Efficient gold recovery by microbial electrochemical technologies.

The applicability of microbial electrochemical technologies for the recovery of gold was investigated. Two-chamber microbial fuel cells (MFC) with bioanodes buried in sediment were used in two operating modes. The cathodes (gold foil or graphitized paper), submerged in HAuCl4, solutions, were short-circuited with the bioanodes, and thus for the first time, the microbial electrochemical snorkel (MES) was applied for gold recovery. Operation in MFC mode, where the cathode and the anode were connected through an external resistor equal to the internal resistance of the system was also implemented. The electrochemical results along with the microscopic analyses, XPS data, and the estimated rate constants show the better performance of the MES over the MFC and predict the putative mechanism of the cathodic gold deposition. The gold removal and recovery reached ca. 95% within a day and the cathodic efficiency approached almost 100%. 7% higher gold recovery and 5% higher gold removal were achieved in the MES mode, which reveals the advantage of the operation under short-circuit conditions. The deposited on the cathode gold is in its elemental state. The similar results obtained with the two types of cathodes justify replacing the gold electrodes with much cheaper graphitized paper to reduce the cost. In addition, it has been demonstrated that gold can be also recovered by MES from the aqueous solutions of its complex Na3[Au(S2O3)2], simulating leachates from printed circuit board waste, which expands the limits of its practical application.

New Insights on the Nickel State Deposited by Hydrazine Wet-Chemical Synthesis Route in the Ni/BCY15 Proton-Conducting SOFC Anode.

Yttrium-doped barium cerate (BCY15) was used as an anode ceramic matrix for synthesis of the Ni-based cermet anode with application in proton-conducting solid oxide fuel cells (pSOFC). The hydrazine wet-chemical synthesis was developed as an alternative low-cost energy-efficient route that promotes 'in situ' introduction of metallic Ni particles in the BCY15 matrix. The focus of this study is a detailed comparative characterization of the nickel state in the Ni/BCY15 cermets obtained in two types of medium, aqueous and anhydrous ethylene glycol environment, performed by a combination of XRD, N2 physisorption, SEM, EPR, XPS, and electrochemical impedance spectroscopy. Obtained results on the effect of the working medium show that ethylene glycol ensures active Ni cermet preparation with well-dispersed nanoscale metal Ni particles and provides a strong interaction between hydrazine-originating metallic Ni and cerium from the BCY15 matrix. The metallic Ni phase in the pSOFC anode is more stable during reoxidation compared to the Ni cermet prepared by the commercial mechanical mixing procedure. These factors contribute toward improvement of the anode's electrochemical performance in pSOFC, enhanced stability, and a lower degradation rate during operation.

Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides.

To double the energy density of lithium- and sodium-ion batteries there is a need to activate simultaneously cationic and anionic redox reactions at the intercalation-type electrodes. In contrast to the cationic redox activity, the oxygen redox activity enforces an enhancement in the surface reactivity of the oxides leading to their poor reversibility and cycling stability. Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-storage materials as an efficient buffer supplying and receiving oxygen during alkali ion intercalation. As a proof-of-concept, the study is focused on CeO2 as a modifier of sodium nickel-manganese oxide with a three-layer sequence, P3-Na2/3Ni1/2Mn1/2O2. The CeO2-modified P3-Na2/3Ni1/2Mn1/2O2 displays a drastic increase in the reversible capacity following the order Na+ intercalation < Li+ intercalation < Li+,Na+ cointercalation.

Mesoporous alumina from colloidal biotemplating of Al clusters.

A simple and green synthesis route was disclosed for the achievement of mesoporous alumina microparticles employing polysaccharide nanoparticles (α-chitin nanorods) as templates. Pore textures can be tuned by the cationic alumina precursor. Compared to small cations, the use of Al13 and Al30 oxo-hydroxo clusters leads to better defined and elongated mesopores. Electron microscopy and spectroscopic ((13) C, (27) Al NMR, XPS) measurements demonstrated that this is related to the effective coating of α-chitin nanorods by these pre-condensed colloids.

