorbents, the adsorption capacity for Ag⁺ reached 102 mg/g. This excellent adsorption ability is due to the abundance of thiol groups that act as the active sites, facilitating the adsorption of the massive metal ions on the surface of the microspheres. Furthermore, the adsorption isotherm data follows the Freundlich model. The structure and content of the silica microspheres were investigated by scanning and high‐resolution transmission electron microscopy, energy dispersive X‐ray spectroscopy, and Raman analysis, and the fluorescence properties were characterized by fluorescence microscopy.     

A novel and simplified procedure for patterning hydrophobic and hydrophilic SAMs for microfluidic devices by using UV photolithography

This work describes how selective patterning of hydrophobic and hydrophilic areas inside microchannels of microfluidic devices can be achieved by combining well-known chemical protocols and standard photolithography equipment (365 nm). Two techniques have been performed and compared. The first technique is based on the preparation of self-assembled monolayers of photocleavable organosilane and the second one on photoassisted grafting (365 nm) of self-assembled monolayers (SAMs) on a silicon or glass substrate. In the first case, we begin with monolayers carrying an o-nitrobenzyl function (hydrophobic area) that is photochemically cleaved, revealing a carboxylic acid group (hydrophilic area). The problem is that the energy necessary to cleave this monolayer is too high and the reaction time is more than 1 h with 50 mW/cm(2) irradiation flux. To overcome this practical disadvantage, we propose another approach that is based on the thiol-ene reaction with benzophenone as photoinitiator. In this approach, a monolayer of mercaptopropyltrimethoxysilane (MPTS) is prepared first. Subsequently, a hydrocarbon chain is photografted locally onto the thiol layer, forming a hydrophobic surface while the reminding unmodified thiol surface is oxidized into sulfonic acid (hydrophilic area). We demonstrated the feasibility of this approach and synthesized high-quality self-assembled monolayers by UV grafting with an irradiation time of 30 s at 365 nm (50 mW/cm(2)). The modified surfaces have been characterized by contact angle measurements, X-ray photoelectron spectroscopy (XPS), AFM, and multiple internal reflection infrared spectroscopy (MIR-FTIR). The difference in the contact angles on the hydrophilic and hydrophobic surfaces reached a remarkable 77 degrees. We have also demonstrated that this method is compatible with selective surface grafting inside microfluidic channels.     

Nanoscale patterning of organosilane molecular thin films from the gas phase and its applications: fabrication of multifunctional surfaces and large area molecular templates for site-selective material deposition

A simple methodology to fabricate micrometer- and nanometer-scale patterned surfaces with multiple chemical functionalities is presented. Patterns with lateral dimensions down to 110 nm were made. The fabrication process involves multistep gas-phase patterning of amine, thiol, alkyl, and fluorinated alkyl-functional organosilane molecules using PDMS molds as shadow masks. Also, a combination process of channel diffused plasma etching of organosilane molecular thin films in combination with masked gas-phase deposition to fabricate multilength scale, multifunctional surfaces is demonstrated.     

Cell patterning using a template of microstructured organosilane layer fabricated by vacuum ultraviolet light lithography

Micropatterning techniques have become increasingly important in cellular biology. Cell patterning is achieved by various methods. Photolithography is one of the most popular methods, and several light sources (e.g., excimer lasers and mercury lamps) are used for that purpose. Vacuum ultraviolet (VUV) light that can be produced by an excimer lamp is advantageous for fabricating material patterns, since it can decompose organic materials directly and efficiently without photoresist or photosensitive materials. Despite the advantages, applications of VUV light to pattern biological materials are few. We have investigated cell patterning by using a template of a microstructured organosilane layer fabricated by VUV lithography. We first made a template of a microstructured organosilane layer by VUV lithography. Cell adhesive materials (poly(d-lysine) and polyethyleneimine) were chemically immobilized on the organosilane template, producing a cell adhesive material pattern. Primary rat cardiac and neuronal cells were successfully patterned by culturing them on the pattern substrate. Long-term culturing was attained for up to two weeks for cardiac cells and two months for cortex cells. We have discussed the reproducibility of cell patterning and made suggestions to improve it.     

Self-assembly of gold nanoparticles to carbon nanotubes using a thiol-terminated pyrene as interlinker

Gold nanoparticles were self-assembled onto the surface of solubilized carbon nanotubes through an interlinker of bi-functionalized molecule (PHT) terminated with pyrenyl unit at one end and thiol group at the other end. While the fluorescence of PHT is quenched moderately by the carbon nanotubes, the fluorescence is almost totally quenched by the further binding of gold nanoparticles. The enhancement of the Raman responses of nanotubes by the gold nanoparticles is also observed. These results imply there are charge transfer interactions between nanotubes and gold nanoparticles.     

