Effect Of Surface Adsorption Research Articles

Doping Strategies for Monolayer MoS2 via Surface Adsorption: A Systematic Study

Using density functional theory calculations, we have systematically explored the effect of surface adsorption of different atoms on the electronic properties of monolayer molybdenum disulfide (MoS2). We have chosen a few representative members from each group in the periodic table, ranging from alkali metals (group I) to halogens (group VII), and calculated the electronic band structure of the adatom–MoS2 system for the most energetically stable location of the adatom adsorbed on MoS2. The calculated value of charge transfer from the adsorbed adatom to MoS2 and resultant shifting of the Fermi level to the conduction band suggest that the group I (Li, Na, K) and group II metals (Mg, Ca) are the most effective adatoms to enhance the n-type mobile carrier density in MoS2. Our calculation is in good agreement with the experimental observation for K [Nano Lett. 2013, 13, 1991].

Inhibition effect of CO on hydrogen permeability of Pd–Ag membrane applied in a microchannel module configuration

The surface adsorption effect of CO on the hydrogen permeability of a 12.5 micron-thick Pd77Ag23 membrane has been evaluated quantitatively under experimental conditions close to the operating conditions of the highly-efficient membrane reformer (MRF) system developed by Tokyo Gas. The permeability of the membrane was measured in the conditions of CO concentration between 1 and 5 vol.% at a temperature and pressure of up to 500 °C and 0.6 MPa, respectively. High feed flow rates and a microchannel module configuration were applied in the flux measurements to ensure that the results are obtained with limited influence of concentration polarization adjacent to the membrane surface and hydrogen depletion along the microchannel length. While the CO inhibition effect was close to negligible at 500 °C, it was significant at lower temperatures. At a feed pressure of 0.2 MPa, the CO inhibition effect was only 0.2% at a CO concentration of 1 vol.% and the effect was 3.6% at a CO concentration of 5 vol.% at 500 °C. The CO inhibition effect were 3.4% for 1 vol.% CO and 14.1% for 5 vol.% CO at 400 °C. Measurements were also carried out at a high feed pressure of 0.6 MPa to evaluate the pressure dependence of the CO inhibition effect. The CO inhibition effect decreased to 0.7% at a CO feed concentration of 5 vol.% at 500 °C. Lower CO inhibition effect were also observed at 450 and 400 °C compared to the data obtained with the feed pressure of 0.2 MPa, while the inhibition levels were almost the same at 350 °C. Though the CO inhibition effect is larger at a lower feed pressure of 0.2 MPa, the effect was only 0.2% at 1 vol.% CO at 500 °C, which is close to the operating conditions of the MRF system. This study quantitatively revealed that the CO inhibition effect on hydrogen flux is extremely small when the membrane is operated at temperatures equal to or higher than 500 °C, even for state-of-the-art thin membranes. The performance of the Tokyo Gas MRF seems thus mainly limited by concentration polarization effects.

Reduced Graphene Oxide (rGO)/BiVO4 Composites with Maximized Interfacial Coupling for Visible Lght Photocatalysis

This paper describes the construction of reduced graphene oxide (rGO)/BiVO4 composites with maximized interfacial coupling and their application as visible light photocatalysts. Thin rGO sheets (<5 nm) could completely cover BiVO4 polyhedrons with highly active (040) facets exposed through an evaporation-induced self-assembly process. In addition to the increased surface adsorption effect of rGO, a considerable enhancement of the photoactivity of BiVO4 has been demonstrated through the degradation of methylene blue upon the covering of rGO. The improved photocatalytic activity is attributed to the formation of well-defined rGO/BiVO4 interfaces, which greatly enhances the charge separation efficiency.

