Adsorption Charge Transfer Research Articles

The adsorption of amantadine antiparkinsonian drug on the B24N24 and Al24N24 nanoclusters: An investigation using the density functional theory

By employing the density functional theory (DFT), the present investigation studied the adsorption of an anti-Parkinson drug called Amantadine (AM) onto the nanoclusters of B24N24 and Al24N24. Through their –NH2 group, the molecules of Amantadine interacted with the B or Al head of the AlN(BN) nanoclusters, and it was found that the change in the free Gibbs energy was –32.3 (−27.2) kcal/mol. The increased dosage of Amantadine led to weaker AM/cluster interactions, which is attributable to the steric effect. The molecule of Amantadine was subjected to electrostatic adsorption onto the nanoclusters of AlN and charge transfer adsorption onto the nanoclusters of BN. The Amantadine adsorption led to a dramatic decrease from 4.47 eV to 3.63 eV in the work function of the AlN nanoclusters. As a result, the electron field emission improved. Thus, one may use AlN nanoclusters as an Φ-type chemical sensor for the detection of Amantadine molecules. The AM adsorption onto the BN nanoclusters resulted in noticeable HOMO destabilization and decreased HOMO-LUMO energy gap from 6.84 eV to 5.67 eV. Consequently, a great increase was observed in the electrical conductivity of the BN nanoclusters. As a result, one may use BN nanoclusters as a suitable candidate for manufacturing electronic sensors with the capability of detecting Amantadine.

A local point of view of the Cu(100) → NiTPP charge transfer at the NiTPP/Cu(100) interface.

A precise understanding, at the molecular level, of the massive substrate → adsorbate charge transfer at the NiTPP/Cu(100) interface has been gained through the application of elementary symmetry arguments to the structural determination of the NiTPP adsorption site by photoelectron diffraction (PED) measurements and Amsterdam density functional calculations of the free D4h NiTPP electronic structure. In particular, the PED analysis precisely determines that, among the diverse NiTPP chemisorption sites herein considered (fourfold hollow, atop, and bridge), the fourfold hollow one is the most favorable, with the Ni atom located at 1.93 Å from the surface and at an internuclear distance of 2.66 Å from the nearest-neighbors of the substrate. The use of elementary symmetry considerations enabled us to provide a convincing modeling of the NiTPP-Cu(100) anchoring configuration and an atomistic view of the previously revealed interfacial charge transfer through the unambiguous identification of the adsorbate π* and σ* low-lying virtual orbitals, of the substrate surface atoms, and of the linear combinations of the Cu 4s atomic orbitals involved in the substrate → adsorbate charge transfer. In addition, the same considerations revealed that the experimentally reported Ni(II) → Ni(I) reduction at the interface corresponds to the fingerprint of the chemisorption site of the NiTPP on Cu(100).

Highly sensitive chemiresistive H2S gas sensor based on graphene decorated with Ag nanoparticles and charged impurities

Herein, we report a highly sensitive and selective H2S gas sensor based on graphene decorated with Ag nanoparticles (AgNPs) and charged impurities fabricated using a simple wet chemical method. Doping on as-grown chemical vapor deposited graphene was achieved by immersion in an aqueous solution of AgNO3/Fe(NO3)3 for 4min followed by the decoration with adsorbed AgNPs and charged impurities. The AgNPs utilized in this process were formed by the reduction of Ag+ ions, since the Ag+/Ag0 reduction potential is higher than that of Fe3+/Fe0.The above treatment changed the electronic properties of graphene, achieving a dramatic resistivity change in the presence of H2S gas by generating surface sites for its adsorption and dissociation and thus allowing real time H2S level monitoring at ambient temperature with an immediate response.Doped graphene was demonstrated to selectively and repeatedly sense H2S gas within six minutes, with the limit of detection being below 100ppb. The corresponding mechanism is believed to feature a charge carrier density change of graphene to adsorbate charge transfer, with the sensor surface trapping or releasing electrons upon exposure to H2S gas.

Electric Field Effect on Condensed-Phase Molecular Systems. III. The Origin of the Field-Induced Change in the Vibrational Frequency of Adsorbed CO on Pt(111)

The effect of an external electric field on the C–O stretch frequency, ν(C–O), of carbon monoxide was studied for CO in different environments of condensed molecular films: (I) chemisorbed CO on Pt(111) covered with amorphous solid water (ASW), (II) CO trapped in an ASW matrix, (III) chemisorbed CO on Pt(111) covered with solid Ar, and (IV) CO trapped in a solid Ar matrix. Changes in ν(C–O) of these samples under an electric field were measured to investigate the Stark frequency shift and the effect of metal–adsorbate charge transfer on the frequency change. The electric field was applied up to 4.3 × 108 V·m–1 using the ice film capacitor method. Reflection absorption infrared spectroscopy was used to monitor the spectral changes of the ν(C–O) band. The Stark shift was measured from the ν(C–O) change of isolated CO in the ASW matrix under the field. The effect of metal–adsorbate charge transfer was estimated for chemisorbed CO by measuring the ν(C–O) shift under the field and subtracting the electrostatic...

