Adsorption Of Sulfate Ions Research Articles

Experiments on adsorption at hydrous metal oxide surfaces using attenuated total reflection infrared spectroscopy (ATRIRS) (IUPAC Technical Report)

Abstract This article seeks to encourage the adoption of modern methods of surface analysis in teaching contexts by introducing the use of attenuated total reflection infrared spectroscopy (ATRIRS) in analysis of adsorption reactions at hydrous metal oxide thin films. The first experiment shows how outer-sphere adsorption of perchlorate ion is distinguished from inner-sphere adsorption of ethanedioate (oxalate) ion at TiO2 surfaces. The second experiment shows how the nature of adsorption of sulfate ion to iron oxide surfaces changes with pH. In the third experiment, the variation of the amount of benzene-1,2-diol (catechol) adsorbed to TiO2 with solution concentration enables an adsorption constant to be derived from the adsorption isotherm.

Experimental investigation of the concomitant effect of potential determining ions Mg2+/SO42− and Ca2+/SO42− on the wettability alteration of oil-wet calcite surfaces

Modifying the concentration of potential determining ions (PDIs) in the brine can result in alteration of the surface wetting properties towards more water-wet state, which is the desired wetting state in fractured carbonate reservoirs. However, few studies have discussed the interactions between these PDIs and their mechanisms of wettability alteration. Accordingly, the aim of this study was to investigate the concomitant effect of PDIs at different molar ratios on the wettability of oil-wet calcite surfaces as well as the interactions between the ions. Two combinations of wettability modifying agents (Mg2+/SO42−) and (Ca2+/SO42−) were considered. Contact angle and zeta potential measurements were performed to evaluate the effect of these combined ions and explore possible wettability alteration mechanisms. Results revealed that both PDIs groups were able to reduce the contact angle significantly and expel carboxylate group from the surface. Besides, combinations of PDIs were more effective in wettability alteration compared to those ions alone. It was also observed that equal concentrations of magnesium and sulfate provide more water-wet state. However, for combinations of calcium and sulfate, the most water-wet state was achieved when lower concentrations of calcium and higher concentrations of sulfate were used. Zeta potential measurements showed that the performance of each PDI in changing surface wettability is critically affected by the concentration of the other ions present in the same solution. Results indicated that when low concentration of magnesium ions is used, the adsorption of sulfate ions on the rock surface and the interaction of magnesium ions with the carboxylate group is the main mechanism of wettability alteration by magnesium and sulfate ions. However, at high concentration of magnesium ions, no adsorption of sulfate ions was detected which means that sulfate serves as a catalyst for wettability alteration by Mg2+/SO42− and the formation of a complex Mg-carboxylate group is the dominant mechanism. Moreover, the use of cationic surfactant along with the combined PDIs resulted in strong water-wet conditions.

2-Amino-4-(4-methoxyphenyl)-thiazole as a novel corrosion inhibitor for mild steel in acidic medium

The inhibitory effects of 2-amino-4-(4-methoxyphenyl)-thiazole (MPT) on mild steel corrosion were evaluated in 0.5 M H2SO4 and 1 M HCl solutions, respectively. From the analysis of potentiodynamic polarization curves and electrochemical impedance spectroscopy, MPT can effectively inhibit the corrosion of mild steel in acidic solutions. Under the optimal conditions, the inhibition efficiency (η) was as high as 95% in 0.5 M H2SO4 solution. The inhibition property of MPT was much better than that of the reported corrosion inhibitor 2-amino-4-phenylthiazole (APT). Polarization curves also demonstrated that MPT mainly inhibited the anodic corrosion of mild steel in HCl solution and the cathodic corrosion in H2SO4 solution, respectively. The adsorption of MPT on the surface of mild steel was found to obey Langmuir adsorption isotherm in both acid solutions. Quantum calculations suggest that the addition of electron donor group (−OCH3) endowed the molecule better adsorption ability on mild steel surface. The interaction between protonated MPT and anions on Fe (0 0 1) surface was firstly investigated using molecular dynamic stimulations, and the results showed that with the adsorption of sulfate ions, MPTH+ had a superior binding energy on the surface of Fe. The investigation of UV–vis spectrum demonstrated the direct correlation of the experimental data and the theoretical calculations.

