Values Of Adsorption Free Energy Research Articles

Investigation of adsorption performance of calcium oxide particles upon various treatments.

This study describes the improvements of adsorption capacities for raw calcium oxide (CaO) particles subjected to ultrasonication, activation with nitric acid and thermal treatments. The influence of acids and bases on CaO particle surface was assessed with respect to several variables including treatment methods, adsorption contact times, particle size and specific surface area characteristics, concentration and temperature along with various thermodynamic parameters. Structural analyses and physical characteristics of CaO particles were evaluated using FT-IR and SEM methods. SEM micrographs of samples revealed uniform distributions of CaO particles of average diameter 0.5-2.0µm. The CaO surfaces showed CH3COOH as having the greatest amounts of adsorbate and modeling of the experimental adsorption isotherm data agreed well with the Freundlich adsorption isotherm. Enhancements in adsorption performance of untreated CaO particles were noted with the ultrasonication, activation with HNO3 and thermal treatment processes. The Langmuir-type adsorption demonstrated that single layer adsorption capacities of adsorbate CH3COOH at 25oC on sonicated CaO (386.6mg/g), with nitric acid and thermal activation (354.9 and 320.8mg/g, respectively) were greater than that of the unsonicated CaO (296.3mg/g) particles. Adsorption spontaneities of the processes were confirmed by the decreases in adsorption free energy values, ΔGads0, changing from -16.1 to -17.1kJmol-1 with temperature range 283-338K.

Augmenting bi-functional catalytic efficiency in vanadium based pseudo-monolayer: Chemical paradigm of functionalization, vacancy and external stimuli

Since the exfoliation of graphene, two-dimensional (2D) ultrathin materials have attracted a lot of attention in several applications for energy harvesting for the ongoing quest for green and sustainable environment. One of such ultrathin materials could be envisaged in the form transition metal tri-chalcogenide based 2D pseudo-monolayers. In this theoretical work, we have rigorously investigated the bi-functional catalytic reaction mechanism corresponding to water-splitting on vanadium-based tri-chalcogenide monolayers VS3. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the two main reactions which consist water splitting process, which are being explored in VS3 system from the perspective of first principles electronic structure calculations within the framework of density functional theory (DFT) formalism. We have explored the effect of functionalization, vacancy induced defect and external strain (both bi-axial and uni-axial) on the catalytic activity, which can be reflected from the over-potential corresponding to the reaction coordinate mapping constructed from the adsorption free energy values. We have also determined the projected density of states, work function, charge density distribution and correlated all such electronic structure analysis with the catalytic activity enhancement in the VS3 pseudo monolayer. Overall, we have investigated the competing effect of strain, functionalization, and vacancy induced defect on the bi-functional catalytic activity enhancement, which can be further experimentally validated for efficient hydrogen generation. Our systematic electronic structure calculations reveals the defected and nitrogen doped VS3 as the promising candidate for HER and OER activity respectively, which have been further enhanced under the influence of external strain.

Electrochemical analysis of extracellular electron transfer process of Pseudomonas aeruginosa NEJ07R using pyocyanin on a carbon electrode

Indirect extracellular electron transfer (IEET), or mediated electron transfer (MET), is a process that has attracted attention for its application in electrochemical-microbial technologies for power generation, wastewater treatment, or electrofermentation. Pseudomonas aeruginosa is a bacterium known to carry out IEET because it produces its own redox mediator (RM), pyocyanin (PYO), which has electrochemical properties such as a high electron transfers rate and low resistance to charge transfer. However, other physical processes, such as PYO adsorption on the electrode, can alter that function. In this work, interaction parameters and adsorption-free energy values were determined to obtain an adsorption mechanism on a carbon-based electrode. Furthermore, the effect of PYO addition and its adsorption were studied in the IEET process of P. aeruginosa NEJ07R. The electrochemical profiling of PYO by cyclic voltammetry (CV) and chronocoulometry (CC) measurements allowed the calculation of the Laviron interaction parameter (ν'gθT). Since the values of ν'gθT > 0, it was determined that PYO maintains attractive interactions with the surface in cathodic and anodic reaction. Moreover, the low interaction free energies (ΔG0' ≈ −2.91 ×10−5 ± 1.28 ×10−8 kJ/cm3 and -−2.92 ×10−5 ± 2.74 ×10−8 kJ/cm3 for reduction and oxidation, respectively) suggests that the interactions are weak. As for the IEET of P. aeruginosa NEJ07R, the microbial catalysis process on a carbon cloth electrode was confirmed by adding PYO to the electrochemical cell. Electrochemical and FT-IR characterization confirmed the adsorption of PYO on the surface, so it is proposed that P. aeruginosa NEJ07R takes advantage of PYO adsorption to carry out IEET.

