Temperature dependence of adsorption parameters of n-butanol and n-valeric acid at their adsorption on mercury electrode from aqueous solutions

Adsorption parameters that enter into the Frumkin isotherm and the model of two parallel capacitors are calculated based on the data of the regression analysis of differential capacitance curves of a mercury electrode in solutions of n-butanol and n-valeric acid at 25, 50, and 75°C. The analysis of the temperature dependences of these parameters allowed free energies, entropies, and enthalpies of adsorption to be found. It is shown that the hydrophobic effect, which is associated with the increase in the enthalpy of liquid water when adsorbate molecules leave it, makes a substantial contribution into the adsorption free energy of studied compounds.     

Determining Sodium Kryptate Adsorption Parameters on a Mercury Electrode in 1 M Na2SO4

The adsorption of a complex of sodium cations with a macrocyclic ligand (Kryptofix^R 222, composition C₁₈H₃₆N₂O₆) as a function of its concentration in 1 M Na₂SO₄ is studied by measuring the differential capacitance on a stationary Hg drop. Adsorption parameters of sodium kryptate are found using a regression analysis method and various versions of a model of two parallel capacitors complemented with the Frumkin adsorption isotherm. The differential capacitance curves, calculated on the basis of these, are compared with experimental data. The difference in model versions that most adequately describe the adsorption data, established for systems in 0.1 and 1 M Na₂SO₄, is explained by the influence of the supporting electrolyte on the adsorption layer structure. Conclusions are made on the absence in the system under study of the salting-out from the bulk solution and on a change in the properties of an adsorption layer of sodium kryptate in the region of potentials of the anodic adsorption–desorption peak following expansion of the adsorption region.     

Effect of Artabotrys odoratissimus extract as an environmentally sustainable inhibitor for mild steel corrosion in 0.5 M H2SO4 media

Artabotrys odoratissimus inhibitory effect on mild steel (MS) corrosion in 0.5 M H₂SO₄ solution has been assessed utilizing mass loss, electrochemical potentiodynamic polarization, and impedance spectroscopy techniques. The Artabotrys odoratissimus plant has a wide range of bioactive compounds. Phytochemicals were tested for ethanolic Artabotrys odoratissimus leaves extract (AOLE) using the FeCl₃ test, Salkowaski's test, and others. Corrosion tests were conducted at varying inhibitor concentrations and temperatures. The inhibitory impact of AOLE on corrosion of MS was reported to improve with increasing concentration. Polarization experiments revealed that AOLE is a mixed kind of inhibitor and the inhibition efficacy (η_w) for MS is 93.27% for 1.25 g/L AOLE. For Electrochemical impedance spectroscopy (EIS), maximal inhibitory efficacy (η_w) was 91.62% due to AOLE adsorption on the MS surface. The obtained results using each methodology are highly consistent and closely resemble each other. The adsorption of AOLE molecules on an MS surface from the bulk of the solution causes the inhibitor's inhibition action, and the adsorption mechanism follows Langmuir adsorption isotherm. The computed $\Delta G_{ads}^o$ values ranged between ?32.919 and ?33.520 kJ mol^?1, implying a spontaneous and exothermic inhibitory action. The thermodynamic and activation parameters are often used to understand corrosion inhibition mechanisms. The comparison of corrosion product and pure extract FT-IR spectrum indicates the nature of AOLE adsorption on the MS surface. The surface morphology of MS samples was assessed using atomic force microscopy (AFM), scanning electron microscope (SEM), and contact angle techniques.     

Inhibition effect of hexadecyl pyridinium bromide on the corrosion behavior of some austenitic stainless steels in H2SO4 solutions

The inhibition effect of hexadecyl pyridinium bromide (HDPB) as a cationic surfactant on the corrosion behavior of some Egyptian austenitic stainless steel SS 304L, SS 316H and SS 304H in 0.5 M H₂SO₄ solutions was investigated by using potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results indicate that HDPB is a good inhibitor for the samples under investigation in 0.5 M H₂SO₄ solutions. In addition, the inhibition efficiency η% increases with the inhibitor concentration while decreases with the increasing temperature referring to physical adsorption. The adsorption of the inhibitor obeys a Temkin adsorption isotherm. Polarization curves show that HDPB is a mixed inhibitor in H₂SO₄ solutions. The results obtained from polarization and impedance measurements are in good agreement. Activation-free energies, enthalpies, and entropies for the inhibition process of HDPB were determined.     

