Cross-Linked β-Cyclodextrin for Removal of Toxic Metals from Wastewater
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Date
2019-11-21
Authors
Boureeni, Rasha Waleed
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Publisher
An-Najah National University
Abstract
Water is one of the essential renewable resources to preserve all forms of life. Human activities has an counter effect on the bodies of water. Water contamination occurs by addition of dangerous chemicals or foreign substances to water. The need to maintain a cleaner environment for the survival of aquatic and terrestrial lives is very important that increasingly concerns the ecologist. The most serious problem is environmental pollution of heavy metals and minerals in wastewater. So using adsorbents to remove toxic metals ions from contaminated water is necessary since they cause disruption to human organelles as they are a non-biodegradable contaminant.
β-Cyclodextrin (β-CyD) is cyclic oligosaccharide composed of 7 glucopyranose units linked by glycosidic bonds. It is a water-soluble carbohydrate with high performance for absorbing organic matters. In this work, β-cyclodextrin was modified to be insoluble in water and used in wastewater purification. The crosslinking will be carried out by reacting β-cyclodextrin with the polycarboxylic citric acid. The cross-linking adds a new functionality to β-cyclodextrin which is carboxyl groups. This modified β-cyclodextrin is a very good candidate to be used in wastewater purification from both metals and organic materials. The cross-linked β-cyclodextrin polymer was prepared by two methods A & B. The same procedure used for preparing the two polymers; the only difference is the amount of citric acid was three times the amount of beta-cyclodextrin in the polymer (B), while the quantities were equal in the polymer (A).
The new cross-linked β-cyclodextrin (co-β-CyDe-CA) was successfully prepared. Fourier Transform Infrared (FT-IR) results confirm the formation of the cross-linked β-cyclodextrin polymers (A, B). The removal experiments of toxic metal ions were carried under a wide range of pH, adsorbent dosage, temperature, initial concentration and contact time. Over 98% removal efficiency of the prepared polymers was achieved after 180 min, at pH around 9 and temperature about 30°C using 0.1 g weight of dosage and initial concentration of 50 mg/L of 10 mL of lead ions aqueous solution. The experimental results show that (co-β-CyDe-CA) was able to almost completely removes Pb(II) rapidly in the first few minutes with high efficiency. Under best conditions and room temperature the removal was the highest.
It was found that removal of toxic metal ions from aqueous solution using the prepared polymers was explained well by Freundlich model (R2= 0.99). This model describes the adsorption on to the heterogeneous surfaces possessing adsorption sites with different affinities.
Toxic metal ions removal by using the prepared polymers can be described by pseudo second order isotherm model. The pseudo second order model well represented the removal kinetics of both polymer (B), and polymer (A). The qe(calc.) value that obtained by this model was almost equal to the qe(exp.) an indication that the limiting step.
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Cross-Linked β-Cyclodextrin for Removal of Toxic Metals from Wastewater