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.     

Density Functional Theory Study on the Adsorption of CN on Transition Metal M（100） （M = Ni,Pd, Pt,Cu, Ag and Au） Surfaces

The adsorption of cyanide on the top site of a series of transition metal M（100） （M = Cu, Ag, Au, Ni, Pd, Pt） surfaces via carbon and nitrogen atoms respectively, with the CN axis perpendicular to the surface, has been studied by means of density functional theory and cluster model. Geometry, adsorption energy and vibrational frequencies have been determined, and the present calculations show that the adsorption of CN through C-end on metal surface is more favorable than that via N-end for the same surface. The vibrational frequencies of CN for C-down configuration on surface are blue-shifted with respect to the free CN, which is contrary to the change of vibrational frequencies when CN is adsorbed by N-down structure. Furthermore, the charge transfer from surface to CN causes the increase of surface work function.     

First-principles Study on the Properties of CaO(100) Surface Adsorbing Carbon Dioxide

The increasing carbon dioxide emissions have a huge impact on the global environment. Carbonation reaction of CaO is regarded as a potential method to capture carbon dioxide. The density functional theory calculations have been performed to investigate the adsorption of CO_2 on CaO(100) surface. This paper systematically studied the adsorption of CO_2 at different adsorption sites on CaO(100) surface and the influence of adsorption angle on adsorption energy. Based on the studying of adsorption sites, adsorption energy and electronic structure of the CO_2/CaO(100) systems, chemical adsorption mainly happens when CO_2 molecules are absorbed on the CaO(100) surfaces, but physical adsorption may also happen. The research found that CO_2 molecules reacted with surface O atom through C, forming monodentate surface carbonate species and tridentate carbonate. Among them, low-coordinated monodentate ligands have a higher stability than tridentate ligands due to the shorter C–OS bond length of monodentate ligands.     

Density Functional Theory Studies on the Adsorption of CO2 on Different CaO Surfaces

Carbon dioxide adsorbed on different kinds of CaO surfaces has been investigated with the help of the first principle density functional theory plane wave calculations. Various possible configurations have been considered and the calculated results showed that CO2 was strongly adsorbed by C atom bonded with the CaO （001） and （110） surfaces with adsorption energies of 1.38 and 3.22 eV, respectively. The adsorption of CO2 molecule on defect surfaces is complicated compared with that on the pristine surfaces. The adsorption energy of CO2 absorbed on the CaO（110） surface is larger than that of CaO（001） surface when the type of defect surface is the same.     

DFT Study on the Effect of Hydrogen-bond Formation on the Adsorption of Aminotriazines on Graphene

DFT calculations have been performed to explore the aminotriazine adsorption on graphene surfaces.Relative energies,equilibrium geometries and electronic structures of monomer and dimer of aminotriazine molecules adsorbed at the surface were investigated and analyzed in details.It was found that the hydrogen atoms in the NH2 group of aminotriazine molecules are directed toward the graphene surface,and the adsorption energy increases as the NH2 group is added.The adsorbed aminotriazine molecules facilely form a dimer through the hydrogen bonding interactions,and the two aromatic rings of optimized structure of 2-amino-1,3,5-triazine(B) dimmer(denoted by B2) and melamine(D) dimmer(denoted by D2) are parallel to the graphene sheet.The large deviation of the averaged adsorption energy of B2 and D2 compared to monor adsorption may reflect the increase of π-π repulsion and the effect of hydrogen bond formation.The electronic structure analyses reveal that the formation of hydrogen bonds in melamine dimer has great influence on the adsorption mode at the graphene surface.     

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.     

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.     

The Effect of the Oxygen Preadsorption on the Adsorption of Nitric Oxide on Mo (111)

The adsorption of nitric oxide adsorption on clean Mod(111), Mo(111)/O2-(4×4), Mo(111)/O2-(1×3), Mo(111)/O2-(112) facets and Mo(111) oxide surfaces was studied. Mass 28 (N2) desorption spectra show two high temperature peaks at approximate 1030 (β1) and 1200K (β2). For NO exposures less than 0. 1 L only the ft peak was observed. At higher exposures, the ft peak appeared and small amounts of N2O as well as NO desorbed. The preadsorption of oxygen blocked the β2 desorption partially on the (4×4) and (1×3) surfaces and fully on the (112) facet and oxide surfaces. In addition, the β1 desorption peak shifted to higher temperatures with increasing oxygen preexposure.     

