Electrostatic Attractive Forces Research Articles

TMN4 complex embedded graphene as efficient and selective electrocatalysts for chlorine evolution reactions

In the industrial large-scale chlor-alkali process, the electrocatalytic chlorine evolution reaction (CER) is a crucial half anodic reaction. However, the concomitant oxygen evolution reaction (OER) is unavoidable by using the noble metal-based dimensionally stable anodes (DSAs) as CER benchmark catalysts. Through purposely screening six TMN4 complexes embedded graphene with the demonstrated low performance of OER, our density functional theory (DFT) results predict that NiN4 complex embedded graphene (NiN4@G) can efficiently catalyse the CER. This single-atom catalyst (SAC) shows superior CER activity with the ultralow thermodynamic overpotential of 0.014 V via the Cl* intermediate instead of the formation of the ClO*. Moreover, its high theoretical overpotential of OER inherently promotes the selectivity of chlorine evolution. The analyses of the bonding mechanism between TM and Cl atoms reveal that their electrostatic attraction forces can be a good descriptor for the discovery of high-performance CER electrocatalysts. Our findings may broaden the scope of CER catalysts design beyond DSAs with the maximized metal atom utilization.

English

In the present study, modeling of 19 adsorption isotherms, 8 kinetic models and thermodynamics of methylene blue (MB) adsorption on chitosan flakes synthesized using Archachatina marginata shell wastes was investigated in a batch mode. The operational parameters’ effects on the MB adsorption were studied. The model parameters were statistically analyzed using 10 error functions. The choices of the best fitted adsorption and kinetic models were based on the comparison of the sum of normalized error (SNE) and two statistical tools of information-based criteria. The 5-p Fritz-Schlüender isotherm best fitted the experimental adsorption data of MB on chitosan flakes based on SNE whereby maximum adsorption capacity, , of 143.6660 mg/g was obtained.  The adsorption rate of MB on chitosan flakes was kinetically described by pseudo second-order model at all initial concentrations of MB investigated, with film diffusion being the rate-controlling step and the adsorption process chemisorption-influenced. The calculated thermodynamic parameters, = 4.23 kJ/mol, = 0.4563 kJ/(mol K), negative  values revealed that the adsorption of MB onto chitosan flakes was physical, endothermic, spontaneous, energetically favorable and exergonic.  The reaction mechanism of the adsorption of MB onto chitosan flakes was proposed taking cognizance of the electrostatic force of attraction between the negatively charged surface of the chitosan (biosorbent) and the positively charged MB.   Key words: chitosan, dye adsorption, isotherm, kinetics, thermodynamics, information-based criteria.

STUDY OF TOXICITY OF L-THYROXIN IMMOBILIZED CHITOSAN AND THE NATURE OF DRUG-POLYMER INTERACTION

STUDY OF TOXICITY OF L-THYROXIN IMMOBILIZED CHITOSAN AND THE NATURE OF DRUG-POLYMER INTERACTION

Reverse Micellar Extraction of Copper Ions from Wastewater: Modelling and Simulation

The waste streams from various agencies like textile, leather, electroplating, and process industries are generating pollutants in the form of effluents or by products. These waste streams consist of various carcinogenic pollutants such as dyes and heavy metals above the permissible limits. Numerous effluent treatment techniques have been implemented for the removal of these pollutants before their discharge into the water body. In this work, reverse micellar extraction was used for the removal of copper ions (heavy metal ions) from the waste stream. Mathematical models namely, the ion exchange reaction model and electrostatic model were developed in order to compare the experimental data with model predictions with regard to the effect of process parameters such as initial metal ion concentration, sodium bis-2-ethyl hexyl sulphosuccinate (AOT) concentration, and organic to aqueous phase volume ratio on final copper ion concentration in the aqueous phase. The ion exchange reaction model was based on chemical and electrostatic interactions between heavy metal ions and the surfactant head groups at the reverse micellar interface, whereas the electrostatic model was based on the adsorption of metal ions on the reverse micellar interface due to electrostatic force of attraction with no chemical bonding. The developed mathematical models were found in close agreement with the experimental data. Atomic absorption spectroscopy (AAS) was used to measure the metal ion concentration in the aqueous phase.

