Hydrophobic interaction adsorption of whey proteins: effect of temperature and salt concentration and thermodynamic analysis

The adsorptive behavior of bovine serum albumin (BSA) and beta-lactoglobulin (beta-lg) on hydrophobic adsorbent was studied at four temperatures and different salt concentrations. The Langmuir model was fitted by experimental equilibrium data showing that an increase in temperature and salt concentration results in an increase on the capacity factor of both proteins. A thermodynamic analysis coupled with isotherm measurements showed that salt concentration and temperature affected the enthalpic and entropic behavior of the adsorption process of both proteins, mainly to the beta-lg. The fast variation in the Z value for temperature over than 303.1K suggest a great conformational change occurring in the beta-lg structure, which almost duplicated the maximum adsorption capacity of this protein.     

Equilibrium and a two-stage batch adsorber design for reactive or disperse dye removal to minimize adsorbent amount

The adsorption of a reactive dye (Reactive Yellow K-4G) and a disperse dye (Disperse yellow brown S-2RFL) onto polyepicholorohydrin-dimethylamine (EPIDMA) cationic polymer modified bentonite (EPIDMA-bentonite) in batch adsorber was studied, respectively. Two equilibrium models, the Langmuir and Freundlich models were selected to follow the adsorption process. It was shown that the equilibrium experimental data for reactive dye adsorption could be well described by the Freundlich model, but for disperse dye the Langmuir model could be better. Based on the well correlated adsorption isotherm, an adsorption process design model was developed for the design of a two-stage batch adsorber to predict the minimum amount of adsorbent to achieve a specified percentage of dye removal at a given volume of wastewater effluents. The adsorption process design analysis indicated that compared with the single-stage batch adsorption, the two-stage process could significantly save adsorbent to meet the higher demands of dye removal efficiency.     

Removal of Astrazon Yellow 7GL from aqueous solutions by adsorption onto wheat bran

Adsorption kinetic and equilibrium of a basic dye (Astrazon Yellow 7GL) from aqueous solutions at various initial dye concentration (50-300 mg/l), pH (4-10), adsorbent dosage (2-8 g/l), particle size (354-846 microm) and temperature (30-50 degrees C) on wheat bran were studied in a batch mode operation. The result showed that the amount adsorbed of the dye increased with increasing initial dye concentration and contact time, whereas particle size and pH had no significant affect on the amount of dye adsorbed by the adsorbent. A comparison of kinetic models on the overall adsorption rate showed that dye/adsorbent system was best described by the pseudo second-order rate model. The removal rate was also dependent on both external mass transfer and intra-particle diffusion. The low value of the intraparticle diffusivity, 10(-11) cm2/s, indicated the significant influence of intraparticle diffusion on the kinetic control. The adsorption capacity (Q0) calculated from the Langmuir isotherm was 69.06 mg/g for at pH 5.6, 303 K for the particle size of 354 microm. The experimental data yielded excellent fits with Langmuir and Tempkin isotherm equations. Different thermodynamic parameters showed that the reaction was spontaneous and endothermic in nature.     

Biosorption of Lead from Industrial Wastewater Using Chrysophyllum albidum Seed Shell

The shell of the seed of Chrysophyllum albidum carbon was used to adsorb lead (Pb) from aqueous solution, the sorption process with respect to its equilibria and kinetics as well as the effects of pH, contact time, adsorbent mass, adsorbate concentration, and particle size on adsorption were also studied. The most effective pH range was found to be between 4.5 and 5 for the sorption of the metal ion. The first-order rate equation by Lagergren was tested on the kinetic data and the adsorption process followed first-order rate kinetics. Isotherm data were analyzed for possible agreement with the Langmuir and Freundlich adsorption isotherms; the Freundlich and Langmuir models for dynamics of metal ion uptake proposed in this work fitted the experimental data reasonably well. However, equilibrium sorption data were better represented by Langmuir model than Freundlich. The adsorption capacity calculated from Langmuir isotherm was 72.1 mg Pb (II) g^{- 1} at initial pH of 5.0 at 30°C for the particle size of 1.00 to 1.25 mm with the use of 2.0 g/100 ml adsorbent mass. The structural features of the adsorbent were characterized by Fourier transform infrared (FTIR) spectrometry; the presence of hydroxyl, carbonyl, amide, and phosphate groups confirms the potential mechanism adsorption of the adsorbent. This readily available adsorbent is efficient in the uptake of Pb (II) ion in aqueous solution, thus, it could be an excellent alternative for the removal of heavy metals and organic matter from water and wastewater.     

