Effect Of Surface Charge Research Articles

Substantial impact of surface charges on electrochemical reaction kinetics on S vacancies of MoS2 using grand-canonical iteration method.

The surface charges of catalysts have intricate influences on the thermodynamics and kinetics of electrochemical reactions. Herein, we develop a grand-canonical iteration method based on density functional theory calculations to explore the effect of surface charges on reaction kinetics beyond the traditional Butler-Volmer picture. Using the hydrogen evolution reaction on S vacancies of MoS2 as an example, we show how to track the change of surface charge in a reaction and to analyze its influence on the kinetics. Protons adsorb on S vacancies in a tough and charge-insensitive water splitting manner, which explains the observed large Tafel slope. Grand-canonical calculations report an unanticipated surface charge-induced change of the desorption pathway from the Heyrovsky route to a Volmer-Tafel route. During an electrochemical reaction, a net electron inflow into the catalyst may bring two effects, i.e., stabilization of the canonical energy and destabilization of the charge-dependent grand-canonical part. On the contrary, a net outflow of electrons from the catalyst can reverse the two effects. This surface charge effect has substantial impacts on the overpotential and the Tafel slope. We suggest that the surface charge effect is universal for all electrochemical reactions and significant for those involving interfacial proton transfers.

Modulating in vitro gastrointestinal digestion of nanocellulose-stabilized pickering emulsions by altering particle surface charge

An in vitro model of human gastrointestinal digestion was introduced to investigate the effects of surface charge of cellulose nanoparticles on emulsion structure during gastric phase, lipase activity, bile salt diffusion, and free fatty acid (FFA) release. Four carboxymethylated cellulose nanofibrils (CNF; C0, C0.36, C0.72, and C1.24) were used, showing different surface charge (p < 0.05). First, four carboxymethylated CNFs had no inhibition effects on lipase activity and bile salt diffusion. Moreover, we found that the lipid emulsion containing CNF formed gel structure to induce oil droplets aggregation during simulated gastric phase. Additionally, the particle surface charge greatly influenced the gel structure of emulsion where a denser gel structure was observed in the C0 (lowest surface charged CNF) stabilized emulsion. Finally, the released FFA results showed that the formed gel structure lowered the lipid emulsion digestion attributed to the restricted adherent area of oil droplets for lipase and bile salt.

Combined Effects of Core Rigidity and Surface Charge of Polymeric Nanomicelles on the Cellular Uptake Efficiency

Combined Effects of Core Rigidity and Surface Charge of Polymeric Nanomicelles on the Cellular Uptake Efficiency

Casimir force between semiconductor and metal and compensation of surface charges

Measurement of the Casimir forces is restricted by well-conducting materials, for which the residual electrostatic force can be compensated. For semiconductors and dielectrics, it is considered as impossible due to the effect of surface charging. In this paper, the possibility to compensate for the electrostatic interaction between a metal and poor conducting material is analyzed. It is shown that the electrostatic force can be compensated at certain conditions. For semiconductors, it is possible if the sign of the surface charges is opposite to that of the main carriers. Otherwise, the compensating potential is too large and distance dependent. For dielectrics, the surface charges can be compensated for a thin dielectric film deposited on a good conductor. These findings open the way to investigate the Casimir interaction for poor-conducting materials.

Profound Changes in Functional Structure and Dynamics of Serum Albumin in Children with Nephrotic Syndrome: An Exploratory Research Study.

Patients with nephrotic syndrome (NS) suffer from urinary loss of albumin. As a cause, previous studies focused on the glomerular filter rather than analyzing the molecular properties of albumin itself. Later one was initiated by clinical observations indicating unexplained molecular alterations of human serum albumin (HSA) in an NS pediatric patient. Therefore, we examined serum from eight pediatric patients with steroid-sensitive and -resistant NS and compared it with serum from healthy subjects as well as commercial HSA. We used dynamic and electrophoretic light scattering to characterize the protein size and effective surface charge and electron paramagnetic resonance spectroscopy to measure the local environment and binding dynamics of up to seven fatty acids associated with HSA. Our findings suggest that pronounced differences in binding behavior and surface charge of HSA could enhance their filtration through the GBM, leading to direct toxicity of HSA to podocytes.