Augmented Self-Association by Electrostatic Forces in Thienopyrrole-Fused Thiadiazoles that Contain an Ester instead of an Ether Linker.

During the self-assembly of π-conjugated molecules, linkers and substituents can potentially add supportive noncovalent intermolecular interactions to π-stacking interactions. Here, we report the self-assembly behavior of thienopyrrole-fused thiadiazole (TPT) fluorescent dyes that possess ester or ether linkers and dodecyloxy side chains in solution and the condensed phase. A comparison of the self-association behavior of the ester- and ether-bridged compounds in solution using detailed UV-vis, fluorescence, and NMR spectroscopic studies revealed that the subtle replacement of the ether linkers by ester linkers leads to a distinct increase in the association constant (ca. 3-4 fold) and the enthalpic contribution (ca. 3 kcal mol-1 ). Theoretical calculations suggest that the ester linkers, which are in close proximity to one another due to the π-stacking interactions, induce attractive electrostatic forces and augment self-association. The self-assembly of TPT dyes into well-defined 1D clusters with high aspect ratios was observed, and their morphologies and crystallinity were investigated using SEM and X-ray diffraction analyses. TPTs with ester linkers exhibit a columnar liquid crystalline mesophase in the condensed phase.

Encapsulation of halocadmate anion via hydrogen bonding: synthesis and characterization of bis(diethylenetriamine)cobalt(III) complex containing hexabromocadmate anion.

In this work, the encapsulation of [CdBr6]4- by six cations, [Co(dien)2]3+ has been described with the help of single crystal X-ray structural study in the complex, mer-[Co(dien)2]2[CdBr6]Br2. The complex anion, [CdBr6]4- has been obtained through solution method while attempting to synthesize complex dianion, [CdBr4]2-. This newly synthesized complex has been initially characterized by elemental analyses and spectroscopic studies (IR, NMR and UV-Visible). IR and NMR studies have been used for the isomeric identification of [Co(dien)2]3+. Single crystal X-ray structure determination has revealed the presence of two complex cations, [Co(dien)2]3+, one complex anion, [CdBr6]4-, and two Br- anions. The complex has crystallized in monoclinic crystal system with space group, P21/n. The study of intermolecular interactions has confirmed the stability of crystal structure through N-H type H-bonding interactions besides electrostatic forces of attraction.

The Dietary Nutrient Trimethylamine N-Oxide Affects the Phospholipid Vesicle Membrane: Probable Route to Adverse Intake.

Trimethylamine N-oxide (TMAO), a choline-containing dietary supplement obtained from red meat, egg, and other animal resources, on excess accumulation is known to cause cardiovascular diseases (CVDs) like atherosclerosis. To understand the molecular mechanism of the pathogenesis of TMAO-induced CVDs, we have set up 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membrane in water that mimicked the endothelial cell membrane-blood interface of the artery wall and investigated the effect of an elevated concentration of TMAO on the membrane. We found that TMAO exerts an "action at a distance" mechanism through electrostatic force of attraction that significantly alters various properties of the membrane, like hydrophobicity, lateral organization, and interfacial water dynamics, which elevates the rigidity of the membrane. Such an effect was found to be further amplified in the presence of known causes of CVDs, i.e., high content of cholesterol (Chol). Therefore, TMAO-induced membrane rigidity may restrict the intrinsic elasticity of an artery membrane, expected to be introducing "hardening of the arteries", which makes the membrane atherosclerotic.

