The effect of solvent choice on the mechanical properties of carbon nanotube–polymer composites

The effect of solvent choice on the mechanical properties of polymer nanotube composites has been investigated. Composites of double-walled nanotubes in polyvinyl alcohol were fabricated using water, DMSO and NMP as solvents. Various amounts of solvent remained trapped in both polymer and composite films even after drying as measured thermogravimetrically. In general, the glass transition temperature decreased as solvent content increased. However, deviations from this behavior suggested the presence of trapped NMP at the polymer–nanotube interface. Both static and dynamic mechanical measurements showed increases in mechanical properties on the addition of nanotubes for water and DMSO-based composites. However, for NMP-based composites, the mechanical properties were reduced compared to the polymer at room temperature. However, the NMP-based composites became significantly stiffer than their polymer counterparts at elevated temperatures suggested thermally assisted NMP desorption from the interface. Unlike the calorimetric measurements, dynamic mechanical measurements of the glass transition temperature showed no significant anomalies, again suggesting desorption of NMP from the interface at higher temperature. This work shows that solvent choice can have a dramatic effect on the mechanical properties of polymer–nanotube composites.     

Exploring the Immunotoxicity of Carbon Nanotubes

Mass production of carbon nanotubes (CNTs) and their applications in nanomedicine lead to the increased exposure risk of nanomaterials to human beings. Although reports on toxicity of nanomaterials are rapidly growing, there is still a lack of knowledge on the potential toxicity of such materials to immune systems. This article reviews some existing studies assessing carbon nanotubes’ toxicity to immune system and provides the potential mechanistic explanation. Yanmei Yu and Qiu Zhang contributed equally to this work.     

Self-templated synthesis of large-scale hierarchical anatase titania nanotube arrays on transparent conductive substrate for dye-sensitized solar cells

The large-scale hierarchical anatase titania nanotube arrays on transparent conductive substrate are fabricated via in situ conversion from anatase titania nanowire arrays. The first-step hydrothermal reaction is the growth of ultra-long anatase titania nanowire arrays, and the second-step hydrothermal reaction is the conversion of titania nanowire arrays to titania nanotube arrays modified with a large number of nanosheets. The resultant hierarchical titania nanotube array film provides a large surface area and superior light scattering ability. Dye-sensitized solar cell based on the hierarchical titania nanotube array photoanode obtains a power conversion efficiency as high as 5.96% and shows a prominent increase compared to the pristine titania nanowire array photoanode (2.12%). In addition, the most interesting result is that an optimized efficiency of 7.54% is achieved for the cell based on the hierarchical titania nanotube array photoanode with titania sol modification.     

The role of interfacial interactions in the dynamic mechanical response of functionalized SWNT-PS nanocomposites

The dynamic mechanical properties of nanocomposites of functionalized single-walled carbon nanotubes dispersed in polystyrene are reported as a function of temperature. For nanocomposites containing less than 0.1 wt% nanotubes, the enhancement of the magnitude of the complex modulus , where E′ and E″ are the elastic and loss moduli, respectively, exceeded the predictions of the Halpin-Tsai model (this model is often used to predict the properties of macroscopic composites). In this concentration range, however, the loss tangent, tan δ = E″/E′, of the nanocomposite remained comparable to that of pure PS, i.e., comparable elasticity. At larger concentrations the mechanical response became more elastic than PS, but the magnitude of the complex modulus fell appreciably below predictions based on the Halpin-Tsai model. An alternate hypothesis that relies on the role of attractive interactions between the nanotubes and polystyrene chains, and consistent with previous Raman scattering and glass transition temperature data, is proposed to describe the observed dynamic response.     

