Surface Charge Redistribution Research Articles

The charging characteristics of particle–particle contact

Particle–particle collisions play a crucial role in the triboelectric charging in particle-laden flows. However, the mechanism of the charging pattern is still poorly understood. In the present work, electrostatic charging experiments of particle–particle collisions were conducted to explore the charge transfer with different-sized particles. The experimental results show that the polarity of the transferred charge varies with the material type. The influence of the initial charges on the charge transfer was observed, and the influence degree was compared for different materials. The charging behaviors were analyzed based on the charge transfer model driven by the electric potential difference. Through electrostatic analysis, the electric potential difference arising from the electric field of the preexisting surface charges was numerically calculated for the dielectric materials with polarization effects and the ideal non-polarizable material. It was revealed that the potential difference alters significantly owing to the surface charge redistribution of dielectric materials. Dielectric polarization was numerically investigated by varying particle size and relative permittivity of the material. The numerical results explain the discrepancies in the charging tendency of various materials in the experiments.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Advances in enrichment of phosphorylated peptides and glycopeptides by smart polymer-based materials

翻译后修饰是蛋白质组学研究的前沿和重点,它不仅调节着蛋白质的折叠、状态、活性、定位以及蛋白质间的相互作用,也能帮助科学家更全面地了解生物体的生命过程,为疾病的预测、诊断和治疗提供更加强大的支撑和依据。翻译后修饰产物(例如磷酸化肽和糖肽)丰度很低,且存在着强烈的背景干扰,很难直接用质谱进行分析,因此迫切需要开发高效的富集材料和技术来选择性富集翻译后修饰产物。近年来,智能聚合物基材料通过外部物理、化学或生物刺激可逆地改变其结构和功能,实现对磷酸化肽和糖肽高度可控的吸附和脱附,进而衍生开发出一系列新颖的富集方法,极大地吸引研究者们的兴趣。一方面,智能聚合物基材料的响应变化包括材料疏水性的增加或减少、形状和形貌的改变、表面电荷的重新分布以及亲和配体的暴露或隐藏等特性。这些特性使得目标物和智能聚合物基材料之间的亲和力可以通过简单改变外部条件(如温度、pH值、溶剂极性和生物分子等)实现更可控和更智能的精细调节。另一方面,智能聚合物基材料为集成功能模块提供了便捷的可扩展平台,例如特定的识别组件,显著提高了目标物质的分离选择性。智能聚合物基材料在分离方面展现出巨大的潜力,这为蛋白质翻译后修饰产物的分析和研究带来了希望。围绕上述主题,该文依据Web of Science近20年来近50篇代表性文献,概述了智能聚合物基材料在磷酸化肽和糖肽分离及富集中的发展方向。

In-Situ Surface Reconstruction of InN Nanosheets for Efficient CO2 Electroreduction into Formate.

Probing and understanding the intrinsic active sites of electrocatalysts is crucial to unravel the underlying mechanism of CO2 electroreduction and provide a prospective for the rational design of high-performance electrocatalysts. However, their structure-activity relationships are not straightforward because electrocatalysts might reconstruct under realistic working conditions. Herein, we employ in-situ measurements to unveil the intrinsic origin of the InN nanosheets which served as an efficient electrocatalyst for CO2 reduction with a high faradaic efficiency of 95% for carbonaceous product. During the CO2 electroreduction, InN nanosheets reconstructed to form the In-rich surface. Density functional theory calculations revealed that the reconstruction of InN led to the redistribution of surface charge that significantly promoted the adsorption of HCOO* intermediates and thus benefited the formation of formate toward CO2 electroreduction. This work establishes a fundamental understanding on the mechanism associated with self-reconstruction of heterogeneous catalysts toward CO2 electroreduction.

