Positive Values Of ΔS Research Articles

Synthesis and characterization of the molecularly imprinted mesoporous silica based on the self-assembly technique for selective recognition of lomefloxacin in aqueous solution

Based on double-imprinting (surfactant and lomefloxacin templates) concept and self-assembly technique, a new molecularly imprinted mesoporous silica (MIP-MS) was prepared to understand and characterize the mechanism of fast binding and selective recognition of lomefloxacin (LOM) by the adsorption isotherms model, the adsorption kinetic models, and the competitive adsorption. The MIP-MS was prepared by using LOM and surfactant micelles as the templates formed through self-hydrolyzed, self-condensed, and co-condensation of tetraethoxysilane and methyltriethoxysilane in alkaline media, and with the covalently anchored organic groups in the mesoporous silica matrix. Both the molecularly imprinted polymer (MIP) and non-imprinted mesoporous polymer (NIP) were prepared for comparison. The surface area, pore size and pore volume of the MIP-MS are 270 m2 g−1, 4.42 nm and 0.28 cm3 g−1, respectively. The kinetics studies showed that the pseudo-second-order model was consistent with the kinetic data of the MIP-MS with the fast binding templates (the 95 % uptake of LOM within 10 min). The equilibrium data, at various temperatures, were described successfully by the Langmuir and Freundlich isotherm models. The Freundlich model was found to fit the experiment data well. The thermodynamics parameters (positive values of ΔS, negative values of ΔH and ΔG) indicated that the binding system for the MIP-MS was entropy-gained, exothermic, and the spontaneous adsorptive forces were stronger on MIP-MS than on NIP and MIP. The MIP-MS showed fast binding, higher affinity, and selectivity for the template of LOM compared with the NIP and MIP.

Sol–gel derived ion imprinted thiocyanato-functionalized silica gel as selective adsorbent of cadmium(II)

A Cd(II)-imprinted thiocyanato-functionalized silica gel adsorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol–gel process for the selective adsorption of Cd(II) ion in aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different conditions (such as the pH of solutions, the contact time and the initial concentrations of Cd(II) ions) on the adsorption capacity of Cd(II) were investigated. The optimum pH of adsorption was in the range of 4–8.5. The adsorption equilibrium could be reached in 20 min. The relatively selectivity coefficients of the imprinted silica were higher than those of the non-imprinted adsorbents. Ho’s pseudo-second-order model well described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich–Peterson isotherm model, and the experimental value of maximum adsorption capacity for Cd(II) was 72.8 mg·g−1. The positive value of ΔH o suggested endothermic nature of Cd(II) adsorption on the imprinted silica adsorbent. Increase in entropy of adsorption reaction was shown by the positive value of ΔS o and the negative value of ΔG o indicating that the adsorption was spontaneous in nature.

Removal of cadmium from aqueous solution by organic-inorganic hybrid sorbent combining sol-gel processing and imprinting technique

An organic-inorganic hybrid sorbent with high adsorption capacity was prepared by surface imprinting technique combined with sol-gel processing with 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane as a functional precursor and silica as the support for the removal of Cd(II) ion from aqueous solution, and was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, nitrogen gas sorption and thermogravimetric analysis. The influences of different adsorption parameters, such as pH value of solution, contact time and the initial concentrations of Cd(II) ions on the adsorption amount of Cd(II), were examined. The optimum pH for adsorption was found to be in the range of 4–8. The adsorption rate of Cd(II) on the imprinted hybrid sorbent was rapid. The relative selectivity coefficients of the imprinted hybrid sorbent were higher than those of the non-imprinted sorbent. Ho’s pseudosecond-order model best described the kinetics of the adsorption reaction. The adsorption process of metals followed Redlich-Peterson and Langmuir isotherms models, and the experimental value of maximum adsorption capacity for Cd(II) was 77.2mg·g−1. The positive values of ΔH ○ suggested endothermic nature of Cd(II) adsorption on the imprinted hybrid sorbent. Increase in entropy of adsorption reaction was shown by the positive values of ΔS ○ and the negative values of ΔG ○ indicating that the adsorption was spontaneous.

