Eleni A. Deliyanni

Sorption of As(V) ions by akaganéite-type nanocrystals.

A priority pollution problem, the removal of arsenate oxyanions from dilute aqueous solutions by sorption onto synthetic akaganéite (beta-FeO(OH)) was the aim of the present study. This is an innovative inorganic adsorbent material prepared in the laboratory, following a new method of preparation. The effect of akaganéite and arsenate concentration, the contact time, temperature, solution pH value, and ionic strength variation on the treatment process was mainly investigated during this study. Typical adsorption isotherms were determined, which were found to fit sufficiently the typical Langmuir equation. The mechanism of sorption was examined by electrokinetic, X-ray diffraction, Fourier transmission infrared and scanning electron microscopy measurements. Promising results were obtained, due to the favourite characteristics of the adsorbent applied.

Akaganéite-type β-FeO(OH) nanocrystals : preparation and characterization

Abstract The preparation of nanocrystalline β-FeO(OH) by precipitation from an aqueous solution of the chloride salt and the investigation of relative surface properties of the iron oxyhydroxide gel were the aims of this study. A new advantageous method using ammonium carbonate as precipitating agent is presented by which the synthesis of akaganeite (β-FeO(OH) was accomplished. Akaganeite was transformed to iron oxide hydroxide (FeOOH) and finally to hematite (α-Fe 2 O 3 ) after thermal treatment at 473 and 673 K, respectively. The use of a volatile agent for the hydrolysis process, the special method of chloride ion removal, as well as the freeze-drying technique, led to the production of a material consisting of nanocrystals with high surface area and defined pore size distribution.

Mercury(II) Removal with Modified Magnetic Chitosan Adsorbents

Two modified chitosan derivatives were prepared in order to compare their adsorption properties for Hg(II) removal from aqueous solutions. The one chitosan adsorbent (CS) is only cross–linked with glutaraldehyde, while the other (CSm), which is magnetic, is cross-linked with glutaraldehyde and functionalized with magnetic nanoparticles (Fe3O4). Many possible interactions between materials and Hg(II) were observed after adsorption and explained via characterization with various techniques (SEM/EDAX, FTIR, XRD, DTG, DTA, VSM, swelling tests). The adsorption evaluation was done studying various parameters as the effect of pH (optimum value 5 for adsorption and 2 for desorption), contact time (fitting to pseudo–first, –second order and Elovich equations), temperature (isotherms at 25, 45, 65 °C), in line with a brief thermodynamic analysis (ΔG0 < 0, ΔH0 > 0, ΔS0 > 0). The maximum adsorption capacity (fitting with Langmuir and Freundlich model) of CS and CSm at 25 °C was 145 and 152 mg/g, respectively. The reuse ability of the adsorbents prepared was confirmed with sequential cycles of adsorption-desorption.

Akaganeite and goethite-type nanocrystals: synthesis and characterization

The synthesis of iron oxyhydroxides and hydroxides is reported in this work, by the use of a novel, simple and low-cost method. The preparation involves the hydrolysis of aqueous solutions of ferric salts followed by membrane purification and freeze drying of the products. Three different iron precursors have been tested and combined to three different volatile precipitating agents. The obtained products were akaganeite, goethite and iron(III) hydroxide. Irrespective of the starting materials used, all three products, although different in chemical nature, presented some very interesting and unique features; they consisted of nanoparticles with mean sizes ranging from 1 to 10 nm and they had very high surface areas and pore sizes in the meso- and micropore regions. The produced materials were examined by powder X-ray diffraction for crystalline phase identification, TEM and XRD for particle size estimation and nitrogen sorption for surface area, pore volume and pore size distribution measurement.

The role of chitosan as nanofiller of graphite oxide for the removal of toxic mercury ions

The present study focuses on the role of chitosan (CS) as nanofiller of graphite oxide (GO) in order to prepare composite materials with improved Hg(II) adsorption properties. The removal of Hg(II) from aqueous solutions was studied using adsorbents as graphite oxide (GO), graphite oxide nanofilled with chitosan (GO/CS) and magnetic chitosan (GO/mCS). Many possible interactions between materials and Hg(II) were observed after adsorption and explained via characterization with various techniques (SEM/EDAX, FTIR, XRD, DTG). The adsorption evaluation was done studying various parameters as the effect of pH (both in adsorption and desorption), contact time (pseudo-second order fitting), temperature (isotherms at 25, 45, 65 °C), in line with a brief thermodynamic analysis (ΔG(0), ΔH(0), ΔS(0)). The maximum adsorption capacity (fitting with Langmuir model) of GO at 25 °C was Qmax=187 mg/g, while after the CS nanofilling (formation of the composite GO/CS), Qmax was increased to 381 mg/g with a further enhancement for GO/mCS (Qmax=397 mg/g).

