Model For Coadsorption Research Articles

Insights into performance enhancement mechanism of GaAs(100) photocathode by Cs/Li/O and Cs/Li/NF3 co-deposition

To verify the effects of additional Li introduction on the Cs-O and Cs-NF3 activation processes of GaAs(100) photocathodes, Cs-Li-O and Cs-Li-NF3 co-adsorption models of GaAs(100) β2(2 × 4) surfaces with different Cs/Li ratios are investigated, on the basis of pristine Cs-O and Cs-NF3 adsorption models. Residual gases including CO2, H2O, CO and H2 are introduced to the Cs-Li-O and Cs-Li-NF3 co-adsorption models to compare the damaging effects of typical residual gases. Simulation results show that the optimal Cs/Li ratio is 3:1, wherein 6Cs-2Li-1NF3 surface model exhibits smaller work function and 6Cs-2Li-1O surface model has better immunity to residual gases. Meanwhile, 6Cs-2Li-1O surface has better resistance abilities to CO2, CO and H2 than 6Cs-1O surface, while the resistances of 6Cs-2Li-1NF3 surface to H2O, CO and H2 are worse than those of 6Cs-1NF3 surface. From the perspective of charge transfer, a reverse dipole moment [Cs/Li-gas] and two positive dipole moments, i.e., [Cs/Li-surface] and [Cs/Li-O/NF3] are formed. Therefore, it is inferred that, the Cs-Li-O activation recipe, in comparison to the Cs-O activation recipe, can improve the photoemission stability of GaAs photocathodes, whereas the Cs-Li-NF3 activation recipe can increase quantum efficiency but is more sensitive to residual gases.

Cs/O co-adsorption on C-doped GaAs surface: From first-principles simulation to experiment

C-doped GaAs is considered a potential material for negative electron affinity photocathodes, where the p-type doped property is beneficial to photoemission. To clarify the stability and efficiency during Cs/O activation, the gradient concentration of Cs adsorption and Cs/O co-adsorption models of C-doped GaAs are established. The work function, adsorption energy, and surface dipole moment are intensified by first principles calculation based on density functional theory. Experimental results demonstrate that Cs/O activation effectively enhances the performance of C-doped GaAs photocathodes, resulting in high levels of quantum efficiency. Therefore, we conclude that C-doped GaAs photocathodes have the potential to significantly improve the photoelectric emission performance and stability of GaAs photocathodes, making them a viable candidate for future applications.

Interfacial Adsorption Mechanism of Diethyldithiocarbamate in High-Sulfur Residue Flotation

Diethyldithiocarbamate (DDTC) is employed in the sulfide ore flotation process due to its excellent collection performance. Herein, we investigated the interfacial adsorption behavior of DDTC on the four main mineral phases of high-sulfur residue: sulfur, pyrite, sphalerite, and lead sulfate. The adsorption behavior of DDTC and H2O, namely, the adsorption structure and the energy and electron localization function cross section, were explored using density function theory calculation. The results were helpful in constructing a coadsorption model of DDTC and H2O, which was validated by pure mineral flotation and characterization of Fourier transform infrared spectra. The coadsorption model indicated that the adsorption of DDTC on sulfur, sphalerite, and lead sulfate was weak with physical bonding, while its adsorption on pyrite was strong with chemical bonding. Practical bench-scale high-sulfur residue flotation was performed, and the result was different from that obtained from pure mineral flotation. Our developed model predictions and mineral fugacity pattern analysis were synergistically used to explain this difference. Overall, this work proposes for the first time a coadsorption model of DDTC and H2O and provides important insights into interfacial adsorption in high-sulfur residue flotation.

Chemical cleaning of oxides on GaAs (0 0 1) surface: A theoretical research

In this study, solid–liquid interaction models of 40 % HF, 40 % HCl, 40 % H2SO4, H2O on Ga2O3 and As2O3 adsorbed GaAs (001) β2(2 × 4) surface were built, using mean square displacement (MSD) results calculated by molecular dynamics methods, the cleaning ability of three solutions and water on Ga2O3 and As2O3 was researched. The co-adsorption models of solution molecules and oxides on GaAs (001) β2(2 × 4) were constructed, and the chemical cleaning mechanism was studied through the first-principles method. Electron density difference was used to analyze the charge transferring between solution molecules and oxides adsorbed surface. Valence band maximum(VBM), conduction band minimum (CBM) of the surface, highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of solution molecules and oxides were used to analyze the electron transfer mechanism. Mulliken bond population and bond length were used to analyze the desorbing ability of solution molecular.

