Nikolaos Lazaridis

Reactive and basic dyes removal by sorption onto chitosan derivatives

In this study, the removal of a reactive (Remazol Yellow Gelb 3RS) and a basic (Basic Yellow 37) dye from aqueous solutions was investigated using cross-linked chitosan derivatives as sorbents (either powder or beads), which have been grafted with carboxyl and amide groups. The sorption behavior of the materials was examined through equilibrium, kinetic and pH-edges experiments. The reuse of sorbents was affirmed by sequential sorption-desorption cycles. Three isotherms (Langmuir, Freundlich, and Langmuir-Freundlich) were used to fit the equilibrium data, while the pseudo-second order equation for the kinetic data. Chitosan powder presented higher sorption capacity than beads. Chitosan grafted with amide groups was found superior sorbent for reactive dye at pH 2 (Q(max)=1211 mg/g), while chitosan grafted with carboxyl groups for basic dye at pH 10 (Q(max)=595 mg/g). For both cases the optimum contact time was 4 h using 1 g/L sorbent. The characterization of sorbents was achieved by scanning electron microscopy, particle size analysis and FTIR spectroscopy.

Optimization of chitosan and β-cyclodextrin molecularly imprinted polymer synthesis for dye adsorption

In this study, two types of novel molecularly imprinted polymers (MIPs) were prepared, for toxic and carcinogenic dyes adsorption. Substrates of the polymeric matrix of the two MIPs were β-cyclodextrin and chitosan. The conditions in the polymerization/imprinting stage and in the rebinding/adsorption step were optimized. The effect of a range of parameters (polymer, cross-linker, and initiator concentrations, reaction time and pH) on the selectivity and adsorption capacity of the dye-MIPs were investigated. Their dye rebinding properties were demonstrated by equilibrium batch experiments (fitting with Freundlich model) and their kinetic rates were exported by the pseudo-first order model. Additionally, a thermodynamic evaluation was carried out through the determination of enthalpy, entropy, and free energy. The selectivity of MIPs was elucidated by their different rebinding capabilities in a trichromatic mixture (composed of related structurally dyes). Regeneration/reuse of the dye-loaded polymers was evaluated via sequential adsorption-desorption cycles.

Poly(itaconic acid)-grafted chitosan adsorbents with different cross-linking for Pb(II) and Cd(II) uptake.

Two novel chitosan (CS) adsorbents were prepared in powder form, after modification with the grafting of itaconic acid (CS-g-IA) and cross-linking with either glutaraldehyde (CS-g-IA(G)) or epichlorohydrin (CS-g-IA(E)). Their adsorption properties were evaluated in batch experiments for Cd(II) or Pb(II) uptake. Characterization techniques were applied to the prepared adsorbents as swelling experiments, TGA, SEM, XRD, and FTIR. Adsorption mechanisms were suggested for different pH conditions. Various adsorption parameters were determined as the effect of pH, contact time, and temperature. The maximum adsorption capacities for Cd(II) uptake were 405 and 331 mg/g for CS-g-IA(G) and CS-g-IA(E), respectively, revealing the capacity enhancement after grafting (124 and 92 mg/g were the respective values before grafting, respectively). A similar grafting effect was observed for Pb(II) uptake, proving its adsorption effectiveness on the CS backbone. The reuse of adsorbents was tested with 20 adsorption-desorption cycles.

Relating Interactions of Dye Molecules with Chitosan to Adsorption Kinetic Data

The scope of the present work is the study of the adsorption behavior of two dyes of different nature/class on several chitosan derivatives. The adsorbents used were grafted with different functional groups (carboxyl, amido, sulfonate, N-vinylimidazole) to increase their adsorption capacity and cross-linked to improve their mechanical resistance. This complete kinetic analysis was realized at 25, 45, and 65 degrees C to observe the effect of temperature on adsorption rates for each adsorbent-adsorbate system. Activated carbon was also used as an adsorbent for reference/comparison. The experimental equilibrium data were successfully fitted to the Langmuir-Freundlich (L-F) isotherms, presenting high correlation coefficients (R(2) approximately 0.998). A detailed pore-surface diffusion with local adsorption-desorption model has been developed to describe the adsorption kinetics in chitosan adsorbents. The existence of kinetic data in several temperatures assists in recognizing the diffusion mechanism in the adsorbent particles. The findings on diffusion mechanisms and the corresponding coefficients, from using the model to match the experimental data, are compatible with the expected adsorbent-dye interactions based on their chemical structure.

N-(2-Carboxybenzyl) grafted chitosan as adsorptive agent for simultaneous removal of positively and negatively charged toxic metal ions.

A chitosan material, cross-linked and grafted with N-(2-carboxybenzyl) groups, was evaluated as adsorbent to sufficiently remove both positively charged ions (Cu(II), Ni(II)) and negatively charged ones (Cr(VI), As(V)) from aqueous solutions. After complete characterization study with FTIR, SEM and BET analysis, the evaluation of adsorption was done with experiments at pH range 2-12 and then varying the initial concentrations of ions. Langmuir-Freundlich equation was used to fit the adsorption data and showed maximum adsorption capacities 308 mg/g at 25 °C for copper and 381 mg/g for nickel ions. The adsorption capacity of As(V) was 208 mg/g and 175 mg/g for Cr(VI). Also, a mechanistic (phenomenological) model of adsorption kinetics is employed to fit the kinetic data found using parameters with physical meaning, and clearly understand the process dynamics. The regeneration of adsorbents was presented in ten cycles of reuse (adsorption-desorption), showing the strong reuse potential of the adsorbent used.

