Deposition of colloid particles on protein layers: fibrinogen on mica

Colloid particle deposition was applied to characterize fibrinogen (Fb) monolayers on mica, which were produced by controlled adsorption under diffusion transport. By adjusting the time of adsorption and the bulk Fb concentration, monolayers of desired surface concentration were obtained. The surface concentration of Fb was determined directly by AFM enumeration of single molecules adsorbed over the substrate surface. It was proven that Fb adsorbed irreversibly on mica both at pH 3.5 and at pH 7.4 with the rate governed by bulk transport. The electrokinetic properties of Fb monolayers produced in this way were studied using the streaming potential method. The dependence of the apparent zeta potential of Fb monolayers was determined as a function of the coverage. It was shown that for pH 3.5 the initial negative zeta potential of the mica substrate was converted to positive for Fb coverage exceeding 0.16. On the other hand, for pH 7.4, the zeta potential of a Fb-covered mica remained negative for the entire coverage range. The charge distribution in Fb monolayers was additionally studied using the colloid deposition method, in which negatively and positively charged polystyrene latex particles (ca. 800 nm in diameter) were used. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH 3.5 and 7.4, respectively. These results suggested that for pH 7.4, the distribution of charge on Fb molecules was heterogeneous, characterized by the presence of positive patches, whereas the average zeta potential was negative, equal to -19 mV. The utility of the colloid deposition method for studying Fb monolayers was further demonstrated in deposition experiments involving positive latex particles. It was shown that for a rather broad range of fibrinogen coverage, both the positive and the negative latex particles can adsorb on surfaces covered by Fb, which behaved, therefore, as superadsorbing surfaces. It was also concluded that the colloid deposition method can be used to determine the Fb bulk concentration for the range inaccessible for other methods.     

Protonation of Lysozymes and Its Consequences for the Adsorption onto a Mica Surface

Several physicochemical properties of chicken egg white lysozyme (LSZ) in electrolyte solutions were determined. The hydrodynamic diameter of LSZ at an ionic strength of 0.15 M was found to be 4.0 nm. Using the determined parameters, the number of uncompensated (electrokinetic) charges, N(c), on the molecule surface was calculated from the electrophoretic mobility data. It was found that the N(c) = 2.8 at pH = 3.0 and an ionic strength of I = 0.15 M. At the lower ionic strength, I = 1 × 10(-3) M, this positive charge increased to N(c) = 5.6 at a pH = 3.0 The physicochemical characteristics were supplemented by the dynamic viscosity measurements. The intrinsic viscosity and the hydrodynamic diameter results were compared with theoretical predictions from Brenner's model. Using this approach, it was found that the effective molecule length of LSZ is equal to L(ef) = 5.6 nm. Additional information on the LSZ adsorbed films was obtained by the contact angle measurements. The notably large contact angles were measured on LSZ films formed under the conditions where both the LSZ and the mica were oppositely charged. The higher the positive zeta potential of LSZ, the greater the contact angle measured, which indicates that LSZ affinity for the adsorption on mica increases with its uncompensated charge. The adsorption dependence on the zeta potential of LSZ was explained, assuming a roughly uniform distribution of the net charge on the molecule surface. This assumption is supported by the results of depositing negatively charged, fluorescent latex particles onto the mica surface, which had been modified by LSZ adsorption. The highest latex coverage was formed on mica surfaces that had first been coated with LSZ solutions of lower pH, as a result of the increasing charge of LSZ monolayers in this condition.     