Oxygen vacancy mediated surface charge redistribution of Cu-substituted LaFeO3 for degradation of bisphenol A by efficient decomposition of H2O2

The novel catalyst LaCu0.5Fe0.5O3-δ with oxygen vacancies (OVs) was prepared and demonstrated excellent stability and activity for the degradation of bisphenol A. The removal rate of 92.1 % and H2O2 utilization efficiency of 70.4 % were obtained due to the efficient hydroxyl radical generation mediated by OVs. The density functional theory calculation showed that the substitution of Cu and formation of OVs significantly increases the charge density near the active sites. Bader charge analysis revealed that the charge offset accelerated the reduction of Fe. The elevation of electron transfer efficiency also promotes the valence transition of copper and iron atoms. The reversible electronic transition between Fe2+ ⇆ Fe3+, Cu+ ⇆ Cu2+ and Cu2+ ⇆ Fe2+ involved in this reaction were considered to be enhanced and the homolytic bond clearage of H2O2 was simultaneously promoted, facilitated by the electron-rich region combined with OVs on the surface of LaCu0.5Fe0.5O3-δ.

First-principles study on structural stability and electronic properties of GaAs nanowire undergoing surface oxidization

In this study, the structural stability and electronic properties for oxidized GaAs nanowire surfaces are systematically investigated through first-principles calculations based on density functional theory. Various oxidized nanowire surface models with two interaction types (adsorption and substitution) and different coverages of O atoms (one O, two O, three O and four O atoms) are built. The formation energy, atomic structure, Mulliken charge distribution, work function and dipole moment for each oxidized model are calculated and analyzed. The calculations indicate that the structural stability of oxidized nanowire surfaces is gradually enhanced with increasing O coverage, where O adsorption models are more energetically favorable than O substitution cases. In addition, O atoms interacting with GaAs nanowire surfaces have an obvious influence on the atomic structures near surface layer region, especially the thickness of the first bilayer. Moreover, the incorporation of O atoms leads to the redistribution of surface charge, which is further aggravated with higher coverage of O atoms. Overall, the dipole moment induced by O adsorption or substitution will increase surface work function and thus weaken the surface emission ability.

Surface Study of Fe3O4 Nanoparticles Functionalized With Biocompatible Adsorbed Molecules.

Surfaces of iron oxide of ferrimagnetic magnetite (Fe3O4) nanoparticles (MNPs) prepared by Massart's method and their functionalized form (f-MNPs) with succinic acid, L-arginine, oxalic acid, citric acid, and glutamic acid were studied by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR-S), UV-vis, thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The XPS analysis of elements and their chemical states at the surface of MNPs and f-MNPs revealed differences in chemical bonding of atoms, content of carbon–oxygen groups, iron oxide forms, iron oxide magnetic properties, adsorbed molecules, surface coverage, and overlayer thickness, whereas the Auger parameters (derived from XPS and Auger spectra) and elastic and inelastic scattering probabilities of electrons on atoms and valence band electrons (derived from REELS spectra) indicated modification of surface charge redistribution, electronic, and optical properties. These modified properties of f-MNPs influenced their biological properties. The surfaces biocompatible for L929 cells showed various cytotoxicity for HeLa cells (10.8–5.3% of cell death), the highest for MNPs functionalized with oxalic acid. The samples exhibiting the largest efficiency possessed smaller surface coverage and thickness of adsorbed molecules layers, the highest content of oxygen and carbon–oxygen functionalizing groups, the highest ratio of lattice O2− and OH− to C sp2 hybridizations on MNP surface, the highest ratio of adsorbed O− and OH− to C sp2 hybridizations on adsorbed molecule layers, the closest electronic and optical properties to Fe3O4, and the lowest degree of admolecule polymerization. This high cytotoxicity was attributed to interaction of cells with a surface, where increased content of oxygen groups, adsorbed O−, and OH− may play the role of additional adsorption and catalytic sites and a large content of adsorbed molecule layers of carboxylic groups facilitating Fenton reaction kinetics leading to cell damage.

Demulsification and oil recovery from oil-in-water cutting fluid wastewater using electrochemical micromembrane technology

Abstract A novel electrochemical micromembrane technology coupling membrane and electric method was developed to demulsify oily wastewater and recover oil. The diameter of the oil droplets increased to 55.0 μm from the initial 7.0 μm after treating the emulsion with the electrochemical micromembrane technology. Chemical oxygen demand removal rate and oil recovery reached 87.89% and 5173 mg/L, respectively, after cycling for 90 min at 10.0 V voltage with a 10.0 mm electrode distance, a 5.0 μm micromembrane pore size and a 0.5 L/min flow rate. Micromembrane pore sizes of 1.0 and 5.0 μm were both effective for decreasing chemical oxygen demand and recovering oil. The recovered oil was the mixture of mineral oil and ester according to the Raman infrared spectroscopy analysis. Surface charge redistribution and electrogenerated destruction for hydrophilic groups of surfactant molecules are responsible for oil coalescence. The electrochemical micromembrane technology used in this study offer an attractive treatment option to demulsify oily wastewater.

