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The addition of iron (Fe) can in certain cases have a strong positive effect on the activity of cobalt and nickel oxide nanoparticles in the electrocatalytic oxygen evolution reaction (OER). The reported optimal Fe dopant concentrations are, however, inconsistent, and the origin of the increased activity due to Fe dopants in mixed oxides has not been identified so far. Here, we combine density functional theory calculations, scanning tunneling microscopy, and OER activity measurements on atomically defined Fe-doped Co oxyhydroxide nanoparticles supported on a gold surface to establish the link between the activity and the Fe distribution and concentration within the oxyhydroxide phase. We find that addition of Fe results in distinct effects depending on its location on edge or basal plane sites of the oxyhydroxide nanoparticles, resulting in a nonlinear OER activity as a function of Fe content. Fe atom substitution itself does not lead to intrinsically more active OER sites than the best Co sites. Instead, the sensitivity to Fe promoter content is explained by the strong preference for Fe to locate on the most active edge sites of oxyhydroxide nanoparticles, which for low Fe concentrations stabilizes the particles but in higher concentrations leads to a shell structure with less active Fe on all edge positions. The optimal Fe content thereby becomes dependent on nanoparticle size. Our findings demonstrate that synthesis strategies that adjust not only the Fe concentration in mixed oxides but also its distribution within a catalyst nanoparticle can lead to enhanced OER performance.

The realization of electronic devices based on heterostructures of metallic, semiconducting, or insulating two-dimensional materials relies on the ability to form structurally coherent and clean interfaces between them, vertically or laterally. Lateral two-dimensional heterostructures that fuse together two different materials in a well-controlled manner have attracted recent attention, but the methods to form seamless interfaces between structurally dissimilar materials, such as graphene and transition-metal dichalcogenides (TMDCs), are still limited. Here, we investigate the structure of the lateral interfaces that arise between monolayer MoS 2 flakes on Au(111) and two families of armchair graphene nanoribbons (GNRs) created through on-surface assisted Ullmann coupling using regular organobromine precursors for GNR synthesis. We find that parallel alignment between the GNR armchair edge and MoS 2 leads to van der Waals bonded nanoribbons, whereas a perpendicular orientation is characterized by a single phenyl-group of the GNR covalently bonded to S on the edge. The edge-on bonding is facilitated by a hydrogen treatment of the MoS 2 , and temperature control during growth is shown to influence the nanoribbon width and the yield of covalently attached nanoribbons. Interestingly, the temperatures needed to drive the intramolecular dehydrogenation during GNR formation are lowered significantly by the presence of MoS 2 , which we attribute to enhanced hydrogen recombination at the MoS 2 edges. These results are a demonstration of a viable method to make laterally bonded graphene nanostructures to TMDCs to be used in further investigations of two-dimensional heterostructure junctions.

Methane, which has a high energy storage density and is safely stored and transported in our existing infrastructure, can be produced through conversion of the undesired energy carrier H 2 with CO 2 . Methane production with standard transition-metal catalysts requires high-temperature activation (300-500 °C). Alternatively, semiconductor metal oxide photocatalysts can be used, but they require high-intensity UV light. Here, we report a Ru metal catalyst that facilitates methanation below 250 °C using sunlight as an energy source. Although at low solar intensity (1 sun) the activity of the Ru catalyst is mainly attributed to thermal effects, we identified a large nonthermal contribution at slightly elevated intensities (5.7 and 8.5 sun) resulting in a high photon-to-methane efficiency of up to 55% over the whole solar spectrum. We attribute the excellent sunlight-harvesting ability of the catalyst and the high photon-to-methane efficiency to its UV-vis-NIR plasmonic absorption. Our highly efficient conversion of H 2 to methane is a promising technology to simultaneously accelerate the energy transition and reduce CO 2 emissions., Competing Interests: The authors declare no competing financial interest.

