Adsorption and dissociation of NH3 on clean and hydroxylated TiO2 rutile (110) surfaces: a computational study

The adsorption and dissociation of NH(3) on the clean and hydroxylated TiO(2) rutile (110) surfaces have been investigated by the first-principles calculations. The monodentate adsorbates such as H(3)N-Ti(a), H(2)N-Ti(a), N-Ti(a), H(2)N-O(a), HN-O(a), N-O(a) and H-O(a), as well as the bidentate adsorbate, Ti-N-Ti(a) can be formed on the clean surface. It is found that the hydroxyl group enhances the adsorption of certain adsorbates on the five-fold-coordinated Ti atoms (5c-Ti), namely H(2)N-Ti(a), HN-Ti(a), N-Ti(a) and Ti-N-Ti(a). In addition, the adsorption energy increases as the number of hydroxyl groups increases. On the contrary, the opposite effect is found for those on the two-fold-coordinated O atoms (2c-O). The enhanced adsorption of NH(x) (x = 1-2) on the 5c-Ti is due to the large electronegativity of the OH group, increasing the acidity of the Ti center. This also contributes to diminish the adsorption of NH(x) (x = 1-2) on the two-fold-coordinated O atoms (2c-O) decreasing its basicity. According to potential energy profile, the NH(3) dissociation on the TiO(2) surface is endothermic and the hydroxyl group is found to lower the energetics of H(2)N-Ti(a)+H-O(a) and HN-Ti(a)+2{H-O(a)}, but slightly raise the energetic of Ti-N-Ti(a)+3{H-O(a)} compare to those on the clean surface. However, the dissociation of NH(3) is found to occur on the hydroxylated surface with an overall endothermic by 31.8 kcal/mol and requires a barrier of 37.5 kcal/mol. A comparison of NH(3) on anatase surface has been discussed. The detailed electronic analysis is also carried out to gain insights into the interaction nature between adsorbate and surface.     

Molecular orientation of CO adsorbed on clean and Al-modified Ru(0 0 0 1) surfaces

Chemisorption of CO on the bare and Al precovered Ru(0 0 0 1) surface as well as on the Al₂Ru surface alloy, was studied by means of angle-resolved photoelectron spectroscopy using unpolarised He II radiation. Whereas CO molecules stand upright on the clean Ru(0 0 0 1) surface, as deduced by applying the symmetry selection rules of photoemission, they adsorb in a tilted geometry on the Al-precovered Ru(0 0 0 1) surface. On an Al₂Ru surface alloy, produced by annealing the Al-covered Ru(0 0 0 1) surface up to 1100 K, the CO molecules are again found to stand upright, as on the clean Ru(0 0 0 1) surface. The Al atoms, incorporated into the topmost Ru layer, do not have a significant influence on the orientation of the axis of the CO molecules.     

Effect of iron and humic acid on photodegradation of some pesticides adsorbed on clay surfaces

Photochemistry studies can be helpful in assessing the environmental fate of chemicals. For this reason, the photodegradation kinetic studies of the two pesticides orthophenylphenol (OPP) and monuron, largely used in agriculture, were carried out in solid phase. The fungicide OPP and the herbicide monuron were irradiated on the clay fractions (montmorillonite and modified clays) using a suntest simulator. The phototransformation of the parent compound was followed by HPLC technique. The photodegradation process appears to follow the first order reaction. Kinetic parameters were determined and the experimental results show that the photodegradation of these substrates was enhanced in presence of K-montmorillonite, in comparison with Fe(III) exchanged montmorillonite and montmorillonite complexed with humic acid complexes. This study has shown that the iron and humic acid adsorbed on clay surfaces did not increase the degradation rate.     

Infrared study of photooxidation of nitrogen oxides and ammonia adsorbed on alumina

Changes in the IR spectra of nitrogen oxides and ammonia adsorbed on Al₂O₃ caused by UV irradiation indicate that in the presence of gaseous or liquid (–196°C) O₂ photooxidation takes place, resulting mostly in the formation of surface NO ₃ ^– ions.

---

- - , Al₂O₃, , (–196°C) NO ₃ ^– .

