Pre-adsorbed Surfaces Research Articles

CO oxidation mechanism on surfaces of B-site doped SrFeO3-δ-based perovskite materials for thermochemical water splitting

Density functional theory (DFT) calculations were performed to explore the reaction mechanism of CO oxidation on both the perfect and O pre-adsorbed surfaces of B-site (B = Al, Zr, Nb and W) doped SrFeO3-δ-based perovskite materials. Our calculations showed that metal doping benefited the adsorption of molecular CO over the perfect surface, while it inhibited the adsorption of molecular CO over the O pre-adsorbed surface. The reaction of CO with lattice oxygen of SrFeO3 was inhibited with the doping of Zr, Nb and W, but promoted by the doping of Al. The reaction of CO with surface pre-adsorbed O of SrFeO3 was found to be thermodynamically inhibited by the doping of Al, Zr, Nb and W. This study provided significant insights into the interaction of CO with the surfaces of doped SrFeO3-δ perovskite materials for thermochemical water splitting applications.

Adsorption/dissociation process of H2S on different FeS2(1 0 0) surfaces

Interactions between H2S and an FeS2(100) surface significantly affect the corrosion of carbon steel, and effects of pre-adsorbed atoms on the H2S adsorption/dissociation process remain unclear. Herein, we adopted the Hubbard U-corrected GGA + U method of density functional theory and considered the effect of spin polarization. The stability order of different FeS2 low-dimensional surfaces was calculated. The adsorption/dissociation mechanism of H2S on perfect and pre-adsorbed FeS2(100) surfaces was explored, and the theoretical basis of the improved hydrogen barrier effect in FeS2 was revealed. The stability order of different FeS2 low-dimensional surfaces was (100) > (110) > (111). The adsorption capacity of H2S on the surface of the pre-adsorbed FeS2(100) was stronger and dissociated spontaneously. Pre-adsorbed oxygen atoms significantly promoted the H2S adsorption/dissociation process. Owing to the ETS1H of H atoms and interaction energy between H and SH, the dissociated Ea on the pre-adsorbed surface decreased. Hydrogen atoms are prone to overflowing of H2 molecules on the perfect surface of FeS2(100), and FeS2 had better hydrogen barrier properties. This study enhances our understanding of structural properties of FeS2 and the interaction of H2S with different FeS2(100) surfaces, providing guidance for developing corrosion protection, hydrogen barrier materials, and catalytic systems.

Influence of mucin pre-adsorption for lipoteichoic acid adsorption on titanium surfaces.

We investigated the adsorption of lipoteichoic acid (LTA) on titanium surfaces by using the quartz crystal microbalance (QCM) method, and confirmed the influence of mucin (MUC) pre-adsorption on LTA adsorption. Two injection methods were evaluated. Namely, Method A: single-step injection of LTA solution to the Ti sensor, and Method B: MUC solution was injected to the Ti sensor followed by LTA injection on the MUC pre-adsorbed surface. QCM measurement revealed that the adsorbed amount of LTA by Method A was low and constant regardless of the increase in LTA concentration. In contrast, the adsorption amount of LTA in Method B increased according with increasing concentration of LTA and was significantly higher than that of Method A. The hydrophobic surface after MUC pre-adsorption was presumed to contribute to the enhancement of LTA adsorption. Our results revealed that MUC pre-adsorption to Ti is necessary for LTA adsorption in living tissue.

Comparative study on the adsorption behaviors of O and Cl on Fe(110) surfaces with different Cr content

Joint density functional theory calculations have been performed to investigate the interactions of atomic oxygen and chlorine with the Fe(110) and Cr-doped Fe(110) surfaces both in vacuum and in aqueous solution. The results show that Cr doping on the top of surface makes the atomic oxygen adsorption more thermodynamically favorable but slightly decreases the absorbability of chlorine. Subsurface doping atom makes little contribution to the adsorption characteristics of the cases considered in this study, which indicates that doping on the first layer is a reasonable and simplified approach for studying adsorption properties on iron surfaces. The adsorption strength of O decreases on Cl pre-adsorbed surfaces, demonstrating a competition relationship between the two species. This result is consistent with the adsorption theory of passivation, which attributes Cl-induced corrosion to its inhibition of oxygen adsorption. Cr surface doping can significantly decreases the negative effects caused by chloride ion, resulting in the formation of protective oxide film.

Stabilizing the OOH* intermediate via pre-adsorbed surface oxygen of a single Ru atom-bimetallic alloy for ultralow overpotential oxygen generation

Achieving an ultra-low overpotential for oxygen generation over pre-adsorbed surface oxygen on a Ru single atom anchored metal alloy.