Theoretical and experimental local reactivity parameters of 3-substituted coumarin derivatives.

Local reactivity descriptors, such as atomic charges, atomic electrostatic potential and atomic Fukui indices were computed for a series of 3-substituted coumarin (2-oxo-2H-1-benzopyran) derivatives, using density functional theory (DFT) and Möller-Plesset methods (MP2). The variation of those properties as a function of the substituents was compared with the variation of the measured XPS binding energies. The atomic electrostatic potentials and XPS binding energies serves as indicators of the electrophilicity of a given center within a molecule, while the atomic Fukui indices describe its degree of electronic localization, known as atomic softness. The correlation between those theoretical and experimental properties allowed us to follow the effect of electron withdrawing substituents on the electrophilicity of a given atomic center. The Fukui indices provided additional information about the softening/hardening of the center of interest due to presence of different substituents to the coumarin system. On the basis of these analysis, the 1,2-addition would be favored for 3-acetyl, 3-phosphono, and 7-diethylamino substituents, while 3-carboxyl, 3-ethoxycarbonyl, and 3-nitro substituent would favor 1,4-addition. The substituted coumarins would preferably react with soft nucleophiles at position 2 and with hard nucleophiles at position 4.

Ultrafast charge transfer at monolayer graphene surfaces with varied substrate coupling.

The charge transfer rates of a localized excited electron to graphene monolayers with variable substrate coupling have been investigated by the core hole clock method with adsorbed argon. Expressed as charge transfer times, we find strong variations between ~3 fs (on graphene "valleys" on Ru(0001)) to ~16 fs (quasi-free graphene on SiC, O/Ru(0001), or SiO2/Ru). The values for the "hills" on Gr/Ru and on Gr/Pt(111) are in between, with the ratio 1.7 between the charge transfer times measured on "hills" and "valleys" of Gr/Ru. We discuss the results for Gr on metals in terms of hybridized Ru-C orbitals, which change with the relative Gr-Ru alignment and distance. The charge transfer on the decoupled graphene layers must represent the intrinsic coupling to the graphene empty π* states. Its low rate may be influenced by processes retarding the spreading of charge after transfer.

Efficient mesoporous silica-titania catalysts from colloidal self-assembly.

Mesoporous silica-titania materials of tunable composition and texture, which present a high catalytic activity in the mild oxidation of sulfur compounds, have been obtained by combining the spray-drying process with the colloidal self-assembly of α-chitin nanorods (biopolymer acting as a template) and organometallic oligomers.

Vibrational characterization of ethylene adsorption and its thermal evolution on Si(001)-(2 x 1): identification of majority and minority species.

The vibrational and structural properties of a single-domain Si(001)-(2 x 1) surface upon ethylene adsorption have been studied by density functional cluster calculations and high-resolution electron energy loss spectroscopy. The detailed analysis of the theoretically and the experimentally determined vibrational frequencies reveals two coexisting adsorbate configurations. The majority species consist of ethylene molecules which are di-sigma bonded to the two Si atoms of a single Si-Si dimer. The local symmetry of this adsorption complex is reduced to C(2) for ethylene saturation coverage as determined by surface selection rules for the vibrational excitation process. The symmetry reduction includes the rotation of the C-C bond around the surface normal and the twist of the methylene groups around the C-C axis. Experimentally, 17 ethylene-derived modes are found and assigned for the majority and the minority species based on a comparison with calculated vibrational frequencies. The minority species which can account up to 14% of the total ethylene coverage is spectroscopically identified for the first time. It is assigned to ethylene molecules di-sigma bonded to two adjacent Si-Si dimers (in an end-bridge configuration). One part of the minority species desorbs molecularly at 665 K, about 50 K higher than the majority species, whereas the remaining part dissociates to adsorbed acetylene at temperatures around 630 K. For the latter, a di-sigma end-bridge like bonding configuration is proposed based on a comparison with vibrational data for adsorbed acetylene on Si(100)-(2 x 1).