Molecular-Scale Structure of Electrode-Electrolyte Interfaces: The Case of Platinum in Aqueous Sulfuric Acid.

Knowledge of the molecular composition and electronic structure of electrified solid-liquid interfaces is key to understanding elemental processes in heterogeneous reactions. Using X-ray absorption spectroscopy in the interface-sensitive electron yield mode (EY-XAS), first-principles electronic structure calculations, and multiscale simulations, we determined the chemical composition of the interfacial region of a polycrystalline platinum electrode in contact with aqueous sulfuric acid solution at potentials between the hydrogen and oxygen evolution reactions. We found that between 0.7 and 1.3 V vs Ag/AgCl the electrical double layer (EDL) region comprises adsorbed sulfate ions with hydrated hydronium ions in the next layer. No evidence was found for bisulfate or Pt-O/Pt-OH species, which have very distinctive spectral signatures. In addition to resolving the long-standing issue of the EDL structure, our work establishes interface- and element-sensitive EY-XAS as a powerful spectroscopic tool for studying condensed phase, buried solid-liquid interfaces relevant to various electrochemical processes and devices.

Ionic hydration structure, dynamics and adsorption mechanism of sulfate and sodium ions in the surface of calcium silicate hydrate gel: A molecular dynamics study

Molecular dynamics was utilized to investigate ionic structure, dynamics and adsorption behaviors of the sulfate and sodium ions highly solvated in the nanometer channel of calcium silicate hydrate (C–S–H) with two different Ca/Si ratios. Due to H-bond connection from silicate oxygen sites and attraction of surface calcium ions, a stable adsorption layer of water molecules was formed in the vicinity of the hydrophilic silicate channel: clear layered arrangements, strong orientation preferences and extremely low diffusion coefficients. Furthermore, the adsorption mechanisms differ for the sulfate and sodium ions confined in the gel pore of C–S–H: while sodium ions are connected onto the non-bridging oxygen sites by Na-Onb bonding, the sulfate ions can be attracted by the calcium ions, leading to the aggregation of Ca-SO4 ionic pairs. In the surface region, since the hydration shell of the solvated ions are partly substituted by the adsorbed water molecules, surface calcium ions and silicate oxygen sites, the diffusion of these ions is dramatically immobilized. Both the adsorbed Na+ and SO42− ions display extended exchange time for their solvation shells and longer residence time for their ionic clusters, as compared with those in aqueous solution. Besides, the increase in the surface Ca/Si ratio disturbs the local ordered arrangements and reduces the stability of the hydration layer. At high Ca/Si ratio, the highly solvated calcium ions contribute to the transformation from the outer adsorbed sulfate ions to the inner adsorbed species, enhancing the anions immobilization near the silicate surface.

Behaviour of the rare earths during goethite (α-FeOOH) precipitation from sulphate-based solutions

Goethite (α-FeOOH) precipitation is an effective means of removing iron in a filterable form from processing solutions, and the behaviour of the rare earths during goethite precipitation was investigated. Increasing concentrations of the light rare earth ions, to 10g/L, yielded precipitates having nearly constant Fe contents. Both the SO4 and REE contents increased in a linear manner as the concentration of the light rare earth ions increased, and REE contents as high as 0.5% Gd were obtained. The products made from the more dilute light rare earth solutions consisted of dominant goethite (α-FeOOH) with trace-to-minor amounts of lepidocrocite (γ-FeOOH), but the amount of lepidocrocite decreased significantly with increasing atomic number or with increasing concentration of a given rare earth ion. Increasing concentrations of Ce3+ gave similar results except that partial oxidation of Ce3+ resulted in minor CeO2 contents in some of the precipitates. Increasing concentrations, to 10g/L, of the heavy rare earth ions yielded precipitates having essentially constant Fe contents, and goethite was the only product detected. In contrast, both the rare earth and SO4 contents of the precipitates increased in a linear manner as the concentrations of the heavy rare earth ions increased. The adsorption of sulphate ions on goethite seems to be responsible for the observed SO4 contents of the precipitates. The extent of rare earth incorporation in goethite increases as the atomic number of the rare earth increases, and a 1.4% Lu content was realized from a 5g/L Lu3+ solution. However, it is not clear whether the rare earth ions are adsorbed on the goethite or are incorporated in the goethite structure, and further work is required to clarify the mode of rare earth incorporation.