An Insight into Electrostatic Field Effects on SO3 Adsorption by CaO with CO2, SO2 and H2O: A DFT Approach

ABSTRACT Because of the compulsory installation of electrostatic precipitators in coal-fired power plants, SO3 and particles in flue gas inevitably pass through areas with electric field and electric charge distributed. CaO is the highest alkaline content in fly ash and has strong interactions with SO3. Therefore, it is important to understand the effects of the electric field on the binding energies of SO3 and CaO. Density functional theory calculations were applied to examine the electrostatic field dependence of SO3 adsorption on the CaO(100) surface. The energetic, geometric and electronic nature of the modeled systems was analyzed. Trends of the adsorption energy variation in a positive or negative electrostatic field presented great differences. When the electrostatic field was small, it was observed that the required adsorption energy was reduced regardless of the positive or negative electrostatic field. With increased electrostatic field strength, the adsorption energy showed an increasing trend in a positive field, while the adsorption energy decreased in a negative field. The positive field enhanced the charge density changes of the surface O across the Ca around the OCaO, while the negative field enhanced the change of the charge density of the Ca below the OCaO. The SO42–-like structure accumulated electrons as a unit and the charge transfer of the SO42– increased with the incremental adsorption energy in a linear relationship. On the H pre-adsorbed surface, the total increment was much smaller than in previous cases in a positive field, and the total variation was negligible in a negative field.

Low temperature humidity sensor based on Ge nanowires selectively grown on suspended microhotplates

The gas sensing properties of germanium (Ge) monocrystalline nanowires (NWs) at temperatures up to 100°C have been demonstrated for the first time. The devices have been fabricated based on an energy efficient and site-specific vapor-liquid-solid growth of NW meshes on top of microhotplates, which contain a buried heater and top electrodes. The devices have been investigated for the detection of oxygen, nitrogen dioxide and carbon monoxide gases, showing the important effect played by pre-adsorbed surface oxygen in the response to the different gases. The Ge NW-based devices exhibit p-type conductivity and show high selectivity in their response towards water vapor. Water vapor interaction is not dependent on the presence of oxygen and the adsorption leads to electron donation in the Ge nanowires. TEM analysis of the NWs proves that they are covered by a thin, outer germanium oxide layer, which is stable and does not grow upon exposure to these gases and operation temperatures up to 100°C. The presence of this oxide layer plays a key role in the sensing mechanisms.

Role of protein environment and bioactive polymer grafting in the S. epidermidis response to titanium alloy for biomedical applications

Joint implant-related infections, namely by Staphylococci, are a worldwide problem, whose consequences are dramatic. Various methods are studied to fight against these infections. Here, the proposed solution consists in grafting a bioactive polymer on joint implant surfaces in order to allow the control of the interactions with the living system. In this study, sodium styrene sulfonate, bearing sulfonate groups, was grafted on the surface of titanium alloys. Scanning Electron Microscopy, colorimetric method, Fourier-transformed infrared spectroscopy and contact angle measurements were applied to characterize the surfaces. Bacterial adhesion studies were studied on poly(sodium styrene sulfonate) grafted Ti6Al4V and Ti6Al4V surfaces previously adsorbed by proteins involved in the bacteria adhesion process. Fibrinogen and fibronectin were demonstrated to increase staphylococcal adhesion on Ti6Al4V surfaces. Ti6Al4V grafted sodium styrene sulfonate surfaces inhibited the adhesion of Staphylococcus epidermidis in 37% and 13% on pre-adsorbed surfaces with fibrinogen and fibronectin, respectively. The mechanism of the observed inhibiting bacteria adhesion properties is related to the differences of proteic conformations induced by poly(sodium styrene sulfonate) grafting.

Cultured Primary Macrophage Activation by Lipopolysaccharide Depends on Adsorbed Protein Composition and Substrate Surface Chemistry

Recent efforts show that significantly reducing implant-adsorbed proteins does not avoid the foreign body response. Fluorinated surfaces are commonly used to passivate cell-mediated inflammatory responses to implanted materials but adsorb host proteins and facilitate the attachment and proliferation of macrophages. This study considers in vitro macrophage activation to fluorinated TeflonAF® compared to tissue-culture polystyrene using pre-adsorbed proteins (fibrinogen, BSA, collagen and elastin). Primary macrophage cultures adhere on all pre-adsorbed protein surfaces in a protein concentration-dependent manner and activate to the same extent after 72 h, regardless of surface chemistry. However, macrophages alter their cultured adherent morphology depending on which protein is pre-adsorbed to these surfaces. Macrophages cultured on TeflonAF® on all pre-adsorbed proteins produced overall higher levels of the pro-inflammatory cytokines — TNF-α, IL-6, IL-1β or MCP-1 — than those cultured on tissue-culture polystyrene and those cultured in serum-free media. However, at 72 h, macrophages adherent on BSA or fibrinogen pre-adsorbed surfaces failed to exhibit increased amounts of TNF-a, IL-6 or IL-1/S on either TeflonAF® or TCPS, as well as MCP-1 on TCPS, in the presence of activating lipopolysaccharide. Different cell responses to pre-adsorbed proteins reflect substrate-specific regulation of macrophage cytokine secretion, indicative of LPS tolerance distinct from secondary macrophage cultures, and also distinct from macrophages adherent to surfaces in the absence of proteins. This result has bearing on connecting macrophage adhesion via adsorbed proteins on (fluorinated) biomaterials, and their resulting chronic activation that yields the FBR and possibly reduces effective macrophage clearance of microbes around implanted materials.