Kinetic stability of tetrazaporphin in binary H2SO4-AcOH and H2SO4-DMSO solutions

The state and kinetic stability of tetrazaporphin (I) in acetic acid and in dimethyl sulfoxide (DMSO) in the presence of H₂SO₄ were investigated. Partial protonatiqn of I to give I-AcOH₂ associates occurs in acetic acid. The kinetic parameters of the reaction involving the destruction of tetrazaporphin in the presence of H₂SO₄ in acetic acid and DMSO solutions were determined. The mechanism of the destruction is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 932–936, July, 1984.     

Synergistic inhibition effects between leaves and stem extracts of Sida acuta and iodide ion for mild steel corrosion in 1 M H2SO4 solutions

The synergistic action caused by iodide ions on the corrosion inhibition of mild steel in 1 M H₂SO₄ by leaves and stem extracts of Sida acuta was studied using weight loss and hydrogen evolution methods at 30–60 °C. It was found that the leaves and stem extracts of S. acuta inhibited the acid induced corrosion of mild steel. Addition of iodide ions enhances the inhibition efficiency to a considerable extent. The inhibition efficiency increases with increase in the iodide ion concentration but decreases with rise in temperature. Adsorption of the extracts alone and in combination of iodide ion was found to obey Freundlich adsorption isotherm at all temperatures studied. Inhibition mechanism is deduced from the temperature dependence of the inhibition efficiency as well as from assessment of kinetic and activation parameters that govern the processes. The synergism parameter (S₁) is defined and evaluated from the inhibition efficiency values. This parameter for the different concentrations of iodide ions from the two techniques employed is found to be greater than unity indicating that the enhanced inhibition efficiency of the extracts caused by the addition of iodide ions is due to synergism.     

Essential oil of Salvia aucheri mesatlantica as a green inhibitor for the corrosion of steel in 0.5 M H2SO4

Essential oil of aerial parts of Salvia aucheri Boiss. var. mesatlantica was obtained by hydrodistillation and analyzed by GC and GC/MS. The oil was predominated by camphor (49.59%). The inhibitory effect of this essential oil was estimated on the corrosion of steel in 0.5 M H₂SO₄ using electrochemical polarization and weight loss measurements. The corrosion rate of steel is decreased in the presence of natural oil. The inhibition efficiency was found to increase with oil content to attain 86.12% at 2 g/L. Polarization curves revealed that the oil of S. aucheri mesatlantica acts as mixed type inhibitor with a strong predominance of anodic character. The temperature effect on the corrosion behavior of steel in 0.5 M H₂SO₄ without and with the inhibitor at 2 g/L was studied in the temperature range from 303 to 343 K, the associated activation energy have been determined. The adsorption of oil on the steel surface was found to obey Langmuir’s adsorption isotherm.     

Anion-exchange behaviour of 12 elements in H2SO4 and HF−H2SO4 medium

Anion-exchange data have been obtained for the elements As, Hf, Mo, Nb, Pa, Re, Sb, Sn, Ta, Tc, W, and Zr in 0.1 to 10M H₂SO₄ and in HF–H₂SO₄ mixtures of combination extending from 0.1 to 10M HF and from 0.1 to 10M H₂SO₄. The distribution ratios for mixed solutions are presented in form of adsorption contour lines.     

