Eveliina Repo

Heavy metals adsorption by novel EDTA-modified chitosan–silica hybrid materials

Novel adsorbents were synthesized by functionalizing chitosan-silica hybrid materials with (ethylenediaminetetraacetic acid) EDTA ligands. The synthesized adsorbents were found to combine the advantages of both silica gel (high surface area, porosity, rigid structure) and chitosan (surface functionality). The Adsorption potential of hybrid materials was investigated using Co(II), Ni(II), Cd(II), and Pb(II) as target metals by varying experimental conditions such as pH, contact time, and initial metal concentration. The kinetic results revealed that the pore diffusion process played a key role in adsorption kinetics, which might be attributed to the porous structure of synthesized adsorbents. The obtained maximum adsorption capacities of the hybrid materials for the metal ions ranged from 0.25 to 0.63 mmol/g under the studied experimental conditions. The adsorbent with the highest chitosan content showed the best adsorption efficiency. Bi-Langmuir and Sips isotherm model fitting to experimental data suggested the surface heterogeneity of the prepared adsorbents. In multimetal solutions, the hybrid adsorbents showed the highest affinity toward Pb(II).

Removal of Co(II) and Ni(II) ions from contaminated water using silica gel functionalized with EDTA and/or DTPA as chelating agents.

In this study, the removal of Co(II) and Ni(II) ions from contaminated water was investigated using silica gel materials functionalized with both ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). The modified adsorbents were characterized using elemental analysis, surface area and pore size analysis, and zeta potential analysis. The adsorption and regeneration studies were conducted in batch mode. The optimum conditions for the removal of both metals at an initial concentration of 10mg/L were 2g/L of dose, pH 3, 50 rpm of agitation speed and 4h of contact time. The removal of Co(II) and Ni(II) by EDTA- and/or DTPA-modified silica gels was substantially higher than that by their unmodified form. The maximum Co(II) and Ni(II) uptakes by the EDTA-modified silica gel were 20.0 and 21.6 mg/g, comparable to their adsorption capacities by DTPA-modified silica gel (Co(II): 16.1mg/g; Ni(II): 16.7 mg/g). At the same concentration of 10mg/L, the removal of both metals by the modified adsorbents ranged from 96% to 99%. The two-site Langmuir model was representative to simulate adsorption isotherms. The kinetics of Co(II) and Ni(II) adsorption by modified silica gels followed pseudo-second-order.

EDTA-Cross-Linked β-Cyclodextrin: An Environmentally Friendly Bifunctional Adsorbent for Simultaneous Adsorption of Metals and Cationic Dyes

The discharge of metals and dyes poses a serious threat to public health and the environment. What is worse, these two hazardous pollutants are often found to coexist in industrial wastewaters, making the treatment more challenging. Herein, we report an EDTA-cross-linked β-cyclodextrin (EDTA-β-CD) bifunctional adsorbent, which was fabricated by an easy and green approach through the polycondensation reaction of β-cyclodextrin with EDTA as a cross-linker, for simultaneous adsorption of metals and dyes. In this setting, cyclodextrin cavities are expected to capture dye molecules through the formation of inclusion complexes and EDTA units as the adsorption sites for metals. The adsorbent was characterized by FT-IR, elemental analysis, SEM, EDX, ζ-potential, and TGA. In a monocomponent system, the adsorption behaviors showed a monolayer adsorption capacity of 1.241 and 1.106 mmol g(-1) for Cu(II) and Cd(II), respectively, and a heterogeneous adsorption capacity of 0.262, 0.169, and 0.280 mmol g(-1) for Methylene Blue, Safranin O, and Crystal Violet, respectively. Interestingly, the Cu(II)-dye binary experiments showed adsorption enhancement of Cu(II), but no significant effect on dyes. The simultaneous adsorption mechanism was further confirmed by FT-IR, thermodynamic study, and elemental mapping. Overall, its facile and green fabrication, efficient sorption performance, and excellent reusability indicate that EDTA-β-CD has potential for practical applications in integrative and efficient treatment of coexistenting toxic pollutants.

Aminopolycarboxylic acid functionalized adsorbents for heavy metals removal from water.

