The adsorption of phosphamidon on the surface of antimony(V) phosphate: A thermodynamic study

The thermodynamics of the adsorption of phosphamidon on antimony(V) phosphate cation exchanger has been studied at 30, 45 and 50°C and the thermodynamic equilibrium constant (K₀), standard free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated to predict its adsorption behaviour. All the data are adequately represented by the Freundlich isotherms.     

Surfactant assisted preparation and characterization of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger

Carboxymethyl cellulose Sn(IV) phosphate composite nano-rod like cation exchanger with diameter in the range of 20–40 nm, length in the range of 100–150 μm and particle size in the range of 21–38 nm have been successfully prepared by surfactant assisted sol–gel method. Scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, fourier transform infra red spectroscopy and thermogravimetric analysis-differential thermal analysis studies were carried out to study the structure and morphology of this composite nano-rod like cation exchanger. Freundlich adsorption isotherm is well fitted for the adsorption of pyridine on the surface of this composite nano-rod like cation exchanger. The thermodynamic parameters such as Freundlich constant, thermodynamic equilibrium constant (K ₀), standard free energy changes (ΔG ⁰), standard enthalpy changes (ΔH ⁰) and standard entropy changes (ΔS ⁰) have been evaluated. These parameters indicated that the adsorption of pyridine on the surface of composite nano-rod like cation exchanger was feasible, spontaneous and exothermic in nature which suggests for the potential application of pyridine removal from water.     

Adsorption thermodynamic and desorption studies of U(VI) on modified silica gel (SiAPMS-HL)

In this study, the adsorption process was examined by various isotherm models Langmuir, Freundlich and Dubinin–Radushkevich and equilibrium data were successfully described by Langmuir model. Adsorption thermodynamics of uranium (VI) on modified silica gel (SiAPMS-HL) has been studied within a temperature range from 293 to 333 K and the thermodynamic parameters, such as equilibrium constant (K _D), standard free energy changes (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°), have been obtained. The desorption studies were conducted in batch system to investigate the kind, concentration and volume of the eluent.     

Thermodynamics and kinetics of adsorption of Cu(II) from aqueous solutions onto a new cation exchanger derived from tamarind fruit shell

A novel cation exchanger (TFS-CE) having carboxylate functionality was prepared through graft copolymerization of hydroxyethylmethacrylate onto tamarind fruit shell (TFS) in the presence of N,N′-methylenebisacrylamide as a cross-linking agent using K₂S₂O₈/Na₂S₂O₃ initiator system, followed by functionalisation. The TFS-CE was used for the removal of Cu(II) from aqueous solutions. At fixed solid/solution ratio the various factors affecting adsorption such as pH, initial concentration, contact time, and temperature were investigated. Kinetic experiments showed that the amount of Cu(II) adsorbed increased with increase in Cu(II) concentration and equilibrium was attained at 1 h. The kinetics of adsorption follows pseudo-second-order model and the rate constant increases with increase in temperature indicating endothermic nature of adsorption. The Arrhenius and Eyring equations were used to obtain the kinetic parameters such as activation energy (E_a) and enthalpy (ΔH^#), entropy (ΔS^#) and free energy (ΔG^#) of activation for the adsorption process. The value of E_a for adsorption was found to be 10.84 kJ · mol^?1 and the adsorption involves diffusion controlled process. The equilibrium data were well fitted to the Langmuir isotherm. The maximum adsorption capacity for Cu(II) was 64 · 10 mg · g^?1 at T = 303 K. The thermodynamic parameters such as changes in free energy (ΔG^°), enthalpy (ΔH^°), and entropy (ΔS^°) were derived to predict the nature of adsorption process. The isosteric heat of adsorption increases with increase in surface loading indicating some lateral interactions between the adsorbed metal ions.     

