Equilibrium Sorption Parameters Research Articles

APPLICATION OF SUPER-CROSSLINKED POLYMERS AS CARRIERS OF HETEROGENEOUS BIOCATALYSTS FOR INULINHYDROLYSIS REACTION

n this work the study of adsorption immobilization of inulinase on super-crosslinked macroporous sorbents based on styrene and divinylbenzene: low-base anion exchanger A100, high-base anion exchanger A500R, strong acid cation exchanger C100H was carried out. The influence of the duration of the sorption process, the value of the concentration of hydrogen ions and the concentration of protein in solution on the amount of immobilized enzyme and the activity of the obtained heterogeneous biocatalysts is considered. It was revealed that adsorption reaches its max-imum value on average after 4 h at pH of 4.7-5.0 for the sorbents under consideration. The activity of the obtained heterogeneous biocatalysts is 64.8-83.5% of the activity of free inulinase. Although the activity of inulinase during adsorption on the polymer carriers used in the work decreases, the integral amount of the resulting product will be higher than for the native catalyst.The isotherms of inulinase adsorption on super-crosslinked polymers have been studied. The high stability of the obtained heterogeneous biocatalysts is explained by the high sorption capacity of super-crosslinkedsorbents. It was revealed that immobilized inulinase can be used during 8-11 consecutive cycles of the substrate hydrolysis reaction.Using the BET adsorption theory, the enzyme sorption isotherms were analyzed and the equilibrium sorption parameters werecalculated: the maximum amount of sorbed inulinase, the constants characterizing the sorbate-sorbent and sorbate-sorbate interaction. Among the considered carriers, the highest value of the sorption equilibrium constant (KL=4.25±0.04 l/mmol) corresponds to the inulinase-cation exchanger biocatalyst, the sorption ca-pacity of which is also the largest. The data obtained is of interest for evaluating the effectiveness of the use of sorbents as inulinase carriers in subsequent technological operations of processing of inulin-containing raw materials.

Reduction and Biosorption of Cr(VI) from Aqueous Solutions by Acid-Modified Guava Seeds: Kinetic and Equilibrium Studies

Abstract The use of guava seeds (GS) and acid-modified guava seeds (MGS) for the removal of Cr(VI) from aqueous solutions was investigated. Batch-type experiments were performed with Cr(VI) aqueous solutions and biosorbents to determine the kinetic and equilibrium sorption parameters. Results indicated that GS and MGS were capable of reducing and remove Cr(VI) from solutions, but the reduction was only observed at some experimental conditions. Infrared analysis showed that several functional groups were involved in the reduction, and biosorption of Cr(VI), particularly alcohol, phenolic, carboxylic, and methoxymethyl structures. The mechanisms of reduction and biosorption depended upon the type of biosorbent, pH, and temperature of the system. The pseudo-second-order kinetic model describes the kinetic sorption data, and the Langmuir-Freundlich (L-F) model describes the isotherm data in most cases. Significantly high total chromium biosorption capacities were obtained. Acid modification of guava seeds improves chromium biosorption performance.

Selective sorptive removal of Methyl Red from individual and binary component solutions by mesoporous organosilicas of MCM-41 type

Organosilicas with chemically immobilized 3-aminopropyl and Methyl Red-containing surface groups were prepared by sol-gel condensation of tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane in the presence of dye as part of the mixed micelles or dye-containing silane as silica source. The hexagonally arranged mesoporous structure of synthesized materials was confirmed by low-temperature nitrogen adsorption-desorption, x-ray diffraction, and TEM studies. Chemical composition of MCM-41-type organosilicas was established by FT-IR spectroscopy and chemical analysis of surface layer. Sorption of Methyl Red by organosilicas was studied from diluted phosphate buffer solutions in dependence of medium pH, duration of contact, and equilibrium concentration of dye. It was found that effective removal of Methyl Red takes place at pH values within a range of 2.5−5. Kinetic curves of Methyl Red sorption on organosilicas were analyzed by the Lagergren, Ho-McKey, and Weber-Morris kinetic models. It was found that the pseudo-second-order model fits the kinetics of Methyl Red sorption on all synthesized materials and the intraparticle diffusion is not the only one mechanism controlling the rate of Methyl Red sorptive removal. The parameters of equilibrium sorption of Methyl Red on organosilicas of MCM-41 type were calculated using Langmuir, Freundlich, Redlich-Peterson, and Brunauer-Emmett-Teller models. Sorption of acid dyes with geometry similar or substantially different from Methyl Red on mesoporous silicas was studied from single and binary component mixtures in aqueous solutions with pH 4.8 and 5.5. It was found that selective sorption process is highly dependent on the structural characteristics and protolytic state of silica surface as well as acid dye.

