Light absorption and hydrophobicity of a polystyrene/multiwall carbon nanotube composite with surface nanostructures

This paper describes an investigation into how combined carbon nanotube doping and surface nanostructuring affects the surface properties of polystyrene. Multiwall carbon nanotubes (MWCNTs) have unique anisotropic electrical properties that can be utilized for light absorption, electromagnetic shielding and nanoscale electostatic forces. Polystyrene was doped with 5 wt% MWCNTs and the resulting composite was wetted onto a porous anodic alumina template to form a nanostructure surface of nanotubes. Scanning electron microscopy revealed a hierarchical surface structure with the composite nanotubes bundled together as the MWCNTs increased the attractive forces between the composite nanotubes. Water droplet testing revealed that this hierarchical surface structure was superhydrophobic. Though the presence of the MWCNTs caused a direct increase in absorption, the hierarchical surface structure increased reflection. The addition of 5 wt% of the anionic surfactant Sodium Dodecyl Benzene Sulfonate to ensure MWCNT dispersal did not significantly change hydrophobicity or light absorption despite the hierarchical surface structure becoming finer. The created composite has potential use as a surface layer on an organic surface cell as it provides reduced cleaning needs and electrical disturbance but further work is required to reduce the reflection.

Highly Ordered TiO2 Nanotube Arrays with Engineered Electrochemical Energy Storage Performances

Nanoscale engineering of regular structured materials is immensely demanded in various scientific areas. In this work, vertically oriented TiO₂ nanotube arrays were grown by self-organizing electrochemical anodization. The effects of different fluoride ion concentrations (0.2 and 0.5 wt% NH₄F) and different anodization times (2, 5, 10 and 20 h) on the morphology of nanotubes were systematically studied in an organic electrolyte (glycol). The growth mechanisms of amorphous and anatase TiO₂ nanotubes were also studied. Under optimized conditions, we obtained TiO₂ nanotubes with tube diameters of 70–160 nm and tube lengths of 6.5–45 μm. Serving as free-standing and binder-free electrodes, the kinetic, capacity, and stability performances of TiO₂ nanotubes were tested as lithium-ion battery anodes. This work provides a facile strategy for constructing self-organized materials with optimized functionalities for applications.

NiFe Alloy Nanotube Arrays as Highly Efficient Bifunctional Electrocatalysts for Overall Water Splitting at High Current Densities

A bubble-releasing assisted pulse electrodeposition method was developed to create metallic alloy, NiFe, nanotube arrays in one step. The NiFe alloy nanotube array exhibited excellent bifunctional electrolytic activities, achieving low overpotentials of 100 mV for the hydrogen evolution reaction and 236 mV for the oxygen evolution reaction at 10 mA cm^-2, both in 1 M KOH at room temperature. For overall water splitting, the NiFe alloy nanotube array delivered 10 mA cm^-2 at an ultralow cell voltage of 1.58 V, among the top tier of the state-of-the-art bifunctional electrocatalysts. The NiFe alloy nanotube array also exhibited ultrastability at high current densities, experiencing only a minor chronoamperometric decay of 6.5% after a 24 h operation at 400 mA cm^-2. The success of the present binder-free nanotube array-based electrode can be attributed to the much enlarged reaction surface area, one-dimensionally guided charge transport and mass transfer offered by the nanotube structure, and improved product crystallinity provided by the pulse current electrodeposition. The nanotube array structure proves to be a promising new architecture design for electrocatalysts.

Fabrication of Core-Shell Nanotube Array for Artificial Photosynthesis Featuring an Ultrathin Composite Separation Membrane

Macroscale arrays of cobalt oxide-silica core-shell nanotubes with high aspect ratio and ultrathin walls of less than 20 nm have been fabricated. The silica shells feature embedded oligo-para(phenylenevinylene) molecules for charge transport across the insulating silica layer, which is tightly controlled by their electronic properties. The assembly is based on the use of a sacrificial Si nanorod array template combined with atomic layer deposition, covalent anchoring of organic wire molecules, and dry cryo-etching. High-resolution TEM imaging of samples prepared by microtome affords structural details of single core-shell nanotubes. The integrity of silica-embedded organic wire molecules exposed to atomic layer deposition, thermal treatment, and harsh etching procedures is demonstrated by grazing angle ATR FT-IR, FT-Raman, and XPS spectroscopy. The inorganic oxide-based core-shell nanotubes with ultrathin gas-impermeable, proton-conducting silica shells functionalized by molecular wires enable complete nanoscale photosynthetic units for CO₂ reduction by H₂O under membrane separation. Arrays of massive numbers of such core-shell nanotube units afford a design that extends the separation of the incompatible H₂O oxidation and CO₂ reduction catalysis environments across the continuum of length scales from nanometers to centimeters.