This contribution addresses standing questions about the nature and consequences of the ion self-assembly and magnetic structures, as well as the molecular motion of the crystalline structure as a function of the temperature, in halometalate materials based on imidazolium cation. We present the magnetic structure and magnetostructural correlations of 1-ethyl-2,3-dimethylimidazolium tetrachloridoferrate, (Edimim)[FeCl 4 ], resolved by neutron diffraction studies. Single-crystal, synchrotron powder X-ray diffraction and powder neutron diffraction techniques have been combined to follow the temperature evolution on its crystallographic structure from 2 K close to its melting point (340 K). In this sense, slightly above room temperature (307 K) (Edimim)[FeCl 4 ] presents a single-crystal to single-crystal transition (SCSC), from phase I (space group P2 1 /n) to phase II (P2 1 /m), accompanied by a notable increase in the disorder of the imidazolium cation, as well as in the metal complex anion. The temperature evolution and solid-phase transitions of the presented compound were followed in detail by synchrotron X-ray powder diffraction (SXPD), which confirms the occurrence of another phase transition at 330 K, phase III (P2 1 /m), the crystal structure of which was elucidated from the SXPD pattern. Moreover, this material presents an anisotropic thermal expansion with a switch from axial positive to negative thermal expansion coefficients as the temperature is raised above the first phase transition, which has been correlated with the molecular motion of the imidazolium-based molecules, producing not only a shortening of the counterion···counterion distances but also the occurrence of different quasi-isoenergetic crystal structures as a function of the temperature.

Well-characterized metal oxides supported on single crystal surfaces serve as valuable model systems to study fundamental chemical properties and reaction mechanisms in heterogeneous catalysis or as new thin film metal oxide catalysts in their own right. Here, we present scanning tunneling microscopy and X-ray photoelectron spectroscopy results for cobalt oxide nanoislands that reveal the detailed atomistic mechanisms leading to transitions between Co-O bilayer and O-Co-O trilayer, induced by oxidation in O 2 and reductive vacuum annealing treatments, respectively. By comparing between two different noble metal substrates, Au(111) and Pt(111), we further address the influence of the substrate. Overall, nanoisland edges act to initiate both the oxidation and reduction processes on both substrates. However, important influences of the choice of substrate were found, as the progress of oxidation includes intermediate steps on Au(111) not observed on Pt(111), where the oxidation on the other hand takes place at a significantly higher rate. During reductive treatment of trilayer, the bilayer structure gradually reappears on Pt(111), but not on Au(111) where the reduction rather results in the appearance of a stacked cobalt oxide morphology. These observations point to strong differences in the catalytic behavior between Au and Pt supported cobalt oxides, despite the otherwise strong structural similarities.

Expanded porphyrins are large-cavity macrocycles with enormous potential in coordination chemistry, anion sensing, photodynamic therapy, and optoelectronics. In the last two decades, the surface science community has assessed the physicochemical properties of tetrapyrrolic-like macrocycles. However, to date, the sublimation, self-assembly and atomistic insights of expanded porphyrins on surfaces have remained elusive. Here, we show the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an "expanded hemiporphyrazine", through a unique growth mechanism based on long-range orientational self-assembly. Furthermore, a spatially controlled "writing" protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocycles. Finally, the capability of these surface-confined macrocycles to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements.

The present work provides two new examples of supramolecular metal-organic frameworks consisting of three-dimensional extended noncovalent assemblies of wheel-shaped heptanuclear [Cu7(μ-H2O)6(μ3-OH)6(μ-adeninato-κN3:κN9)6](2+) entities. The heptanuclear entity consists of a central [Cu(OH)6](4-) core connected to six additional copper(II) metal centers in a radial and planar arrangement through the hydroxides. It generates a wheel-shaped entity in which water molecules and μ-κN3:κN9 adeninato ligands bridge the peripheral copper atoms. The magnetic characterization indicates the central copper(II) center is anti-ferromagnetically coupled to external copper(II) centers, which are ferromagnetically coupled among them leading to an S = 5/2 ground state. The packing of these entities is sustained by π-π stacking interactions between the adenine nucleobases and by hydrogen bonds established among the hydroxide ligands, sulfate anions, and adenine nucleobases. The sum of both types of supramolecular interactions creates a rigid synthon that in combination with the rigidity of the heptameric entity generates an open supramolecular structure (40-50% of available space) in which additional sulfate and triethylammonium ions are located altogether with solvent molecules. These compounds represent an interesting example of materials combining both porosity and magnetic relevant features.