Optimization of lead adsorption from lead-acid battery recycling unit wastewater using H2SO4 modified activated carbon

During the recycling of exhausted lead-acid battery, large amount of wastewater is discharged, which contains the toxic Pb(II) ions in high concentration. In this study, the granular activated carbon after modification with sulfuric acid has been used to remove the Pb(II) ions from this wastewater. Adsorbents were characterized using Fourier Transform Infrared, Scanning Electron Microscope, and X-Ray Diffraction analyzer. Taguchi orthogonal L16 array (4^3) was used for batch adsorption study with four levels of three factors initial pH, adsorbent dose, and contact time. Optimum level of parameters was fourty + nd pH 4.5, time 240 min, and dose 0.05 g/50 mL using signal-to-noise ratio (larger-the-better response). Analysis of variance technique was used to signify the adsorption experiment model. The effect of parameters on uptake capacity of adsorbent has been evaluated. Maximum adsorbent capacity for Pb(II) uptake from wastewater of battery recycling unit was found 8.19 mg/g after modification with sulfuric acid. To further understand the mechanism of adsorption, isotherm and kinetic studies were carried out. Experimental data were well fitted with Langmuir isotherm model and pseudo-second-order kinetic model. The study suggested that H₂SO₄ modified granular activated carbon can be potentially used to remove Pb(II) from lead-acid battery recycle wastewater.     

Refining adsorption parameters of n-butyl alcohol at the interface of mercury electrode with aqueous NaF and Na2SO4 solutions by correcting the adsorbate concentration

As an adjunct to the regression analysis of differential capacitance curves, which allows refining the adsorption parameters, a program, which takes into account possible errors in volume concentrations of organic substances, is developed. Using this procedure, the earlier data on the differential capacitance of a mercury electrode in aqueous solutions of normal butanol (1-BuOH) containing either 0.1 M NaF or 0.05 and 0.5 M Na₂SO₄ as the supporting electrolyte are analyzed. This allows obtaining the most accurate values of adsorption parameters for the systems mentioned above within the framework of the model of two parallel capacitors and the Frumkin isotherm. It is shown that, when a linear dependence of the intermolecular interaction parameter on the electrode potential is taken into account, the standard deviation of experimental capacitance values from those calculated using the mentioned model is 6.8–8.8%, which points to very high accuracy of this phenomenological model.     

Inhibitive assessment of 1-(7-methyl-5-morpholin-4-yl-thiazolo[4,5-d]pyrimidin-2-yl)-hydrazine as a corrosion inhibitor for mild steel in sulfuric acid solution

In this study, the inhibitive effect of synthesized 1-(7-methyl-5-morpholin-4-yl-thiazolo[4,5-d]pyrimidin-2-yl)-hydrazine (MMTPH) as a new corrosion inhibitor for mild steel in 0.5 M sulfuric acid medium is investigated employing potentiodynamic polarization, electrochemical impedance spectroscopy and linear polarization resistance techniques. The results show MMTPH reduces anodic dissolution, retards the hydrogen evolution reaction and its adsorption follows Langmuir’s adsorption isotherm. Any increase in temperature will in turn increase corrosion current densities; however, the presence of MMTPH hinders the rate. In solutions with inhibitor concentration of 200 ppm, temperature elevations as great as 30° (25–55 °C) result in a drop of about 45 % in inhibition efficiency (99–55 %). Thermodynamic adsorption parameters show that the MMTPH is absorbed by a spontaneous exothermic process and the adsorption mechanism is physical. Quantum chemical method shows that the MMTPH molecules can be directly adsorbed at the steel surface on the basis of donor–acceptor interactions between π-electrons of pyrimidine, N atoms of hydrazine and vacant d-orbitals of iron atoms.     

Aqueous extract of Acacia cyanophylla leaves as environmentally friendly inhibitor for mild steel corrosion in 1 M H2SO4 solution