A highly sensitive graphene oxide based label-free capacitive aptasensor for vanillin detection

Biosynthetic production of vanillin via microbial biotransformation offers a low-cost alternative for manufacturers to meet the consumer demands for natural vanillin. However, identifying the high vanillin-producing microbial strains among multitudinous samples using the current analytical techniques such as liquid chromatography (LC) and mass spectroscopy (MS) is time consuming, cumbersome and costly. Here, we propose an alternative low-cost and rapid aptamer-based capacitive assay for sensitive and selective vanillin recognition based on the preferential binding affinity and stability of the aptamer-vanillin complex. This redox-free approach measures the changes in non-faradaic capacitance of transducing graphene-oxide (GO) activated gold electrodes immobilized with vanillin-specific aptamer. Aptamer-vanillin interaction on the GO surface alters the aptamer conformation causing surface charge redistribution detected via capacitance-frequency characteristics. The aptasensor showed a wide dynamic detection range of 10 pM-10 nM and a low limit of detection (LOD) of ~9.91 pM, which is the best reported so far. Finally, validation of the capacitive aptasensing against high-performance LC (HPLC) reference containing vanillin dissolved in a complex M9 medium with interfering compounds (ferulic acid and glycerol), to mimic typical microbial biotransformation, demonstrated good sensitivity and selectivity. The successful proof-of-concept can be translated to high-throughput electronic multi-analyte screening kits supplementary to existing analytical tools.

Optically Governed Dynamic Surface Charge Redistribution of Hybrid Plasmo-Pyroelectric Nanosystems.

Though plasmonic effect is making some headway in the energy harvesting realm, its fundamental charge transfer mechanism to a large extent is attributed to the hot-carrier generation at the contact interface. Herein this work attempts to elucidate the physical origin of light induced plasmo-pyroelectric enhancement based on charge density manipulation on surface state in the vicinity of the metal-ferroelectric contact interface. More importantly, by tuning the band bending, it is shown that the charge density on the surface state of a hybrid plasmo-pyroelectric (BaTiO3 -Ag) nanosystem can be manipulated and largely increased under the resonant blue light illumination (363 nm). It is also demonstrated that owing to this effect, the spatial pyroelectric activity of a hybrid plasmo-pyroelectric nanosystem governs 46% enhancement in pyroelectric coefficient. This research highlights the optically regulated charge density in plasmo-pyroelectric nanosystems, which could pave a new avenue for energy harvesting/conversion devices with distinguished advantages in wireless, photonic-controlled, localized, and dynamic stimulation.

N-Modified NiO Surface for Superior Alkaline Hydrogen Evolution.

Boosting the sluggish kinetics of the hydrogen evolution reaction in alkaline environments is key for the large-scale application of water-alkali and chlor-alkali electrolysis. In this study, nitrogen atoms are used to precisely modulate electrochemical active sites on the surface of nickel oxide with low-coordinated oxygen atoms, to achieve enhanced kinetics in alkaline hydrogen evolution. Theoretical and experimental results demonstrate that surface charge redistribution after modulation facilitates both the initial water dissociation step and the subsequent recombination of Had from low-coordinated oxygen sites and desorption of OHad- from nickel sites, thus accelerating the overall hydrogen evolution process. The N-modulated nickel oxide enriched in low-coordinated oxygen atoms exhibits significantly enhanced activity with a small overpotential of -100 mV at the current density of -10 mA cm-2 and a robust stability over 90 h for hydrogen evolution in 1.0 m KOH.