Ab Initio Studies of Work Function Changes of CO Adsorption on Clean and Pd-Doped ZnGa2O4(111) Surfaces for Gas Sensors

We performed first-principles calculations to study the adsorption of the CO molecules on both clean and Pd-doped ZnGa2O4(111) surfaces. The adsorption reaction and work function of the CO adsorption models were examined. The CO molecules on the clean and Pd-doped ZnGa2O4(111) surfaces exhibit maximum work function changes of −0.55 eV and −0.79 eV, respectively. The work function change of Pd-doped ZnGa2O4(111) for detecting CO is 1.43 times higher than that of the clean ZnGa2O4(111). In addition, the adsorption energy is also significantly reduced from −1.88 eV to −3.36 eV without and with Pd atoms, respectively. The results demonstrate ZnGa2O4-based gas sensors doped by palladium can improve the sensitivity of detecting CO molecules.

The roles of Cl− and OH− in the dissociation of H2O molecules on an Al surface: A first-principles calculation

Previous work has confirmed that O2 can promote the dissociation of H2O, but the effect of OH− on the dissociation of H2O is not clear, and the synergistic effect of Cl− in the dissociation process is also worthy of study. In this work, we have systematically studied the roles of Cl− and OH− in the process of H2O dissociation on an Al surface through first-principles calculations. Several typical H2O and OH− co-adsorption models have been designed, and the conditions of OH−-induced H2O dissociation are discussed. By comparing models without Cl− and with pre-adsorbed Cl−, the dissociation mechanism of H2O molecules can be well explained in terms of the ratio of the reaction energy to the binding energy of the adsorbate. Based on electronic structure analysis, we surmise that Cl− plays a catalytic role in H2O dissociation on an Al surface, even though it does not directly participate in the dissociation reaction.

Prediction of structural and electronic properties of Cl2 adsorbed on TiO2(100) surface with C or CO in fluidized chlorination process: A first-principles study

Based on the first-principles calculations of density functional theory, co-adsorption models of C or CO with Cl2 on rutile TiO2 (100) surface were established. The adsorption structures and electronic properties during chlorination process were predicted. Then, the adsorption energy, charge density, electron density difference and density of state of the adsorption structures were calculated and analyzed. The stabilities of the adsorption structures and the charge distributions between atoms were studied. It was found that both C and CO could promote the adsorption reactions of Cl2 on TiO2 (100) surface, and C was more favorable to the adsorption process. The results show that the adsorption process of Cl2 on TiO2(100) surface was physisorption, and the co-adsorption processes of C or CO with Cl2 on TiO2(100) surface were chemisorptions.

Prediction of Structural and Electronic Properties of C and Cl2 Adsorbed on the Rutile TiO2 (110) Surface.

The study of the adsorption mechanism of C and Cl2 on the TiO2 (110) surface is of great significance for the formulation of the technological parameters in the fluidized chlorination process. Based on the first-principles calculations of density functional theory, the co-adsorption models of C and Cl2 on the rutile TiO2 (110) surface under different ratios were established. The adsorption structure, adsorption energy, charge density, and density of states were calculated and analyzed to reveal the reaction mechanism of C and Cl2 adsorbed on the rutile TiO2 (110) surface under different ratios. The results showed that with the increase of the ratio of C atoms in the reaction process, the complete adsorption possibility of Cl atoms on the surface of TiO2 (110) increased. Both Ti6c and C atoms were electron providers, while O3c and O2c were electron acceptors. The bonding interactions between C and O2c or C and Cl atoms were stronger, and the stabilities were higher. When C bonded with O2c and two Cl atoms, respectively, the overlapping peak width of C and O2c atoms was greater at the high energy level, and the electron delocalization was enhanced, and more electrons were transferred around the two Cl atoms. When C bonded with O2c and one Cl atom, respectively, the electron activity at the low energy level was higher, and the stability of the chemical bond was lower.

