Effect Of Surface Coverage Research Articles

Hygroscopicity of Microplastic and Mixed Microplastic Aqueous Ammonium Sulfate Systems.

A growing body of research suggests the presence and long-range transport of microplastics in the atmosphere. However, the interactions between these microplastics and atmospheric aerosol are poorly understood. Environmental microplastics vary in color, morphology, and chemical composition and become oxidized over time by UV, mechanical, and biological action. Once introduced to the atmosphere, these microplastics will likely become mixed with atmospheric aerosol. Determining how microplastics interact with aerosol particles and how they may alter aerosol physical properties, including water uptake and loss, is necessary to understand the impact of these microplastics on our environment. Herein, we investigate the effect of microplastics on the water activity of bulk water and ammonium sulfate solutions. We compare a variety of plastic compositions and microplastic morphologies including plastics that have been aged by UV irradiation and mechanical forces in the lab. In addition, we investigate the water uptake and loss in microplastic samples through dynamic vapor sorption. We find an increase in total water sorption for UV-aged plastics compared to pristine plastics. Finally, we investigate the effect of fractional surface coverage on the equilibration time scale.

Self-assembly of N-heterocyclic carbenes on Au(111)

Although the self-assembly of organic ligands on gold has been dominated by sulfur-based ligands for decades, a new ligand class, N-heterocyclic carbenes (NHCs), has appeared as an interesting alternative. However, fundamental questions surrounding self-assembly of this new ligand remain unanswered. Herein, we describe the effect of NHC structure, surface coverage, and substrate temperature on mobility, thermal stability, NHC surface geometry, and self-assembly. Analysis of NHC adsorption and self-assembly by scanning tunneling microscopy and density functional theory have revealed the importance of NHC-surface interactions and attractive NHC-NHC interactions on NHC monolayer structures. A remarkable way these interactions manifest is the need for a threshold NHC surface coverage to produce upright, adatom-mediated adsorption motifs with low surface diffusion. NHC wingtip structure is also critical, with primary substituents leading to the formation of flat-lying NHC2Au complexes, which have high mobility when isolated, but self-assemble into stable ordered lattices at higher surface concentrations. These and other studies of NHC surface chemistry will be crucial for the success of these next-generation monolayers.

Multi-step cefazolin sodium release from bioactive TiO2 nanotubes: Surface and polymer coverage effects

Bacterial implant-related infections have been pointed out as the leading cause of metal implant failure. Recently, nanotexturization of biomaterials surface associated with antibiotic loading revealed itself as a promising strategy for enhancing osseointegration while mitigating bacterial infections. However, fewer studies describe the effects of multi-step local drug delivery. This study investigates 1 mg Cefazolin Sodium (CS) release from anodic nanotextured titanium-based devices and the effect of polymer coverage with differential aqua solubility characteristics (Chitosan—CH and Carboxymethylcellulose—CM). Results show that larger inner pore diameters are related to longer drug release times on uncovered samples. The polymeric coverage decreases the release rates, highlighting the Carboxymethylcellulose boosting the Cefazolin release time by 51–77 fold. All biomaterials exhibited a low or absent hemolytic activity and considerable bacteria inactivation. In summary, 40 °C/CM-based samples present the most promising results for drug release devices.

H Resurface and Hot H Promoted H2 Recombination on Ni(111): Effects of Arrangement, Surface Coverage, and Lattice Motion

Subsurface H can affect catalytic reactivity and selectivity. H resurface and H2 recombination with a subsurface H on Ni(111) were investigated by the quantum instanton method, and the arrangement,...

Dispersibility of Poly(vinyl acetate) Modified Silica Nanoparticles in Carbon Dioxide with Several Cosolvents.

