2 research outputs found
Chitosan–Silica Hybrid Composites for Removal of Sulfonated Azo Dyes from Aqueous Solutions
In this study, the
influence of the chitosan immobilization method
on the properties of final hybrid materials was performed. Chitosan
was immobilized on the surface of mesoporous (ChS2) and fumed silica
(ChS3) by physical adsorption and the sol–gel method (ChS1).
It was found that physical immobilization of chitosan allows to obtain
hybrid composites (ChS) with a homogeneous distribution of polymer
on the surface, relatively wide pores, and specific surface area of
about 170 m<sup>2</sup>/g, pH<sub>PZC</sub> = 5.7 for ChS3 and 356
m<sup>2</sup>/g and pH<sub>PZC</sub> = 6.0 for ChS2. The microporous
chitosan–silica material with a specific surface area of 600
m<sup>2</sup>/g and a more negatively charged surface (pH<sub>PZC</sub> = 4.2) was obtained by the sol–gel reaction. The mechanisms
of azo dye adsorption were studied, and the correlation with the composite
structure was distinguished. The generalized Langmuir equation and
its special cases, that is, Langmuir–Freundlich and Langmuir
equations, were applied for the analysis of adsorption isotherm data.
The adsorption study showed that physically adsorbed chitosan (ChS1
and ChS2) on a silica surface has a higher sorption capacity, for
example, 0.48 mmol/g for the acid red 88 (AR88) dye (ChS2) and 0.23
mmol/g for the acid orange 8 (AO8) dye (ChS1), compared to the composite
obtained by the sol-gel method [ChS1, 0.05 mmol/g for the AO8 dye].
For a deeper understanding of the behavior of immobilized chitosan
in the adsorption processes, various kinetic equations were applied:
first-order, second-order, mixed 1,2-order (MOE), multiexponential,
and fractal-like MOE as well as intraparticle and pore diffusion model
equations. In the case of AO8 dye, the adsorption rates were differentiated
for three composites: for ChS3, 50% of the dye was removed from the
solution after merely 5 min and almost 90% after 80 min. The slowest
adsorption process controlled by the diffusion rate of dye molecules
into the internal space of the pore structure was found for ChS1 (225
min halftime). In the case of ChS2, the rates for various dyes change
in the following order: acid orange (AO7) > orange G (OG) >
acid red
1 (AR1) > AR88 > AO8 (halftimes: 10.5 < 15.7 < 23.7 <
34.9
< 42.9 min)
Imidazole-2yl-Phosphonic Acid Derivative Grafted onto Mesoporous Silica Surface as a Novel Highly Effective Sorbent for Uranium(VI) Ion Extraction
A new
imidazol-2yl-phosphonic acid/mesoporous silica sorbent (ImPÂ(O)Â(OH)<sub>2</sub>/SiO<sub>2</sub>) was developed and applied for uraniumÂ(VI)
ion removal from aqueous solutions. The synthesized material was characterized
by fast kinetics and an extra-high adsorption capacity with respect
to uranium. The highest adsorption efficiency of UÂ(VI) ions was obtained
for the reaction system at pH 4 and exceeded 618 mg/g. The uraniumÂ(VI)
sorption proceeds quickly in the first step within 60 min of the adsorbent
sites and ion interactions. Moreover, the equilibrium time was determined
to be 120 min. The equilibrium and kinetic characteristics of the
uraniumÂ(VI) ions uptake by synthesized sorbent was found to follow
the Langmuir–Freundlich isotherm model and pseudo-second-order
kinetics rather than the Langmuir, Dubinin–Radushkevich, and
Temkin models and pseudo-first-order or intraparticle diffusion sorption
kinetics. The adsorption mechanism for uranium on the sorbent was
clarified basing on the X-ray photoelectron spectroscopy (XPS) analysis.
The model of UO<sub>2</sub><sup>2+</sup> binding to surface of the
sorbent was proposed according to the results of XPS, i.e., a 1:1
U-to-P ratio in the sorbed complex was established. The regeneration
study confirms the ImPÂ(O)Â(OH)<sub>2</sub>/SiO<sub>2</sub> sorbent
can be reused. A total of 45% of uranium ions was determined as originating
from the sorbent leaching in the acidic solutions, whereas when the
basic solutions were used, the removal efficiency was 12%