A Monolayer Composite of h-BN Doped by a Nano Graphene Domain: As Sensitive Material for SO2 Gas Detection

The development of two-dimensional materials with gas-sensitive properties has been a research focus in the field of materials science. Considering the excellent properties of graphene and hexagonal boron nitride, a monolayer composite is put forward and its potential for gas sensing has been investigated by density functional theory. Compared to common gases in the atmosphere and three other toxic gases, sulfur dioxide tends to have a strong mutual effect with this composite. Together with electronic analyses, it is proved that the composite presents excellent sensitivity toward sulfur dioxide molecules and the conductivity can be used as a vital parameter to diagnose the status of gas sensor. What’s more, a co-adsorption model demonstrates a favorable performance in high moisture working environment. Thus, we can reasonably draw the conclusion that the presented composite could be an eligible candidate for sulfur dioxide gas detection.

Research on flotation mechanism of wolframite activated by Pb(II) in neutral solution

Hydration models of wolframite, lead ions, benzo hydroxamic acid ions (BHA), and their co-adsorption models were created to simulate the adsorption processes using the density functional theory (DFT). Pure minerals flotation tests, analysis of reagent adsorption capacity and infrared spectrum of products were carried out. The results indicate that the mechanism of Pb(II) activation in BHA flotation of wolframite in a neutral solution environment was probably due to the traction from Pb(II) on the H2Os around the site of the manganese on the wolframite surface reduced the hydration, making them more easily adsorbed by BHA. Therefore, the activation of Pb(II) on BHA adsorption is indirect.

Application of a co-adsorption model for the design of CIL/CIP circuits

ABSTRACTOne of the main problems in the design of carbon adsorption circuits for the processing of high silver gold ores is that the commonly used gold adsorption models are unable to replicate the frequently observed displacement of silver on carbon by gold in the first contactors of carbon-in-pulp/carbon-in-leach (CIP/CIL) trains operating with high metal loadings on carbon and high silver gold ratios.A model has been developed by Curtin University’s Gold Technology Group to simulate the competitive co-adsorption of gold and silver by activated carbon. The model utilises multi-component equilibrium isotherms and film-diffusion rate equations to describe the adsorption of gold and silver onto activated carbon. The model has been validated using laboratory and plant data.Case studies are presented to demonstrate the application of the model for the design of a greenfield project processing a gold/silver ore.

Computational Modeling of Copper Deposition in through Silicon Via Structures

Copper electrodeposition is critical to integrated circuit manufacturing, ranging in scale from nanometer features in damascene plating to micrometer scale through-silicon via structures and even millimeter scale printed circuit board fabrication. Essential to this technology is electrodeposition of void-free copper in high aspect ratio cavities, which is achieved through various additives that enable bottom-up filling. In through-silicon-via structures, void-free filling can be realized with micro-to-milli molar concentrations of polyether suppressor and chloride additives. A variety of analytical measurements have shown chloride adsorption on copper is a necessary precursor to formation of a polyether blocking layer to suppress deposition. In this study, experimental measurements and computational models are presented exploring the dynamics of polyether and chloride adsorption during copper deposition. Microelectrode measurements eliminate solution iR effects, while demonstrating comparable results to rotating disk electrode systems at equivalent transport conditions. A two-additive co-adsorption model for polyether and chloride is presented, comparing simulations to experimental feature filling at conditions when chloride transport is limiting formation of the inhibiting ad-layer (< 80 μmol/L). Suppression breakdown is related to the local polyether coverage, which is in turn limited by the chloride coverage on the depositing interface. A passive-active transition of copper deposition is associated with limited flux of chloride in the feature. At higher chloride concentrations (≥ 80 μmol/L), sidewall breakdown during deposition occurs nearer to the bottom of the via, followed by a shift to bottom-up growth.

Cs and Cs-O co-adsorption on Zn-doped GaAs nanowire surfaces: A first-principles calculations

The Cs-only and CsO co-adsorption process of Zn-doped GaAs nanowire surface with negative electron affinity are investigated utilizing the first-principles calculations based on density function theory. The 1Cs, 2Cs, 3Cs and 4Cs adsorption models are built to simulate the process of Cs-only adsorption, while 3Cs/1O, 3Cs/2O and 3Cs/3O models are established to study CsO co-adsorption process. The adsorption energy, work function, Mulliken charge distribution and dipole moment for each adsorption model are discussed, respectively. During the Cs-only adsorption process, as increasing Cs coverage, the adsorption energy increases accordingly, indicating that the stability of Cs-only adsorption model is gradually weakened. After O adsorption on Cs-covered GaAs nanowire surface, the reduction of adsorption energy means that O incorporation can make the surface adsorption structure more stable. For Cs-only adsorption models, the work function obviously decreases owing to first dipole moment induced by Cs. However, excessive Cs adsorption on the Zn-doped nanowire surface will result in the ‘Cs-kill’ phenomenon. After O atom incorporation, the work function of Cs-covered nanowire surface further decrease, owing to the dual-dipole caused by Cs, O adatoms and nanowire surface atoms. The lowest work function can be obtained for 2O co-adsorption model, indicating the optimized atomic ratio of Cs/O is 3:2. These calculations provide an attempt to explore the adsorption mechanism of CsO on nanowire surfaces, and the results are expected to be verified by the experimental results in the future.