Characterization of poly(ethylene imine) layers on mica by the streaming potential and particle deposition methods

Deposition kinetics of polystyrene latex (averaged particle size of 0.66 microm) on mica covered by poly(ethylene imine) (PEI), a cationic polyelectrolyte having an average molecular mass of 75,000 g mol(-1), was studied using the impinging-jet method. The hydrodynamic radius of PEI, determined by PCS measurements, was 5.3 nm. The electrophoretic mobility of PEI was measured as a function of pH for ionic strengths of 10(-3) and 10 (-2) M, which made it possible one to determine the amount of electrokinetic charge of the molecule and its zeta potential. Formation of the polyelectrolyte layer on mica was followed by measuring the streaming potential in the parallel-plate channel. From these measurements, the dependence of the apparent zeta potential of mica on the surface coverage of PEI was determined. The amount of adsorbed PEI on mica was calculated from the convective diffusion theory. These results were quantitatively interpreted in terms of the theoretical model postulating a particle-like adsorption mechanism for PEI with not too significant shape deformation upon adsorption. On the other hand, the Gouy-Chapman model postulating the adsorption in the form of flat disks was proved inappropriate. After the surface was fully characterized, particle deposition experiments were carried out with the aim of finding the correlation between the polymer coverage and the initial rate of latex particle deposition. In the range of small polyelectrolyte coverage, a monotonic relation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Theta(PEI)>0.25, the initial particle deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. These results were interpreted theoretically by postulating that an effective immobilization of colloid particles occurred on local polyelectrolyte assemblages containing between two and three PEI molecules.     

Colloid particle and protein deposition - electrokinetic studies

Recent developments in the electrokinetic determination of particle, polyelectrolyte and protein deposition at solid/electrolyte interfaces, are reviewed. In the first section basic theoretical results are discussed enabling a quantitative interpretation of the streaming current/potential and microelectrophoretic measurements. Experimental results are presented, pertinent to electrokinetic characteristics of simple (homogeneous) surfaces such as mica, silica and various polymeric surfaces used in protein studies. The influence of the ionic strength, background electrolyte composition and pH is discussed, and the effective (electrokientic) charge of these interfaces is evaluated. In the next section, experimental data obtained by streaming potential measurements for colloid particle mono- and bilayers are presented and interpreted successfully in terms of available theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of more complicated experiments performed for polyelectrolyte and protein covered surfaces. Results are discussed, obtained for cationic polyelectrolytes (PEI, PAH) and fibrinogen adsorbing on mica, interpreted quantitatively in terms of the theoretical approach postulating a heterogeneous 3D charge distribution. The Gouy-Chapman model, based on the continuous charge distribution proved inadequate. Interesting experimental data are also discussed, obtained by electrophoretic methods in the case of protein adsorption on colloid latex particles. In the last section, supplementary results on particle deposition on heterogeneous surfaces produced by controlled protein adsorption are discussed. Quantitative relationships between the amount of adsorbed protein, zeta potential of the interface and the particle coverage are specified. Possibility of evaluating the heterogeneity of protein charge distribution is pointed out. The anomalous deposition of colloid particles on protein molecules bearing the same sign of zeta potential, which contradicts classical DLVO theory, is interpreted in terms of the fluctuation theory. It is concluded that theoretical and experimental results obtained for model colloid systems and flat interfaces can be effectively used for interpretation of protein adsorption phenomena, studied by electrophoresis. In this way the universality of electrokinetic phenomena is underlined.     

Reversible and irreversible adsorption of particles on homogeneous surfaces

The kinetics of localized reversible and irreversible adsorption of interacting particles on homogeneous surfaces was analysed. Asymptotic analytical equations were derived for the surface blocking parameter B(0), and for adsorption kinetics and adsorption isotherms in the limit of low and high surface concentrations. It was found that the geometrical blocking effect was much more pronounced than the Langmuir model predicts, especially for high surface concentrations and low ionic strengths of suspensions.The new adsorption isotherm formulated indicates that for a large adsorption constant, K_a, the equilibrium surface concentration becomes proportional to K^−1/3_a, whereas in the Langmuir model this quantity is approached as K⁻¹_a (for K_a ≫I). In the case of irreversible adsorption the theoretical predictions were experimentally tested by applying the direct microscope observation method. Monodisperse suspensions of negatively charged latex particles were used in these experiments with silanized mica sheets as the adsorbing surface. Our theoretical predictions were quantitatively confirmed, indicating that the Langmuir model is not appropriate for describing localized adsorption of particles on homogeneous surfaces.     