Optimum Sorption Isotherm by Linear and Nonlinear Methods for Safranin onto Alkali-Treated Rice Husk

Rice husk, a lignocellulosic by-product of the agroindustry, was treated with alkali and used as a low-cost adsorbent for the removal of safranin from aqueous solution in batch adsorption procedure. In order to estimate the equilibrium parameters, the equilibrium adsorption data were analyzed using the following two-parameter isotherms: Freundlich, Langmuir, and Temkin. A comparison of linear and nonlinear regression methods in selecting the optimum adsorption isotherm was applied on the experimental data. Six linearized isotherm models (including four linearized Langmuir models) and three nonlinear isotherm models are thus discussed in this paper. In order to determine the best-fit isotherm predicted by each method, seven error functions namely, coefficient of determination (r ²), the sum of the squares of the errors (SSE), sum of the absolute errors (SAE), average relative error (ARE), hybrid fractional error-function (HYBRID), Marquardt's percent standard deviation (MPSD), and the chi-square test (χ²) were used. It was concluded that the nonlinear method is a better way to obtain the isotherm parameters and the data were in good agreement with the Langmuir isotherm model.     

Adsorption of methylene blue dye from aqueous solution by sugar extracted spent rice biomass

This study was aimed at using sugar extracted spent rice biomass (SRB) as a potential adsorbent to remove methylene blue (MB) dye from aqueous solution. The SRB was used without any modification. A three factor full factorial experimental design (2(3)) was employed to investigate the effect of factors (adsorbent dose, dye concentration, temperature) and their interaction on the adsorption capacity and color removal. Two levels for each factor were used; adsorbent dose (0.25-0.5g/100mL), dye concentration (25-50mg/L), and temperature (25-45°C). Initial dye concentration and adsorbent dosage were found as significant factors for the adsorption of MB dye. Langmuir isotherm (R(2)>0.998) best explained the equilibrium of MB adsorption on SRB with monolayer adsorption capacity of 8.13mg/g. The pseudo-second order model (R(2)>0.999) was best fitted to explain the adsorption kinetics. Thermodynamic investigation revealed that the adsorption process was spontaneous, endothermic, and was feasible to treat dyeing wastewater.     

Human Serum Protein Adsorption onto Synthesis Nano-Hydroxyapatite

Adsorption of human serum proteins (Albumin and total protein) onto high purity synthesis nano-hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, has been studied in a wide temperature range by UV–visible spectrophotometer. Adsorption isotherm is basically important to describe how solutes interact with adsorbent, and is critical in optimizing the use of adsorbent. In the present study, the experimental results were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (DR) models to obtain the characteristic parameters of each model and square of the correlation coefficients (R²). According to the results, the DR isotherm model had the best agreement with the experimental data. The effect of temperature on adsorption of human serum proteins (HSP) onto the synthesized nano-HA was studied. The experimental results indicated that temperature increase generally causes an increase in the adsorption of HSP onto the nano-HA. This is basically due to the effect of temperature on the HSP activity and its diffusion rate on HA surfaces.     

Biosorption of Chromium,Copper, and Nickel Ions by Tamarindus Indica Fruit Nut Testa

Biosorption of chromium, copper, and nickel from aqueous solution by Tamarindus indica fruit nut testa (TFNT) in its pristine and acid-treated forms was studied under equilibrium and column-flow conditions. TFNT, a tannin-containing material, was characterized by energy dispersion x-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectral techniques and surface analysis. The effect of experimental variable parameters such as pH, concentration of metal ions, amount of adsorbent, and contact time on adsorption was investigated. Batch isothermal equilibrium data were analyzed on the basis of Langmuir and Freundlich adsorption isotherms. The kinetics of the adsorption process were studied in terms of Lagergren first-order kinetic model. The monolayer adsorption capacities of pristine and acid-treated forms of tamarind seed coat were found to be 44.8 and 77.5 mg/g for Cr(VI), 55.8 and 99.0 mg/g for Ni(II), and 84.7 and 85.4 mg/g for Cu(II) ions, respectively. The column-flow adsorption data were used to obtain breakthrough curves. The biosorbent loaded with the metal ions was regenerated using 1.0 M HCl and the regenerated bed was used for subsequent adsorption-desorption cycle.     