Surface functional groups of two different types of combustion aerosols, a conventional diesel (EN 590) and a hydrotreated vegetable oil (HVO) soot, have been investigated using heterogeneous chemistry (i.e., gas-particle surface reactions). A commercial sample of amorphous carbon (Printex XE2-B) was analyzed as a reference substrate. A Knudsen flow reactor was used to carry out the experiments under molecular flow conditions. The selected gases for the titration experiments were: N(CH3)3 for the identification of acidic sites, NH2OH for the presence of carbonyl groups, CF3COOH and HCl for basic sites of different strength, and O3 and NO2 for reducing groups. Reactivity with N(CH3)3 indicates a lower density of acidic functionalities for Printex XE2-B in relation to diesel and HVO soot. Results for NH2OH experiments indicates that commercial amorphous carbon exhibits a lower abundance of available carbonyl groups at the interface compared to the results from diesel and HVO soot, the latter being the one with the largest abundance of carbonyl functions. Reactions with acids indicate the presence of weak basic oxides on the particle surface that preferentially interact with the strong acid CF3COOH. Finally, reactions with O3 and NO2 reveal that diesel and especially HVO have a significantly higher reactivity with both oxidizers compared to that of Printex XE2-B because they have more reducing sites by roughly a factor of 10 and 30, respectively. The kinetics of titration reactions have also been investigated.

Exerting control over the near-infrared (NIR) plasmonic response of nanosized metals and semiconductors can facilitate access to unexplored phenomena and applications. Here we combine electrostatic self-assembly and Cd(2+)/Cu(+) cation exchange to obtain an anisotropic core-shell nanoparticle cluster (NPC) whose optical properties stem from two dissimilar plasmonic materials: a gold nanorod (AuNR) core and a copper selenide (Cu(2-x)Se, x ≥ 0) supraparticle shell. The spectral response of the AuNR@Cu2Se NPCs is governed by the transverse and longitudinal plasmon bands (LPB) of the anisotropic metallic core, since the Cu2Se shell is nonplasmonic. Under aerobic conditions the shell undergoes vacancy doping (x > 0), leading to the plasmon-rich NIR spectrum of the AuNR@Cu(2-x)Se NPCs. For low vacancy doping levels the NIR optical properties of the dually plasmonic NPCs are determined by the LPBs of the semiconductor shell (along its major longitudinal axis) and of the metal core. Conversely, for high vacancy doping levels their NIR optical response is dominated by the two most intense plasmon modes from the shell: the transverse (along the shortest transversal axis) and longitudinal (along the major longitudinal axis) modes. The optical properties of the NPCs can be reversibly switched back to a purely metallic plasmonic character upon reversible conversion of AuNR@Cu(2-x)Se into AuNR@Cu2Se. Such well-defined nanosized colloidal assemblies feature the unique ability of holding an all-metallic, a metallic/semiconductor, or an all-semiconductor plasmonic response in the NIR. Therefore, they can serve as an ideal platform to evaluate the crosstalk between plasmonic metals and plasmonic semiconductors at the nanoscale. Furthermore, their versatility to display plasmon modes in the first, second, or both NIR windows is particularly advantageous for bioapplications, especially considering their strong absorbing and near-field enhancing properties.

