Standard Entropy Change Research Articles

Thermodynamic Analysis of the Experimental Equilibria for the Liquid-Phase Etherification of Isobutene with C1 to C4 Linear Primary Alcohols

The chemical equilibrium of the liquid-phase syntheses of 2-methoxy-2-methylpropane (MTBE), 2-ethoxy-2-methylpropane (ETBE), 2-methyl-2-propoxypropane (PTBE), and 1-tert-butoxybutane (BTBE) by reaction of isobutene with methanol, ethanol, 1-propanol, and 1-butanol, respectively, has been studied. Four different ion exchange resins as the catalysts, and two different reactor systems, namely, a batch reactor and a setup of tubular reactors, were used. Temperature and pressure were in the range 313–383 K and 1.5–2.0 MPa, respectively. MTBE and ETBE synthesis reactions experiments were carried out mainly to validate the reliability of the reaction systems. Experiments in PTBE and BTBE etherifications allowed estimating thermodynamic properties for those reactions and involved species, namely, molar standard enthalpy and entropy changes of reaction and molar enthalpy change of formation of the four ethers. A comparison of estimated reaction thermodynamic values among the homologous series of linear alcohols, and with results quoted in the literature, when available, has been made.

Preparation of a porous, magnetic, quaternary chitosan salt by preadsorption and desorption for azo dye adsorption from water

ABSTRACTA porous magnetic quaternary chitosan salt (pre‐CS/EPTAC/Fe3O4) was successfully prepared via a kind of novel method of preadsorption and desorption. The physicochemical properties of pre‐CS/EPTAC/Fe3O4 were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and vibrating sample magnetometry. The adsorption of pre‐CS/EPTAC/Fe3O4 for methyl orange (MO) showed much higher dye uptakes compared with Npre‐CS/EPTAC/Fe3O4 without the preadsorption and desorption of MO, and the maximum adsorption capability for MO was 486.1 mg/g. Adsorption isotherms and adsorption kinetics were well fitted by the Freundlich isotherm model and the pseudo‐second order model, respectively. Thermodynamic parameters, such as the standard free energy change, enthalpy change, and entropy change, were also calculated; this indicated that the adsorption was spontaneous and exothermic. The introduction of MO preadsorption and desorption into the process of preparation improved not only the adsorption of MO but also the adsorption of acid red 1 and orange G. Furthermore, pre‐CS/EPTAC/Fe3O4 particles could be easily regenerated and remained almost constant (98.5%) for six cycles of adsorption and desorption. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43448

Equilibrium, kinetic and thermodynamic studies of Pb(II) adsorption from aqueous solutions on HCl-treated Egyptian kaolin

HCl activated (HK) and untreated (UnK) Egyptian (Sinai) kaolin were characterized. The adsorption parameters of Pb(II) on UnK and HK were examined in aqueous solutions. The equilibrium adsorption data were described using Langmuir and Freundlich adsorption isotherm models. The monolayer adsorption capacities were 34.5 and 23.8mgg−1 at pH 5.5 and 25°C for the HK and UnK, respectively. The experimental data fitted well the pseudo-second-order kinetics model. The thermodynamic parameters standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy changes (ΔS°) for the adsorption process were calculated. The negative value of the Gibbs free energy confirms that the adsorption processes are spontaneous and thermodynamically favorable while the positive value of ΔH° supports the endothermic physical adsorption process. HK was applied successfully for removing Pb(II) (67.5–99.3%) from spiked water samples and >98% of the loaded Pb(II) ions was recovered by 1molL−1 HNO3. The successful removal of Pb(II) from the studied water samples indicates that HK can be used efficiently for pollution remediation of fresh water from lead.

Preparation of Amine-Modified Polyacrylonitrile Fibers: Copper Removalin Aqueous Solution.

