Frumkin Models Research Articles

Bis(dimethylpyrazolyl)-aniline-s-triazine derivatives as efficient corrosion inhibitors for C-steel and computational studies.

4,6-Bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-phenyl-1,3,5-triazin-2-amine (PTA-1), N-(4-bromophenyl)-4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazin-2-amine (PTA-2) and 4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-(4-methoxyphenyl)-1,3,5-triazin-2-amine (PTA-3) were synthesized and characterized. Their corrosion inhibition of carbon C-steel in 0.25 M H2SO4 was studied by electrochemical impedance. The inhibition efficiency (IE%) of triazine was superior due to the cumulative inhibition of triazine core structure and pyrazole motif. Potentiodynamic polarizations suggested that s-triazine derivatives behave as mixed type inhibitors. The IE% values were 96.5% and 93.4% at 120 ppm for inhibitor PTA-2 and PTA-3 bearing -Br and -OCH3 groups on aniline, respectively. While PTA-1 without an electron donating group showed only 79.0% inhibition at 175 ppm. The adsorption of triazine derivatives followed Langmuir and Frumkin models. The values of adsorption equilibrium constant K°ads and free energy change ΔG°ads revealed that adsorption of inhibitor onto steel surface was favoured. A corrosion inhibition mechanism was proposed suggesting the presence of physical and chemical interactions. Density functional theory computational investigation corroborated nicely with the experimental results. Monte Carlo simulation revealed that the energy associated with the metal/adsorbate arrangement dE ads/dN i, for both forms of PTA-2 and PTA-3 with electron donating groups (-439.73 and -436.62 kcal mol-1) is higher than that of PTA-1 molecule (-428.73 kcal mol-1). This aligned with experimental inhibition efficiency results.

On the adsorption kinetics of an eco‐friendly surfactant n‐decyl‐β‐D‐maltopyranoside

AbstractEco‐friendly surfactant alkyl polyglycosides (APGs) have garnered ample interest in the literature. However, the adsorption kinetics of APGs at an air‐water interface has not been studied to date. Consequently, this study aimed at investigating the adsorption kinetics of the APG n‐decyl‐β‐D‐maltopyranoside (β‐C10G2) at a freshly created air‐water interface. The dynamic and equilibrium surface tension (ST) of the aqueous β‐C10G2 solutions were experimentally measured at varying concentrations using a pendant bubble tensiometer and the ST data were examined via theoretical simulations using the Langmuir and Frumkin models. The fitting results revealed that the Frumkin model (with K = −2.9) well‐predicted the equilibrium ST data; signifying a considerable cohesive intermolecular force amidst the adsorbed β‐C10G2 molecules. The theoretical mixed‐controlled ST profiles (predicted by the Frumkin model) described the dynamic ST data reasonably well, but the adsorption rate constant increased significantly at increasing concentration. A comparison on the ST data of β‐C10G2 and β‐C12G2 (n‐dodecyl‐β‐D‐maltopyranoside) was also conducted and a relatively greater surface‐activity and lower cmc of the latter alkyl glycoside was observed.

Application of synthesized Fish Scale Chito-Protein (FSC) for the treatment of abattoir wastewater: Coagulation-flocculation kinetics and equilibrium modeling

This work explores the use of chito-protein synthesized from fish scale as a bio-coagulant in Abattoir wastewater (AW) treatment. The effect of settling time, pH, adsorbent dosage, and temperature of coagulation on Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), turbidity, and Color from the AW sample were studied. The kinetic study was carried out using four process equilibrium models which are Langmuir, Freundlich, Frumkin, and Tempkin to investigate the mechanism of the reaction. SEM and FTIR spectral analyses were used to evaluate the surface morphology and chemical composition of the bio-coagulant. A low pH, 3 g of dosage in 250 mL vessel, settling period of 30 to 35 min, and temperatures of 323 K for all parameters resulted in the most efficient pollutant elimination. Turbidity, however, had an optimal temperature of 313 K. The result of the study shows that Langmuir model provided the best fit from the equilibrium models compared to Freundlich, Frumkin, and Temkin's models. The experimental data suited the Elovich, Pseudo-first, and Second order kinetic models’ analysis and the high values of the regression coefficient of 0.90 supported the idea of perikinetic as the governing mechanism of coag-flocculation in the study. It can be inferred from this study that fish scale as a bio-coagulant provides a significant resource for abattoir wastewater treatment.