Development of a simple method for quantitation of methanesulfonic acid at low ppm level using hydrophilic interaction chromatography coupled with ESI-MS

A simple, sensitive and robust method using HILIC–ESI-MS has been developed for the determination of methane sulfonic acid (MSA) at low ppm level in order to verify the effectiveness of controlling the formation of genotoxic sulfonate esters in the downstream synthetic step, by which produces active pharmaceutical ingredient (API). Stationary phases with positively charged functional groups such as triazole and amino phases were evaluated for the retention of alkyl sulfonic acids. The MSA was quantitated at 1–10ppm relative to the API using a Cosmosil column (triazole stationary phase) in HILIC mode and the control of MSA can be monitored effectively using the HILIC–ESI-MS methodology. In addition, to provide general guidance for the HILIC–ESI-MS method development, the retention behavior of propanesulfonic acid (PSA) in HILIC mode was investigated using a Unison UK-Amino column to have a better understanding of the HILIC separation mechanism. The results showed reasonable evidence that the combined effect of surface adsorption and ion-exchange played a dominant role for sulfonic acids when using a mobile phase within typical HILIC operation range (0.05–0.20 aqueous volume fraction) while the ion-exchange effect becomes increasingly important in a mobile phase with higher water content. The advantage of using ESI-MS detection in HILIC mode was also demonstrated by the observation that the sensitivity of PSA increased substantially with increasing acetonitrile fraction in mobile phase from 0.80 to 0.95.

Crystal growth by oriented attachment: kinetic models and control factors

Crystal growth mechanism, kinetics, and microstructure development play fundamental roles in tailoring materials with controllable sizes and morphologies. Oriented attachment (OA) involves the spontaneous self-organization of adjacent nanocrystals, resulting in crystal growth by addition of solid particles that share a common crystallographic orientation. It is common for crystal growth to occur by more than one mechanism simultaneously, such as OA and coarsening. This complexity leads to the difficulty in studying the OA growth mechanism. Here, we briefly review progress in kinetic models involving OA and the impact of this mechanism on materials science. We concentrate mostly on recent findings that relate different OA behaviors to surface chemistry and growth conditions, aiming to elucidate this crystal growth mechanism. To explore OA-limited growth, the influence of the Ostwald ripening (OR) mechanism needs to be known and quantified. The introduction of capping ligands has been reported to play multiple roles, including i) promoting or inhibiting aggregation and thus influencing OA growth, or ii) hindering OR from occurring and thus facilitating OA. A detailed survey of nanocrystal growth kinetics under the effect of surface adsorption is presented and summarized.

Comment on “The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry’s Law Constants for Fluorotelomer Alcohols”

Comment on “The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry’s Law Constants for Fluorotelomer Alcohols”

Reply to Comment on “The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry’s Law Constants for Fluorotelomer Alcohols”

Reply to Comment on “The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry’s Law Constants for Fluorotelomer Alcohols”

Experimental and theoretical investigation into the elimination of organic pollutants from solution by layered double hydroxides

This work aims at revealing the role of pristine layered double hydroxide (LDH) materials in the elimination of organic pollutants from solution. Typical LDH samples, ZnCr- and MgAl-LDHs (with Zn2+/Cr3+ or Mg2+/Al3+ molar ratio 2), are prepared and used for the removal of methylene blue (MB), methyl orange (MO), and formaldehyde. The systematic investigations of structural characterization and periodic density functional theory (DFT) calculation of the LDH samples demonstrate that: (1) no electron–hole pairs could be generated for MgAl-LDHs under the irradiation of visible light due to the large calculated gap energy above 5.0eV. (2) ZnCr-LDHs are sensitive to the irradiation of visible light with the calculated gap energy between 2.0 and 3.0eV, but the rapid charge recombination and low efficiency in electron/hole separation would suggest that photocatalytic activity of ZnCr-LDHs would be greatly limited. In the experimental work, ZnCr- and MgAl-LDHs show no photocatalytic activity for the removal of formaldehyde under the visible light. The disposal of the organic dyes molecules in the solution would be caused by the photoassisted degradation and surface adsorption effect rather than the photocatalysis impact for both LDH samples. This is confirmed by the elimination tests that carry out in the dark condition with the similar procedure under visible light irradiation. Moreover, the two types of LDH samples exhibit the different adsorption capability for the MB and MO molecules due to the different colloidal properties of the LDH samples, which is revealed by Zeta potential measurement. The above finding that elimination of organic dyes from solution by the pristine LDH samples through photoassisted degradation and adsorption processes would be important for the rational design and use of clay-like materials for the treatment of sewage containing toxic compounds.

