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Transition metals, such as iron (Fe)- or cobalt (Co)-based nanomaterials, are promising electrocatalysts for oxygen reduction reactions (ORR) in fuel cells due to their high theoretical activity and low cost. However, a major challenge to using these metals in place of precious metal catalysts for ORR is their low efficiency and poor stability, thus new concepts and strategies should be needed to address this issue. Here, we report a hybrid aciniform nanostructures of Fe nanofragments embedded in thin nitrogen (N)-doped graphene (Fe@N-G) layers via a heat treatment of graphene oxide-wrapped iron oxide (Fe2O3) microparticles with melamine. The heat treatment leads to transformation of Fe2O3 microparticles to nanosized zero-valent Fe fragments and formation of core-shell structures of Fe nanofragments and N-doped graphene layers. Thin N-doped graphene layers massively promote electron transfer from the encapsulated metals to the graphene surface, which efficiently optimizes the electronic structure of the graphene surface and thereby triggers ORR activity at the graphene surface. With the synergistic effect arising from the N-doped graphene and Fe nanoparticles with porous aciniform nanostructures, the Fe@N-G hybrid catalyst exhibits high catalytic activity, which was evidenced by high E1/2 of 0.82 V, onset potential of 0.93 V, and limiting current density of 4.8 mA cm−2 indicating 4-electron ORR, and even exceeds the catalytic stability of the commercial Pt catalyst.

The effect of alloying with transition metals (Ni, Co, Fe) on the adsorption strength of phosphoric acid on Pt alloy surfaces was investigated using electrochemical analysis and first-principles calculations. Cyclic voltammograms of carbon-supported Pt3M/C (M = Ni, Co, and Fe) electrocatalysts in 0.1 M HClO4 with and without 0.01 M H3PO4 revealed that the phosphoric acid adsorption charge density near the onset potential on the nanoparticle surfaces was decreased by alloying with transition metals in the order Co, Fe, Ni. First-principles calculations based on density functional theory confirmed that the adsorption strength of phosphoric acid was weakened by alloying with transition metals, in the same order as that observed in the electrochemical analysis. The simulation suggested that the weaker phosphoric acid adsorption can be attributed to a lowered density of states near the Fermi level due to alloying with transition metals.

Spin-polarized density functional theory studies of hydrogen sulfide (H2S) adsorption and decomposition on Ni(100) and Ni3Al(100) surfaces were conducted to understand the aluminum (Al) alloying effect on H2S dissociation. For such purpose, we first determined the near surface structure of fully ordered Ni3Al alloy along the [100] direction by calculating the Al segregation energy to the surface and then examined the adsorption energies of the adsorbates (H2S, HS, S, and H) and the activation barriers for the H2S and HS decomposition by using Climbing Image-Nudged Elastic Band method. We found that regardless of the way to terminate the surface, Al atom in bimetallic Ni3Al(100) tends to exist in the first surface layer, rather than in the second or third layer, and the Ni3Al(100) surface can substantially retard the H2S decomposition by reducing the adsorption energy of sulfur compounds compared to the pure Ni(100) case. Finally, we presented how the Al in Ni3Al modifies the activity of surface Ni atoms toward the sulfur compounds by calculating the local density of states and charge distribution in alloying components. This work hints the importance of knowing how to properly tailor the reactivity of Ni based materials to enhance the resistance for sulfur poisoning.

Described herein is the development of a novel Co-based oxygen electrode catalyst coupled with unique carbon structures. The present carbon shell coated Co nanoparticles of which the surface composites are modified by phosphorus incorporation, exhibit efficient oxygen reduction activities as well as oxygen evolving properties.

Edge-exposed MoS2 nano-assembled structures are designed for high hydrogen evolution reaction activity and long term stability. The number of sulfur edge sites of nano-assembled spheres and sheets is confirmed by Raman spectroscopy and EXAFS analysis. By controlling the MoS2 morphology with the formation of nano-assembled spheres with the assembly of small-size fragments of MoS2, the resulting assembled spheres have high electrocatalytic HER activity and high thermodynamic stability.