In this study, Polyacrylonitrile (PAN) fibers were prepared by a simple and effective electrospinning method. Subsequently, the PAN fibers were modified by diethylenetriamine (DETA) to produce aminated polyacrylonitrile (APAN) fibers. Finally, the adsorbability of copper ions on the surface of the fibers was examined in an aqueous solution. The characteristics of APAN fibers were analyzed using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD); The surface amination was confirmed by FTIR. The adsorption data fitted well with the Freundlich isotherm. Thermodynamic parameters of the adsorption process were calculated. The standard Gibb's free energy change, standard enthalpy change, and standard entropy change was -1.46 KJ/mol, -54.72 kJ/mol, and -178.75 kJ/mol/K, respectively. Furthermore, the results show that adsorption of copper onto APAN fibers were spontaneous and exothermic in nature. The equilibrium adsorption capacity of PAN fibers was only 0.10 mg g(-1) for 10 mg L(-1) of copper solution removal under pH 6 and 298 K. In contrast, the equilibrium adsorption capacity of APAN fibers was 45.05 mg g(-1) under the same conditions. The prepared APAN fibers exhibit high efficiency for Cu(II) removal from Waste water and may be used as a reference for future investigation.

Adsorption Kinetics and Binding Studies of Protein Quantum Dots Interaction: A Spectroscopic Approach.

Protein Quantum dots interaction is crucial to investigate for better understanding of the biological interactions of QDs. Here in, the model protein Bovine serum albumin (BSA) was used to evaluate the process of protein QDs interaction and adsorption on QDs surface. The modified Stern-Volmer quenching constant (Ka), number of binding sites (n) at different temperatures (298 308 and 318K ± 1) and corresponding thermodynamic parameters (ΔG < 0, ΔH < 0, and ΔS > 0) were calculated. The quenching constant (Ks) and number of binding sites (n) is found to be inversely proportional to temperature. It signified that static quenching mechanism is dominant over dynamic quenching. The standard free energy change (ΔG < 0) implies that the binding process is spontaneous, while the enthalpy change (ΔH < 0) suggest that the binding of QDs to BSA is an enthalpy-driven process. The standard entropy change (ΔS > 0) suggest that hydrophobic force played a pivotal role in the interaction process. The adsorption process were assessed and evaluated by pseudofirst-order, pseudosecond-order kinetic model, and intraparticle diffusion model.

Interaction of new kinase inhibitors cabozantinib and tofacitinib with human serum alpha-1 acid glycoprotein. A comprehensive spectroscopic and molecular Docking approach

In the current study we have investigated the interaction of newly approved kinase inhibitors namely Cabozantinib (CBZ) and Tofacitinib (TFB) with human Alpha-1 acid glycoprotein (AAG) under simulated physiological conditions using fluorescence quenching measurements, circular dichroism, dynamic light scattering and molecular docking methods. CBZ and TFB binds to AAG with significant affinity and the calculated binding constant for the drugs lie in the order of 104. With the increase in temperature the binding constant values decreased for both CBZ and TFB. The fluorescence resonance energy transfer (FRET) from AAG to CBZ and TFB suggested the fluorescence intensity of AAG was quenched by the two studied drugs via the formation of a non-fluorescent complex in the static manner. The molecular distance r value calculated from FRET is around 2 nm for both drugs, fluorescence spectroscopy data was employed for the study of thermodynamic parameters, standard Gibbs free energy change at 300K was calculated as −5.234kcal mol−1 for CBZ-AAG interaction and −6.237kcal mol−1 for TFB-AAG interaction, standard enthalpy change and standard entropy change for CBZ-AAG interaction are −9.553kcal mol−1 and −14.618cal mol−1K−1 respectively while for AAG-TFB interaction, standard enthalpy and standard entropy change was calculated as 4.019kcal mol−1 and 7.206cal mol−1K−1 respectively. Protein binding of the two drugs caused the tertiary structure alterations. Dynamic light scattering measurements demonstrated the reduction in the hydrodynamic radii of the protein. Furthermore molecular docking results suggested the Hydrophobic interaction and hydrogen bonding were the interactive forces in the binding process of CBZ to AAG while in case of TFB only hydrophobic interactions were found to be involved, overlap of the binding site for two studied drugs on the AAG molecule was revealed by docking results.