Surface Characterization of Sepiolite by Inverse Gas Chromatography

Inverse gas chromatography (IGC) was applied to characterize the surface of sepiolite. The adsorption thermodynamic parameters (the standard enthalpy (ΔH ⁰), entropy (ΔS ⁰) and free energy of adsorption (ΔG ⁰)), the dispersive component of the surface energy (γ _S ^d ), and the acid/base character of sepiolite surface were estimated by using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (ΔG ^sp ), the specific enthalpy of adsorption (ΔH ^sp ), and the specific entropy of adsorption (ΔS ^sp ) of polar probes on sepiolite were determined. ΔH ^sp were correlated with the donor and modified acceptor numbers of the probes to quantify the acidic K _A and the basic K _D parameters of the sepiolite surface. The values obtained for the parameters K _A and K _D indicated an acidic character for sepiolite surface.     

Adsorption properties of amine modified lignin-hydrogel composite for uranyl ions: Theoretical and experimental insights

A new modified material was synthesized and characterized as ethylene diamine modified (EA) Polyacrylamide (PAA)-Lignin (L). The adsorption features of EA modified PAA-L were studied for uranyl ions. The characterization experiments were evaluated by FT-IR spectroscopic techniques, scanning electron microscopy (SEM), and PZC analysis. Adsorption of UO₂²⁺ ions as a function of concentration, pH, temperature, and time of adsorption were studied. The adsorption phenomenon of UO₂²⁺ ions onto PAA-L-EA from aqueous medium was successfully evaluated by various equilibrium models such as Langmuir, Freundlich, and Dubinin-Radushkevich (DR). The (Qe) maximum adsorption capacity values for Langmuir model was calculated as 0.792 kg mol^?1 by using experimental data. The constant values of thermodynamic parameters such as (ΔG°), (ΔH°) and (ΔS°) were calculated and it has observed that the mechanism of adsorption was found compatible with endothermic and spontaneous owing to increasing disorderliness at solution/solid system. The adsorption mechanism is compatible with Elovich and intraparticle diffusion models. The power of the interaction between modified lignin and uranyl ?on was explained in the light of Hard and Soft Acid-Base Principle.     

Equilibrium and kinetics studies on adsorption of Cu(II) from aqueous solutions onto a graft copolymer of cross-linked starch/acrylonitrile (CLSAGCP)

A synthetic graft copolymer of cross-linked starch/acrylonitrile was used as an adsorbent for the removal of Cu(II) ions from an aqueous solution of copper nitrate hexahydrate Cu(NO₃)₂ · 6H₂O at different temperatures and fixed pH. The amount adsorbed increased with increasing concentration of Cu(II) ions and decreasing temperature. The length of time taken to reach equilibrium of the adsorption of Cu(II) ions was the same at all temperatures tested. Kinetics studies showed that the adsorption process obeyed first-order reversible kinetics and the adsorption isotherms followed the Freundlich model. Furthermore, the thermodynamic parameters, i.e. standard free energy (ΔG^∘), standard enthalpy (ΔH^∘), and standard entropy (ΔS^∘), of the adsorption process were calculated and the results are discussed in detail.     

Forward ion-exchange kinetics of heavy metal ions on the surface of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod-like cation exchanger

The Nernst?CPlanck equations with some additional assumptions was used in this study to investigate the forward kinetics and ion-exchange mechanism of heavy metal ions viz. Ni²⁺?CH⁺, Cu²⁺?CH⁺, Mn²⁺?CH⁺ and Zn²⁺?CH⁺ on the surface of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod-like cation-exchanger. It was observed that heavy metals' exchange processes were imparted by the particle diffusion-controlled phenomenon. Some physical parameters i.e., fractional attainment of equilibrium U(??), self-diffusion coefficients (D _o), energy of activation (E _a), and entropy of activation (??S*) were estimated. These investigations revealed that the equilibrium is attained faster at higher temperature probably because of availability of thermally enlarged matrix of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod-like cation-exchange material. The physical parameters observed for this composite cation exchanger were also compared with other composite ion exchangers. The results showed that the ion-exchange phenomenon is more feasible on the surface of this composite cation exchanger as compared with the other ion exchangers which indicated the usefulness of this composite ion exchanger in various applications.     

