Abstract: We introduce a simple enhanced sampling approach for the calculation of free energy differences and barriers along a one-dimensional reaction coordinate. First, a small number of short nonequilibrium simulations are carried out along the reaction coordinate, and the Jarzynski equality is used to learn an approximate free energy surface from the nonequilibrium work distribution. This free energy estimate is represented in a compact form as an artificial neural network and used as an external bias potential to accelerate rare events in a subsequent molecular dynamics simulation. The final free energy estimate is then obtained by reweighting the equilibrium probability distribution of the reaction coordinate sampled under the influence of the external bias. We apply our reweighted Jarzynski sampling recipe to four processes of varying scales and complexities.spanning chemical reaction in the gas phase, pair association in solution, and droplet nucleation in supersaturated vapor. In all cases, we find reweighted Jarzynski sampling to be a very efficient strategy, resulting in rapid convergence of the free energy to high precision.

Abstract: The electrochemical behavior of some of the most relevant endocrine-disrupting phenols using unmodified carbon screen-printed electrodes (SPEs) is described for the first time. Experiments were made to assess the electrochemical behavior of phenol (PHOH), pentachlorophenol (PCP), 4-tert octylphenol (OP) and bisphenol A (BPA) and their determination in the most favorable conditions, using voltammetric methods such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and square wave voltammetry (SWV) in Britton Robinson (BR) buffer. Further, the usefulness of the electrochemical approach was validated with real samples from a local river and was compared to commercial phenols test kit, which is commonly used for on-site screening in industrial streams and wastewaters. Finally, the approach was compared with a lab-bench standard method using real samples, i.e., high-performance liquid chromatography with a photodiode array detector (HPLC-DAD).

Abstract: Infrared absorption spectra of oxygen precipitates in boron-doped silicon with a boron concentration between 10(17) and 10(19) cm(-3) are analyzed, applying the spectral function representation of composite materials. The aspect ratio of the platelet precipitates is determined by transmission electron microscopy measurements. The analysis shows that in samples with moderate doping levels (<10(18) B cm(-3)) SiOγ precipitates are formed with the same composition as in the lightly doped case. In the heavily boron-doped (>10(18) cm(-3)) samples, however, the measured spectra of the precipitates are consistent with a mixture of SiO2 and B2O3, with a volume fraction of B2O3 as high as 0.41 in the most heavily doped case. (C) 2004 The Electrochemical Society.

Abstract: Co and Fe nanowires and/or nanotubes are electrochemically synthesized through nanoporous membranes. By combining high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and energy filtered TEM techniques, their structural and crystallographic characteristics are precisely determined. The synthesis was shown to produce cigar-shaped single monocrystalline Co and Fe nanowires with a diameter of about 60 nm. All wires were surrounded by an epitaxial oxide layer (Co3O4 or Fe3O4) of roughly 10 nm. The Fe nanotubes were built up of Fe3O4 nanocrystals. Electron diffraction showed that all nanocrystals had a common crystallographic axis, creating a pseudomonocrystalline wall in the nanotubes. (C) 2003 The Electrochemical Society.

Abstract: The performance of SnO2 ceramic anodes doped with copper and antimony oxides was examined in cryolite alumina melts under anodic polarization at different cryolite ratios, temperatures, times, and current densities. The corroded part consists of a narrow strong corrosion zone at the anode surface with damage of the intergrain contacts and a large increase in porosity, a wider moderate corrosion zone with a smaller porosity increase, and a Cu depletion zone, where the ceramic retains its initial microstructure and a slight porosity increase occurs due to the removal of the Cu-rich inclusions. Mechanical destruction of the anode was never observed in the 10100 h tests. A microstructural model of the ceramic was suggested, consisting of grains with an Sb-doped SnO2 grain core surrounded by an ~200 to 500 nm grain shell where SnO2 was simultaneously doped with Sb and Mn+ (M=Cu2+,Fe3+,Al3+). The grains were separated by a few nanometers thick Cu-enriched grain boundaries. Different secondary charge carrier (holes) concentrations and electric conductivities in the grain core and grain shell result in a higher current density at the intergrain regions that leads to their profound degradation, especially in the low temperature acidic melt.