A thermodynamic study of interaction of Ag+, Mg2+, Ca2+, and K+ cations with 4-hydroxyphenyl-2,5-bis(2-benzofuranyl)pyridine in some binary mixed non-aqueous solvents

In the present work the complexation process between Ag+ and Mg2+ cations and 4-hydroxyphenyl-2,5-bis(2-benzofuranyl)pyridine (HBFPY) ligand was studied in pure dimethylformamide (DMF), ethanol (EtOH), acetonitrile (AN) and in (DMF-EtOH), (AN-EtOH) and (DMF-AN) binary mixed solvent solutions at different temperatures using the conductometric method. Also in this work the complexation reaction between Ca2+, K+ cations and HBFPY ligand, was studied in pure dimethylformamide (DMF), propanol (PrOH), 1,4-dioxane (DOX), ethanol (EtOH) and in DMF-PrOH, DMF-DOX and DMF-EtOH binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between this ligand and the studied cations is 1 : 1 [ML]. In most cases, addition of HBFPY to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The stability constant of [Mg(HBFPY)]2+ complex in various neat solvents at 15°C decreases in order: EtOH > DMF > AN and the stability constant of [Ag(HBFPY)]+ complex in various neat solvents at 35°C decreases in order: DMF > EtOH. The values of standard enthalpy changes (ΔH°c) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS°c) were calculated from the relationship ΔH°c,295.15= ΔH°c–298.15ΔS°c.

Zinc and nickel adsorption onto a low-cost mineral adsorbent: kinetic, isotherm, and thermodynamic studies

In this study, adsorption of zinc and nickel ions from aqueous solutions by low-cost dolomite was investigated. Dolomite, as a mineral adsorbent, is ample in most countries of the world. Morphology of adsorbent surface and the nature of the dolomite powder were examined using the scanning electron microscope. The process has been studied as a function of contact time, pH, initial concentrations, temperature, and adsorbent dosage. The experimental data were evaluated using three isotherm and kinetic models, including the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models for kinetics and Freundlich, Langmuir and Temkin for isotherms. The results showed that the adsorption isotherm data were fitted well by the Langmuir isotherm and adsorption kinetics followed the pseudo-second-order model for both metal ions. The thermodynamic parameters, such as the change in standard free energy, enthalpy, and entropy, were also determined. The calculated parameters indicated that adsorption process was spontaneous and endothermic in nature. The adsorption capacity of zinc and nickel onto dolomite powder found to be 21.85 and 20.09 mg/g, respectively.

Studies on Binding of Widely used Drugs with Human Serum Albumin at Different Temperatures and PHs

The study on the interaction of human serum albumin (HSA) with three widely used drugs (diclofenac sodium (DIC), furosemide (FUR) and dexamethasone phosphate (DEX)) was investigated by fluorescence method. Fluorescence emission spectra of HSA in presence of the studied drugs was recorded at excitation wavelength 278 nm and showed that the studied drugs act as quenchers. A decrease in fluorescence emission at 340 nm was attributed to changes in environment of the protein fluorophore caused due to presence of the ligand. The modified Stern–Volmer equation was used as a mathematical model to calculate the binding constants between the drug and HSA. The binding constants for the studied drugs with HSA were found inversely related with temperature. The thermodynamic parameters, the changes of standard Gibbs free energy (ΔG°), enthalpy change (DH°) and entropy change (DS°) for the drug-HSA interaction were calculated according to van't Hoff equation. Among the thermodynamic parameters, the values of ΔG° were: -25.83, -25.29 and -25.09 kJ/mol for the drugs DIC, FUR and DEX, respectively, and the values of ΔH° and ΔS° were negative suggested that the hydrogen bonding and van der Waals forces were the predominant intermolecular forces in stabilizing the drug-HSA complex formed. The effect of pH on the binding of the studied drugs to human serum albumin in phosphate buffer solutions (pH 6.0-8.0) has been investigated in this study. The results showed that the binding of each studied drug was decreased with pH studied and the results were attributed according to the ionic forms of both protein and drug in the pH range studied. Finally, the distances between the donor (HSA) and the acceptor (drug) were estimated to be 2.98, 3.52 and 5.30 nm for the drugs DIC, FUR and DEX, respectively, based on Förster’s resonance energy transfer theory (FRET).