The efficiency of Acacia cyanophylla leaves extract as an environmentally friendly inhibitor for mild steel in aerated aqueous 1 M H₂SO₄ solution has been investigated by potentiodynamic polarization measurements and electrochemical impedance spectroscopy techniques. Addition of inhibitor decreases the corrosion current whereas the corrosion potential values show slight shifts in positive directions. Inhibition efficiency was found to be about 93% (the maximum value was determined from the polarization curve). Efficiencies obtained from both electrochemical techniques are in good agreement. Adsorption of Acacia cyanophylla leaves extract on mild steel surface in 1 M H₂SO₄ solution obeys Langmuir adsorption isotherm. Polarization curves were also obtained at different temperatures in order to measure changes of corrosion rate. Corrosion current increases and inhibition efficiency decreases with temperature increasing in H₂SO₄ solutions with and without Acacia cyanophylla extract. Corrosion parameters also changed with exposure time. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermodynamic properties of {(NH4)2SO4(aq) + Li2SO4(aq)} and {(NH4)2SO 4(aq) + Na2SO4(aq)} at a temperature of 298.15 K

The water activities and osmotic coefficients of aqueous solutions of {(NH₄ )₂SO ₄ +  Li ₂SO ₄} and {(NH₄ )₂SO ₄ +  Na ₂SO ₄} have been determined at a temperature of 298.15 K with a hygrometric method, at molalities in the region 0.2 mol · kg ^− 1 to saturation of the solutes for different fractional ionic-strengthsy =  0.2, 0.5, and 0.8 of (NH ₄)₂SO ₄. The experimental results are compared with the predictions obtained from our extended compared additivity model, as well as the models reported by Zdanovskii, Stokes and Robinson, Pitzer, and Lietzke-Stoughton. From these measurements, parameters of Pitzers model have been determined. These were used to predict solute activity coefficients in the mixture and calculate the excess Gibbs function at total molalities for different y for these systems.     

A contribution to the voltammetric study of cystine and cysteine at Pt electrodes in 0.5 M H2SO4

Both cysteine and cystine adsorb at the Pt electrode according the Frumkin—Temkin isotherm with the heterogeneity factor f = 51 for cysteine and 21 for cystine. Both the adsorbed cysteine and cystine give in a solution without any dissolved cystine or cysteine almost identical first cyclic voltammetric curves. Each substance dissolved in the electrolyte gives two oxidation peaks which differ when the oxidation is carried out at a “reduced” or an “oxidized” Pt electrode. On the basis of the dependence of the height and potential of the peaks on polarization rate and concentration (in the case of oxidation of dissolved substances) and of coulometric measurements the following conclusions have been made concerning the kinetics and mechanism:(i) Neither cysteine nor cystine change their oxidation state on adsorption at the electrode.(ii) The final oxidation product of both adsorbed cysteine and cystine may be the cysteic acid.(iii) For cysteine there are two adsorbed species, one strongly adsorbed, the other one weakly adsorbed.(iv) The oxidation of dissolved cysteine takes place via the weakly adsorbed species, the surface concentration of which is influenced by the coverage of the strongly adsorbed species. This process is described by an electrode reaction rate equation.(v) In the overall oxidation of cysteine one electron is transferred while the detailed mechanism requires an oxidation by splitting-off two electrons with a subsequent ion—substrate dimerization reaction.     

Thermal and gas (CH4 and C2H4) adsorption characteristics of nitric acid-treated clinoptilolite

In this study, in order to consider the effect of the time of the nitric acid treatment on thermal, structural and gas adsorption properties, clinoptilolite was modified with 1.0 M acid solutions at 80 °C for 2, 4, 6, 12 and 24 h. Structural and thermal properties of natural and acid-treated clinoptilolites were investigated by powder X-ray diffraction, X-ray fluorescence, thermogravimetric analysis, differential thermal analysis and nitrogen adsorption methods. Methane (CH₄) and ethylene (C₂H₄) are hazardous gases for human and plant health, respectively. Therefore, some measures should be taken to reduce emissions of methane and ethylene. CH₄ and C₂H₄ adsorption capacities of clinoptilolite (CLN) from Turkey and that of acid-treated forms at 273 K up to 100 kPa were found between 0.556–0.683 and 0.470–1.295 mmol g^?1, respectively.