The removal of sulfonamide antibiotics (SAs) by activated carbon was investigated by using granular activated carbon (GAC) tests and density functional theory (DFT) simulations. The GAC absorption tests show the removal efficiency of 68.4~90.7% and 99.0~99.9% in 1 and 24 hours, respectively. In both GAC tests, the removal efficiency of sulfamethazine (SMZ) was the highest followed by those of sulfathiazole (STZ) and sulfamethoxazole (SMTZ): SMZ > STZ > SMTZ. In DFT adsorption simulations, we found that the 4-aminobenzenesulfonamide parts of SMZ and STZ and the 3-methyl-1,2-oxazol-5-amine part of SMTZ are preferentially adsorbed on the edges of graphene model, provided that the adsorbates keep their structures without dissociation upon adsorption process. The adsorption energies of SMZ, STZ, and SMTZ are -4.91, -4.64, and -4.62 eV, respectively. This adsorption strength (SMZ > STZ > STMZ) agrees with the trend of the removal efficiency of SAs by GAC. In addition, dissociative adsorption configurations of SAs are discussed.

The structural and electronic properties of Hg, SO(2), HgS, and HgO adsorption on Au(111) surfaces have been determined using density functional theory with the generalized gradient approximation. The adsorption strength of Hg on Au(111) increases by a factor of 1.3 (from -9.7 to -12.6 kcal/mol) when the number of surface vacancies increases from 0 to 3; however, the adsorption energy decreases with more than three vacancies. In the case of SO(2) adsorption on Au(111), the Au surface atoms are better able to stabilize the SO(2) molecule when they are highly undercoordinated. The SO(2) adsorption stability is enhanced from -0.8 to -9.3 kcal/mol by increasing the number of vacancies from 0 to 14, with the lowest adsorption energy of -10.2 kcal/mol at 8 Au vacancies. Atomic sulfur and oxygen precovered-Au(111) surfaces lower the Hg stability when Hg adsorbs on the top of S and O atoms. However, a cooperative effect between adjacent Hg atoms is observed as the number of S and Hg atoms increases on the perfect Au(111) surface, resulting in an increase in the magnitude of Hg adsorption. Details of the electronic structure properties of the Hg-Au systems are also discussed.

Preventing the release of mercury from coal-fired power plants continues to be a challenge. The design of effective and affordable control strategies depends upon the speciation of mercury from the high temperature region of the boiler to the lower temperature environment of the stack. Both homogeneous and heterogeneous oxidation pathways play a role in determining mercury's speciation over the temperature range of coal-fired flue gas. This review explores the current state of knowledge associated with the kinetically-limited homogeneous reaction pathways in addition to the complexities associated with heterogeneous oxidation processes. In particular, oxidation pathways associated with selective catalytic reduction and precious metal catalysts are considered. In addition, adsorption mechanisms on various materials are discussed, including fly ash and activated carbon for flue gas applications and precious metals for fuel gas applications.

The mechanisms of the oxygen reduction reaction (ORR) on defective graphene-supported Pt13 nanoparticles have been investigated to understand the effect of defective graphene support on the ORR and predict details of ORR pathways. We employed density functional theory (DFT) predictions using the projector-augmented wave (PAW) method within the generalized gradient approximation (GGA). Free energy diagrams for the ORR over supported and unsupported Pt13 nanoparticles were constructed to provide the stability of possible intermediates in the electrochemical reaction pathways. We demonstrate that the defective graphene support may provide a balance in the binding of ORR intermediates on Pt13 nanoparticles by tuning the relatively high reactivity of free Pt13 nanoparticles that bind the ORR intermediates too strongly subsequently leading to slow kinetics. The defective graphene support lowers not only the activation energy for O2 dissociation from 0.37 to 0.16 eV, but also the energy barrier of the rate-limit...