Sulfate Adsorption onto and Desorption from Silicon Dioxide Films

Sulfate ion adsorption onto and desorption from silicon dioxide surface has been investigated using a quartz crystal microbalance with dissipation monitoring capability (QCM-D). A viscoelastic model was used to calculate adsorption/desorption amount. Experimental results indicate that the adsorption from Na2SO4 and K2SO4 solutions at a pH of 6.8 results in the formation of a multilayer sulfate film with co-adsorption of Na+ or K+ ions. Sulfate ion uptake varied linearly with sulfate concentration in the range 0.01 M to 0.6 M. The first order rate constant for sulfate desorption with DI water is approximately 0.04 s−1 and 0.12s−1 for flow rates of 0.2 ml/min and 1.0 ml/min, respectively.

Sulfate Adsorption onto and Desorption from Silicon Dioxide Films

Sulfate ion adsorption onto and desorption from silicon dioxide surface has been investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) capability. A viscoelastic model was used to calculate adsorption/desorption amount. The sulfate ion uptake at pH 6.8 varied linearly with sulfate concentration in the range 0.01 M to 0.6 M. Based on the hydrated radius of sulfate ion, the adsorption (uptake) amount indicated multilayer adsorption. The first order rate constant for sulfate desorption with DI water is approximately 0.04 s-1 and 0.12s-1 for flow rates of 0.2 ml/min and 1.0 ml/min, respectively.

Study on removal behavior and separation efficiency of naturally occurring bentonite for sulfate from water by continuous column and batch methods

The removal of sulfate using Jordanian bentonite has been investigated in this study. The surface of the bentonite was modified by calcinations at different temperature. The batch experiments of the equilibrium studies were carried out under different operating conditions. Kinetic modeling for the removal of sulfate ion was investigated using a pseudo-second-order, intraparticle diffusion and Elovich kinetic models to predict the rate constants and equilibrium capacities for this process using column reactor. It was found that intraparticle diffusion of the sulfate ion is the rate limiting step and played an important role in the mechanism of sulfate ion adsorption depending on the obtained activation energy, which was 32.8 kJ/mol. Also, the sorption isotherm analyzed using both the Langmuir and Freundlich models as a function of temperature. The isothermal data found to be fitted Langmuir model rather than Freundlich model. The positive value of ΔH (15.2 kJ/mol) indicated that the adsorption of sulfate ions on the adsorbent was an endothermic process and the positive value of ΔS (22.1 J/mol.K) indicated that the adsorption is favorable with small positive value of the free energy (ΔG).

Effective adsorption of sulfate ions with poly(m-phenylenediamine) in aqueous solution and its adsorption mechanism

Sulfate adsorption by poly(m-phenylenediamine)s (PmPDs) with various oxidation states synthesized through chemically oxidative polymerization was investigated. Series of sorption experiments were conducted, and the adsorption mechanism and the relationship between oxidation state and adsorption performance were studied with the characterization of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), pH tracking and energy calculation. The results show that the adsorption performance in acidic solution is improved with the decrease of oxidation state of poly(m-phenylenediamine) (PmPD). The rate constant is as high as 425.5 mg/(g·min) in the short equilibrium time of 30 min. The estimated highest adsorptivity of sulfate ions is 95.1%. According to the Langmuir equation, the adsorbance is 108.5 mg/g. The sulfate desorption efficiency is about 95% and the accumulative adsorbance is up to 487.95 mg/g in 5 cycles.

