Influence of alcohols on the lower consolute behavior and thermodynamic approach of Triton X-114 aqueous two-phase systems

The addition of foreign material to surfactants shows the change in temperature at which the clouding process occurs. This work evaluates the impact of n-alcohols on Cloud Point (CP) of nonionic surfactant Triton X-114 at variable concentrations. It was found that the CP of pure Triton X-114 shows concentration-dependent variation. The presence of lower alcohols improves CP value whereas the addition of higher alcohols brings down CP with variation as concentration increases. These effects can be clarified in view of the site of the impact of molecular design of added substances on the stability of micelle organization. The foaming ability and foam stability data are also used to discuss the stability of micellar accumulation. Considering CP as a threshold temperature of the solubility, the thermodynamic parameters of the clouding process ΔG⁰_cl, ΔH⁰_cl, and ΔS⁰_cl, have been assessed, using the “Phase Separation Model”. The outcomes of the work demonstrate that the clouding phenomenon of Triton X-114 is an exothermic and non-spontaneous process.     

Factors influencing the mechanism of surfactant catalyzed reaction of vitamin C-ferric chloride hexahydrate system

The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous ethanol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Activation parameters, ΔE _a, ΔH ^#, ΔS ^#, ΔG ^≠, for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ_max), minimum area per surfactant molecule (A _min), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π_max), Gibb’s energy of micellization (ΔG _M°), Gibb’s energy of adsorption (ΔG _ad°), were calculated. It was found that the reaction in the presence of surfactant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant.     

微量量热法研究阴离子表面活性剂在DMA/长链醇体系中CMC和热力学函数

在N,N-二甲基乙酰胺(DMA)/长链醇非水溶液体系中, 利用微量量热仪, 研究阴离子表面活性剂十二烷基羧酸钠(SLA)、十二烷基硫酸钠(SDS)的临界胶束浓度(CMC)和热力学函数. 本文在十二烷基羧酸钠, 十二烷基硫酸钠的N,N-二甲基乙酰胺溶液中, 分别加入长链醇(庚醇、辛醇、壬醇、癸醇), 测定体系的热功率-时间曲线. 借助热力学理论, 由测得曲线, 进一步得到临界胶束浓度和热力学函数(ΔH_m⁰, ΔG_m⁰和ΔS_m⁰). 讨论了温度、醇的碳原子数目、醇的浓度与热力学参数之间的关系. 结果表明, 对十二烷基羧酸钠或十二烷基硫酸钠的DMA溶液, 在含有相同浓度的各种醇的体系中, CMC, ΔH_m⁰和ΔS_m⁰的值随着温度的升高而增加, 而ΔG_m⁰的值随着温度的升高而降低. 在相同温度及相同浓度的醇体系中, CMC, ΔH_m⁰,ΔG_m⁰和ΔS_m⁰的值都随着醇中碳原子数目的增加而降低. 在相同温度及相同醇的体系中, CMC, ΔG_m⁰的值随着醇的浓度的增加而增大, 而ΔH_m⁰, ΔS_m⁰的值随着醇的浓度的增加而减少.     

Adsorption of acid red 114 and reactive black 5 in aqueous solutions on dendrimer‐conjugated magnetic nanoparticles

The adsorption of the dyes Acid Red 114 and Reactive Black 5 in aqueous solutions on polyhydroxyl dendrimer magnetic nanoparticles (Fe₃O₄@SiO₂‐TRIS) was studied in a batch system. The Fe₃O₄@SiO₂‐TRIS NPs were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscopy. Experiments were performed under different conditions such as the initial dye concentration, adsorbent dose, and pH. The pseudo‐second‐order model provided a very good fit for the two anionic dyes. The Langmuir and Freundlich adsorption models were used to describe the equilibrium isotherms at different temperatures, and the former agreed very well with the experimental data. However, the adsorption capacity of Fe₃O₄@SiO₂‐TRIS NPs was reduced during surface modification, which could be due to the dye occupying the binding sites of the dendrimer. Thermodynamic parameters, namely the change in free energy (ΔG⁰), enthalpy (ΔH⁰), and entropy (ΔS⁰), were also determined.     