Influencing factors on heterogeneous water oxidation catalysis by di-μ-oxo dimanganese complex on mica as a synthetic model of photosystem II

The influencing factors on heterogeneous water oxidation catalysis (WOC) were investigated in a synthetic photosystem II model developed by adsorbing [(OH₂)(terpy)Mn^III(μ-O)₂Mn^IV(terpy)(OH₂)]³⁺ (terpy = 2,2′:6′,2″-terpyridine) (1) as an oxygen evolving center onto mica. For chemical WOC using a Ce⁴⁺ oxidant, the catalytic activity of 1 on mica increased by a factor of 2.3 or 1.4 by co-adsorption (0.015 mmol g^?1) of redox-inactive trications of Al³⁺ or Ce³⁺ with 1 (0.15 mmol g^?1), respectively, whereas it decreased by co-adsorption (0.25 mmol g^?1) of excess Al³⁺ or Ce³⁺. The cooperative catalysis by two equivalents of the adsorbed 1 for water oxidation could be facilitated by enrichment of 1 by trications at their low co-adsorption conditions. The decreased catalytic activity at high trications co-adsorption conditions could be explained by impeded penetration of Ce⁴⁺ oxidant ions into a mica interlayer. For photochemical WOC containing a [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) photoexcitation center in mica, the drying treatment at 65 °C under the vacuum after 1 adsorption was required in adsorbate preparation, possibly to maintain favorable arrangement of 1 and [Ru(bpy)₃]²⁺ in a mica interlayer. The drying treatment at 65 °C under the vacuum after [Ru(bpy)₃]²⁺ adsorption inactivated the photochemical WOC. The proton-coupled electron transport from interior [Ru(bpy)₃]²⁺ centers to ones near the surface in mica is considered to be suppressed by the drying treatment, which could be responsible for the inactivated photochemical WOC.     

Adsorption and thermodynamics of biosurfactant,surfactin, monolayers at the air-buffered liquid interface

Adsorption of surfactin, a powerful lipopeptide biosurfactant, at the air-liquid interface has been investigated in this article. The adsorption took place from buffered solutions containing relatively high concentrations of surfactin co- and counterions. Dynamic surface tension measurements were used to follow the self-assembly of surfactin at the interface until equilibrium surface pressure Π ^e is reached at a given surfactin concentration (C _s). Gibbs adsorption equation in conjunction with the Langmuir adsorption isotherm was used to predict surfactin surface excess as a function of the biosurfactant concentration up to the critical micelle concentration (CMC). The predicted surface excess at saturation (Γ _∞ ) is 1.05?±?0.05 μmol m^?2, corresponding to an area per molecule (A _∞ ) of 159?±?8 Å². The adsorption equilibrium constant (K?=?(1.5?±?0.6)?×?10⁶ M^‐?1) was also estimated from the nonlinear regression of Π ^e???C _s data in region B of the Π ^e???ln?C _s plot. The value of K suggests that surfactin has strong affinity for the interface, which is in line with its known high surface activity. Gibbs elasticity (E _G) of the interfacial surfactin monolayers, which is an important thermodynamic property, was also predicted at different surfactin concentrations. The limiting value (at the CMC) of E _G was found to be 183 mN m^?1, which is comparable to those reported in the literature for similar systems. The findings reported in this work reveal that the surface tension measurements coupled with appropriate theoretical analysis could provide useful information comparable to those obtained using highly sophisticated techniques.     