Size- and shape-controlled synthesis of copper chalcogenide nanocrystals (NCs) is of paramount importance for a careful engineering and understanding of their optoelectronic properties and, thus, for their exploitation in energy- and plasmonic-related applications. From the copper chalcogenide family copper telluride NCs have remained fairly unexplored as a result of a poor size-, shape-, and monodispersity control that is achieved via one-step syntheses approaches. Here we show that copper telluride (namely Cu(2-x)Te) NCs with well-defined morphologies (spheres, rods, tetrapods) can be prepared via cation exchange of preformed CdTe NCs while retaining their original shape. The resulting copper telluride NCs are characterized by pronounced plasmon bands in the near-infrared (NIR), in analogy to other copper-deficient chalcogenides (Cu(2-x)S, Cu(2-x)Se). We demonstrate that the extinction spectra of the as-prepared NCs are in agreement with theoretical calculations based on the discrete dipole approximation and an empirical dielectric function for Cu(2-x)Te. Additionally we show that the Drude model does not appropriately describe the complete set of Cu(2-x)Te NCs with different shapes. In particular, the low-intensity longitudinal plasmon bands for nanorods and tetrapods are better described by a modified Drude model with an increased damping in the long-wavelength interval. Importantly, a Lorentz model of localized quantum oscillators describes reasonably well all three morphologies, suggesting that holes in the valence band of Cu(2-x)Te cannot be described as fully free particles and that the effects of localization of holes are important. A similar behavior for Cu2-xS and Cu(2-x)Se NCs suggests that the effect of localization of holes can be a common property for the whole class of copper chalcogenide NCs. Taken altogether, our results represent a simple route toward copper telluride nanocrystals with well-defined shapes and optical properties and extend the understanding on vacancy-doped copper chalcogenide NCs with NIR optical resonances.

We report a combined study using magnetization and Raman spectroscopy on the magnetic ionic liquid 1-ethyl-3-methylimidazolium tetrachloroferrate, Emim[FeCl4]. This material shows a long-range antiferromagnetic ordering below the Néel temperature T(N) ≈ 3.8 K. The effects of pressure on the magnetic properties have been studied using a miniature piston-cylinder CuBe pressure cell. This three-dimensional ordering is strongly influenced when hydrostatic pressure is applied. It is observed that low applied pressure is enough to modify the magnetic interactions, inducing a transition from antiferromagnetic to ferrimagnetic ordering. Raman spectroscopy measurements reveal important information about the existence of isolated [FeCl4](-) anions and the absence of dimeric [Fe2Cl7](-) units in the liquid and solid states. These features seem to suggest that the superexchange pathways responsible for the appearance of magnetic ordering are mediated through Fe-Cl-Cl-Fe. Furthermore, the liquid-solid phase transition exhibits a magnetic hysteresis near room temperature, which can be tuned by weak pressures.

Designing nanoscale objects with the potential to perform externally controlled motion in biological environments is one of the most sought-after objectives in nanotechnology. Different types of chemically and physically powered motors have been prepared at the macro- and microscale. However, the preparation of nanoscale objects with a complex morphology, and the potential for light-driven motion has remained elusive to date. Here, we go a step forward by designing a nanoscale hybrid with a propeller-resembling shape, which can be controlled by focused light under biological conditions. Our hybrid, hereafter "Au@DNA-origami", consists of a spherical gold nanoparticle with self-assembled, biocompatible, two-dimensional (2D) DNA sheets on its surface. As a first step toward the potential utilization of these nanoscale objects as light-driven assemblies in biological environments, we show that they can be optically trapped, and hence translated and deposited on-demand, and that under realistic trapping conditions the thermally induced dehybridization of the DNA sheets can be avoided.

Imaging localized plasmon modes in noble-metal nanoparticles is of fundamental importance for applications such as ultrasensitive molecular detection. Here, we demonstrate the combined use of optical dark-field microscopy (DFM), cathodoluminescence (CL), and electron energy-loss spectroscopy (EELS) to study localized surface plasmons on individual gold nanodecahedra. By exciting surface plasmons with either external light or an electron beam, we experimentally resolve a prominent dipole-active plasmon band in the far-field radiation acquired via DFM and CL, whereas EELS reveals an additional plasmon mode associated with a weak dipole moment. We present measured spectra and intensity maps of plasmon modes in individual nanodecahedra in excellent agreement with boundary-element method simulations, including the effect of the substrate. A simple tight-binding model is formulated to successfully explain the rich plasmon structure in these particles encompasing bright and dark modes, which we predict to be fully observable in less lossy silver decahedra. Our work provides useful insight into the complex nature of plasmon resonances in nanoparticles with pentagonal symmetry.