Modified Calcium Alginate Beads with Sodium Dodecyl Sulfate and Clay as Adsorbent for Removal of Methylene Blue

In present study, we have investigated the effect of an anionic surfactant sodium dodecyl sulfate (SDS) and clay on calcium alginate beads was studied to remove methylene blue (MB) and to improve the adsorption capacity. The effects of various experimental parameters, such as shaking rate, initial dye concentration, temperature, and pH on the adsorption rate, have been studied. Equilibrium studies showed that the sorption of the dye was enhanced in presence of SDS. Scanning electron microscope (SEM) analysis showed that SDS entrapped beads have more pores and cavities which could be responsible for improved adsorption of MB. The kinetics of cationic dye adsorption nicely followed pseudo-second-order process. The evaluated thermodynamic parameters (ΔG ^o, ΔH ^o, ΔS ^o) suggest endothermic adsorption of MB. The results revealed that the surfactant entrapped alginate could be considered as potential adsorbents for MB removal from aqueous solutions.     

Solubilization of caffeic acid into the cationic micelles and biogenic synthesis of silver nanoparticles for the degradation of dye

Solubilization of caffeic acid into the aqueous solution of cationic cetyltrimethlyammonium bromide (CTAB) has been studied by using differential spectroscopic and conductivity methods. The solubility of caffeic acid increases with increasing the CTAB concentrations. The solubilization constant of caffeic acid into CTAB (K_X = 1.8 × 10⁵), standard free energy (ΔG⁰_P = ?30.0 kJ/mol), and relative solubility (S_t/S₀ = 53.5) were estimated at room temperature from UV–visible data. The critical micellar concentration (CMC) of CTAB decreases linearly with caffeic acid concentration due to the presence of hydrophobic benzene moiety. The interaction of caffeic acid with CTAB has also been discussed. The solubilized caffeic acid was used as a reducing agent for the preparation of silver nanoparticles (AgNPs). The as-prepared AgNPs were used as an activator of persulphate. The generated reactive oxygen species (OH^?) and reactive sulphur species SO₄^-?) were responsible for the degradation of xylenol orange dye in water.     

Thermal deformation thermodynamics of a smectite mineral

A method has been purposed to calculate some of the thermodynamic quantities for the thermal deformation of a smectite without using any basic thermodynamic data. The Hanç?l? (Keskin, Ankara, Turkey) bentonite containing a smectite of 88% by volume was taken as material. Thermogravimetric (TG) and differential thermal analysis (DTA) curves of the sample were obtained. Bentonite samples were heated at various temperatures between 25–900°C for the sufficient time (2 h) until to establish the thermal deformation equilibrium.Cation-exchange capacity (CEC) of heated samples was determined by using the methylene blue standard method. The CEC was used as a variable of the equilibrium. An arbitrary equilibrium constant (K _a) was defined similar to chemical equilibrium constant and calculated for each temperature by using the corresponding CEC-value. The arbitrary changes in Gibbs energy (ΔG _a ⁰ ) were calculated from K _a-values. The real change in enthalpy (ΔH ⁰) and entropy (ΔS ⁰) was calculated from the slopes of the lnK vs. 1/T and ΔG vs. T plots, respectively. The real changes in Gibbs energy (ΔG ⁰) and real equilibrium constant (K) were calculated by using the ΔH ⁰ and ΔS ⁰ values. The results at the two different temperature intervals are summarized as below: ΔG ₁ ⁰ =ΔH ₁ ⁰ ?ΔS ₁ ⁰ T=?RTlnK ₁=47000?53t, (200–450°C), and ΔG ₂ ⁰ =ΔH ₂ ⁰ -ΔS ₂ ⁰ T=?RTlnK ₂=132000?164T, (500–800°C).     