Interactions of 4,6-Dimethyldibenzothiophene with the Surface of Activated Carbons

Two carbon samples, commercial wood-based carbons and laboratory-derived polymer-based carbon, were oxidized to two different levels of surface acidity. The resulting adsorbents were characterized using adsorption of nitrogen, potentiometric titration, FTIR, SEM/EDAX, and elemental analysis. On the carbons obtained, the adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from hexadecane was carried out in the range of the initial concentrations between 10 and 150 ppmw sulfur. The results indicate that pores with diameters less than 10 A are important for adsorption of 4,6-DMDBT. Chemical transformations, likely oxidation, occur in larger pores, and the extent of this process is governed by the availability of oxidants. Those oxidants might be either chemisorbed oxygen and/or iron oxides present in an inorganic matter. Surface acidic groups, when located in larger pores, attract 4,6-DMDBT via specific interactions, and this can increase the amount adsorbed. When the density of these groups is high, they create obstacles for the effective packing of the adsorbate in the pore space and, thus, the amount adsorbed decreases.

Modeling the sorption of metal ions from aqueous solution by iron-based adsorbents

The possibility of using iron-based adsorbents (i.e. akaganéite or goethite) to remove heavy metal ions from aqueous solutions was the aim of the present review paper. Synthesized material was used in two forms, i.e. in fine powder of nanocrystals and in the form of grains (as granular). The main examined parameters were the quantity of sorbent, the presence of ionic strength, the pH value of solution and the metals speciation, including the presence of complexing agents. The removal efficiency of the packed-bed column was examined and compared. Typical adsorption models were discussed and the bed depth-service time equation has been applied to the sorption results in order to model the column operation.

Magnetic Graphene Oxide: Effect of Preparation Route on Reactive Black 5 Adsorption

In this study, the effect of preparation route of magnetic graphene oxide (mGO) on Reactive Black 5 (RB5) adsorption was investigated. The synthesis of mGO was achieved both with (i) impregnation method (mGOi nanoparticles), and (ii) co-precipitation (mGOp nanoparticles). After synthesis, the full characterization with various techniques (SEM, FTIR, XRD, DTA, DTG, VSM) was achieved revealing many possible interactions/forces of dye-composite system. Effects of initial solution pH, effect of temperature, adsorption isotherms and kinetics were investigated in order to conclude about the aforementioned effect of the preparation method on dye adsorption performance of the magnetic nanocomposites. The adsorption evaluation of the magnetic nanoparticles presented higher adsorption capacity of mGOp derivative (188 mg/g) and lower of mGOi (164 mg/g). Equilibrium experiments are also performed studying the effect of contact time (pseudo-first and -second order equations) and temperature (isotherms at 25, 45 and 65 °C fitted to Langmuir and Freundlich model). A full thermodynamic evaluation was carried out, calculating the parameters of enthalpy, free energy and entropy (ΔH0, ΔG0 and ΔS0).

Removal of dorzolamide from biomedical wastewaters with adsorption onto graphite oxide/poly(acrylic acid) grafted chitosan nanocomposite

A novel graphite oxide/poly(acrylic acid) grafted chitosan nanocomposite (GO/CSA) was prepared and used as biosorbent for the removal of pharmaceutical compound (dorzolamide) from biomedical synthetic wastewaters. The performance was evaluated taking into account pH, kinetics and thermodynamics of adsorption. GO/CSA presented higher adsorption capacity in comparison with the parent materials (graphite oxide and poly(acrylic acid) grafted chitosan). All adsorbents prepared were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and potentiometric titration. The surface features were also evaluated after the dorzolamide adsorption in order to derive the adsorption mechanism. It was suggested that the reactive groups of GO and CSA can interact with the amino groups of dorzolamide and mainly the abundance of carboxyl groups of GO/CSA composite was the main reason for its enhanced adsorption capacity.

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.