The structural and electronic properties of Pt13 nanoparticles adsorbed on monovacancy defective graphene have been determined to understand oxygen adsorption on Pt nanoparticles based upon density functional theory predictions using the generalized gradient approximation. We demonstrate that a monovacancy site of graphene serves a key role as an anchoring point for Pt13 nanoparticles, ensuring their stability on defective graphene surfaces and suggesting their enhanced catalytic activity toward the interaction with O2. Strong hybridization of the Pt13 nanoparticle with the sp2 dangling bonds of neighboring carbon atoms near the monovacancy site leads to the strong binding of the Pt13 nanoparticle on defective graphene (−7.45 eV in adsorption energy). Upon both adsorption of the Pt13 nanoparticle on defective graphene and O2 on Pt13–defective graphene, strong charge depletion of the Pt atom at the interfaces of Pt–C and Pt–O2 is observed. Pt13 nanoparticles are able to donate charge to both defective grap...

The structural, electronic, and magnetic properties of Fe13 and Al13 nanoparticles adsorbed on monovacancy defective graphene have been determined using density functional theory with the generalized gradient approximation (GGA). Graphene vacancies are used as anchoring points for these pure metal nanoparticles, ensuring their isolated stability on the surface, thereby maximizing their catalytic reactivity through the availability of undercoordinated surface sites along with a high surface area. The results of this work indicate that the strong binding of Fe13 and Al13 nanoparticles on defective graphene (−6.98 and −3.84 eV in adsorption energy, respectively) is due to strong hybridization of the nanoparticles with the sp2 dangling bonds of neighboring carbons near the vacancy. Charge difference and Bader charge analyses of the Fe13 and Al13 adsorbed systems suggest that charge redistribution of defective graphene occurs to a greater extent in the Fe13 system than in the Al13 system due to the strongly hy...

Polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) may pose a worldwide pollution problem because of their persistence, long-range transport capability, and predisposition to bioaccumulate. The ubiquitous presence of PBBs and PBDEs has heightened interest in determination of their fate. We report results for a fugacity-based dynamic environmental and bioaccumulation model of the fate of hexabromobiphenyl (hexaBB) discharged into the Saginaw Bay region of Lake Huron, USA. We calculated transient fugacity profiles of hexaBB in Lake Huron and Lake Erie water and sediment during the 1970s, 1980s, and 1990s. The hexaBB concentrations in the environmental compartments were used as inputs for a dynamic bioaccumulation model of Lake Huron and Lake Erie aquatic biota. The model results indicate that the sediment compartments of Lakes Huron and Erie serve as reservoirs for the accumulation and slow transfer of hexaBB to the food web constituents of these lakes. We present bioaccumulation factors (BAFs) and compare the predicted hexaBB concentrations in lake trout from the bioaccumulation model with measurements during the period 1980 to 2000. An uncertainty analysis for this model suggests that errors associated with input parameter uncertainty can be reduced by refining estimates of the sediment degradation half-life of hexaBB. The corroborated PBB model has carryover application for modeling the fate of polybrominated diphenyl ether (PBDE) contaminants in the Great Lakes. By fitting model outputs to field measurement data using the transformed least square fit method, we report estimations of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) emission rates into the Lake Huron and Lake Erie watershed areas. Environ. Toxicol. Chem. 2011; 30:1018–1025. © 2011 SETAC

Pt-Pd nanoparticles are structure-engineered by successive electroless deposition and galvanic displacement technique, to manifest a shell-core configuration. Based on the microscopic analysis, the nanoparticles present an uniform distribution. When applied as an electrocatalyst, they are confirmed to be highly active toward both methanol and ethanol oxidation reaction for a prolonged time. In addition, the catalyst is more resistive against CO-poisoning than conventional Pt catalyst. The stable activity of Pt-Pd catalyst is ascribed to the surface-tuned electronic property of Pt over-layer, which leads to a weak adsorption strength to CO and a high affinity to OH. The modified binding ability of surface Pt was reflected by CO-stripping experiment and by monitoring of electrochemical surface area over multiple times. The observed chemical stability of as-prepared catalyst is further proved and supplemented by a computational investigation via density functional theory calculation. The experimental and theoretical outcomes indicate that the catalyst is suitable and applicable for the direct methanol and ethanol oxidation in DAFC. Figure 1