The dispersibility and stabilization of silica nanoparticles with surface-capped poly(vinyl acetate) (PVAc) chains are examined in carbon dioxide with four different cosolvents. Three surface coverages of silica-PVAc were formed by using different weight ratios of the silica and PVAc. The dispersibilities of three silica-PVAc nanoparticles in CO2 with the four cosolvents were tested in a rotatable high-pressure variable-volume view cell. The effects of surface coverage, cosolvent type, pressure, and particle concentration on dispersion were investigated. Results show that, in the experimental pressure range (5.5 to 20 MPa), the pressure has no significant effect on the dispersion of nanoparticles, and the cosolvent is the key factor in dispersing silica-PVAc particles in CO2. 1-Butanol is an adequate cosolvent to disperse silica-PVAc in CO2 with any coverage of PVAc on the surface of the particles when the concentration of particles is smaller than 0.31 wt %. Ethanol can only improve the dispersibility of particles with a high surface coverage of PVAc when the concentration of particles is smaller than 0.14 wt %. 1-Hexanol and ethyl acetate cannot disperse the particles in CO2 with any coverage of PVAc. Molecular dynamics simulations were carried out to study the nanoparticle-CO2-cosolvent dispersions. Results suggest that 1-butanol has a good solubility in the CO2 condensed phase and can effectively absorb onto the nanoparticle surface, which help to prevent the formation of nanoparticle aggregation. The precipitation of nanoparticles in the nanoparticle/1-hexanol/CO2 and nanoparticle/ethyl acetate/CO2 systems is attributed to the relatively low solubility of CO2 in 1-hexanol and ethyl acetate. The precipitation of nanoparticles in the nanoparticle/ethanol/CO2 system is the result of less hindrance of ethanol molecules to the aggregation of nanoparticles.

Molecular dynamics simulations of adsorption behavior of organic friction modifiers on hydrophilic silica surfaces under the effects of surface coverage and contact pressure

The effects of surface coverage and contact pressure on the adsorption of organic friction modifiers (OFMs) on the hydroxylated SiO 2 surfaces were studied by molecular dynamics. Two typical OFMs with different polarities (R–OH and R–NH 2 ) were discussed. R–OH molecules formed a dense monolayer which was strengthened by increasing coverage and pressure. R–NH 2 molecules formed loose adsorption layers, which were further dispersed by increasing coverage but transformed to a compact monolayer by increasing pressure. The adsorption amount of R–NH 2 decreased clearly with the increase of coverage, but increased from ~70% to 100% with the increase of pressure. As for R–OH, the adsorption amount was always kept above 90%. Obviously, the high pressure benefits the OFM adsorption at static conditions. Also, the high surface coverage enables more adsorbed molecules on SiO 2 surfaces, which enhances the anti-pressure ability of adsorption layers and thereby reduces the friction and wear. • The adsorption of OFMs on SiO 2 surfaces with effects of surface coverage and pressure is studied. • High contact pressure benefits the OFM adsorption at static conditions. • High surface coverage enhances the anti-pressure ability of OFM monolayers.

Impact of the Coverage of Aptamers on a Nanoparticle on the Binding Equilibrium and Kinetics between Aptamer and Protein.

Knowledge of the interaction between aptamer and protein is integral to the design and development of aptamer-based biosensors. Nanoparticles functionalized with aptamers are commonly used in these kinds of sensors. As such, studies into how the number of aptamers on the nanoparticle surface influence both kinetics and thermodynamics of the binding interaction are required. In this study, aptamers specific for interferon gamma (IFN-γ) were immobilized on the surface of gold nanoparticles (AuNPs), and the effect of surface coverage of aptamer on the binding interaction with its target was investigated using fluorescence spectroscopy. The number of aptamers were adjusted from an average of 9.6 to 258 per particle. The binding isotherm between AuNPs-aptamer conjugate and protein was modeled with the Hill-Langmuir equation, and the determined equilibrium dissociation constant (K'D) decreased 10-fold when increasing the coverage of aptamer. The kinetics of the reaction as a function of coverage of aptamer were also investigated, including the association rate constant (kon) and the dissociation rate constant (koff). The AuNPs-aptamer conjugate with 258 aptamers per particle had the highest kon, while the koff was similar for AuNPs-aptamer conjugates with different surface coverages. Therefore, the surface coverage of aptamers on AuNPs affects both the thermodynamics and the kinetics of the binding. The AuNPs-aptamer conjugate with the highest surface coverage is the most favorable in biosensors considering the limit of detection, sensitivity, and response time of the assay. These findings deepen our understanding of the interaction between aptamer and target protein on the particle surface, which is important to both improve the scientific design and increase the application of aptamer-nanoparticle based biosensor.

