Preparation of cellulose acetate blended with chitosan nanostructured membrane via electrospinning for Cd 2+ adsorption in artificial wastewater

Abstract

This study focused on using chitosan (CS) as the functional polymer in the cellulose acetate (CA) matrix to provide reactive ion exchange sites for heavy metal ions. Pure CA and CA/CS blends (wt % 95:5, 90:10 and 85:15) were electrospun to determine the most qualified blend for the adsorption experiment. The morphologies of the electrospun nanostructured membranes were investigated using Scanning Electron Microscopy. The average fiber diameter was found to decrease with increasing CS concentration. CA and CS interaction was confirmed using Fourier Transform Infrared Spectroscopy. Upon characterization, the blend with 15% CS had the best properties for the adsorption process. The adsorption capacities of pure CA and CA/CS blend at different membrane loading and initial concentration showed a significant increase from 67.25 mg Cd²⁺/g pure CA membrane to 110.48 mg/g CS doped membrane. The experiment revealed that the adsorption kinetics of pure CA and CA/CS blend for Cd²⁺ were described by the pseudo-second order reaction model. The adsorption isotherm data for Cd²⁺on the surface of pure CA and CA/CS blend best fit the Freundlich isotherm and can be used to describe adsorption of Cd²⁺. This study produced an innovative nanostructured membrane for the removal of Cd²⁺ in wastewater.

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IOP Conference Series: Earth and Environmental Science
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Preparation of cellulose acetate blended with chitosan nanostructured
membrane via electrospinning for Cd2+ adsorption in artificial
wastewater
To cite this article: R R Aquino et al 2018 IOP Conf. Ser.: Earth Environ. Sci. 191 012137
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The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
1
Preparation of cellulose acetate blended with chitosan
nanostructured membrane via electrospinning for Cd2+
adsorption in artificial wastewater
R R Aquino1,3, M S Tolentino1,3, S C S Amen1, M A V Arceo1, M E S Dolojan1 and
B A Basilia1,2
1School of Chemical, Biological, and Materials Engineering and Sciences, Mapúa
University, 658 Muralla St., Intramuros, Manila 1002, Philippines
2Industrial Technology Development Institute, Department of Science and Technology,
Bicutan, Taguig City, Metro Manila 1631, Philippines
E-mail: rraquino@mapua.edu.ph/marvstolentino@yahoo.com
Abstract. This study focused on using chitosan (CS) as the functional polymer in the cellulose
acetate (CA) matrix to provide reactive ion exchange sites for heavy metal ions. Pure CA and
CA/CS blends (wt % 95:5, 90:10 and 85:15) were electrospun to determine the most qualified
blend for the adsorption experiment. The morphologies of the electrospun nanostructured
membranes were investigated using Scanning Electron Microscopy. The average fiber diameter
was found to decrease with increasing CS concentration. CA and CS interaction was confirmed
using Fourier Transform Infrared Spectroscopy. Upon characterization, the blend with 15% CS
had the best properties for the adsorption process. The adsorption capacities of pure CA and
CA/CS blend at different membrane loading and initial concentration showed a significant
increase from 67.25 mg Cd2+/g pure CA membrane to 110.48 mg/g CS doped membrane. The
experiment revealed that the adsorption kinetics of pure CA and CA/CS blend for Cd2+ were
described by the pseudo-second order reaction model. The adsorption isotherm data for Cd2+
on the surface of pure CA and CA/CS blend best fit the Freundlich isotherm and can be used to
describe adsorption of Cd2+. This study produced an innovative nanostructured membrane for
the removal of Cd2+ in wastewater.
1. Introduction
It is a fact that living organisms, specifically humans, need varying amounts of some heavy metals
such as iron, copper, zinc, cobalt, manganese and molybdenum. These heavy metals help in
maintaining body metabolism. However, most of these elements are only required by humans and
other living organisms in minute amounts because excessive quantities can be harmful to the organism
[1]. Contamination of aquatic media by heavy metal loaded effluents from mining, smelting,
electroplating operations, and other industrial sources is a serious environmental problem that is very
difficult and expensive to tackle because these heavy metals are toxic, persistent, and non-
biodegradable [2].
Remediation of heavy metals from different water sources could be a challenge because unlike
organic pollutants, these heavy metals do not deteriorate. Various methods such as membrane
filtration, ion-exchange, chemical precipitation/coagulation, electrolytic reduction, solvent extraction,
and absorption techniques have been used to treat effluents loaded with heavy metals; but most of