An impedimetric chemical sensor for determination of detergents residues

A new impedimetric sensor based on an interdigitated electrode array with electrode digits located at the bottom of microcapillaries formed in silicon dioxide is presented. Microcapillaries are opened at the top, so that in contact with an electrolyte solution the ac current flows close to the surface of the capillary wall from one electrode to another and is significantly affected by changes in the surface conductance at the SiO2/electrolyte interface. Adsorption of detergents on the sensor surface affects the charge distribution in the electrical double layer and thus the surface conductance. These changes are registered by measuring impedance. Effect of surface adsorption of ionic and non-ionic surfactants on the sensor impedance is studied. The sensor is shown to be able to measure commercial detergents residues in a tap water starting from 5ppm even in solutions with high electrolyte conductivity.

Protein Antigen Adsorption to the DDA/TDB Liposomal Adjuvant: Effect on Protein Structure, Stability, and Liposome Physicochemical Characteristics

Understanding the nature of adjuvant-antigen interactions is important for the future design of efficient and safe subunit vaccines, but remains an analytical challenge. We studied the interactions between three model protein antigens and the clinically tested cationic liposomal adjuvant composed of dimethyldioctadecylammonium (DDA) and trehalose 6,6'-dibehenate (TDB). The effect of surface adsorption to DDA/TDB liposomes on colloidal stability and protein physical stability/secondary structure was investigated by dynamic light scattering, circular dichroism, Fourier transform infrared spectroscopy and differential scanning calorimetry. Bovine serum albumin and ovalbumin showed strong liposome adsorption, whereas lysozyme did not adsorb. Upon adsorption, bovine serum albumin and ovalbumin reduced the phase transition temperature and narrowed the gel-to-liquid phase transition of the liposomes implying interactions with the lipid bilayer. The protein-to-lipid ratio influenced the liposome colloidal stability to a great extent, resulting in liposome aggregation at intermediate ratios. However, no structural alterations of the model proteins were detected. The antigen-to-lipid ratio is highly decisive for the aggregation behavior of DDA/TDB liposomes and should be taken into account, since it may have an impact on general vaccine stability and influence the choice of analytical approach for studying this system, also/especially at clinically relevant protein-to-lipid ratios.

Effect of surface adsorption of carbon on the surface tension of liquid Fe–Mn–C alloys

The influences of temperature, manganese, and carbon on the surface tension of liquid ternary Fe–Mn–C systems were investigated. The measurements were carried out with the sessile drop method in the temperature range of 1653–1834 K. The manganese and carbon contents were changed between 4.79–9.89 and 1.07–4.20 wt%, respectively. It was demonstrated that the surface tension varied as a linear function of temperature for all the examined samples. With increasing manganese content, the surface tension decreased. When the weight fraction of manganese with respect to iron was fixed, the surface tension decreased with increasing carbon content. From thermodynamic consideration, it was considered that carbon preferentially adsorbed on the metal surface as carbon atoms rather than manganese carbide.

Effect of oxygen-related surface adsorption on the efficiency and stability of ZnO nanorod array ultraviolet light-emitting diodes

Ultraviolet light-emitting diodes using MgZnO-coated and bare ZnO nanorod arrays as active layers were manufactured. Both types were exposed to ambient air over a 1-yr period to assess their stability. By monitoring the electroluminescence evolution with air-exposure time and comparing the changes of electroluminescence and x-ray photoelectron spectra before and after vacuum desorption, it is concluded that surface-adsorbed O2 and OH− species, as acceptor and donor surface states, quench ultraviolet electroluminescence, and favor undesirable surface-mediated nonradiative and deep-level recombination. The MgZnO coating prevents surface adsorption, and so the coated nanorod device shows higher efficiency and stability than the uncoated one.