Adsorptive Removal of Ni2+from Aqueous Solution by Low Cost Cellulosic Adsorbent-Adsorption Kinetics and Isotherm Study

AbstractAdsorptive removal of Ni2+from aqueous solution by low cost cellulosic adsorbent was investigated with respect to adsorption kinetics and adsorption isotherm. Adsorbent was characterized by BET surface area, SEM, EDX, FTIR and Zeta potential technique and reported earlier. The surfaces contain carbonyl and hydroxyl functional groups, which act as binding sites for Ni2+ion. Adsorption kinetics of Ni2+was tested by first order, Elovich, parabolic diffusion and Bangham kinetic equations. Thermodynamic parameters like ΔH≠, ΔS≠and ΔG≠were calculated from the kinetic data. The rate of adsorption was high at high adsorption temperature. Positive values of ΔS≠reflect some structural exchange among the active site of the adsorbent and metal ion. Freundlich, Langmuir, Temkin isotherms and distribution coefficient were found fit to the adsorption isotherm data.

Equilibrium and thermodynamics of azo dyes biosorption onto Spirulina platensis

The equilibrium and thermodynamics of azo dye (tartrazine and allura red) biosorption onto Spirulina platensis biomass were investigated. The equilibrium curves were obtained at 298, 308, 318 and 328 K, and four isotherm models were fitted the experimental data. Biosorption thermodynamic parameters (ΔG, ΔH and ΔS) were estimated. The results showed that the biosorption was favored by a temperature decrease. For both dyes, the Sips model was the best to represent the equilibrium experimental data (R²>0.99 and ARE<5.0%) and the maximum biosorption capacities were 363.2 and 468.7 mg g-1 for tartrazine and allura red, respectively, obtained at 298 K. The negative values of ΔG and ΔH showed that the biosorption of both dyes was spontaneous, favorable and exothermic. The positive values of ΔS suggested that the system disorder increases during the biosorption process.

Comparison of Adsorptive Removal of Total Nitrogen (T-N) and Total Phosphorous (T-P) in Aqueous Solution using Granular Activated Charcoal (GAC)

The present study is to explore the possibility of utilizing granular activated charcoal (GAC) for the removal of total phosphorous (T-P) and total nitrogen (T-N) in aqueous solution. Batch adsorption studies were carried out to determine the influences of various factors like initial concentration, contact time and temperature. The adsorption data showed that GAC has a similar adsorption capacity for both T-N and T-P. The adsorption degree of T-N and T-P on GAC was highly concentration dependent. It was found that the adsorption capacity of GAC is quite favorable at a low concentration. At concentrations of 1.0 mg L-1 of T-P and 2.0 mg L-1 of T-N, approximately 97 % of adsorption was achieved by GAC. The equilibrium data were fitted well to the Langmuir isotherm model. The pseudo-second-order kinetic model appeared to be the better-fitting model because it has higher R2 compared with the pseudo-first-order and intra-particle kinetic model. The theoretical adsorption equilibrium qe,cal from pseudo-second-order kinetic model were relatively similar to the experimental adsorption equilibrium qe,exp. To evaluate the effect of thermodynamic parameters at different temperatures, the change in free energy ΔG, the enthalpy ΔH and the entropy ΔS were estimated. Except for adsorption of T-P at 278 K, the ΔG values obtained were all negative at the investigated temperatures. It indicates that the present adsorption system occurs spontaneously. The adsorption process of T-N by GAC was exothermic in nature, whereas T-P showed endothermic behavior. In addition, the positive values of ΔS imply that there was the increase in the randomness of adsorption of T-N and T-P at GAC-solution interface.