Due to the excellent chelating properties of aminopolycarboxylic acid (APCAs), they can be used for the removal of metals from contaminated waters. This paper reviews the research results obtained for both commercial and self-prepared adsorbents functionalized with four most common APCAs: iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). The structural characteristics and unique metal binding properties of these chelating adsorbents are presented. The theory of the adsorption phenomena is discussed based on the kinetics of adsorption, equilibrium adsorption isotherm models, and thermodynamic models. The most important applications of APCA-functionalized adsorbents are also described. APCA-functionalized adsorbents are found to be highly promising materials for metal removal from contaminated waters.

Cauliflower-like CdS microspheres composed of nanocrystals and their physicochemical properties

Cauliflower-like cadmium sulfide (CdS) microspheres composed of nanocrystals have been successfully synthesized by a hydrothermal method using poly(ethylene glycol) (PEG) as the template coordination agent and characterized by a variety of methods. Our experiments confirmed that the size of the CdS microspheres could be easily modified by controlling the chain length of PEG. Powder X-ray diffraction and Raman spectroscopy measurements revealed the cubic structure of the CdS microspheres; morphological studies performed by HR-SEM and HR-TEM methods showed the cauliflower-like structure of the synthesized CdS microspheres. Each microsphere was identified to be created by the self-assembly of CdS nanocrystals and is attributed to the oriented aggregation of the CdS nanocrystals around a polymer-Cd(2+) complex spherical framework structure. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) analysis confirmed the stoichiometries of the CdS microspheres. Diffuse reflectance spectrum (DRS) measurements showed that increasing the PEG chain length increased the band gap value of the CdS microspheres slightly, from 1.99 to 2.06 eV. The cauliflower-like CdS microspheres could be applied to photocatalytic degradation studies.

Capture of Co(II) from its aqueous EDTA-chelate by DTPA-modified silica gel and chitosan

The adsorption of Co(II) by diethylenetriaminepentaacetic acid (DTPA)-modified silica gel and chitosan in the presence of EDTA and other interfering species was studied. Co(II) removal ranged from 93% to 96% from the solutions where Co(II) was totally chelated by EDTA. The amount of oxalate or Fe(II) did not affect the adsorption of Co(II) in the case of DTPA-chitosan. However, increasing the amount of oxalate enhanced the adsorption performance of DTPA-silica gel, probably due to the formation of new active sites on the silica gel surface. DTPA-chitosan was also effective in simulated decontamination solutions. For DTPA-silica gel, the rate of adsorption of free Co(II) was controlled by pore diffusion, but the rate of adsorption of Co(II)EDTA was controlled by the surface chelation reaction, which was attributed to the inhibited diffusion of Co(II)EDTA inside the silica gel mesopores. However, the macroporous structure of DTPA-chitosan enabled pore diffusion of both Co(II) and Co(II)EDTA. The equilibrium isotherms of DTPA-silica gel were best described by a BiLangmuir model, in which there are two different adsorption sites on the silica gel surface assigned to different speciations of DTPA. For DTPA-chitosan, the data fit best with a Sips model, which indicates system heterogeneity. Finally, measurements with capillary electrophoresis showed an increase in dissolved EDTA during adsorption, demonstrating the ability of DTPA-modified adsorbents to release Co(II) from its EDTA chelate. This promising result can provide a basis for applying the studied materials to the treatment of water effluents containing Co(II) chelated by EDTA by a simple one-step adsorption process.

An EDTA-β-cyclodextrin material for the adsorption of rare earth elements and its application in preconcentration of rare earth elements in seawater.