Self-assembly of the surfactant mixtures on graphene in the presence of electrolyte: a molecular simulation study

The insolubility of graphene nanosheets in aqueous media has been a limitation for the practical applications of this unique material. The non-covalent functionalization of graphene with mixed surfactants is an effective procedure for preparation of stable graphene dispersions. Physical adsorption of surfactants onto graphene surfaces is a significant stage in the dispersion of graphene nanosheets in the aqueous environment. Studies have shown that the presence of electrolyte greatly affects the adsorption process of pure surfactants on solid surfaces. Examination of mixed surfactants adsorption on graphene in the presence of electrolyte will help to better understand the mechanism of molecular interactions between the graphene nanosheets and mixed surfactants. Therefore, in this study, we used molecular dynamics simulations to investigate the adsorption of mixed surfactants on graphene in the presence of electrolyte and to study the morphology of assemblies formed from mixed surfactants on graphene. We investigate the effects of electrolyte concentration and surface coverage of surfactants' mixture on the adsorption process and structural changes in the assemblies formed on graphene nanosheets. We have found that increasing the ionic strength of electrolyte reinforces stretching of surfactants adsorbed on graphene toward the aqueous phase, and this leads to a clear volume expansion in the structure of graphene-surfactant mixture hemi-spherical micelles. In fact, screening effect of electrolyte ions on electrostatic repulsion between charged head-groups made molecules approach each other, leading to a more compact assembly of surfactants on graphene surface. As hemi-spherical micelles of mixed surfactants-graphene expanded, the steric repulsion between these micelles also increased, which in turn, inhibited the re-aggregation of graphene sheets covered with surfactants.

Evaluation of the corrosion inhibition effect of the combined admixture of rosemary and cinnamon cassia oil on mild steel in weak acid electrolyte

The corrosion resistance of mild steel (MS) in 0.5 M H2SO4 and HCl solution with specific concentrations of the intermixture of rosemary and cinanamon cassia essential oil extracts (RCC) was studied by potentiodynamic polarization method, open circuit potential analysis (OCP) and optical macroscopy. Information obtained showed RCC effectively inhibited MS corrosion from the lowest to the highest concentrations in both acids with lowest inhibition result of 95.30% and 94.19%, and highest inhibition efficiency of 99.21% and 97.69%. RCC exhibited dominant cathodic inhibition effect in H2SO4 due to suppression of the reduction reactions while in HCl RCC displayed mixed inhibition properties due to surface coverage effect in the presence of Cl− anions. OCP showed RCC increased the thermodynamic tendency of MS to corrosion in H2SO4 solution despite effective inhibition performance with significant electronegative shift in corrosion potential. In HCl significant electropositive potential displacement was observed relative to the potential of the control MS due to adsorbed protonated RCC molecules unto the steel. Adsorption of RCC molecules on MS aligned with Langmuir, Frumkin and Freundlich isotherm models through chemisorption mechanism in both acids with average correlation coefficient value above 0.9. Optical images of MS in both acids without RCC showed severe surface degradation with the degree of degradation being higher from H2SO4 solution. Optical images from RCC inhibited steel depict effective surface protection.