New insight on hydrogen evolution reaction activity of the most exposure (0 1 1) surface and its monovacancy defect for FeP system: A theoretical perspective

We systemically investigated the hydrogen evolution reaction (HER) catalytic activity for the most exposure (0 1 1) surface and its monovacancy defect for FeP system using periodic density functional theory (DFT). The calculated values of adsorption free energy of H* (ΔGH*) reveal that (0 1 1) surface has high HER catalytic activity. In addition, the formation of monovacancy defect with Fe or P at (0 1 1) surface keeps good HER catalytic activity. We hope this letter can shed new light on further understanding HER in relation to FeP system and give guidance for design of transition metal phosphides.

Surfactant-impregnated activated carbon for enhanced adsorptive removal of Ce(IV) radionuclides from aqueous solutions

The surfactants cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (NaLS) were utilized for modifying the activated carbon’s surface. The materials were characterized using BET–N2, scanning electron microscope, and Fourier transform infrared (FT-IR) spectroscopy. Adsorption of Ce(IV) radionuclides from aqueous solutions by activated carbon (AC) and surfactant-impregnated AC was studied. The obtained data showed that adsorption of Ce(IV) is strongly dependent on the solution pH and AC–NaLS exhibits the widest pH-range of maximum removal. The experimental adsorption capacity of AC–NaLS (0.069mmol/g) for Ce(IV) is found to be nearly twice greater than that of AC (0.036mmol/g). The adsorption kinetics of Ce(IV) onto AC and AC–NaLS were analyzed by linear and non-linear fittings to the pseudo-first-order, pseudo-second-order and Elovich kinetic models. Of these models, the pseudo-second-order is the best kinetic expression for describing the experimental data. The diffusion studies indicated that adsorption of Ce(IV) radionuclides on AC and AC–NaLS is controlled by film diffusion. Linear and non-linear fittings of the adsorption equilibrium data for Ce(IV) onto AC and AC–NaLS revealed that the Dubinin–Radushkevich (D–R) isotherm model fits the experimental data better than Freundlich and Langmuir models. The values of adsorption free energy, E, calculated from both linear and non-linear methods suggested that Ce(IV) radionuclides are physically adsorbed onto AC and AC–NaLS.

Effect of succinic acid on carbon steel corrosion in produced water of crude oil

Succinic acid has been evaluated as a corrosion inhibitor for carbon steel corrosion in produced water of crude oil using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and FTIR techniques. The results showed that the inhibition efficiency increased with increase in succinic acid concentration but decreased with rise in temperature. The best inhibition efficiency was obtained by adding 50ppm succinic acid at pH 3. Inhibition efficiency values obtained from polarization and EIS are in reasonably good agreement. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated and discussed. Polarization curves showed that the succinic acid act as a mixed-type inhibitor. The corrosion inhibition is attributed to physical adsorption of the succinic acid on the carbon steel surface. Succinic acid adsorption follows Temkin isotherm with negative values of adsorption free energy. Succinic acid adsorption on the electrode surface was fast and completed within 30min.

Simulation of multiphase systems utilizing independent force fields to control intraphase and interphase behavior

Fixed-charge empirical force fields have been developed and widely used over the past three decades for all-atom molecular simulations. Most simulation programs providing these methods enable only one set of force field parameters to be used for the entire system. Whereas this is generally suitable for single-phase systems, the molecular environment at the interface between two phases may be sufficiently different from the individual phases to require a different set of parameters to be used to accurately represent the system. Recently published simulations of peptide adsorption to material surfaces using the CHARMM force field have clearly demonstrated this issue by revealing that calculated values of adsorption free energy substantially differ from experimental results. Whereas nonbonded parameters could be adjusted to correct this problem, this cannot be done without also altering the conformational behavior of the peptide in solution, for which CHARMM has been carefully tuned. We have developed a dual-force-field approach (Dual-FF) to address this problem and implemented it in the CHARMM simulation package. This Dual-FF method provides the capability to use two separate sets of nonbonded force field parameters within the same simulation: one set to represent intraphase interactions and a separate set to represent interphase interactions. Using this approach, we show that interfacial parameters can be adjusted to correct errors in peptide adsorption free energy without altering peptide conformational behavior in solution. This program thus provides the capability to enable both intraphase and interphase molecular behavior to be accurately and efficiently modeled in the same simulation.