     

The interaction of iron pyrite with oxygen, nitrogen and nitrogen oxides: a first-principles study

Sulphide materials, in particular MoS(2), have recently received great attention from the surface science community due to their extraordinary catalytic properties. Interestingly, the chemical activity of iron pyrite (FeS(2)) (the most common sulphide mineral on Earth), and in particular its potential for catalytic applications, has not been investigated so thoroughly. In this study, we use density functional theory (DFT) to investigate the surface interactions of fundamental atmospheric components such as oxygen and nitrogen, and we have explored the adsorption and dissociation of nitrogen monoxide (NO) and nitrogen dioxide (NO(2)) on the FeS(2)(100) surface. Our results show that both those environmentally important NO(x) species chemisorb on the surface Fe sites, while the S sites are basically unreactive for all the molecular species considered in this study and even prevent NO(2) adsorption onto one of the non-equivalent Fe-Fe bridge sites of the (1 × 1)-FeS(2)(100) surface. From the calculated high barrier for NO and NO(2) direct dissociation on this surface, we can deduce that both nitrogen oxides species are adsorbed molecularly on pyrite surfaces.     

Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces

The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).     

A density-functional theory study of water on clean and hydrogen preadsorbed Rh(111) surfaces

We study the water bilayer on clean and hydrogen preadsorbed Rh(111) surfaces by means of density-functional theory with the generalized gradient approximation and the van der Waals density functional, to investigate the influence of adsorbed hydrogen on the adsorption state of water. We found that adsorbed hydrogen interacts repulsively with water through its 1b(1) and 4a(1) orbitals. The repulsion dominates at high hydrogen coverage, resulting in a hydrophobic Rh(111)-H surface.     

Influence of the nature of membrane ionogenic groups on water dissociation and electrolyte ion transport: A rotating membrane disk study

Polarization properties of electromembrane systems (EMS) consisting of a heterogeneous membrane, either the MK-41 phosphonic acid membrane or the MK-40 sulfonic acid membrane, and dilute sodium chloride solutions are investigated with the rotating membrane disk method. For the MK-41/0.01 M NaCl and MK-41/0.001 M NaCl EMS, effective ion transport numbers and partial current-voltage curves (CVC) are measured for sodium and hydrogen ions, and limiting-current densities and the diffusion-layer thickness are calculated as functions of the rotation rate of the membrane disk. With the theory of the overlimiting state of EMS, internal parameters of the systems under investigation—the diffusion-layer thickness, the space-charge distribution, and electric-field strengths in the diffusion layer and in the membrane—are calculated from experimentally obtained CVC and the dependence of effective transport numbers on current density. The catalytic influence of ionogenic groups on the dissociation rate of water is analyzed quantitatively. Partial CVC for H⁺ ions are calculated for the space-charge region in MK-40 and MK-41 membranes. Analogous CVC for bipolar membranes containing sulfonic acid and phosphonic acid groups are compared. The dissociation mechanism of water is the same in all EMS and is independent of the membrane type and the nature of the functional groups.     

Metallic nature and surface diffusion of CO adsorbed on Ru nanoparticles in aqueous media: A 13C NMR study

We report the first observation of the 13C nuclear magnetic resonance spectroscopy (NMR) of 13CO, adsorbed from 13CO saturated 0.5 M sulfuric acid solutions, onto the surfaces of commercial Ru-black nanoparticles. The 13C NMR spectra consist of a symmetrically broadened peak having a large isotropic shift as compared to CO adsorbed onto supported Ru catalysts. The variation of the spin-lattice relaxation rate follows Korringa behavior, indicating the metallic nature of adsorbed CO, in addition to varying across the spectrum in a Korringa-like manner. Motional narrowing of the NMR spectrum at higher temperatures, together with an additional contribution to the spin-lattice relaxation rate, indicate that adsorbed CO undergoes rapid diffusion on the particle surfaces. A two-band model analysis of the NMR results indicates that the CO adsorption bond is weaker on Ru as compared to either Pt or Pd. This is also supported by a reduction in the activation energy for CO diffusion on Ru vs either Pt or Pd nanoparticles.     