Recycled mesoporous magnetic composites with high surface area derived from plastic and de-oiled sludge wastes: An empirical comparison on their competitive performance for toxic Cr (VI) removal

The current study focused on the comparative removal of hexavalent chromium using two magnetically modified hybrid adsorbent composites. Their precursor chars were prepared from bio sludge and plastic waste derivatives. The coating of magnetite on the chars' surface was evident from the SEM micrographs. Infusion of magnetite nanoparticles in the native chars aided in the reduction of the composite particles' sizes, thus, forming high surface area composites. Screening of uptake capacities among various blends of char and magnetite were surveyed. Composites of both kinds with a 1:5 ratio of char: iron salts composition answered well. The pHZPC and zeta potential values of the composites indicated the neutral charge on the composites' surface. This suggested the need for a highly acidic environment for efficient Cr(VI) removal. Optimum economic conditions for Cr(VI) removal were obtained from the batch studies (solution pH - 1.5; contact time - (a) MPC [magnetic plastic char] - 60 min (b) MBC [magnetic biochar] - 40 min; temperature – 25 °C). The maximum monolayer adsorption capacity of MPC and MBC were found to be 84.67 mg/g and 53.83 mg/g respectively. Isotherm, kinetic and thermodynamic studies revealed the adsorption systems’ inclination towards physisorption. From the characterization and modeling results, electrostatic force of attraction and pore filling was anticipated to be the mechanism of adsorption for both MPC and MBC. Thus, in the relative removal studies, MBC was found to compete better than MPC due to its enhanced porosity and surface area.

Effects of Geomaterial-Originated Fillers on Microstructure and Mechanical/Physical Properties of α- and β-Chitosan-Based Films.

Edible films and coatings with good mechanical/physical properties are highly required for carrying medical substances and food packaging. So, solvent-cast films of α- or β-chitosan filled with palygorskite, montmorillonite or geopolymer-containing material (GCM), were prepared, and the effects of their clay contents (up to 50 wt.%) on the mechanical/physical properties were assessed. The microstructure of the films was investigated using FT-IR spectroscopy, SEM and thermal analysis. The results showed that, except for the films composed of GCM and β-chitosan, the mechanical properties of the films with limited (up to 5 wt.%) to moderate (5–25 wt.%) amounts of fillers increased as a result of the attractive electrostatic forces formed between the fillers and chitosan functional groups (–NH3+, CH2OH and NHCOCH3). However, due to the occurrence of coarse aggregates, the strength of filler-rich films declined. The addition of fillers led to an increase in porosity and water absorption of the films, but it had irregular effects on their wettability and water vapor transmission rate. These observations as well as the thermal stability of the films were discussed in relation to the characterization results.

Hybrid nanocoatings of self-assembled organic-inorganic amphiphiles for prevention of implant infections

Antimicrobial coatings are one of the most promising strategies to prevent bacterial infections in orthopedic and dental implants. Combining antimicrobial agents with different antimicrobial mechanisms might have synergistic effects and be more potent. Others have shown that nanocomposites of silver nanoparticles (AgNPs) decorated with antimicrobial peptides (AMPs) show increased potency as free agents in solution. However, similar nanocomposites have not been explored to coat biomaterials through cooperative weak electrostatic attraction forces between AMP, AgNPs and substrates in need of protection against infection. In this work, we synthesized self-assembled antimicrobial amphiphiles of an AMP, GL13K. Then, we decorated the AMP nanostructures with AgNPs, which were finally used to coat etched Ti (eTi) surfaces. The strong hydrogen bonding between the AMP amphiphiles and the polar eTi yielded a robust and stable coating. When compared to single AgNP or single AMP coatings, our hybrid nanocoatings had notably higher in vitro antimicrobial potency against multiple bacteria strains related to implant infection. The hybrid coating also showed relevant antimicrobial activity in an in vivo subcutaneous infection model in rats. This work advances the application of AgNP/AMP nanocomposites as effective coatings for prevention of implant infections. Statement of significanceHigh morbidity, mortality and elevated costs are associated with orthopedic and dental implant infections. Conventional antibiotic treatment is ineffective due to barrier-like extracellular polymeric substances in biofilms and the increasing threat from antibiotic resistance. Antimicrobial coatings are one of the most promising strategies, but the performance is usually unsatisfactory, especially when tested in vivo. Here, we present a hybrid nanocoating with different modes of action to prevent implant infections using self-assembled antimicrobial peptide (AMP) amphiphiles decorated with silver nanoparticles (AgNPs). When compared to single AgNP or AMP coatings, our hybrid nanocoatings showed significant increases in antimicrobial potency against multiple implant infection-related bacterial strains in vitro and in an in vivo rat subcutaneous infection model.