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
2
them are either too expensive or incapable of eliminating trace levels of heavy metal ions, especially
from very dilute solutions [3].
A developing technology being used in water treatment for the removal of heavy metals is
biosorption which overcomes the selective disadvantage of usual adsorption processes. It involves the
use of different biological materials as adsorbents or ion exchange media for chelating heavy metals
[4]. In this regard, biopolymers, which are renewable and more environment friendly, became the
interest of recent studies for the adsorption of heavy metals.
In the discipline of nanotechnology, nanocomposites with polymer matrices have become
animportant area of current research and development. Polymers combine a number of favorable
features, including flexibility, processability, low cost, size in the nanometer range, diverse
functionalities, and microphase separation. Many commercial polymeric membrane materials have
good mechanical, thermal and chemical properties, but the lack of reactive functional groups on the
polymer backbones is a drawback. Due to this reason, membranes which are made from these
materials often need to be enhanced and modified. Cellulose and its derivativescontain reactive
hydroxyl groups, which can be modified with other reactive functional groups to obtain adsorptive
membranes. One method to fabricate adsorptive membranes can be the introduction of amine groups
into cellulose or its derivatives such as cellulose acetate (CA). However, CA membranes lack of
reactive functional groups on the polymer backbones which affects the separation efficiency of the
membranes. Hence, other materials are blended with CA to overcome this disadvantage and to
enhance the CA membrane’s adsorption capacity. More recently, chitosan (CS) which is a promising
adsorptive material for various applications, have been combined to CA due to its abundance of the
free amine groups for the adsorption of heavy metal [5].
In this study, researchers aimed to produce an electrospun CA/CS blend nanostructured membrane
for Cd2+ removal in synthetic wastewater. The morphology, molecular properties, and mechanical
properties of the resulting nanostructured membrane were characterized using Scanning Electron
Microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, and Universal Testing Machine
(UTM). Kinetic studies for the adsorption process and adsorption isotherms were also investigated.
The ability of the produced nanostructured membrane in removing Cd2+ ions in wastewater was
studied. However, this study only utilized synthetic wastewater containing Cd2+. Furthermore, it is not
concerned with the mechanism of the adsorption process, effect of solvent and with the organic
materials that would be collected upon experimentation.
2. Methodology
The polymers were dissolved first in their corresponding solvent in 70:30 ratio, CA in trichloroacetic
acid and CS in dichloromethane. The CA/CS blend were then prepared with concentrations of 100%-
0%, 95%-5%, 90-10% and 85%-15% CA to CS solution concentration, respectively. The solution was
stirred continuously until a viscous solution was obtained. The blended solutions of varying
concentration underwent the electrospinning process utilizing the following parameters: processing
conditions at room temperature (25°C), applied voltage at 30 kV and the tip-to-collector distance was
fixed at 18 cm. The electrospun CA/CS nanostructured membranes were characterized using different
analytical techniques; namely, scanning electron microscopy (SEM), Fourier transform infrared (FT-
IR) spectroscopy and testing of mechanical strength using the universal testing machine (UTM). Pure
CA dope and CA/CS fibers, that satisfied the most desired properties, were used for adsorption
experiment. The pure CA membrane and the best CA/CS blend membrane of different amounts (from
0.025 g to 0.0875 g with 0.0125 g interval) were used as adsorbent in a 250 mL Erlenmeyer flask
containing 50 mL of 50 ppm concentration of Cd2+ solution. From these fiber dosages and volume, the
liquor to sorbent ratio ranges from 500:1 to 2000:1. Different sample preparations were conducted and
the samples were subjected to Atomic Absorption Spectrophotometer (AAS) analyzer to determine the
effect of adsorbent dosage, adsorption kinetics (from the effect of contact time on adsorption capacity
of the membranes for Cd2+ ions), and adsorption isotherm (fitted to Langmuir and Freundlich isotherm
models).