Adsorption of UO2 2+ on poly(N,N-diethylacrylamide-co-acrylic acid): effects of pH, ionic strength, initial uranyl concentration, and temperature

We prepared poly(N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) microgels which could efficiently remove UO₂ ²⁺ from aqueous solutions. In this study, the effect of adsorption parameters such as pH value, adsorbent dose, shaking time, and temperature has investigated. It is found that the pseudo-second-order model is more suitable for our experiment. The adsorption kinetic data indicated that the chemical adsorption was the swiftness processes, the adsorption equilibrium could be achieved within 30 min. And there are very good correlation coefficients of linearized equations for Langmuir isotherm model, which indicated that the sorption isotherm of the hydrogel for UO₂ ²⁺ can be fitted to the Langmuir isotherm model. The adsorption process was spontaneous (?G ⁰ < 0) and exothermic (?H ⁰ < 0). The adsorbed UO₂ ²⁺ can be desorbed effectively by 0.1 M HNO₃ and the adsorption capacity is not significantly reduced after five cycles. Present study suggests that this P(DEA-co-AA) can be used as a potential adsorbent for sorption UO₂ ²⁺ and also provide a simple, fast separation method for removal of UO₂ ²⁺ ions from aqueous solution.     

Adsorption and migration of <Superscript>241</Superscript>Am in aerated zone soil

As an important radioisotope in nuclear industry and other fields, ²⁴¹ Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful reference for disposal of ²⁴¹Am waste with low-medium radioactivity, the adsorption and migration behavior of ²⁴¹Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that more than 98% of the total ²⁴¹Am could be adsorbed from ²⁴¹Am solution of 0.32·10⁻⁷−1.1·10⁻⁷ mol/l by the soil at pH 4–9. The adsorption of ²⁴¹Am on the soil was a pH-dependent process at pH<4, but for pH>4, the adsorption rate of ²⁴¹Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption of ²⁴¹Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of ²⁴¹Am and adsorption capacities of ²⁴¹Am can be described by the Freundlich adsorption equation. Adsorption of ²⁴¹Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated EDTA solution, C₂O₄ ²⁻ and CO₃ ²⁻. It was also noted that the adsorption rate of ²⁴¹Am drops in solutions containing Eu³⁺ or Nd³⁺, even 0.5 times above the ²⁴¹Am concentration. A migration distance of 8 mm for ²⁴¹Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient sorbent for ²⁴¹Am and can inhibit the migration of ²⁴¹Am.     

An efficient p-tetranitrocalix[4]arene based adsorbent for the removal of carbofuran from aqueous media

Present study describes the adsorption of carbofuran (CF) from aqueous solutions using p-tetranitrocalix[4]arene based modified silica through batch and column methods. Various parameters were optimized including initial pesticide concentrations (5 mg L^?1), pH (2–10), contact time (60 min) and adsorbent dosage (30 mg). Modified silica was characterized by FT-IR and scanning electron microscope. The adsorption was further explained by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models. Moreover, adsorption kinetics and adsorption thermodynamics were also investigated. Adsorption in dynamic mode was evaluated by breakthrough volumes and the Thomas model, applying batch conditions using 30 mg of modified silica at pH 5. It has been noticed that CF removal efficiency of modified silica was 98 % as compared to bare silica (48 %). Adsorption of CF on modified silica was found to be multilayer and physical in nature. Consequently, adsorption obeys pseudo-second-order kinetic equation following external mass transfer diffusion process as the rate-limiting step. Thermodynamic parameter (ΔG, ΔS, ΔH) values suggest that the adsorption of CF is spontaneous and exothermic in nature. Thomas model rate constant k _TH (cm³ mg^?1 min^?1) and maximum solid phase concentration (q _o mg g^?1) was found to be 0.52 and 12.3, respectively, in dynamic mode.     

