Properties of atomic intercalated carbon K4 crystals

The stability of atomic intercalated carbon $K_{4}$ crystals, XC$_{2}$ (X=H, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ga, Ge, As, Se, Br, Rb or Sr) is evaluated by geometry optimization and frozen phonon analysis based on first principles calculations. Although C $K_{4}$ is unstable, NaC$_{2}$ and MgC$_{2}$ are found to be stable. It is shown that NaC$_{2}$ and MgC$_{2}$ are metallic and semi conducting, respectively

Comprehensive study of sodium, copper, and silver clusters over a wide range of sizes 2=<N=<75

The geometric and electronic structures of NaN, CuN, and AgN metal clusters are systematically studied based on the density functional theory over a wide range of cluster sizes 2=<N=<75. A remarkable similarity is observed between the optimized geometric structures of alkali and noble metal clusters over all of the calculated cluster sizes N. The most stable structures are the same for the three different metal clusters for approximately half the cluster sizes N considered in this study. Even if the most stable structures are different, the same types of structures are obtained when the meta-stable structures are also considered. For all of the three different metal clusters, the cluster shapes change in the order of linear, planar, opened, and closed structures with increasing N. This structural type transition leads to a deviation from the monotonic increase in the volume with N. A remarkable similarity is also observed for the N dependence of the cluster energy E(N) for the most stable geometric structures. The amplitude of this energy difference is larger in the two noble metal clusters than in the alkali metal cluster. This is attributed to the contribution of $d$ electrons to the bonds. The magic number is defined in the framework of total energy calculations for the first time. In the case of NaN, a semi-quantitative comparison between the experimental abundance spectra (Knight et al., Phys. Rev. Lett., 52, 2141 (1984)) and the total energy calculations is carried out. The changing aspect of the Kohn-Sham eigenvalues from N=2 to N=75 is presented for the three different metal clusters. The feature of the bulk density of states already appears at N=75 for all of three clusters. With increasing N, the HOMO-LUMO gap clearly exhibits an odd-even alternation and converges to 0.Comment: 21 pages, 10 figure

Crystallinity depends on choice of iron salt precursor in the continuous hydrothermal synthesis of Fe–Co oxide nanoparticles

A series of Fe–Co oxide nanoparticles (NPs) were prepared by a continuous hydrothermal method using iron nitrate and ammonium iron citrate as alternative iron precursors. The crystallinity, Fe/Co composition and element spatial distribution in the synthesised NPs were investigated using X-ray diffraction (XRD), aberration-corrected scanning transmission electron microscopy (ac-STEM) imaging, energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). Strong dependence on the choice of iron salt was observed. We demonstrate that the presence of ammonium citrate markedly improves the crystallinity of the NPs; an ordered cobalt ferrite alloy is formed. We suggest this is due to the formation of a homogenous reaction environment during the thermal decomposition of ammonium citrate, and the formation of complexes among citrate, Fe and Co ions

The rapid size- and shape-controlled continuous hydrothermal synthesis of metal sulphide nanomaterials

Continuous flow hydrothermal synthesis offers a cheap, green and highly scalable route for the preparation of inorganic nanomaterials which has predominantly been applied to metal oxide based materials. In this work we report the first continuous flow hydrothermal synthesis of metal sulphide nanomaterials. A wide range of binary metal sulphides, ZnS, CdS, PbS, CuS, Fe₍₁₋ᵪ₎S and Bi₂S₃, have been synthesised. By varying the reaction conditions two different mechanisms may be invoked; a growth dominated route which permits the formation of nanostructured sulphide materials, and a nucleation driven process which produces nanoparticles with temperature dependent size control. This offers a new and industrially viable route to a wide range of metal sulphide nanoparticles with facile size and shape control

Atomistic origin of high-concentration Ce³⁺ in {100}-faceted Cr- substituted CeO₂ nanocrystals

Improving the potential of promising CeO2-based nanocatalysts in practical applications requires an atomic-scale analysis of the effects of active dopants on the distribution of Ce valence states and the formation of oxygen vacancies (VOs). In this study, a Cr dopant is introduced into the cubic {100}-faceted CeO2 nanocrystals (NCs) with an average size of 7.8 nm via supercritical water. The Cr dopants substitute Ce sites in the amount of approximately 3 mol%. Based on the aberration-corrected STEM-EELS, the effects of Cr dopant on the distribution of cation valence states in the Cr-doped CeO2 NCs are investigated layer by layer across the ultrafine Cr-substituted CeO2 NC perpendicular to the {100} exposed facet. It is found that an increased amount of Ce3+ cations is present in Cr-substituted CeO2 NCs, particularly in the internal atomic layers, compared to the pristine CeO2 NCs. The atomic-scale analysis of the local structure combined with theoretical calculations demonstrates that Cr dopant reduces the formation energy of VOs and increases mobility of oxygen atoms for the nano-sized CeO2. These effects, in principle, result in an improved oxygen storage capacity and provide a fundamental understanding of role of the dopant in the formation and distribution of VOs in the doped CeO2 NCs

A Decaheme Cytochrome as a Molecular Electron Conduit in Dye-Sensitized Photoanodes.

In nature, charge recombination in light-harvesting reaction centers is minimized by efficient charge separation. Here, it is aimed to mimic this by coupling dye-sensitized TiO2 nanocrystals to a decaheme protein, MtrC from Shewanella oneidensis MR-1, where the 10 hemes of MtrC form a ≈7-nm-long molecular wire between the TiO2 and the underlying electrode. The system is assembled by forming a densely packed MtrC film on an ultra-flat gold electrode, followed by the adsorption of approximately 7 nm TiO2 nanocrystals that are modified with a phosphonated bipyridine Ru(II) dye (RuP). The step-by-step construction of the MtrC/TiO2 system is monitored with (photo)electrochemistry, quartz-crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM). Photocurrents are dependent on the redox state of the MtrC, confirming that electrons are transferred from the TiO2 nanocrystals to the surface via the MtrC conduit. In other words, in these TiO2/MtrC hybrid photodiodes, MtrC traps the conduction-band electrons from TiO2 before transferring them to the electrode, creating a photobioelectrochemical system in which a redox protein is used to mimic the efficient charge separation found in biological photosystems.This work was supported by the BBSRC (grants BB/K009753/1, BB/K010220/1, and BB/K009885/1), the EPSRC (EP/H00338X/2; PhD studentship to Emma Ainsworth), the Christian Doppler Research Association and the OMV Group. The authors appreciate Dr. Liang Shi (PNNL) and Dr. Marcus Edwards (UEA) for providing the S. oneidensis strain and the protocol allowing for purification of MtrC.This is the final published version of the article. It was originally published in Advanced Functional Materials (Hwang ET, Sheikh K, Orchard KL, Hojo D, Radu V, Lee C-Y, Ainsworth E, Lockwood C, Gross MA, Adschiri T, Reisner E, Butt JN, Jeuken LJC, Advanced Functional Materials 2015, 25, 2308–2315, doi: 10.1002/adfm.201404541) http://dx.doi.org/10.1002/adfm.201404541