Photochemical Outcomes of Adsorbed Oxygen: Desorption, Dissociation, and Passivation by Coadsorbed Water

A mixed Fe + Cr oxide surface was used to explore the photochemical fate of adsorbed O2 under ultra-high-vacuum conditions. The mixed oxide surface possessed a magnetite-like (111) structure based on low-energy electron diffraction, with its chemical behavior resembling that of Fe3O4(111). Oxygen adsorption at 40 K resulted in two chemisorption states, a strongly bound form desorbing in temperature-programmed desorption (TPD) at 230 K and a weakly bound form evolving at 100 K. The former was assigned to charge transfer adsorption at Fe2+ sites and the latter to electrostatic binding at Fe3+ sites. A minority state was also detected at ∼160 K and tentatively assigned to adsorption at Cr3+ sites. The 230 K O2 state was the focus of photochemical studies employing four wavelengths of light from the red to the UV. Irrespective of wavelength, O2 molecules in the 230 K state preferentially photodesorbed when irradiated, with comparable rates across the visible and an order of magnitude higher in the UV. Approxi...

Density functional theory screening of gas-treatment strategies for stabilization of high energy-density lithium metal anodes

To explore the potential of molecular gas treatment of freshly cut lithium foils in non-electrolyte-based passivation of high-energy-density Li anodes, density functional theory (DFT) has been used to study the decomposition of molecular gases on metallic lithium surfaces. By combining DFT geometry optimization and Molecular Dynamics, the effects of atmospheric (N2, O2, CO2) and hazardous (F2, SO2) gas decomposition on Li(bcc) (100), (110), and (111) surfaces on relative surface energies, work functions, and emerging electronic and elastic properties are investigated.The simulations suggest that exposure to different molecular gases can be used to induce and control reconstructions of the metal Li surface and substantial changes (up to over 1 eV) in the work function of the passivated system. Contrary to the other considered gases, which form metallic adlayers, SO2 treatment emerges as the most effective in creating an insulating passivation layer for dosages ≤1 mono-layer. The substantial Li → adsorbate charge transfer and adlayer relaxation produce marked elastic stiffening of the interface, with the smallest change shown by nitrogen-treated adlayers.

Assessing carbon-based anodes for lithium-ion batteries: a universal description of charge-transfer binding.

Many key performance characteristics of carbon-based lithium-ion battery anodes are largely determined by the strength of binding between lithium (Li) and sp(2) carbon (C), which can vary significantly with subtle changes in substrate structure, chemistry, and morphology. Here, we use density functional theory calculations to investigate the interactions of Li with a wide variety of sp(2) C substrates, including pristine, defective, and strained graphene, planar C clusters, nanotubes, C edges, and multilayer stacks. In almost all cases, we find a universal linear relation between the Li-C binding energy and the work required to fill previously unoccupied electronic states within the substrate. This suggests that Li capacity is predominantly determined by two key factors-namely, intrinsic quantum capacitance limitations and the absolute placement of the Fermi level. This simple descriptor allows for straightforward prediction of the Li-C binding energy and related battery characteristics in candidate C materials based solely on the substrate electronic structure. It further suggests specific guidelines for designing more effective C-based anodes. The method should be broadly applicable to charge-transfer adsorption on planar substrates, and provides a phenomenological connection to established principles in supercapacitor and catalyst design.

The Role of Reducible Oxide–Metal Cluster Charge Transfer in Catalytic Processes: New Insights on the Catalytic Mechanism of CO Oxidation on Au/TiO2 from ab Initio Molecular Dynamics

To probe metal particle/reducible oxide interactions density functional theory based ab initio molecular dynamics studies were performed on a prototypical metal cluster (Au20) supported on reducible oxides (rutile TiO2(110)) to implicitly account for finite temperature effects and the role of excess surface charge in the metal oxide. It is found that the charge state of the Au particle is negative in a reducing chemical environment whereas in the presence of oxidizing species coadsorbed to the oxide surface the cluster obtained a net positive charge. In the context of the well-known CO oxidation reaction, charge transfer facilitates the plasticization of Au20, which allows for a strong adsorbate induced surface reconstruction upon addition of CO leading to the formation of mobile Au-CO species on the surface. The charging/discharging of the cluster during the catalytic cycle of CO oxidation enhances and controls the amount of O2 adsorbed at oxide/cluster interface and strongly influences the energetics of all redox steps in catalytic conversions. A detailed comparison of the current findings with previous studies is presented, and generalities about the role of surface-adsorbate charge transfer for metal cluster/reducible oxide interactions are discussed.