Dual cloud point extraction coupled with hydrodynamic-electrokinetic two-step injection followed by micellar electrokinetic chromatography for simultaneous determination of trace phenolic estrogens in water samples

A dual cloud point extraction (dCPE) off-line enrichment procedure coupled with a hydrodynamic–electrokinetic two-step injection online enrichment technique was successfully developed for simultaneous preconcentration of trace phenolic estrogens (hexestrol, dienestrol, and diethylstilbestrol) in water samples followed by micellar electrokinetic chromatography (MEKC) analysis. Several parameters affecting the extraction and online injection conditions were optimized. Under optimal dCPE–two-step injection–MEKC conditions, detection limits of 7.9–8.9 ng/mL and good linearity in the range from 0.05 to 5 μg/mL with correlation coefficients R ²?≥?0.9990 were achieved. Satisfactory recoveries ranging from 83 to 108 % were obtained with lake and tap water spiked at 0.1 and 0.5 μg/mL, respectively, with relative standard deviations (n?=?6) of 1.3–3.1 %. This method was demonstrated to be convenient, rapid, cost-effective, and environmentally benign, and could be used as an alternative to existing methods for analyzing trace residues of phenolic estrogens in water samples.

Optimization of fundamental parameters in routine production of 90Y-hydroxyapatite for radiosynovectomy

Hydroxyapatite was applied as a carrier adsorbing ⁹⁰Y³⁺ ions for ⁹⁰Y-HA colloid production. The radiopharmaceutical colloid was prepared by adding an acidic solution of ⁹⁰YCl₃ to HA suspension in saline solution. Effective parameters on labeling of ⁹⁰Y-HA were evaluated. Adsorption and cation-exchange properties were studied using inductively coupled plasma elemental analysis and N₂ adsorption–desorption isotherm method. Radionuclidic purity was over 99.9 %. Labeling yield and radiochemical purity were >99 %. Radiochemical purity was evaluated also in human albumin for 7 days at 37 °C. Biodistribution studies have shown complete retention of injected radioactivity at the administration site up to 72 h.     

Removal of cadmium(II) and lead(II) ions from model aqueous solutions using sol–gel-derived inorganic oxide adsorbent

A study was conducted concerning the preparation and application of a novel synthetic oxide adsorbent of MgO-SiO₂ type. The material was prepared via a sol–gel route, utilizing magnesium ethoxide and tetraethoxysilane as precursors of magnesium oxide and silica respectively, and ammonia as a catalyst. The powder was comprehensively analyzed with regard to chemical composition (EDS method), crystalline structure, morphology, characteristic functional groups, electrokinetic stability and porous structure parameters (BET and BJH models). The synthesized oxide adsorbent is amorphous, with irregularly shaped particles, a relatively large surface area of 612 m²/g, and negative surface charge over almost the whole pH range. Comprehensive adsorption studies were performed to investigate the adsorption of Cd(II) and Pb(II) ions on the MgO–SiO₂ oxide adsorbent, including evaluation of adsorption kinetics and isotherms, the effect of pH, contact time and mass of adsorbent. It was shown that irrespective of the conditions of the adsorption process, the synthesized MgO–SiO₂ adsorbent exhibits slightly better affinity to lead(II) than to cadmium(II) ions (sorption capacity of 102.02 mg(Pb²⁺)/g and 94.05 mg(Cd²⁺)/g). The optimal time for removal of the analyzed metal ions was 60 min, although adsorption reached equilibrium within 10 min for Pb(II) and within 15 min for Cd(II) ions, which was found to fit well with a type 1 pseudo-second-order kinetic model. Additionally, adsorption efficiency was affected by the pH of the reaction system—better results were obtained for pH ≥7 irrespective of the type of metal ion.     