Morphology of hydroxyapatite coated nanotube surface of Ti-35Nb-xHf alloys for implant materials

The purpose of this research is to study the morphology of hydroxyapatite coated nanotube surface of Ti-35Nb-xHf for implant materials using various experiments. For this study, Ti-35Nb-xHf (x = 0, 3, 7 and 15 wt.%) alloys were prepared by arc melting and heat treated for 12 h at 1000 °C in an argon atmosphere and then water quenching. Nanotube formation on the Ti-35Nb-xHf alloys was achieved by anodizing in H₃PO₄ electrolytes containing 0.8 wt.% NaF at room temperature. Anodization was carried out using an electrochemical method and all experiments were conducted at room temperature. Hydroxyapatite (HA) was deposited on the nanotubular Ti-35Nb-xHf alloys surface for the biomaterials by radio-frequency (RF) magnetron sputtering method. The morphologies of nanotubular and HA coated surface were characterized by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The wettability of HA coated surface was measured by contact angle goniometer.The microstructure of Ti-35Nb-xHf alloys was transformed needle-like to equiaxed structure with Hf content and α″ phase decreased, whereas β phase increased as Hf content increased. HA coating surface was affected by microstructure of bulk and morphology of nanotube formation. In case of low Hf content, tip of nanotube formed at β phase was coated with HA film, whereas α″ phase was not coated with HA film. In case of high Hf content, nanotube surface was coated uniformly with HA film. The wettability of HA coated nanotubular surface was higher than that of non coated samples.     

Preparation and improvement of nickel catalyst supported ordered mesoporous spherical silica for thermocatalytic decomposition of methane

The thermocatalytic alteration of CH₄ into highly pure hydrogen and filaments of carbon was investigated on a series of Ni-catalysts with various contents (25, 40, 55, and 70 wt%) supported mesoporous spherical SiO₂. The silica with ordered structure and high specific surface area (1136 m²/g) was synthesized using the Stöber technique with TEOS as a silica precursor and CTAB as the template in a simple synthesis system of aqueous-phase. This technique led to the preparation of mesoporous spherical silica. The prepared samples were characterized using BET, TPR, XRD, TPO, and SEM analyses. The prepared catalysts with different nickel loading showed the BET surface area ranging from 225.0 to 725.7 m²/g. These results indicated that an increase in nickel content decreases the surface area and leads to a subsequent collapse of a pore structure. SEM analysis confirmed a spherical nanostructure of catalysts and revealed that with the increase in loading of Ni, the particle size enlarged, because of the agglomeration of the particles. The results implied that the high methane conversion of 54% obtained over the 55 wt% Ni/SiO₂ at 575 °C and this sample had higher stability at lower reaction temperature than the other prepared catalysts, slowly deactivation was observed for this catalyst at a period of 300 min of time on stream.     

Preparation of cobalt coated TiO2 and WO3–TiO2 nanotube films via photo-assisted deposition with enhanced photocatalytic activity under visible light illumination

Highly ordered TiO₂ and WO₃–TiO₂ nanotubes were prepared by one-step electrochemical anodizing method and cobalt has been successfully deposited on these nanotubes by photo-assisted deposition process. The morphology, crystal structure, elemental composition and light absorption capability of samples were characterized by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray spectrometer and ultraviolet–visible spectroscopy methods. All cobalt loaded samples show an appearance of red shift relative to the unloaded samples. The degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of these novel visible-light-responsive photocatalysts. Results showed that the photocatalytic activity of bare WO₃–TiO₂ samples is higher than that with undoped TiO₂ sample. Compared with unmodified TiO₂ and WO₃–TiO₂, the Co/TiO₂ and Co/WO₃–TiO₂ samples exhibited enhanced photocatalytic activity in the degradation of methylene blue. Kinetic research showed that the reaction rate constant of Co/WO₃–TiO₂ is approximately 2.26 times higher than the apparent reaction rate constant of bare WO₃–TiO₂. This work provides an insight into designing and synthesizing new TiO₂–WO₃ nanotubes-based hybrid materials for effective visible light-activated photocatalysis. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photocatalytic activity.     