The gas-phase dissociation of perchloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cis-DCE) on zerovalent iron Fe(110) was investigated using periodic density functional theory (DFT) with the generalized gradient approximation (GGA) and climbing image nudged elastic band method (CI-NEB). Activation energies and dechlorination rate constants for reductive beta-elimination of the chloroethene compounds were calculated using an Arrhenius equation with theoretically calculated vibrational frequencies for the compounds. Activation energies were found to decrease as the chlorination number increases. The reaction rate-limiting step for PCE dissociation occurs at the second chlorine cleavage, while the rate-limiting steps for TCE and cis-DCE occur at the first chlorine cleavage. The activation energies of PCE, TCE, and cis-DCE at their rate-limiting steps are 9.9, 16.6, and 23.8 kJ/mol, respectively. Energy profiles along the reaction coordinate for the dechlorination paths are presented. The relative gas-phase reactivity order among chlorothenes on Fe(110) was found to be PCETCEcis-DCE. At room temperature (300 K), the PCE dechlorination rate is 14 and 338 times faster, respectively, than that of TCE and cis-DCE. Details regarding the electronic properties of the transition states of the dechlorinated compounds are reported.

Adsorption of perchloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cis-DCE) on zerovalent iron is investigated using density functional theory (DFT) to evaluate hypotheses concerning the relative reactivity of these compounds on zerovalent iron. Four different chloroethene adsorption modes on the Fe(110) surface were studied using periodic DFT and the generalized gradient approximation (GGA). Of the adsorption sites examined, the atop site, where the chloroethene C==C bond straddles a surface iron atom, was the most energetically favorable site for the adsorption of all three chloroethenes. Electronic structure and property analyses provide an indication of the extent of sp2-sp3 hybridization. The strong hybridization of the pi-bonding orbital between the chloroethene C==C bond and the iron surface suggests that adsorbed chloroethenes are strongly activated on Fe(110) and are likely precursors for subsequent chloroethene dissociation on the Fe surface. When the effect of solvation is indirectly taken into account in the DFT simulations by considering the hydration energies of chloroethenes in bulkwater,the ordering ofthe adsorption energies of chloroethenes from the aqueous phase onto Fe(110) is in agreement with experimental observation (PCETCEcis-DCE). Electronic properties of the adsorbed configurations of chloroethenes are also presented.

To date, carbon-based materials including various carbon nanostructured materials have been extensively used as an electrocatalyst support for proton exchange membrane fuel cell (PEMFC) applications due to their practical nature. However, carbon dissolution or corrosion caused by high electrode potential in the presence of O2 and/or water has been identified as one of the main failure modes for the device operation. Here, we report the first TiN nanofiber (TNF)-based nonwoven structured materials to be constructed via electrospinning and subsequent two-step thermal treatment processes as a support for the PEMFC catalyst. Pt catalyst nanoparticles (NPs) deposited on the TNFs (Pt/TNFs) were electrochemically characterized with respect to oxygen reduction reaction (ORR) activity and durability in an acidic medium. From the electrochemical tests, the TNF-supported Pt catalyst was better and more stable in terms of its catalytic performance compared to a commercially available carbon-supported Pt catalyst. For example, the initial oxygen reduction performance was comparable for both cases, while the Pt/TNF showed much higher durability from an accelerated degradation test (ADT) configuration. It is understood that the improved catalytic roles of TNFs on the supported Pt NPs for ORR are due to the high electrical conductivity arising from the extended connectivity, high inertness to the electrochemical environment and strong catalyst-support interactions.