Thermodynamic study of competitive inhibitors’ binding to urease

Three competitive inhibitors of urease: boric acid, 2-mercaptoethanol and phosphate buffer pH 6.45, were subjected to the studies of temperature effects on their binding to the enzyme. The first of their kind for these systems, the studies were carried out at temperatures between 15 and 35 °C in HEPES buffers. The Michaelis K M and inhibition K i constants determined for the uninhibited and inhibited urease reactions, respectively, were found to increase with an increase in temperature, importantly, the inhibition remaining competitive irrespective of temperature. The inverse of the constants were further analyzed as equilibrium constants of substrate and inhibitor binding reactions resulting in the formation of ES and EI complexes. The reactions were thermodynamically analyzed with use of the van’t Hoff equation. Found pH-independent in the pH range 6.45–7.0, the changes in the standard enthalpy (ΔH° = −14 kJ mol−1) and the Gibbs free energy ( $$ \Delta G_{298}^{^\circ } $$ = −14 kJ mol−1) for the substrate binding were negative, proving favorable for an exothermic and spontaneous reaction. With the standard entropy change ΔS° close to zero, the reaction is enthalpy driven. The thermodynamic functions of the inhibitor binding by contrast, were found strongly correlated with the inhibitory strengths of the inhibitors in the order: boric acid > 2-mercaptoethanol > phosphate buffer pH 6.45. Accordingly, boric acid demonstrated the changes in the thermodynamic functions considerably bigger (ΔH° = −42 kJ mol−1, $$ \Delta G_{298}^{^\circ } $$ = −23 kJ mol−1) than the substrate and the other two inhibitors. Those for 2-mercaptoethanol were ΔH° = −20 kJ mol−1 and $$ \Delta G_{298}^{^\circ } $$ = −17 kJ mol−1, while for phosphate buffer pH 6.45, ΔH° = −17 kJ mol−1, and $$ \Delta G_{298}^{^\circ } $$ = −13 kJ mol−1, and although slightly bigger, they were found practically comparable in value with those of the substrate, features that apparently result from the comparable values of K M and K is. Remarkably, the inhibitors showed negative values of ΔS° (to various degrees) proving that their binding to the enzyme, like that of the substrate, is driven by enthalpy.

Solubility and thermodynamic properties of sulfuryl fluoride in water

The solubility of sulfuryl fluoride in water was experimentally measured over the pressure from P=(0 to 600)kPa and T=(283.15 to 308.15)K using isochoric saturation method. Results show that SO2F2 solubility increases with increasing pressure and decreases with increasing temperature. Using the experimental solubility data, Henry’s law constants and the thermodynamic properties such as the standard Gibbs free energy, enthalpy, and entropy changes of SO2F2 solvation were obtained. Henry’s law constant based on mole fraction and molality of SO2F2 in water vary from (432.21 to 1052.96)MPa and (7.78 to 18.96)MPa at T=(283.15 to 308.15)K, respectively.

