聚合物对多壁碳纳米管的包覆改性研究

探讨了聚合物对碳纳米管的包覆改性.将多壁碳纳米管(MWNTs)通过浓硫酸和浓硝酸的混酸(体积比=3∶1)处理,使其带上羧基.将羧化MWNTs与甲基丙烯酸缩水甘油酯(GMA),苯乙烯双组分接枝聚苯乙烯(PS-g-(GMA-co-St))通过溶液共混方法,使其接在MWNTs上的羧基和GMA所带的环氧基团之间发生酯化反应,实现MWNTs表面接枝上PS-g-(GMA-co-St).扫描电镜观察表明,羧化MWNTs平均管径约为40nm,而接枝上PS-g-(GMA-co-St)的改性MWNTs管径可达约100nm.用四氢呋喃(THF)对表层包覆的PS-g-(GMA-co-St)刻蚀后,其直径降回到约40nm,这和先前观察到的羧化MWNTs的直径基本一致.对刻蚀后的MWNTs样品的FT-IR分析也表明MWNTs表面上存在接枝PS.表面经过PS-g-(GMA-co-St)修饰后,可以形成包覆层,为MWNTs在聚合物基体中分散、制备纳米功能材料提供了途径.     

Carbon nanotube assisted synthesis of CeO2 nanotubes

CeO₂ nanotubes have been synthesized facilely using carbon nanotubes (CNTs) as templates by a liquid phase deposition method. The properties of the CeO₂ nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) as well as thermogravimetry and differential thermal analysis (TG-DTA). The obtained CeO₂ nanotubes with a polycrystalline face-centered cubic phase have a uniform diameter ranging from 40 to 50 nm. The CeO₂ nanotubes are composed of many tiny interconnected nanocrystallites of about 10 nm in size. The pretreatment of CNTs and calcination temperature were confirmed to be the crucial factors determining the formation of CeO₂ nanotubes. A possible formation mechanism has been suggested to explain the formation of CeO₂ nanotubes.     

Chemical modification and the photoluminescence stabilization of titanic acid nanotubes

1 Introduction In 1998, Kasuga et al. obtained a new kind of nanotubular materials by treating anatase TiO2 power with concentrated NaOH aqueous solution[1,2]. This work soon aroused general concern due to their exten- sive applications in the photoelectr…     

Blue TiO2 nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting

In the past years there has been a great interest in self-doped TiO₂ nanotubes (blue TiO₂ nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue TiO₂ nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue TiO₂ nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed TiO₂ nanotubes. The annealing temperature of undoped TiO₂ nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue TiO₂ nanotubes was achieved by adjusting the cathodic polarization parameters. Blue TiO₂ nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm^-2) compared to the undoped TiO₂ nanotube arrays (0.19 mA cm^-2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.     

EuF3 nanotubes fabricated via Eu(NO3)3/cysteamine as precursor and their derived thermosensitive nanogels

In this paper, we report a novel solution route to obtain rare earth nanotubes. Firstly, the complex of Eu(NO₃)₃/cysteamine (Eu-Complex) was used as the precursor, then nanotubes of EuF₃ were fabricated from the precursor and NaF. Secondly, the EuF₃ nanotubes reacted with acrylic acid (AA) and converted into vinyl decorated nanotubes. Finally, the decorated nanotubes copolymerized with N-isopropylacrylamide via free radical polymerization and thermosensitive EuF₃ nanotubes/poly (N-isopropylacrylamide) (PNIPAm) nanogels were prepared. In order to investigate the mechanism to produce the nanotubes, the morphology structures of samples at different reaction stages were studied via TEM, and the formation mechanism of nanotubes is proposed. The chemical composition was confirmed by FTIR, XRD, XPS and elemental analyzer. The optical property of the as-prepared nanotubes and the nanogels was investigated in detail by photoluminescence (PL). The results suggest that, compared with their bulk counterparts, the nanogels present different thermosensitive fluorescence behavior, for instance, around their low critical solution temperature (LCST), the variation of PL emission intensity of the nanogels is slightly gentler.     

Lithium-ion batteries based on vertically-aligned carbon nanotube electrodes and ionic liquid electrolytes

In conjunction with environmentally benign ionic liquid electrolytes, vertically-aligned carbon nanotubes (VA-CNTs) sheathed with and without a coaxial layer of vanadium oxide (V(2)O(5)) were used as both cathode and anode, respectively, to develop high-performance and high-safety lithium-ion batteries. The VA-CNT anode and V(2)O(5)-VA-CNT cathode showed a high capacity (600 mAh g(-1) and 368 mAh g(-1), respectively) with a high rate capability. This led to potential to achieve a high energy density (297 Wh kg(-1)) and power density (12 kW kg(-1)) for the prototype batteries to significantly outperform the current state-of-the-art Li-ion batteries.     