Hierarchical Configuration of NiCo₂S₄ Nanotube@Ni-Mn Layered Double Hydroxide Arrays/Three-Dimensional Graphene Sponge as Electrode Materials for High-Capacitance Supercapacitors

Three dimensional (3D) hierarchical network configurations are composed of NiCo2S4 nanotube @Ni-Mn layered double hydroxide (LDH) arrays in situ grown on graphene sponge. The 3D graphene sponge with robust hierarchical porosity suitable for as a basal growth has been obtained from a colloidal dispersion of graphene oxide using a simple directional freeze-drying technique. The high conductive NiCo2S4 nanotube arrays grown on 3D graphene shows excellent pseudocapacity and good conductive support for high-performance Ni-Mn LDH. The 3D NiCo2S4@Ni-Mn LDH/GS shows a high specific capacitance (Csp) 1740 mF cm(-2) at 1 mA cm(-2), even at 10 mA cm(-2), 1267.9 mF cm(-2) maintained. This high-performance composite electrode proposes a new and feasible general pathway as 3D electrode configuration for energy storage devices.

Phosphopeptide separation using radially aligned titania nanotubes on titanium wire

Phosphoproteomic analysis offers a unique view of cellular function and regulation in biological systems by providing global measures of a key cellular regulator in the form of protein phosphorylation. Understanding the phosphorylation changes between normal and diseased cells or tissues offers a window into the mechanism of disease and thus potential targets for therapeutic intervention. A key step in these studies is the enrichment of phosphorylated peptides that are typically separated and analyzed by using liquid chromatography mass spectrometry. The mesoporous titania beads/particles (e.g., Titansphere TiO2 beads from GL Sciences Inc., Japan) that are widely used for phosphopeptide enrichment are expensive and offer very limited opportunities for further performance improvement. Titiania nanotube arrays have shown promising characteristics for phosphopeptide separation. Here we report a proof-of-concept study to evaluate the efficacy of nanotubes on Ti-wire for phosphoproteomics research. We used titania nanotubes radially grown on titanium wires as well as the commercial beads to separate phosphopeptides generated from mouse liver complex tissue extracts. Our studies revealed that the nanotubes on metal wire provide comparable efficacy for enrichment of phophopeptides and offer an ease of use advantage versus mesoporous beads, thus having the potential to become a low cost and more practical material/methodology for phosphopeptide enrichment in biological studies.

One-step electrochemical growth of a three-dimensional Sn-Ni@PEO nanotube array as a high performance lithium-ion battery anode

Various well-designed nanostructures have been proposed to optimize the electrode systems of lithium-ion batteries for problems like Li(+) diffusion, electron transport, and large volume changes so as to fulfill effective capacity utilization and increase electrode stability. Here, a novel three-dimensional (3D) hybrid Sn-Ni@PEO nanotube array is synthesized as a high performance anode for a lithium-ion battery through a simple one-step electrodeposition for the first time. Superior to the traditional stepwise synthesis processes of heterostructured nanomaterials, this one-step method is more suitable for practical applications. The electrode morphology is well preserved after repeated Li(+) insertion and extraction, indicating that the positive synergistic effect of the alloy nanotube array and 3D ultrathin PEO coating could authentically optimize the current volume-expansion electrode system. The electrochemistry results further confirm that the superiority of the Sn-Ni@PEO nanotube array electrode could largely boost durable high reversible capacities and superior rate performances compared to a Sn-Ni nanowire array. This proposed ternary hybrid structure is proven to be an ideal candidate for the development of high performance anodes for lithium-ion batteries.

Vertically ordered hematite nanotube array as an ultrasensitive and rapid response acetone sensor

Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.

In-plane mechanical response of TiO2 nanotube arrays - intrinsic properties and impact of adsorbates for sensor applications

In-plane mechanical response of TiO2 nano-tube arrays is intrinsically characterized by very low elastic moduli and significant damping, while both are strongly affected by presence of adsorbates. These findings suggest use of TiO2 nanotube arrays as novel types of sensors, actuators as well as highly stretchable coatings in biomedical applications.

Aptamer based surface enhanced Raman scattering detection of vasopressin using multilayer nanotube arrays

Here we present an optofluidic surface enhanced Raman spectroscopy (SERS) device for on-chip detection of vasopressin using an aptamer based binding assay. To create the SERS-active substrate, densely packed, 200 nm diameter, metal nanotube arrays were fabricated using an anodized alumina nanoporous membrane as a template for shadow evaporation. We explore the use of both single layer Au structures and multilayer Au/Ag/Au structures and also demonstrate a facile technique for integrating the membranes with all polydimethylsiloxane (PDMS) microfluidic devices. Using the integrated device, we demonstrate a linear response in the main detection peak intensity to solution phase concentration and a limit of detection on the order of 5.2 microU/mL. This low limit of detection is obtained with device containing the multilayer SERS substrate which we show exhibits a stronger Raman enhancement while maintaining biocompatibility and ease or surface reactivity with the capture probe.