The electronic structures of sulfonamide antibiotics (the ground state and the lowest singlet excited-state geometries) have been investigated by using density functional theory (DFT) simulations. Experimental studies on the removal of sulfamethazine, sulfathiazole and sulfamethoxazole by ozone have also been conducted by using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS). The calculated ground and excited state geometries exhibited low energy of the inter-ring bonds, which suggests the weakest bonds that can be broken during the ozone oxidation process. The orbital energy calculations (HOMO-LUMO and its energy gap) demonstrate that the smaller HOMO-LUMO energy gap, the higher reactivity toward ozone oxidation. Additionally, the current study suggests potential products of the three pharmaceutical compounds based on their electronic properties, which may help better understand the unknown reaction pathways of the pharmaceutical compounds.

Stable alternative catalyst supports to replace conventional carbon-based materials in polymer electrolyte membrane fuel cells (PEMFCs) are being explored to achieve dramatic improvements in the performance and durability of fuel cells. Herein, conductive Ti3+ self-doped and carbon-coated TiO2-reduced graphene oxide (rGO) hollow nanosphere-supported Pt nanoparticles (Pt/rGO/TiO2) are investigated as cathode electrocatalysts for PEMFCs. Importantly, the rGO/TiO2 hollow nanospheres display excellent electrochemical stability under high potential cycling (1.2–1.7 V) compared with conventional carbon black (CB) support materials that normally induce electrochemical corrosion during fuel cell operation. The Pt/rGO/TiO2 is tested to establish its catalytic activity and stability using accelerated durability testing that mimics the conditions and degradation modes encountered during long-term fuel cell operation. The Pt/rGO/TiO2 cathode catalyst demonstrates comparable catalytic activity toward oxygen reduction and exhibits much higher stability than the Pt/CB one at high potentials in terms of minimal loss of the Pt electrochemical surface area. More importantly, Pt/rGO/TiO2 displays a negligible voltage drop over long-term cycling during practical fuel cell operation. The high stability of the Pt/rGO/TiO2 electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of PEMFC cathode catalysts.

In this presentation, using first-principles calculation, the function of samarium (Sm) 4f states and Sm-perturbed O 2p states in enhancing the sulfur tolerance of Sm-doped CeO2 was elucidated. We find that the sulfur tolerance of Sm-doped CeO2 is closely related to the modification of O 2p states by the strong interaction between Sm 4f and O 2p states. In particular, the availability of unoccupied O 2p states near the Fermi level is responsible for enhancing the sulfur tolerance of Sm-doped CeO2 compared to the pure CeO2[1]. To better understand the importance of unoccupied O 2p states, the effect of various 4f shell dopants (Pr, Pm, and Eu) on the activity of surface lattice oxygen are also investigated. This work also hints on the importance of properly engineering the activity of oxygen ion in CeO2-based materials by adding dopant in order to develop sulfur-tolerant solid oxide fuel cell anode. [1] DH Lim, HS Kim, SP Yoon, J Han, CW Yoon, SH Choi, SW Nam, and HC Ham, Physical Chemistry Chemical Physics 16 (22), 10727-10733, (2014)

The role of samarium (Sm) 4f states and Sm-perturbed O 2p states in determining the sulfur tolerance of Sm-doped CeO2 was elucidated by using the density functional theory (DFT) + U calculation. We find that the sulfur tolerance of Sm-doped CeO2 is closely related to the modification of O 2p states by the strong interaction between Sm 4f and O 2p states. In particular, the availability of unoccupied O 2p states near the Fermi level is responsible for enhancing the sulfur tolerance of Sm-doped CeO2 compared to the pure CeO2 by increasing the activity of the surface lattice oxygen toward sulfur adsorption, by weakening the interaction between Sm–O, and by increasing the migration tendency of the subsurface oxygen ion toward the surface.

Density functional theory studies demonstrate that defective graphene-supported Cu nanoparticles can modify the structural and electronic properties of copper for enhancing electrochemical reduction of carbon dioxide (CO2) into hydrocarbon fuels (CH4, CO, and HCOOH). We not only provide improved understanding of CO2 conversion mechanisms on both Cu and the Cu nanoparticle system, but also explain a key factor for enhanced CO2 conversion. A promising catalytic material for CO2 conversion into hydrocarbon fuels may allow for geometry flexibility upon interaction with a key intermediate of CHO*.