Silicon nanotube anode for lithium-ion batteries

This work describes a promising strategy for large-scale fabrication of silicon (Si) nanotubes. The process began with preparation of silica nanotubes using rod-like NiN₂H₄ as a template and the resulting silica nanotubes were then converted to Si nanotubes by a thermal reduction process assisted with magnesium powder. The electrochemical properties of Si nanotubes were investigated as anode of lithium-ion batteries. It was demonstrated that the as-developed Si nanotubes showed significantly improved rate capability and long-term cycling performance compared with commercial silicon meshes.     

Structural evaluation and photocatalytic properties of Pt-supported titanate nanotubes

Pt nanocrystal-supported titanate nanotubes as a photocatalyst were prepared by hydrothermal treatment and subsequent heat-treatment in H₂ atmosphere (H₂ reduction) of a mixture of these titanate nanotubes and H₂PtCl₆. TEM results showed that Pt nanoparticles (a few nm in diameter and 5 to 10 nm in length) with good crystallinity were entrapped inside titanate naotubes and were closely precipitated on the surface of titanate nanotubes. These Pt nanocrystal-supported titanate nanotubes possessed the high ability for HCHO decomposition.     

Significant enhancement of the photoelectrochemical activity of TiO2 nanotubes

In the present work, we report on a facile and effective approach to significantly enhance the photocatalytic activity of TiO₂ nanotubes. The TiO₂ nanotubes prepared by the electrochemical oxidation of titanium in dimethyl sulfoxide (DMSO) with 2% HF were treated in a methanol solution under UV light irradiation. In comparison with the untreated TiO₂ nanotubes, the treatment resulted in a dramatic increase in the donor density of the TiO₂ nanotubes by approximately 3 orders of magnitude. The treated TiO₂ nanotubes exhibited a 15-fold enhancement in photocurrent and a 6.8-fold increase in the photoelectrochemical degradation of 4-nitrophenol, significant for hydrogen generation and wastewater treatment.     

Mechanical Properties of WS2 Nanotubes

Their mesoscopic dimensions (including a nanometer scale diameter and a micrometer scale length) make nanotubes a unique and attractive object of study, including the study of their mechanical properties and fracture in particular. The investigation of the mechanical properties of individual WS₂ nanotubes is a challenging task due to their small size. Hence, various microscopy based techniques were used to overcome this challenge. The Young’s modulus was studied by techniques like atomic force microscope (AFM) and scanning electron microscope (SEM); it was also calculated by using the density-functional-based tight-binding (DFTB) method. Tensile tests and bending tests of individual WS₂ nanotubes were performed as well. Furthermore, the shock wave resistance of these nanotubes was tested. The Young’s modulus of WS₂ nanotubes was found to be in the range of 150–170 GPa, which is in good agreement with DFTB calculations. WS₂ nanotubes also showed tensile strength as high as 16 GPa and fracture strain of 14%. These results indicate the high quality of these nanotubes which reach their theoretical strength. The interlayer shear (sliding) modulus was found to be ca. 2 GPa, this value is in good agreement with DFTB calculations. Moreover, the nanotubes were able to withstand shock waves as high as 21 GPa.     

Photocatalytic Crystalline and Amorphous TiO2 Nanotubes Prepared by Electrospinning and Atomic Layer Deposition

In this work core/shell composite polymer/TiO₂ nanofibers and from those TiO₂ nanotubes were prepared. First, poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) fibers were synthetized by electrospinning. They were covered with a 100 nm thick amorphous TiO₂ layer by atomic layer deposition at 50 °C. Later the polymer core was removed by two different methods: dissolution and annealing. In the case of dissolution in water, the as-prepared TiO₂ nanotubes remained amorphous, while when annealing was used to remove the polymers, the TiO₂ crystallized in anatase form. Due to this, the properties of amorphous and crystalline TiO₂ nanotubes with exactly the same structure and morphology could be compared. The samples were investigated by SEM-EDX, ATR-IR, UV-Vis, XRD and TG/DTA-MS. Finally, the photocatalytic properties of the TiO₂ nanotubes were studied by decomposing methyl-orange dye under UV light. According to the results, crystalline anatase TiO₂ nanotubes reached the photocatalytic performance of P25, while amorphous TiO₂ nanotubes had observable photocatalytic activity.     