Interaction of manganese(II) with methyl salicylate ethyl salicylate and phenyl salicylate

The proton ligand stability constants of methyl salicylate, ethyl salicylate and phenyl salicylate and the stepwise stability constants of manganese(II) complexes with these have been determined potentiometrically in aqueous ethanol system 50/50 (v/v) at 25°C at different ionic strengths, viz. 0.050 M, 0.075 M, 0.100 M and at 35 and 45°C at an ionic strength of 0.05 M. The thermodynamic stability constants of the complexes have been evaluated from the various values by extrapolating to zero ionic strength at 25°C. The thermodynamic parameters such as free energy changes (ΔG), enthalpy changes (ΔH) and entropy changes (ΔS) involved have been calculated.     

Kinetics and mechanism of ion exchange of Fe3+, Cd2+ and Na+/H+ on Lewatite S-100 cation exchanger in aqueous and aqueous-detergent media

Sorption mechanism of Fe (III), Cd (II) and Na (I) on cation exchange resins in H-form was investigated from aqueous and aqueous-detergent media by a modified limited batch technique. The cation exchange studies involved the sorption of metallic ions onto a Lewatite S-100 exchanger. Effects of mesh size of the exchanger, temperature and detergent on the exchange rate have been investigated. The mechanisms of cation exchanges have been determined in the temperature range of 25–65°C. In all cases of the reactions ions, diffusion is found to be the rate determining step in the exchange process. The exchange rate in the exchange process was found to increase with a decrease of particle size and an increase of temperature. However, in case of the influence of detergent, the exchange reactions are dependent on the reaction technique. The effective-diffusion coefficients have been evaluated at three different temperatures. The energy barriers (ΔE_a), entropies of activation (ΔS*), (ΔH*) and (ΔG*) for various sorption systems have also been calculated. The results are discussed in terms of size and valences of the counter ions. No change in the internal structure of Lewatite S-100 is inferred due to the sorption of counter ions.     

Characterization and thermal kinetic studies on charge-transfer complexes of 4,4′-bipyridine with benzoquinone derivatives

4,4′-Bipyridine belong to an important class of compounds with wide applications in different fields and since the formation charge transfer compounds give opportunity to improve the physical and chemical properties of different donors so charge transfer compounds of 4,4′-bipyridine (Bpy) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone [chloranilic acid] (CHA) and 2,3,5,6-tetrachloro-1,4-benzoquinone [choloranil] (CHL) were studied. The stoichiometries of the reactions were determined from photometric titration methods. Although the thermodynamic parameters [Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy change (ΔS°)] were calculated. The thermal decomposition of the complexes follows first order kinetics and thermodynamic parameters of the decomposition were calculated. The structural morphology was investigated by scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM) and show that these molecules are of nanosize.     

Isothermal titration calorimetry (ITC) method to study drug/ion exchanger interaction

An isothermal titration calorimetry (ITC) method to measure the heat effects evolving from the binding between cation exchanger Amberlite ® IRP 69 and the cationic drug substances propranolol hydrochloride (PROP), metoprolol tartarate (METO), acebutolol hydrochloride (ACEB) and chlorpheniramine maleate (CPR) has been developed. The method gives repeatable results with an error about 5% for the beta-blockers PROP, METO and ACEB, and about 10% for the antihistamine CPR. The calculation of the thermodynamic parameters enthalpy change (ΔH _bind) and Gibbs free energy change (ΔG _bind) show significant differences between the different drug substances.     

Thermodynamic aspects of the host-guest chemistry of pyrogallol[4]arenes and peralkylated ammonium cations

The stability constants (K), standard free energy (ΔG^o), enthalpy (ΔH^o), and entropy changes (ΔS^o) for the complexation of pyrogallol[4]arenes with ammonium cations of different size and shape have been determined in ethanol at 298 K by isothermal titration calorimetry. The trends observed in the thermodynamic parameters for 1:1 and/or 1:2 host-guest complexation correspond to the systematic structural changes of the guest molecules. On the basis of the results obtained we compare the complexation properties with two other resorcin[4]arenes and discuss the thermodynamic aspects of this supramolecular host-guest interactions.     

