Sorption of arsenic species using chitosan based biopolymer sorbent materials
Abstract
The research focuses on the design and characterization of two- (chitosan/glutaraldehyde)
and three-component (chitosan/glutaraldehyde/β-cyclodextrin) biopolymer sorbent materials.
The chitosan prepolymer investigated had a low molecular weight (~ 50,000-190,000 gmol-1)
and high molecular weight (~ 150,000-375,000 gmol-1) whereas glutaraldehyde was used as the
cross linking agent for each biopolymer. Two component chitosan/glutaraldehyde co-monomers
were reacted at variable mole ratios (1:15, 1:25 and 1:35). Three-component copolymers
containing β-cyclodextrin (β-CD) were obtained by reacting variable mass ratios of β-CD with
chitosan (1-3, 1-1 and 1-1/3; chitosan/β-CD (w/w)). The chitosan/glutaraldehyde fraction was
held constant at a 1:6 mole ratio comparable to the two-component copolymers. The two- and
three-component biopolymer materials were characterized using TGA, FT-IR spectroscopy and
elemental analysis (C, H & N). The solid-solution isotherm properties in aqueous solutions for
the biopolymers were characterized with two detection methods (UV-Vis and ICAP-OES) with
two types of adsorbates, respectively; p-nitrophenol (PNP) and arsenate oxoanion (HAsO4
2-) at
alkaline conditions.
The Langmuir (i.e. Sips restricted) and the Sips sorption isotherm models were utilized to
obtain sorption parameters at pH 8.5 and 295 K, (i.e. surface area estimates, sorption capacities
and removal efficiencies) for each biopolymer material. The surface area estimates are as
follows for the 1:15, 1:25 and 1:35 chitosan-based two-component biosorbent materials: the Sips
restricted values are 46.7, 46.7 and 31.6 m2g-1 and the Sips values are 124, 46.7 and 31.6 m2g-1
for the low molecular weight chitosan material. The Sips restricted are 58.7, 54.2 and 64.7 m2g-1
and for the Sips are 79.8, 64.7 and 96.3 m2g-1 for the high molecular weight chitosan material,
respectively. The surface area estimates are as follows for the 1-3, 1-1 and 1-1/3 chitosan and
v
β-cyclodextrin three-component biopolymer materials: for the Sips restricted are 34.6, 54.2 and
116 m2g-1 and for the Sips are 275, 51.2 and 161 m2g-1, respectively. Removal efficiencies are
dependent upon the pH, temperature, and the relative amount of sorbent and sorbate. The
removal efficiencies of p-nitrophenol by the biopolymers ranged between 7.1 and 48.9% for low
and high molecular weight chitosan biosorbent materials. The removal efficiencies of pnitrophenol
by three components, the chitosan, β-cyclodextrin and glutaraldehyde biopolymers
ranged between 7.3 and 28.0%. The removal efficiencies of the arsenate oxoanion by the
biopolymers ranged between 30.7 and 92.2% for low and high molecular weight chitosan
biosorbent materials. The removal efficiencies of arsenate oxoanion by the three-component
biopolymers (chitosan, β-cyclodextrin and glutaraldehyde) ranged between 22.8 and 55.4%. The
removal efficiencies for the unmodified commercial chitosan (high and low molecular weight)
and activated carbon sorbent materials was negligible (~ 0%).
The Langmuir (i.e. Sips restricted) and the Sips sorption isotherms both showed similar
“best-fit” results for the sorption in aqueous solution data which resulted in neither isotherm
model being favoured over the other.