Theoretical Studies of Solvent Effects on Binding of Sn (CH3)2(N-acetyl-L-cysteinate) with Single-walled Carbon Nanotube

The potential of nanotechnology to revolutionise medicine in particular seems endless, and one significant application of this technology is the use of carbon nanotubes for the targeted delivery of drug molecules. Sn(CH3)2(N-acetyl-L-cysteinate) is a drug that has been proposed as a therapeutic against the human hepatocarcinoma HCC Hep G2 cells. In our model, (N-acetyl-Lcysteinato-O,S) dimethyl tin(IV) (Sn(CH3)2(N-acetyl-L-cysteinate)) was binded to carbon nanotube. Quantum chemical ab initio calculations at HF/ (LanL2DZ+STO-3G), and HF/ (LanL2DZ+6-31G) levels in gas phase and solution have been carried out to calculate the optimized geometry, energies, dipole moments and thermochemical analysis of Sn(CH3)2(N-acetyl-L-cysteinate)-CNT complex. Results from frequency calculation (large negative values of the ΔG and high positive values of ΔS) confirmed the structural stability of the Sn(CH3)2(NAC) – CNT in both gas phase and in solution. NMR parameters such as isotropic magnetic shielding constants (σiso), anisotropic magnetic shielding tensors (σaniso), Chemical shifts (δ) and total atomic charges were also calculated using the GIAO and CSGT approaches in both gas phase and in solution to determine the structural characterization of the complex. The results in solution show that the δ, σiso, and σaniso are sensitive to hydrogen-bonding interactions. A different influence of various hydrogen bond types, N5-H·····O, C-O1·····H, and C=O24·····H was observed on the calculated NMR parameters. Finally the NMR parameters obtained from GIAO method are in good agreement with the CSGT results.

Ultrasound-assisted adsorption of 4-dodecylbenzene sulfonate from aqueous solutions by corn cob activated carbon

This study was aimed at removal of 4-dodecylbenzene sulfonate (DBS) ions from aqueous solutions by ultrasound-assisted adsorption onto the carbonized corn cob (AC). The main attention was focused on modeling the equilibrium and kinetics of adsorption of DBS onto the AC. The AC was prepared from ground dried corn cob by carbonization and activation by carbon dioxide at 880°C for 2h in a rotary furnace. The adsorption isotherm data were fitted by the Langmuir model in both the absence and the presence of ultrasound (US). The maximum adsorption capacities of the adsorbent for DBS, calculated from the Langmuir isotherms, were 29.41mg/g and 27.78mg/g in the presence of US and its absence, respectively. The adsorption process in the absence and the presence of US obeyed the pseudo second-order kinetics. The intraparticular diffusion model indicated that the adsorption of DBS ions on the AC was diffusion controlled as well as that US promoted intraparticular diffusion. The ΔG° values, −24.03kJ/mol, −25.78kJ/mol and −27.78kJ/mol, were negative at all operating temperatures, verifying that the adsorption of DBS ions was spontaneous and thermodynamically favorable. The positive value of ΔS°=187J/molK indicated the increased randomness at the adsorbent–adsorbate interface during the adsorption of DBS ions by the AC.

Ligand Effects on Reactivity of Cobalt Acyl Complexes

Hydrogenolysis reactions of cobalt acyl complexes, [Co(CO)3(L)(COR)] (L = phosphine, R = Me, nPr) have been monitored using in situ IR spectroscopy at moderate temperatures (<75 °C) and pressures (<25 bar). The reactions provide a model for the product-formation step in phosphine-modified, cobalt-catalyzed hydroformylation. The reaction kinetics are dependent on L, with the fastest rate being observed for the complex containing n-pentyl-9-phosphabicyclo[4.2.1]nonane (a5-PhobPC5). The observed dependence of rate on H2 and CO pressure is consistent with a mechanism involving initial CO dissociation, followed by reaction of [Co(CO)2(L)(COR)] with H2. Isotopic exchange experiments, monitored by IR spectroscopy, demonstrate that both terminal and acetyl carbonyls of [Co(CO)3(L)(COR)] exchange with free 13CO. Kinetic data are also reported for reactions of [Co(CO)3(L)(COR)] with triphenyltinhydride. A zero-order dependence on [Ph3SnH] (at large excess) and positive values of ΔS‡ demonstrate rate-determining CO dissociation. For a series of less bulky, symmetrical phosphines, the rates follow the sequence PEt3 < PMe2Ph ∼ PEtPh2 < PPh3 < P(4-ClC6H4)3, in accord with their electron-donating strength. Higher rates are found for more bulky phosphines, and the fastest rate is again found for L = a5-PhobPC5. Calculations using density functional theory indicate that the CO dissociation energy for [Co(CO)3(L)(COMe)] is influenced by the stereoelectronic properties of L, with steric bulk having a substantial effect. X-ray crystal structures are reported for [Co(CO)3(PEtPh2)(COMe)], [Co(CO)3(s-PhobPC5)]2, and [Co(CO)3(a5-PhobPC5)]2.

