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Polymers 2018, 10(1), 25; doi:10.3390/polym10010025

Chitosan–Zinc(II) Complexes as a Bio-Sorbent for the Adsorptive Abatement of Phosphate: Mechanism of Complexation and Assessment of Adsorption Performance

Water and Wastewater Engineering Research Group, School of Engineering, Aalto University, P.O. Box 15200, FI-00076 Aalto, Finland
COMP Centre of Excellence, Department of Applied Physics, School of Science, Aalto University, FI-00076 Aalto, Finland
Author to whom correspondence should be addressed.
Received: 21 October 2017 / Revised: 20 December 2017 / Accepted: 22 December 2017 / Published: 25 December 2017
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
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This study examines zinc(II)–chitosan complexes as a bio-sorbent for phosphate removal from aqueous solutions. The bio-sorbent is prepared and is characterized via Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Point of Zero Charge (pHPZC)–drift method. The adsorption capacity of zinc(II)–chitosan bio-sorbent is compared with those of chitosan and ZnO–chitosan and nano-ZnO–chitosan composites. The effect of operational parameters including pH, temperature, and competing ions are explored via adsorption batch mode. A rapid phosphate uptake is observed within the first three hours of contact time. Phosphate removal by zinc(II)–chitosan is favored when the surface charge of bio-sorbent is positive/or neutral e.g., within the pH range inferior or around its pHPZC, 7. Phosphate abatement is enhanced with decreasing temperature. The study of background ions indicates a minor effect of chloride, whereas nitrate and sulfate show competing effect with phosphate for the adsorptive sites. The adsorption kinetics is best described with the pseudo-second-order model. Sips (R2 > 0.96) and Freundlich (R2 ≥ 0.95) models suit the adsorption isotherm. The phosphate reaction with zinc(II)–chitosan is exothermic, favorable and spontaneous. The complexation of zinc(II) and chitosan along with the corresponding mechanisms of phosphate removal are presented. This study indicates the introduction of zinc(II) ions into chitosan improves its performance towards phosphate uptake from 1.45 to 6.55 mg/g and provides fundamental information for developing bio-based materials for water remediation. View Full-Text
Keywords: zinc–chitosan complexes; characterization; bio-sorbent; phosphate; adsorption; mechanism; thermodynamic zinc–chitosan complexes; characterization; bio-sorbent; phosphate; adsorption; mechanism; thermodynamic

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Yazdani, M.R.; Virolainen, E.; Conley, K.; Vahala, R. Chitosan–Zinc(II) Complexes as a Bio-Sorbent for the Adsorptive Abatement of Phosphate: Mechanism of Complexation and Assessment of Adsorption Performance. Polymers 2018, 10, 25.

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