Abstract: In the present work, a novel graphene (GN) and gelatin (GTN) composite was prepared and used as an immobilization matrix for hemoglobin (Hb). Compared with Hb immobilized on a bare, GN or GTN modified glassy carbon electrode (GCE), a stable and pair of well-defined quasi redox couple was observed at an Hb modified GN/GTN composite GCE at a formal potential of −0.306 V versus Ag|AgCl. The direct electrochemical behavior of Hb was greatly enhanced by the presence of both GTN and GN. A heterogeneous electron transfer rate constant (Ks) was calculated as 3.82 s−1 for Hb immobilized at GN/GTN modified GCE, which indicates the fast direct electron transfer of Hb toward the electrode surface. The biosensor shows a stable and wide linear response for H2O2 in the linear response range from 0.1 μM to 786.6 μM with an analytical sensitivity and limit of detection of 0.48 μAμM−1 cm−2 and 0.04 μM, respectively. The fabricated biosensor holds its high selectivity in the presence of potentially active interfering species and metal ions. The biosensor shows its satisfactory practical ability in the commercial contact lens solution and human serum samples.

Abstract: Sensitive multi-element analysis techniques were applied to water samples collected in the vicinity of a small Zn-Pb-Cu sulfide mineralization in the region of Menez-Albot (Finistère, France). The variation of the trace-element content along a local stream shows the presence of the mineralization, mainly through a simultaneous positive anomaly in solution for a group of about 10 elements (e.g. Ni, Cu, Zn, As, Sb) which are connected with this type of mineralization. The anomaly decreases steeply due to the influx of swamp water rich in Fe, Mn and organic matter. The precipitation barrier is reflected in the stream sediment composition. Contamination from fertilizers was observed in some samples.

Abstract: Lanthanumcerium oxide (LCO) films were deposited on Ni-5%W substrates by chemical solution deposition (CSD) from water-based precursors. LCO films containing different ratios of lanthanum and cerium ions (from CeO2 to La2Ce2O7) were prepared. The composition of the layers was optimized towards the formation of LCO buffer layers, lattice-matched with the superconducting YBa2Cu3Oy layer, useful for the development of coated conductors. Single, crack-free LCO layers with a thickness of up to 140 nm could be obtained in a single deposition step. The crystallinity and microstructure of these lattice-matched LCO layers were studied by X-ray diffraction techniques, RHEED and SEM. We find that only layers with thickness below 100 nm show a crystalline top surface although both thick and thin layers show good biaxial texture in XRD. On the most promising layers, AFM and (S)TEM were performed to further evaluate their morphology. The overall surface roughness varies between 3.9 and 7.5 nm, while the layers appear much more dense than the frequently used La2Zr2O7 (LZO) systems, showing much smaller nanovoids (12 nm) than the latter system. Their effective buffer layer action was studied using XPS. The thin LCO layers supported the growth of superconducting YBCO deposited using PLD methods.

Abstract: The thermal behavior under air of LiFePO(4)-based powders was investigated through the combination of several techniques such as temperature-controlled X-ray diffraction, thermogravimetric analysis and Mossbauer and NMR spectroscopies. The reactivity with air at moderate temperatures depends on the particle size and leads to progressive displacement of Fe from the core structure yielding nano-size Fe(2)O(3) and highly defective, oxidized Li(x)Fe(y)PO(4) compositions whose unit-cell volume decreases dramatically when the temperature is raised between 400 and 600 K. The novel LiFePO(4)-like compositions display new electrochemical reactivity when used as positive electrodes in Li batteries. Several redox phenomena between 3.4 V and 2.7 V vs. Li were discovered and followed by in-situ X-ray diffraction, which revealed two distinct solid solution domains associated with highly anisotropic variations of the unit-cell constants.