Adsorption of phosphate into waste oyster shell: thermodynamic parameters and reaction kinetics

The present study explored the feasibility of exploiting an oyster shell as an adsorbent to remove the phosphate pollutants under different laboratory experimental conditions. The batch sorption was investigated for the solution temperature and the size of the oyster shell fragments. The results demonstrated that phosphate uptake capacity (qe) increased with an increase in the solution temperature from 20 to 30°C and a decrease in the oyster shell diameter from 590 to 180μm at an initial phosphate solution concentration of 10 mg/L. The thermodynamic parameters of the adsorption process were calculated. The positive value of ΔH° (40.61 kJ/mol) indicated that the adsorption of phosphate on oyster shell was endothermic; the positive value of ΔS showed good affinity of the phosphate toward the oyster shell; the positive value of ΔG (12.60 kJ/mol) suggested that the adsorption of phosphate into an oyster shell was a nonspontaneous reaction. Following the evaluation of the thermodynamic parameters, different kinetic models, including pseudo-second-order, Elovich, and intra-particle diffusion kinetics models, were studied to evaluate the adsorption process of the phosphate into an oyster shell. The pseudo-second-order kinetic model best fitted the phosphate adsorption into a waste oyster shell. This showed that the chemisorption mechanism plays a significant role in the adsorption process. The linear form of Elovich model revealed that the actually reacting solid surface, oyster shell, was energetically heterogeneous. The intra-particle diffusion model demonstrated that the diffusion mechanism was not the dominant rate-limiting step. The above results successfully established good potentiality for the application of waste oyster shell as a phosphate pollutant removal source.

Ab initio studies of single-wall carbon nanotube for drug delivery of (N- acetyl-L-cysteinato-O, S) diphenyl tin (IV) anticancer drug

Carbon nanotubes (CNT) have emerged as a new alternative and efficient tool for transporting and translocating therapeutic molecules. CNT can be attached to drugs, and used to deliver their cargos to cells and organs. In this work, the interaction behavior of the anticancer drug Sn(C6H5)2(N-acetyl-L-cysteinate) that is called (N-acetyl-Lcysteinato-O,S) diphenyl tin (IV) when binding single-walled carbon nanotubes was studied based on the Quantum chemicalab initio calculations by using the HF/ (LanL2DZ+STO-3G) and HF/ (LanL2DZ+6-31G) levels in both gas phase and solution. Thermodynamical analysis (large negative values of the ΔG and high positive values of ΔS) confirmed the structural stability of the Sn(C6H5)2(N-acetyl-L-cysteinato-O,S) – CNT in both gas phase and in solution. Also, The thermodynamic analysis show that Sn(C6H5)2(N-acetyl-L-cysteinato-O,S) – CNT has maximum stability in methanol at 313K. Moreover, nuclear magnetic resonance (NMR) parameters such as chemical shift tensor (δ), total atomic charge and asymmetry parameter (η) have been calculated using the Gauge Independent Atomic Orbital (GIAO) method, results being compared with CGST data. From the NMR calculations, it can be seen that the NMR parameters (δ, η) at the sites of nitrogen and oxygen are significantly influenced by intermolecular hydrogen- bonding interactions but the quantity at the site of S-27 is influenced by nonspecific solute-solvent interaction such as polarisability/polarity. Key words: Sn(C6H5)2(N-acetyl-L-cysteinate), ab initio, single wall carbon nanotubes(SWCNT), drug delivery.

