Ionization Equilibrium Research Articles

Probing the physical properties of the intergalactic medium using SRG/eROSITA spectra from blazars

Most baryonic matter resides in the intergalactic medium (IGM). This diffuse gas is primarily composed of ionized hydrogen and helium and fills the space between galaxies. Observations of this environment are crucial for better understanding the physical processes in it. We present an analysis of the IGM absorption using blazar spectra from the first eROSITA all-sky survey (eRASS1) performed onboard of the Spectrum-Roentgen-Gamma mission (SRG) and XMM-Newton X-ray observations. First, we fit the continuum spectra using a log-parabolic spectrum model and fixed the Galactic absorption. Then, we included a collisional ionization equilibrium model, namely IONeq, to account for the IGM absorption. The column density N(H) and metallicity (Z) were set as free parameters. At the same time, the redshift of the absorber was fixed to half the blazar redshift as an approximation of the full line-of-sight absorber. We measured IGM-N(H) for 147 sources for SRG and 10 sources for XMM-Newton. We found a clear trend between IGM-N(H) and the blazar redshifts that scales as (1 + z)1.63 ± 0.12. The mean hydrogen density at z = 0 is n0 = (2.75 ± 0.63)×10−7 cm−3. The mean temperature over the redshift range is log(T/K) = 5.6 ± 0.6, and the mean metallicity is Z = 0.16 ± 0.09. We found no acceptable fit using a power-law model for the temperatures or metallicities as a function of the redshift. These results indicate that the IGM contributes substantially to the total absorption seen in the blazar spectra.

Origin and Composition of the Galactic Diffuse X-Ray Emission Spectra by Unresolved X-Ray Sources

Galactic diffuse X-ray emission (GDXE) can be spatially segmented into Galactic center X-ray emission (GCXE), Galactic ridge X-ray emission (GRXE), and Galactic bulge X-ray emission (GBXE). The X-ray spectra of GDXE are expressed by the assembly of compact X-ray sources, which are either white dwarfs (WDs) or X-ray active stars consisting of binaries with late-type stars. WDs have either a strong magnetic field or a weak magnetic field. WDs and X-ray active stars are collectively called compact X-ray stars. However, spectral fittings by the assembly of all compact X-ray stars for GCXE, GRXE, and GBXE are rejected, leaving significant excess near the energies of the Kα, Heα, and Lyα lines. These excesses are found in the collisional ionization equilibrium (CIE) plasma. Thus, the spectra of GRXE and GBXE are improved by adding CIE supernova remnants (SNRs). However, the GCXE spectrum is still unacceptable, with significant data excess due to radiative recombination emission (recombining plasma (RP)). The GCXE fit is then significantly improved by adding aged RP-SNRs. Aged RP-SNRs are made by a past big flare of Sgr A* emitting either hard X-rays or low-energy cosmic rays. The big flares may excite Fe and Ni atoms in cold diffuse gas (cold matter (CM)) and emit fluorescent X-ray lines. The CIE-SNRs, RP-SNRs, and CM are called diffuse X-ray sources. This paper presents the spectral fits by the assembly of all the compact and diffuse X-ray sources together with high-quality spectra and a combined fit among all the GDXE of GCXE, GRXE, and GBXE. This provides the first scenario to quantitatively and comprehensively predict the origin of the GDXE spectra.

Maintaining the concentration equilibrium of proton and hydroxide ions by construction of bis(2-aminoethyl)amine-based inner helmholtz plane toward long-life zinc metal anodes

Despite the merits of high safety and low cost, the development of rechargeable aqueous Zn metal batteries is oppressed by the short cycling life of Zn metal anodes, due to the hydrogen evolution reaction (HER) and the formation of irreversible Zn4SO4(OH)6·nH2O that are caused by the decomposition of H2O molecules adsorbed in the inner Helmholtz plane (IHP) of Zn metal anodes. To solve this issue, we herein use bis(2-aminoethyl)amine (B2AA) organic molecules as additives to suppress Zn corrosion and HER via reconstructing the IHP and maintaining the concentration equilibrium of protons and hydroxide ions, thus achieving long-term and highly reversible Zn metal batteries. Density functional theory calculations and molecule dynamics simulations reveal that B2AA are preferentially adsorbed on the interface of Zn anode owing to the high adsorption energy, forming a water-deficient IHP via repelling ≈19% of H2O molecules. Additionally, the −NH2/−NH− groups of B2AA can reversibly capture H+ derived from the decomposition of H2O and dynamically neutralize OH−, thus suppressing the corrosion reaction. Using an aqueous electrolyte involving B2AA, symmetric Zn//Zn cells exhibit a long cycling life of 2400 h at 10 mA cm−2. Matched with a NH4V4O10 (NVO) cathode, the Zn//NVO full cell delivers a high initial capacity of 147.24 mAh/g at 10 A/g, and maintains a high capacity retention of 66% after 3000 cycles.