DYNAMICS OF GAS-SURFACE INTERACTIONS:REACTION OF MOLECULAR OXYGEN WITH ADSORBED CARBON ON NICKEL

A model LEPS potential has been used to describe the interaction ofan oxygen molecule with a carbon atom adsotbed on Ni(100)surface,whichwas determined by solving the genetalized eigenvalue equation.The potentialenergy surfaces show that the O_2 approaching the Ni(100)face with O—Obond parallel to the erystal face is more profitable to the atom dissociationchemisorptions,carbon dioxide and earbon monoxide.Based on these surfaces,the quasiclassical trajectory calculations have been obtained for the molecule ofoxygen scattered by a nickel surface covered by a carbun atom.The trajectoriesillustrate the molecular dynamical characters of molecular and dissociativechemisorptions,and the CO cesorption.The probabilities of various adsorptionsare given by changing translational.viorational and rotational energies.As aresult,the rules of probability of adsorption are also discussed.     

A DFT Study of CO Adsorption on the Cu2O（111） Surface with Oxygen Vacancy

First-principles calculations based on density functional theory （DFr） and the generalized gradient approximation （GGA） have been used to study the adsorption of CO molecule on the Cu2O（111） oxygen-vacancy surface. Calculations indicate that the C-O bond is weakened upon adsorption compared with that over perfect surface. In addition, with the density increase of the defective sites, the adsorption energies of the defect-CO configuration increase whereas the C-O bond nearly remains constant.     

Density Functional Theory Study of HCN Adsorption on Small Gold Clusters

A theoretical study was carried out on the adsorption of hydrocyanic acid on small Aun （n ≤ 7） clusters using density functional methods. For HCN adsorption on gold clusters, no dependence was found with respect to the even-odd alternation in relation to the number of gold atoms in the cluster. The HCN molecule is adsorbed at simple adsorption sites （1-fold coordination）, perpendicular to the adsorption site. The largest adsorption energy is only about 74.61 kJ·mol^-1, which indicates that the HCN molecule does not decompose and the C-N bond retains triple bond, and that the C-H and C-N stretching frequencies are only weakly perturbed. The adsorbed C-N and C-H stretching frequencies are blue- and red-shifted compared with the values of free HCN, respectively.     

Spreading fully at the ice-water interface is required for high ice recrystallization inhibition activity

Although materials for ice recrystallization inhibition(IRI) are essential for the cryopreservation of cells and tissues, there exists no guiding mechanism for the design of such materials. Therefore, the construction of materials for IRI relies on the try-and-error strategy. Herein, through changing the tacticity of hydroxyl groups on poly(vinyl alcohol)(PVA) backbones with the affinities of PVAs to ice unchanged, we experimentally find IRI activity decreases significantly for isotactic PVA in comparison to that of atactic PVA. Molecular dynamics simulation shows atactic PVA spreads fully at the ice-water interface due to its much stronger interaction with water. This indicates atactic PVA can cover more ice surface and possess a higher IRI activity when the same amount of PVAs are used, which is consistent with the results that PVA can cover the same amount of ice surface more efficiently through experimentally measuring the adsorption of PVAs on the ice surface. A guiding mechanism of high active IRI materials can be obtained: only having affinity to ice is not enough to obtain high IRI activity(i.e., only small amount of materials is required to reduce the size of ice crystals to ca.(35±10) μm), IRI agents must also have high affinity to water, i.e., low interfacial energies, to both ice and water. The former is to guarantee the adsorption of the IRI agent on the ice surface, and the latter is required for the IRI agent to spread sufficiently at the ice-water interface. Therefore, each IRI molecule can effectively block the diffusion of water onto the ice surface, and consequently inhibits the growth of ice. A spreading coefficient of IRI agents is therefore introduced to quantitatively assess the capability of IRI agents to spread at the ice-water interface.     

THEORETICAL STUDY OF VARIOUS ADSORPTION STATES OF OXYGEN ON SILVER SURFACE

The various adsorption states of oxygen on different sites of silver surfaces have been studied using CNDO method. The result shows that a fairly strong, adsorption bond is formed when oxygen molecule is adsorbed, in lying down position with its axis parallel to the surface, at the surface bridge site having larger silver-silver distance. In this case, the adsorbed oxygen molecule has fairly strong tendency to dissociate. The most favorite sites on Ag(110) and Ag(111) surfaces for oxygen molecules or atoms to be adsorbed have been suggested after calculation and analysis. The differences of oxygen adsorption on these two surfaces mentioned above have been compared. The most stable adsorption states of oxygen are O_2~(2-), O~(2-) on Ag(110) and O_2~-, O~-on Ag(111). On silver film or polycrystalline silver, O_2~(2-), O_2~-, O~(2-), O~- may coexist. The results are in agreement with experiments.     