Study of physical chemistry on biosorption of zinc by using Chlorella pyrenoidosa

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Biosorption of heavy metals by metabolically inactive biomass of microbial organisms is an innovative and alternative technology for removal of these pollutants from aqueous solution. Presence of heavy metals in the aquatic system is posing serious problems. Zinc has been used in many industries and removal of Zn ions from waste water is significant. Biosorption is one of the economic methods used for removal of heavy metals. In the present study, the biomass obtained from the dried Chlorella pyrenoidosa was used for evaluating the biosorption characteristics of Zn ions in aqueous solutions. Batch adsorption experiments were performed with this material and it was found that the amount of metal ions adsorbed increased with the increase in the initial metal ion concentration. In this study effect of agitation time, initial metal ion concentration, temperature, pH and biomass dosage were studied. Maximum metal uptake (qmax) observed at pH 5 was 101.11 mg/g. The biosorption followed both Langmuir and Freundlich isotherm model. The adsorption equilibrium was reached in about 1 h. The kinetic of biosorption followed the second-border rate. The biomass could be regenerated using 0.1 M HNO3. A positive value of ΔH° indicated the endothermic nature of the process. A negative value of the free energy (ΔG°) indicated the spontaneous nature of the adsorption process. A positive value of ΔS° showed increased randomness at solid-liquid interface during the adsorption of heavy metals, it also suggests some structural changes in the adsorbate and the adsorbent. FTIR Spectrums of Chlorella pyrenoidosa revealed the presence of hydroxyl, amino, carboxylic and carbonyl groups. The scanning electron micrograph clearly revealed the surface texture and morphology of the biosorbent.

Studies on the complexation of Pr(III) and Nd(III) with glycyl–glycine (gly–gly) using spectral analysis of 4f–4f transitions and potentiometric titrations

The interaction of gly–gly with Pr(III) and Nd(III) have been studied in different aquated organic solvents like CH3OH, CH3CN, dioxane and DMF by using 4f–4f transitions spectra. Various energy interaction parameters like Slater Condon (Fk), Racah (Ek), Lande (ξ4f), nephelauxetic effect (β), bonding (b1/2) and percent covalency (δ) parameters have been calculated to explain the nature of complexation. The intensity parameters like oscillator strength (P) and Judd–Ofelt parameters (Tλ, λ=2, 4, 6) also support the mode of binding of gly–gly to metal ions. The results show that Pr(III) and Nd(III) with gly–gly form complexes by ionic linkages with carboxylate anion with weak covalency. The protonation constants and metal–ligand stability constants have also been determined by potentiometric measurements in aqueous medium at different temperatures (290, 300 and 310K) at constant ionic strength, 0.1moldm−1. The results show the formation of metal–ligand complexes in the stoichiometric ratio 1:1. The stability of complexes is more in Nd(III) complexes as compared to Pr(III) complexes. Thermodynamic parameters (ΔG, ΔH and ΔS) of complexes were also calculated and the negative values of ΔG and ΔH show that the complex reactions are spontaneous and exothermic. The positive values of ΔS indicate high stability of complex reactions which are enthalpy-driven.

Equilibrium and kinetic studies of copper (II) ion uptake by modified wheat shells

Abstract Natural adsorbents such as shells of unmodified wheat (RW), and modified wheat (MW) were assessed for Cu(II) adsorption from aqueous solutions. The removal of Cu(II) by these adsorbents from aqueous solution was investigated by using several parameters such as modificiation, contact time, temperature and pH. The extent of Cu(II) removal increased with increasing contact time, temperature and pH and also with modification by Reactive Orange 122 of adsorbent. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Freundlich equation fits better than the Langmuir equation. In addition, the adsorption data obtained at different temperatures of Cu(II) by adsorbents were applied to pseudo first-order, pseudo second-order and Weber-Morris equations, and the rate constants of first-order adsorption (k 1), the rate constants of second-order adsorption (k 2) and diffusion rate constants (k 3) at these temperatures were calculated, respectively. The rates of adsorption were found to conform to pseudo second-order kinetics with good correlation (R 2 ⩾ 0.989). The data obtained from adsorption isotherms at different temperatures were used to calculate some thermodynamic quantities such as free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°). It is found that ΔG° is negative, indicating that the nature of adsorption process for Cu(II) is spontaneous. The positive value of ΔH° indicates that the adsorption of Cu(II) onto adsorbents is an endothermic process. The positive value of ΔS° reflects the affinity of the adsorbent for Cu(II). As a result, the present work indicates that the wheat shells MW chemically by Reactive Orange 122, possess more efficiency in adsorbing Cu(II) ions than the unmodified one (RW).