Effect of Chloride Concentration on Copper Deposition in Through Silicon Vias

Bottom-up Cu deposition in metallized through silicon vias (TSV) depends on a co-adsorbed polyether–Cl− suppressor layer that selectively breaks down within recessed surface features. This work explores Cu deposition when formation of the suppressor blocking layer is limited by the flux of Cl−. This constraint leads to a transition from passive surfaces to active deposition partway down the via sidewall due to coupling between suppressor formation and breakdown as well as surface topography. The impact of Cl− concentration and hydrodynamics on the formation of the suppressor surface phase and its potential-dependent breakdown is examined. The onset of suppression breakdown is related to the local Cl− coverage as determined by the adsorption isotherm or transport limited flux. A two-additive co-adsorption model is presented that correlates the voltammetric potential of suppression breakdown with the depth of the passive-active transition during TSV filling under conditions of transport limited flux and incorporation of Cl−. The utility of potential waveforms to optimize the feature filling process is demonstrated. At higher Cl− concentrations (≥80 μmol/L), sidewall breakdown during Cu deposition occurs near the bottom of the via followed by a shift to bottom-up growth like that seen at higher Cl− concentrations.

Interactions of Oxygen and Water Molecules with Pyrite Surface: A New Insight.

Pyrite is the most common sulfide in nature, and it is well-known for its roles in acid mine drainage, flotation separation of useful metal (Cu, Pb, Zn, and Mo) sulfide minerals, optoelectronic and photovoltaic application, pneumoconiosis, and even in the origin of life. However, the detailed oxidation behaviors of pyrite are still unclear and not well-understood. New oxidation pathways by O2 on the pyrite (100) surface have been found in this work for the first time using density functional theory simulation; that is, besides Fe sites, S sites are also possible oxidation sites in the initial oxidation state of pyrite, where easier and stronger oxidation may occur. This is the first time to confirm the other researchers' conjecture on the direct oxidation of S sites, which explains the isotopic composition experiments that a minor amount of O2 is permanently incorporated into SO42- during pyrite oxidation (O in SO42- is mainly derived from water). We constructed various H2O-O2 coadsorption models on the pyrite surface by considering the adsorption sequence of H2O and O2. It is found that the H2O molecule undergoes step-wise dissociation in the presence of the O2 molecule. Hydroxyl radical •OH is the reactive oxygen species during H2O dissociation. Cyclic voltammetric measurements confirm the presence of •OH. In addition, H2O2 may also be formed on the surface in terms of H2O-then-O2 sequence adsorption.

Ab Initio Prediction of Adsorption Isotherms for Gas Mixtures by Grand Canonical Monte Carlo Simulations on a Lattice of Sites.

Gibbs free energies of adsorption on individual sites and the lateral (adsorbate-adsorbate) interaction energies are obtained from quantum chemical ab initio methods and molecular statistics. They define a Grand Canonical Monte Carlo (GCMC) Hamiltonian for simulations of gas mixtures on a lattice of adsorption sites. Coadsorption of CO2 and CH4 at Mg2+ sites in the pores of the metal-organic framework CPO-27-Mg (Mg-MOF-74) is studied as an example. Simulations with different approximations as made in widely used coadsorption models such as the ideal adsorbed solution theory (IAST) show their limitations in describing adsorption selectivities for binary mixtures.