     

Adsorption and Corrosion Inhibition Behavior of L-Cystine and Synergistic Surfactants Additives on Mild Steel in 0.1 M H2SO4

The adsorption and corrosion inhibition behavior of mild steel in 0.1 M H₂SO₄ in presence of L-cystine and L-cystine in combination with surfactants sodium dodecyl sulfate and cetyltrimethyl ammonium bromide at 30–60°C was investigated using weight loss and potentiodynamic polarization measurements. Inhibition efficiency of L-cystine is synergistically enhanced on addition of surfactants. Surface morphology of corroded steel samples was evaluated using scanning electron microscopy and atomic force microscopy, which further confirmed the existence of an adsorbed protective film on the mild steel surface. Calculated thermodynamic parameters reveal that adsorption process is spontaneous and obey Langmuir adsorption isotherm.     

Thermodynamics of phase equilibria of the K2SO4 +Rb2SO4+H2O system at 25°C

Activities of water in the K₂SO₄+Rb₂SO₄+H₂O system at 25°C have been measured isopiestically. On the basis of the experimental activities of water ternary parameters of the Pitzer equations have been calculated. According to our data and experimental solubility data from the literature, continous solid solutions between K₂SO₄ and Rb₂SO₄ are formed in this system. With the use of the Guggenheim polynomial for simulating excess functions of solid solutions on the basis of the original and literature solubility data, excess Gibbs energies of solid solution formation as well as a solubility diagram have been calculated. Results of the solubility calculation are in good agreement with experimental data.     

Quaternary diffusion coefficients of NaCl−MgCl2−Na2SO4 −H2O synthetic seawaters by least-squares analysis of taylor dispersion profiles

Equations are developed to calculate the nine inter diffusion coefficients of four-component solutions by least-squares analysis of the refractive index profiles across Taylor dispersion peaks. The pre-exponential weighting factors and the eigenvalues of the diffusion coefficient matrix are used as the fitting parameters instead of the diffusion coefficients. This simplifies the fitting equations and speeds up the convergence. The analysis is tested on dilute aqueous solutions of sucrose + glycine + urea, and then used to determine the interdiffusion coefficients of aqueous NaCl+MgCl₂+Na₂SO₄ solutions at compositions corresponding to synthetic seawaters of salinities 5, 15, 25 and 35. The results are used to predict the concentration profiles that develop when seawater interdiffuses with fresh water.     

Inhibitive action of ethanol extracts from Nauclea latifolia on the corrosion of mild steel in H2SO4 solutions and their adsorption characteristics

The inhibitive action of ethanol extracts from leaves (LV), bark (BK) and roots (RT) of Nauclea latifolia on mild steel corrosion in H₂SO₄ solutions at 30–60 °C was studied using weight loss and gasometric techniques. The extracts were found to inhibit the corrosion of mild steel in H₂SO₄ solutions and the inhibition efficiencies of the extracts follow the trend: RT > LV > BK. The inhibition efficiency increased with the extracts concentration but decreased with temperature rise. Physical adsorption of the phytochemical components of the plant on the metal surface is proposed as the mechanism of inhibition. The adsorption characteristics of the inhibitor were approximated by the thermodynamic-kinetic model of El-Awady et al.     

Simultaneous solubility of SO2 and NH3 in (salt + H2O) and enthalpy change upon dilution of (SO2 + NH3 + salt + H2O) in (salt + H2O) {salt = (NH4)2SO4 or Na2SO4}: Experimental results and model predictions

The simultaneous solubility of sulfur dioxide and ammonia in aqueous solutions of (ammonium sulfate or sodium sulfate) was measured by a synthetic method in the temperature range from 313.6 to 373.2 K and at pressures up to 2.5 MPa. Furthermore, the enthalpy change upon diluting aqueous solutions of sulfur dioxide, ammonia and (ammonium sulfate or sodium sulfate) in aqueous solutions of the same salt was measured in a batch calorimeter at about 313 and 352 K. The experimental results are used for comparison with predictions from a thermodynamic model for the vapor–liquid equilibrium and the enthalpy of dilution of those chemical reacting systems. In that model, activity coefficients are calculated from Pitzer's molality-scale-based Gibbs excess energy model, where all interaction parameters are either adopted from previous investigations on the properties of the binary and ternary sub-systems (if available) or they are neglected (if they are not available).