A new three-dimensional hydroxide-arsenate compound called compound 2 has been synthesized by heating (in air) of the sarkinite phase, Mn(2)(OH)AsO(4) (compound 1), with temperature and time control. The crystal structure of this high-temperature compound has been solved by Patterson-function direct methods. A relevant feature of this new material is that it is actually the first member of the adamite-type family with mixed-valence manganese(II,III) and electronic conductivity. Crystal data: a = 6.7367(5) Å, b = 7.5220(6) Å, c = 9.8117(6) Å, α = 92.410(4)°, β = 109.840(4)°, γ = 115.946(4)°, P1̅. The unit cell content derived from Rietveld refinement is Mn(8)(O(4)H(x))(AsO(4))(4). Its framework, projected along [111], is characterized by rings of eight Mn atoms with the OH(-)/O(2-) inside the rings. These rings form an almost perfect hexagonal arrangement with the AsO(4) groups placed in between. Bond-valence analysis indicates both partial deprotonation (x ≅ 3) and the presence of Mn in two different oxidation states (II and III), which is consistent with the electronic conductivity above 300 °C from electrochemical measurements. The electron paramagnetic resonance spectra of compound 1 and of its high-temperature form compound 2 show the presence of antiferromagnetic interactions with stronger magnetic coupling for the high-temperature phase. Magnetization measurements of room-temperature compound 1 show a complex magnetic behavior, with a three-dimensional antiferromagnetic ordering and magnetic anomalies at low temperatures, whereas for compound 2, an ordered state is not reached. Magnetostructural correlations indicate that superexchange interactions via oxygen are present in both compounds. The values of the magnetic exchange pathways [Mn-O-Mn] are characteristic of antiferromagnetic couplings. Notwithstanding, the existence of competition between different magnetic interactions through superexchange pathways can cause the complex magnetic behavior of compound 1. The loss of three-dimensional magnetic ordering by heating of compound 1 could well be based on the presence of Mn(3+) ions (d(4)) in compound 2.

The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions., (© 2011 American Chemical Society)

Formation of self-assembled chains of tetrathiafulvalene (TTF) on the Cu(100) surface has been investigated by scanning tunneling microscopy and density functional theory calculations that include semiempirical van der Waals (vdW) interaction corrections. The calculations show that the chain structures observed in the experiments can only be explained by including the vdW interactions. The molecules are tilted along the chain in order to achieve maximal intermolecular interaction. The chains are metastable on the surface, which is consistent with the experimental observation that they disappear after annealing. The fact that all TTF chains observed in the experiment are short might be possibly explained by the interplay between the stabilizing vdW molecule-molecule interaction and the destabilizing rearrangement of surface atoms due to the strong molecule-substrate interaction.

We present a versatile and controlled route to immobilize gold nanoparticles (NPs) on the surface of living cells, while preserving the sensing and optothermal capabilities of the original colloid. Our approach is based on the controlled and selective binding of Au NPs to phospholipids prior to cell incubation. We show that in the presence of the cells the lipid-bound Au NPs are delivered to the cellular membrane and that their diffusion is rather slow and spatially limited, as a result of lipid binding. Avoiding nonspecific membrane labeling, this approach is of general application to several types of colloids and cells and thereby provides a platform for controlled plasmonic and optothermal investigations of living cell membranes.

A modified seeded growth process has been used for the controlled synthesis of quasispherical, CTAB-stabilized gold nanoparticles from 12 up to 180 nm with narrow size distributions. The UV-visible spectra of the aqueous colloids show distinct bands corresponding to dipole and quadrupole plasmon modes, for diameters above 100 nm, in close agreement with predictions based on Mie theory. The assignment of the modes is demonstrated by calculation of near field enhancement maps based on the boundary element method. Apart from other applications, since absorption is drastically reduced above 600 nm, while scattering is largely increased, these particles open new possibilities for construction of highly efficient photonic structures.