Structural Changes in Self-Catalyzed Adsorption of Carbon Monoxide on 1,4-Phenylene Diisocyanide Modified Au(111)

The self-accelerated adsorption of CO on 1,4-phenylene diisocyanide (PDI)-derived oligomers on Au(111) is explored by reflection–absorption infrared spectroscopy and scanning tunneling microscopy. PDI incorporates gold adatoms from the Au(111) surface to form one-dimensional −(Au–PDI)n– chains that can also connect between gold nanoparticles on mica to form a conductive pathway between them. CO adsorption occurs in two stages; it first adsorbs adjacent to the oligomers that move to optimize CO adsorption. Further CO exposure induces PDI decoordination to form Au–PDI adatom complexes thereby causing the conductivity of a PDI-linked gold nanoparticle array on mica to decrease to act as a chemically drive molecular switch. This simple system enables the adsorption process to be explored in detail. DFT calculations reveal that both the −(Au–PDI)n– oligomer chain and the Au–PDI adatom complex are stabilized by coadsorbed CO. A kinetic “foot-in-the-door” model is proposed in which fluctuations in PDI coordination allow CO to diffuse into the gap between gold adatoms to prevent the PDI from reattaching, thereby allowing additional CO to adsorb, to provide kinetic model for allosteric CO adsorption on PDI-covered gold.

Strong resistance of citrate anions on metal nanoparticles to desorption under thiol functionalization.

Thiols are widely utilized to functionalize metal nanoparticles, including ubiquitous citrate-stabilized gold nanoparticles (AuNPs), for fundamental studies and biomedical applications. For more than two decades, citrate-to-thiol ligand exchange has been used to introduce functionality to AuNPs in the 5-100 nm size regime. Contrary to conventional assumptions about the completion of ligand exchange processes and formation of a uniform self-assembled monolayer (SAM) on the NP surface, coadsorption of thiols with preadsorbed citrates as a mixed layer on AuNPs is demonstrated. Hydrogen bonding between carboxyl moieties primarily is attributed to the strong adsorption of citrate, leading to the formation of a stabilized network that is challenging to displace. In these studies, adsorbed citrates, probed by Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) analyses, remain on the surface following thiol addition to the AuNPs, whereas acetoacetate anions are desorbed. XPS quantitative analysis indicates that the surface density of alkyl and aryl thiolates for AuNPs with an average diameter of ∼40 nm is 50-65% of the value of a close-packed SAM on Au(111). We present a detailed citrate/thiolate coadsorption model that describes this final mixed surface composition. Intermolecular interactions between weakly coordinated oxyanions, such as polyprotic carboxylic acids, can lead to enhanced stability of the metal-ligand interactions, and this needs to be considered in the surface modification of metal nanoparticles by thiols or other anchor groups.

Acetaldehyde and acetic acid adsorption on TiO2 under dry and humid conditions

Adsorption plays a key role in the volatile organic compound (VOC) photocatalytic oxidation performance and kinetic behavior. It can lead to VOC mixture sequential treatment or even photocatalyst deactivation. The aim of this work is to determine qualitative and quantitative data regarding VOC adsorption on P25 TiO2. Acetaldehyde and acetic acid adsorption on TiO2 have been studied under both dry and humid conditions. Three experimental methods have been used: breakthrough curves, room temperature desorptions and temperature-programmed desorptions. First, acetaldehyde and acetic acid adsorptions are studied individually. Dry and humid experiments provide complementary pieces of information to identify the adsorption modes, in accordance with literature. The Langmuir model parameters (adsorption constant (K), reversible and irreversible maximum adsorbed amounts (qm,rev and qm,irr), and adsorption enthalpy ΔH) are determined for each VOC. Based on experimental results, a model for acetaldehyde and water co-adsorption is proposed, taking into account the specific interaction between acetaldehyde and water molecule. Regarding acetic acid, a reactive adsorption pathway is proposed and a kinetic model is developed to describe the reactive adsorption. Finally, in order to understand multi-VOC interaction on TiO2 surface, the sequential adsorption of acetaldehyde and acetic acid is investigated and confronted with the single-VOC data. As a result, single VOC adsorption parameters are useful to understand and predict multi-VOC photocatalytic oxidation.

Theoretical Model for CO Adsorption and Dissociation on Clean and K-Doped β-Mo2C Surfaces

We studied the effect of K on the adsorption and dissociation of CO on the β-Mo2C (001) surface by density functional theory calculations. Molecular CO adsorbs more strongly on Mo-terminated surfaces than on C-terminated ones. Adsorption is energetically more favorable in the presence of preadsorbed potassium. The CO molecule withdraws electron density from the surface, being more extended on the K-doped surface. The CO dissociation was also evaluated, and reaction pathways were modeled, revealing that the C-terminated surface is energetically less favorable than the Mo-terminated one. For both surfaces, the activation energy barrier for dissociation increases with the K content. C–O vibrational frequencies were also computed on K-modified surfaces.