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

Maryam Yazdani,Riku Vahala,Kevin Conley,Elina Virolainen

doi:10.3390/polym10010025

Abstract

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.

Highlights

Phosphate is an important element for many natural organisms, yet in high concentrations, it can cause serious eutrophication in natural waters [1,2,3,4,5]
This study developed zinc(II)–chitosan bio-sorbents for phosphate removal from aqueous solution
The effect of operational parameters, e.g., pH, dose and contact time, on the adsorption phosphate by the complexes was explored in detail

Summary

Introduction

Phosphate is an important element for many natural organisms, yet in high concentrations, it can cause serious eutrophication in natural waters [1,2,3,4,5]. The exceeding amount of nutrients leads to the excessive growth of plants and algae. This phenomenon reduces the dissolved oxygen in the water, which disturbs the natural balance of organisms, and causes, e.g., mass fish death [1,6]. Phosphorus dissolves into natural waters from weathered rocks, peat land and forests, and it gets into the communal wastewaters through agriculture, human settlement and industry [7,8]. Miettinen et al [8] have studied the connection of phosphorus and bacterial growth in drinking water sources and showed

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Conclusion