Effects of rare earth additions on the microstructural evolution and microhardness of Sn30Bi0.5Cu and Sn35Bi1Ag solder alloys

The effects of trace amounts of rare earth (RE) additions on the melting property, microstructural evolution and microhardness of SnBiCu and SnBiAg solder alloys were studied by differential scanning calorimetric tester, Vickers hardness tester and microstructural observation. The results indicated that with the additions of RE, the melting property of the SnBiCu–xRE and SnBiAg–xRE (x = 0, 0.25 and 0.5) solder alloys changed slightly. The microstructures of the β-Sn phase, Cu6Sn5 and Ag3Sn intermetallic compounds (IMCs) in the solder matrices were refined due to the surface adsorption effect of RE. In addition, the microhardness of the solder alloys increased remarkably with the additions of RE because of the refined microstructures. Moreover, the formed Cu6Sn5 IMC layers in SnBiCu–xRE/Cu and SnBiAg–xRE/Cu solder joints were much thinner than those in the undoped-RE SnBiCu/Cu and SnBiAg/Cu solder joints after reflowing and aging tests. This is because the RE decreased the interfacial energy of Cu6Sn5 IMC layer and then suppressed the Cu atoms to react with Sn atoms to form Cu6Sn5 IMC layer.

Effects of iron surface adsorption and sample handling on iron solubility measurements

Seawater samples from two separate cruises in the Southern Ocean (ANTXXI/3 (EIFeX) and ANTXXIII/9) were collected for measurements of iron solubility by 55Fe addition. For both sets of samples, a significant loss of the dissolved portion of the added Fe was observed during the 72 hour duration of each Fe solubility measurement incubation. The decrease in dissolved Fe was related to Fe precipitation and adsorption onto bottle walls. The dissolved Fe data can be successfully modeled assuming that two colloidal Fe species (organically complexed Fe and inorganic Fe) were quickly formed following the addition of dissolved Fe(III) to the seawater. Model results indicate that Fe dissociated from weak organic complexes was the main contributor to wall sorption during the first 6 h following Fe addition, and that most of the Fe deposited after the first 6 h arose from the dissociation of colloidal inorganic species. Effects of sample freezing on Fe solubility measurements are also discussed.

The Effect of Surface Adsorption and Molecular Geometry on the Determination of Henry's Law Constants for Fluorotelomer Alcohols

Fluorotelomer alcohols (FTOHs) are one important subgroup of perfluorinated compounds (PFCs), yet Henry's law constant (KH) of FTOHs, which is also known as the air–water partition coefficient, rem...

Effect of OH −/Al 3+ ratio on the coagulation behavior and residual aluminum speciation of polyaluminum chloride (PAC) in surface water treatment

The coagulation behavior, residual aluminum ratio of three PAC coagulants as well as content and proportion of different residual Al speciation during the treatment of a specific surface water were investigated in this paper. Experimental results suggested that surface adsorption and entrapment effect worked effectively in turbidity removal regarding this specific water. PAC 20 was appropriate to remove hydrophilic natural organic matter (NOM), while PAC 15 and PAC 23 were appropriate to remove hydrophobic fraction NOM. PAC, especially PAC 20, could reduce the content of total dissolved Al and dissolved monomeric Al with comparatively higher toxicity. PAC 20 showed lower concentration for every residual Al species. The majority of total residual Al existed in the form of unsoluble particulate Al (about 62–93% for PAC 15, 65–92% for PAC 20 and 54–78% for PAC 23). Among total dissolved Al in the effluent treated with PAC 15 and PAC 23, dissolved organically-bound Al was almost the major speciation (about 40–92% for PAC 15 and 37–86% for PAC 23). There existed no dissolved organically-bound monomeric Al in purified water treated with three PAC samples. Residual Al ratio of PAC varied in the following order: PAC 15 > PAC 23 > PAC 20. Besides, Al speciation in coagulants likely remained in treated water at lower dosage.

Chilling Out: A Cool Aqueous Environment Promotes the Formation of Gas–Surface Complexes

SO(2), an important atmospheric pollutant, has been implicated in environmental phenomena such as acid rain, climate change, and cloud formation. In addition, SO(2) is fundamentally interesting because it forms spectroscopically identifiable complexes with water at aqueous surfaces. Vibrational sum frequency spectroscopy (VSFS) is used here to further investigate the mechanism by which SO(2) adsorbs to water at tropospherically relevant temperatures (0-23 °C). The spectral results lead to two important conclusions. SO(2) surface affinity is enhanced at colder temperatures, with nearly all of the topmost water molecules showing evidence of binding to SO(2) at 0 °C as compared to a much lower fraction at room temperature. This surface adsorption results in significant changes in water orientation at the surface, but is reversible at the temperatures examined here. Second, the SO(2) complex formation at aqueous surfaces is independent of aqueous solution acidity. One challenge in previous uptake studies was the ability to distinguish between the effects of surface adsorption as compared to bulk accommodation. The surface and vibrational specificity of these studies make this distinction possible, allowing a selective study of how the aqueous properties temperature and pH influence SO(2) surface affinity.