Low-swelling chitosan derivatives as biosorbents for basic dyes.

In this study, three different chitosan microsphere derivatives were prepared as sorbents for basic dyes. Preparation was succeeded by a novel cross-linking method based on ionic gelation with tripolyphosphate and subsequent covalent cross-linking with glutaraldheyde in order to address the large amount of swelling of the powdered form of the respective derivatives. Basic blue 3G (dye) was selected as the sorbate, and chitosan microsheres grafted with acrylamide and acrylic acid were used as biosorbents. Techniques such as FTIR spectroscopy, SEM, and swelling measurements facilitated the evaluation of the materials. Sorption-desorption experiments over the whole pH range were carried out to reveal the optimum value of sorption-desorption. The Langmuir isotherm model was used to fit the equilibrium experimental data, giving a maximum sorption capacity of 0.808 mmol/g at 338 K. An intraparticle diffusion model was employed to fit the kinetic data, and the resulting diffusion coefficients were in the range of (1-10) x 10(-11) m(2)/s. Thermodynamic analysis showed that the sorption process was spontaneous and endothermic with an increased randomness. In addition, sorption experiments were realized with a mixture of three basic dyes at various concentrations of sorbents.

POWDERED ACTIVATED CARBON SEPARATION FROM WATER BY FOAM FLOTATION

Abstract Powdered activated carbon was separated from dilute aqueous suspensions (200–1000 mg/L) by foam flotation using surfactants (anionic or cationic). The effects of surfactant type, pH value of the suspension, initial carbon and surfactant concentrations, flotation time, and air flow rate on the dispersed-air flotation of powdered activation carbon were investigated. In optimum conditions the powdered activated carbon separation was almost complete. The ζ-potential of powdered activated carbon was also measured in the presence and absence of surfactants. Finally, carbon flotation was examined after the carbon had adsorbed chromate ions from an acidic solution (pH 2). Almost complete separation of Cr(VI)-loaded carbon was obtained by using an anionic surfactant.

Magnetic modification of microporous carbon for dye adsorption

In this study, impregnation of microporous activated carbon with magnetite was achieved by co-precipitation of iron salts onto activated carbon. The evaluation of the adsorption ability of this material was examined using the anionic dye Reactive Black 5 as model dye pollutant (adsorbate). The effect of pH, ionic strength, contact time and initial dye concentration were also studied. It was found that high pH and high ionic strength favor the adsorption of Reactive Black 5. The adsorption kinetics and isotherms were well fitted by the fractal BS model and Langmuir model, respectively. The impregnation with magnetite decreases the adsorption capacity of activated carbon. Thermal re-activation of dye-loaded activated carbons was also succeeded. The characterization of the magnetic carbons was investigated by various techniques (SEM/EDAX, VSM, BET, FTIR, XRD, DTG) revealing many possible interactions in the carbon-dye system.

Removal of Cr(VI), Mo(VI), and V(V) Ions from Single Metal Aqueous Solutions by Sorption or Nanofiltration

The removal of Cr(VI), Mo(VI), or V(V) anions from single metal aqueous solutions was studied. Two alternative treatment methods were applied: (1) sorption of these anions onto commercially available akaganeite (β-FeOOH) or (2) nanofiltration, using a commercial spiral-wound pilot-scale unit. During sorption experiments, kinetics and equilibrium were mainly studied. A modified second-order kinetic model was found to better fit the kinetic results. Freundlich isotherms better described (slightly) chromium and molybdenum equilibrium sorption experiments; whereas Langmuir isotherm better described vanadium equilibrium. During nanofiltration experiments, the influence of pH and of initial anion concentration was mainly studied, using a fixed background electrolyte concentration.

REMOVAL OF METAL IONS FROM SIMULATED WASTEWATER BY SACCHAROMYCES YEAST BIOMASS: COMBINING BIOSORPTION AND FLOTATION PROCESSES

Aqueous solutions containing heavy metals can be successfully treated by a combination of biosorption and flotation, in order to remove (or recover) the contained metals. Nonliving biomass of yeast Saccharomyces, which is a solid industrial by-product, was found to be a suitable biosorbent of metal ions (zinc, copper, and nickel). It was found also possible to reuse it after the appropriate desorption treatment. Electrokinetic behavior of biomass as well as elution and multiple-cycles operation were investigated. The dispersed-air flotation technique, which was selected for generation of bubbles, was subsequently examined for solid/liquid separation, in order to harvest the metals-loaded biomass downstream. The main parameters affecting the flotation process were studied, such as the solution pH, the concentration of flotation collector (surfactant), the preliminary biomass modification, and the biomass concentration. The biosorptive flotation method was found promising for remediation applications of wastewaters containing toxic metals.