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
3
3. Results and discussion
3.1. Effect of CS content on fiber structure
The SEM images were obtained at different magnifications for all electrospun CA/CS blends which
confirmed the effects of CS content on the surface characteristics of the membranes. As can be seen on
figure 1, varying the amount of CS in the CA/CS blend established a visible effect in the generated
nanostructured membrane. It was observed that as the CS concentration increases, smaller fiber
diameter is obtained. This behavior between nanostructured membrane diameter and concentration is
because CS acts as a partial polyelectrolyte and increases the polymer solution conductivity, thereby
decreasing the diameter of the nanostructured membranes [6,7]. Another reason for this decrease in
diameter with increase in concentration can be observed due to the partial clogging or restriction to
flow at the tip of needle. This clogging can be attributed to higher viscosity of the solution of CS in
acetic acid [8].
Figure 1. SEM micrographs of electrospun pure CA and CA/CS blends at low (first row) and high
(second row) magnifications, with their corresponding average diameters in nanometers.
3.2. Molecular structure of the fibers
The electrospun nanostructured membranes were subjected to FTIR analysis and based on the results
(figure 2), interaction took place between CA and CS polymers. This was evident due to the
significant difference in the appearance of new peaks and shifting of existing peaks. As CS was added
up to 15%, noticeable shifting at lower frequencies were observed at wavenumbers ranging from
3000-3500 cm-1. Increasing the amount of CS present in the matrix created a shift from 3216 cm-1 to
3208 cm-1 up to 3192 cm-1 which indicates that an increased amount of amine groups promotes its
interaction with the OH groups and signifies its incorporation into the CA matrix. The shifting of the
absorption band seen at around 1754 cm-1 for the 5%, 10% and 15% membrane represents the
characteristic absorption band attributed to the coincidedester-carbonyls (acetyl groups) in cellulose
acetate, while the shifting of the absorption band observed at around 2900 cm-1 is attributed to the
carbon-hydrogen bonds (C-H) carbon-hydrogen deformation in cellulose acetate.

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
4
Figure 2. FTIR spectra for a.) pure CA; CA/CS blends b.) 5% CS,
c.) 10% CS, d.) 15% CS; and e.) pure CS.
3.3. Mechanical analysis of membrane
Based on the results obtained from UTM as shown in table 1, it can be observed that the values for the
mechanical properties decrease with the increase of amount of CS in the membrane. The decrease in
the mechanical strength of the different CA/CS blend nanostructured membrane may be attributed to
the decrease in intermolecular attraction between the molecules of the blended polymers. CS shows a
good performance in adsorption of heavy metal [9]; however, it is also known to have poor
mechanical strength [10] so the decrease in the mechanical properties was already expected. The fiber
mechanical properties are dependent on fiber orientation and as the fiber disorientation increases,
mechanical properties decrease. Based on SEM results (figure 1), as CS increases, the disorientation of
the fibers also increases resulting in the decrease of mechanical properties of the CA/CS blend. Upon
performing ANOVA, the values of the mechanical properties of the nanostructured membrane
displayed no significant difference since its F critical value (3.490) is greater than F value (0.1328),
and P value (0.9387) is greater than 0.05 significance level. Nevertheless, the mechanical properties of
the fabricated nanostructured membrane were not given emphasis and were not considered in the
determination of the best blend to be used in the adsorption study.
Table 1. Mechanical properties of electrospun pure CA and CA/CS blends.
Blend
Stiffness
(MPa)
Elongation
(mm)
Tensile Stress
at Yield (MPa)
Tensile Strain
at Yield (mm/mm)
0%
0.31255 ± 0.122423
33.32755
0.02085
0.17175
5%
0.15336 ± 0.103723
39.08769
0.01207
0.21691
10%
0.20900 ± 0.057700
19.07539
0.01232
0.13714
15%
0.21755 ± 0.187500
18.08215
0.01515
0.14167

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
5
3.4. Adsorption study
Based on the fiber characterization, blend with 15% CS loading had the best properties needed for the
adsorption process. This CS blend was used together with pure CA nanostructured membranes to
compare the adsorption capacity of both fibers at different dosage.
3.4.1. Effect of adsorbent dosage. Figure 3 shows that the adsorption of Cd2+ increases rapidly as the
amount of the fibers increases. This is due to the presence of larger surface area for adsorption at
higher adsorbent concentration. For pure CA (figure 3(a)), a considerable increase in uptake was
observed when the amount was increased from 0.025 g to 0.05 g and addition of adsorbent beyond this
point result in a decrease of adsorption capacity. The decrease in adsorption capacity as adsorbent
dosage increased is because the adsorption equilibrium may not have been attained. It also means that
all the Cd2+ ions from the solution adhered to the adsorbent while there were still available sites for
adsorption [11]. The result also shows that 50 ppm of Cd2+ was enough to saturate 0.05 g of pure CA
fiber. The same behavior was observed for CA/CS blend (figure 3(b)). The adsorption capacity of the
fiber increases up to 0.0375 g then decreases with further increase in the adsorbent dosage. The results
obtained imply that 0.0375 g of CA/CS blend was enough to attain equilibrium at 50 ppm
concentration compared to 0.05 g of pure CA.
Figure 3. Adsorption capacity of a.) pure CA and b.) CA/CS (15%) fibers for Cd2+ as a function of
adsorbent dosage at different time intervals.
3.5. Kinetics study
3.5.1. Effect of contact time. As can be seen from figure 4(a), CA/CS blend has higher adsorption
capacity than pure CA. The adsorption of Cd2+ on fibers reached equilibrium after 6 hours wherein the
adsorption capacity curve flattens. The adsorption occurred rapidly during the first 6 hours, which was
possibly because of the active sites abundantly available on the adsorbent [12]. As the final
concentration decreases, it lowers the concentration gradient which leads to a decrease and steadiness
on the rate of adsorption [11].
Figure 4. a.) Effect of contact time on the adsorption capacity of the fibers for Cd2+, b.) pseudo first-
order and c.) pseudo second-order model plots for the adsorbents.