Dependence of field-effect biosensor sensitivity on photo-induced processes in Si and its conductivity type

The effect of photoelectron processes in n-Si and p-Si on the glucose sensitivity of a capacitive field-effect biosensor based on electrolyte/oxide/semiconductor structure was investigated. We obtained that illumination of n-Si/SiO2/PEI structure during the GOx adsorption increases the glucose sensitivity by three times compare to GOx adsorption in the dark. In contrast, p-Si illumination during the GOx adsorption led to a decrease in sensor sensitivity from 2.9 mV/mM to 2.2 mV/mM. The result is explained by a change in the density of immobilized GOx molecules due to a change in the electrostatic forces of attraction under illumination and stabilization of the photo-generated charge on the surface electronic states of the Si/SiO2 and SiO2/PEI interfaces after illumination.

Study of a MOEMS XOR gate based on optical ring resonator

Based on ring resonator with Microelectromechanical systems, optical XOR logic gate is proposed in this paper to realize the optical logic gate application. The proposed gate is basically structured on an optical ring resonator with 7 μm radius and resonance wavelength of 1.55 μm which is placed on the edge of a thin SiC circular diaphragm. In order to apply input voltages to electrodes, two very thin circular gold layers with 50nm air gap spacing are deposited under the diaphragm. Input voltages are considered as logic inputs and resonance wavelength shift as logic output. When an input DC voltage is applied across the diaphragm, an attractive electrostatic force is created between two electrodes. As a result, the diaphragm is deformed and an internal stress is created. This in turn changes the resonator refractive index due to the photoelastic effect and thus shifts its resonance wavelength about 35nm. COMSOL Multiphysics and MATLAB are carried out to verify FEA and numerical analysis of the designed structure, respectively. A good agreement between the simulations and analytical results is obtained. Enhancement of the wavelength shift and FSR are resulted. The proposed structure is used as an optical XOR gate for the first time.

CO2 Adsorption Enhanced by Tuning the Layer Charge in a Clay Mineral.

Due to the compact two-dimensional interlayer pore space and the high density of interlayer molecular adsorption sites, clay minerals are competitive adsorption materials for carbon dioxide capture. We demonstrate that with a decreasing interlayer surface charge in a clay mineral, the adsorption capacity for CO2 increases, while the pressure threshold for adsorption and swelling in response to CO2 decreases. Synthetic nickel-exchanged fluorohectorite was investigated with three different layer charges varying from 0.3 to 0.7 per formula unit of Si4O10F2. We associate the mechanism for the higher CO2 adsorption with more accessible space and adsorption sites for CO2 within the interlayers. The low onset pressure for the lower-charge clay is attributed to weaker cohesion due to the attractive electrostatic forces between the layers. The excess adsorption capacity of the clay is measured to be 8.6, 6.5, and 4.5 wt % for the lowest, intermediate, and highest layer charges, respectively. Upon release of CO2, the highest-layer charge clay retains significantly more CO2. This pressure hysteresis is related to the same cohesion mechanism, where CO2 is first released from the edges of the particles thereby closing exit paths and trapping the molecules in the center of the clay particles.