Polymer dispersions and their interaction with mortar constituents and ceramic tile surfaces studied by zeta-potential measurements and atomic force microscopy

The interaction between mineral surfaces and organic polymer dispersions with different monomer base and protective colloids as present in tile adhesive mortar systems was investigated by measuring the ζ-potential and by direct observation by atomic force microscopy (AFM). The charge situation of pure mineral powders and pure polymer dispersions as well as their interaction in presence of different cementitious aqueous solutions was studied. The binding of Ca++ ions leads to positive ζ-potentials for quartz or ceramic in calcium containing aqueous solutions and acts as a transmitter of attractive forces. However, the adsorption of sulfate ions may disturb such attraction. The interaction between polymer dispersions and ceramic (polished and original tile) or mica surfaces influenced by the presence of artificial cementitious pore solutions was observed by AFM. A flat index (height/diameter of latex particles in contact with these surfaces) was defined to quantify the polymer–mineral interface affinity. The different flat indices for different polymer–substrate combinations are mainly related to two parameters, the glass transition temperature of the copolymer and the stabilization system (steric versus cationic). Furthermore tapping phase imaging revealed significant heterogeneities in the inner structure of the polymer particles and inhomogeneous distribution at their surface probably related to local variations of the protective colloid, especially polyvinyl alcohol.

Organization of Water and Atmospherically Relevant Ions and Solutes: Vibrational Sum Frequency Spectroscopy at the Vapor/Liquid and Liquid/Solid Interfaces

The nature of water's hydrogen-bonding network is a vital influence on the chemistry that occurs at interfaces, but a complete understanding of interfacial water has proven elusive. Even-order nonlinear optical spectroscopies, such as vibrational sum frequency generation (VSFG) spectroscopy and heterodyne detected phase-sensitive sum frequency generation (PS-SFG) spectroscopy, are inherently surface specific. With the advent of advances in these spectroscopic techniques, researchers can now explore many long-standing questions about the dynamics and structures present at the vapor-water and water-solid interfaces. Of special interest to the atmospheric chemistry community is the accommodation of ions and solutes by water's hydrogen-bonding network. A better understanding of how ions and solutes behave in hydrogen-bonded water has afforded a fresh perspective of aqueous aerosols, because the interactions involved therein drive phenomena such as the hydrolysis of atmospheric chemical species. In this Account, we present work from our laboratory focusing on applying VSFG and the recently developed PS-SFG techniques to probe the perturbation of water's hydrogen-bonding network at the vapor-water interface by a variety of ions and solutes. We also present very recent results from our laboratory on the direct observation of the adsorption of ions at the water-CaF(2) interface. We begin by discussing the influence of ions and solutes on interfacial water structure. Results for halide salts and the acid analogs on interfacial water structure are shown to be quite different, as would be expected from differences in surface tension measurements that have been known for a long time. Also examined are systems with the largely polarizable molecular anions nitrate (NO(3)(-)), sulfate (SO(4)(2-)), carbonate (CO(3)(2-)), and bicarbonate (HCO(3)(-)).These systems feature more complicated influences on interfacial water structure than halide-containing solutions; however, our conventional VSFG results for both nitrate and sulfate solutions are in agreement with recent PS-SFG results and molecular dynamics simulations. We also discuss recent PS-SFG work on carbonate and bicarbonate systems in which the accommodation of the bicarbonate ion at the vapor-water interface is in stark contrast to the carbonate results. Perturbation of interfacial water by solutes is examined for solutions of dimethyl sulfoxide and methylsulfonic acid. PS-SFG results for these systems are striking: they illustrate the dramatic changes that interfacial water molecules undergo in the presence of solutes that are not observed with conventional VSFG. Finally, we discuss direct sulfate ion adsorption for the aqueous sodium sulfate-CaF(2) interface, with the goal of elucidating water behavior at this surface.

Adsorption of Sulfate Ions from Aqueous Solution by Surfactant-Modified Palygorskite

The objectives of this work are to study palygorskite modified by a surfactant, octodecyltrimethylammonium chloride (OTMAC), and to study for the potential use of the surfactant-modified palygorskite (SMP) as an adsorbent for the adsorption of sulfate ions from aqueous solutions. The surface characters of SMP were undertaken by scanning electron microscopy (SEM), FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), and N2 adsorption. The FTIR spectra and XPS showed that the surfactant (OTMAC) had effectively grafted on palygorskite. A batch technique was carried out to evaluate parameters affecting adsorption including pH, the amount of SMP, treatment time, and initial SO42– concentration. The adsorption isotherms of SMP for sulfate ions were described by Langmuir, Freundlich, and Dubinin–Radushkevich equations, and the Freundlich model was best to express the adsorption process. The thermodynamic data indicated that the adsorption was an endothermic and spontaneous process. Results of kinetic experiments showed that the adsorption was best described by the pseudosecond-order kinetics model. Above all, the adsorption of sulfate ions extended the application of palygorskite to the removal of anions and wastewater purification.

