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.     

Hydrostatic-pressure induced phase transition of phonons in single-walled nanotubes

We study the effect of the hydrostatic pressure on the phonons in single-walled carbon nanotubes (SWNTs) in a magnetic field. We calculate the magnetic moments of the phonons using a functional integral technique, and find that the phonons in SWNTs undergo a pressure-induced phase transition from the paramagnetic phase to the diamagnetic phase under hydrostatic pressure 2 GPa. We explain the mechanism of generating this phase transition.     

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.     

Polyquercetin/MWNT‐modified Electrode for the Determination of Natural Phenolic Antioxidants

Novel highly sensitive voltammetric method for the gallic acid, catechin and epigallocatechin gallate (EGCG) quantification has been developed using glassy carbon electrode modified with multi‐walled carbon nanotubes and polyquercetin (polyquercetin/MWNT/GCE). The effect of electropolymerization parameters (number of cycles, monomer concentration and polarization window) on the electrode characteristics has been evaluated. The electrode surface has been characterized with SEM, CV and EIS. The linear dynamic ranges of 0.50–10 and 10–750 μM for gallic acid, 0.10–10 and 10.0–250 μM for catechin and 0.050–10 and 10–100 μM for EGCG have been obtained in differential pulse mode with the detection limits of 0.10, 0.024 and 0.014 μM, respectively. The approach has been successfully applied for the tea antioxidant capacity evaluation (AOC). The positive correlations with antioxidant activity towards DPPH^• and total phenolics (r =0.7845 and 0.7658 at r _crit=0.4227, n =22) have been obtained.     

Electrical and Sensing Properties of Single‐Walled Carbon Nanotubes Network: Effect of Alignment and Selective Breakdown

The electrical transport and NH₃ sensing properties of randomly oriented and aligned SWNT networks were presented and discussed. The results indicate that aligned SWNT‐FETs have better FET characteristics due to the reduced number of interconnected nodes. This was particularly true as the resistance of the devices increased. Gated electrical breakdown was implemented to selectively remove metallic (m‐) SWNTs, thereby reducing scattering centers. This technique provided significant improvements in FET characteristics resulting in greater on/off ratio (e.g. 10⁴). AC dielectrophoretic alignment followed by selective electrical breakdown of m‐SWNTs can significantly enhance the semiconducting properties of SWNT networks which resulted in highly sensitive sensors.     

A microscopy study of the effect of heat treatment on the structure and properties of anodised TiO2 nanotubes

Titanium oxide (TiO₂) nanotubes prepared by anodisation of titanium in an aqueous electrolyte and glycerol have been heat treated in the temperature range 200-600 °C to control the conversion of the amorphous structure to nano-crystalline anatase and rutile. The phase changes have been monitored are observed at lower temperatures (100 °C or more) than previously reported. The sensitivity of the different techniques, each of which depends on the size of the crystalline phase, can explain the discrepancy with previous results. Transmission electron microscopy (TEM) has shown the phase changes which have occurred and which have been reported in an earlier publication; phenomena such as the collapse of the structures are explained. The TEM results are consistent with the Raman and XRD data, apart from the transformation temperatures, and also shed light on the nature of an amorphous phase found on the surfaces of the nanotubes.     

甲基铝氧烷纳米管分子结构的理论研究

用密度泛函理论对[(AlOMe)₂]_n、[(AlOMe)₃]_n和[(AlOMe)₄]_n (n=1～10)作为重复单元组成的甲基铝氧烷(MAO)纳米管进行了研究,计算了其所有体系的结合能和总能量．结果表明,[(AlOMe)₃]_n和[(AlOMe)₄]_n具有稳定的纳米管结构,在所有研究系统中n=3时具有最稳定的结构．考察发现,[(Al₅O₅)]_n和[(Al₇O₇)]_n两种结构的二聚体具有无规则、扭曲的结构,不能继续增长形成纳米管结构．     

Electrocatalytic Oxidation of Diethylaminoethanethiol and Hydrazine at Single‐walled Carbon Nanotubes Modified with Prussian Blue Nanoparticles

In this work, edged plane pyrolytic graphite electrode EPPGE was modified with functionalised single‐walled carbon nanotubes and Prussian blue nanoparticles (PB). The modified electrode was characterised by techniques such as TEM, FTIR, XPS, EDX and cyclic voltammetry. The EPPGE‐SWCNT‐PB platform exhibited enhanced electron transport and catalytic efficiency towards the oxidation of Diethylaminoethanethiol (DEAET) and hydrazine compared with the other electrodes studied. The EPPGE‐SWCNT‐PB showed good electrochemical stability in the analytical solution, showing limit of detection in the micromolar range and catalytic rate constant of 3.71×10⁶ and 7.56×10⁶ cm³ mol^?1 s^?1 for DEAET and hydrazine respectively. The adsorption properties of these analytes that impact on their detection at the SWCNT‐PB film modified electrode were evaluated and discussed.     

Streptavidin Modified Carbon Nanotube Based Graphite Electrode for Label‐Free Sequence Specific DNA Detection

Disposable graphite pencil electrodes (PGE) modified with multiwalled carbon nanotubes (MWCNTs)‐streptavidin (STR) conjugates were used for electrochemical monitoring of label‐free DNA hybridization. The surface morphology of PGE electrode before and after hybridization was characterized by scanning electron microscopy. Electrochemical impedance spectroscopy was used to monitor each step of the construction of the DNA biosensor. The biosensor was demonstrated to have excellent selectivity, being able to differentiate complementary sequences from a noncomplementary ones and in addition select the target sequence of DNA from a mixture of other DNA without loss in current sensitivity.     

Voltammetric Determination of L‐Dopa on Poly(3,4‐ethylenedioxythiophene)‐Single‐Walled Carbon Nanotube Composite Modified Microelectrodes

In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4‐)ethylenedioxythiophene and single‐walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4‐dihydroxy‐L ‐phenylalaines (L ‐dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film‐coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10 V s^?1, also gave rise to two well‐resolved oxidation peaks for L ‐dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L ‐dopa in the concentration range between 0.1 to 20 μM with a detection limit of 100 nM.