Theoretical Study and Adsorption Behavior of Urea on Mild Steel in Automotive Gas Oil (AGO) Medium

The continuous search for eco-friendly corrosion inhibitors due to differences in corrosive media remains an important point in corrosion control. The experimental studies on the corrosion inhibition of urea on mild steel in automotive gas oil (AGO) was conducted using gasometric techniques and scanning electron microscope (SEM). The theoretical approach on the density functional theory (DFT) on the urea molecule was carried out using Gaussian 09 software. The adsorption behavior of urea molecules on the surface of the mild steel was analyzed using Frumkin and Flory-Huggins adsorption isotherms models and Gibb’s free energy, respectively. The result of the experimental study shows a poor corrosion inhibitory effect of urea on mild steel in automobile gas oil (AGO) medium as the inhibition efficiency decreased from 69.30% in week 1 to 12% in week 11 at 200 ppm of inhibitor. The adsorption of urea on the mild steel surface obeys Frumkin’s adsorption isotherm model. Gibb’s free energy of adsorption of urea molecules onto mild steel surface revealed a physisorption mechanism. SEM results showed the non-inhibitive nature of urea on the studied mild steel. Quantum chemical parameters such as HOMO, LUMO, electron affinity, electronegativity, and the fraction of electrons transferred to the metal surface were calculated and interpreted to compare the experimental and theoretical results. The theoretical findings in the current investigation were not in agreement with the experimental result, thereby creating a need for further study using the electrochemical method.

Inhibition Effect of Aminophen Fluid Derivative on the Corrosion of 1070 Aluminum

The corrosion mitigation effect of aminophen (an organic fluid derivative) on 1070 aluminum alloy was studied in 1 M HCl solution by potentiodynamic polarization and weight loss analysis. Data obtained showed aminophen performed poorly at low concentrations (2.5%, 5% and 7.5%) with optimal value of 49.9% and 30% (potentiodynamic polarization and weight loss analysis) at 7.5% aminophen concentration. At 10% concentration, significant improvement in inhibition efficiency value was observed (53% and 61.33%), but the value is below the threshold minimum for effective inhibition. Effective inhibition efficiency occurred at 12.5% and 15% aminophen concentration with values of 71% and 81.67% at 12.5% concentration, and 89% and 70.77% at 15% concentration. Plots from weight loss indicated stable thermodynamic behavior throughout the exposure hours. Aminophen demonstrated anodic-cathodic type inhibition characteristics with dominant cathodic inhibition action. Corrosion inhibition behavior of aminophen aligned with Frumkin and Freundlich adsorption isotherm models. However, thermodynamic calculations show adsorption did not occur. Inhibition behavior of aminophen on 1070 aluminum occurred through modification of the corrosive media.

On a phthalate ester's adsorption kinetics: DBP in 5 wt% aqueous MeOH solution

Although phthalate esters such as dibutyl phthalate (DBP) have attracted much attention in the literature, the surface-active nature of DBP was not well understood until now; particularly, the adsorption kinetics of DBP when dissolved in solvents other than water. In this study, the adsorption kinetics of DBP in a 5 wt% aqueous methanol solution was investigated. A pendant bubble tensiometer was utilized for measuring the dynamic and equilibrium surface tension (ST) of DBP solutions at nine bulk concentrations ranging from 0.37 to 4.0 (10−8 mol/cm3). Theoretical simulations were performed using the Langmuir and Frumkin models, for a mixed-controlled and diffusion-controlled adsorption process, to investigate the adsorption kinetics of DBP molecules. The results showed the Frumkin model better described the equilibrium ST data. Using the Frumkin model, a comparison between the dynamic ST data and theoretical ST profiles revealed that the adsorption of DBP onto the air-water interface was of mixed-control; thereby indicating a non-negligible intermolecular interaction amongst the adsorbed DBP molecules. In addition, a new approach, by evaluating the ratio between the adsorption rate and desorption rate, of examining the effect of solvent on DBP's adsorption kinetics was briefly discussed as well.

