The mineral greigite presents similar surface structures to the active sites found in many modern-day enzymes. We show that particles of greigite can reduce CO2 under ambient conditions into chemicals such as methanol, formic, acetic and pyruvic acid. Our results also lend support to the Origin of Life theory on alkaline hydrothermal vents.

The renewed interest in magnetite (Fe3O4) as a major phase in different types of catalysts has led us to study the oxidation-reduction behaviour of its most prominent surfaces. We have employed computer modelling techniques based on the density functional theory to calculate the geometries and surface free energies of a number of surfaces at different compositions, including the stoichiometric plane, and those with a deficiency or excess of oxygen atoms. The most stable surfaces are the (001) and (111), leading to a cubic Fe3O4 crystal morphology with truncated corners under equilibrium conditions. The scanning tunnelling microscopy images of the different terminations of the (001) and (111) stoichiometric surfaces were calculated and compared with previous reports. Under reducing conditions, the creation of oxygen vacancies in the surface leads to the formation of reduced Fe species in the surface in the vicinity of the vacant oxygen. The (001) surface is slightly more prone to reduction than the (111), due to the higher stabilisation upon relaxation of the atoms around the oxygen vacancy, but molecular oxygen adsorbs preferentially at the (111) surface. In both oxidized surfaces, the oxygen atoms are located on bridge positions between two surface iron atoms, from which they attract electron density. The oxidised state is thermodynamically favourable with respect to the stoichiometric surfaces under ambient conditions, although not under the conditions when bulk Fe3O4 is thermodynamically stable with respect to Fe2O3. This finding is important in the interpretation of the catalytic properties of Fe3O4 due to the presence of oxidised species under experimental conditions.

We have used computational methodology based on the density functional theory to describe both copper­(I) and copper­(II) oxides, followed by the investigation of a number of different low index CuO surfaces. Different magnetic orderings of all the surfaces were studied, and reconstructions of the polar surfaces are proposed. A detailed discussion on stabilities, electronic structure, and magnetic properties is presented. CuO(111) and CuO­(11) were found to have the lowest surface energies, and their planes dominate in the calculated Wulff morphology of the CuO crystal. We next investigated the adsorption of CO2 on the three most exposed CuO surfaces, viz., (111), (11), and (011), by exploring various adsorption sites and configurations. We show that the CO2 molecule is activated on the CuO surfaces, with an adsorption energy of −93 kJ/mol on the (011) surface, showing exothermic adsorption, while (111) and (11) surfaces show comparatively weak adsorption. The activation of the CO2 molecule is characterized by large structural transformations and significant charge transfer, i.e., forming a negatively charged bent CO2 –δ species with elongated C–O bonds, which is further confirmed by vibrational analyses showing considerable red shift in the frequencies as a result of the activation.

Although [Ni(S 2 CNBu i 2 ) 2 ] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145°C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120°C a mixture of Ni 3 S 4 (polydymite) and NiS results. A combined experimental and theoretical study gives mechanistic insight into the decomposition process and can be used to account for the observed differences. Upon dissolution in the primary amine, octahedral trans-[Ni(S 2 CNBu i 2 ) 2 (RNH 2 ) 2 ] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90−100°C leads to changes consistent with the formation of amide-exchange products, [Ni(S 2 CNBu i 2 ){S 2 CN(H)R}] and/or [Ni{S 2 CN(H)R} 2 ]. DFT modeling shows that exchange occurs via nucleophilic attack of the primary amine at the backbone carbon of the dithiocarbamate ligand(s). With hexylamine, amide-exchange is facile and significant amounts of [Ni{S 2 CN(H)Hex} 2 ] are formed prior to decomposition, but with oleylamine, exchange is slower and [Ni(S 2 CNBu i 2 ){S 2 CN-(H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100°C to afford nickel sulfides, even in the absence of primary amine, as shown from thermal decomposition studies of [Ni{S 2 CN(H)Hex} 2 ]. DFT modeling of [Ni{S 2 CN(H)R} 2 ]shows that proton migration from nitrogen to sulfur leads to formation of a dithiocarbimate (S 2 CNR) which loses isothiocyanate (RNCS) to give dimeric nickel thiolate complexes [Ni{S 2 CN(H)R}(μ-SH)] 2 . These intermediates can either lose dithiocarbamate(s) or extrude further isothiocyanate to afford (probably amine-stabilized) nickel thiolate building blocks, which aggregate to give the observed nickel sulfide nanoparticles. Decomposition of the single or double amide-exchange products can be differentiated, and thus it is the different rates of amideexchange that account primarily for the formation of the observed nanoparticulate nickel sulfides. ■ INTRODUCTIONDithiocarbamate complexes 1 find extensive use as single-source precursors (SSPs) toward a range of metal sulfides 2 both as thin films and nanoparticles. 3−8 Their attractiveness for such applications stems from their ease of synthesis from cheap and readily available starting materials and the ability to tune the solubility, volatility, and decomposition properties of the complexes via simple changes to the amine substituents. The volatility and stability of side-products are also an advantage as they lead to their easy removal from the desired sulfide materials. Such syntheses generally involve decomposing dithiocarbamate complexes in high boiling primary amines, which can act as both the solvent and capping agent, among the most widely used being oleylamine. 9 While the solid-state structures of the dithiocarbamate precursors are easily established for example by single-crystal X-ray diffraction (XRD) studies, 1 in contrast little is known regarding their structure within the amine solution and the decomp...

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform, faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each color quantum dot is functionalized with a different surface receptor via a facile ligation process. These receptors undergo nonspecific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range.

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Greigite (Fe3S4) and its analogue oxide, magnetite (Fe3O4), are natural minerals with an inverse spinel structure whose atomic-level properties may be difficult to investigate experimentally. Here, [D. Rickard and G. W. Luther, Chem. Rev. 107, 514 (2007)] we have calculated the elastic constants and other macroscopic mechanical properties by applying elastic strains on the unit cells. We also have carried out a systematic study of the electronic properties of Fe3S4 and Fe3O4, where we have used an ab initio method based on spin-polarized density functional theory with the on-site Coulomb repulsion approximation (Ueff is 1.0 and 3.8 eV for Fe3S4 and Fe3O4, respectively). Comparison of the properties of Fe3S4 and Fe3O4 shows that the sulfide is more covalent than the oxide, which explains the low magnetization of saturation of greigite cited in several experimental reports.

We present density functional theory calculations with a correction for the long-range interactions (DFT-D2) of the bulk and surfaces of mackinawite (FeS), and subsequent adsorption and dissociation of NO x gases (nitrogen monoxide (NO) and nitrogen dioxide (NO 2 )). Our results show that these environmentally important molecules interact very weakly with the energetically most stable (001) surface, but adsorb relatively strongly onto the FeS (011), (100) and (111) surfaces, preferentially at Fe sites via charge donation from these surface species. The NO x species exhibit a variety of adsorption geometries, with the most favourable for NO being the monodentate Fe-NO configuration, whereas NO 2 is calculated to form a bidentate Fe-NOO-Fe configuration. From our calculated thermochemical energy and activation energy barriers for the direct dissociation of NO and NO 2 on the FeS surfaces, we show that NO prefers molecular adsorption, while dissociative adsorption, i.e. NO 2 (ads) -[NO(ads) + O(ads)] is preferred over molecular adsorption for NO 2 onto the mackinawite surfaces. However, the calculated high activation barriers for the further dissociation of the second N-O bond to produce either [N(ads) and 2O(ads)] or [N(ads) and O 2 (ads)] suggest that complete dissociation of NO 2 is unlikely to occur on the mackinawite surfaces.