Theoretically predicted innovative palladium stripe dopingcobalt(111) surface with excellent catalytic performance for carbonmonoxide oxidative coupling to dimethyl oxalate

Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction.In this study,we theoretically predict that Pd stripe doping Co(111)surface exhibits excellent performance than pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface,and clearly expound the catalytic mechanisms through the density functional theory(DFT)calculation and micro-reaction kinetic model analysis.It is obtained that the favorable reaction pathway is COOCH_(3)-COOCH_(3)coupling pathway over these four catalysts,while the rate-controlling step is COOCH_(3)+CO+OCH_(3)→2COOCH_(3)on Pd stripe doping Co(111)surface,which is different from the case(2COOCH_(3)→DMO)on pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface.This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.

Comparison of Pb and Cd adsorption to the surface coatings and surficial sediments collected in Xianghai Wetland

Surface coatings and surficial sediments were obtained in four natural waters in Xianghai Wetland in China to study the role of surface coatings and surficial sediments in controlling the transporting and cycling of heavy metals in aquatic environments. Pb and Cd adsorption to the surface coatings and surficial sediments were measured under controlled laboratory conditions(mineral salts solution with defined speciation, ionic strength 0 05 mol/L, 25℃ and pH 6 0 for surface coatings; and 0 005 mol/L CaCl 2 solution, 25℃ and pH 6 0 for surficial sediments). The Langmuir adsorption isotherm was applied to estimate equilibrium coefficients of Pb and Cd adsorption to the surface coatings and surficial sediments, and the component analyses of surface coatings and surficial sediments were also carried out. Correlation analyses between the maximum adsorption of Pb and Cd(Г max ) and the components in the surface coatings and surficial sediments suggested that there was a statistically significant trend for Pb and Cd adsorption(Г max ) to the surface coatings to increase with increasing in contents of Fe and Mn oxides in the surface coatings and surficial sediments. And the metal adsorption abilities of surface coatings were much stronger than those of surficial sediments, highlighting that in the same water, i.e. at the same pH and initial metal concentrations, the metals(such as lead and cadmium) in supernatant were feasible to be adsorbed by surface coatings than surficial sediments. The more importance of surface coatings than surficial sediments for adsorbing and cycling of heavy metals in aquatic environments was evidenced.

DFT Investigation of the Adsorption/dissociation Mechanisms of Methyl Nitrite on the Pd(111) Surface

The adsorption behavior of methyl nitrite （MN） on the closed-packed Pd（111） sur- face has been investigated in detail by using density functional theory （DFT）. MN binds to the surface in two alternative forms, using the nitrogen atom attached to the surface. An overall net charge transfer from the substrate to the cis-MN molecule is also confirmed. In addition, the reaction mechanism for the dissociation of MN on the Pd（111） surface has been identified and compared with the methanol decomposition via O-H scission. The results demonstrate that MN is a more active reactant than methanol for the oxidative addition to the Pd catalyst. The possible reason has been analyzed from the adsorption behaviors and reaction barriers, that is, MN is chemically absorbed on the Pd（111） surface; the CHaO-NO bond scission, leading to the formation of adsorbed methoxy species, is much more favorable than that of the O-H bond scission and has a large exothermic behavior.

A Periodic Density Functional Study on Adsorption Properties of Methoxy on Au(111) Surface

Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.

First-principles Study on Geometric and Electronic Structures of Si（111）-√7× √3-In Surface Reconstruction

In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calculations. Their scanning tunneling microscopic images and work functions are simulated and compared with experimental results. In this way, the hex-H3＇ and rect-T1 models are identified as the experimental configurations for the hexagonal and rectangular types, respectively. The structural evolution mechanism of the In/Si（lll） surface with indium coverage around 1.0 monolayer is discussed. The 4×1 and -√7× √3 phases are suggested to have two different types of evolution mechanisms, consistent with experimental results.

DFT Study of Thiophene Adsorption on the Pd(111) and Pt(111) Surfaces

Thiophene adsorption on the（111） surfaces of Pd and Pt have been investigated by density functional theory.The results indicate that the adsorption at the hollow sites is the most stable.To our interest,the molecular plane of thiophene ring is distorted with C=C bond being elongated to 1.450 and C–C bond being shortened to 1.347 ,and the C–H bonds tilt 13.91～44.05o away from this plane.Furthermore,analysis on population and density of states verified the calculated adsorption geometries.Finally,charge analysis suggests that thiophene molecule is an electron acceptor,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.

Theoretical Study on the Adsorption and Decomposition of Methanol over the Pt-Mo(111)/C Surface

The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo（111）/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt（111）/C surface and that of CO,the adsorption energies of CO are higher,and Pt（111）/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo（111）/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt（111）/C.