Theory of Work Function and Potential of Zero Charge for Metal Nanostructured and Rough Electrodes

We developed a general theory for the work function and potential of zero charge of arbitrary shaped nanostructured and rough metal. Theory accounts for the influence of adsorbed solvent layer, i.e., partial to full solvent coverage, on work function (WF). We show that the change in local WF is due to redistribution of surface charge caused by local surface curvature and adsorbing dipoles. Special cases of spherical and ellipsoidal geometries are obtained from the generic curvature-dependent WF equation to illustrate the size and shape effects. Theory predicts increase in WF of immersed nanoparticles with decrease in their size, while change in shape causes nonuniform WF over the surface. Theory shows anomalous fluctuations in WF for a surface with multiscale roughness, viz., the Weierstrass–Mandelbrot function as a surface. Ensemble or surface averaged work function of randomly curved rough surface is predicted to depend on average mean and Gaussian curvatures. The intrinsic field of various metals regul...

Intensity control of individual DBD plasma filament. II. Fundamental physical mechanism

Filamentary volume dielectric barrier discharge (DBD) produces patterned plasma structures that are currently being explored for reconfigurable metamaterial applications. Previous work has demonstrated control of the presence and intensity of a single DBD plasma filament (within an array of filaments) by biasing a low voltage needle electrode. The results were attributed to redistributed charge inside the DBD due to the modified electric field created by the needle electrode. In the present work, results from a 3D electrodynamic field simulation bolster this argument. Results show that increasing needle bias voltage causes changes in the transverse electric field structure, resulting in redistribution and build-up of surface charge at the needle location. This reduces the needle plasma filament intensity and eventually extinguishes the filament. Specifically, extinguishment of the filament corresponds with the following transitions in the field profile: (1) the applied longitudinal electric field profile along the needle lies below that of the adjacent mesh filament; (2) the surface charge on the dielectric at the needle and adjacent mesh locations is equal; and (3) the transverse electric field reverses direction and forces charge toward the needle location. The calculated surface charge on the dielectric barrier agrees with experimentally measured filament light intensity to within 8%, in agreement with theoretical predictions. Analysis of the data and trends suggests a method for predicting filament pattern formation and reducing the necessary voltage bias.

Binding of Amphipathic Cell Penetrating Peptide p28 to Wild Type and Mutated p53 as studied by Raman, Atomic Force and Surface Plasmon Resonance spectroscopies

BackgroundMutations within the DNA binding domain (DBD) of the tumor suppressor p53 are found in >50% of human cancers and may significantly modify p53 secondary structure impairing its function. p28, an amphipathic cell-penetrating peptide, binds to the DBD through hydrophobic interaction and induces a posttranslational increase in wildtype and mutant p53 restoring functionality. We use mutation analyses to explore which elements of secondary structure may be critical to p28 binding. MethodsMolecular modeling, Raman spectroscopy, Atomic Force Spectroscopy (AFS) and Surface Plasmon Resonance (SPR) were used to identify which secondary structure of site-directed and naturally occurring mutant DBDs are potentially altered by discrete changes in hydrophobicity and the molecular interaction with p28. ResultsWe show that specific point mutations that alter hydrophobicity within non-mutable and mutable regions of the p53 DBD alter specific secondary structures. The affinity of p28 was positively correlated with the β-sheet content of a mutant DBD, and reduced by an increase in unstructured or random coil that resulted from a loss in hydrophobicity and redistribution of surface charge. ConclusionsThese results help refine our knowledge of how mutations within p53-DBD alter secondary structure and provide insight on how potential structural alterations in p28 or similar molecules improve their ability to restore p53 function. General significanceRaman spectroscopy, AFS, SPR and computational modeling are useful approaches to characterize how mutations within the p53DBD potentially affect secondary structure and identify those structural elements prone to influence the binding affinity of agents designed to increase the functionality of p53.

Redistribution of mobile surface charges of an oil droplet in water in applied electric field

Most researches on oil droplets immersed in aqueous solutions assume that the surface charges of oil droplets are, similar to that of solid particles, immobile and distributed uniformly under external electric field. However, the surface charges at the liquid–liquid interface are mobile and will redistribute under external electric field. This paper studies the redistribution of surface charges on an oil droplet under the influence of the external electrical field. Analytical expressions of the local zeta potential on the surface of an oil droplet after the charge redistribution in a uniform electrical field were derived. The effects of the initial zeta potential, droplet radius and strength of applied electric field on the surface charge redistribution were studied. In analogy to the mobile surface charges, the redistribution of Al2O3-passivated aluminum nanoparticles on the oil droplet surface was observed under applied electrical field. Experimental results showed that these nanoparticles moved and accumulated towards one side of the oil droplet under electric field. The redistribution of the nanoparticles is in qualitative agreement with the redistribution model of the mobile surface charges developed in this work.