Equilibrium Sorption of Histidine on Clinoptilolite

Sorption of histidine in the cationic and zwitterionic forms on a framework aluminosilicate, clinoptilolite, has been investigated. The contributions of the exchange and nonexchange mechanisms of sorption to the sorption capacity have been determined. It has been shown that monolayer histidine sorption on clinoptilolite by the ion-exchange mechanism proceeds due to the electrostatic interaction between $${\text{NH}}_{3}^{ + }$$ groups of the amino acid and electronegative sites of the sorbent matrix. In the region of equivalent exchange, a smaller value of the ion-exchange component of the sorption of histidine zwitterions is due to the Coulomb repulsion between the dissociated carboxyl groups of the amino acid and the negatively charged aluminum–oxygen clinoptilolite matrix. The isotherm of histidine sorption from dilute solutions has been described using the Langmuir theory. The equilibrium sorption parameters have been found. It has been concluded that polymolecular layers of the amino acid are formed as a result of association via hydrogen bonding, as well as dipole–dipole and hydrophobic interactions.

In Ukrainian

Templated sol-gel synthesis of MCM-41‑type mesoporous silicas was realized in the presence of azo dyes (alizarin yellow and methyl red) as co-templates and silanes obtained on their basis as structure-forming components. It has been found from the results of low-temperature adsorption-desorption of nitrogen that using of azo dyes and dye-containing silanes in sol-gel synthesis leads to the substantial increase of surface area and total pore volume, and decrease of pore diameter of obtained mesoporous organosilicas. The X-ray diffraction analysis proved formation of hexagonally arranged structure of mesopores in synthesized organosilicas. It has been demonstrated due to visualization of mesoporous structure by transmission electron microscopy that all synthesized materials have hexagonally arranged structure of cylindrical pores, entrances to which are oriented outside of particles that provide accessibility of functional groups for sorbate molecules. Obtained organosilicas of MCM-41 type were used in study of dyes sorption from diluted phosphate buffer solutions as dependent on their equilibrium concentration, pH of medium, and duration of contact. It has been found that the most efficient sorption of alizarin yellow takes place at рН ~ 3 and methyl red at рН = 2.5-5.0. Analysis of kinetic curves carried out using Lagergren, Ho‑McKey, and Weber-Morris models has shown that process of azo dyes sorption by organosilicas is described by kinetic model of pseudo‑second order. The parameters of equilibrium sorption of alizarin yellow and methyl red on organosilicas of MCM‑41 type were calculated using Langmuir, Freundlich, Redlich‑Peterson, and Brunauer‑Emmett‑Teller models. Sorption of a number of acid dyes from their individual solutions was studied at pH 4.8. It has been found that chemical immobilization of methyl red on silica surface causes increase of acid dyes sorption. The contribution of cooperative interactions, which arise between the aromatic groups of azo dyes immobilized in surface layer of silica and dye molecules in a solution, in the process of their sorption was confirmed. Modification of silica surface with capable to self-aggregation dyes is a promising way in chemical design of sorption-active materials.

Green biosorbents based on chitosan-montmorillonite beads for anionic dye removal

Chitosan/KSF-montmorillonite beads were prepared at 1–25% w/w ratios by reaction of the biopolymer and the clay mineral with sodium tripolyphosphate as crosslinking agent. The synthesized biocomposites were characterized by CHN elemental analysis, XRD (X-Ray diffraction), FTIR (Fourier transform infrared), 13C NMR (Nuclear magnetic resonance), thermogravimetry, SEM (Scanning electron microscopy), TEM (Transmission electron microscopy) and measurements of point of zero charge (pHpzc). The results suggested that hybrid materials were properly obtained and also their properties were improved compared to the pristine chitosan and montmorillonite. Further, the beads were evaluated in the adsorption of Remazol Blue under batch operations obtained for different conditions at pH (2–8), contact time (0–660min) and dye concentration (100–1600mgL−1). Kinetic and equilibrium sorption parameters were evaluated using pseudo- first and pseudo-second rate models and Langmuir and Freundlich equations. The results were promising and suggested that the sorbents can be applied for removing anionic dyes from wastewater even in acidic medium.

