Semiconducting single-walled carbon nanotubes are studied in the diffusive transport regime. The peak mobility is found to scale with the square of the nanotube diameter and inversely with temperature. The maximum conductance, corrected for the contacts, is linear in the diameter and inverse temperature. These results are in good agreement with theoretical predictions for acoustic phonon scattering in combination with the unusual band structure of nanotubes. These measurements set the upper bound for the performance of nanotube transistors operating in the diffusive regime.

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Molybdenum carbide (Mo2C) is recognized as an alternative electrocatalyst to noble metal for the hydrogen evolution reaction (HER). Herein, a facile, low cost, and scalable method is provided for the fabrication of Mo2C‐based eletrocatalyst (Mo2C/G‐NCS) by a spray‐drying, and followed by annealing. As‐prepared Mo2C/G‐NCS electrocatalyst displays that ultrafine Mo2C nanopartilces are uniformly embedded into graphene wrapping N‐doped porous carbon microspheres derived from chitosan. Such designed structure offer several favorable features for hydrogen evolution application: 1) the ultrasmall size of Mo2C affords a large exposed active sites; 2) graphene‐wrapping ensures great electrical conductivity; 3) porous structure increases the electrolyte–electrode contact points and lowers the charge transfer resistance; 4) N‐dopant interacts with H+ better than C atoms and favorably modifies the electronic structures of adjacent Mo and C atoms. As a result, the Mo2C/G‐NCS demonstrates superior HER activity with a very low overpotential of 70 or 66 mV to achieve current density of 10 mA cm−2, small Tafel slope of 39 or 37 mV dec−1, respectively, in acidic and alkaline media, and high stability, indicating that it is a great potential candidate as HER electrocatalyst.

Self-assembled three-dimensional (3D) hierarchical umbilicate Bi 2 WO 6 microspheres from nanoplates have been synthesized by a new controllable hydrothermal route on a large scale. It was found that citrate played multifold roles in the formation process of Bi 2 WO 6 hierarchical microspheres in our reaction system. In order to obtain well-assembled Bi 2 WO 6 microspheres, NaHCO 3 was used to adjust pH values of the reaction solution and establish a buffer system by the equilibrium of the formation and dissociation of carbonic acid. On the basis of XRD analysis and TEM observation of the products at the different reaction time periods, the formation mechanism of Bi 2 WO 6 hierarchical microspheres was proposed. UV-vis diffuse reflectance spectra indicated that as-synthesized Bi 2 WO 6 hierarchical microspheres had absorption in both UV and visible light areas. The BET surface area of the sample was ca. 24.1 m 2 /g, which was 35 times higher than that of the Bi 2 WO 6 powder prepared by the solid-state reaction method. The hierarchical umbilicate Bi 2 WO 6 microspheres exhibited good photocatalytic activity in degradation of Rhodamine-B (RhB) under 150 W Xe lamp light irradiation. In addition, the wettability of Bi 2 WO 6 films fabricated by as-obtained Bi 2 WO 6 microspheres was also studied.

Due to its intrinsic structure and characteristics, small size and monodispersity, control of singlecrystalline Cu 2 O polyhedra in aqueous media is a challenge, which is important to overcome to achieve enhanced photocatalytic activity. Here, we use heterogeneous nucleation, rather than homogeneous nucleation, of Cu 2 O with gold nanorods as seeds to realize subsequent uniform crystal growth. We obtained nearly monodisperse octahedral Au@Cu 2 O nanocrystals with single-crystalline shells, which are distinct from the pentagonal column-shaped structures previously described. Due to the fact that one Au@Cu 2 O holds only one Au nanorod, two formulas were deduced for convenient size control of the Cu 2 O shell. The formulas were calculated by adjusting the amount of Au rods that are relatively quantified. The formula also allows the size of the final product to be predicted when a given amount of gold seeds are employed. The experimental results agree well with the calculated data. The result of larger surface area and improved charge separation from core-shell interaction, made five samples of different sizes exhibit excellent photocatalytic activity toward MO degradation. The synthetic strategy reported here provides a clue to monodispersity and size control of core-shell nanocrystals, which is useful in developing new catalysts with better performance that are urgently needed in the fields of both science and technology.

The sidewalls of vertically aligned, multiwalled carbon nanotubes were functionalized using azide photochemistry, and DNA oligonucleotides were synthesized in situ from the reactive group on each photoadduct to produce water-soluble DNA-coated nanotubes. The functional DNA sites on the nanotubes were visualized from gold nanoparticles modified with complementary DNA and using TEM. The sidewall functionalization enabled further DNA-directed modification of the nanotubes' surfaces with nanoparticles. The DNA-coated vertically aligned nanotubes offer the architecture for a highly loaded three-dimensional DNA chip.

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

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