Smartphone-enabled green anthocyanin sensor for Fe(III) sensing on paper using capillary-driven microfluidics

Chemical wastes, such as synthetic dyes and coloring agents, pose significant concerns due to their detrimental impact on human health and ecosystems. As an eco-friendly alternative, the study of natural dyes and coloring agents has gained momentum over the last decade, owing to their biodegradability and reduced environmental and health risks. Here, we report a novel approach employing a butterfly pea anthocyanin paper-based sensor to quantify Fe(III) ions in water. Compared to previous green sensing techniques reliant on heavy instrumentations, this approach offers enhanced accessibility, cost-effectiveness, and user-friendliness. Notably, this study is the first example of natural dye sensing on a capillary microfluidics system. The capillary-driven microfluidic system ensures user-friendly operation and allows the sensing platform to be directly immersed in water without reagent loss. The device's design involves drying the butterfly pea-derived anthocyanin reagent within a pH-controlled paper substrate embedded in the capillary-driven microfluidic system. Smartphone-based colorimetric signal generation and quantification was achieved within seconds for a working range of 50–800 mg/L, with the device's detection limit of 43 mg/L using ImageJ and 55 mg/L using the smartphone app. This green sensing methodology has the potential to be used for groundwater sources with elevated Fe(III) levels. Additionally, this platform can be used in chemistry educational settings as an effective means to understand fundamental concepts such as acid-base reactions, base strength, ionic equilibrium, and metal complexation in a user-friendly microfluidic system.

Facile construction of ZIF-94/PAN nanofiber by electrospinning for the removal of Co(II) from wastewater

This study aimed to synthesize a novel nanofiber adsorbent based on metal–organic frameworks (MOFs), ZIF-94-PAN, by incorporating ZIF-94 into polyacrylonitrile (PAN) through electrospinning. The investigation of the adsorption characteristics of ZIF-94-PAN for cobalt ions was undertaken, yielding findings that suggest an optimum ZIF-94 loading content within the ZIF-94-PAN composite of 8%. The adsorption experiments revealed that, under pH 8.3 and 298 K, ZIF-94-PAN-8% attained cobalt ion equilibrium adsorption (139.08 mg/g). Additionally, the adsorption kinetics of cobalt ions exhibited conformity with the pseudo-second-order model, whereas adherence to the Freundlich isotherm model indicated a non-homogeneous, endothermic process. XPS analysis unveiled that the adsorption mechanism was characterized by the coordination of nitrogen and oxygen atoms within ZIF-94-PAN with cobalt ions. This study effectively addressed the challenges of separating and recovering MOFs adsorbents by fabricating them as nanofibers. The remarkable adsorption performance and stability of the ZIF-94-PAN nanofibers highlight their potential for removing cobalt-contaminated wastewater.

The Saha ionisation equilibrium shift correction model applied to MPT-OES for analysing complex matrix samples: an example for brine samples

The Saha-IESC (Saha Ionisation Equilibrium Shift Correction) is a novel approach designed to correct for ionisation interference in the analysis of various solution samples.

X-Rays from RS Ophiuchi’s 2021 Eruption: Shocks In and Out of Ionization Equilibrium

The recurrent nova RS Ophiuchi (RS Oph) underwent its most recent eruption on 2021 August 8 and became the first nova to produce both detectable GeV and TeV emission. We used extensive X-ray monitoring with the Neutron Star Interior Composition Explorer Mission (NICER) to model the X-ray spectrum and probe the shock conditions throughout the 2021 eruption. The rapidly evolving NICER spectra consisted of both line and continuum emission that could not be accounted for using a single-temperature collisional equilibrium plasma model with an absorber that fully covered the source. We successfully modeled the NICER spectrum as a nonequilibrium ionization collisional plasma with partial covering absorption. The temperature of the nonequilibrium plasma shows a peak on day 5 with a kT of approximately 24 keV. The increase in temperature during the first five days could have been due to increasing contribution to the X-ray emission from material behind fast polar shocks or a decrease is the amount of energy being drained from the shocks into particle acceleration during that period. The absorption showed a change from fully covering the source to having a covering fraction of roughly 0.4, suggesting a geometrical evolution of the shock region within the complex global distribution of the circumstellar material. These findings show evidence of the ejecta interacting with some dense equatorial shell initially, and with less dense material in the bipolar regions at later times during the eruption.