Micellization of a cationic and an anionic surfactant in the presence of diphenylcarbazide in aqueous media and the effect of micelle surface charge on the complexation of the solubilised ligand with metal ions

ABSTRACT In the present study, we carried out conductometric and surface tension analyses to report the critical micelle concentration (CMC) of tetradecyltrimethyl ammonium bromide (TTAB) and sodium dodecyl sulphate (SDS) as a function of the concentration of a diphenylcarbazide (DPC). It is found that the micellization of TTAB becomes unfavourable while that of SDS becomes favourable in the presence of DPC. This indicates a substantial difference in the mutual interaction of the sparingly soluble ligand with the cationic and the anionic surfactants. The complexation ability of the solubilised DPC with hydrated Zn(II) and Cd(II) ions at varying concentrations of the cationic and anionic surfactants was studied by UV–Vis spectral analyses. With increasing the concentration of both surfactants up to their respective CMC values, the absorbance of the metal–DPC complex increases. However, the absorbance of the complex in TTAB micelles sharply decreases, showing almost zero values beyond the CMC, but that in SDS remains almost steady with increasing the concentration of the surfactant, as evidenced from the visible spectra.

Effect of initial particle size and surface charge on the formation of the plasma protein corona on chitosan‐based nanoparticles

AbstractWhen a nanoparticle interacts with the biological environment, its surface is covered by a layer of biomolecules such as proteins and lipids called a protein corona. Given the importance and impact of the protein corona on the fate of nanoparticles in the body, it is important to study the interaction of nanoparticles with proteins. This study investigated the impact of the initial size and surface charge of nanoparticles on the changes in protein corona thickness on chitosan‐based nanoparticles after exposure to blood plasma. To be able to separate the chitosan‐based nanoparticles from the blood plasma, magnetic nanoparticles were coated with chitosan (with a positive charge) and carboxymethyl chitosan (CMC; with a negative charge) in two different size ranges of 200–250 and 300–350 nm. The coated nanoparticles' chemical composition, properties, and morphology were investigated using Fourier‐transform infrared spectroscopy, X‐ray diffraction, dynamic light scattering (DLS), zeta potential measurements, transmission electron microscopy, and field emission scanning electron microscope. The results confirmed the formation of nanoparticles based on chitosan and CMC. Subsequently, these nanoparticles were exposed to blood plasma to examine the protein corona that formed. The DLS and zeta potential measurements showed that the surface charge and particle size of the nanoparticles significantly influenced the formation of the protein corona. The results revealed that the smaller particle size and the positive surface charge of the nanoparticles resulted in the formation of a thicker corona. In addition, it showed that after exposure to the blood plasma proteins, the positive charge of the particles changed to a negative charge.

S-scheme regulated Ni2P-NiS/twinned Mn0.5Cd0.5S hetero-homojunctions for efficient photocatalytic H2 evolution

Effective bulk phase and surface charge separation is critical for charge utilization during the photocatalytic energy conversion process. In this work, the ternary Ni2P-NiS/twinned Mn0.5Cd0.5S (T-MCS) nanohybrids were successfully constructed via combining Ni2P-NiS with T-MCS solid solution for visible light photocatalytic H2 evolution. T-MCS is composed of zinc blende Mn0.5Cd0.5S (ZB-MCS) and wurtzite Mn0.5Cd0.5S (WZ-MCS) and those two alternatively arranged crystal phases endow T-MCS with excellent bulk phase charge separation performance for the slight energy level difference between ZB-MCS and WZ-MCS. S-scheme carriers transfer route between NiS and T-MCS can accelerate the interfacial charge separation and retain the active electrons and holes, meanwhile, co-catalyst Ni2P as electron receiver and proton reduction center can further optimize the H2 evolution reaction kinetics based on the surface Schottky barrier effect. The above-formed homo-heterojunctions can establish multiple charge transfer channels in the bulk phase of T-MCS and interface of T-MCS and Ni2P-NiS. Under the synergistic effect of twinned homojunction, S-scheme heterojunction, and Schottky barrier, the ternary Ni2P-NiS/T-MCS composite manifested an H2 production rate of 122.5 mmol h–1 g–1, which was 1.33, 1.24, and 2.58 times higher than those of the NiS/T-MCS (92.4 mmol h–1 g–1), Ni2P/T-MCS (98.4 mmol h–1 g–1), and T-MCS (47.5 mmol h–1 g–1), respectively. This work demonstrates a promising strategy to develop efficient sulfides photocatalyst toward targeted solar-driven H2 evolution through homo-heterojunction engineering.