Adsorption of Cd(II) ions from aqueous solutions using activated carbon prepared from olive stone by ZnCl2 activation

This study is aimed to remove Cd(II) ions from aqueous solutions by adsorption. As adsorbent, activated carbon prepared from olive stone, an agricultural solid by-product was used. Different activating agent (ZnCl(2)) amounts and adsorbent particle size were studied to optimize adsorbent surface area. The adsorption experiments were conducted at different parameters such as, adsorbent dose, temperature, equilibrium time and pH. According to the experiments results, the equilibrium time, optimum pH, adsorbent dosage were found 60 min, pH > 6 and 1.0 g/50 ml respectively. The kinetic data supports pseudo-second order model and intra-particle model but shows very poor fit for pseudo-first order model. Adsorption isotherms were obtained from three different temperatures. These adsorption data were fitted with the Langmuir and Freundlich isotherms. In addition, the thermodynamic parameters, standard free energy (DeltaG(0)), standard enthalpy (DeltaH(0)), standard entropy (DeltaS(0)) of the adsorption process were calculated. To reveal the adsorptive characteristics of the produced active carbon, BET surface area measurements were made. Structural analysis was performed using SEM-EDS. The resulting activated carbons with 20% ZnCl(2) solution was the best sample of the produced activated carbons from olive stone with the specific surface area of 790.25 m(2)g(-1). The results show that the produced activated carbon from olive stone is an alternative low-cost adsorbent for removing Cd(II).     

Scavenging Rhodamine B dye using moringa oleifera seed pod

Moringa oliferia seed pod was modified using orthophosphoric acid (H₃PO₄) and used as adsorbent for sequestering Rhodamine B (Rh-B) dye from aqueous solution. The acid-modified adsorbent (MOSPAC) was characterized using Scanning Electron microscopy (SEM), Fourier Transform Infra Red (FTIR), Energy Dispersive X-ray (EDX), pH point of zero charge (pH_pzc) and Boehm Titration (BT) techniques, respectively. Operational parameters such as contact time, initial dye concentration, adsorbent dosage, pH and solution temperature were studied in batch process. Optimum dye adsorption was observed at pH 3.01. Equilibrium adsorption data was tested data using four different isotherm models: Langmuir, Freundlich, Temkin and Dubinin-Radushkevich. Langmuir isotherm model fitted most with maximum monolayer adsorption capacity of 1250 mg g^–1. Pseudo-second-order kinetic model provided the best correlation for the experimental data. Thermodynamic study showed that the process is endothermic, spontaneous and feasible. MOSPAC is an effective adsorbent for the removal of RhB dye from aqueous solutions.     

Removal of Cu2+ from aqueous solution by adsorption onto a novel activated nylon-based membrane

A novel activated nylon-based membrane was prepared and applied as an adsorbent for the removal of Cu2+ from aqueous solutions. It involved three stages: (i) deposition of a chitosan layer that functionalized the nylon membrane, (ii) cross-linking with epichlorohydrin to stabilize the polymer layer and enabling grafting, and (iii) iminodiacetic acid grafting. SEM and EDX techniques were used to characterize the composition of the membranes. Dynamic adsorption experiments on membranes were carried out at various pH values, contact times, adsorption dosages and initial metal concentrations to determine optimum membrane adsorption properties. The adsorption isotherm relating to Cu2+ fitted the Langmuir equation and an adsorption equilibrium constant and adsorption capacity of 2.345x10(-3)mg/ml and 10.794mg/g were determined, respectively. The experimental data was analyzed using two adsorption kinetic models, pseudo-first-order and pseudo-second-order with the latter system providing the best fit. Finally complete regeneration of the activated nylon membrane was possible using 100mmol/l Na2EDTA.     

Microwave assisted thermal treatment of defective coffee beans press cake for the production of adsorbents

Defective coffee press cake, a residue from coffee oil biodiesel production, was evaluated as an adsorbent for removal of basic dyes (methylene blue – MB) from aqueous solutions. The adsorbent was prepared by microwave treatment, providing a significant reduction in processing time coupled to an increase in adsorption capacity in comparison to conventional carbonization in a muffle furnace. Batch adsorption tests were performed at 25 °C and the effects of particle size, contact time, adsorbent dosage and initial solution pH were investigated. Adsorption kinetics was better described by a second-order model. The experimental adsorption equilibrium data were fitted to Langmuir, Freundlich and Tempkin adsorption models, with Langmuir providing the best fit. The results presented in this study show that microwave activation presents great potential as an alternative method in the production of adsorbents.     

