Removal of Lead and Nickel Ions from Wastewater by Genipin Crosslinked Chitosan/Poly(ethylene glycol) Films

Crosslinked chitosan/poly(vinyl alcohol) nanofibers functionalized by ionic liquid for heavy metal ions removal

Nanostructure adsorbents namely nanofibers have been demonstrated to have a high adsorption rate and are efficient to treat wastewater. Herein, chitosan/poly(vinyl alcohol) (PVA) blend nanofiber membranes prepared by electrospinning method were crosslinked using glutaraldehyde and functionalized with 1-allyl-3-methylimidazolium chloride to be used as a potential bio-sorbent for heavy metal ions removal. The chitosan was first hydrolyzed before electrospinning with PVA, followed by crosslinking and further functionalized by ionic liquid to overcome the limitation of chitosan which has low adsorption capacity and unsuitable physical properties for the adsorption process. The morphology and the chemical bond formed were investigated by using field emission scanning electron microscopy with energy dispersive x-ray spectroscopy (FESEM-EDX) and Fourier transform infrared (FTIR) showing that the hydrolyzed chitosan/PVA nanofiber membranes were successfully crosslinked and functionalized. The synthesized adsorbent was evaluated in pure heavy metal ions solutions namely Pb(II), Mn(II), and Cu(II) and shown best performance for Pb(II) ions. The highest adsorption capacity recorded for Pb(II) ions was 166.34 mg/g and are well fitted to the Freundlich isotherm model and pseudo-second-order kinetic model to describe the adsorption equilibrium and kinetic rate of the Pb(II) uptake, respectively. The synthesized adsorbent clearly shows a great capability to remove Pb(II) ions.

Efficient adsorption of Cd2+ from aqueous solution using metakaolin geopolymers

In this study, geopolymers were prepared using metakaolin (MK) raw material under different alkali activator moduli (SiO₂/Na₂O = 0.8, 1.2, 1.6, 2.0 M ratio) in order to analyze their capacity and mechanism for adsorbing cadmium (Cd²⁺) from solution. Instrumental analyses including X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared (FTIR), and Brunauer-Emmett-Teller (BET) were performed to examine the mineralogical features of the MK and geopolymers before and after Cd²⁺ adsorption. The effect of initial pH, temperature, contact time, and initial concentration on Cd adsorption performance was studied to obtain the equilibrium isotherm. Kinetic data of the geopolymers fitted the pseudo-second-order kinetic model well. Moreover, the adsorption equilibrium data of Cd²⁺ adsorbed by the geopolymers fitted the Langmuir model better than the Freundlich model. The result shows that chemisorption dominates Cd²⁺ adsorption by geopolymers and that the adsorption capacity differs when prepared using different alkali-activated modulus agents. The geopolymer prepared using an alkali activator modulus of 0.8 M (molar ratio) exhibited the best Cd²⁺ adsorption performance with a maximum adsorption capacity of 70.3 mg g^-1. The removal rate of Cd²⁺ by geopolymer still remained above 85% after five round of recycling.

Selective adsorption of silver(I) ions over copper(II) ions on a sulfoethyl derivative of chitosan

This study presents a simple and effective method of preparation of N-(2-sulfoethyl) chitosan (NSE-chitosan) that allows obtaining a product with a degree of modification up to 1.0. The chemical structure of the obtained polymers was confirmed by FT-IR and 1H NMR spectroscopies. Cross-linking of N-(2-sulfoethyl) chitosans by glutaraldehyde allows preparation of sorbents for removal and concentration of metal ions. Capacity of sorbents towards hydroxide ions was determined depending on the degree of sulfoethylation under static and dynamic conditions. Dissociation constants of functional amino groups of the analyzed sorbents were determined by potentiometric titration. It was shown that basicity of the amino groups decreased (wherein pKa decreased from 6.53 to 5.67) with increase in degree of sulfoethylation. It explains the significant influence of sulfo groups on selectivity of sorption of metal ions on N-(2-sulfoethyl) chitosan-based sorbents. The investigated substances selectively remove copper(II) and silver(I) ions from solutions of complex composition. Wherein the selectivity coefficient KAg/Cu increased to 20 (pH 6.5, ammonium acetate buffer solution) with increase in degree of sulfoethylation of the sorbent up to 1.0.

Efficient removal of lead (II) ions and methylene blue from aqueous solution using chitosan/Fe-hydroxyapatite nanocomposite beads

Chitosan is a well-known sorbent and effective in the uptake of anionic or reactive dyes, but it has deficiency in adsorption of basic dyes. In this work, chitosan/Fe-substituted hydroxyapatite composite beads were prepared in a different ratio via embedding of hydroxyapatite into chitosan solution for removal of basic dye and heavy metal from aqueous solution. The composite beads were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy in order to reveal their composition and surface morphology. In this particular study, methylene blue (MB) and lead (Pb (II)) ions were selected as representatives of dye and a heavy metal, respectively. The various experimental conditions affecting dye adsorption were explored to achieve maximum adsorption capacity. Moreover, the kinetic, thermodynamic and adsorption isotherm models were employed for the description of the heavy metal and dye adsorption processes. The results indicated that the prepared hydrogel is an efficient adsorbent for the aforementioned dye and metal concomitant with the ability of regeneration without losing the original activity and stability for water treatment applications.

Simple synthesis and chelation capacity of N-(2-sulfoethyl)chitosan, a taurine derivative

This study presents a simple and effective synthesis method of N-(2-sulfoethyl)chitosan (NSE-chitosan) via a reaction between sodium 2-bromoethanesulfonate and chitosan that allows polymer transformation without using additional reagents and organic solvents. The chemical structure of the obtained NSE-chitosan was characterized by FT-IR and (1)H NMR spectroscopies. Thermogravimetric study of NSE-chitosan coupled with FT-IR analysis has shown stability of the polymer up to 200 °C, which almost does not change with the increase of degree of substitution (DS). The sorption of transition and alkaline earth metal ions from multicomponent solutions on NSE-chitosan was investigated. The synthesized sorbents showed the selective recovery of silver(I) and copper(II) ions from ammonium acetate buffer solution. The increase of DS enhanced the selectivity to silver(I) ions sorption in comparison with copper(II) ions. Selectivity coefficients K(Ag/Cu) increase from 1.3 to 10.9 with DS increasing up to 0.7 (ammonium acetate buffer solution, pH 6.5). Sorption isotherms of transition metal ions on NSE-chitosan with DS = 0.5 have been fitted using Langmuir, Freundlich, and Redlich-Peterson models. The maximum sorption capacities of sorbent in ammonium acetate buffer solution at pH 6.0 were 1.72 mmol/g for Cu(II), 1.23 mmol/g for Ag(I) and below 0.5 mmol/g for Co(II), Zn(II), Cd(II), Pb(II), Mn(II) and Ni(II) ions.