Deflection Modelling of MEMS Cantilever Beam Through Collocation Method Taking B-Splinesas Approximating Functions

The Mathematical Modeling and Analysis of cantilever beam adhesion problem, under the action of electrostatic attraction force iscarried out. The model uses Euler-Bernoulli beam theory for one end fixed and other end free type beams for small deflection. A MATLAB code has prepared to predict and plot the deflection profile of MEMS cantilever beam during the action of stiction force on application of applied voltage as snap down occurs. The model predicts the cantilever behavior on occurrence of snap downvoltage. To envisage the deflection profile, A collocation method employing B-Spline as approximating functions & Gaussian quadrature point as collocation points has been utilized for solving the governing equation by keeping the four end boundary conditions of cantilever beam in mind. The numerical results reveal the deflection profile of the MEMS cantilever Beam, which are validated with the previous data & deflection profile available by numerous published research papers

Preparation of acrylic acid modified alkalized MXene adsorbent and study on its dye adsorption performance

A novel AA-alk-MXene adsorbent was prepared by grafting acrylic acid (AA) onto alkalized single/few layers of MXene nanosheets for removing dyes from wastewater. The results of XRD, XPS, TG and Raman confirmed the successful grafting of AA onto the alkalized MXene nanosheets. A series of adsorption experiments were used to study the adsorption of AA-alk-MXene for the anionic dye congo red (CR) and cationic dye methylene blue (MB). Effects of AA dosage, contact time, initial dye concentration, temperature and pH for adsorption process were studied. The adsorption data shows that the adsorption process followed pseudo second-order kinetic model and Langmuir isotherm adsorption model. It was found that the maximum adsorption capacity of 2 ml AA modified sample for CR and MB was 264.46 mg/g and 193.92 mg/g, respectively. Meanwhile, the experiment also studied the adsorption mechanism of AA-alk-MXene. Electrostatic attraction, hydrogen bonding and interlayer force may be the main driving force for adsorption.

Effect of calcination temperature on morphology and phase transformation of MnO2 nanoparticles: A step towards green synthesis for reactive dye adsorption

Green synthesis of manganese oxide nanoparticles (NPs) was carried out by sol-gel method using Acacia Concinna fruit extract for removal of reactive dye. The effect of calcination temperature on its morphology was investigated. α-MnO2 and Mn3O4 NPs were synthesized at 400 °C and 900 °C respectively and were characterized by PXRD, SEM, TEM, FTIR, BET, Raman and TGA. As-synthesized MnO2 NPs were investigated for the adsorption of Reactive Blue 21 (RB-21) dye. The effect of pH, adsorbent dose, agitation speed, initial dye concentration and temperature on dye removal was explored. pHpzc was calculated from zeta potential study showing positive surface charge below pH 3.18 resulting in electrostatic force of attraction between adsorbate and adsorbent. Both linear and non-linear regression approaches were utilised for the fitting of kinetic models and adsorption isotherms. Adsorption data follows a pseudo second order kinetics and fits well with the Freundlich isotherm model. Thermodynamic parameters such as ΔHo, ΔSo and ΔGo were determined. The dye removal efficiency, in case of MnO2 NPs at pH 3.0 was obtained to be 98% whereas for Mn3O4, no such dye adsorption was observed. The mechanism of adsorption was studied theoretically confirming π-π interaction and H-bonding between the MnO2 and RB dye molecules.

Adsorptive removal of metformin on specially designed algae-lignocellulosic biochar mix and techno-economic feasibility assessment