Selective synthesis of boron nitride nanotubes by self-propagation high-temperature synthesis and annealing process

Four types of BN nanotubes are selectively synthesized by annealing porous precursor in flowing NH₃ and NH₃/H₂ atmosphere at temperature ranging from 1000 to 1200 °C in a vertical furnace. The as-synthesized BN nanotubes, including cylinder, wave-like, bamboo-like and bubble-chain, are characterized by XRD, FTIR, Raman, SEM, TEM and HRTEM. Three phenomenological growth models are proposed to interpret growth scenario and structure features of the four types of BN nanotubes. Selectivity of nanotubes formation is estimated as approximately 80-95%. The precursor containing B, Mg, Fe and O prepared by self-propagation high-temperature synthesis (SHS) method plays a key role in selective synthesis of the as-synthesized BN nanotubes. Chemical reactions are also discussed.     

Improvement the wastewater purification by TiO2 nanotube arrays: The effect of etching-step on the photo-generated charge carriers and photocatalytic activity of anodic TiO2 nanotubes

The current study demonstrates how the etching step in anodization process effects on the photocatalytic activity of TiO₂ nanotubes. In this regard, the TiO₂ nanotubes were made by one-step and two-step anodization process on two different substrates Ti and etched-Ti foils, respectively. The results revealed that two-step anodization process is a beneficial way to prepare highly well-organized structure and regular surface. The two-step anodization by an enhancement in the fluoride ions diffusion led to a decrease in nanotubes' porosity and an increment in the nanotubes’ surface area, a factor of roughness, and the ratio of length to diameter, respectively. As a consequence of the improvement in geometrical properties, the two-step TiO₂ nanotubes led to the intensification of photocurrent density (from 0.383 to 0.677 mA cm⁻²⁾ and photoconversion efficiency (from 0.18% to 0.29%) in comparison with the one-step nanotubes, respectively. Further, a synergetic impact of the photoelectrochemical measurement and photocatalytic process was observed. The degradation efficiencies of 2,4-dichlorophenol by two-step nanotubes increased from 47 to 55% under visible light, and from 58 to72% under UV irradiation, which it was attributed to more light harvesting, more photo-generated electrons, higher separation efficiency and improvement in geometrical properties. Furthermore, the kinetic study showed that the reactions follow first-order kinetics and the reaction rate constants by two-step nanotubes are 1.25 and 1.44 times as great as those of one-step nanotubes under visible and UV irradiation, respectively. Moreover, the reusability tests showed that 2-step TiO₂ nanotubes has good stability and is active even up to the Fifth run.     

Synthesis and Catalytic Studies of Uniform Os &; Os–Pd Nanoparticles Supported on MWNTs

Os and Os–Pd nanoparticles supported on multi-walled carbon nanotubes were prepared by vacuum pyrolysis at 573 K using the [Os₃CO₁₀(NCMe)₂] and [Pd(acac)₂] as precursors. The nanoparticles prepared showed a narrow size distribution (Os: 1.8 nm; Os–Pd: 4.3 nm) and were decorated evenly on the surface of the nanotubes. By controlling the metal-to-nanotube ratio, Os nanotubes were prepared using the carbon nanotubes as a template. The catalysis of Os–Pd nanoparticles towards CVD carbon nanotube synthesis was studied. Dedicated to Professor Gunther Schmid on the occasion of his 70th birthday.     

Skin Constituents as Cosmetic Ingredients. Part III: A Molecular Modeling Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface

Tetrakis(4-hydroxylphenyl)porphyrin (THPP) modified multi-walled carbon nanotubes were synthesized. Meanwhile, THPP or tetrakis(4-hydroxylphenyl)porphyrin cobalt(II) (CoTHPP) was introduced on the surface of carboxyl-functionalized multi-walled carbon nanotubes (MWNTs-COOH) and amino-functionalized multi-walled carbon nanotubes (MWNTs-NH₂) to form a series of complexes, respectively. TEM images indicated that the assemblies were made of the short chipping carbon nanotubes and the long assembled carbon nanotubes. The UV-vis spectra and fluorescence spectra were used to investigate the properties of the porphyrins assembled on the carbon nanotubes.     