The separation and recovery of Rare earth elements (REEs) from diluted aqueous streams has attracted great attention in recent years because of ever-increasing REEs demand. In this study, a green synthesized EDTA-cross-linked β-cyclodextrin (EDTA-β-CD) biopolymer was prepared and employed in adsorption of aqueous REEs, such as La(III), Ce(III), and Eu(III). EDTA acts not only as cross-linker but also as coordination site for binding of REEs. The adsorption properties for the adsorption of REEs by varying experimental conditions were carried out by batch tests. The kinetics results revealed that the surface chemical sorption and the external film diffusion were the rate-determining steps of the adsorption process. The obtained maximum adsorption capacities of EDTA-β-CD were 0.343, 0.353, and 0.365mmolg(-1) for La(III), Ce(III) and Eu(III), respectively. Importantly, the isotherms fitted better to Langmuir than Freundlich and Sips models, suggesting a homogenous adsorption surface for REEs on the adsorbent. Moreover, the multi-component adsorption, which was modeled by extended Sips isotherms, revealed adsorbents selectivity to Eu(III). More significantly, the successful recoveries of the studied ions from tap water and seawater samples makes EDTA-β-CD a promising sorbent for the preconcentration of REEs from diluted aqueous streams.

Meso- and microporous soft templated hydrothermal carbons for dye removal from water

The hydrothermal carbonization (HTC) technique has shown a great ability in the synthesis of carbon materials with special properties for a wide range of different applications. Here, a hypersaline salt mixture (LiCl–ZnCl2) combined with hydrothermal carbonization was applied in order to obtain sulfur containing micro- and mesoporous (0.3–40 nm) monolithic carbons with high surface areas (400–550 m2 g−1) and well developed porosity (0.4–1.2 cm3 g−1). Fructose was used as a carbon source and sulfur was introduced in an aromatic configuration as 2-thiophenecarboxaldehyde. The resulting carbon materials showed a promising removal capacity (qe = 0.3 mmol g−1) towards methylene blue and the adsorption followed the Sips isotherm independent of the pH. Intraparticle diffusion appeared to control the adsorption kinetics. Carbon materials could be easily regenerated with simple ethanol washing. The dye pollutant could be completely desorbed from the adsorbents surface, while the adsorbent still maintained removal efficiency of above 90% during three cycles.

Adsorption behavior of hydrothermally treated municipal sludge & pulp and paper industry sludge

Aim of the study was to investigate how hydrothermal carbonization changes adsorption efficiency toward metal ions of typical sludges. Hydrothermal carbonization is a novel and green method of treating biomasses. Reactions take place in an aqueous environment at relatively mild temperature and high pressure resulting a different end biomass structure than obtained from traditional pyrolysis. Anaerobically digested sludge (ADS) and pulp and paper industry sludge (INS) were utilized as a feedstock. Adsorption behavior of ADS and INS was examined towards Pb(II), Cr(III), Cr(VI), As(III) and As(V). Both ADS and INS were found to remove Pb(II) effectively and followed Sips adsorption isotherm. Adsorption kinetics was fast and followed pseudo-second order model. Furthermore, intraparticle diffusion was observed to be partly responsible in the adsorption process. Hydrothermal carbonization indicated high potential for the production of novel carbonaceous materials for metal removal from waters.

Effect of Competing Anions on Arsenate Adsorption onto Maghemite Nanoparticles

Abstract This paper reports the effect of several competing anions on arsenate adsorption with maghemite nanoparticles. Sulphate (as SO 4 ), nitrate (as NO 3 -N), phosphate (as PO 4 -P) ions and silicate (as SiO 2 ) were studied in dual solution with arsenate. Moreover, the combined effect of ions and other water characteristics were examined with a natural groundwater sample which was spiked with a certain amount of arsenate. Arsenate batch adsorption experiments were carried out with two different kinds of maghemite-a commercially available one and a homemade one using the sol-gel process. Sulphate (≤250 mg·L −1 ) and nitrate (≤12 mg·L −1 ) had a negligible effect on the arsenate (0.5 mg·L −1 ) adsorption at pH 3. However, both phosphate (≤2.9 mg·L −1 ) and silicate (≤50 mg·L −1 ) had an adverse impact on arsenate (≤3 mg·L −1 ) adsorption at pH 7. Phosphate (≤1.5 mg·L −1 ) showed minimal competition with arsenate (0.5 mg·L −1 ), while silicate (≤10 mg·L −1 ) inhibition was insignificant for all studied As(V) concentrations at pH 3. The removal of arsenate from the groundwater sample was as efficient as from laboratory water for 0.5 mg·L −1 As(V) both at pH 3 and pH 7.