An evaluation of coal fly ash as an adsorbent for the removal of methylene blue from aqueous solutions: kinetic and thermodynamic studies

Abstract

In this study the effect of the dose and particle size of the adsorbent, initial dye concentration, initial pH, contact time and temperature were investigated for the removal of by means of fly ash (FA) methylene blue (MB) from an aqueous solution. The FA dose was found to be 2.0?g and the under 270 mesh sized particles were found to be effective particles for adsorption. The adsorption process reached its maximum value at 0.5?mg/L dye concentration and attained equilibrium within 10?minutes. The adsorption isotherm was found to follow the Langmuir model. The estimated adsorption free energy (ΔG^o), enthalpy change (ΔH^o), and entropy change (ΔS^o) for the adsorption process were ?37.77?kJ mol^?1, ?13.44?kJ mol^?1 and 122 J mol^?1 K^?1 respectively at 298 K. The maximum adsorption capacity is 0,12?mg g^?1 at 298 K and 0,07?mg g^?1 at 398 K. The adsorption process was exothermic, feasible and spontaneous. The positive value of ΔS^o shows the affinity of FA for MB while the low value of ΔG^o suggests a physical adsorption process.     

Thermodynamic activation parameters for viscous flow of dilute aqueous solutions of ethylenediamine,trimethylenediamine and N,N-dimethyltrimethylenediamine

The density and the viscosity data have been used to determine the thermodynamic activation parameters, free energies (ΔG ^?), enthalpies (ΔH ^?) and entropies (ΔS ^?), for viscous flow of the systems; water (W) + ethylenediamine (ED), W + trimethylenediamine (TMD) and W + N,N-dimethyltrimethylenediamine (DMTMD) in the temperature range of 303.15–323.15 K over the composition range of 0 ≤ X ₂ ≤ 0.45, where X ₂ is the mole fraction of diamines. On addition of diamines to water, ΔG ^?, ΔH ^? and ΔS ^? values increase sharply, pass through a maximum and then decline. The heights of maximum in the ΔG ^? versus X ₂ curve vary as, W + DMTMD > W + TMD > W + ED. For all systems, the excess properties, ΔG ^{? E} , ΔH ^{? E} and ΔS ^{? E} are positive. The observed increase in thermodynamic values may be due to combined effect of hydrophobic hydration of diamines and water–diamine interaction as a result of hydrophilic effect.     

Liquid phase adsorption of Congo red dye on functionalized corn cobs

This study investigates the adsorption of Congo red (CR) dye onto corn cob based activated carbon (CCAC) in the batch process. The activated carbon was characterized using FTIR, SEM, and EDX techniques, respectively. The effect of operational parameters such as the initial dye concentration (10–50?mg/L), contact time (5–160 minutes), and solution temperature (30–50°C) were studied. The amount of the CR dye adsorbed was found to increase as these operational parameters increased. Kinetic data for CR dye adsorption onto CCAC were best represented by the pseudo second-order kinetic model. Four different isotherms namely Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models were used to test the adsorption data. It fitted the Langmuir isotherm model most. Thermodynamic parameters such as ΔH⁰, ΔS⁰, and ΔG⁰ were evaluated. The adsorption process was found to be exothermic and spontaneous. The study shows that CCAC is an effective adsorbent for the adsorption of CR dye from aqueous solution.     

Removal of Thiram from Aqueous Solutions

In this study activated carbon was used for the removal of thiram from aqueous solutions. Adsorption experiments were carried out as a function of time, initial thiram concentration and temperature. Equilibrium data fitted well to the Freundlich and Langmuir equilibrium models in the studied concentration range. Adsorption kinetics followed a pseudo second‐order kinetic model rather than pseudo first‐order model. The results from kinetic experiments were used to describe the adsorption mechanism. Both boundary layer and intraparticle diffusion played important role in the adsorption mechanism of thiram. Thermodynamic parameters (ΔG₀, ΔH₀, and ΔS₀) were determined and the adsorption process was found to be an endothermic one. The negative values of ΔG⁰ at different temperatures were indicative of the spontaneity of the adsorption process.     

