Transport phenomena of sulfonated dyes into cellulose membrane: Effects of urea on parallel diffusion of mono azo dyes

 Effects of urea on transport phenomena of sulfonated azo dyes with different aggregation constants into water-swollen cellulose membrane have been studied at 25–55 °C. The results were analyzed on the basis of a parallel transport theory of surface and pore diffusion. Addition of urea decreased equilibrium adsorption of the dyes onto cellulose and increased the surface and pore diffusivities for the parallel diffusion model of the dye with high aggreg-ation constant. Temperature dependence of the effects was also discussed. Received: 30 November 1996 Accepted: 7 April 1997     

Effects of type of adsorption isotherms on parallel diffusion of sulfonated dyes into porous cellulose membrane

Transport phenomenon of three sulfonated azo dyes, C.I. Acid Red 88, C.I. Direct Yellow 12, and C.I. Direct Blue 15 into water-swollen cellulose membranes has been analyzed on the basis of parallel transport theory by surface and pore diffusion. Langmuir equation was applied into the mass balance equation to estimate dye concentration in the pores. The results were compared with the results obtained by applying Freundlich equation in our previous papers. The surface diffusivity (D _s) and the pore diffusivity (D _p) for the parallel diffusion model obtained by applying Langmuir equation agreed with those obtained by applying Freudlich equation. The theoretical concentration profiles for parallel diffusion calculated usingD _s andD _p coincided accurately with the experimental data when we applied either Langmuir or Freundlich equations.     

A Film-Pore-Surface Diffusion Model for the Adsorption of Acid Dyes on Activated Carbon

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80, Acid Red 114 and Acid Yellow 117 removal have been investigated. A three-resistance mass transport model based on film, pore and surface diffusion control has been applied to model the concentration decay curves. The model incorporates an effective diffusion coefficient D _eff, which is dependant on the equilibrium solid phase concentration or fractional surface coverage. The results of the film-pore-surface diffusion model are compared with the data obtained from the basic film-pore diffusion model. It has been found that the film-pore-surface diffusion model provides a major improvement over the data correlated by the film-pore diffusion model. Also, the relationship between surface diffusion and fractional surface coverage has been investigated for the adsorption of acid dyes on activated carbon.     

A Film-Pore-Surface Diffusion Model for the Adsorption of Acid Dyes on Activated Carbon

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80, Acid Red 114 and Acid Yellow 117 removal have been investigated. A three-resistance mass transport model based on film, pore and surface diffusion control has been applied to model the concentration decay curves. The model incorporates an effective diffusion coefficient D _eff, which is dependant on the equilibrium solid phase concentration or fractional surface coverage. The results of the film-pore-surface diffusion model are compared with the data obtained from the basic film-pore diffusion model. It has been found that the film-pore-surface diffusion model provides a major improvement over the data correlated by the film-pore diffusion model. Also, the relationship between surface diffusion and fractional surface coverage has been investigated for the adsorption of acid dyes on activated carbon.     

Mixture diffusion of sulfonated dyes into cellulose membrane. III. Application of parallel diffusion model to binary system of direct dyes with different affinity

Mixture diffusion of two dyes (C.I. Direct Blue 15 (DB15) and C.I. Direct Yellow 12 (DY12)) with different affinity onto the substrate into cellulose membrane from the binary solution was studied at 55°C. Uptake curves and concentration–distance profiles were measured experimentally in the ratios (DB15:DY12) 1:0.5, 1:1 and 1:2. It was examined whether the diffusion of the dyes could be analyzed based on the parallel diffusion theory of surface and pore diffusion. It was revealed that the diffusion of DB15 with higher affinity could be analyzed based on the model in the ratios 1:0.5 and 1:1, although the theoretical value deviated slightly from the data in the concentration–distance profile in the ratio 1:1. On the other hand, the diffusion of DY12 with smaller affinity could not be described by the model, because the diffusivity of the dye changed during the adsorption process against the assumption of the model.     

Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite

The adsorption of two dyes, namely, Acid Red 57 (AR57) and Acid Blue 294 (AB294), onto acid-activated bentonite in aqueous solution was studied in a batch system with respect to contact time, pH, and temperature. Acidic pH was favorable for the adsorption of these dyes. The surface characterization of acid-activated bentonite was performed using the FTIR technique. The pseudo-first-order and pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The dynamic data fitted the pseudo-second-order kinetic model well and also followed the intraparticle diffusion model up to 90 min, but diffusion is not the only rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were determined. The Freundlich model agrees very well with experimental data. The activation energies of adsorption were also evaluated for the adsorption of AR57 and AB294 onto activated bentonite.     

Adsorption of direct dyes from aqueous solutions by carbon nanotubes: determination of equilibrium, kinetics and thermodynamics parameters

This study examined the feasibility of removing direct dyes C.I. Direct Yellow 86 (DY86) and C.I. Direct Red 224 (DR224) from aqueous solutions using carbon nanotubes (CNTs). The effects of dye concentration, CNT dosage, ionic strength and temperature on adsorption of direct dyes by CNTs were also evaluated. Pseudo second-order, intraparticle diffusion and Bangham models were adopted to evaluate experimental data and thereby elucidate the kinetic adsorption process. Additionally, this study used the Langmuir, Freundlich, Dubinin and Radushkevich (D-R) and Temkin isotherms to describe equilibrium adsorption. The adsorption percentage of direct dyes increased as CNTs dosage, NaCl addition and temperature increased. Conversely, the adsorption percentage of direct dyes decreased as dye concentration increased. The pseudo second-order model best represented adsorption kinetics. Based on the regressions of intraparticle diffusion and Bangham models, experimental data suggest that the adsorption of direct dyes onto CNTs involved intraparticle diffusion, but that was not the only rate-controlling step. The equilibrium adsorption of DR86 is best fitted in the Freundlich isotherm and that of DR224 was best fitted in the D-R isotherm. The capacity of CNTs to adsorb DY86 and DR224 was 56.2 and 61.3 mg/g, respectively. For DY86, enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were 13.69 kJ/mol and 139.51 J/mol K, respectively, and those for DR224 were 24.29 kJ/mol and 172.06 J/mol K, respectively. The values of DeltaH(0), DeltaG(0) and E all indicate that the adsorption of direct dyes onto CNTs was a physisorption process.     

Diffusion of monoanionic dyes in nylon

The diffusion of three monoanionic dyes [Orange II (C.I. Acid Red 7) and two chromium complex dyes] in nylon 6 is discussed on the basis of dye distribution obtained by the film-roll method. Variations of the diffusion coefficients with dye concentration depend characteristically on the dye species and in one case show a maximum near the dye concentration stoichiometric to the amino endgroup concentration in the nylon. These concentration dependences are interpreted on the assumption of two thermodynamically distinct dye populations in equilibrium.     

Analysis of diffusion models for protein adsorption to porous anion-exchange adsorbent

The ion-exchange adsorption kinetics of bovine serum albumin (BSA) and gamma-globulin to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments. Various diffusion models, that is, pore diffusion, surface diffusion, homogeneous diffusion and parallel diffusion models, are analyzed for their suitabilities to depict the adsorption kinetics. Protein diffusivities are estimated by matching the models with the experimental data. The dependence of the diffusivities on initial protein concentration is observed and discussed. The adsorption isotherm of BSA is nearly rectangular, so there is little surface diffusion. As a result, the surface and homogeneous diffusion models do not fit to the kinetic data of BSA adsorption. The adsorption isotherm of gamma-globulin is less favorable, and the surface diffusion contributes greatly to the mass transport. Consequently, both the surface and homogeneous diffusion models fit to the kinetic data of gamma-globulin well. The adsorption kinetics of BSA and gamma-globulin can be very well fitted by parallel diffusion model, because the model reflects correctly the intraparticle mass transfer mechanism. In addition, for both the favorably bound proteins, the pore diffusion model fits the adsorption kinetics reasonably well. The results here indicate that the pore diffusion model can be used as a good approximate to depict protein adsorption kinetics for protein adsorption systems from rectangular to linear isotherms.     

