Abstract
This work investigates the application of 5-hydroxymethyl-furfural (HMF) as a grafting agent to chitosan (CS). The material produced was further modified by cross-linking. Three different derivatives were tested with molecular ratios CS/HMF of 1:1 (CS-HMF1), 2:1 (CS-HMF2) and 10:1 mol/mol (CS-HMF3)) to remove Cu2+ and Cd2+ from aqueous solutions. CS-HMF derivatives were characterized both before, and after, metal ions adsorption by using scanning electron microscopy (SEM), as well as Fourier-transform infrared (FTIR) spectroscopy thermogravimetric analysis (TGA), and X-Ray diffraction analysis (XRD). The CS-HMF derivatives were tested at pH = 5 and showed higher adsorption capacity with the increase of temperature. Also, the equilibrium data were fitted to Langmuir (best fitting) and Freundlich model, while the kinetic data to pseudo-first (best fitting) and pseudo-second order equations. The Langmuir model fitted better (higher R2) the equilibrium data than the Freundlich equation. By increasing the HMF grafting from 130% (CS-HMF1) to 310% (CS-HMF3), an increase of 24% (26 m/g) was observed for Cu2+ adsorption and 19% (20 mg/g) for Cd2+. By increasing from T = 25 to 65 °C, an increase of the adsorption capacity (metal uptake) was observed. Ten reuse cycles were successfully carried out without significant loss of adsorption ability. The reuse potential was higher of Cd2+, but more stable desorption reuse ability during all cycles for Cu2+.
Highlights
In recent years, there have been many published studies addressing the efficient decontamination or removal of various heavy metal ions from aqueous systems [1,2]
The discussion of experimental findings starts with the presentation of characterization results (SEM, X-Ray diffraction analysis (XRD))
Similar adsorption behavior was revealed for CS-HMF2ad and CS-HMF3ad
Summary
There have been many published studies addressing the efficient decontamination or removal of various heavy metal ions from aqueous systems [1,2]. Some good candidates are polymeric materials that can be modified, in order to obtain additional functional groups (grafting reactions) The latter is crucial because this method can drastically improve the adsorption capacity of the material. Chitosan is an amino-based polysaccharide and has a chemical type poly-β-(1→4)-2-amino-2-deoxy-D-glucose This polymer can be produced in abundance by following N-deacetylation reaction of chitin, which is its origin compound [21,22,23]. It must be mentioned that it is utopic to believe that there is one technique, or one adsorbent material, which can be successfully remove all heavy metal ions For this reason, in the present study, we select to remove with chitosan adsorbent materials one very toxic (Cd) and one highly-concentrated metal ion (Cu) from aqueous media. Equilibrium data, while the pseudo-first (PS1) and pseudo-second (PS2) order equations were applied to model the experimental kinetic data
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