Coupling Fe0 nano particles with living and dead Azolla filicoloides to improve removal of methylene blue from aqueous solution

Fe0 nano particles (FNPs) were connected to the cell wall of the dead and living Azolla filicoloides as an aquatic fern, individually. FNPs mean size was decreased due to the stabilization, especially using the living one. It was compared the results of X-ray photoelectron spectroscopy (XPS), saturation magnetization (Ms), zeta potential (ZP) and thermal analysis (DSC and TGA) of the dead and living Azolla connected to FNPs, and also the findings of potentiometric titration (PT) of the cell wall's pectin of the dead and living Azolla. It was confirmed (by XRD and XPS) that Fe0 nano particles when were connected to the living Azolla did not produce Fe3O4 due to oxidation unlike the bare FNPs and the connected form to the dead Azolla, by reason of the more stabilization (more surface protection) of nano iron particles after connecting to the living Azolla. To adsorb methylene blue by these agents at the optimum pre-treatment pH 10 and adsorption pH 8, the parameters of equilibrium sorption, rate constant of second-order sorption and activation energy were obtained as: living Azolla–FNPs>dead Azolla–FNPs>FNPs>dead Azolla, while, their thermodynamic parameters (ΔG°, ΔH° and ΔS°) had the reverse arrangement. It was also studied the various factors rule such as photoperiod and the presence of heavy metals on the living Azolla growth coupled with FNPs and its MB removal ability.

Polyamide Fibers Covered with Chlorhexidine: Thermodynamic Aspects

Results of dynamic and equilibrium of sorption of a reactive dye Remazol Brilliant Blue, and a bactericidal agent, Digluconate of Chlorhexidine over Polyamide fibers are presented with the aim of supplying the fiber with bactericidal properties. However, adsorption of Chlorhexidine onto Polyamide is scarce due to the lack of interactions between the reactive groups of the fiber and the antiseptic molecule. Therefore, in order to provide the fiber surface with anionic groups, fiber has been previously dyed with Remazol Brilliant Blue which increases the negative charge of the fiber surface due to the presence of its sulfonate end groups. Thermodynamic parameters of equilibrium sorption in the two situations, fiber/dye and fiber-dye/Chlorhexidine, have been analyzed, as function of the temperature, pH and concentration of the dye in the pretreatment. Results show that when sorption of Remazol Brilliant Blue reaches the value of about 50 mmol/ kg at the higher temperature and concentration tested, the amount of Chlorhexidine adsorbed exhibits its maximum value which is 6 mmol/kg. Both processes, adsorption of Remazol Brilliant Blue and adsorption of Chlorhexidine, fit well to Langmuir adsorption model, suggesting the existence of some kinds of specific interactions between adsorbent and adsorbate. Thermodynamic functions show that the interaction is endothermic and spontaneous in all the rage of temperature tested. The kinetic studies show that sorption of Remazol Brilliant Blue is better described by pseudo-first order model, while sorption of Chlorhexidine fits better to pseudo-second order model, and seems to be quicker process. According to the obtained results, chemical interaction between the vinyl-sulfone group of Remazol Brilliant Blue and the amine groups of Polyamide fiber, followed by electrostatic interactions between the guanine group of the Chlorhexidine and the sulfonate group of the dye must be considered in order to explain the adsorption process.