Adsorption kinetics of azinphosmethyl from aqueous solution onto pyrolyzed Horseshoe sea crab shell from the Atlantic Ocean

The adsorption behavior of azinphosmethyl on pyrolyzed Horseshoe Crab (Limulus polyphemus) outer shell, as a residue, from the Atlantic Ocean, collected along the Maine coast, USA, has been studied with regards to its kinetic and equilibrium conditions, taking into account adsorbate concentrations of 2 x 10(-3), 4 x 10(-3), 6 x 10(-3), and 8 x 10(-3), as well as temperatures of 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C. The yield of adsorption of azinphosmethyl from aqueous solution ranged from 56.1% to 61% with temperature increasing. Kinetic studies showed that adsorption rate decreased as the initial azinphosmethyl concentration increased. It was found, that the adsorption reaction obeyed first-order kinetics. The overall rate constants were estimated for different temperatures. The activation energy for adsorption was about 1.52 kJmol(-1), which implies that azinphosmethyl mainly adsorbed physically onto Horseshoe Crab outer shell. Langmuir and Freundlich isotherms were applied to the experimental data and isotherm constants were calculated. The thermodynamic parameters DeltaG0, DeltaH0 and DeltaS0 for the adsorption reaction were evaluated based on equilibrium data and in connection with this result the thermodynamic aspects of adsorption reaction were discussed. The adsorption was found to be endothermic in nature. The adsorbent used in this study proved highly efficient for the removal of azinphosmethyl.     

Sulfate-induced effects in the on-pathway intermediate of the bacterial immunity protein Im7

Intermediates have now been identified in the folding of a number of small, single-domain proteins. Here we describe experiments to determine the effect of Na(2)SO(4) on the properties of the on-pathway intermediate formed early during the folding of the four-helical protein, Im7. This intermediate, studied previously in 0.4 M Na(2)SO(4), contains three of the four native helices and is fascinating in that several residues in helices I, II, and IV make non-native interactions that stabilize this state. Whether these contacts form as a consequence of the presence of Na(2)SO(4), however, remained unresolved. Using kinetic analysis of the effect of Na(2)SO(4) on the unfolding and refolding kinetics of Im7*, combined with detailed analysis of the resulting chevron plots, we show that decreasing the concentration of Na(2)SO(4) from 0.4 to 0 M destabilizes the intermediate and rate-limiting transition (TS2) states by 7 and 10 kJ mol(-)(1), respectively, and has little effect on the relative compactness of these states compared with that of the unfolded ensemble (beta(I) approximately 0.8, beta(TS2) approximately 0.9 in 0 to 0.4 M Na(2)SO(4)). Analysis of 10 variants of the protein in 0.2 M Na(2)SO(4) using Phi-values showed that the structural properties of the intermediate and TS2 are not altered significantly by the concentration of the kosmotrope. The data demonstrate that the rapid formation of a compact intermediate stabilized by non-native interactions during Im7* folding is not induced by high concentrations of the stabilizing salt, but is a generic feature of the folding of this protein.     

Preparation,Characterization and Application of Magnetic Fe3O4-CS for the Adsorption of Orange I from Aqueous Solutions

Fe₃O₄ (Fe₃O₄-CS) coated with magnetic chitosan was prepared as an adsorbent for the removal of Orange I from aqueous solutions and characterized by FTIR, XRD, SEM, TEM and TGA measurements. The effects of pH, initial concentration and contact time on the adsorption of Orange I from aqueous solutions were investigated. The decoloration rate was higher than 94% in the initial concentration range of 50–150 mg L⁻¹ at pH 2.0. The maximum adsorption amount was 183.2 mg g⁻¹ and was obtained at an initial concentration of 400 mg L⁻¹ at pH 2.0. The adsorption equilibrium was reached in 30 minutes, demonstrating that the obtained adsorbent has the potential for practical application. The equilibrium adsorption isotherm was analyzed by the Freundlich and Langmuir models, and the adsorption kinetics were analyzed by the pseudo-first-order and pseudo-second-order kinetic models. The higher linear correlation coefficients showed that the Langmuir model (R² = 0.9995) and pseudo-second-order model (R² = 0.9561) offered the better fits.     