Comparative study of carbon black and activated carbon adsorbents for removal of carbofuran from aqueous solution

Three commercial carbon samples of carbon black, namely Black Pearl 2000 (BP 2000), extruded activated carbon (EAC), and granular activated carbon (GAC), were evaluated as adsorbents for the removal of carbofuran from water. The specific surface area and micropore volume of the adsorbents were studied by BET measurements and t-plot, respectively. Batch experiments were conducted to examine the effects of the adsorbents as a function of the initial concentration of carbofuran, adsorption contact time, and solution pH. As per the results, the equilibrium uptake for carbofuran on all adsorbents increased with an increase in the initial carbofuran concentration in solution, and the removal potential of carbofuran followed the order BP 2000 > GAC > EAC. The amount of carbofuran uptake at equilibrium was applied to investigate the suitability of the Langmuir, Freundlich, and Temkin models. The results indicated that the equilibrium data obey the Langmuir isotherm model better than Freundlich, and Temkin models. The adsorption kinetics data were used to compare the feasibility of the two models: pseudo-first-order kinetic and pseudo-second-order kinetic. The data fit the pseudo-second-order model well. The ranking order of adsorbents in terms of adsorption kinetic constants was as follows: BP 2000 > EAC > GAC. Thermodynamics studies were carried out and various thermodynamics parameters such as standard free energy changes (ΔG), standard enthalpy change (ΔH), and standard entropy change (ΔS) were calculated. The values of ΔG were found as negative, which confirms the spontaneous nature of the adsorption processes. The results of the study supported the usability of BP 2000, EAC, and GAC as promising adsorbents for carbofuran adsorption.

Chemical modification of expanded glass aggregate with N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) for the adsorptive removal of Cr(III) ion

In this study, the silylant agent 3-aminopropyl trimethoxysilane (APTES) was anchored on expanded glass aggregate (GA) to prepare a new adsorbent. N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) bonded to amino-functionalized GA adsorbent with reflux. Developed adsorbent (GA-APTES-TTU) was characterized using thermal analysis (TGA) and scanning electron microscopy (SEM). TGA and SEM studies indicated that modification of the glass aggregate (GA) surfaces was successfully performed. The adsorption studies exhibited that the GA-APTES-TTU could be efficiently used for the removal of Cr(III) from aqueous solutions. The effects of pH, adsorbent dosage, ion concentration, time, and temperature were investigated as adsorption parameters. The maximum removal of Cr(III) was observed at pH 4. The adsorption equilibrium was achieved in 120min and adsorption of Cr(III) followed the Langmuir isotherm model. The maximum adsorption capacity for Cr(III) was 0.4305mmol/g with GA-APTES-TTU. Thermodynamic parameters such as the standard free energy (ΔGo), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated in order to explain the mechanism of adsorption process. The thermodynamic data showed that Cr(III) adsorption was spontaneous, endothermic, and a physisorption reaction. In addition, the adsorption kinetic data fitted to the pseudo-second order model.

The effect of surface modification of mesoporous carbons on Auramine-O dye removal from water

Mesoporous carbon of regular structure was subjected to oxidation by ammonium persulfate at 30, 60 or 100 °C. The mesostructure and pore evolution were characterised by XRD, TEM, and N2 sorption techniques. The functional groups present on the surface of the carbon materials were identified by FTIR and thermogravimetric studies. It was established that the micropores and small mesopores could be blocked by the surface oxides attached under mild oxidation. High densities of surface oxygen complexes, especially carboxylic groups, were generated on the surface of mesoporous carbons. All materials obtained were tested for the removal of Auramine-O from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH and initial dye concentration. Removal of this cationic dye in basic solutions was more effective than in acidic solutions. The highest sorption capacity towards Auramine-O was obtained for the carbon sample oxidised by ammonium persulfate solution at 100 °C. Fitting equilibrium data to Langmuir and Freundlich isotherms showed that Langmuir model was more suitable to describe the Auramine-O adsorption. The changes in standard enthalpy (ΔH0), standard entropy (ΔS0) and Gibbs free energy (ΔG0) were analysed. Thermodynamic study showed that the adsorption of Auramine-O was a spontaneous and exothermic process.