Hydrogenation of cinnamaldehyde to cinnamyl alcohol with metal phosphides: Catalytic consequences of product and pyridine doping

Selective hydrogenation of α,β-unsaturated aldehydes is challenging due to the competition between unsaturated functional groups (CC and CO) with the catalyst. This study probes the use of metal phosphides as selective catalysts for cinnamaldehyde hydrogenation. Monometallic phosphides (MP; M = Ni, Co, Ru) showed high affinity to CC hydrogenation, with 98 % selectivity to hydrocinnamaldehyde with both Ni2P and Co2P. Bimetallic RuMoP improved the cinnamyl alcohol (COL) selectivity up to 91 %, while bimetallic NiMoP preferred CC hydrogenation to hydrocinnamaldehyde. Density functional theory (DFT) suggested greater charge transfer between the carbonyl oxygen and Mo sites on the surface leading to a lower activation energy barrier for cinnamaldehyde hydrogenation to COL. Product and pyridine doping studies resulted in an increased selectivity to COL possibly through surface coverage effects. Lastly, diffuse reflectance infrared Fourier transform spectra and DFT provided insights into the CAL adsorption mode and the reaction mechanism that supported the experimental observation.

Coupling Surface Coverage and Electrostatic Effects on the Interfacial Adlayer–Water Structure of Hydrogenated Single-Crystal Platinum Electrodes

Atomically flat, single-crystal solid–liquid interfaces attract considerable interest through their electrochemical relevance and well-defined structure facilitating controlled atomistic characteri...

A self-adjusting platinum surface for acetone hydrogenation

We show that platinum displays a self-adjusting surface that is active for the hydrogenation of acetone over a wide range of reaction conditions. Reaction kinetics measurements under steady-state and transient conditions at temperatures near 350 K, electronic structure calculations employing density-functional theory, and microkinetic modeling were employed to study this behavior over supported platinum catalysts. The importance of surface coverage effects was highlighted by evaluating the transient response of isopropanol formation following either removal of the reactant ketone from the feed, or its substitution with a similarly structured species. The extent to which adsorbed intermediates that lead to the formation of isopropanol were removed from the catalytic surface was observed to be higher following ketone substitution in comparison to its removal, indicating that surface species leading to isopropanol become more strongly adsorbed on the surface as the coverage decreases during the desorption experiment. This phenomenon occurs as a result of adsorbate-adsorbate repulsive interactions on the catalyst surface which adjust with respect to the reaction conditions. Reaction kinetics parameters obtained experimentally were in agreement with those predicted by microkinetic modeling when the binding energies, activation energies, and entropies of adsorbed species and transition states were expressed as a function of surface coverage of the most abundant surface intermediate (MASI, C3H6OH*). It is important that these effects of surface coverage be incorporated dynamically in the microkinetic model (e.g., using the Bragg-Williams approximation) to describe the experimental data over a wide range of acetone partial pressures.

First-Principles Modeling of the Repassivation of Corrosion Resistant Alloys: Part II. Surface Adsorption Isotherms for Alloys and the Chloride Susceptibility Index

Quantitatively predicting the corrosion resistance of alloys is vital to the design and application of the next generation of superior corrosion resistant alloys (CRAs). Here, the Chloride Susceptibility Index (CSI), a scientifically based quantitative descriptor for repassivation tendency of CRAs, is proposed as a metric constructed through combining atomistically resolved information regarding adsorption and alloy surface composition with environmental conditions such as applied potential, temperature, pH, and Cl− concentration. Using this method, the response of CRAs to relevant environments can be predicted. CSI is determined by: (1) estimation of thermoequilibrium surface coverages of O and Cl by a Langmuir isotherm model using adsorption energies of different species (O, Cl, OH, H2O) obtained from DFT. (2) determination of CSI by integrating Cl surface coverage over a realistic window of applied potentials, thereby incorporating the effect of Cl surface coverage and electrochemical environment simultaneously. A series of Ni-Cr-X alloys was used as an example to develop and validate the method through studying the effect of different alloy solutes X on chloride resistance. The trends and relations predicted by CSI are in qualitative agreements with experimental observations. Moreover, a quantitative correlation is found between CSI and the repassivation potential.