The role of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol in the inhibition of nickel–aluminum bronze alloy corrosion: electrochemical and DFT studies

Inhibition of corrosion of nickel–aluminum bronze alloy (NAB) by use of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol (APTT) was investigated by monitoring weight loss and open-circuit potentials (OCP), and by use of electrochemical impedance spectroscopy (EIS). Quantum chemical data were calculated by use of the density functional theory (DFT) model. Results showed that APTT inhibits corrosion of NAB alloy fairly well. The efficiency of inhibition increases with increasing concentration of APTT, and adsorption of the inhibitor obeys the Langmuir adsorption isotherm model. Negative values of adsorption free energy indicate chemical adsorption is spontaneous. The theoretical study showed that sulfur and nitrogen atoms (S, N7 and N8) were the reactive sites.

Some Polysorbate Compounds as Corrosion Inhibitors for Carbon Steel in Hydrochloric Acid

Some commercial non-ionic surfactants polysorbate, namely, polysorbate 80, polysorbate 40 and polysorbate 20, were tested as inhibitors for corrosion of C-steel in 2.0M HCl solution using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy techniques. It was found that all the three used compounds act as inhibitors for acid corrosion of C-steel. The inhibition efficiencies obtained by the three techniques were almost the same, and increase with increasing the hydrocarbon chain length and the surfactant concentration. The polarization studies show that these compounds act as mixed inhibitors. The inhibition action of these surfactants can be explained by their ability to adsorb on the metal surface making a barrier to mass and charge transfer. It was found that the adsorption of these surfactants follows Langmuir adsorption isotherm. The negative values of adsorption free energy indicating that the adsorption process is spontaneous and increases, for different surfactants, in the same direction as inhibition efficiency.

Surface Properties of Polyacid–Poly(N-Vinyl Pyrrolidone) Complexes

The effect of the complexation of polyacrylic (PAA) and polymethacrylic (PMAA) acids with poly(N-vinyl pyrrolidone) (PVP) on their surface properties was studied by measuring surface tension, conductivity, and the viscosity of aqueous mixed polymer solutions, as well as by the potentiometric titration at 293.15 K. The values of relaxation times and the surface activity of polycomplexes were calculated from kinetic data and the surface tension isotherms of the solutions. The complexation was found to increase the surface layer relaxation time, surface activity, and the ability of the macromolecules to reduce the surface tension of solvent. The values of adsorption free energy were calculated for PVP and polycomplexes. They were equal to –22.0, –23.0, and –24.8 kJ/base-mole (per one mole of PVP monomer unit) for PVP and PMAA–PVP and PAA–PVP polycomplexes, respectively.

Steroid biomarker-clay mineral adsorption free energies: Implications to petroleum migration indices

Enrichments of 14β,17β steranes over 5α,20R steranes in petroleums relative to shale source rocks have bee discussed inthe literature and ascribed to possible migrational geochromatographic processes involving mineral surfaces. Liquid−solid chromatographic (LSC) effects arise from adsorption free energy (AFE) differences between various chemical compounds and an active surface. If nonmaturational concentration differences of 14β,17β/5α,20R sterane isomers in petroleum arise frommigrational geochromatographic effects, then those differences must be reflected by sterane-mineral AFE differences. Accordingly, AFE values for 23 selected steroid biomarkers, including saturated-isomerized, mono-,di-, and triaromatized and partially cracked structures were measured on montmorillonite clay using a chromatographic technique. Those data conform to LSC theory: laboratory migration rates for biomarkers on montmorillonite of increasing water content can be calculated from AFE values. Biomarker AFE values are shown to depend on specific structural chemical features, i.e. aromatic carbon number and stereochemistry, in a systematic way. Quantitative contributions of those features to AFE values are calculated and rules are developed which permit the prediction of relative chromatographic migration rates for related biomarker compounds. Finally, AFE valuess are used to calculate 253 possible biomarker pair concentration ratio variations (measurable by GC-MS) expected for clay mineral LSC-type geochromatographic effects.