A novel zerovalent manganese for removal of copper ions: synthesis, characterization and adsorption studies

Synthesis of nanoscale zerovalent manganese (nZVMn) by chemical reduction was carried out in a single pot system under inert environment. nZVMn was characterized using a combination of analytical techniques: Ultraviolet–Visible Spectroscopy, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersive X-ray, BET surface area and Point of Zero Charge. The adsorption physicochemical factors: pH, contact time, adsorbent dose, agitation speed, initial copper ion concentration and temperature were optimized. The kinetic data fitted better to Pseudo second-order, Elovich, fractional power and intraparticle diffusion models and their validity was tested by three statistical models: sum of square error, Chi-square (χ2) and normalized standard deviation (Δq). Seven of the two-parameter isotherm models [Freundlich, Langmuir, Temkin, Dubinin–Kaganer–Raduskevich (DKR), Halsey, Harkin–Jura and Flory–Huggins] were used to analyse the equilibrium adsorption data. The Langmuir monolayer adsorption capacity (Qmax = 181.818 mg/g) obtained is greater than other those of nano-adsorbents utilized in adsorption of copper ions. The equilibrium adsorption data were better described by Langmuir, Freundlich, Temkin, DKR and Halsey isotherm models considering their coefficient of regression (R2 > 0.90). The values of the thermodynamic parameters: standard enthalpy change ∆H° (+50.27848 kJ mol−1), standard entropy change ∆S° (203.5724 J mol−1 K−1) and the Gibbs free energy change ∆G° revealed that the adsorption process was feasible, spontaneous, and endothermic in nature. The performance of this novel nanoscale zerovalent manganese (nZVMn) suggested that it has a great potential for effective removal of copper ions from aqueous solution.

Characterization, isotherm and kinetic study of Phaseolus vulgaris husk as an innovative adsorbent for Cr(VI) removal

Phaseolus vulgaris husk as a novel, very common milling agro waste, showed good performance for mutagenic Cr(VI) removal from chromium enriched aqueous solution. The study involves batch experiments to investigate the effects of influencing parameters, such as pH, temperature, contact time, initial Cr(VI) concentration, and adsorbent dose, on the adsorption process. Results showed a maximum of 99.88% removal of Cr(VI) at pH 1.16, temperature 20 °C and adsorbent dose of 6 g L−1. The adsorption equilibrium data followed the Freundlich model, suggesting a heterogeneous nature of the adsorbent surface and the correlation coefficient for pseudo-second-order kinetic model was found to be very high, showing its applicability during the adsorption process. The maximum Cr(VI) uptake capacity was 3.4317mg g−1. Thermodynamic parameters like standard free energy change (−7.175 kJ mol−1), enthalpy change (−8.29 kJ mol−1) and entropy change (0.005 kJ mol−1 K−1) revealed the spontaneous and exothermic nature of adsorption of Cr(VI) onto P. vulgaris husk. Desorption with 1mol L−1 NaOH followed by 1mol L−1 HCl was effective (92.76%) and, hence, it exhibited the possibility of recycling of used husk.

Thermodynamic and aggregation properties of aqueous dodecyltrimethylammonium bromide in the presence of hydrophilic ionic liquid 1,2-dimethyl-3-octylimidazolium chloride

The effect of a trisubstituted imidazolium based hydrophilic ionic liquid (IL), 1,2-dimethyl-3-octylimidazolium chloride [odmim][Cl] on the thermodynamic and aggregation properties of dodecyltrimethylammonium bromide (DTAB) at temperatures 298.15–318.15K has been studied by conductivity measurements in aqueous media. From the temperature dependence of critical micelle concentration (cmc), various thermodynamic parameters of micellization viz. standard free energy change (ΔGm°), standard enthalpy change (ΔHm°) and standard entropy change (ΔSm°) have been evaluated. Further fluorescence probe analysis has been utilized to obtain cmc value in order to validate the cmc values obtained from conductivity measurements. The micelles formed just like in aqueous medium and cmc values were found to be changing at different wt% of IL than in water. The cmc value of aqueous DTAB solution decreases until 2.0wt% of IL in the medium. The properties of aqueous DTAB solution change in a different way at higher concentration of IL. The variation in chemical shifts of surfactant protons in the presence of IL revealed that the electrostatic interactions have a prominent influence on the DTAB micellization in IL/water systems. It is shown that the modification in aggregation properties of DTAB is related to the lipophilicity of interacting ions.