Density functional theory (DFT) studies of mercury oxidation on Au(111) are conducted to determine the potential Hg oxidation mechanisms taking place on catalytic gold surfaces by using the Perdew and Wang approximation (PW91) described by a generalized gradient approximation (GGA). The Hg oxidation was examined via a Langmuir-Hinshelwood mechanism where each Hg(0) and Cl2 (or HCl) species is separately adsorbed on the gold surface and the bimolecular reaction occurs through the formation of bound HgCl and HgCl2. For this, the Climbing Image-Nudged Elastic Band (CI-NEB) method has been employed to calculate the activation energies of HgCl and HgCl2 formation pathways. In the three-step Hg oxidation mechanism (Hg → HgCl → HgCl2), the second Cl attachment step is endothermic which is the reaction rate-limiting step, while the first Cl attachment step is exothermic. This observation implies that Hg oxidation prefers a pathway in which HgCl and HgCl2 are formed, rather than a pathway directly oxidizing Hg to HgCl2. In the presence of H atoms due to HCl dissociation on the Au surface, the H atoms lower the activation energy for Hg oxidation by consuming the electron charge of Au atoms, thereby weakening the strength of interaction between Cl and the Au surface and lowering an energy required to detach Cl from the Au surface. This mechanism is in the absence of site competition on the Au surface. In addition, details of the electronic properties of these systems are discussed.

This study evaluates the ability of Beijerinckia indica (B. indica) as a biomaterial for aerobic biofilm barriers. B. indica's ability to remove phenanthrene was measured using a two-phase partitioning bioreactor. Approximately 500 mg/L of phenanthrene was gradually removed over a two week period under aerobic conditions of the bioreactor. B. indica's ability to reduce hydraulic conductivity was evaluated using rigid wall soil columns inoculated with the bacteria. B. indica formed a large quantity of strongly adhesive biofilm among soil particles, reducing the hydraulic conductivity in the soil columns by 2 or 3 orders of magnitude. To assess recovery of the biofilm, the formed biofilm was purposely destroyed by introducing landfill leachate into the soil columns. The biofilm recovery test showed that the hydraulic conductivity increased after leachate introduction. However, re-permeation of nutrient solution restored the permeability to its original lower value, which suggests a full recovery of the damaged biofilm. This study suggests that B. indica may be used as a possible biomaterial for aerobic biofilm barriers for the removal of phenanthrene from groundwater, provided that sufficient substrate and electron acceptor are provided to the treatment system.

Benzaldehyde (I) forms a Pt-bound pyrylium with PtCl2 that undergoes intermolecular [3 + 2] cycloaddition with alkenes to form oxygen-bridged intermediates with good stereoselectivity.