Octadecylamine cobalt(III) dimethyl glyoximato complexes: synthesis,thermodynamics of micellization,steady-state photolysis and biological activities

A new class of surfactant–cobalt(III) complexes of the type trans-[Co(DH)₂(OA)X], where DH = dimethylglyoxime, OA = octadecylamine, X = Cl^?, Br^?, I^?, N₃ ^?, NO₂ ^?, SCN^? or OA, were synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in ethanol solution were obtained by measuring absorption at ~250 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG _m ⁰ , ΔH _m ⁰ and ΔS _m ⁰ ). Steady-state photolysis and cyclic voltammetry of the complexes were studied. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms.     

Characterization of Surfactant-Diblock Copolymer Interactions and Its Thermodynamic Studies

The interaction of nonionic diblock copolymer poly(ethylene oxide butylene oxide) (E₆₂B₂₂) with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) were studied using surface tension, conductivity, and dynamic laser light scattering techniques. Surface tension measurements were used to determine critical micelle concentration and thereby its free energy of adsorption (ΔG_ads), free energy of micellization (ΔG_m), surface excess concentration (Γ), and minimum area per molecule (A). Conductivity measurements were used to determine critical micelle concentration (CMC) critical aggregation concentration (CAC) at different temperatures, enthalpy of micellization (ΔH_m), free energy of micellization and entropy of micellization (ΔS_m). Changes in physicochemical properties of the micellized block copolymer were studied by using dynamic laser light scattering. The effect of surfactant on the size and properties of block copolymer has also been discussed.     

Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

The aggregation behavior of metal dodecyl sulfates (MDS), [Na¹⁺, Mg²⁺, Mn²⁺, Co²⁺, and Ni²⁺] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion dissociation (β) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (ΔG_m ⁰), enthalpy (ΔH_m ⁰), and entropy (ΔS_m ⁰) were evaluated. The enthalpy of micellization decreases strongly with increasing temperature. ΔG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc) _T,P , versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.     

Ab initio studies of three-membered ring formation through intramolecular nucleophilic substitution

Three-membered ring (3MR) forming processes of ⁻X(SINGLE BOND)CH₂(SINGLE BOND)CH₂(SINGLE BOND)F and ⁻CH₂(SINGLE BOND)C((SINGLE BOND)Y)(SINGLE BOND)CH₂(SINGLE BOND)F (X(DOUBLE BOND)CH₂, O, or S and Y(DOUBLE BOND)0 or S) through a gas phase neighboring group mechanism (S_Ni) are studied theoretically using the ab initio molecular orbital method with the 6–31+G* basis set. When electron correlation effects are considered, the activation (ΔG^≠) and reaction energies (ΔG⁰) are lowered by ca. 10 kcal mol⁻¹, indicating the importance of the electron correlation effect in these reactions. The contribution of entropy of activation (−TΔS^≠) at 298 K to ΔG^≠ is very small, and the reactions are enthalpy controlled. The ΔG^≠ and ΔG⁰ values for these ring closure processes largely depend on the stabilities of the reactants and the heteroatom acting as a nucleophilic center. The Bell–Evans–Polanyi principle applies well to all these reaction series. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1773–1784, 1997     

Hydrophobic effect for anionic dye - cationic surfactant interaction in aqueous and mixed solvent

Abstract

The interaction between anionic dyes [Reactive Orange 122 (R.O 122), Reactive Blue 19 (R.B 19), Reactive Violet 5 (R.V 5) and Acid Green 20 (A.G 20)] with cationic surfactant cetyltrimethylammoniun bromide (CTAB) has been investigated by spectrophotometry and conductance technique. The used dyes are characterized by tautomeric behavior which affects the mechanism of the interaction. Various parameters such as dye structure, surfactant composition, solvent composition, temperature and pH of the medium were studied. The spectral data were applied for calculating the binding constant between dye and surfactant (K_b), fraction of micellization (?_mic), and standard free energy change of binding (ΔG°_b) in 0,10,20 and 30 v/v % acetonitile (AN). Conductance technique was constructed to estimate the ion pairing constant (K_a) at different temperatures and v/v % AN. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) for ion pair formation were evaluated. The role of hydrophobic and electrostatic effect on dye-surfactant interaction was discussed.     