Sorption, desorption and displacement of ibuprofen, estrone, and 17β estradiol in wastewater irrigated and rainfed agricultural soils

Sorption and leaching potential of ibuprofen, estrone and 17β estradiol were tested in two agricultural soils: one irrigated using municipal wastewater and the other used in rainfed agriculture. Batch sorption–desorption experiments and undisturbed soil column assays were carried out using both soils to which were added a mixture of the target compounds. The three compounds were sorbed to a different extent by both soils: estrone>17β estradiol>ibuprofen. Higher sorption was observed in the irrigated soil, which was attributed to the accumulation of organic matter caused by wastewater irrigation. Desorption of hormones was hysteretic in the irrigated soil, while ibuprofen showed low hysteresis in both soils. Retardation of the compounds' displacement was consistent with the sorption pattern observed in the batch tests. Retardation factor (RF) was similar for the three compounds in the two tested soils, indicating that the target compounds are much more mobile in the soil columns than would be predicted based on their equilibrium sorption parameters. The results obtained in the experiments clarify the role of wastewater irrigated soils as a filter and degradation media for the target micropollutants.

Tunable macromolecular-based materials for the adsorption of perfluorooctanoic and octanoic acid anions

The sorption properties of tunable urethane-based copolymer materials containing β-cyclodextrin (β-CD) were evaluated with perfluorooctanoic acid (PFOA) and octanoic acid (OA) anions in aqueous solutions, respectively. The copolymer materials are herein referred to as macromolecular imprinted materials (MIMs) since their design strategy incorporates a porogen macromolecule (β-CD) within a cross-linked hexamethylene diisocyanate (HDI) framework. We report the tunable uptake of OA and PFOA anions from aqueous solution with variable adsorption modes, in accordance with the composition of the MIMs. The sorption results with granular activated carbon (GAC) were compared at 295K and pH values exceeding the pKa values of each adsorbate. The BET and Sips models provided estimates of the monolayer sorption capacity (Qm) and related equilibrium sorption parameters. The Qm value for GAC with PFOA was ∼1.4mmol/g; whereas, a greater Qm value for PFOA (up to 2.6mmol/g) was observed with the MIMs. GAC displays greater sorption capacity toward PFOA at relatively low Ce values and saturation of the monolayer occurs at Ce∼0.5mM. The MIMs/PFOA system displays monolayer completion at values of Ce∼1mM and multilayer sorption when Ce>1mM. Equilibrium sorption of PFOA onto MIMs occurs at the inclusion sites of β-CD and interstitial binding sites of the polymeric framework. Surface adsorption of the PFOA anion occurs between the PFOA carboxylate head group and dipolar interstitial domains of the cross-linker framework. The MIMs sorbents display tunable and favorable binding with PFOA and OA anions where the uptake (per mg MIMs) with PFOA was ∼5–33% (5μM–5mM) and with OA was ∼0.5–5% (1–20mM). The overall sorptive uptake of OA and PFOA anions by the MIMs sorbents meets or exceeds those observed for GAC.

ANALYSIS OF FACTORS DETERMINING THE BEHAVIOUR OF CHROMIUM IN SOME ROMANIAN SOILS

Chromium (Cr) is one of the most common metal contaminants in soil because of its use in ore refining, production of steel and alloys, metal plating, tanneries, wood preservation, and pigmentation. In soil environment, the most stable oxidation states of chromium are Cr (III) and Cr (VI). While Cr (III) is considered an essential trace element for the functioning of living organisms, Cr (VI) is toxic and carcinogenic to humans via inhalation for long exposures, since it is easily soluble and mobile in soils and can be leached into surface water or groundwater, and taken up by plants. The efficacy of remediation processes are highly dependent on chromium sorption and desorption kinetics and on the influence of competing solute anions. Models to predict the transport of Cr(VI) in soils must therefore incorporate these effects. The objective of the study was to speciate and to evaluate various soil Cr species in relation to soil properties. Adsorption and reduction of added Cr(VI) were characterized in soils with contrasting pH, organic matter contents, and chemical and mineralogical properties. Batch experiments are used to determine equilibrium sorption parameters for chromium by soil and to study sorption kinetics that are relevant to soil contamination sites. The distribution of metal contaminant in soils can be strongly localized by transport limitations and redox gradients within soil aggregates. The soils adsorption and reduction capacities were eventually overwhelmed, however, and permitted the passage of Cr(VI) into the underlying ground water.