Surface segregation and adsorption effects of iron–technetium alloys from first-principles

Surface properties of Tc-rich and Fe-rich portions of the Tc–Fe binary alloy phase diagram were computed in this work on the basis of density functional theory. Tc and Fe were found to have minimal degrees of mixing in the parent phases, consistent with the experimentally derived phase diagram. The influence of oxygen on surface phase stability was also studied, with no significant impact on surface segregation or degree of surface mixing. Oxygen adsorption was shown to change the ordering of surface facets in Tc, such that the pyramidal phase becomes lower in energy than the prismatic phase, even with low coverage of oxygen. No evidence for increased surface segregation upon oxidation was found for the solid-solution phases. A potential–pH surface Pourbaix diagram was derived for Tc and H, OH and O adsorbed sub-monolayers were shown to be precursors to oxide formation. While Tc and Fe have similar reactivities and properties in their parent phases, and hence, also in solid-solution, the properties of the intermetallic are expected to be significantly different due to the size-mismatch between the elements.

Progress of nanocrystalline growth kinetics based on oriented attachment

The crystal growth mechanism, kinetics, and microstructure development play a fundamental role in tailoring the materials with controllable sizes and morphologies. The classical crystal growth kinetics-Ostwald ripening (OR) theory is usually used to explain the diffusion-controlled crystal growth process, in which larger particles grow at the expense of smaller particles. In nanoscale systems, another significant mechanism named "oriented attachment (OA)" was found, where nanoparticles with common crystallographic orientations directly combine together to form larger ones. Comparing with the classical atom/molecular-mediated crystallization pathway, the OA mechanism shows its specific characteristics and roles in the process of nanocrystal growth. In recent years, the OA mechanism has been widely reported in preparing low-dimension nanostructural materials and reveals remarkable effects on directing and mediating the self-assembly of nanocrystals. Currently, the interests are more focused on the investigation of its role rather than the comprehensive insight of the mechanism and kinetics. The inner complicacy of crystal growth and the occurrence of coexisting mechanisms lead to the difficulty and lack of understanding this growth process by the OA mechanism.In this context, we review the progress of the OA mechanism and its impact on materials science, and especially highlight the OA-based growth kinetics aiming to achieve a further understanding of this crystal growth route. To explore the OA-limited growth, the influence of the OR mechanism needs to be eliminated. The introduction of strong surface adsorption was reported as the effective solution to hinder OR from occurring and facilitate the exclusive OA growth stage. A detailed survey of the nanocrystal growth kinetics under the effect of surface adsorption was presented and summarized. Moreover, the development of OA kinetic models was systematically generalized, in which the "molecular-like" kinetic models were built to take the OA nanocrystal growth behavior as the collision and reaction between molecules. The development of OA growth kinetics can provide a sufficient understanding of crystal growth, and the awareness of underlying factors in the growth will offer promising guidance on how to control the size distribution and shape development of nanostructural materials.

Nonlinear Marangoni instability of a liquid jet in the presence of electric field

AbstractThe work discusses the linear and nonlinear stability of cylindrical surface deformations between two incompressible fluids. The interface is carrying a uniform surface charge. The inner fluid is assumed to be a liquid jet. Both fluids are modeled as a special type of a Newtonian viscous fluid. Furthemore, the effect of surface adsorption is taken into account. Both fluids are assumed to be dielectric and the stability is discussed in the presence of a constant electric field in axial direction. The analysis is performed along the lines of a multiple scale perturbation expansion with additional slow time and space variables. The various stability criteria are discussed both analytically and numerically. The results are displayed in many plots showing the stability criteria in various parameter planes. The results show the dual role of the electric field and the negative rate of change of surface tension with the concentration of surfactant on the system stability, in both the linear and nonlinear steps. The nonlinear theory, when used to investigate the stability of liquid jet, appears accurately to predict new unstable regions.