Effect of Colloidal Surface Charge on Desiccation Cracks.

We report the effect of polarity and surface charge density on the nucleation and growth kinetics of desiccation cracks in deposits of colloids formed by drying. We show that the average spacing between desiccation cracks and crack opening are higher for the deposit of positively charged colloids than that of negatively charged colloids. The temporal evolution of crack growth is found to be faster for positively charged particle deposits. The distinct crack patterns and their kinetics are understood by considering the spatial arrangement of particles in the deposit, which is strongly influenced by the substrate-particle and particle-particle interactions. Interestingly, the crack spacing, the crack opening, and the rate at which the crack widens are found to increase upon decreasing the surface charge of the colloids.

Gradience Free Nanoinsertion of Fe3O4 into Wood for Enhanced Hydrovoltaic Energy Harvesting.

Hydrovoltaic energy harvesting offers the potential to utilize enormous water energy for sustainable energy systems. Here, we report the utilization and tailoring of an intrinsic anisotropic 3D continuous microchannel structure from native wood for efficient hydrovoltaic energy harvesting by Fe3O4 nanoparticle insertion. Acetone-assisted precursor infiltration ensures the homogenous distribution of Fe ions for gradience-free Fe3O4 nanoparticle formation in wood. The Fe3O4/wood nanocomposites result in an open-circuit voltage of 63 mV and a power density of ∼52 μW/m2 (∼165 times higher than the original wood) under ambient conditions. The output voltage and power density are further increased to 1 V and ∼743 μW/m2 under 3 suns solar irradiation. The enhancement could be attributed to the increase of surface charge, nanoporosity, and photothermal effect from Fe3O4. The device exhibits a stable voltage of ∼1 V for 30 h (3 cycles of 10 h) showing good long-term stability. The methodology offers the potential for hierarchical organic-inorganic nanocomposite design for scalable and efficient ambient energy harvesting.

Acetylcholinesterase Adsorption on Modified Gold: Effect of Surface Chemistry on Enzyme Binding and Activity.

Surface chemistry plays a crucial role in the performance of biosensors and biocatalysts, where enzymes directly interact with a solid support. In this work, we investigated the effect of surface charge and hydrophobicity on the binding and activity of acetylcholinesterase (AChE) following direct adsorption to modified gold surfaces. Surface modifications included self-assembled monolayers (SAMs) terminated with -COO-, -NH3+, -OH, and -CH3 functional groups at varying mole %. We also investigated the effects of positively and negatively charged helical peptides covalently coupled to the SAM. Using spectroscopic ellipsometry, we measured the surface concentration of AChE on each modified surface after 1 h of adsorption. We found that surface concentration was directly proportional to surface hydrophobicity (r = 0.76). The highest binding was observed on the more hydrophobic surfaces. We also measured the specific activity of AChE on each surface using a colorimetric assay and found that activity was inversely proportional to surface hydrophobicity (r = -0.71). The highest activity was observed on the more hydrophilic surfaces. Plotting specific activity versus surface concentration showed a similar relationship, with the highest activity observed at low AChE densities (∼20% of a monolayer) on surfaces terminated with 50% -COO- or -NH3+ and 50% -CH3 functional groups. Interestingly, this is similar to the approximate composition of hydrophobic versus hydrophilic amino acid residues on the surface of AChE. These surfaces also exhibited the highest total activity: a ∼100% improvement over bare gold due to a combination of moderate binding and high activity retention. This work highlights the importance of developing new attachment strategies beyond direct adsorption that promote, tune, and optimize both high binding and high activity retention.