Manipulating photocatalytic pathway and activity of ternary Cu2O/(001)TiO2@Ti3C2Tx catalysts for H2 evolution: Effect of surface coverage

A Cu2O/(001)TiO2@Ti3C2Tx photocatalyst was synthesized via a wet-chemistry reduction method by N, N-dimethylformamide (DMF). By scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), it was revealed that the surface coverage of photocatalyst increased with the loading amount of Cu2O, while the particle size of Cu2O did not change significantly. The photocatalytic activity and mechanism of ternary Cu2O/(001)TiO2@Ti3C2Tx photocatalyst heavily depend on the surface coverage of copper species. When the surface coverage of photocatalyst by Cu2O was low, the Ti3C2Tx acted as hole reservoir. Cu2O was firstly reduced in situ to metallic copper by excited electrons. Then the reverse movement of carriers enabled the spatial separation of photogenerated electron-hole pairs, and afforded relatively high hydrogen evolution (more than 1100 μmol h−1 (g CuOx TiO2)−1). When the coverage of Cu2O on (001)TiO2@Ti3C2Tx was too high at high loading amounts, Ti3C2Tx failed to play the role of hole trapping. Under that circumstance, the photocatalytic reaction follows p-n junction mechanism, leading to low hydrogen productivity. The results here shed light on the relationship between structure and activity of Cu2O/(001)TiO2@Ti3C2Tx, which was conducive to the development of the MXene-based photocatalysts.

Surface coverage effects on water gas shift activity of ZrO2 supported Mo sulfide catalysts

ZrO2-supported Mo sulfide water gas shift (WGS) catalysts were prepared by the incipient wetness impregnation method with varying MoO3 surface coverage. TEM, XRD, Raman spectroscopy and XPS characterization revealed the formation of a topmost Mo-S layer and Mo-O subsurface in the ZrO2-supported Mo sulfide catalysts above MoO3 monolayer surface coverage. The CO conversion during WGS reaction over the ZrO2-supported Mo sulfide catalysts increased with Mo content up to the monolayer coverage and correlated with the extent of Mo sulfidation.

Combined Effects of the Surface Urban Heat Island with Landscape Composition and Configuration Based on Remote Sensing: A Case Study of Shanghai, China

Rapid urbanization leads to changes in surface coverage and landscape patterns. This results in urban heat island (UHI) effects and a series of negative ecological consequences. Considering this concern and taking Shanghai as an example, this paper concentrates on the effects of surface coverage and landscape patterns on urban land surface temperature (LST). The research is based on quantitative retrieval of remote sensing data with consideration of methods in multiple disciplines, including landscape ecology, geographic information systems, and statistical analysis. It concludes that, over time, the thermal environment of Shanghai is becoming critical. The average LST ranking of different surface coverage is as follows: Construction land (CL) > bare land (BL) > green land (GL) > agricultural land (AL) > water body (WB). LST varies significantly with the type of surface coverage. CL contributes the most to the UHI, while WB and GL have obvious mitigation effects on the UHI. The large area, low degree of landscape fragmentation, and complex outlines lead to low LST rankings for GL, WB, and AL and a high LST ranking for CL. The conclusions indicate that CL should be broken down by GL and WB into discrete pieces to effectively mitigate UHI effects. The research reveals UHI features and changes in Shanghai over the years and provides practical advice that can be used by urban planning authorities to mitigate UHI.

Design Considerations of Liquid Gated High Field Modulated FET Biosensor for Enhanced Sensing Characteristics

Medical diagnostics are rapidly evolving to meet the requirements of personalized medicine and home-care based in-vitro diagnostics are in very high demand. Translating the clinical blood based assays into home-care tests pose several challenges. Primarily, we need to develop a compact, portable system that can enable the end user to perform the assay with minimal protocols that can be carried out without prior training, cost-effective and quick response time. More importantly, the home-care tests should retain the sensitivity and selectivity of the laboratory based assays. We previously developed high field modulated field effect transistor (FET) biosensors for the direct detection of protein biomarkers in whole blood. In this work, we investigate the sensor structure in detail to assess the parameters that govern the sensing characteristics. The basic sensor structure includes a functionalized reference electrode to which gate voltage is applied, placed at a narrow gap from the extended gate metal, which is connected to the FET’s gate terminal. The test solution containing the target analyte is placed across the gap such that it is sandwiched between the reference electrode and extended gate metal, together forming the sensing region. It was revealed from our previous studies that there are two ways in which the field generated across the test solution can be modulated: by applying higher amplitude of gate voltage and by decreasing the gap between the electrodes. It was found that at smaller gap distances, the potential drop in the solution is linearly dependent on the gap between the electrodes, and hence higher sensitivity can be observed for smaller gap configurations. In this work we initially explore the gap dependence of sensor response for micron scale and nano scale gap distances. The results indicate that noise characteristics and sensitivity are improved when the gap between the reference electrode and extended gate metal is decreased. The geometry of the sensing areas are also studied to evaluate the optimal electric field distribution across the test solution to generate enhanced sensing characteristics. Finally the surface functionalization is investigated to analyse the effect of surface coverage and number of receptor binding sites on the sensor performance. Through the integration of sensor design, geometry and optimal surface functionalization, we can improve the sensing characteristics, while satisfying the practical considerations of implementation of a home-care whole blood assay.