Batch sorption of metformin hydrochloride (MET) onto a specially designed biochar mix consisting of both macro (MAC) and micro (MIC) algae, rice husk and pine sawdust was conducted. Pyrolysis of both MAC and MIC algae mixture was done followed by chemical activation with hydrogen-peroxide. Additionally, sorption of MET under the influence of pH was separately investigated. Batch studies of isotherms were well described by Freundlich model with high non-linearity and Freundlich exponent values ranged anywhere from 0.12 to 1.54. Heterogeneity of MET adsorption to the bonding sites was attributed to the surface functional groups of the modified biochar. Amongst the four biochars, the activated macroalgae biochar (MACAC) and microalgae biochar (MICAC) depicted favourable adsorption of MET with maximum adsorption at pH 7. Up to 76% of MET removal from the environment was obatained using the MACAC biochar. Scanning electron micrographs coupled with energy dispersive X-ray, as well as elemental analyses confirmed formation of oxygen containing surface functional groups due to activation strengthening chemisorption as the main sorption mechanism. Further, Fourier transform infra-red spectroscopy and other surface functional group analyses along with Zeta potential measurements reinforced our proposed sorption mechanism. Lowest zeta potential observed at pH 7 enhanced the electrostatic force of attraction for both the biochars. Negative zeta potential value of the biochars under different pH indicated potential of the biochars to adsorb other positively charged contaminants. From a techno-economic perspective, capital expenditure cost is not readily available, however, it is envisaged that production of pyrolyzed biochar from algal biomass could make the process economically attractive especially when the biochar could be utilised for high-end applications.

Complementary Vacuum Field Emission Transistor

A complementary vacuum field emission device structure is proposed, and its operation is analyzed by multiphysics simulation. A freely moving double-clamped cantilever, which balances the electrostatic attraction force and elastic restoration force, is used as the source electrode while the drain electrode is fixed. The electron-emitting cathode is formed on the source for the n-type device and on the drain for the p-type. Thus, complementary current–voltage characteristics are obtained only with Fowler–Nordheim tunneling electron transport. The impact of various design parameters such as vacuum gap, cantilever beam thickness, gate width, and tip offset on the drain and gate leakage currents is investigated. Inverter logic operation is verified successfully using complementary devices.

Magnetic separation of micron-sized particles: process study and regression modelling using moving least squares and multivariable power least squares method

The presence of fine particles has reduced the quality of water resources. Unfortunately, the fine particles normally take a longer time to be removed. Realizing this, the present study aims to employ a magnetic adsorbent to assist a fast separation of the fine particles from their solution. Here, micron-sized SiO2 particles were used as the model fine particles; meanwhile, the magnetic adsorbent was designed by functionalizing iron oxide nanoparticles (IONPs) with chitosan. A process study was done based on the effects of medium pH, IONPs concentration, and contact time. Results implied that both bare IONPs and chitosan functionalized-IONPs (denoted as CF-IONPs) were best in removing SiO2 at pH 4 owing to the electrostatic attraction force. However, as compared to the bare counterpart, CF-IONPs is more suitable for large scale application as it is effective in a wider pH range, requires lesser adsorbent dosage and shorter adsorption time. Despite that, removal of SiO2 using both types of adsorbents were found to follow pseudo-second order kinetic. The obtained data was modeled using either the moving least squares (MLS) or multivariable power least squares (MPLS) method. In particular, the indices of each parameter obtained from the MPLS-generated equation indicated that the most dominant parameter that governing the SiO2 removal by bare IONPs is medium pH, while the one for CF-IONPs is contact time.

Au Nanoparticle Monolayer Nanosheets as Flexible Transparent Conductive Electrodes

Flexible and transparent conductive electrodes are fundamental components used in advanced optical and electronic devices and organic electronics. In this work, we demonstrated a method for fabricating transparent conductive electrodes of Au nanosheets using UV irradiation on Au nanoparticle (AuNP) monolayer on water. The adsorbed AuNP monolayer was formed from the electrostatic attractive force between the anionic capping molecules on AuNPs dispersed in water with a cationic insoluble surfactant monolayer on water. UV irradiation promoted the decomposition of the surfactant deposited on the AuNPs, thereby transforming the AuNPs into mesh-like nanosheets that served as flexible and transparent conducting electrodes. The AuNP dispersions were also proven to be reusable in preparing conductive Au nanosheets for transparent flexible electrodes.