Dynamics of interfacial layers for sodium dodecylbenzene sulfonate solutions at different salinities

This study investigates the adsorption mechanisms and the dilational surface rheology of the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) at the air–liquid interface, in the presence and absence of NaCl over a wide range of SDBS concentrations. We also evaluate the Langmuir and Frumkin models in order to predict the dynamic adsorption of SDBS solutions. Our results reveal that the equilibrium surface tension of SDBS solutions is a monotonically decreasing function of NaCl concentration. However, the dilational viscoelastic properties of SDBS solutions are found to be a non-monotonic function of NaCl concentration. NaCl manifests opposing effects on the dilational viscoelastic moduli of the gas–liquid interface, depending on the frequency of surface oscillation and surfactant bulk concentration. Our measured dilational surface elasticity and viscosity data show a shift in the surfactant transition concentration, at which the viscoelastic moduli reach their maximum values, towards smaller surfactant bulk concentrations with increasing salt concentration. It is attributed to suppressing the electrostatic repulsion between the hydrophilic head groups of surfactant molecules in the presence of electrolytes. The maximum viscoelastic moduli at different NaCl concentrations is found to be the reflection of the relative impact of enhanced adsorption and increased diffusion exchange between bulk and interface.

Evaluation of the corrosion inhibition effect of the combined admixture of rosemary and cinnamon cassia oil on mild steel in weak acid electrolyte

The corrosion resistance of mild steel (MS) in 0.5 M H2SO4 and HCl solution with specific concentrations of the intermixture of rosemary and cinanamon cassia essential oil extracts (RCC) was studied by potentiodynamic polarization method, open circuit potential analysis (OCP) and optical macroscopy. Information obtained showed RCC effectively inhibited MS corrosion from the lowest to the highest concentrations in both acids with lowest inhibition result of 95.30% and 94.19%, and highest inhibition efficiency of 99.21% and 97.69%. RCC exhibited dominant cathodic inhibition effect in H2SO4 due to suppression of the reduction reactions while in HCl RCC displayed mixed inhibition properties due to surface coverage effect in the presence of Cl− anions. OCP showed RCC increased the thermodynamic tendency of MS to corrosion in H2SO4 solution despite effective inhibition performance with significant electronegative shift in corrosion potential. In HCl significant electropositive potential displacement was observed relative to the potential of the control MS due to adsorbed protonated RCC molecules unto the steel. Adsorption of RCC molecules on MS aligned with Langmuir, Frumkin and Freundlich isotherm models through chemisorption mechanism in both acids with average correlation coefficient value above 0.9. Optical images of MS in both acids without RCC showed severe surface degradation with the degree of degradation being higher from H2SO4 solution. Optical images from RCC inhibited steel depict effective surface protection.

Synergistic effect of sage and jojoba oil extracts on the corrosion inhibition of mild steel in dilute acid solution

The synergistic effect of sage and jojoba oil extract on the corrosion inhibition of low carbon steel was evaluated with potentiodynamic polarization resistance technique, weight loss method and open circuit potential measurement. Experimental data confirmed effect inhibition performance of the admixed compound with average value above 80%. The presence of the compound in the acid solution shifts the corrosion potential values (with respect to time) to the positive direction due to surface coverage of the metal surface. The compound displays mixed inhibition behavior and the mechanism of inhibition was determined to be through chemisorption adsorption mechanism according to Langmuir, Frumkin and Freundlich isotherm models. Optical images of inhibited mild steel surface significantly contrast the corroded non-inhibited steel.

Corrosion inhibition properties of the combined admixture of essential oil extracts on mild steel in the presence of SO42− anions

The combined admixture of essential oil extracts, salvia officinalis and simmondsia chinensis was studied at low concentrations to assess their corrosion inhibition performance on mild steel in 1 M H2SO4 solution. Electrochemical studies were performed with potentiodynamic polarization test and weight loss analysis while open circuit potential measurement was employed to assess the thermodynamic stability of the corrosion properties of the compound with respect to time. Results obtained showed optimal inhibition efficiency of 86.58% and 83.29% at 6% and 5% volumetric concentration from the electrochemical test. The corrosion potential of the inhibited steel displaced significantly in the positive direction compared to the significant negative displacement of corroded steel due to surface coverage from the inhibitor molecules on the inhibited steel. Thermodynamic calculations showed chemisorption adsorption mechanism according to Langmuir, Frumkin and Freundlich adsorption isotherm models. Optical images of inhibited mild steel surface significantly contrast the corroded non-inhibited steel which showed the presence of surface oxides, general deterioration and macro pits.

