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. 2019 Oct 11;11(10):1658.
doi: 10.3390/polym11101658.

Eco-Friendly β-cyclodextrin and Linecaps Polymers for the Removal of Heavy Metals

Alberto Rubin Pedrazzo  1 , Alessandra Smarra  2 , Fabrizio Caldera  3 , Giorgia Musso  4 , Nilesh Kumar Dhakar  5 , Claudio Cecone  6 , Asma Hamedi  7   8 , Ilaria Corsi  9 , Francesco Trotta  10
Affiliations

Eco-Friendly β-cyclodextrin and Linecaps Polymers for the Removal of Heavy Metals

Alberto Rubin Pedrazzo et al. Polymers (Basel). .

Abstract

Environment-friendly nanosponges, having a high content of carboxyl groups, were synthesized by crosslinking β-cyclodextrin and linecaps, a highly soluble pea starch derivative, with citric acid in water. Additionally, pyromellitic nanosponges were prepared by reacting β-cyclodextrin and linecaps with pyromellitic dianhydride in dimethyl sulfoxide and used in comparison with the citric nanosponges. After ion-exchange of the carboxyl groups H+ with sodium ions, the ability of the nanosponges to sequester heavy metal cations was investigated. At a metal concentration of 500 ppm, the pyromellitate nanosponges exhibited a higher retention capacity than the citrate nanosponges. At lower metal concentrations (≤50 ppm) both the citrate and the pyromellitate nanosponges showed high retention capacities (up to 94% of the total amount of metal), while, in the presence of interfering sea water salts, the citrate nanosponges were able to selectively adsorb a significantly higher amount of heavy metals than the pyromellitate nanosponges, almost double in the case of Cu2+.

Keywords: citric acid polymers; crosslinked polymers; heavy metal adsorption; linecaps; nanosponge; β-cyclodextrin.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
β-cyclodextrin (β-CD) and amylose structure. From left to right, side view and front view of β-CD, side and front view of a 30 glucose units amylose chain.
Figure 2
Figure 2
Schematic representation of the synthesis reaction of β-PMDA (a) and β-CITR (b).
Figure 3
Figure 3
Fourier transform infrared analysis in attenuated total reflectance mode (FTIR-ATR) analysis of β-CITR (a) and LC-CITR (b) polymers before (solid lines) and after ion-exchange (dashed lines). Thermogravimetric analysis (TGA) of β-CITR (c) and LC-CITR (d) polymers before (solid lines) and after ion-exchange (dashed lines). The green lines indicate the TGA curve first derivative. Scanning electron microscopy (SEM) images of LC-CITR at 30× (e) and 400× (f) magnification.
Figure 4
Figure 4
Cu2+ adsorption over time by the β-CITR-Na+ (a) and LC-CITR-Na+ (b) polymers, added to 500 ppm Cu2+ solution.
Figure 5
Figure 5
Metal adsorption tests performed in 500 ppm metal solutions. The NSs’ adsorption capacity is expressed as a percentage of the initial amount of metal (a), weight ratio adsorbed metal to NS (b) and moles of adsorbed metal per gram of NS (c).
Figure 6
Figure 6
Cu2+ (a,b) and Zn2+ (c,d) adsorption tests on low concentration metal solutions. The amount of complexed metal ions is expressed as a percentage of the initial amount of metal (a,c) and as moles of adsorbed metal per gram of NS (b,d).
Figure 7
Figure 7
Cu2+ (a,b) and Zn2+ (c,d) adsorption tests on low concentration metal solutions prepared in artificial sea water. The amount of complexed metal ions is expressed as a percentage of the initial amount of metal (a,c) and as moles of adsorbed metal per gram of NS (b,d).
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