A kinetic study of the biodegradation of textile dye mixtures by Pleurotus ostreatus fungus

The concentrations of textile dyes in a ternary mixture during biodegradation by the fungus Pleurotus ostreatus were obtained at three temperatures. The reactions followed first-order kinetics. Thermodynamic data were obtained for the degradation of each dye. High values of ΔH ‡ show the reaction is enthalpy-driven and positive values of ΔS ‡ indicate the activated complexes are less structured than the reactants. High values of ΔG ‡ and E a explain the low rates of biodegradation of the three dyes.

Removal of Lead from Aqueous Solution by an Efficient Low Cost Biosorbent

AbstractRemoval of Pb(II) ion from aqueous solution on modified sawdust obtained from Morus alba was investigated. The sample was characterized by BET surface area, EDX, FTIR and Zeta potential technique. The surface contains carbonyl and hydroxyl functional groups which act as binding sites for Pb(II) ion. Adsorption kinetics of Pb(II) on sawdust was tested by pseudo first order, Elovich and parabolic diffusion kinetic equations. The adsorption data were found to fit to Freundlich, Langmuir and Tempkin isotherms. The rate of adsorption was high at high temperature. Thermodynamic parameters like ΔH, ΔS and ΔG were calculated from the kinetic data. The positive values of ΔS reflect some structural exchange among the active site of the adsorbent and metal ion. The negative values of Gibbs free energy (ΔG) show the spontaneous nature of the process.

Synthesize of polypyrrole nanocomposite and its application for nitrate removal from aqueous solution

The aim of this research work is to investigate sorption characteristic of polypyrrole coated on the sawdust (PPy/SD) for the removal of NO3− from aqueous solutions and wastewater. The sorption of NO3− is carried out by batch method. The optimum conditions of sorption were found to be: a sorbent dose of 0.6g in 100ml of NO3− solution, contact time of 20min and pH=5. In optimum condition, removal efficiency was 84.2% for the NO3−. Three equations, i.e. Morris–Weber, Lagergren and pseudo second order have been tested to track the kinetics of removal process. The Langmuir, Freundlich and D–R are subjected to sorption data to estimate sorption capacity. It can be concluded that PPy/SD has potential to remove NO3− ions from aqueous solutions at different concentrations. Also the effect of temperature on the process was investigated. It was found that the temperature has positive effect on the process and the negative ΔG values indicated thermodynamically feasible and spontaneous nature of the sorption. The positive value of ΔS reveals the increased randomness at the solid–solution interface during the fixation of the ion on the surface of the sorbent.

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.

A Use of Cedar Cone for the Removal of a Cationic Dye from Aqueous Solutions by Sorption

In this study, cedar cone (CC), a forest waste, available in large quantity in Algeria, is proposed as novel material for the removal of basic dye Rhodamine B (RhB) from aqueous solutions. The effect of operating parameters such as the sorbent dose, initial dye concentration, stirring speed and solution temperature on the sorption kinetics of RhB was studied. The removal of RhB by sorbent increased with an increase in sorbent dose and initial concentration. Kinetic models, the pseudo-first and pseudo-second order rate equations were applied. The obtained results show that the sorption of RhB by CC was best described by the pseudo- second order kinetic model. Sorption equilibrium isotherms of RhB at different temperatures was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. The results indicate that the Langmuir model fits the data better. The thermodynamic study of Rhb sorption by CC reveals that the sorption process is spontaneous(ΔG°<0) and endothermic (ΔH°>0).The low and positive value of ΔS° indicates that affinity of Rbh molecules to the sorbent surface.

Adsorption of Grape Seed Procyanidins on Macroporous Adsorbent Resin: Isotherms and Thermodynamics

The adsorption properties,including the adsorption isotherms,thermodynamics,of grape seed procyanidins onto macroporous resin HZ818 are investigated.Both the Langmuir and Freundlich equations can provide a good fit to the adsorption isotherms, which indicates an endothermic and a favorable process in our study.The capacities of the adsorption increase with temperature. The negative values of ΔG and values of ΔH lower than 40 kJ/mol indicate a spontaneous physical adsorption, and the positive values of ΔS show the increased randomness at the solid/solution interface during the adsorption process.