Effects of carbon quantum dots (CQD) on the energy storage capacity of a novel synthesized short-chain dyad

Abstract The present paper deals with the photophysical and time resolved spectroscopic investigations performed on the pristine short chain dyad, (E)-4-(((9H-fluorene-2-yl)imino)methyl)-N,Ndimethylaniline (NNDMBF) and its nanocomposite forms with CQD or NCQD. The experimental results with dyad-CQD (or NCQD) demonstrate that more than 80% trans structure of the ground state dyad could be protected in the environment of CQD (or NCQD) even on photoexcitation. Formations of elongated trans- conformers show in favor of efficient energy-storage systems. The stability of extended conformation has been hinted to be due to combination of surface coverage and surface trap effects, the later process seems to be the dominating one.

Design Considerations of Liquid Gated High Field Modulated FET Biosensor for Enhanced Sensing Characteristics

Medical diagnostics are rapidly evolving to meet the requirements of personalized medicine. We previously developed high field modulated field effect transistor (FET) biosensors for the direct detection of protein biomarkers in whole blood. In this work, we investigate the sensor structure in detail to assess the parameters that govern the sensing characteristics. The basic sensor structure includes a functionalized reference electrode to which gate voltage is applied, placed at a narrow gap from the extended gate metal, which is connected to the FET’s gate terminal. It was revealed from our previous studies that there are two ways in which the field generated across the test solution, placed in the gap, can be modulated: by applying higher amplitude of gate voltage and by decreasing the gap between the electrodes. It was found that at smaller gap distances, the potential drop in the solution is linearly dependent on the gap between the electrodes, and hence higher sensitivity can be observed for smaller gap configurations. In this work we initially explore the gap dependence of sensor response for micron scale gap distances. The results indicate that noise characteristics and sensitivity are improved when the gap between the reference electrode and extended gate metal is decreased. The geometry of the sensing areas are also studied to evaluate the optimal electric field distribution across the test solution to generate enhanced sensing characteristics. Finally the surface functionalization is investigated to analyse the effect of surface coverage and number of receptor binding sites on the sensor performance.

Effect of various seed metals on uniformity of Ag layer formed by atmospheric plasma reduction on polyethylene terephthalate substrate: An application to electromagnetic interference shielding effectiveness

Dry plasma reduction under atmospheric pressure is a unique approach for stably, continuously, easily, and uniformly fabricating Ag layer on the metal seeds-polyethylene terephthalate (PET) substrate. In this study, effects of particle size, surface uniformity, surface coverage, and film thickness of metal seeds such as Ag, Cu, Fe and Ni on the formation of uniform Ag layer were studied on the basis of their surface free energies and critical radius, which further leads to variations in the sheet resistance levels of the silver layers. The root mean square roughness and sheet resistance of the Ag layer PET substrate were decreased with the deposition of metal seeds. Among the added seed metals, Ni seed has shown best uniformity. Furthermore, the fabricated films were applied for electromagnetic interference (EMI) shielding. Among the added seed metals, Ni has shown the highest electromagnetic interference shielding effectiveness. The present study will be useful for the development of various low-cost metal films in the field of EMI shielding.