Anti-biofouling membranes via hydrogel electron beam modification – A fundamental and applied study

Biofouling is still a major challenge in membrane science and accounts for up to 70% of the total costs of membrane-operated filtration systems. Thus, in this work, a thin layer of diverse synthetic hydrogels has been applied via electron beam-initiated polymerization on a polyethylene terephthalate (PET) track-etched membrane (fundamental study) as a simple model membrane and on a conventional used polyethersulfone (PES) ultrafiltration membrane (applied study) to study its anti-biofouling properties. The effect of hydrophilicity, roughness, surface charge, and degree of swelling of the attached hydrogel on algae (Chlorella Vulgaris) fouling was studied in a fundamental way, and long-time tests in a membrane bioreactor (MBR, filtration area 1.5 m2) over 11 months were performed on an applied scale. The hydrophilicity, roughness, and surface charge had only a minor to no effect on algae fouling. Only the degree of swelling had an impact on biofouling. The membranes with hydrogels with a low degree of swelling (6%) showed a lower loss of permeability (only 5%) after fouling, compared to a 25% loss with the highest degree of swelling (25%). During the operation over 11 months in a membrane bioreactor (MBR), the permeability is higher (ca. 10%) in a module equipped with hydrogel modified membranes, compared to a module with reference membranes. Thus, modification of membranes with a thin layer of a hydrogel results in an anti-biofouling surface. The degree of swelling is a decisive parameter to control biofouling.

Thermo-Osmosis in Charged Nanochannels: Effects of Surface Charge and Ionic Strength.

Thermo-osmosis refers to fluid migration due to the temperature gradient. The mechanistic understanding of thermo-osmosis in charged nano-porous media is still incomplete, while it is important for several environmental and energy applications, such as low-grade waste heat recovery, wastewater recovery, fuel cells, and nuclear waste storage. This paper presents results from a series of molecular dynamics simulations of thermo-osmosis in charged silica nanochannels that advance the understanding of the phenomenon. Simulations with pure water and water with dissolved NaCl are considered. First, the effect of surface charge on the sign and magnitude of the thermo-osmotic coefficient is quantified. This effect was found to be mainly linked to the structural modifications of an aqueous electrical double layer (EDL) caused by the nanoconfinement and surface charges. In addition, the results illustrate that the surface charges reduce the self-diffusivity and thermo-osmosis of interfacial liquid. The thermo-osmosis was found to change direction when the surface charge density exceeds -0.03C · m-2. It was found that the thermo-osmotic flow and self-diffusivity increase with the concentration of NaCl. The fluxes of solvent and solute are decoupled by considering the Ludwig-Soret effect of NaCl ions to identify the main mechanisms controlling the behavior. In addition to the advance in microscopic quantification and mechanistic understanding of thermo-osmosis, the work provides approaches to investigate a broader category of coupled heat and mass transfer problems in nanoscale space.

A Voltammetric Sensor Based on Aluminophosphate Zeolite and a Composite of Betulinic Acid with a Chitosan Polyelectrolyte Complex for the Identification and Determination of Naproxen Enantiomers

A voltammetric sensor was developed based on a glassy carbon electrode with aluminophosphate zeolite finely dispersed on its surface, modified with a polyelectrolyte complex of chitosan with succinyl chitosan and betulinic acid, for the selective detection and determination of naproxen enantiomers. The electrochemical and analytical characteristics of the sensor were studied, and the effective electrode surface area (A = 9.8 ± 0.5 mm2) and charge transfer resistance (Ret = 649.9 ± 0.4 Ω) were calculated. In determining naproxen enantiomers, calibration characteristics are linear in the range from 2.5 × 10–5 to 1 × 10–3 M with limits of detection of 1.1 × 10–7 and 1.5 × 10–7 M and limits of quantification of 3.6 × 10–7 and 4.9 × 10–7 M for R- and S-naproxen, respectively. The sensor is more sensitive to R-naproxen (∆Ep = 60 mV, ipR/ipS = 1.40). The proposed sensor was used to recognize and determine naproxen enantiomers in human urine and plasma samples. Statistical evaluation of the results by the standard addition method showed that there was no systematic error.