碳纳米管微结构的改变对其容量性能的影响

以KOH为活性剂，通过在高温下将碳纳米管进行活化处理来实现对碳纳米管管壁结构的改变，得到了比表面积和孔容分别是活化处理前约3倍和1.5倍的活性碳纳米管.将活化处理前后两种碳纳米管分别制作成电化学超级电容器电极，在充满氩气的无水手套箱组装成模拟电化学超级电容器，在恒流充放电模式下进行电化学可逆容量的测试，发现活性碳纳米管的电化学容量远高于活化前碳纳米管，是它的2倍.从而发现碳纳米管被打断，管壁变粗糙的活性碳纳米管比一般碳纳米管更适合用于电化学超级电容器电极材料.     

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.     

碳纳米管的活化处理及对其电化学容量影响的研究

采用KOH为活性剂,对碳纳米管进行活化处理,经透射电子显微镜和高分辨透射电子显微镜从不同角度观察,发现得到了两端开口,管长较短,管壁粗糙的活性碳纳米管．用氮气自动吸附仪测试了活化前后两种碳纳米管的比表面积,发现活性碳纳米管具有比活化前碳纳米管更高的有效比表面积,将这两种碳纳米管分别作为电极材料应用于电化学超级电容器,经测试,发现活化后的碳纳米管的电化学容量大大提高,在有机电解液中达到了50F／g．     

Effect of interaction between poly(ethylene terephthalate) and carbon nanotubes on the morphology and properties of their nanocomposites

Poly(ethylene terephthalate) (PET) nanocomposites were prepared by melt‐extruding mixtures of PET and functionalized multiwalled carbon nanotubes (MWNTs) with some interaction with PET molecules. For the functionalization of MWNTs, benzyl isocyanate and phenyl isocyanate with different molecular flexibility were employed on the surface of the MWNTs via chemical modification, respectively. The reaction for functionalization of MWNTs was confirmed by FTIR and transmission electron microscopy (TEM) measurements. TEM observations indicated that both benzyl and phenyl isocyanate groups covered the surface of the MWNTs after functionalization. The PET nanocomposites containing isocyanate groups showed improved mechanical properties, including the tensile strength and tensile modulus, compared with those with pristine and acid‐treated nanotubes. These improvements were ascribed to π–π interactions between the aromatic rings of PET molecules and the isocyanate group in MWNTs. The functionalized MWNTs showed a better dispersion of carbon nanotubes in the matrix polymer and a different fractured cross‐section morphology in scanning electron microscope measurements relative to the pristine MWNTs. The crystallinity of the functionalized MWNT‐PET nanocomposites was significantly higher than that of the pristine and acid‐treated MWNTs. FTIR results indicated that the presence of carbon nanotubes induced trans‐conformation of PET chains, and trans conformation was particularly dominant in PET composites incorporating MWNT‐phenyl. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 900–910, 2008     

Functionalization of multi-walled carbon nanotubes with coumarin derivatives and their biological evaluation

We report the synthesis and the characterization of different multi-walled carbon nanotubes (MWCNTs) linked to natural molecules, 5,7-coumarins and/or oleic acid, obtained from purified pristine MWCNTs by a cascade of chemical functionalization. The activities of these modified MWCNTs were investigated in vitro on human umbilical vein endothelial cells (HUVECs) by evaluating their ability to influence cell viability and to induce cell apoptosis. Our data showed that pristine MWCNTs are markedly cytotoxic; conversely, the carboxylated carbon nanotubes, much more readily dispersed in aqueous solutions and CNT-Link, the key intermediate designed by us for the drug anchorage, are biocompatible at the tested concentrations (1 and 10 μg ml(-1)).     