First-principles investigation of adsorption of N2O on the anatase TiO2 (1 0 1) and the CO pre-adsorbed TiO2 surfaces

First-principles spin-polarized density functional theory computations in generalized gradient approximation to investigate the adsorption of N2O on the neutral and negative surfaces of the anatase TiO2 (101) and on the neutral and positive surfaces of CO pre-adsorbed TiO2 were carried out. The adsorption energies for N2O adsorbed on the TiO2 and the CO pre-adsorbed surfaces were obtained. Mechanisms for redox reaction of CO+N2O conversion to CO2+N2 on the neutral and positive TiO2 surfaces have been proposed and their photocatalytic involvement is described.

Formation processes of an ordered mixed structure: Cu( [formula omitted])-( [formula omitted]) R45°-Li,Mg

The formation processes of a ( 2 2 × 2 ) R45° structure formed by the coadsorption of Li and Mg on Cu(0 0 1) at room temperature, whose structure has been determined [Surf. Sci. 493 (2001) 91], are examined by low-energy electron diffraction (LEED). By depositing Mg atoms on the Li pre-adsorbed (2×1) surface, a sequence of LEED patterns (2×1)→ c(4×4)→(2 2 × 2 ) R45° was observed. The c(4×4) LEED pattern is proved to be due to the coexistence of the (2×1)-Li and ( 2 2 × 2 ) R45°-Li,Mg structures. On the other hand, when Li was adsorbed on the Mg pre-adsorbed surface, a disordered surface was formed until the ( 2 2 × 2 ) R45°-Li,Mg structure appeared at Li coverage of about 0.22. Different formation processes of the ( 2 2 × 2 ) R45° structure in the two adsorption sequences are discussed at the atomic level.

Oxidation and growth of Mg thin films on Ru(001)

The oxidation and growth of ultra-thin Mg films on a Ru(001) substrate have been studied using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS) in the temperature range of 300–1500 K. Our results suggest that the growth of Mg thin films follows a layer-by-layer mode. Upon oxygen adsorption at 300 K, two O 1s peaks were detected on the Mg film. The peak at 532.2–532.6 eV could be attributed to either dioxygen or partially reduced species (O δ− , δ<2), whereas that at 530.1–530.6 eV is due to lattice oxygen in MgO. Annealing of the oxidized film to 800 K causes the conversion of the dioxygen or partially reduced species to the oxide state. Thermal desorption peaks of MgO were directly detected at 1000–1127 and 1350–1380 K, respectively. However, initial evaporation of Mg atoms onto an oxygen pre-adsorbed surface yields a fully oxidized MgO. Further Mg deposition results in the formation of a partially oxidized film with the observation of an O 1s peak at 532.2 eV.

Adsorption and reaction of methanol and carbon dioxide on model ZnO/Ag catalysts

The adsorption and decomposition reactions of carbon dioxide and methanol have been studied on clean Ag(100), O/Ag(100) and ZnO/Ag(100) surfaces. The clean Ag(100) surface itself is unreactive in so far as no low-pressure adsorption of either molecule is observed at ambient temperatures. At lower temperatures a weakly chemisorbed molecular state of methanol may be distinguished. In the presence of pre-adsorbed surface oxygen, however, uptake of both molecules is seen at 300 K to give carbonate and methoxy species. The methoxy species may undergo dehydrogenation to yield formaldehyde or oxidation to surface formate which then decomposes at ca. 390–400 K. The growth of ZnO on the Ag(100) surface leads to the gradual suppression of the chemistry of the silver surface and the appearance of desorption features which relate closely to those seen from polycrystalline ZnO samples or the non-polar faces of ZnO crystals. The uptake of CO2 is strongly inhibited by annealing the oxide films; this is attributed to the ordering of the oxide surface to generate a polar surface. In the case of methanol adsorption, desorption features also reveal the formation of carbonate-like intermediates on the ZnO surface.