Biosorptive removal of arsenic from drinking water

A biomass derived from the plant Momordica charantia has been found to be very efficient in arsenic(III) adsorption. An attempt was made to use this biomass for arsenic(III) removal under different conditions. The parameters optimized were contact time (5-150 min), pH (2-11), concentration of adsorbent (1-50 g/l), concentration of adsorbate (0.1-100mg/l), etc. It was observed that the pH had a strong effect on biosorption capacity. The optimum pH obtained for arsenic adsorption was 9. The influence of common ions such as Ca(2+), Mg(2+), Cd(2+), Se(4+), Cl(-), SO(4)(2-), and HCO(3)(-), at concentrations varying from 5 to 1000 mg/l was investigated. To establish the most appropriate correlation for the equilibrium curves, isotherm studies were performed for As(III) ion using Freundlich and Langmuir adsorption isotherms. The pattern of adsorption fitted well with both models. The biomass of M. charantia was found to be effective for the removal of As(III) with 88% sorption efficiency at a concentration of 0.5mg/l of As(III) solution, and thus uptake capacity is 0.88 mg As(III)/gm of biomass. It appears that this biomass should be used as a palliative food item. Further it also appears that the dietary habits may play a role in the toxic effects of ingested arsenic.     

Differential sensitivity of stomatal and non-stomatal components to NaCl or Na2SO4 salinity in horsegram, Macrotyloma uniflorum (Lam.)

14CO2 assimilation rate (P), leaf diffusive conductance (gs), photosynthetic electron flow, and activities of enzymes of Calvin cycle were studied in a horsegram [Macrotyloma uniflorum (Lam.)] in response to salinity induced by NaCl or Na2SO4. A significant reduction in P and gs by both salt treatments was registered. Na2SO4 caused a greater reduction in gs than the NaCl salinity. Studies with isolated chloroplasts confirmed a greater sensitivity to NaCl than to Na2SO4. Salinity inhibited the photosynthetic electron transport. The activity of ribulose-1,5-bisphosphate carboxylase (E.C.4.1.1.39) was under salinity inhibited more than the activities of other three enzymes of the Calvin cycle, ribulose-5-phosphate kinase (E.C.2.7.1.19), ribose-5-phosphate isomerase (E.C.5.3.16), and NADP-glyceraldehyde-3-phosphate dehydrogenase (E.C.1.2.13). These inhibitions lead to a reduced capacity for ribulose-1,5-bisphosphate regeneration. Isolated chloroplasts extracted from salt stressed plants and supplemented with the substrates of Calvin cycle could elevate P, but the P was always lower than in the controls. Decreased P in horsegram exposed to high salinity can be attributed to both stomatal and non-stomatal components, however, the sensitivity to the salt source, NaCl or Na2SO4, was different.     

Adsorption-desorption of BSA to highly substituted dye-ligand adsorbent: quantitative study of the effect of ionic strength

Cibacron Blue 3GA was immobilized on Sepharose CL-6B to obtain a highly substituted dye-ligand adsorbent which dye concentration was 17.4?μmol dye per gram wet gel. This adsorbent had a highly binding capacity for bovine serum albumin (BSA). The effects of ionic strength on the adsorption and desorption of BSA to the adsorbent were studied. Adsorption isotherms were expressed by the Langmuir model. The quantitative relationships between the model parameters and the ionic strength were obtained. The desorptions were performed by adding salt to the BSA solutions in which adsorption equilibria had been reached. Adding salt to the solution resulted in the desorption of the bound protein. It was found that the isotherm obtained from the desorption experiments agreed well to the isotherm obtained from the adsorption experiments at the same ionic strength. The result demonstrated that the adsorption of BSA to the highly substituted adsorbent was reversible.     

Adsorption of Methylene Blue Dye on Pure and Carbonized Water Weeds

The influence of process variables in batch adsorption has been used to assess the removal of methylene blue dye from aqueous solution using pure and carbonized biomasses of water hyacinth and water spinach. Dried leaves of the water weeds were carbonized at temperature up to 750°C. The optimum removal of dye was achieved at pH 10, 30°C, and 55 min at a dye concentration of 10 mg/L. In an attempt to describe the adsorption process, the equilibrium isotherm for each adsorbent was determined using Langmuir and Freundlich adsorption isotherm models. Maximum adsorption capacities based on the Langmuir model for pure and carbonized water hyacinth were (mg/g) 7.05 and 2.07, respectively, whereas those of pure and carbonized water spinach were 1.25 and 5.32, respectively. It was observed that the equilibrium data were well fit by both the Freundlich and Langmuir isotherms as R ² > .97. This study demonstrates that the two waterweeds are effective, environmentally friendly, and inexpensive biomaterials for the removal of color from industrial effluents.