Experimental and computational chemistry studies on the inhibition of aluminium and mild steel in 0.1 M HCl by 3-nitrobenzoic acid

ABSTRACTThe effectiveness of 3-nitrobenzoic acid towards the inhibition of the corrosion of mild steel and aluminium in solution of HCl was investigated using theoretical and experimental methods (weight loss, thermometric, polarization, FTIR and SEM techniques). Inhibition efficiency of 3-nitrobenzoic acid, evaluated from weight loss technique ranged from 71% to 90% and from 71% to 82% for mild steel and aluminium, respectively. Results from linear polarization and potentiodynamic studies were comparable to weight loss results. Calculated kinetic (activation energy), thermodynamic (changes in entropy and enthalpy) and adsorption parameters indicated that the adsorption of the inhibitor on the surface of the respective metal is accompanied by molecular association and is endothermic, spontaneous and favoured the mechanism of physical adsorption. Best-fitted adsorption isotherms were Langmuir and Frumkin models, which gave evidences for the existence of interaction, characterized by attractive behaviour of the inhibitor on both mild steel and aluminium surfaces. Scanning electron micrographs of the metal before and after inhibition clearly revealed that the inhibitor prevented crevice and pitting corrosion by forming adsorbed protective layer on the respective metal surface. FTIR spectra of the inhibitor and the corrosion products indicated the formation of new bond, existence of interaction between the inhibitor molecules and the involvement of some functional groups in the adsorption and inhibition processes. Quantum chemical study revealed that the inhibitor is adsorbed on the metal surface through the nitro functional group in the ring. Calculated semi empirical parameters were comparable to those reported for excellent corrosion inhibitors.

Reversible Partitioning of Nanoparticles at an Oil–Water Interface

The reversible adsorption of nanoparticles (NPs) to oil-water interfaces has been observed experimentally, however, models capable of interpreting and predicting the equilibrium partitioning of particles between bulk media and fluid interfaces are still lacking. Here we characterize the adsorption of 5 nm gold NPs functionalized with ion-pair ligands at the toluene-water interface. Partitioning of the NPs between the bulk aqueous phase and the interface is measured via absorbance spectroscopy for two different aqueous-phase pH values (11.0 and 11.7) and over several orders of magnitude of aqueous phase NP concentration. The surface pressure of the interfacial film in equilibrium with the bulk aqueous phase is measured using the pendant drop method. We determine the range of surface pressure where the adsorption is reversible as well as conditions under which the adsorbed NPs are irreversibly adsorbed at the oil-water interface. We analyze together the adsorption and surface pressure isotherms to obtain the two-dimensional equations of state (EOS) for the NPs in equilibrium with the bulk aqueous phase. The experimental data are then compared to the Frumkin models. We find that the adsorption isotherm and the equation of state show good agreement at low coverage with the Frumkin equations; however, both curves cannot be described with the same parameters. We also show that the low-coverage portion of the EOS can also be described by a wetting model. We hypothesize that deviations from models at higher coverage are likely due to nonequilibrium effects and possible coadsorption.

Adsorption of phenol and methylene blue from aqueous solutions by pyrolytic tire char: Equilibrium and kinetic studies

Acid-treated pyrolytic tire char (PTC) was studied as an adsorbent for the removal of phenol and methylene blue (MB) dye from aqueous solutions. PTC was derived via pyrolysis of used rubber tires at 450°C in oxygen-free atmosphere. Textural characteristics and surface chemical nature of the adsorbent were examined through a battery of techniques such as X-ray diffraction, porosimetry, Boehm titration, and point of zero charge determination. The adsorption characteristics of phenol and MB dye were evaluated on the basis of equilibrium and kinetic studies. The adsorption kinetic data fitted better to pseudo-second kinetic model. Equilibrium isotherms were analyzed by Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Frumkin models. Langmuir and Freundlich isotherm models were found to fit the adsorption data of phenol and MB, respectively. The maximum adsorption capacities of phenol and MB on PTC were found to be 51.92 and 65.81mgg−1, respectively. In the case of phenol, the adsorption mechanisms can be attributed to π–π electron donor/acceptor interaction, hydrogen bonding of phenol with surface groups of PTC. On the other hand, electrostatic attraction between the carboxylic groups of PTC surface and cationic dye is responsible for the adsorption of MB. The effect of temperature on the organics’ adsorption was studied and the thermodynamic parameters (ΔH, ΔS and ΔG) were determined for each of the studied systems. The adsorption for both pollutants was found to be thermodynamically spontaneous (ΔG<0), although it was exothermic (ΔH<0) for phenol vs endothermic (ΔH>0) for MB.