A method for calculating the mean ion charge in a short-lived non-equilibrium plasma—Its application to diagnostics of the laser spark

The described method is intended for application as a diagnostic tool for a nonstationary, short-lived plasma (in particular, for the laser-produced plasma). It is based on taking into account the lifetime of a laser-produced plasma, which is so short (several nanoseconds) that it is not enough for the ionization equilibrium to be established. Among mechanisms leading to appearance of an ion with a given charge Z in the plasma, only the electron-collisional ionization is considered, because contributions of other phenomena turn out to be negligible. The method is discussed as an example of a plasma excited on the Xe gas-jet target. The necessary collisional cross sections of ions from+7Xe to+16Xe have been calculated specifically for this study using a quantum-mechanical numerical simulation, with its principles and features being also presented in the paper. To demonstrate capabilities of the method, it has been applied to one of the experimental cases when the plasma was produced by the laser beam focused on the Xe gas-jet target. The time-integrated energy of laser radiation absorbed in the plasma was measured, and the absorption coefficient, μ, was derived from it with a correction for the plasma lifetime, which was several times shorter than the laser pulse. Using the method described here, the values of ⟨Z⟩ and then μ were calculated as a function of temperature. The time-averaged plasma temperature, T, in the above-mentioned experiment was believed to be equal to that at which the calculated and experimentally determined values of μ coincided. The following results were obtained: T = 42 eV, ⟨Z⟩ = 10.2.

Calculation of the formation enthalpy and the ionic equilibrium constant of organic substances by quantum chemistry methods

Using composite methods of quantum chemical calculations and the atomization method, the values of the enthalpy of formation for a test set of 79 compounds in gas phase were calculated with an accuracy of 3.8, 4.5, 4.7 kJ/mol for the G4, G4MP2, CBS-QB3 methods, respectively. According to the results of statistical analysis of deviations of theoretical values from experimental ones, the presence of an error occurring at the geometry optimization step due to unaccounted correlation effects was revealed. For aliphatic amines and alcohols from the considered set of compounds, the values of the p K a for aqueous solutions were calculated by the G4 method including solvent effects by CPCM model. The existence of a correlation between the error in the p K a calculation and the differences in energy values between the highest occupied and lowest unoccupied molecular orbitals for conjugated acidic and basic forms in the solution phase is revealed. A method is put forward to refine the calculation results, using which the p K a values for 20 amines and 20 alcohols were determined with an accuracy of 0.67 and 0.87 p K a units, respectively.

Two-photon Production in Low-velocity Shocks

The Galactic interstellar medium abounds in shocks with low velocities v s ≲ 70 km s−1. Some are descendants of higher velocity shocks, while others start off at low velocity (e.g., stellar bow shocks, intermediate velocity clouds, spiral density waves). Low-velocity shocks cool primarily via Lyα and two-photon continuum, augmented by optical recombination lines (e.g., Hα), forbidden lines of metals and free-bound emission, free–free emission. The dark far-ultraviolet (FUV) sky, aided by the fact that the two-photon continuum peaks at 1400 Å, makes the FUV band an ideal tracer of low-velocity shocks. GALEX FUV images reaffirm this expectation, discovering faint and large interstellar structure in old supernova remnants and thin arcs stretching across the sky. Interstellar bow shocks are expected from fast stars from the Galactic disk passing through the numerous gas clouds in the local interstellar medium within 15 pc of the Sun. Using the bests atomic data available to date, we present convenient fitting formulae for yields of Lyα, two-photon continuum, and Hα for pure hydrogen plasma in the temperature range of 104–105 K. The formulae presented here can be readily incorporated into time-dependent cooling models as well as collisional ionization equilibrium models.