Influence of size and surface charge on the adsorption behaviour of silicon dioxide nanoparticles on sand particles

The use of silicon dioxide (SiO2) nanoparticles as additives and filter materials in the oil and gas industry for mitigating sand control and fines migration problems has garnered significant attention in recent years. Despite the growing interest, the effect of size and surface charge on the adsorption behaviour of silicon dioxide nanoparticles on sand particles remains inadequately studied. This study aimed to address this knowledge gap by investigating the influence of size and surface charge on the adsorption isotherm of silicon dioxide nanoparticles onto sand particles. The SiO2 nanoparticles were synthesized using the sol-gel method into three different sizes (30, 70, and 120 nm), effectively providing different reactive surface areas, which were confirmed through the use of Dynamic Light Scattering (DLS) and Brunauer-Emmett-Teller (BET). The surface charge of the silicon dioxide was altered by functionalizing into a negatively charged carboxyl group and a positively charged quaternary ammonium group which was confirmed using Fourier-transform infrared (FTIR) spectroscopy and zeta potential. Ultraviolet-visible (UV–vis) spectroscopy was used to determine the concentration of adsorbed nanoparticles in solutions with different ionic strength and electrolyte type. Data analysis involved regression models, ANOVA, and t-tests. The adsorption isotherm was best fitted by the Langmuir model, indicating monolayer adsorption. The result indicates that SiO2 size, SiO2 concentration, and SiO2 charge levels significantly affect adsorption behaviour, whereas electrolyte type and electrolyte concentration do not have a significant effect. Smaller nanoparticles exhibited higher adsorption capacity, and positively charged nanoparticles displayed greater affinity for adsorption. The presence of electrolyte and its concentration although statistically insignificant, had a negative impact on the electrostatic interactions. This study provides insights into the effect of size and surface charge on nanoparticle adsorption of nanoparticles onto sand particles, contributing to the field of sand control and fines migration.

Interfacial Charge Transfer Modulated Static Friction Resistance of Water Drops.

The sliding of liquid drops over solid surfaces is a common phenomenon in nature and crucial in a variety of technological applications. Frictional dissipation along the contact line and viscous dissipation has long been regarded to dominate drop sliding. However, the ubiquitous solid-liquid interface charge transfer has received little attention. In this study, we systematically investigated the interfacial charge transfer between water drops and polarized poly(vinylidene fluoride) (ferroelectric insulator) surfaces and the effects of surface charge on static friction resistances acting on water drops. It is found that static friction resistance, reflected by the corresponding critical sliding angle, has a fourth-order function dependence on the surface potential as revealed by experiments and theoretical modeling. Interfacial charge transfer could either strengthen or weaken the surface potential up to the charge density carried by the water drops and substrates, thus resulting in the change of static friction resistance during sequential drop sliding. These findings apply to generalized problems for water at solid surfaces with charged interfaces (water, solid, or both are charged) and highlight the pivotal role of charge transfer at liquid-solid interfaces in governing drop motion.

Surface charge induced self-assembled nest-like Ni3S2/PNG composites for high-performance supercapacitors

The paper presents a self-assembly approach to synthesize Ni3S2/N, P co-doped graphene (PNG) composite electrode materials for supercapacitors with high energy storage performance and structural stability. Innovatively, the self-assembly approach is induced via the surface charge effect utilizing a two-step hydrothermal method. The doping of nitrogen (N) and phosphorus (P) atoms regulates the surface charge distribution on graphene nanosheets. Therefore, in the synthesized Ni3S2/PNG heterostructures, Ni3S2 nanowires are interwoven into nests and uniformly attached to PNG. The design of the electrode materials with such a special structure not only supports each other to improve the stability of the materials but also facilitates the rapid diffusion of electrolyte ions. Based on the advantages of composition and structure, Ni3S2/PNG has a high specific capacitance of 1117C g−1 at a current density of 1 A/g and excellent rate performance. The asymmetric supercapacitors (ASC) assembled with Ni3S2/PNG and PNG as positive and negative materials respectively have a high energy density of 62 Wh kg−1 at a power density of 158 W kg−1.

Rivastigmine-DHA ion-pair complex improved loading in hybrid nanoparticles for better amyloid inhibition and nose-to-brain targeting in Alzheimer’s