Physicochemical Characterization and Corrosion Inhibition Potential of Ficus benjamina (FB) Gum for Aluminum in 0.1 M HCl

Examination of the physical (colour, odour, pH, solubility in various solvent) and chemical (GCMS and FTIR) characteristics of Ficus benjamina gum revealed that the gum is yellowish in colour, mildly acidic and ionic in nature. Major constituents of the gums were found to be sucrose and d-glucose, which constituted 60.92 % of its chemical constituents while various carboxylic acids (albietic acid (1.00 %); hexadecanoic acid (4.41 %); 9-octadecanoic acid (1.00 %), stearic acid (3.01 %); oleic acid (0.10 %); octadecanoic acid (9.12 %) and 6,13-pentacenequinone (20.43 %) accounted for the remaining constituents. Functional groups identified in the gum were found to be those typical for other carbohydrates. From the knowledge of the chemical structures of compounds that constitutes the gum, the corrosion inhibition potentials of the gum was ascertained and from weight loss analysis, the gum was found to be an active inhibitor against the corrosion of aluminum in solutions of tetraoxosulphate (VI) acid. The gum acted as an adsorption inhibitor that favours the mechanism of chemical adsorption and supported the Frumkin and Dubinin-Radushkevich adsorption models. doi: 10.14456/WJST.2015.94

Influence of the nature of the electrode material and process variables on the kinetics of the chlorine evolution reaction. The case of IrO2-based electrocatalysts

Kinetic studies on the chlorine evolution reaction (ChlER) on oxide-based materials have been the subject of a number of papers since the seventies, following the introduction of DSAs (Dimensionally Stable Anodes) in chlor-alkali plants. On the basis of experimental data, different pathways have been proposed for the reaction over the years. Actually, specific experimental conditions and different approaches in sample preparation may lead to conflicting explanations. In the present paper, the ChlER kinetics has been studied at four electrode materials based on iridium and titanium oxides (with a 1:2 molar ratio). Electrodes were synthetized at two temperatures (350 and 450°C) and by two different preparation methods: physical vapor deposition (rf-magnetron sputtering) and a conventional sol-gel technique, using special precursors developed in our laboratory. Both methodologies guarantee a high level of reproducibility. As also observed by other authors, experimental data have shown a lack of linearity in Tafel plots, high b slopes and reaction orders with respect to chloride ≤ 1, which have been justified on the basis of a Volmer-Heyrovsky pathway, by considering a model proposed by Tilak and Conway in 1992. This approach highlighted the role of the adsorbed intermediates, also at low overpotentials, for all electrode materials. To analyze further the kinetics, Langmuir and Frumkin models for intermediates adsorption were considered. Values for the lateral interaction parameter g were estimated, which ranged between 1 and 10, in all cases. Concerning the effect of pH, its influence on the ChlER rate seems to be related only with electrode surface modifications, without any involvement of protons in the rate determining step of the process. A slight inhibiting effect was assessed, by increasing the protons concentration. Eventually, impedance spectroscopy analysis did not appear sensitive to intermediate adsorption, plausibly because of the low variation of the coverage within the Tafel region; a poorly resolved contribution related to porosity was found in the case of samples prepared at 350°C.

Physicochemical Study and Corrosion Inhibition Potential of Ficus tricopoda for Aluminium in Acidic Medium

Gas chromatography mass spectrophotometer (GCMS) analysis of Ficus tricopoda gum indicated the presence of 4.75, 56.15, 32.10 and 7.00 % of camphene, sucrose, 2methylene cholestan-3-ol and 7-hexadecenal, respectively. Several stretching and bending vibrations were observed in the Fourier transformed infra-red (FTIR) spectrum of the gum. Physicochemical examinations of the gum revealed that it is pale yellow in colour, mildly acidic, ionic and display characteristics of sour taste. The solubility of the gum in water was found to increase with increase in temperature. Knowledge of the chemical constitution of the gum (hence chemical structures of its constituents) was useful in predicting the corrosion inhibition potential of Ficus tricopoda (FT) gum. Consequently, the gum was found to be a good adsorption inhibitor for the corrosion of aluminum in solution of H 2SO 4. The adsorption of the gum (which, followed first order kinetic) was found to be endothermic at FT gum critical concentration of 0.3 g/L and exothermic at concentrations above the critical limit. The short coming of the Langmuir adsorption model in describing the existent of interaction between the molecules of the gum was complimented by the Frumkin and Dubinin-Radushkevich adsorption models. Calculated values of activation and free energies of activation indicated that the adsorption of Ficus tricopoda gum on Al surface exhibited both physical and chemical adsorption mechanism.