Solubility of gallic acid in liquid mixtures of (ethanol + water) from (293.15 to 318.15) K

The solubility of gallic acid in (water + ethanol) binary solvents was determined from (293.15 to 318.15) K at atmospheric pressure using a thermostatted reactor and UV/vis spectrophotometer analysis. The effects of binary solvents composition and temperature on the solubility were discussed. It was found that gallic acid solubility in (water + ethanol) mixed solvents presents a maximum-solubility effect. Two empirical equations were proposed to correlate the solubility data. The calculated solubilities show good agreement with the experimental data within the studied temperature range. Using the experimentally measured solubilities, the thermodynamic properties of dissolution of the gallic acid such as Gibbs energy (Δ_solG°), molar enthalpy of dissolution (Δ_solH°), and molar entropy of dissolution (Δ_solS°) were calculated.     

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 120 min and adsorption of Cr(III) followed the Langmuir isotherm model. The maximum adsorption capacity for Cr(III) was 0.4305 mmol/g with GA-APTES-TTU. Thermodynamic parameters such as the standard free energy (ΔG^o), 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.     

Interactions Between Surface Active Ionic Liquid and Procaine Hydrochloride Drug in Aqueous Solution

Complex formation between the anesthetic drug, procaine hydrochloride and a surface active ionic liquid (SAIL), 1-tetradecyl-3-methylimidazolium chloride, [C₁₄mim][Cl], in aqueous medium has been investigated using surface tension, fluorescence and DLS measurements at 298.15 K and conductance at 288.15, 298.15 and 308.15 K. Critical aggregation concentration (CAC), degree of ionization (α), and various thermodynamic parameters were determined using the conductivity measurements. The interfacial behavior of SAIL at different concentrations of the drug was evaluated from surface tension measurements by calculating a series of surface parameters and CAC values. Fluorescence spectroscopy was used to evaluate the binding constant (K) and the standard state Gibbs energy change (ΔG°) for the formation of drug–SAIL complexes, which confirms the existence of cation–π interactions between the drug molecules and imidazolium ring of the SAIL molecules. The CAC values were found to decrease with increase in the concentration of the drug, which is due to the balancing between hydrophobic and electrostatic interactions. Dynamic light scattering provides sufficient information about the size of the aggregates and the variation in the hydrodynamic diameters pertaining to the changes in the drug concentration. The results from above methods show that the aggregation process of SAIL is favored by increases in the concentration of the drug. It is demonstrated that with the better understanding of the interactions, [C₁₄mim][Cl] can be judiciously utilized in making use of procaine hydrochloride.     

Equilibrium,kinetics and thermodynamics study of phenols adsorption onto activated carbon obtained from lignocellulosic material (<Emphasis Type="Italic">Eucalyptus Globulus labill</Emphasis> seed)

Activated carbon was prepared from lignocellulosic material (Eucalyptus Globulus labill seed) by chemical activation with ZnCl₂ at two different concentrations (10 and 25 % m/v) named ACS25 and ACS10. The textural characteristics of the activated carbons (ACs) were determined by N₂ adsorption isotherms; these exhibit B.E.T. surface areas of 250 and 300 m² g^?1 for ACS25 and ACS10, respectively, with micropore volume contents of 0.140 and 0.125 cm³ g^?1 in the same order. In addition, the FTIR and Boehm methods were conducted for the chemical characterisation of ACs, where many groups with basic character were found, which favours the adsorption of phenols. The prepared carbonaceous adsorbents were used in the adsorption of wide pollutants monosubstituted phenol derivatives: phenol, 4-nitrophenol and 4-chlorophenol. The effect of temperature on the thermodynamics, kinetic and equilibrium of phenols adsorption on ACs was thoroughly examined. The adsorption kinetics adjusted properly for a pseudo-second-order kinetic model. However, the Elovich model (chemisorption) confirms that phenols adsorption did not occur via the sharing of electrons between the phenolic ring and basal plane of ACs because is not properly adjusted, so the process is given by physisorption. The thermodynamic parameters [i.e. Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°)] were also evaluated. The overall adsorption process was exothermic and spontaneous in nature. The values found in the thermodynamic study, confirm that the adsorption process corresponds to a clearly physical process.     