High temperature-polymer electrolyte membrane fuel cell (HT-PEMFC) utilizing phosphoric acid doped polybenzimidazol membrane is a promising power supply for a number of stationary applications. At high operating temperature, significant enhancement in oxygen reduction reaction (ORR) kinetics is expected. However, typically the cell performance of HT-PEMFC is lower than that of conventional Nafion-based PEMFCs. One of important reason is the strong adsorption of phosphoric acid or anions, so called ‘phosphoric acid poisoning’, which blocks the active sites on Pt/C. Alloying with transition metals have been suggested for an efficient way to improve the performance of HT-PEMFC as the alloying may provide enhanced intrinsic ORR activity and improved tolerance against the phosphoric acid poisoning. Experimental observation and computational simulations revealed that lowered adsorption energy of OH on alloy of Pt and transition metal nanoparticle catalysts (PtM/C) provided the enhanced ORR activity1. However, there were few reports investigating effect of transition metal alloying on the phosphoric acid tolerance. Recently, He et al. demonstrated improved tolerance against the phosphoric acid poisoning in bulk PtSn2 and PtNi nanoparticle3 alloy surfaces. They postulated that ligand effect or geometric effect may be responsible for the tolerance of alloy surfaces. As a theoretical investigation of the alloying effect, Savizi and Janik calculated potential dependence of phosphoric acid adsorption free energy4 on Pt(111) surfaces, using density functional theory (DFT) simulations. However, there has been no further study, including PtM/C electrocatalysts. In this research, we investigated the effect of transition metal alloying on the phosphoric acid poisoning in Pt3M (where, M = Fe, Co, Ni) nanoparticle catalyst (Pt3M/C) surfaces. Using the cyclic voltammetry, adsorption strength of phosphoric acid on Pt3M/C was analyzed. Also, the effect of transition metal alloying on the adsorption strength of phosphoric acid in Pt3M/C was analyzed based on the DFT simulations. Combination of electrochemical analysis and DFT simulations allowed investigating systematically the effect of alloying on the phosphoric acid adsorption in Pt3M/C surfaces. References 1. I.E.L. Stephens, A.S. Bondarenko, U. Gronbjerg, J. Rossmeisl, I. Chorkendorff, Energy Environ. Sci., 5, 6744 (2012). 2. Q. He, X. Yang, W. Chen, S. Mukerjee, B. Koel, S. Chen, Phys. chem. Chem. Phys., 12, 12544 (2010). 3. Q. He, B. Shyam, M. Nishijima, D. Ramaker, S. Mukerjee, J. Phys. Chem. C, 117, 4877 (2013). 4. I. S. P. Savizi, M. J. Janik, Electrochim. Acta 56, 3996 (2011).

The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.

Methanotrophs have been widely investigated for in situ bioremediation due to their ubiquity and their ability to degrade halogenated hydrocarbons through the activity of methane monooxygenase (MMO). It has been speculated that cells expressing the soluble form of MMO (sMMO) are more efficient in cleaning up sites polluted with halogenated hydrocarbons due to its broader substrate range and relatively fast degradation rates compared cells expressing the other form of MMO, the particulate MMO (pMMO). To examine this issue, the biodegradation of mixtures of chlorinated solvents, i.e., trichloroethylene (TCE), trans -dichloroethylene ( t -DCE), and vinyl chloride (VC), by Methylosinus trichosporium OB3b in the presence of methane using either form of MMO was investigated over longer time frames than those commonly used, i.e., days instead of hours. Growth of M. trichosporium OB3b along with pollutant degradation were monitored and analyzed using a simple comparative model developed from the Ω model created for analysis of the competitive binding of oxygen and carbon dioxide by ribulose bisphosphate carboxylase. From these findings, it appears that at concentrations of VC, t -DCE, and TCE greater than 10 μM each, methanotrophs expressing pMMO have a competitive advantage over cells expressing sMMO due to higher growth rates. Despite such an apparent growth advantage, pMMO-expressing cells degraded less of these substrates at these concentrations than sMMO-expressing cells during active growth. If the concentrations were increased to 100 μM, however, not only did pMMO-expressing cells grow faster, they degraded more of these pollutants and did so in a shorter amount of time. These findings suggest that the relative rates of growth substrate and pollutant degradation are important factors in determining which form of MMO should be considered for pollutant degradation.

2-(3-Benzyloxy)prop-1-ynyl)benzaldehyde with PtCl(2) in toluene would form Pt-pyryliums that underwent [3+2] cycloaddition with alkenes to the oxygen-bridged (5H-benzo[7]annulen-5-ylidene)platinum(ii) intermediates with good stereoselectivities. Their tandem rearrangement afforded diverse types of polycycles depending on the electronic nature of the alkenes.

목적 : 요로감염은 소아 발열의 흔한 원인이며 합병증으로 초래되는 신 반흔은 고혈압이나 만성신부전으로 진행할 수 있다. 본 연구에서는 요로감염에 의한 발열지속기간이 신 반흔이나 방광요관역류 등 위험요소에 영향을 미치는지 알고자 하였다. 방법 : 2002년 3월부터 2007년 3월까지 소아 청소년과에 입원한 15세 미만...