Surfactant adsorption on solid surfaces: recognition between heterogeneous surfaces and adsorbed surfactant aggregates

We study the possibility of the recognition of surface heterogeneities with surfactant adsorption by performing Monte Carlo simulations. It is found that when each patch size of a heterogeneous surface is capable of being commensurate with the size of aggregates adsorbed on the constituent homogeneous surfaces, the adsorption isotherm of the system will display both adsorption characteristics for each homogeneous surface. Otherwise, one or more adsorption characteristics will be spoiled or destroyed. Therefore, the adsorption isotherm of surfactants on a heterogeneous surface provides a signal of recognition.     

The nature of unsupported uranium-ruthenium bonds: a combined experimental and theoretical study

Four new uranium-ruthenium complexes, [(Tren(TMS))URu(η(5)-C(5)H(5))(CO)(2)] (9), [(Tren(DMSB))URu(η(5)-C(5)H(5))(CO)(2)] (10), [(Ts(Tolyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (11), and [(Ts(Xylyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (12) [Tren(TMS)=N(CH(2)CH(2)NSiMe(3))(3); Tren(DMSB)=N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts(Tolyl)=HC(SiMe(2)NC(6)H(4)-4-Me)(3); Ts(Xylyl)=HC(SiMe(2)NC(6)H(3)-3,5-Me(2))(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(η(5)-C(5)H(5))(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(η(5)-C(5)H(5))(3)URu(η(5)-C(5)H(5))(CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.     

Controlling the reactivity of adsorbed DNA on template surfaces

The ability to place DNA on surfaces with increased and controllable reactivity is of fundamental importance in the development of next-generation DNA and protein biochips. The present work demonstrates the ability to control both the localization of the DNA on a surface and its reactivity by a self-assembly approach that is dependent on two variables: DNA structure and surface environment. Here we utilize a two-step adsorption scheme to control the adsorption and reactivity of DNA embedded within two types of alkyl thiol monolayers (either methyl-terminated or hydroxyl-terminated). In addition, by changing the structure of the chemisorbed DNA from fully single stranded to a 50% double stranded at its side adjacent to the surface, we were able to observe a clear dependence of DNA reactivity on both the DNA structure and the type of alkyl thiol monolayer covering the surface. The adsorption and the reactivity yield of the DNA were monitored either by its ability to hybridize to a complementary target molecule or by an enzymatic reaction involving DNA phosphorylation catalyzed by the enzyme T4 polynucleotide kinase.     

Desorption of oxygen and nitrogen from iron surfaces Application of X-ray photoelectron spectroscopy to surface analysis

The patterns of desorption of oxygen and nitrogen from metal surfaces were examined and applied in the determination of gaseous elements in metal samples. The abundance of gaseous elements on metal surfaces is controlled by thermal desorption and diffusion to or from the surface. A heat treatment suitable for the separation of adsorbed gases from those in the bulk sample is discussed. Preheating of the metal samples at ca. 300 degrees in a vacuum reduces the residual adsorbates to a minimum and retards the diffusion of the gaseous elements from the bulk to the surface.     

The adsorption and dissociation of O2 on Cu low-index surfaces

The extended LEPS of O(2)-Cu single crystal plane systems is constructed by means of 5-MP (the 5-parameter Morse potential). Both the adsorption and dissociation of O(2) on Cu low-index surfaces are investigated with extended LEPS in detail. All critical characteristics of the system that we obtain, such as adsorption geometry, binding energy, eigenvalues for vibration, etc., are in good agreement with the experimental results. Our calculated results suggest there are many differences between O(2)-Cu (110) and O(2)-Pd (110) systems. On a Cu (110) surface, O(2) adsorbs in a tilted configuration and there are two lowest energy dissociation channels along the [001] and [10] directions, respectively. We speculate that the adsorption geometry of O(2) on the metal surfaces relates to the lattice constant of metal. Meanwhile, We use the concepts of the molecular dissociation limit and the surface dissociation distance to analyze again the dissociation mechanism of the O(2) on the low-index surfaces.     