Responses of a polycyclic aromatic hydrocarbon-degrading bacterium, Paraburkholderia fungorum JT-M8, to Cd (II) under P-limited oligotrophic conditions

For the bioremediation of mixed-contamination sites, studies on polycyclic aromatic hydrocarbon (PAH) degradation or Cd (II) tolerance in bacteria are commonly implemented in nutrient-rich media. In contrast, in the field, inocula usually encounter harsh oligotrophic habitats. In this study, the environmental strain Paraburkholderia fungorum JT-M8 was used to explore the overlooked Cd (II) defense mechanism during PAH dissipation under P-limited oligotrophic condition. The results showed that the growth and PAH degradation ability of JT-M8 under Cd (II) stress were correlated with phosphate contents and exhibited self-regulating properties. Phosphates mainly affected the Cd (II) content in solution, while the cellular distribution of Cd (II) depended on Cd (II) levels; Cd (II) was mainly located in the cytoplasm when exposed to less Cd (II), and vice versa. The unique Cd (II) detoxification pathways could be classified into three aspects: (i) Cd (II) ionic equilibrium and dose–response effects regulated by environmental matrices (phosphate contents); (ii) bacterial physiological self-regulation, e.g., cell surface-binding, protein secretion and active transport systems; and (iii) specific adaptive responses (flagellum aggregation). This study emphasizes the importance of considering culture conditions when assessing the metal tolerance and provides new insight into the bacterial detoxification process of complex PAH-Cd (II) pollutants.

Osmotic and Gibbs–Donnan equilibrium for ions and neutral solutes

The general set of equations for the equilibrium of two solutions with a mixture of non-permeating and permeating ions and neutral solutes at each side of a permselective membrane is formulated using the principles of electroneutrality and mass conservation law for each solution, and equilibrium conditions: equality of electrochemical potentials at both sides of the membrane for each permeating solution component. There is at least one permeating neutral chemical species (solvent) in the system. The theory is in general valid for non-ideal solutions. The generalized Gibbs–Donnan (G–D) equilibrium coefficients depend on activities/fractions of all species at one side of the membrane, and charges of ions and partial molar volumes of all species. The equilibrium osmotic pressure across the membrane is also provided by the theory and can be calculated using the ratio of activities (or equivalently the G–D factor) of any permeating neutral solute (including solvent) or the ratios of activities (or equivalently the G–D factors) of any two permeating ions.

KAPPA: A Package for the Synthesis of Optically Thin Spectra for the Non-Maxwellian κ-Distributions. III. Improvements to Ionization Equilibrium and Extension to κ < 2

The KAPPA package is designed for calculations of optically thin spectra for the non-Maxwellian κ-distributions. This paper presents an extension of the database to allow calculations of the spectra for extreme values of κ < 2, which are important for accurate diagnostics of the κ-distributions in the outer solar atmosphere. In addition, two improvements were made to the ionization equilibrium calculations within the database. First, the ionization equilibrium calculations now include the effects of electron impact multi-ionization (EIMI). Although relatively unimportant for Maxwellian distribution, EIMI becomes important for some elements, such as Fe and low values of κ, where it modifies the ionization equilibrium significantly. Second, the KAPPA database now includes the suppression of dielectronic recombination at high electron densities, evaluated via the suppression factors. We find that at the same temperature, the suppression of dielectronic recombination is almost independent of κ. The ionization equilibrium calculations for the κ-distributions are now provided for a range of electron densities.

Impact of intensity error on temperature estimation in laser-induced breakdown spectroscopy: a numerical study

Laser-induced breakdown spectroscopy (LIBS) is a cutting-edge technique for the compositional analysis of multi-element materials. Under standard circumstances for laser-induced plasma (T e = 1 eV and N e = 1016 cm−3), we simulated the emission spectrum of a binary alloy (with 70 wt.% Cu–30 wt.% Al). We used the Saha ionization equilibrium formulas to calculate the population of neutral and ionized species of each constituent element, and the Boltzmann distribution to estimate the intensities of emission lines with radiative transition probabilities. The Stark broadening equation is then used to determine the line broadening, yielding a Lorentzian profile for each line. The sum of line emissions of all constituent species will approximate the alloy’s LIBS spectra in an assumption of ideal analytical plasma. Then, we generated random errors in the intensities of spectral lines ranging from 5% to 35%. To investigate temperature estimation accuracy, we utilized three well-established approaches: the Boltzmann plot (BP) method, the Saha–Boltzmann plot (SBP) method, and the Multi-elemental SBP (MESBP) method. As intensity error increases from 5% to 35%, the estimated temperature in the BP method deviates from 0.25% to 18.3%. Whereas the intensity error is almost unaffected using the SBP method and the MESBP method. The temperature deviation is less than 2% in both situations. This study is relevant to calibration-free LIBS, in which the exact temperature determination is crucial for the abundance estimation of trace, major, and minor elements.