Controlled fabrication of organic nanotubes via self-assembly of non-symmetric bis-acylurea

We present novel non-symmetric bis-acylurea organogelators that self-assemble into hollow tubular nanostructures upon cooling in solutions. The bis-acylureas have aliphatic end groups of different lengths divided by a spacer group [?NHCONHCO?(CH₂)₅?CONHCONH?, C5] with two hydrogen bonding sites. Due to the intermolecular biaxial hydrogen bonding, the molecules crystallize into 2D thin layers at first, and then their wrapping ultimately results in nanotubes. On the contrary, symmetric bis-acylureas form multilayered nanosheets which are stabilized by the van der Waals interaction between the stacked layers. The size and shape of the nanotubes can be controlled by varying the difference of the alkyl chain lengths. When the difference is big, for example, eight methylene units (BuC5DD, butyl (Bu) and dodecyl (DD)), uniform nanotubes of 65-nm mean outer diameter are obtained, while a non-symmetric bis-acylurea with one methylene unit difference (UDC5DD, undecyl (UD)) forms a mixture of nanosheets and nanotubes. Template-assisted formation of nanotubes was successfully performed via gelation in inorganic nanopores. We also synthesized a thiol-functionalized non-symmetric bis-acylurea, HS-UDC5Bu (thiol (HS)), which was used as a tubular template for gold nanoparticles.     

Purification of HiPCO carbon nanotubes via organic functionalization

We report a new method for the purification of HiPCO single-wall carbon nanotubes (SWNT), which consists of the following sequence: (a) organic functionalization of the as-produced nanotubes (pristine tubes, p-SWNT), (b) purification of the soluble functionalized nanotubes (f-SWNT), (c) removal of the functional groups and recovery of purified nanotubes (r-SWNT) by thermal treatment at 350 degrees C, followed by annealing to 900 degrees C. Each of these steps contributes to the purification, but only their sequential combination leads to high-purity materials. Organic functionalization makes the SWNT more easy to handle, which results in a better manipulation for potential practical uses. The electronic properties of the purified tubes are investigated via Raman and NIR spectroscopies along with transmission electron microscopy.     

Dynamic surface rearrangement and thermal stability of nitrogen functional groups on carbon nanotubes

Dynamic surface rearrangement and thermal stability of N-functional groups on carbon nanotubes (CNTs), obtained by functionalization of pristine CNTs with NH(3), were studied by temperature-programmed XPS and MS: a link between the stability of the functional group and decomposition temperature have been established and a conversion into graphitic nitrogen was observed.     

Modification of the size of supported clusters by coadsorption of an organic compound: gold and L-cysteine on rutile TiO2(110)

Using X-ray photoelectron spectroscopy we studied the coadsorption of the amino acid L-cysteine and gold on a rutile TiO(2)(110) surface under ultrahigh vacuum conditions. Irrespective of the deposition order, i.e., irrespective of whether L-cysteine or gold is deposited first, the primary interaction between L-cysteine and the gold clusters formed at the surface takes place through the deprotonated thiol group of the molecule. The deposition order, however, has a profound influence on the size of the gold clusters as well as their location on the surface. If L-cysteine is deposited first the clusters are smaller by a factor two to three compared to gold deposited onto the pristine TiO(2)(110) surface and then covered by L-cysteine. Further, in the former case the clusters cover the molecules and thus form the outermost layer of the sample. We also find that above a minimum gold cluster size the gold cluster/L-cysteine bond is stronger than the L-cysteine/surface bridging oxygen vacancy bond, which, in turn, is stronger than the gold cluster/vacancy bond.     

TiO2 nanotubes in dye-sensitized solar cells: Higher efficiencies by well-defined tube tops

Aligned self-organized TiO₂ nanotubes of 15–20 µm length proved to be very promising for application in dye-sensitized solar cells. Conventional anodic nanotube layers usually show an irregular structure (nanograss) or a thin nucleation layer at the top of the nanotube array. In the present paper, we demonstrate that by a simple photoresist based method, well-defined and open TiO₂ nanotube tops can be obtained which significantly enhances their performance when used in DSSCs. In fact, the layers show the highest reported solar energy conversion efficiency up to now for a pristine (particle-free) nanotube layer.     

A comparative study of argon ion irradiated pristine and fluorinated single-wall carbon nanotubes

Effect of Ar(+) ion irradiation on the structure of pristine and fluorinated single-wall carbon nanotubes (SWCNTs) was examined using transmission electron microscopy (TEM), Raman, and x-ray photoelectron spectroscopy (XPS). The TEM analysis revealed retention of tubular structures in both irradiated samples while Raman spectroscopy and XPS data indicated a partial destruction of nanotubes and formation of oxygen-containing groups on the nanotube surface. From similarity of electronic states of carbon in the irradiated pristine and fluorinated SWCNTs observed by XPS, it was suggested that defluorination of nanotubes proceeded with breaking of C-F bonds.