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
6
The experimental data for the adsorption kinetics were fitted using the pseudo first-order and
pseudo second-order kinetic models to identify whether physical or chemical mechanism governs the
adsorption process. The results in figures 4(b) and 4(c) clearly show that the pseudo second-order
model provides a better correlation for the adsorption kinetic data obtained than the pseudo-first order
model. This means that the rate limiting step in the adsorption of Cd2+ would be chemisorption or
chemical sorption which involves valency forces from the exchange and sharing of electrons between
the adsorbent and adsorbate [12]. The potential binding sites that are present are the amines of CS and
hydroxyls of CA.
3.6. Equilibrium study
The results in figure 5 demonstrate that for both fibers, at a fixed adsorbent dose, the adsorption
capacity is linearly increasing with the initial concentration of Cd2+ for the reason that raising the Cd2+
concentration speeds up the diffusion of Cd2+ ions from solution to the adsorbent surface due to the
concentration gradient factor; thus, increasing the driving force for adsorption. For pure CA adsorbent,
an increase in adsorption capacity was observed from 3-6 hours of immersion and decreases at 9 hours
of immersion due to reversibility in the adsorption process. On the other hand, the adsorption capacity
of CA/CS blend was observed to be steady and decreases slightly which suggests that CS dope fibers
was more stable adsorbent for metal species at longer times. It can be seen that CS doped fibers have
higher adsorption capacities for all varied initial concentration of Cd2+ solution compared with the
fiber of pure CA.
Figure 5. Effect of contact time on the adsorption capacity of a.) pure CA and b.) CA/CS (15%) fibers
for Cd2+ at different initial Cd2+ concentrations.
3.7. Isotherm fitting
The equilibrium data were analyzed using Langmuir and Freundlich equilibrium models to obtain the
best fit isotherm. Based on the results obtained (figure 6), the regression coefficients R2 of linear
Freundlich isotherm for Pure CA and CA/CS were found to be both equal to 0.989.
Figure 6. Adsorption isotherm fitting; a.) Langmuir isotherm and b.) Freundlich isotherm.

The 4th International Conference on Water Resource and Environment (WRE 2018)
IOP Conf. Series: Earth and Environmental Science 191 (2018) 012137 IOP Publishing
doi:10.1088/1755-1315/191/1/012137
7
This suggests that Freundlich isotherm is the best-fit model for the experimental data obtained. The
Freundlich isotherm illustrates that the adsorption of Cd2+ happened on a heterogenous multi-layer
surface with uniform energy [12].
4. Conclusion
Nanostructured membrane from CA/CS nanofibres at different CS loading have been successfully
fabricated through electrospinning technique. It was found that the average fiber diameter of the
electrospun nanostructured membranes decreases with increasing CS contents in the polymer blend.
FTIR results showed the interaction between CA and CS with the consistent shifts of hydroxyl, amine
and carbonyl peaks from 5% to 15% CS loading. For the mechanical properties, the decrease in the
mechanical strength of the different CA/CS blend nanostructured membrane may be attributed to the
decrease in intermolecular attraction between the molecules of the CA polymer matrix and CS. Based
on the adsorption study, it was found that the adsorption capacity of the two adsorbents at different
membrane loading and initial concentration showed a significant increase from 67.25 mg Cd2+/g pure
CA nanostructured membrane to 110.48 mg Cd2+/g of CS doped fibrous membrane. Data obtained
from kinetics experiment were best fitted to pseudo second-order model. In varying the initial
concentration of the Cd2+ solution, the adsorption data at equilibrium were best fitted to the Freundlich
isotherm model.
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