Solvent influence upon complexation of N-phenylaza-15-crown-5 with UO2 2+ cation in binary mixed non-aqueous solvents

The complexation reaction of N-phenylaza-15-crown-5 (PhA15C5) with UO₂ ²⁺ cation was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–butanol (AN–BuOH), acetonitrile–dimethylformamide (AN–DMF) and methanol–propylencarbonate (MeOH–PC) binary solutions, at different temperatures by conductometry method. The conductance data show that the stoichiometry of the complex formed between PhA15C5 with UO₂ ²⁺ cation in most cases is 1:1 [M:L], but in some solvent systems a 1:2 [M:L₂] complex is formed in solutions. The results revealed that, the stability constant of (PhA15C5·UO₂)²⁺ complex in the binary mixed solvents varies in the order: AN–BuOH>AN–MeOH>AN–DMF. In the case of the pure organic solvents, the sequence of the stability of the complex changes as: AN>PC>BuOH>DMF. A non-linear relationship was observed for changes of logK_f of (PhA15C5·UO₂)²⁺ complex versus the composition of the binary mixed solvents. The corresponding standard thermodynamic parameters (ΔH_c°, ΔS_c°) were obtained from temperature dependence of the stability constant. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.     

Fe3O4-CuO-activated carbon composite as an efficient adsorbent for bromophenol blue dye removal from aqueous solutions

Dye wastewater from industries is posing tremendous health hazards. The lethal dyes can be eliminated using nanomaterials and scientific approach like adsorption which is facile, cheap, safe as well as ecofriendly. Fe₃O₄-CuO-AC composite was prepared by a hydrothermal method and used for the removal of dyes in wastewater. The composite material was characterized by various techniques such as XRD, SEM, EDS, TEM and FT-IR. The Fe₃O₄-CuO-AC composite was used to treat five types of dyes in water. Fe₃O₄-CuO-AC composite showed the highest adsorption capability for bromophenol blue (BPB) dye. The effects of initial concentration, pH, the amount of adsorbent and temperature were also studied. The optimum conditions were found to be 20 ppm dye concentration, pH 9, an adsorbent dose of 0.06 gL^─1 at 65 °C. A removal efficiency of 97% was obtained for BPB dye during 120 min of adsorption. Kinetic studies indicated that a pseudo-second order is the most suitable model for the adsorption process. The Fe₃O₄-CuO-AC composite showed better adsorption capacity as compare to Fe₃O₄-AC except for the Methyl green dye. The maximum adsorption capacity was found to be 88.60 mg/g for BPB. Additionally, the thermodynamic parameters (ΔS°, ΔH° and ΔG°) showed that the process was spontaneous and exothermic. All the above results revealed that the Fe₃O₄-CuO-AC compositecan be an effective adsorbent for removing dyes from wastewater.     

Adsorption and aggregation properties of novel star-shaped gluconamide-type cationic surfactants in aqueous solution

The adsorption and aggregation behavior of novel star-shaped gluconamide-type cationic surfactants N-dodecyl-N,N-bis[(3-D-gluconylamido)propyl]-N-alkylammonium bromide (C_nDBGB, where n represents hydrocarbon chain lengths of 10, 12, and 14) has been studied on the basis of static/dynamic surface tension, conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM) data. The static surface tension of the C_nDBGB aqueous solution measured at the critical micelle concentration (CMC) is observed to be significantly lower than that of the corresponding monomeric surfactants. The dynamic surface tension results indicate that adsorption process of above CMC is a mixed diffusion–kinetic adsorption mechanism. From the results of temperature dependent conductivity measurements, we could obtain the degree of counterion binding (β) and the thermodynamic parameters such as standard free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of aggregation. With a combination of the DLS and TEM data, a size transformation of the micelles is suggested to occur with an increase in the concentration.