A comprehensive investigation on adsorption of Ca (II), Cr (III) and Mg (II) ions by 3D porous nickel films

The present study reports the removal of Ca (II), Cr (III), Mg (II) ions from aqueous solution using 3D-porous nickel films (3DNFs) as a novel adsorbent material prepared by hydrogen bubble dynamic template (HBDT) method at room temperature. The structure morphology and the phase constitution of 3DNFs were characterized by FESEM, EDS and XRD. Adsorption process of Ca (II), Cr (III), Mg (II) ions was fast as the equilibrium was established within 30min, and the maximum adsorption at equilibrium was 44.1mg/g, 46.4mg/g and 32.7mg/g, respectively. The adsorption kinetics well fitted using a pseudo second-order kinetic model. The adsorption isotherm data of all the three metals fit well the Langmuir and Freundlich adsorption isotherm model. It was found out that kinetics of adsorption varies with initial concentration of metal ions. Thermodynamic parameters (i.e., the standard Gibbs free energies (ΔG), enthalpy change (ΔH), standard entropy change (ΔS)) were also evaluated. Thermodynamic analysis indicated that a high temperature is favored for the adsorption of metal ions by 3DNFs. These results suggest that 3DNFs have good potential application in effective adsorption of metal ions with satisfactory results.

A Comparative Study on the Aggregation and Thermodynamic Properties of Anionic Sodium Dodecylsulphate and Cationic Cetyltrimethylammonium Bromide in Aqueous Medium: Effect of the Co‐solvent N‐Methylacetamide

AbstractThe effect of co‐solvent N‐methylacetamide (NMA) (0.035, 0.046, 0.127, and 0.258 mol kg−1) on the micellization behaviour of anionic surfactant sodium dodecylsulphate (SDS) (3.21–10.35 mmol kg−1) and cationic surfactant cetyltrimethylammonium bromide (CTAB) (0.19–3.72 mmol kg−1) in aqueous solution was explored by employing conductivity measurements at different temperatures (298.15–313.15 K). The critical micelle concentration (CMC) values for SDS and CTAB in aqueous solutions of NMA were determined from the conductivity versus surfactant concentration plots. The variations in the CMC values of SDS with NMA concentration are in striking contrast to those observed in the case of CTAB. The various relevant thermodynamic parameters of micellization, viz. standard enthalpy change, ΔHmo, standard entropy change, ΔSmo, and standard Gibbs free energy change, ΔGmo, were determined using the temperature variation of the CMC values and counterion binding. The results not only relate these thermodynamic parameters to the consequences of intermolecular interactions but are also able to differentiate between SDS–water–NMA and CTAB–water–NMA systems in terms of contributions from head groups as well as alkyl chains of surfactants.

Adsorption of 1,1-dimethylhydrazine (UDMH) from aqueous solution using magnetic carbon nanocomposite: kinetic and thermodynamic study

In this work, removal of UDMH as a pollutant with considerable toxicity is studied using activated carbon magnetic nanocomposite with fast and easy separation. To optimize the process, effective parameters, such as pH, adsorbent dosage, contact time, and temperature, have been investigated. More than 90% UDMH removal efficiency obtained within 30 min of contact time, 20 mg of adsorbent at pH 6 and room temperature. The adsorption behavior was evaluated based on equilibrium data, using both the Langmuir and Freundlich isotherm models. It was found that adsorption data were interpreted by Freundlich model better than Langmuir model with regression coefficient of 0.9971. Besides, the adsorption data were well described by the pseudo-second-order kinetic model. The adsorption thermodynamic parameters showed that the adsorption process is endothermic and spontaneous with positive standard enthalpy of 2.74 J mol−1 and negative standard free energy of 29.08 kJ mol−1, respectively. Also standard entropy changes of 97.56 J mol−1 k−1 was calculated.