Electrochemical Characterization of UNS N08367 and UNS S31603 Alloys in Presence of Chloride and Bromide Solutions

This work presents the interfacial characterization of two UNS corrosion resistance alloys (CRAs), N08367 and S31603 in LiCl and LiBr solutions. The electrochemical nature of these materials in halide solutions demonstrates different mechanisms at the substrate-electrolyte interface. Time and frequency domain electrochemical techniques were used; cyclic polarization tests showed that S31603 was attacked by pitting corrosion for different LiCl and LiBr concentrations. N08367 revealed different mechanisms due to the passivation layer existed under polarization conditions. The current densities increments for the N08367 alloy were attributed to the charge transfer-adsorption mechanism, as evidenced by the EIS data. The pitting potentials of S31603 in LiCl and LiBr solutions were similar. However, the current transients were only found in S31603 in LiCl which might indicate that LiCl had more significant kinetic effect than LiBr. Bias potential was applied for EIS testing to support either active/passive/transpassive behavior for each material. Qualitative analysis could demonstrate the link between EIS and polarization techniques.

Detailing Ionosorption over TiO2, ZrO2, and HfO2 from First Principles

Identifying the principles of surface to adsorbate charge transfer is key to a better understanding of metal oxide materials as both catalysts and gas sensors. The mechanism responsible for gas sen...

Tuning of Charge Densities in Graphene by Molecule Doping

AbstractThe tuning of carrier concentrations in graphene is at the heart of graphene‐based nanoelectronic and optoelectronic applications. Molecular doping, that is, taking charges from the adsorbed molecules, shows promise as a means by which to change carrier density in graphene while retaining relative high mobility. However, poor control over doping concentrations is a major obstacle to practical applications. Here, we show that lattice disorders induced by plasma exposure can be used as anchor groups. These groups serve as centers of molecule adsorption and facilitate orbital overlap between graphene and adsorbates (melamine), thus allowing for selective and tunable doping. The carrier concentration revealed by Raman shift can be progressively adjusted up to 1.4 × 1013 cm−2, depending on the coverage of melamine molecules and doping temperature. The electronic band structures of the graphene–melamine complex were calculated using density functional theory for adsorption over ideal graphene and over non‐ideal graphene with Stone–Wales (5–7‐7–5) defects. It is shown that charge transfer for adsorption on ideal graphene is negligible, while adsorption on graphene with Stone–Wales defects results in weak hole doping, which is consistent with the progressive increase of carrier density with increasing melamine coverage.

DFT study of isocyanate chemisorption on Cu(100): Correlation between substrate–adsorbate charge transfer and intermolecular interactions

The adsorption of isocyanate (−NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole–dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100).

The Role of Metal Contact in the Sensitivity of Single-Walled Carbon Nanotubes to NO2

The interaction of NO2 with single-walled C nanotubes and highly oriented pyrolitic graphite was studied at different temperatures by using high-energy resolution core level photoemission spectroscopy. During NO2 uptake below 200 K, the C1s peak exhibits a similar behavior for the two samples and correspondent NOx (x = 1−3) adspecies form on the surface of nanotubes and graphite. These results indicate the occurrence of equivalent chemical reactions and of comparable charge transfer from the flat and curved C lattice to the oxidizing adsorbates. Starting from 200 K, no NO2 adsorption onand therefore no interaction withC nanotubes takes place. This excludes the possibility that any tube−adsorbate charge transfer influencing the nanotube conductivity occurs above this temperature. However, at 200 K NO2 strongly interacts with Rh nanoclusters dispersed among the C nanotube bundles. The increased work function of the oxidized Rh changes the alignment of the nanotube bands and simulates an efficient hole dopin...

Surface-enhanced Raman scattering and adsorption studies of morphine on silver island film

In this work, surface-enhanced Raman spectroscopy (SERS), infrared adsorption (IR), normal Raman (NR) scattering as well as density functional theory (DFT) computational methods have been employed to investigate the adsorption and orientation of morphine on silver surface. The structure of morphine and its vibrational spectra were determined at B3LYP/6-31G(d) level, and the results were used in the assignment of the vibrational spectra. The calculated data showed fairly good agreement with both corresponding experimentally observed spectra. These results, along with the application of surface selection rules of SERS, suggest that the molecules had a charge transfer adsorption on Ag island film and both planes of its ‘T’ type structure had a rather perpendicular orientation to the substrate mainly via the lone-pair electrons of the oxygens.