纳米Ni(OH)2/Ni-Ti-O 纳米管阵列复合电极的制备及其对甲醇的催化氧化性能

阳极氧化NiTi合金板获得了Ni-Ti-O 纳米管阵列（NTOs）,并将其加热至500℃在氢气气氛中还原处理2h。采用简单的溶盐浸渍法,将Ni(OH)2纳米颗粒负载在NTOs上制备Ni(OH)2/NTOs/NiTi复合电极。采用场发射扫描电子显微镜（FESEM）,X射线光电子能谱（XPS）和循环伏安法（CV）表征电极的表面形貌、电极表面的元素价态和其对甲醇氧化的电催化性能。研究了不同浸渍时间和Ni源浓度等工艺参数对电极微观形貌和电催化氧化性能的影响。结果表明：随着浸渍时间的延长和Ni源浓度的增加,电极上负载的催化纳米颗粒尺寸逐渐增大,氧化峰电流密度先增后降。在25oC时,将NTOs依次浸渍在0.2M NiCl2?6H2O乙醇溶液和0.2M NH4OH乙醇溶液中各12h后,可得到电催化性能良好的纳米Ni(OH)2/NTOs电极,氧化峰电流达到38.41 mA?cm-2。经1000次循环后,电极峰电流密度为原来的75%,表明纳米Ni(OH)2/NTOs电极有良好的循环稳定性,可成为有前景的DMFC的阳极电极候选材料。     

Synthesis, characteristics, and field emission of doped and de-doped polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene) nanotubes and nanowires

Doped and de-doped nanotubes and nanowires of polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene) were synthesized by the electrochemical polymerization method, using Al₂O₃ nanoporous templates. The electrical and optical properties of the nanotubes and nanowires were controlled through various synthetic conditions, such as doping level, dopant, and template-dissolving solvents. The diameters and wall thicknesses of the nanotubes were 100–200 nm and 10–30 nm, respectively. To determine the electrical and optical properties of the nano-systems, I–V characteristic curves with gate bias, dc conductivity, and UV–vis spectra were measured. We observed that the nano-systems were transformed from a conducting state to a semiconducting (or insulating) state through the process of de-doping using the template-dissolving solvents. Possible applications of these nanotubes and nanowires in the construction of nanotip emitters in field emission displays and polymer-based transistors are presented.     

One-pot facile synthesis and electrochemical evaluation of selenium enriched cobalt selenide nanotube for supercapacitor application

The present study emulates a one-pot facile synthesis of selenium-enriched CoSe nanotube using a chemical bath deposition (CBD) procedure. Schematic incorporation of 3D Ni foam current collectors as substrates for the growth of CoSe–Se nanotubes helped us achieve a binder-less thin film coating. The controlled synthesis of CoSe–Se nanotube was carried out by optimizing the temperature and time of the deposition. CoSe–Se nanotubes were grown on a porous Ni foam substrate using lithium chloride as a shape directing agent. The study found that the one dimensional structure of the nanotubes with porous nature results in an uninterrupted network of electroactive sites. Due to the superior conductivity, the as-fabricated material exhibited excellent rate capability and a higher degree of electrolyte ion diffusion across the CoSe–Se crystal structure. The CoSe–Se@Ni foam electrodes exhibited a specific capacitance of 1750.81 F g^?1 at 1 A g^?1. The electrode exhibited excellent cycling stability and showed a capacitance retention of 95% after 4000 charge-discharge cycles. Finally, an asymmetric supercapacitor (ASC) device was fabricated with the as-synthesized CoSe–Se@Ni foam electrode as the cathode, activated carbon@Ni foam electrode as the anode, and a thin filter paper separator soaked in 1 M aqueous KOH electrolyte solution. The ASC device showed a specific capacitance value of 106.73 F g^?1 at 0.5 A g^?1, and achieved an energy density of 37.94 Wh kg^?1 at a power density of 475.30 W kg^?1. The ASC device was utilized in an extended potential window of 1.6 V. The fabricated device displayed exceptional cycling stability with a capacitance retention of 93% after 5000 charge-discharge cycles.