First-principles investigation of stability diagram and electronic properties of SrHfO3 (110) polar terminations

A first-principles thermodynamics characterization of the stabilities and structures of SrHfO3 (110) polar terminations has been performed using density functional theory simulations and the surface grand potential technique. The investigated terminations include the SrHfO-, O2-, HfO-, Sr-, and O-terminated (110) surfaces. Based on the computed surface relaxations (reconstructions), charge redistribution, and electronic structures, the polarity compensation mechanisms of the terminations, i.e., how the polarity compensation criterion is fulfilled, are discussed in detail. To account for the effect of the chemical environment and make a reasonable comparison, the (001) surface and the precipitation of small mono-metal oxide crystals on the grown surfaces are considered in the construction of the stability diagram. Based on the constructed stability phase diagram, the stability regions of the (110) and (001) terminations are determined. Additionally, a comparison of the stability behaviors with several analogues is further drawn.

Single component gold on protonated titanate nanotubes for surface-charge-mediated, additive-free dehydrogenation of formic acid into hydrogen

Surface charge redistribution between gold nanoparticles and protonated titanate nanotubes leads to high catalytic activity of single component gold for additive-free dehydrogenation of formic acid into hydrogen.

Experimental Investigation of Eletrokinetic Stabilization of Gravitational Drainage of Ionic Surfactants Films

Gravitational drainage of vertical films of ionic surfactants supported on a frame with the upper and lower parts being electrodes is studied experimentally. The electric field introduces three additional physical phenomena: (i) the surface charge redistribution, which eventually changes surface elasticity, (ii) the electroosmotic flow in the diffuse layer, and (iii) pressure build-up near the electrode toward which the electroosmotic flow is directed. It is shown that stabilization of the films is possible either due to the traction imposed by the electroosmotic flow directed upward (against gravity), or due to the pressure build-up near the lower end of the frame, in cases where the electroosmotic flow is directed downward (in the gravity direction) and enters a dead end at the lower electrode.

Dependences of ZnO Photoinduced Hydrophilic Conversion on Light Intensity and Wavelengths

The present study explored the effect of light intensity and spectral variation of the actinic light on the hydrophilic conversion of the surface of ZnO nanocoatings. The dependence on light intensity indicates that both formation and destruction of the surface hydrophilic states occurs in parallel. The proposed kinetic mechanism corresponds well with experimental dependences. The spectral dependence of the photoinduced hydrophilic conversion of the ZnO surface suggests the important role of electronic photoexcitation of the solid. Similarity between the spectral distributions of the efficiency of photoinduced hydrophilic conversion and the ratio between the surface concentrations of electrons and holes (estimated on the basis of the ratio between quantum yields of oxygen and methane photostimulated adsorption) infers that the reason for the hydrophilicity alteration is the surface charge redistribution caused by actinic light.

Isoconductivity method to study adhesion of yeast cells to gold electrode

Abstract In this paper, we used impedance spectroscopy and gold electrodes to detect the presence of yeast cells and monitor the attachment of these cells to the electrodes. We analyzed the effect of conductivity changes of the medium and the attachment on the electrode-electrolyte interface impedance. A three-electrode cell was designed to produce a uniform electric field distribution on the working electrode and to minimize the counter electrode impedance. Moreover, we used a small AC overpotential (10 mV) to keep the system within the linear impedance limits of the electrode-electrolyte interface. This study proposes a new method to differentiate the impedance changes due to the attachment of yeast cells from those due to conductivity changes of the medium. The experiments showed that when the difference between the cell suspension and base solution conductivities is within the experimental error, the impedance changes are only due to the attachment of yeast cells to the electrodes. The experiments also showed a strong dependence (decrease) of the parallel capacity of the electrode electrolyte interface with the yeast cell concentration of suspension. We suggest that this decrease is due to an asymmetrical redistribution of surface charges on both sides of cell, which can be modeled as a biologic capacity connected in series with the double layer capacity of the interface. Our results could help to explain the rate of biofilm formation through the determination of the rate of cell adhesion.