Diffusion of acid dyes in nylon film in the presence of inorganic salts

The concentration-dependence measured by steady-state permeation and unsteady-state dyeing methods for a system of acid dye C.I.Acid Blue 182–nylon 6 film in the presence of inorganic salts such as NaCl, Na₂SO₄, and K₂SO₄, was analyzed in terms of parallel diffusion with simultaneous multimodal adsorption. It would found that the dyeing process with added NaCl was governed by surface diffusion with two kinds of Langmuir adsorption, whereas with added Na₂SO₄ and K₂SO₄ it was governed by surface diffusion with three kinds of Langmuir adsorption.     

Direct dyes as molecular sensors to characterize cellulose substrates

Six dyes were selected based on their molecular structure to test theirsuitability as sensors to characterize the fine structure of cellulosesubstrates. Cotton, mercerized cotton and microcrystalline cellulose werechosento represent a variety of pore structures typically encountered in practicalapplications. Internally available surface areas were calculated. It ispostulated that roughly 25% of the Connolly surface areas (CSA) of the sensorsDirect Blue 1, Direct Blue 14, Direct Blue 53, Direct Red 28, and Direct Red 2and 30% of the CSA of Direct Yellow 4 are representative of the space requiredfor the sensor to dock onto cellulose surfaces. Molecular weight of the dyeprobes does not serve as a good indicator of sensor size. Molecular structureisa critical factor to take into account when selecting a probe.     

Parallel pore and surface diffusion of levulinic acid in basic polymeric adsorbents

The equilibrium and kinetics of levulinic acid (LA) adsorption on two basic polymeric adsorbents, 335 (highly porous gel) and D315 (macroreticular), were investigated. Experimental adsorption rates in batch stirred vessels under a variety of operating conditions were described successfully by the parallel pore and surface diffusion model taking into account external mass transfer and nonlinear Toth isotherm. The film-pore diffusion model was matched with the rate data and the resulting apparent pore diffusivities were strongly concentration-dependent and approached to a constant value for 335 adsorbent. Thus, the constant value was taken as the accurate pore diffusivity, while the pore diffusivity in D315 was estimated from the particle porosity. The surface diffusivities decreased with increasing initial bulk concentration for both adsorbents. The inverse concentration dependence was correlated reasonably well to the change of isosteric heat of adsorption as amount adsorbed.     

A parallel pore and surface diffusion model for predicting the adsorption and elution profiles of lispro insulin and two impurities in gradient-elution reversed phase chromatography

Lispro insulin (LPI), a widely used insulin analog, is produced on tons per year scale. Linear gradient reversed phase chromatography (RPC) is used in the production to separate LPI from two impurities, which differ from LPI by a single amino acid residue. A chromatography model for the ternary separation in this RPC process is unavailable from the literature. In this study, a parallel pore and surface diffusion model is developed and verified for LPI and the two impurities. The LPI can be recovered with high yield (≥95%) and high purity (>99.5%). A new method, which requires a small amount of materials and an order of magnitude fewer experiments, has been developed to estimate the solvent-modulated isotherm parameters. A modified reversed phase modulator model is developed to correlate the adsorption isotherms of LPI and impurities. A strategy has been developed for estimating the intrinsic pore diffusivity and surface diffusivity. Since the adsorption affinities decrease by more than three orders of magnitude as organic fraction (φ) increases from 0.19 to 0.40, the apparent diffusivities based on a pore diffusion model or a surface diffusion model can also vary by several orders of magnitude. For this reason, a pore diffusion model or a surface diffusion model with a constant apparent diffusivity cannot predict closely the chromatograms over the same range of organic fractions, concentrations, and loadings. The parallel pore and surface diffusion model with constant diffusivities can predict closely the frontal and elution profiles over a wide range of organic fractions (0.19-0.40), LPI concentrations (0.05-18 g/L), linear velocities (<10 cm/min), and loading volume (0.0004-13 CV). For large loading stepwise and linear gradient elution, the peaks of LPI and the impurities are strongly focused by self-sharpening and gradient focusing effects as a result of the steep decrease of adsorption affinity from the loading φ (0.19) to elution φ (≥0.27). When the ratio of diffusion rate to convection rate is greater than 10, spreading due to diffusion is largely compensated by the focusing effects. As a result, a pore diffusion model with a constant pore diffusivity can predict closely the elution profiles in stepwise and linear gradient elution. The experimental yield values (≥95%) can be predicted to within ±1% by the model.     