TITANS metal-poor reference stars

Context. Representative samples of F-, G-, K-type stars located outside of the solar neighbourhood have started to become available in spectroscopic surveys. The fraction of metal-poor ([Fe/H] ≲ −0.8 dex) giants becomes increasingly relevant towards greater distances. In metal-poor stars, effective temperatures (Teff) based on local thermodynamic equilibrium (LTE) spectroscopy and on former colour–Teff relations – which are still widely used – have been reported to be inaccurate. It is necessary to recalibrate chemical abundances based on these Teff scales in the multiple available surveys in order to bring them to the same standard scale for their simultaneous use. To this end, a complete sample of standards is required, which until now has been restricted to a few stars with quasi-direct Teff measurements. Aims. We aim to provide a legacy sample of metal-poor standards with proven accurate atmospheric parameters. We add 47 giants to the TITANS metal-poor reference stars. Methods. We derived Teff using 3D non-LTE Hα modelling, the accuracy of which was tested against interferometry and with the Infra Red Flux Method (IRFM). We derived surface gravity (log ɡ) by fitting Mg I b triplet lines, and tested their accuracy against asteroseismology. Metallicity was derived using Fe II lines, and we find our results to be identical to the [Fe/H] derived from non-LTE spectral synthesis. Results. The Teff that we find using 3D non-LTE Hα is equivalent to interferometric and IRFM temperatures within a ±46 K uncertainty. We achieve precision of ~50 K for 34 stars with spectra with the highest signal-to-noise ratio (S/N). For log ɡ, we achieve a total uncertainty of ±0.15 dex. For [Fe/H], we obtain a total uncertainty of ±0.09 dex. We find that the ionisation equilibrium of Fe lines under LTE is not valid in metal-poor giants. LTE leads to a small but significant metallicity underestimation of ~0.1 dex when derived from weak Fe I lines, and only provided accurate Teff and log ɡ. This bias totally disappears under non-LTE.

Mechanistic Insights into Water Autoionization through Metadynamics Simulation Enhanced by Machine Learning.

Characterizing the free energy landscape of water ionization has been a great challenge due to the limitations from expensive abinitio calculations and strong rare-event features. Lacking equilibrium sampling of the ionization pathway will cause ambiguities in the mechanistic study. Here, we obtain convergent free energy surfaces through nanosecond timescale metadynamics simulations with classical nuclei enhanced by atomic neural network potentials, which yields good reproduction of the equilibrium constant (pK_{w}=14.14) and ionization rate constant (1.369×10^{-3} s^{-1}). The character of transition state unveils the triple-proton transfer occurs through a concerted but asynchronous mechanism. Conditional ensemble average analyses establish the dual-presolvation mechanism, where a pair of hypercoordinated and undercoordinated waters bridged by one H_{2}O cooperatively constitutes the initiation environment for autoionization, and contributes extremely to the local electric field fluctuation to promote water dissociation.

La3+ and Al3+ loaded D151 as salt‐resistant resins for efficient adsorption of glyphosate: Effects of ionic radius

AbstractLa3+ and Al3+ loaded D151 resin [R‐La and R‐Al, respectively] were used as salt‐resistant resins for the efficient adsorption of glyphosate. The results showed that La3+ with a larger ionic radius could accommodate more glyphosate as ligands, resulting in higher glyphosate adsorption capacity of R‐La than that of R‐Al. Both R‐La and R‐Al exhibited maximum adsorption capacities at pH 2.52, where glyphosate existed in its ionization equilibrium of pKa2. Consistent with the larger ionic radius of La3+, R‐La featured larger qm and KL than R‐Al at the same temperature. Owing to the smaller radius of Al3+, the enthalpy values for the coordination adsorption of glyphosate by R‐Al were larger than those of R‐La at the same adsorption capacity. Owing to the smaller radius of Al3+, R‐Al exhibited stronger coordination adsorption for glyphosate and significantly higher salt tolerance than R‐La. The adsorption mechanisms indicated that both R‐La and R‐Al could adsorb glyphosate through the coordination of La3+ and Al3+ with O atoms of the phosphonate group of glyphosate. At a NaCl concentration range of 0–16%, R‐Al featured excellent salt tolerance and highly stable glyphosate adsorption capacity than 330, D301, R‐La, and the 14 adsorbents reported in the literature.

CHIANTI—An Atomic Database for Emission Lines. XVII. Version 10.1: Revised Ionization and Recombination Rates and Other Updates* *Released on 2023 July 17.