DFT-Based Characterization of the Multiple Adsorption Modes of Nitrogen Oxides on Pt(111)

Pt is the most common catalyst for NO oxidation to NO2, a key reaction in NOx remediation chemistry. In this work, density functional theory calculations and plane-wave supercell models are used to calculate the energies, charge distributions, and vibrational spectra of the stable and metastable states of adsorbed NO, NO2, and NO3 on Pt(111), the most likely active metal face for this catalytic oxidation. NO, NO2, and NO3 are all strong electron acceptors and bind to the Pt(111) surface via charge donation from the surface. NO and NO2, in particular, exhibit a variety of adsorption geometries, the most favorable at low coverage being those that maximize surface−adsorbate charge transfer through binding to multiple surface Pt. At low coverage, the order of binding energies is NO > NO3> NO2, and the oxidation of adsorbed NO to NO2 is endothermic by 0.78 eV. Higher surface coverages favor migration of NO and NO2 to lower-coordination surface sites due to competition for metal d charge density. These changes in surface binding configurations, along with the general decrease in surface−adsorbate bond energies associated with higher surface coverages, both tend to energetically promote NO conversion to NO2 and are important in describing this catalytic chemistry.

ADSORPTION KINETICS OF POTASSIUM ON SrTiO3(100)

In this paper, we study the kinetics of potassium adsorption on SrTiO 3(100) surface at room temperature. The study took place in UHV using AES, EELS, LEED, TPD, and WF measurements. Potassium grows in two-dimensional islands with maximum coverage of 3.9 × 1014 at/cm2. During adsorption charge transfer from the K -4s to Ti -3d energy level has been observed. No K – O compound has been measured. After heating at 1050 K most of the adsorbed potassium desorbs and the SrTiO 3(100) (1 × 1) LEED pattern reappears. There is not any indication of potassium intercalation into the substrate, either at room or at elevated temperature.

Role of Defects in Single-Walled Carbon Nanotube Chemical Sensors

We explore the electronic response of single-walled carbon nanotubes (SWNT) to trace levels of chemical vapors. We find adsorption at defect sites produces a large electronic response that dominates the SWNT capacitance and conductance sensitivity. This large response results from increased adsorbate binding energy and charge transfer at defect sites. Finally, we demonstrate controlled introduction of oxidation defects can be used to enhance sensitivity of a SWNT network sensor to a variety of chemical vapors.

Surface projected electronic band structure and adsorbate charge transfer dynamics: Ar adsorbed on Cu(1 1 1) and Cu(1 0 0)

The influence of the surface projected electronic structure on resonant charge transfer is investigated on the Cu(1 1 1) and Cu(1 0 0) surfaces using core hole clock spectroscopy and wave packet propagation computations. The charge transfer time of core excited Ar ( 2 p 3 / 2 5 4 s 1 ) adsorbed in a dense Ar monolayer is 5.6 ± 0.1 fs and 3.5 ± 0.1 fs for the Cu(1 1 1) and Cu(1 0 0) surfaces. A two times longer residence time on Cu(1 1 1) than on Cu(1 0 0) is also obtained from theory and is attributed to the differences in the projected electronic band structure of the two metal surfaces, especially to the different energies of the surface projected band gap.

Mechanism for NO2 Charging on Metal Supported MgO

NO2 adsorbed on MgO(100) supported by Ag or Pt is explored by density functional theory calculations. NO2 is weakly adsorbed on MgO(100), with a bond involving minor oxide to adsorbate charge transfer. However, if MgO is supported, then the adsorption energy is considerably enhanced and NO2 is adsorbed as a nitrite (N). Analysis reveals that the NO2 excess charge originates from the oxide side of the oxide/metal interface and that the electron abstraction increases the oxide/metal adhesion. The proposed mechanism is general and should apply for oxidizing surface species.

Hydrogen/anion electrosorption at rhodized electrodes as revealed by electrochemical impedance spectroscopy

Electrosorption properties of rhodized electrodes in H 2SO 4 and HClO 4 electrolyte solutions, with and without small concentration of added chloride and (bi)sulphate anions, are investigated by use of the electrochemical impedance spectroscopy. Potentials between the threshold of the hydrogen evolution and initial stage of (oxy)hydroxide formation are applied. Kinetic contributions of hydrogen under-potential deposition (UPD) are over restricted and adsorption of chloride and (bi)sulphate anions over almost whole potential region is clearly marked by present impedance spectra. Added anions, as well as products formed by decomposition of perchlorate ions from HClO 4 electrolyte solution, influenced kinetics of the hydrogen UPD at the rhodized electrode. Adsorption of (bi)sulphate ions from H 2SO 4 electrolyte solution is not detected directly as a kinetic process, but is indicated through increased apparent double-layer capacitance values. Theoretical equation for the frequency dependence of adsorption impedance is derived on the basis of (partial) charge transfer adsorption of ions, the state variable approach, and concept of two-step adsorption. The derived equation is found to be adequate for fitting impedance spectra in the hydrogen/anion transition region. Values of impedance parameters and their potential dependences are discussed and compared to already published data on similar electrodes, including low-index rhodium and platinum single-crystal electrodes.