Theoretical modeling of water vapor transport in cellulose-based materials

The theory of mass transport in porous media is of fundamental importance for different applications such as food, paper packaging, textiles, and wood for building materials. In this study, a theoretical water vapor transport model has been developed for cellulose-based materials, such as paper and regenerated cellulose film. Pore diffusivities were determined from the dynamic moisture breakthrough experiments comprising a stack of paper sheets and regenerated cellulose films in a configuration similar to a packed adsorption column. Other mass transfer parameters were determined from transient moisture uptake rate measurements. The model incorporates pore and surface diffusion as a lump parameter into a variable effective diffusion coefficient. The mass transport, involving both pore and surface diffusions, is evaluated independently. The theoretical water vapor transmission rates (WVTRs) obtained from the model were compared with experimentally determined WVTRs measured under steady-state conditions. The theoretical model, based on intrinsic diffusion, stipulates higher WVTR values compared to the experimental results. However, the theoretical water vapor transfer rates agree well with the experimental results when external mass transfer resistance is incorporated in the model.     

Spectrophotometric Studies on the Aggregation of Some Acid Dyes

The electronic absorption spectra of different acid dyes, mainly C. I. Acid Red 13, 18, 27, 88 and 141, have been investigated in aqueous and non-aqueous solutions. As the concentration of the dye increases the absorption spectrum shifts to shorter wavelengths; this behaviour has been attributed to the formation of higher aggregates. The longer wavelength band, most marked in dilute solutions, is typical of the monomeric dye. The aggregation of these dyes were studied quantitatively using the Maximum Slope Method. The monosulfonic acid dyes Red 141 and 88 and the disulfonic acid dye 13 are aggregated at room temperature with an average aggregation number of 2.0, 2.2 and 1.5, respectively. The trisulfonic acid dyes Red 18 and 27 show very little aggregation at this temperature.     

Adsorption and Surface Properties of Vladipor Cellulose Acetate and Polysulfonamide Membranes

Surface and adsorption characteristics of porous cellulose acetate (UAM) and polysulfonamide (UPM) membranes with pore diameters from 0.015 to 0.1 μm are compared. The specific surface areas of UPM membranes are 130 and 150 cm²/cm², whereas those of UAM membranes vary from 80 to 360 cm²/cm² of the membrane area. The density of negative charges on the pore surface is 5 × 10^{− 8} and about 20 × 10⁻⁸ C/cm² for UAM and UPM membranes, respectively. The adsorption of basic and acidic substances, proteins (cytochrome C and ovalbumin) and dyes (rhodamine 6G and Acid Orange), from aqueous solutions is studied. Far stronger hydrophobic interactions are observed for the UPM than for UAM membranes. The adsorption of basic substances is markedly higher than that of acidic substances because of acidic properties of the membrane surface. The distribution constants for the adsorption of Acid Orange and cytochrome C on the UPM membrane with a pore diameter of 0.1 μm are 50- and 100-fold higher than for the UAM membrane of the same pore diameter and specific surface area. __________ Translated from Kolloidnyi Zhurnal, Vol. 67, No. 6, 2005, pp. 835–838. Original Russian Text Copyright ? 2005 by Khokhlova, Dzyubenko, Berezkin, Bon, Pervov, Shishova, Dubyaga, Mchedlishvili.     