Adsorption of Pb~(2+) and Cu~(2+) with Unburned Desulphurization Slag Modified Nickel Slag

Desulphurization slag modified nickel slag adsorbent was prepared by unburned forming technology. The structure of the sample was characterized by BET,XRD,IR,SEM and EDAX. The adsorption performance of Pb~(2+) and Cu~(2+) onto the resultant adsorbent from aqueous solution was studied. Results indicated that the adsorbent possesses a network pore structure formed by the AFt and C–S–H through cross lapping; the adsorbent contains a large number of Si–OH and Al–OH functional groups. The presence of functional groups not only provides abundant adsorption sites for Pb~(2+) and Cu~(2+),but also improves the adsorption performance of Pb~(2+) and Cu~(2+) from waste water through the complexation of heavy metal ions. The result of specific surface area analysis showed that the adsorbent sample possesses mesoporous structure and the BET specific surface area is 27.15 m~2/g. The solution p H values for the adsorption of Pb~(2+) and Cu~(2+) were optimized to be 6 and 5.5,respectively. The adsorption capacities of Pb~(2+) and Cu~(2+) gradually increase,whereas the removal rates of the two metal ions decrease with increasing the initial concentration of simulated solution. The resultant adsorbent gives a higher adsorption capacity for Cu~(2+) than for Pb~(2+) in the single ion solution. However,it shows preferential adsorption of Pb~(2+) rather than that of Cu~(2+). Meanwhile,results of recyclability indicate the remarkable regeneration capacity,re-adsorption ability and reusability performance of the adsorbent sample.     

Theoretical Investigation of Hydrogen Sulfide Adsorption on the Surface of F Functionalized Carbon and Carbon Silicon Nanotubes (7,0) in the Gas Phase and Water

In order to develop a sensor for the detection of toxic H_2S molecule,the interactions of C–NT and CSi–NT with H_2S molecule were investigated by density functional theory calculations. The effects of F functionalization and water on the adsorption of H_2S gas on C–NT and CSi–NT surfaces were investigated. The studied nanotubes can interact with the H_2S molecule effectively and so adsorptions of H_2S on studied nanotubes are exothermic and possible from the energetic viewpoint. Replacing the C atoms of C–NT with Si atoms may be a good strategy for improving the sensitivity of C–NT towards H_2S. F functionalization and water cause an increase and decrease in the absolute adsorption energy(Ead) values of H_2S on the studied nanotubes,respectively. There are good linearity dependencies between Ead and orbital energy values of studied nanotubes. The Ead and orbital energy values of studied nanotubes can be considered as important parameters to propose suitable nanotubes with increased potential of H_2S adsorption.     

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, AI 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 |aboratory 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 coat-ings. 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, respective-ly, 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.     

Two-dimensional correlation analysis of continuous online in situ ATR-FTIR on the adsorption of butyl xanthate at the surface of α-PbO

The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared(ATR-FTIR) spectroscopy technique and two dimensional(2D) correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm~(-1),1033 cm~(-1) and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g~(-1) after 150 min.     

Study of CO adsorption on perfect and defective pyrite(100)surfaces by density functional theory

First-principles calculations based on density functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of CO molecule on the perfect and defective FeS 2 (100) surfaces. The defective Fe 2 S(100) surfaces are caused by sulfur deficiencies. Slab geometry and periodic boundary conditions are employed with partial relaxations of atom positions in calculations. Two molecular orientations, Cand O-down, at various distinct sites have been considered. Total energy calculations indicated that no matter on perfect or deficient surfaces, the Fe position is relatively more favored than the S site with the predicted binding energies of 120.8 kJ/mol and 140.8 kJ/mol, respectively. Moreover, CO was found to be bound to Fe atom in vertical configuration. The analysis of density of states and vibrational frequencies before and after adsorption showed clear changes of the C–O bond.     

ACCELERATED SYNTHESIS AND RELEASE OF ANGIOTENSIN II IN THE RAT BRAIN DURING ELECTROACUPUNCTURE TOLERANCE

Behaviouzal studies suggested that cerebral angiotensin Ⅱ (AⅡ) plays an important role in the development of tolerance to electroacupuncture (EA) analgesia. Observations made in this study revealed an increase in AⅡ immunoreactivity (AⅡ-it) in both CSF and brain as well as an increase in the cerebral content of AⅠ-ir in rats rendered tolerant to EA. The extracts of brain from rats receiving EA for 1h and 3h were subjected to gel filtration and the elution profile was compared with that of normal brain extract. There was a marked right shift of the AⅡ peak from the large molecule precursor to the small molecule AⅡ-ir.The latter peak showed the same retention time in HPLC system as that of AⅡ. The results suggest that the acceleration of the synthesis and release of AⅡ during s Iong-term EA stimulation might constitute one of the mechanisms for EA tolerance.