Abstract: The highly porous and desolvated (activated) coordination polymer [Zn4O(btb)2] (btb = benzene-1,3,5-tribenzoate; MOF-177) was loaded with the organometallic compounds [Cp2Fe], [Cp*2Zn], [Cu(OCHMeCH2NMe2)2], [CpCuL] (L = PMe3, CNtBu) and [CpPd(3-C3H5)] via solvent-free adsorption from the gas-phase. The inclusion compounds of the type [LnM]a@MOF-177, where [LnM] indicates the respective compound and the parameter a denotes the number of molecules per formula unit of the MOF-177, were characterised by elemental analysis, FT-IR, solid-state NMR spectroscopy and by powder X-ray diffraction (PXRD). Remarkably high effective loadings of up to 11 molecules [Cp2Fe] and 10 molecules [CpPd(3-C3H5)] per cavity were determined. The analytical data prove that the host lattice and the guest molecules interact only by weak van-der-Waals forces without any significant change of the framework or the chemical nature of the included molecules. Cu nanoparticles showing the typical surface plasmon resonance at 580 nm and Pd nanoparticles of about 2.6 nm in size were formed inside the cavities of MOF-177 by the thermally activated hydrogenolysis of the inclusion compounds [CpCuCNtBu]2@MOF-177 and by photolysis of [CpPd(3-C3H5)]10@MOF-177 in an inert atmosphere (Ar). PXRD, FT-IR and NMR studies revealed that the MOF-177 matrix remained unchanged during the decomposition process of the precursors. N2 adsorption studies of the obtained materials Cu@MOF-177 (e.g. 10.6 wt.% Cu, 2309 m2 g-1) and Pd@MOF-177 (e.g. 32.5 wt.%, 1063 m2 g-1) reveal high remaining specific surface areas (Langmuir model).

Abstract: The limitations of the loading of the porous metalorganic framework [Zn4O(bdc)3] (bdc = benzene-1,4-dicarboxylate; MOF-5 or IRMOF-1) with Pd nanoparticles was investigated. First, the volatile organometallic precursor [Pd(5-C5H5)(3-C3H5)] was employed to get the inclusion compound [Pd(5-C5H5)(3-C3H5)]x@MOF-5 via gas-phase infiltration at 10-3 mbar. A loading of four molecules of [Pd(5-C5H5)(3-C3H5)] per formula unit of MOF-5 (x = 4) can be reached (35 wt.% Pd). Second, the metalorganic precursor [Pd(acac)2] (acac = 2,4-pentanedionate) was used and the inclusion materials [Pd(acac)2]x@MOF-5 of different Pd loadings were obtained by incipient wetness infiltration. However, the maximum loading was lower as compared with the former case with about two precursor molecules per formula unit of MOF-5. Both loading routes are suitable for the synthesis of Pd nanoparticles inside the porous host matrix. Homogeneously distributed nanoparticles with diameter of 2.4(±0.2) nm can be achieved by photolysis of the inclusion compounds [Pd(5-C5H5)(3-C3H5)]x@MOF-5 (x 4), while the hydrogenolysis of [Pd(acac)2]x@MOF-5 (x 2) leads to a mixture of small particles inside the network (< 3 nm) and large Pd agglomerates (40 nm) on the outer surface of the MOF-5 specimens. The pure Pdx@MOF-5 materials proved to be stable under hydrogen pressure (2 bar) at 150 °C over many hours. Neither hydrogenation of the bdc linkers nor particle growth was observed. The new composite materials were characterized by 1H/13C-MAS-NMR, powder XRD, ICP-AES, FT-IR, N2 sorption measurements and high resolution TEM. Raising the Pd loading of a representative sample Pd4@MOF-5 (35 wt.% Pd) by using [Pd(5-C5H5)(3-C3H5)] as precursor in a second cycle of gas-phase infiltration and photolysis was accompanied by the collapse of the long-range crystalline order of the MOF.