Sorption of As, Cd and Tl as influenced by industrial by-products applied to an acidic soil: Equilibrium and kinetic experiments

In situ stabilization of toxic elements in contaminated soils by the addition of amendments is being considered as an effective technique for remediation. In this paper, we performed both kinetics and equilibrium-based sorption experiments of three toxic elements (As, Cd and Tl) in soils amended with two by-products (phosphogypsum and sugar foam, rich in gypsum and calcium carbonate, respectively) to ascertain the feasibility of their application for improving the sorption capacity of As, Cd and Tl from the soil at 25, 35 and 50 °C. Kinetic studies indicated that the sorption follows a pseudo-second-order (PSO) kinetics and the sorption is a two-step diffusion process where both film and intraparticle diffusion played important roles in the sorption mechanisms of the elements. The Langmuir isotherms applied for sorption studies showed that the estimated maximum sorption capacity of the elements in control and amended soils decreased in the order of Cd > As > Tl. Using the thermodynamic equilibrium parameters obtained at different temperatures, the thermodynamic constants of sorption (Δ G, Δ H and Δ S) were also evaluated, indicating spontaneous and endothermic nature of the process, except Tl which was exothermic. An optimal scaling procedure was undertaken to determine the relationships between the kinetic and equilibrium sorption parameters. By means of statistical analysis it was seen that these inter-parametric relationships are dependent on the element nature.

Multi-process herbicide transport in structured soil columns: Experiments and model analysis

Model predictions of pesticide transport in structured soils are complicated by multiple processes acting concurrently. In this study, the hydraulic, physical, and chemical nonequilibrium (HNE, PNE, and CNE, respectively) processes governing herbicide transport under variably saturated flow conditions were studied. Bromide (Br −), isoproturon (IPU, 3-(4-isoprpylphenyl)-1,1-dimethylurea) and terbuthylazine (TER, N 2-tert-butyl-6-chloro- N 4-ethyl-1,3,5-triazine-2,4-diamine) were applied to two soil columns. An aggregated Ap soil column and a macroporous, aggregated Ah soil column were irrigated at a rate of 1 cm h − 1 for 3 h. Two more irrigations at the same rate and duration followed in weekly intervals. Nonlinear (Freundlich) equilibrium and two-site kinetic sorption parameters were determined for IPU and TER using batch experiments. The observed water flow and Br − transport were inversely simulated using mobile–immobile (MIM), dual-permeability (DPM), and combined triple-porosity (DP-MIM) numerical models implemented in HYDRUS-1D, with improving correspondence between empirical data and model results. Using the estimated HNE and PNE parameters together with batch-test derived equilibrium sorption parameters, the preferential breakthrough of the weakly adsorbed IPU in the Ah soil could be reasonably well predicted with the DPM approach, whereas leaching of the strongly adsorbed TER was predicted less well. The transport of IPU and TER through the aggregated Ap soil could be described consistently only when HNE, PNE, and CNE were simultaneously accounted for using the DPM. Inverse parameter estimation suggested that two-site kinetic sorption in inter-aggregate flow paths was reduced as compared to within aggregates, and that large values for the first-order degradation rate were an artifact caused by irreversible sorption. Overall, our results should be helpful to enhance the understanding and modeling of multi-process pesticide transport through structured soils during variably saturated water flow.

Application of Two‐Site/Two‐Region Models for Studying Simultaneous Nonequilibrium Transport and Degradation of Pesticides

AbstractQuantitative laboratory study of pesticide sorption and degradation during transport can provide insight into the basic processes affecting pesticide fate in field soils. Accordingly, we demonstrate the application of analytical solutions of two‐site/two‐region transport models useful in studying simultaneous pesticide sorption and degradation. Soil‐column displacement experiments involving 3H2O, Cl, and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) were conducted during steady‐state water flow at two pore‐water velocities and two pesticide concentrations. The soil used is a Valois silty loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). Effluent data from these experiments were used to demonstrate the application of these analytical solutions, as well as a parameter‐estimation computer program based on these solutions. The ability to use laboratory‐derived estimates of equilibrium sorption parameters to describe sorption under flowing conditions was evaluated at each flow velocity. Significant correlation between soil sorption partitioning and degradation prevents the simultaneous determination of both processes using these solutions. However, estimates of degradation obtained from mass balances of the column data were useful in identifying the equilibrium sorption parameters. Data collected elsewhere for 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) herbicide transport were used as an additional example of the application of the model with degradation. Strengths and weaknesses of the models, and suggestions for further study, are presented.