Quantitative Model for the Surface-related Electron Transfer in CdS Quantum Dots

The influence of surface S^2- dangling bonds and surface doped ions（Se^2-, Cu^2＋, and Hg^2＋） on the photoluminescence of Cd^2＋-rich CdS QDs was investigated. A quantitative model was proposed to understand the complex transfer processes of excited electrons in CdS QDs. The transfer of excited electrons from either the conduction band or the Cd^2＋-related trap-state to the surface S^2-related shallow hole trap-state is effective. However, the trap of excited electrons by surface doped ion trap-states from the Cd^2＋-related trap-state is more effective than that from the conduction band. The efficiency of trapping electrons from both the conduction band and the Cd^2＋-related trap-state can be quantitatively understood with the help of the proposed model. The results show that the transfer efficiency of excited electrons is dependent on the location of the energy-level of the relevant surface-related trap-state. The trap of excited electrons by the surface trap-state with energy-level closer to that of the conduction band is more effective, especially for the trap of excited electrons from Cd^2＋-related trap-state.

Formulation optimization of scutellarin-loaded HP-β-CD/chitosan nanoparticles using response surface methodology with Box–Behnken design

The aim of this paper is to investigate and optimize the preparation of scutellarin(SCU)-loaded HP-β-CD/chitosan(CS) nanoparticles(CD/CS-SCU-NPs). CD/CS-SCU-NPs were prepared by ionic cross-linking method and the process and formulation variables were optimized using response surface methodology(RSM) with a three-level, three factor Box–Behnken design(BBD).The independent variables were the added amounts of CS, sodium tripolyphosphate(TPP)and Pluronic F-68 during the preparation. Dependent variables(responses) were particle size and entrapment efficiency. Mathematical equations and respond surface plots were used to correlate independent and dependent variables.The preparation process and formulation variables were optimized to achieve minimum particle size and maximum entrapment efficiency by calculating the overall desirability value(OD). The optimized NP formulation was characterized for particle size, PDI, zeta potential, entrapment efficiency and in vitro drug release.According to the results, an optimized CD/CS-SCU-NP formulation was prepared. Results for particle size, PDI, zeta potential and entrapment efficiency were found to be around 200 nm,0.5, 25 mV, and 70% respectively. For in vitro study, the release of SCU from the NPs exhibited a biphasic release and was in accordance with Higuchi equation. The optimized preparation was simple with the probability for industrialization. The combination use of RSM, BBD and overall desirability values could provide a promising application for incorporating CD into CS nanoparticles as drug delivery carrier and help develop lab-scale procedures.

A DFT Study of Thiophene Adsorption on the Rh(111) Surfaces

Thiophene adsorption on the Rh（111） surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448 and the C–C bond is shortened to 1.390.The C–H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons, reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal. The reaction paths and transition states for desulfurization of the molecule have been investigated. The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV. This second step is slightly difficult, and dissociation into a C4H4 fragment and a sulfur atom is possible, with an energetic barrier of 0.40 eV.

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine（H2Nc） monolayer on Ag（111） surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory（DFT）based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag（111） could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

A Density Functional Theory Study on the Adsorption of CN on Ni(111) Surface

The interaction of cyanide (CN) with different sites on Ni(111) surface is studied by using density functional theory (DFT). Ni19 cluster is used to simulate the surface. The present calculations show that the end-on bonded (through C atom) configuration is much more preferable than the side-on bonded CN or other configurations on the same adsorption site. For all adsorption modes, adsorption energies at the top, bridge, and three-fold sites on Ni(111) are comparable, with the bridge site of the end-on bonded CN (through C atom) more favorable than other adsorption sites. CN vibrational frequencies are red-shifted at all cases, except that the end-on CN bonded (through C atom) on the top site is blue-shifted. The bonding of CN on the Ni(111) surface is large- ly ionic.

Comparison of Pb,Cd Adsorption to Surface Coatings Developed in Natural Waters with that in Plant Effluents

The comparative studies of Pb and Cd adsorption to the surface coatings(Fe, Mn, Al oxides, organic materials, and associated minerals), which were developed on glass slides in five natural and two technical waters(plant effluents), were carried out under controlled laboratory conditions(mineral salts solution with defined speciation, ionic strength 0 05 mol/L, 25 ℃ and pH 6 0). The classical Langmuir adsorption isotherm was applied to estimating the equilibrium coefficients of Pb and Cd adsorption to the surface coatings. The results show that the maximum adsorption of Pb and Cd to the surface coatings mentioned above varied widely. There was a systemic increase in the maximum adsorption of Pb and Cd to the surface coatings with increasing the contents of Mn and Fe oxides in the surface coatings in significant correlation, respectively, not only highlighting the relative importance of the metal oxide fraction for Pb and Cd adsorption to the surface coatings developed in natural and technical water samples, but also implying the same adsorption mechanisms of Pb and Cd to the surface coatings developed both in natural and technical water samples.