Understanding adsorption phenomena: investigation of the dye-cellulose interaction

To understand the structural factors that control the adsorption of acid dyes onto cotton (cellulose), the adsorption of 15 acid dyes from water has been studied. An equilibrium exists between dye adsorbed in the cotton and dye in solution, and by measurement of the temperature dependence (277-333K) of the equilibrium constant, the enthalpy and entropy of binding are obtained. For most dyes adsorption is driven by the binding enthalpy, which is ascribed to van der Waals forces. Acid dyes consist of an aromatic core with peripheral solubilizing groups (generally sulfonates). Dyes in which the sulfonates are on one side of the molecule have the largest binding enthalpy. Assuming a binding geometry where the sulfonates protrude into water pools in the bulk amorphous regions and as much as possible of the dye core touches the surface, then a good correlation exists between the binding enthalpy and the summation of 1/r(6) over all the C, N, and O dye atoms, where r is the distance of each atom from the cellulose surface.     

Pore structure and adsorption performance of the KOH-activated carbons prepared from corncob

Carbonaceous adsorbents with controllable surface area were chemically activated with KOH at 780 degrees C from chars that were carbonized from corncobs at 450 degrees C. The pore properties, including BET surface area, pore volume, pore size distribution, and mean pore diameter of these activated carbons, were characterized by the t-plot method based on N(2) adsorption isotherms. Two groups are classified according to the types of adsorption/desorption isotherms. Group I corncob-derived activated carbons, with KOH/char ratios from 0.5 to 2, exhibited BET surface area ranging from 841 to 1221 m(2)/g. Group II corncob-derived activated carbons, with KOH/char rations from 3 to 6, showed high BET surface areas, from 1976 to 2595 m(2)/g. From scanning electron microscopic (SEM) results, the surface morphology of honeycombed holes on corncob-derived activated carbons was significantly influenced by the KOH/char ratios. The adsorption kinetics of methylene blue, basic brown 1, acid blue 74, 2,4-dichlorophenol, 4-chlorophenol, and phenol from water at 30 degrees C were studied on the two groups of activated carbons, which were suitably described by two simplified kinetic models, pseudo-first-order and pseudo-second-order equations. The effective particle diffusivities of phenols and dyes at the corncob-derived activated carbons of group II are higher than those of ordinary activated carbons. The high-surface-area activated carbons were demonstrated to be promising adsorbents for pollution control and for other applications.     

Determination of sulphonate dyes in water by ion-interaction high-performance liquid chromatography

An ion-interaction high-performance liquid chromatography method for quick separation and determination of the sulphonated dyeAcid Yellow 1, and the sulphonated azo dyes Acid Orange 7, Acid Orange 12, Acid Orange 52, Acid Red 2, Acid Red 26, Acid Red 27 and Acid Red 88 has been developed. An RP-ODS stationary phase is used, and the mobile phase contains an acetonitrile-phosphate buffer (27:73, v/v) mixture at pH 6.7, containing 2.4 mM butylamine as ion-interaction reagent. Good separations were obtained using isocratic elution and spectrophotometric detection at 460 nm. The detection limits for the eight dyes ranged from 7 to 28 microg/l for an injection volume of 100 microl. Spiked tap water samples (100 ml), containing different concentration levels (0.3-1.2 microg/l) of the dyes were analyzed after acidification (pH 3) and preconcentration in disposable solid-phase extraction C18 cartridges.     

Adsorption of dyes on carbon xerogels and templated carbons: influence of surface chemistry

The removal of textile dyes by adsorption onto carbon materials with extended mesoporosity is addressed in the present work. Two types of high surface area carbon adsorbents were prepared, namely a carbon xerogel and a templated carbon. Both materials were subsequently subjected to appropriate treatments in order to modify their surface chemistries, while keeping their textural properties relatively unchanged. The carbon adsorbents were extensively characterized by different techniques in order to correlate their adsorption performances with the corresponding surface properties. The behavior of the different materials was evaluated by determining equilibrium adsorption isotherms of two anionic dyes (Reactive Red 241 and Acid Blue 113) at different pH values. The results are compared with data previously obtained with commercial activated carbons subjected to the same treatments, and discussed in terms of the carbon surface chemistry and the interaction between the dye molecules and the adsorbent surface (dispersive and electrostatic interactions).