Adsorption of n-Alkyl Alcohols by Polyurethane Foam Powder: Kinetics, Isotherms, and Thermodynamics

Abstract Adsorption of different n-alkyl alcohols (hexanol, pentanol, butanol, propanol, ethanol and methanol) out of aqueous media by polyurethane foam, an insulation waste powder, (PUF) was investigated using batch system under controlled conditions. Kinetic data followed more closely to the pseudo-first-order model. The adsorption rate and the related parameters, such as the PUF dosage, n-alkyl alcohol initial concentration, pH, temperature, and ionic strength were studied. The saturation equilibrium was also studied as a function of the related parameters (PUF dose, alcohol initial concentration, temperature, pH and ionic strength). The adsorption isotherm was established for the adsorption of different alcohols on PUF. Linearized Langmuir, Freundlich and Frumkin models were applied to estimate the adsorption constants. It was estimated that the adsorption rate is positively affected by increasing PUF dose, adsorbent concentration, acidity and temperature. The adsorption equilibrium was shifted toward higher adsorption capacity by increasing the PUF dose, substrate concentration, temperature and acidity in the order of: n-hexanol &gt; n-pentanol &gt; n-butanol &gt; n-propanol &gt; ethanol &gt; methanol. It was not affected by ionic strength. The adsorption data fit to Freundlich, Langmuir and Frumkin models, but attained a better correlation to models in the order of as Langmuir &gt; Freundlich &gt; Frumkin. In addition to the Freundlich, Langmuir und Frumkin constants the thermodynamic parameters of activation and adsorption were determined.

Equilibrium adsorption studies on removal of diclofenac sodium from aqueous solution using sawdust–polyaniline (SD–PAn) composites

AbstractIn this work, equilibrium adsorption studies were carried out for the removal of antiinflamatory drug diclofenac sodium (DS) from aqueous solutions using sawdust–polyaniline(SD‐PAn) composite as a potential sorbent at 20, 30, and 40°C. The composite sorbent was characterized by FTIR and SEM analysis. The particles exhibited porous and rough surface. The equilibrium uptake data was interpreted by the Langmuir, the Freundlic, the Temkin, and the Dubinin–Redushkevich (D‐R) isotherm models. The maximum adsorption capacity was found to decrease with increase in temperature, thus indicating exothermic nature of the adsorption process. The thermodynamic parameters were evaluated using Langmuir, Flory–Huggins, Frumkin, and modified‐Frumkin models. The negative values of ΔGads0 and ΔH0 indicated spontaneous and exothermic nature of the adsorption process, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125:1382–1390, 2012

Kinetics, equilibrium, and isotherm of the adsorption of cyanide by MDFSD

Adsorption of cyanide out of aqueous media by moderate density fiberboard saw dust (MDFSD) was investigated using a batch system under controlled conditions. The kinetic data were followed more closely to the pseudo-first-order model. The adsorption rate and the related parameters, such as the MDFSD relative quantity, cyanide initial concentration, pH, temperature, and ionic strength were studied. The saturation equilibrium was also studied as a function of the related parameters (MDFSD quantity, initial concentration, pH and temperature). The adsorption isotherm was established and compared to other isotherms of activated carbon, TDRP and polyurethane foam. Linearized Langmuir, Freundlich and Frumkin models were applied to estimate the adsorption constants.It was estimated through this study that the adsorption rate is positively affected by increasing MDFSD’s relative quantity, adsorbent concentration, acidity and temperature. The adsorption equilibrium was shifted toward higher adsorption capacity by the substrate concentration, temperature and acidity. The adsorption data fit to Freundlich, Langmuir and Frumkin models, but attained a better correlation with the order of models as Langmuir>Frumkin>Freundlich. Activation thermodynamic parameters of adsorption, the adsorption thermodynamic parameters, and Freundlich, Langmuir and Frumkin constants were obtained.

Study of dynamic interfacial tension of alkyl sulphates with different alkyl chain lengths at the water/hexane interface

The adsorption behaviour of alkyl sulphates at the water/oil interface is rather different from that frequently studied at the water/air interface. First of all typical impurities in form of homologous alcohols, immanent for this type of surfactants at the surface of aqueous solutions, are not essential at the water/oil interface due to their high solubility in the oil phase. In the interfacial layers the oil molecules, here hexane, are incorporated into the structure, and have essential impact on the equation of state at low interfacial coverage and in particular at the shorter alkyl chain surfactants. For the longer chain alkyl sulphates (NaC 14SO 4 and NaC 16SO 4) and at high interfacial coverage the hexane molecules are squeezed out of the adsorption layer due to the stronger hydrophobic interaction between the surfactants’ alkyl chains. The adsorption characteristics are discussed in the framework of the two well-known thermodynamics Frumkin and reorientation models.