Removal of Cd(Ⅱ) from Aqueous Solutions by Natural Freshwater Surface Coatings

Natural freshwater surface coatings(biofilms and associated minerals), which were developed in the Nanhu Lake, Changchun, P. R. China, were used as an efficient biosorbent for the removal of Cd(Ⅱ) from aqueous solutions. The batch experiments were carried out to determine the adsorption properties of Cd(Ⅱ) onto the natural surface coatings. The classical Langmuir adsorption isotherm was applied to estimating the equilibrium coefficients of Cd(Ⅱ) adsorbed on the surface coatings. The results show that the maximum adsorption capacity of the surface coatings is 434.78 μmol Cd/m2(being equal to 0.17 mmol Cd/g of surface coatings or 10.38 mmol Cd/g Fe) and the Cd(Ⅱ) removal from solution media by the natural surface coatings was shown to be strongly affected by solution pH and ion strength. The resulted information also indicates that the maximum Cd removal efficiency(CRE) was determined to be approximately 90% at initial Cd mass concentration of 0.1 mg/L(the concentration limit of Cd (Ⅱ) in wastewaters for discharge in aquatic media in Chinese legislation), and the kinetic adsorption of Cd(Ⅱ) onto the surface coatings is fast with around 70% of the total adsorption-taking place in 150 min in solution under the controlled laboratory conditions (mineral salts solution with defined speciation, ionic strength 0.05 mol/L, and 25 ℃). With the advantage of high Cd adsorption capacity, the natural surface coatings appear to be a potentially effective biosorbent for the removal and recovery of Cd (Ⅱ) from polluted water.

Formation and local electronic structure of Ge clusters on Si（111）-7×7 surfaces

We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.

Temperature dependence of surface and structure properties of ZnCdO film

Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy（LMBE） at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction（RHEED） pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy（UPS） measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.

Acetonitrile(CH_3CN)and methyl isocyanide(CH_3NC) adsorption on Pt(111)surface:a DFT study

The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. The most favored ad-sorption structure for CH3 CN is the C--N bond almost parallel to the surface with the C-N bond interaction with adjacent surface Pt atoms. For CH3NC, the most stable configuration is the CH3 NC locates at the face center cubic （fcc） site with the C-atom bonded to three Pt atoms. In addition, the HCN and HNC adsorption has been computed, and the adsorption pattern is nearly similar to the CH3CN and CH3NC, respectively. The adsorbed molecules rehybridize on the surface, be-coming non-linear with a bent C-C-N or C-N-C angle. Furthermore, the binding mechanism of these molecules on the Pt（111） surface is also analyzed.

The STM Images of Pt (111) (<img src="http://latex.codecogs.com/gif.latex?\sqrt{3}\times&space;\sqrt{3}"title="\sqrt{3}\times \sqrt{3}"/>)R30&deg;/CO Surface by DFT Calculations

In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density functional theory (DFT) and the projector-augmented wave (PAW) method. The calculations show that carbon monoxide molecule (CO) adsorbs on FCC site in the Pt (111) ( × )R30°/ surface is energetically favored by the GGA-PBE XC-functional, this is in agreement with most of the theoretical calculations which is using different XC-functional at the most. However, these results strongly conflicted with the existing experiments. Actually the calculated work function for the FCC adsorption is quite different from the experiments while the atop one is in good agreement with experiments. We speculate that the atop adsorption for (CO is favorable for the adsorption case at the most. Furthermore, we have calculated the scanning tunneling microscopy (STM) images for both adsorption geometries and suggest that there should be existed remarkable differences in the STM images. The present work provides a faithful criterion accounting for the local surface geometry in Pt (111) ( × )R30°/CO surface from surface work functions and STM images instead of totalenergy calculations.

Adsorption of HCN on Ni/Pt(111)Bimetallic Surfaces Investigated with Density Functional Theory Method

We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） surfaces. For all bimetallic surfaces,HCN is preferentially tilted with the CN bond parallel to the surface,and adsorption energies increase with an increasing number of layer Ni atoms on the surface. The adsorption energies of HCN on all bimetallic surfaces are larger than that on the Pt（111） surface,whereas the adsorption energies of HCN on 3Ni@Pt（111） and 4Ni@Pt（111） are larger than that on the Ni（111） surface,indicating that the introduction of Ni to the Pt catalyst could increase the activity of bimetallic catalyst in the hydrogenation reaction for nitriles. Larger adsorption energy of HCN leads to a longer C–N bond length and a smaller CN vibrational frequency. The analysis of Bader charge and vibrational frequencies showed obvious weakening of the adsorbed C–N bond and an indication of sp2 hybridization of both carbon and nitrogen atoms.

The Role of Radiative Surface Modes and Longitudinal Excitons in the Formation of Exciton-Polariton Luminescence Spectra of CdS-Type Crystals

The low-temperature (T = 2 K) exciton-polariton luminescence (EPL) spectra in the vicinity of the exciton-resonance frequency An=1 for CdS-type crystals have been theoretically and experimentally investigated with allowance for the mechanical exciton decay . The results of the numerical calculations of the partial and interference contributions of the bulk and radiative surface spectral modes to the EPL in the geometry of additional s- and p-polarized waves emitted into vacuum are analyzed. It is shown that the contributions of purely longitudinal excitons and their interference with polaritons of the upper dispersion branch near the longitudinal frequency ωL to the EPL are small (&sim;10% - 30%);nevertheless, they must be taken into account to obtain quantitative agreement with experimental data. Specifically these contributions are responsible for the formation of an additional line (along with the fundamental AT line) in the case of oblique incidence of radiation.