Single-atom catalysts (SACs) are the smallest entities for catalytic reactions with projected high atomic efficiency, superior activity, and selectivity; however, practical applications of SACs suffer from a very low metal loading of 1-2 wt%. Here, a class of SACs based on atomically dispersed transition metals on nitrogen-doped carbon nanotubes (MSA-N-CNTs, where M = Ni, Co, NiCo, CoFe, and NiPt) is synthesized with an extraordinarily high metal loading, e.g., 20 wt% in the case of NiSA-N-CNTs, using a new multistep pyrolysis process. Among these materials, NiSA-N-CNTs show an excellent selectivity and activity for the electrochemical reduction of CO to CO, achieving a turnover frequency (TOF) of 11.7 s at -0.55 V (vs reversible hydrogen electrode (RHE)), two orders of magnitude higher than Ni nanoparticles supported on CNTs.

Magnetic nanoparticles that display high saturation magnetization and high magnetic susceptibility are of great interest for medical applications. Magnetite nanoparticles display strong ferrimagnetic behavior and are less sensitive to oxidation than magnetic transition metal nanoparticles such as cobalt, iron, and nickel. For in vivo applications, well-defined organic coatings are needed to surround the magnetite nanoparticles and prevent any aggregation. The goal of this research was to develop complexes of magnetite nanoparticles coated with well-defined hydrophilic polymers so that they could be dispersed in aqueous fluids. Focal points have included the following: (1) Investigations of polymer systems that bind irreversibly to magnetite at the physiological pH, (2) the design of block copolymers with anchor and tail blocks to enable dispersion in biological fluids, and (3) investigations of copolymer block lengths to maximize the concentration of bound magnetite. Hydrophilic triblock copolymers with controlled concentrations of pendent carboxylic acid binding groups were designed as steric stabilizers for magnetite nanoparticles. These copolymers were comprised of controlled molecular weight poly(ethylene oxide) tail blocks and a central, polyurethane anchor block containing carboxylic acids. Stoichiometric aqueous solutions of FeCl 2 and FeCl 3 were condensed by reaction with NH 4 OH to form magnetite nanoparticles, and then a dichloromethane solution of the block copolymer was added to adsorb the copolymer onto the magnetite surfaces. Stable magnetite dispersions were prepared with all of the triblock copolymers. The polymer-nanomagnetite conjugates described in this paper had a maximum saturation magnetization of 34 emu/g. Magnetization curves showed minimal hysteresis. Powder X-ray diffraction (XRD), selected area electron diffraction (SAED), and high-resolution electron microscopy (HREM) confirmed the magnetite crystal structure. Transmission electron microscopy (TEM) showed that the dispersions contained magnetite particles coated with the polymers with a mean diameter of 8.8 ( S.D. 2.7 nm.

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The cover picture shows the process of hydrogen and helium insertion/expulsion which has been achieved for the first time with an open fullerene derivative (outlined in the background). The experimental activation barrier for helium decomplexation could be obtained and fully agrees with the calculated value (density functional theory). The barrier for H2 complexation/decomplexation is interestingly almost double that of helium, as illustrated by the energy diagram shown in the foreground. This difference arises from the larger, elongated surface of H2 undergoing greater van der Waals interaction at the transition state relative to that of helium, even though both atoms have the same radii. More about this process can be found in the article by Rubin, Houk, Saunders, Cross et al. on p. 1543 ff.

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The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial-on-sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single-crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga-terminated, lattice planes, whereas the rough facets correspond to the (0001̄), N-terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga-terminated orientation.

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