Spontaneous Formation of Nano‐fibrillar Boehmite and the Enhancement Effect of Polyethylene Glycol

Nano‐fibrillar boehmite is a desirable product due to its high specific surface area and potential application in a wide variety of engineering applications. Inorganic salts are the preferred raw materials for fabricating such products because of their low cost. In this study, nano‐sized (10–20 nm in diameter) boehmite fibrils were fabricated by the hydrothermal (105°C) digestion of a suspension prepared from either aluminum sulfate or nitrate salt under a neutral pH. It appears that the formation of fibrils is spontaneous and thermodynamically favorable. The presence of polyethylene glycol (PEG) was found to further enhance the formation of fibrils by promoting the transportation of aluminum ions to the crystal nuclei. The growth direction of the crystals in the fibrils is normal to the boehmite (020) plane. The formation of boehmite fibrils was greatly reduced under an acidic pH and at a lower digestion temperature due to kinetic restriction. The structures of the immediate products generated from aluminum sulfate and aluminum nitrate were different, which is probably due to the stronger adsorption of sulfate ions on the surface of gelatinous aggregates. The fibrils derived from as‐precipitated and coagulated amorphous aluminum hydroxide grains experienced a series of structural evolutions in which they progressed from a sponge‐like structure to a fibrillar structure with time.

Research on the Behaviors of the Adsorption of Sulfate Ions onto Cross-Linked Chitosan in Wastewater

Formaldehyde cross-linked chitosan was used to adsorb sulfate ions from aqueous solution in this study. Batch experiments were conducted to investigate the conditions of the adsorption, the isotherms and kinetics of the adsorption. The optimized conditions of adsorption were as follows: the adsorbent dosage was 0.5g, the equilibrium time was 240min, the initial concentration of sulfate ions was 153.3mg/L, the temperature was 50°Cand the value of pH was 2.2. The maximum adsorption capacity came up to 14.7 mg/g with the adsorption efficiency got to 95.7%. The equilibrium data fitted Langmuir isothermal model well. In addition, the adsorption process could be explained by the second-order kinetic model, and the chemisorption was the limit step for adsorption velocity.

Effect of Cs + ions on the electrochemical nanogravimetric response of platinum electrode in acid media

Platinum electrodes have been investigated in sulfuric acid solutions in the presence and absence of Cs + ions by electrochemical quartz crystal nanobalance (EQCN). An unusual potential dependence of the quartz crystal frequency response has been observed in the presence of Cs + ions. The frequency decrease is more pronounced in the region of the underpotential deposition of hydrogen, and the frequency decrease in the double layer region diminishes as the concentration ratio of Cs + and H + ions increases. After immersion in Cs 2SO 4 solutions the frequency change was higher than that expected taking into account the density and viscosity. The effects observed can be explained by the specific adsorption of Cs + ions on the Pt surface, which competes with the hydrogen adsorption. At more positive potentials than the potential of zero charge (pzc) a desorption of the Cs + ions starts. In this potential region both Cs + and HSO 4 − ions are adsorbed at the platinum surface. In the double layer region the mass change caused by the desorption of Cs + ions and the starting adsorption of sulfate ions compensates each other.

Effect of sulfate ion adsorption on the rate of copper electrocrystallization on Ag(111) face

The process of copper electrocrystallization on the Ag(111) face was studied in acidic perchlorate-sulfate electrolytes. Enhanced rate of charge transfer in the course of nucleation and growth of epitaxial copper crystallites was observed in the solutions with additives of sulfate ion as a result of local electrostatic effects under specific adsorption of anions. Copper nucleation parameters were estimated in the framework of the diffusion models and atomistic theory of electrochemical nucleation.