Property control of new forms of carbon materials by fluorination

Multiwall carbon nanotubes (MWNTs) based on the template carbonization technique were fluorinated in a temperature range 323-473 K by elemental fluorine. The fluorination of the carbon nanotubes results in functionalization and modification of pristine nanotubes with respect to adsorption and electrochemical properties. Selective fluorination of the inner surface of the carbon nanotubes, brings about a decrease in the surface free energy of the inner surface of the tubes and an increase in colombic efficiency of Li/nanotubes rechargeable cells in an aprotic medium. Electrochemical fluoride-ion doping of fullerene C₆₀ thin films (250-450 nm) was carried out in a fluoride-ion conductive solution, MeCN solution of 1 M Et₄NF·4HF. Galvanostatic oxidation yielded C₆₀F_ca.1-3 where fluorine exists as a semi-ionic species in the cavity surrounded by C₆₀ molecules without forming covalent CF bonds     

Microwave-Assisted Heating Method for the Decoration of Carbon Nanotubes with Zinc Sulfide Nanoparticles

This study focuses on in situ synthesis of ZnS nanoparticles on the surface of multiwalled carbon nanotubes. By microwave-assisted chemical reaction of Zn(Ac)₂·2H₂O and NaS·9H₂O in glycol solution with carbon nanotubes, which were pretreated by oxidization in concentrated HNO₃. Zinc sulfide crystallite densely supported on carbon nanotubes with the diameter about 1 nm. The carbon nanotubes decorated by ZnS were characterized using transmission electron microscopy and x-ray diffraction. It is found that the multi-walled carbon nanotubes can not only act as a substrate but also change the crystal structures of ZnS in the reaction.     

Effect of Photoinduced Size Changes on Protein Refolding and Transport Abilities of Soft Nanotubes

Self‐assembly of azobenzene‐modified amphiphiles (Gly_nAzo, n=1–3) in water at room temperature in the presence of a protein produced nanotubes with the protein encapsulated in the channels. The Gly₂Azo nanotubes (7 nm internal diameter [i.d.]) promoted refolding of some encapsulated proteins, whereas the Gly₃Azo nanotubes (13 nm i.d.) promoted protein aggregation. Although the 20 nm i.d. channels of the Gly₁Azo nanotubes were too large to influence the encapsulated proteins, narrowing of the i.d. to 1 nm by trans‐to‐cis photoisomerization of the azobenzene units of the Gly₁Azo monomers packed in the solid bilayer membranes led to a squeezing out of the proteins into the bulk solution and simultaneously enhanced their refolding ratios. In contrast, photoinduced transformation of the Gly₂Azo nanotubes to short nanorings (<40 nm) with a large i.d. (28 nm) provided no further refolding assistance. We thus demonstrate that pertubation by the solid bilayer membrane wall of the nanotubes is important to accelerate refolding of the denatured proteins during their transport in the narrow nanotube channels.     

Hydrothermal synthesis of potassium titanate nanotubes doped with magnesium,nickel, and aluminum

Study of the phase formation in the systems TiO₂?MO(M₂O₃)?KOH?H₂O (M = Mg, Ni, Al) from crystalline and coprecipitated X-ray-amorphous mixtures demonstrated that doped potassium titanate nanotubes can be obtained in a hydrothermal treatment of coprecipitated hydroxides in the temperature range 170?220°C. The average outer diameter of the thus synthesized nanotubes strongly depends on the element being introduced and is 5 to 10 nm. The nanotubes have a large specific surface area (200?300 m2 g?1) and are stable up to a temperature of 500°C, above which they decompose to give potassium hexatitanate. The nanotubes can be used as sorbents, photocatalysts, and components of composite materials for frictional and construction purposes.     

TiS2 and ZrS2 single‐ and double‐wall nanotubes: First‐principles study

Hybrid density functional theory has been applied for investigations of the electronic and atomic structure of bulk phases, nanolayers, and nanotubes based on titanium and zirconium disulfides. Calculations have been performed on the basis of the localized atomic functions by means of the CRYSTAL‐2009 computer code. The full optimization of all atomic positions in the regarded systems has been made to study the atomic relaxation and to determine the most favorable structures. The different layered and isotropic bulk phases have been considered as the possible precursors of the nanotubes. Calculations on single‐walled TiS₂ and ZrS₂ nanotubes confirmed that the nanotubes obtained by rolling up the hexagonal crystalline layers with octahedral 1T morphology are the most stable. The strain energy of TiS₂ and ZrS₂ nanotubes is small, does not depend on the tube chirality, and approximately obeys to D^–2 law (D is nanotube diameter) of the classical elasticity theory. It is greater than the strain energy of the similar TiO₂ and ZrO₂ nanotubes; however, the formation energy of the disulfide nanotubes is considerably less than the formation energy of the dioxide nanotubes. The distance and interaction energy between the single‐wall components of the double‐wall nanotubes is proved to be close to the distance and interaction energy between layers in the layered crystals. Analysis of the relaxed nanotube shape using radial coordinate of the metal atoms demonstrates a small but noticeable deviation from completely cylindrical cross‐section of the external walls in the armchair‐like double‐wall nanotubes. © 2013 Wiley Periodicals, Inc.