Adsorption kinetics and equilibrium modeling of cesium on copper ferrocyanide

The copper ferrocyanide (CuFC) prepared in this study was characterized using X-ray diffraction and scanning election microscopy. The distribution of particle sizes of the CuFC suspension was determined. The adsorption kinetics data were evaluated for an intraparticle diffusion model, a pseudo-first order model and a pseudo-second order model at temperatures of 288, 298 and 308 K, respectively. It was found that the adsorption process of Cs⁺ on CuFC was best described by a pseudo-second order kinetic model, with a correlation coefficient (R ²) equal to 1.000, and the adsorption rate constant increased with increasing temperature. This result indicated that chemisorptions took place during the adsorption process. The adsorption equilibrium data fit well to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The mean adsorption energy (E) between 11 and 13 kJ/mol at different temperatures indicated that ion exchange was the main mechanism during the adsorption process. Thermodynamic parameters were also evaluated during the adsorption. The values of the standard Gibbs free energy change (ΔG ^o) and standard enthalpy change (ΔH ^o) suggested that the adsorption was a spontaneous and endothermic process. The distribution coefficient (K _d) was more than 2.94 × 10⁶ mL/g when the pH of solution was between 2.6 and 10.9, and the initial Cs⁺ concentration was 100 μg/L. The existence of K⁺ and Na⁺ did not affect the adsorption of Cs⁺ on CuFC when the concentration of K⁺ and Na⁺ in the solution was below 20 and 1,000 mg/L, respectively.     

Changes of zeta potential and particles size of silica caused by DPPC adsorption and enzyme phospholipase A2 presence

The changes in electrokinetic properties of silica suspensions in the presence of 1,2-dipalmitoyl-sn-glycero-3-phospshocholine (DPPC) were investigated via zeta potential, mean diameter and transmittance determinations. Silica particles were precovered with monolayer (ML) or bilayer (BL) of the phospholopid from chloroform solution (SiO₂/DPPC) or covered by DPPC adsorption from aqueous solution (SiO₂+DPPC). The zeta potential and mean diameter of SiO₂/DPPC suspension were measured as a function of NaCl concentration and due to the phospholipase A₂(PLA₂) action in 10^?3 M NaCl solution and buffer Tris at pH=8 and 9. It was found that the DPPC adsorption onto silica surface decreases its the zeta potential, however the suspensions were stable during the experiment time, probably because of steric stabilization. During PLA₂ enzyme action the changes in zeta potential were observed, which were caused by the hydrolysis products, especially palmitic acid molecules, which also had influence on the stability of these systems.     

Corrosion inhibition and adsorption behavior of imidazoline salt on N80 carbon steel in CO2-saturated solutions and its synergism with thiourea

The inhibition and adsorption behavior of 2-undecyl-1-sodium ethanoate-imidazoline salt (2M2) and thiourea (TU) on N80 mild steel in CO₂-saturated 3 wt.% NaCl solutions was studied at 25?°C, pH 4, and 1 bar CO₂ partial pressure using electrochemical methods. It was found that inhibition efficiency (η%) increased with increase in 2M2 concentration but decreased with increase in TU concentration with optimum η% value at 20 mg l^?1 TU. The data suggest that the compounds functioned via a mixed-inhibitor mechanism. The inhibition process is attributed to the formation of an adsorbed film of 2M2 and TU via the inhibitors polycentric adsorption sites on the metal surface which protects the metal against corrosion. A synergistic effect was observed between TU and 2M2. Potential of unpolarizability, E _u, was observed in the presence of 100 mg l^?1 TU which was shifted positively in the presence of 2M2–100 mg l^–1 TU blends, which suggests that the presence of 2M2 stabilized the adsorption of TU molecules on the surface of the metal. The adsorption characteristics of 2M2 were approximated by Langmuir adsorption isotherm.     

Significance of glass transition temperature to polymer latex stabilisation by nonionic surfactants

Equilibrium colloid stability measurements with nonionic surfactant (C₁₂E₈) stabilised polybutyl methacrylate (PBMA) latex dispersions indicate a sudden temperature induced destabilisation coinciding with the glass transition temperature,Tg, of the polymer. In control experiments with polystyrene latex particles of similar size, for whichTg was not approached, the flocculation temperature was significantly higher. The effect is interpreted in terms of a reduced adsorbed layer thickness aboveTg caused by mixing of part of the surfactant molecule with the polymer. This interpretation is supported by DSC, elastic modulus and mechanical damping measurements on films made from dispersions of the same latex containing commercial nonionic surfactants. These measurements indicate a shift inTg in the presence of surfactant consistent with partial penetration of the polymer surface by the surfactant. In addition, C₁₂E₈ adsorption measurements show increased adsorption (or absorption) onto PBMA aboveTg which is irreversible on both dilution and temperature reduction.     