A microcalorimetric study of the different states of argon and nitrogen adsorbed AT 77 K on silicalite-I and ZSM-5

The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16相似文献   

Adsorption of nonionic surfactants on cellulose surfaces: adsorbed amounts and kinetics

Kinetic and equilibrium aspects of three different poly(ethylene oxide) alkylethers (C12E5, C12E7, C14E7) near a flat cellulose surface are studied. The equilibrium adsorption isotherms look very similar for these surfactants, each showing three different regions with increasing surfactant concentration. At low surfactant content both the headgroup and the tail contribute to the adsorption. At higher surface concentrations, lateral attraction becomes prominent and leads to the formation of aggregates on the surface. The general shape of the isotherms and the magnitude of the adsorption resemble mostly those for hydrophilic surfaces, but both the ethylene oxide and the aliphatic segments determine affinity for the surface. The adsorption and desorption kinetics are strongly dependent on surfactant composition. At bulk concentrations below the CMC, the initial adsorption rate is attachment-controlled. Above the CMC, the micellar diffusion coefficient and the micellar dissociation rate play a crucial role. For the most hydrophilic surfactant, C12E7, both parameters are relatively large. In this case, the initial adsorption rate increases with increasing surfactant concentration, also above the CMC. For C12E5 and C14E7 there is no micellar contribution to the initial adsorption rate. The initial desorption kinetics are governed by monomer detachment from the surface aggregates. The desorption rate constants scale with the CMC, indicating an analogy between the surface aggregates and those formed in solution.     

Neutral and zwitterionic dopamine species adsorbed on silver surfaces: A DFT investigation of interaction mechanism

Biomolecules nondissociative adsorption on noble metals is a key process in metallic biosensors implying several questions related to the stability and orientation of such molecules. Here, the neurotransmitter dopamine (DA) adsorption on silver surface is investigated in the context of density functional theory (DFT). Two different dopamine isomers, the neutral (NDA) and zwitterionic (ZDA) species, and two different silver surfaces, Ag (110) and Ag(111), were considered. NDA shows relatively large binding energies, compared to previously studied π-π bonded systems. ZDA adsorbs even much more strongly although this species is less stable than NDA in vacuum. To elucidate the nature of the interaction between adsorbate and substrate, an electronic structure analysis was performed. Adsorbed NDA species suffers the loss of electronic charge, accompanied by a downshift of its molecular levels and the appearance of an attractive interaction of coulombic nature between adsorbate and substrate. The significant ZDA binding can be related to larger electron transfer and coupling between ZDA and Ag orbitals. Moreover, for both species, an important contribution of attractive noncovalent interactions of different degrees can be observed. The Ag substrate produces several modifications on NDA and ZDA vibrational frequencies. Noticeably relevant are the large red/blue shifts undergone by the N-H/O-H stretching bands of zwitterionic species, of up to −670/+430 cm⁻¹.     

The interaction between adsorbed OH and O2 on TiO2 surfaces

Reduced TiO₂(110) surfaces usually have OH groups as a result of H₂O dissociation at oxygen vacancy defects. Because of excess electrons due to OH adsorption, OH/TiO₂ exhibit interesting properties favorable to further O₂ or H₂O adsorption. Both O₂ and H₂O can adsorb and easily diffuse on the OH/TiO₂ surface; such behavior plays a significant role in photocatalysis, heterogeneous catalysis, electronic devices and sensors. Indeed, the processes of H₂O dissociation, O₂ and H₂O diffusion on such TiO₂ surfaces, in the presence of OH groups, are important issues in their own right. Herein, the most recent experimental and theoretical progresses in understanding the interactions between adsorbed OH groups and O₂, or H₂O, over TiO₂(110) surfaces and their implications will be reviewed.     

A combined experimental and computational study on the sulfoxidation by high-valent iron bispidine complexes

Iron-bispidine complexes are efficient catalysts for the oxidation of thioanisole to phenylmethylsulfoxide with iodosylbenzene as oxidant. With the tetradentate bispidine ligand L(1) (L(1) = 2,4-pyridyl-3,7-diazabicyclo[3.3.1]nonane)) the catalytic efficiency is smaller than with the pentadentate bispidine ligand L(2) (L(2) = 2,4-pyridyl-7-(pyridine-2-ylmethyl)-3,7-diazabicyclo[3.3.1]nonane)). Based on the redox potentials (iron complexes with L(1) are stronger oxidants than with L(2)) and known efficiencies in catalytic olefin oxidation and C-H activation reactions, the expectations were different. A DFT-based analysis is used to explain the apparent contradiction, and this is based on differences in the electronic ground states of the ferryl complexes as well as in the oxygen transfer transition states.