Elsevier

Carbohydrate Polymers

Volume 91, Issue 2, 16 January 2013, Pages 631-637
Carbohydrate Polymers

Preparation of amino terminated polyamidoamine functionalized chitosan beads and its Cr(VI) uptake studies

https://doi.org/10.1016/j.carbpol.2012.08.028Get rights and content

Abstract

Chitosan beads, functionalized by amino terminated hyperbranched dendritic polyamidoamine (up to 3rd generation) were prepared by Michael addition of methyl acrylate to amino groups on the chitosan surface and amidation of terminal ester groups by ethylene diamine. All the three generation chitosan beads were used for chromium removal along with raw chitosan beads. However, the 3rd generation polyamidoamine chitosan beads (3ACB) have been protonated using HCl (3ACBP)/loaded with zirconium using ZrOCl2·8H2O (3ACBZr) to enhance the sorption capacity towards Cr(VI). The zirconium loaded chitosan beads showed higher Cr(VI) sorption than the other modified chitosan beads. The zirconium loaded chitosan beads were characterized using SEM, EDAX, FT-IR, XRD, DSC and TGA. The system variables studied include agitation time, initial concentration of sorbate, pH, co-ions in the medium and temperature on the sorption of chromium. The chromium uptake onto 3ACBZr obeys the Freundlich isotherm. Thermodynamic studies revealed that the nature of chromium sorption is spontaneous and endothermic. The mechanism of chromium sorption onto the sorbent was established.

Highlights

► Zr4+ loaded polyamidoamine chitosan beads used to remove Cr(VI) for first time. ► Maximum sorption capacity with the minimum 2 h contact time. ► The Cr(VI) removal is via adsorption/electrostatic attraction. ► Polyamidoamine chitosan beads is a promising sorbent for enhanced removal of Cr(VI).

Introduction

Chitosan, a deacetylated derivative of chitin, is a natural polymer, highly hydrophilic, nontoxic, abundant, biocompatible, and biodegradable polymer (Muzzarelli et al., 2012). Chemical modifications of a large numbers of hydroxyl and amino groups present in chitosan, can obviously improve the physical and chemical properties of chitosan and will open ways to various applications in different fields like biomedical, food ingredients and water treatment (Jayakumar et al., 2010, Tsubokawa and Takayama, 2000). In recent years, hyperbranched polymers, represented as dendrimer, have received great attention because of their multifunctional properties, morphological features and potential use in medical applications, host–guest chemistry, cosmetics, dendritic catalysts (Ravi Kumar et al., 2004, Sashiwa et al., 2002a, Sashiwa et al., 2002b, Sashiwa et al., 2002c). Modification of terminal groups with different functionalities, such as acetamido, hydroxyl, carboxyl, quaternary ammonium leads to the versatile applicability of chitosan as well as dentrimeric materials. Presently, a dendrimer like hyperbranched polyamidoamine was grafted onto the surface of chitosan and used for heavy metal removal (Ma et al., 2009, Qu et al., 2008). Our previous study shows that the Cr(VI) sorption capacity of amino terminated hyperbranched dendritic polyamidoamine was very high when compare to protonated, carboxylated and amine grafted chitosan beads (Kousalya, Rajiv Gandhi, & Meenakshi, 2010). To increase the amino group in chitosan, dendritic chitosan was prepared. Further protonation of amino groups and rare earth metal ion loading increases the Cr(VI) removal than the aminated chitosan beads. The higher Cr(VI) sorption capacity of Zr(IV) loaded chitosan beads is due to its higher positive charge. Chitosan beads functionalized by Zr4+ loaded amino terminated hyperbranched dendritic polyamidoamine have not been reported for chromium removal. The probable mechanism of chromium sorption onto the sorbents was established.

Section snippets

Materials

Chitosan (85% deactetylated) was supplied by Pelican Biotech and Chemicals Labs, Kerala (India). Ethylenediamine, methyl acrylate, acetic acid and K2Cr2O7 were purchased from Merck (India) and all other chemicals used were of analytical grade.

Instrumentation

The FT-IR samples were prepared by mixing 0.01 g of the crushed chitosan beads with 0.1 g of spectroscopy grade KBr and pressing the mixture under higher pressure. Under pressure, the KBr melts and seals the chitosan beads into a matrix. The FT-IR spectra

FT-IR analysis

Fig. 1a shows the FT-IR spectra obtained for 3ACB and 3ACBZr. 3ACB showed a broad band around 3419 cm−1 corresponding to both primary amine and OH stretching groups of the chitosan moiety. Generally, primary amines will show two stretching bands around 3400–3300 cm−1 and 3330–3250 cm−1. In contrast, this was not observed in the present case even though there was primary amine functionality in 3ACB. Instead a very broad band was observed. This may be due to the overlapping of the stretching bands

Conclusions

3ACBZr possess higher SC than the other modified chitosan beads. This is because of the presence of more amine groups and Zr4+ loading. The amount of Cr(VI) ions, adsorbed per unit mass of adsorbents at 303 K from 200 mg/L of Cr(VI), by chitosan beads and 3ACBZr were 21 and 185 mg/g, respectively. All the sorbents need 200 min as the contact time for maximum SC. The SC of the sorbents was influenced by the pH of the medium. The maximum sorption capacity was at 2–4 pH. The sorption data follows

Acknowledgements

The corresponding author is grateful to the DRDO (No. ERIP/ER/0703670/M/01/1066), New Delhi, India for the financial support to carry out this research work. The first author likes to thank CSIR, New Delhi, India for awarding the SRF.

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