The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. IV. Recovery of uranium by amidoximated hydroxypropyl methylcellulose

Amidoxime modified hydroxypropyl methylcellulose (HPMC) films (HPMC-g-AO) were used for the recovery of uranium from aqueous solutions by a complexation process. The adsorption experiments were carried out by immersion of a certain amount of films in UO₂ ²⁺ solutions (resultant pH 4.1) ranging in concentration from 100 to 1,000 ppm. The effect of temperature (25–50 °C) on the adsorption capacity of HPMC-g-AO was investigated at the optimized time. The adsorption kinetics and the thermodynamics as well as the adsorption capacity of HPMC-g-AO films were investigated. The adsorption capacity was found as 765 mg UO₂ ²⁺/g dry film. The kinetic and the thermodynamic parameters (i.e. activation energy, enthalpy, entropy and Gibbs free energy) for the interaction of UO₂ ²⁺ with HPMC-g-AO were calculated based on known basic relations. The results showed that adsorption occurred through strong electrostatic interactions with an enthalpy of ?36.5 kJ/mol. The desorption of UO₂ ²⁺ were investigated using different desorption agents such as EDTA, HCl, NaHCO₃, and NaOH. After the 2 weeks treatment period, the highest desorption yield were found as 23 % with NaHCO₃.     

Thermodynamic studies of methylene blue adsorption onto Fe-doped sulfated titania

Adsorption equilibrium of methylene blue onto Fe-doped sulfated titania (FST) samples was studied at different temperatures (298, 303, and 308 K). Based on the wavelength scanning from 580 to 760 nm, the wavelength of maximum absorbance of methylene blue was determined to be 666 nm and the corresponding calibration curve can be described by the equation of A = 0.0068 + 0.1514C. The adsorption of methylene blue onto FST samples was conformed to the Langmuir isotherms. The absorption capacity of each FST sample for methylene blue increases with increasing temperature. The increase in the adsorption parameters (q _m, b, and K ₀) and the positive ΔH ^θ reveal the endothermic feature of this adsorption process. The negative ΔG ^θ shows the adsorption of methylene blue onto FST samples can be carried out spontaneously at the examined temperatures. Furthermore, with the calcination temperature increases, the variation in crystallization degree, the surface and the sulfur species will obviously influence the adsorption properties of FST samples and the thermodynamic parameters of this adsorption process.     

Carbon dioxide and nitrogen adsorption on porous copolymers of divinylbenzene and acrylic acid

Porous copolymers of divinylbenzene (DVB) and acrylic acid (AA) having DVB:AA ratios of 6:4, 8:2 and 9:1 were prepared following a distillation-precipitation method, using toluene as the porogenic agent. The materials thus obtained, which showed specific surface area in the range of 380–600 m² g^?1 and pore volume in the range of 0.14–0.18 cm³ g^?1, were investigated as possible adsorbents for CO₂ capture from the flue gas of coal-fired power stations. For that purpose, the isosteric heat of adsorption (and CO₂ adsorption capacity) was analysed from N₂ and CO₂ adsorption equilibrium isotherms obtained over a temperature range. For CO₂, q _st resulted to be in the range of 27–31 kJ mol^?1 (the highest value corresponding to the 6:4 sample), while for N₂ a value of q _st ≈ 12 kJ mol^?1 was obtained. Equilibrium adsorption capacity for CO₂ (at ambient temperature and pressure) showed the value of about 1.35 mmol g^?1. These results are discussed in the broader context of corresponding literature data for CO₂ capture using protonic zeolites.