Rivastigmine hydrogen tartrate (RIV-HT) is given orally for Alzheimer's disease. However, oral therapy shows low brain bioavailability, short half-life and gastrointestinal-mediated adverse effects. RIV-HT intranasal delivery can avoid these side effects, but its low brain bioavailability remains challenging. These issues could be solved with hybrid lipid nanoparticles with enough drug loading to enhance RIV-HT brain bioavailability while avoiding oral route side effects. The RIV-HT and docosahexaenoic acid (DHA) ion-pair complex (RIV:DHA) was prepared to improve drug loading into lipid-polymer hybrid (LPH) nanoparticles. Two types of LPH, i.e., cationic (RIV:DHA LPH(+ve)) and anionic LPH (RIV:DHA LPH(-ve)) were developed. The effect of LPH surface charge on in-vitro amyloid inhibition, in-vivo brain concentrations and nose-to-brain drug targeting efficiency were investigated. LPH nanoparticles showed concentration dependant amyloid inhibition. RIV:DHA LPH(+ve) demonstrated relatively enhanced Aβ1-42 peptide inhibition. The thermoresponsive gel embedded with LPH nanoparticles improved nasal drug retention. LPH nanoparticles gel significantly improved pharmacokinetic parameters compared to RIV-HT gel. RIV:DHA LPH(+ve) gel showed better brain concentrations than RIV:DHA LPH(-ve) gel. The histological examination of nasal mucosa treated with LPH nanoparticles gel showed that the delivery system was safe. In conclusion, the LPH nanoparticle gel was safe and efficient in improving the nose-to-brain targeting of RIV, which can potentially be utilized in managing Alzheimer's.

Effects of size and surface charge on the sedimentation of nanoplastics in freshwater

The environmental issues caused by nanoplastics (NPs) are increasingly noticeable. Environmental behavior study of the NPs could provide vital information for their environmental impact assessment. However, associations between NPs' inherent properties and their sedimentation behaviors were seldom investigated. In this study, six types of PSNPs (polystyrene nanoplastics) with different charges (positive and negative) and particle sizes (20–50 nm, 150–190 nm and 220–250 nm) were synthesized, and their sedimentations under different environmental factors, (e.g., pH value, ionic strength (IS), electrolyte type and natural organic matter) were investigated. Results displayed that both particle size and surface charge would affect the sedimentation of PSNPs. The maximum sedimentation ratio of 26.48% was obtained in positive charged PSNPs with size of 20–50 nm, while the minimum sedimentation ratio of 1.02% was obtained in negative charged PSNPs with size of 220–250 nm at pH 7.6. The pH value shift (range of 5–10) triggered negligible changes of sedimentation ratio, the average particle size and the Zeta potential. Small size PSNPs (20–50 nm) showed higher sensitivity to IS, electrolyte type and HA condition than large size PSNPs. At high IS value (ISCaCl2 = 30 mM or ISNaCl = 100 mM), the sedimentation ratios of the PSNPs all increased differently according to their properties, and the sedimentation promoting effect of CaCl2 was more significant on negative charged PSNPs than positive charged PSNPs. When ISCaCl2 increased from 0.9 to 9 mM, the sedimentation ratios of negative charged PSNPs increased by 0.53%–23.49%, while that of positive charged PSNPs increased by less than 10%. Besides, humic acid (HA) addition (1–10 mg/L) would lead to a stable suspension status for PSNPs in water with different degree and perhaps different mechanism due to their charge characteristics. These results showed new light on influence factor studies of NPs' sedimentation and would be helpful for further knowledge of NPs’ environmental behaviors.

Application of community data to surface complexation modeling framework development: Iron oxide protolysis

This study presents a comprehensive community data-driven surface complexation modeling framework for simulating potentiometric titration of mineral surfaces. Compiled community data for ferrihydrite, goethite, hematite, and magnetite are fit to produce representative protolysis constants that can reproduce potentiometric titration data collected from multiple literature sources. Using this framework, the impact of surface complexation model type and surface site density (SSD) on the fit quality and protolysis constants can be readily evaluated. For example, the non-electrostatic model yielded a poor data fit compared to diffuse double layer model and constant capacitance models due to the absence of known surface charge effects. Regardless of the choice of iron oxide mineral, pKa1 decreased with increasing SSD while the opposite tendency was observed for pKa2. This newly developed framework demonstrates a method to reconcile community data-wide potentiometric titration data using Findable, Accessible, Interoperable, Reusable data principles to produce mineral protolysis constants that improve robustness of surface complexation models for applications in metal sorption and reactive transport modeling. The framework is readily expandable (as community data increase) and extensible (as the number of minerals increase). The framework provides a path forward for developing self-consistent, comprehensive, and updateable surface complexation databases for surface complexation and reactive transport modeling.