Thermodynamic denaturation of β-lactoglobulin in the presence of cetylpyridinium chloride

In this work, we determined the stability parameters of bovine β-lactoglobulin, variant A, (BLG-A), in relation to their transition curves induced by cetylpyridinium chloride (CPC) as a cationic surfactant. The experiments took place over the temperature range of 298 K to 358 K. For each transition curve at any specific temperature, the conventional method of analysis, which assumes a linear concentration dependence of the pre- and post-transition base lines, gave the most realistic values for ΔG_D(H₂O). Results show that the minimum value of ΔG_D(H₂O) occurs at T = 328 K. Using the Gibbs–Helmholtz equation, the values of enthalpy, ΔH_D, and entropy, ΔS_D, of denaturation have been calculated considering temperature dependence of ΔG_D at any specified concentration of CPC. The values of 12.05 kJ · mol⁻¹, 18.54 kJ · mol⁻¹, and 18.32 J · mol⁻¹ · K⁻¹, were obtained for ΔG_D(H₂O), ΔH_D(H₂O), and ΔS_D(H₂O), respectively. The results show that the enthalpy term dominates the entropy term.     

Surface activity and thermodynamic properties of water‐soluble polyester surfactants based on 1,3‐dicarboxymethoxybenzene used for enhanced oil recovery

The surface activity and thermodynamic properties for eight low molecular weight nonionic co‐polyester (PE) surfactants have been investigated. Surface and interfacial tensions (IFT) of surfactants in aqueous solutions were measured using the spinning drop technique. From these measurements, the critical micelle concentration (CMC), the surface pressure at CMC (Y_CMC), the maximum surface concentration (Γ_max), the minimum area/molecule at the aqueous solution/air interface (A_min), the effectiveness of surface tension reduction (Π_CMC), the alkane carbon number (n_min) and the IFT at n_min (Y_min) were determined. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic and ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad and ΔS_ad) for these polymeric surfactants were also calculated. Structural effects on micellization and adsorption are discussed in terms of these parameters. The results show that the ΔG_ad values were more negative than ΔG_mic values for these compounds, so that they favored adsorption before the micellization process. They exhibited IFT in the order of 10⁻³ to 10⁻⁴ mN/m against the thin alkane carbon number range 6–9. This range seemed to be prefered for enhanced oil recovery. Copyright © 2000 John Wiley & Sons, Ltd.     

Adsorption of Methylene Blue from Aqueous Solution on High Lime Fly Ash: Kinetic,Equilibrium, and Thermodynamic Studies

Kinetic, equilibrium, and thermodynamic studies were performed for the batch adsorption of methylene blue (MB) on the high lime fly ash as a low cost adsorbent material. The studied operating variables were adsorbent amount, contact time, dye concentration, and temperature. The kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic models and the adsorption kinetic was followed well by the pseudo-second order kinetic model. The equilibrium data were fitted with the Freundlich, Langmuir, and Dubinin Radushkevich (D–R) isotherms and the equilibrium data were found to be well represented by the Freundlich and D–R isotherms. Based on these two isotherms MB is taken by chemical ion exchange and active sites on the high lime fly ash have different affinities to MB molecules. Various thermodynamic parameters such as enthalpy of adsorption (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were investigated. The positive value of ΔH° and negative value of ΔG° indicate that the adsorption is endothermic and spontaneous. The positive value of ΔS° shows the increased randomness at the solid–liquid interface during the adsorption. A single-stage batch adsorber was also designed based on the Freundlich isotherm for the removal of MB by the high lime fly ash.