The CHIANTI atomic database provides sets of assessed data that are used for simulating spectral observations of astrophysical plasmas. This article describes updates that will be released as version 10.1 of the database. A key component of CHIANTI is the provision of ionization and recombination rates that are used to compute the ionization balance of a plasma over a range of temperatures. Parameters for calculating the ionization rates of all stages of ions from H through Zn were compiled and inserted into the CHIANTI database in 2009. These were based on all measurements that were available at the time and supplemented with distorted wave calculations. Since then, there have been a number of new laboratory measurements for ions that produce spectral lines that are commonly observed. Parameters have been fit to these new measurements to provide improved ability to reproduce the ionization cross sections and rate coefficients, and these are added to the database. CHIANTI 10.1 also includes new recombination rates for the phosphorus isoelectronic sequence, and the updated ionization and recombination rates have been used to calculate a new ionization equilibrium file. In addition, CHIANTI 10.1 has new electron collision and radiative data sets for eight ions in the nitrogen and oxygen isoelectronic sequences and updated energy level and wavelength data for six other ions.

Isolating Dust and Free–Free Emission in ONC Proplyds with ALMA Band 3 Observations

The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing external photoevaporation by the cluster’s intense UV field. These “proplyds” are comprised of a disk surrounded by an ionization front. We present ALMA Band 3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the dust disks and free–free emission from the ionization fronts are both detected, and the high-resolution (0.″057) of the observations allows us to spatially isolate these two components. The morphology is unique compared to images at shorter (sub)millimeter wavelengths, which only detect the disks, and images at longer centimeter wavelengths, which only detect the ionization fronts. The disks are small (r d = 6.4–38 au), likely due to truncation by ongoing photoevaporation. They have low spectral indices (α ≲ 2.1) measured between Bands 7 and 3, suggesting the dust emission is optically thick. They harbor tens of Earth masses of dust as computed from the millimeter flux using the standard method although their true masses may be larger due to the high optical depth. We derive their photoevaporative mass-loss rates in two ways: first, by invoking ionization equilibrium and second, by using the brightness of the free–free emission to compute the density of the outflow. We find decent agreement between these measurements and = 0.6–18.4 × 10−7 M ⊙ yr−1. The photoevaporation timescales are generally shorter than the ∼1 Myr age of the ONC, underscoring the known “proplyd lifetime problem.” Disk masses that are underestimated due to being optically thick remains one explanation to ease this discrepancy.

A new surface structural approach for modeling the charging behavior of kaolinite

The concentration of ions in equilibrium with soils and sediments is a function of various interconnected chemical reactions. The charging behavior of minerals provides a set of fundamental information required to model these interactions. Accordingly, in this study, the charging behavior of kaolinite was measured at three concentrations (0.004, 0.04 and 0.40 M) of three electrolytes (LiNO3, NaNO3 and KNO3) using potentiometric titration. The experimental data were described using the CD-MUSIC-G&T model in which ≡AlOH0.5−, ≡SiO− and ≡X− were defined as reactive functional groups on aluminol edge, silanol edge and basal planes, respectively. The charging behavior was a function of the type and concentration of the background electrolytes, but changes in the concentration more than changes in the type of electrolytes affected the surface charge. The thermodynamic equilibrium constants (logK) of the reactions of H+, Li+, Na+, K+ and NO3− with aluminol group were obtained as 9.50, 1.62, 1.37, 1.29 and 10.28 and with silanol group as 4.94, 1.58, 1.79, 2.03 and < −10, respectively. The logK of 4.94 shows that the interaction of H+ ion with the kaolinite ≡SiO− is much stronger than its interaction with the same group on the quartz. The capacitance of both inner and outer Stern layers was measured to be 1.94 F/m2, showing the strong interaction of electrolyte ions with the edge surface. In addition, the equilibrium constants of the reactions of Li+, Na+ and K+ with ≡X− group were obtained as −0.40, −0.02 and 0.32, respectively, which have the same order as reacted with the silanol group. At pH below pHPZC (i.e., <6.3 ± 0.2), increasing ionic strength reduced the surface charge of kaolinite; because increasing electrolyte concentration increased the negative charge on the silanol edge more than increasing the positive charge on the aluminol edge. In addition, it seems that the negative potential due to the isomorphic substitution in the polyhedrons near the edge of kaolinite poses an inward attractive force on the central cations of the edge polyhedrons, which in turn reduces the bonding capacity of ≡Al−OH0.5− and/or ≡Si−O−. Thereby, the adsorption energy of proton and cations on the edge surface may increase due to isomorphic substitution in adjacent polyhedrons.