The Impact of Pore Water Chemistry on Carbonate Surface Charge and Oil Wettability

Water chemistry has been shown experimentally to affect the stability of water films and the sorption of organic oil components on mineral surfaces. When oil is displaced by water, water chemistry has been shown to impact oil recovery. At least two mechanisms could account for these effects, the water chemistry could change the charge on the rock surface and affect the rock wettability, and/or changes in the water chemistry could dissolve rock minerals and affect the rock wettability. The explanations need not be the same for oil displacement of water as for water imbibition and displacement of oil. This article investigates how water chemistry affects surface charge and rock dissolution in a pure calcium carbonate rock similar to the Stevns Klint chalk by constructing and applying a chemical model that couples bulk aqueous and surface chemistry and also addresses mineral precipitation and dissolution. We perform calculations for seawater and formation water for temperatures between 70 and 130°C. The model we construct accurately predicts the surface potential of calcite and the adsorption of sulfate ions from the pore water. The surface potential changes are not able to explain the observed changes in oil recovery caused by changes in pore water chemistry or temperature. On the other hand, chemical dissolution of calcite has the experimentally observed chemical and temperature dependence and could account for the experimental recovery systematics. Based on this preliminary analysis, we conclude that although surface potential may explain some aspects of the existing spontaneous imbibitions data set, mineral dissolution appears to be the controlling factor.

Experimental and molecular dynamics studies on corrosion inhibition of mild steel by 2-amino-5-phenyl-1,3,4-thiadiazole

The corrosion inhibition of mild steel in 0.5 M H 2SO 4 and 1.0 M HCl by 2-amino-5-phenyl-1,3,4-thiadiazole (APT) has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the inhibition efficiency increases with the increase of APT concentration in both acids, and the higher inhibition efficiency is obtained in 0.5 M H 2SO 4. The adsorption of APT molecules on the steel surface obeys Langmuir adsorption isotherm in both acids, and occurs spontaneously. The molecular dynamics method has also been used to simulate the adsorption of ATP molecule and solvent ions on the iron surface. The results show that with the adsorption of sulfate ions the Fe + anion + APT system has the higher negative interaction energy comparing to the case of the adsorption of chloride ions.

Preparation and electrochemical characterization of low-index rhodium single crystal electrodes in sulfuric acid

The electrochemical properties of low-index phase Rh(1 1 1), Rh(1 1 0) and Rh(1 0 0) single crystal bead electrodes, prepared by a novel technique combining electron beam heating with inductive annealing in a controlled atmosphere, have been characterized in 0.1 M H 2SO 4 by cyclic voltammetry and chronoamperometry. Hydrogen and sulfate adsorption as well as surface oxidation depend strongly on the crystallographic orientation of the surface. The potentials of zero total charge ( E pztc) of all three Rh electrodes in 0.1 M H 2SO 4 were determined by the combination of charge displacement and voltammetric experiments. The charge balance reveals unambiguousely that the (√3 × √7) adlayer on Rh(1 1 1) is composed of specifically adsorbed sulfate ions eventually coadsorbed with water molecules. Hydrogen-sulfate coadsorbed with hydronium ions could be excluded. The kinetics of sulfate ion desorption followed by the adsorption of hydrogen at less positive potentials could be represented by a nucleation and growth mechanism coupled with a parallel first order process. The electro-oxidation of irreversibly adsorbed carbon monoxide monolayers was also investigated and revealed distinct structure sensitivity. The reaction pathway on all three low-index phases of Rh proceeds according to a Langmuir–Hinshelwood mechanism and is controlled by nucleation of OH ads at steps and other defect sites followed by a complex growth process on terrace sites. The low surface mobility of CO ads leads to a slow and incomplete CO monolayer electro-oxidation on Rh(1 1 1). The high density of step sites on Rh(1 1 0) and the reversible formation of oxygenated species on Rh(1 0 0) at rather low potentials significantly enhance the electro-oxidation activity leading to the following reactivity sequence: Rh(1 1 1) ≪ Rh(1 1 0) ∼ Rh(1 0 0). The shape of the experimental transients and attempts to model them demonstrate the occurrence of at least two processes occurring in parallel. The long-term response represents clearly a process involving a slow surface-diffusion step.