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Adsorptive removal of Ni2+ ions in wastewater using electrospun
cellulose acetate / iron-modified nanozeolite nanostructured membrane
To cite this article: M S Tolentino et al 2019 IOP Conf. Ser.: Earth Environ. Sci. 344 012044
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The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
1
Adsorptive removal of Ni2+ ions in wastewater using
electrospun cellulose acetate / iron-modified nanozeolite
nanostructured membrane
M S Tolentino1,2,6, R R Aquino3,4, M R C Tuazon3, B A Basilia1,3, M J Llana5
and J A M C Cosico5
1Industrial Technology Development Institute, Department of Science and
Technology, DOST Compound, Gen. Santos Ave., Bicutan, Taguig City 1631,
Philippines
2School of Graduate Studies, Mapúa University, 658 Muralla St., Intramuros, Manila
City 1002, Philippines
3School of Chemical, Biological, and Materials Engineering and Sciences, Mapúa
University, 658 Muralla St., Intramuros, Manila City 1002, Philippines
4Center for Nanomaterials and Membrane Research, Mapúa University, 658 Muralla
St., Intramuros, Manila 1002, Philippines
5Nanotech Analytical Services and Training Corporation (NASAT Labs), Katarungan
Village, Brgy. Poblacion, Muntinlupa City 1781, Philippines
E-mail: marvstolentino@yahoo.com
Abstract. Release of heavy metal contaminated wastewater is one of the major problems being
encountered by many industries due to its hazardous effect on the ecosystem, specifically its
negative impacts on human health. Although essential in small quantities, nickel (Ni) and other
heavy metals could be very dangerous to human health when uptaken at high concentrations. In
this regard, this undertaking focused on the fabrication of nanofibers of cellulose acetate (CA)
with varying concentrations (0, 1.0, 1.2 and 1.4 wt%) of iron-modified nanozeolite (Fe-MNZ)
through electrospinning technique for the adsorption of Ni2+ ions in simulated wastewater. The
membranes produced underwent different characterization techniques to determine the effect of
Fe-MNZ addition on the nanofibers. FTIR result showed changes in the broadness of some
bank peaks which signifies the interaction between CA and Fe-MNZ. SEM results showed
increasing fiber diameter with increasing Fe-MNZ concentration having an 848.08 nm
maximum diameter. Lastly, Freundlich isotherm and pseudo-first order kinetics govern the
adsorption of the Ni2+ ions, with the highest adsorption capacity of 7.46 mg Ni2+ / g membrane.
1. Introduction
As humans continue to develop through the years, rapid industrialization inevitably affects the
environment and poses major problems such as pollution, specifically in different bodies of water. In
particular, untreated wastewater discharges from different industries and human activities such as
mining and smelting, and fossil fuel combustion were some of the main causes of heavy metal
contamination [1]. Heavy metal such as nickel (Ni), could be very hazardous if present in large
amounts, due to high phytotoxicity and can damage fauna in the ecosystem. Also, being exposed to
high quantities of Ni can cause eczema and DNA damage to humans [2]. Conventional technologies,
The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
2
techniques and methods have been studied and employed for the remediation and removal of heavy
metals from the wastewater. But most of the processes involving physico-chemical treatment need
large amount of expensive chemicals [3] and require high energy consumption [4], which turned to be
unideal and non-economical.
Apart from the disadvantages of the conventional techniques for the removal of heavy metals from
water, the use of adsorptive electrospun membranes could be considered as a promising technique
because of membranes’ high adsorption efficiency. Electrospun nanofibers produced exhibit desirable
properties in terms of durability and high adsorption capacity [5,6]. Properties of electrospun
nanofibers with regards to metal ions sorption performance can be enhanced further by
functionalization and modification by the incorporation of mineral fillers [7]. In this regard, cellulose
acetate (CA) has a great potential in this specific application, because aside from being economical,
the presence of many functional groups in CA is a significant property, which makes its surface
reactive, further results to its high adsorption capacity [8,9]. In addition to this, the incorporation of
nanoparticles, specifically iron-modified nanozeolite (Fe-MNZ) to adsorptive membranes could be of
great importance in the field of wastewater treatment wherein great amounts of heavy metals are
needed to be removed before its discharge to the environment.
This study aimed to perform Ni2+ ions adsorption using membrane-reinforced nanoparticles to
understand more evidently the Ni2+ heavy metal ion adsorption that happens in real industrial effluent
systems. Generally, the main objective of this study was to investigate the adsorption of Ni2+ heavy
metal ions using electrospun CA reinforced with (Fe-MNZ). Specific objectives of this study were as
follows: a.) to fabricate CA/Fe-MNZ nanostructured membrane using the electrospinning technique at
optimized electrospinning conditions; b.) to characterize the electrospun CA/Fe-MNZ nanofibers
using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM); and
lastly, c.) to determine the applicable isotherm model and kinetics for the adsorption of Ni2+ heavy
metals ions.
This research only focused on the adsorption of the Ni2+ heavy metal ions. Adsorption experiment
utilizing real samples of wastewater was not conducted. The Fe-MNZ that was used in this study was
synthesized by the researchers from the Materials Science Division of the Department of Science and
Technology, Philippines. For the electrospun CA/Fe-MNZ, all blends underwent characterization and
were used for the adsorption experiments. Desorption and recyclability of the electrospun nanofibers
were not investigated.
2. Methodology
2.1. Fabrication of the electrospun CA/Fe-MNZ nanostructured membrane
CA/Fe-MNZ nanofibers for the adsorption of Ni2+ heavy metal ions were fabricated using the
electrospinning technique. Firstly, the CA (MW = 50,000) was dissolved using 1-Methyl-2-
pyrrolidinone, C5H9NO (NMP) as the solvent, and the resulting solution was continuously stirred
using a sonicator until viscous and homogeneous solution was obtained. Four different blends were
made with the following compositions (wt%) of CA/Fe-MNZ/NMP: Blend 1 – 15/0/85, Blend 2 –
14/1/85, Blend 3 – 13.8/1.2/85 and Blend 4 – 13.6/1.4/85. Upon producing four different blends of
solutions, each blend was subjected to electrospinning process utilizing the following parameters: feed
rate of 1.1 mL/hr, a tip-to-collector distance of 200 mm, 10 mL syringe with 17 mm diameter and 23G
needle, a spinneret width of 110 mm, 25°C room temperature, and 20 kV applied voltage. Aluminum
foil was used to collect the electrospun membranes.
2.2. Characterization of the electrospun CA/Fe-MNZ nanostructured membrane
Fourier Transform Infrared Spectroscopy (FTIR), which was used to determine the interaction
between CA and fired Fe-MNZ based on the changes in their spectra, was conducted at the Chemistry
Laboratory of Mapúa University using Perkin Elmer FTIR Spectrometer. Scanning Electron
Microscopy (SEM), which was used to determine the surface morphologies of the nanofibers produced
The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
3
and to relate the results to their adsorption capability, was provided by Nanotech Analytical Services
and Training Corporation (NASAT Labs).
2.3. Adsorption experiment
The Ni2+ heavy metal ions stock solutions were prepared by the dissolution of 10 mg of NiCl2∙6H2O in
1 L volumetric flask using ultrapure water producing 10 ppm (mg of Ni2+/ L of solution) heavy metal
ion stock solution. For the adsorption experiment, four (4) 1 L beakers were filled with 10 ppm
prepared solution containing Ni2+. Then for each beaker, nanofibers produced using different blends
were placed: M1 (membrane produced using Blend 1) to beaker 1; similar thing was done to other
blends (M2, M3, M4). The solutions with their respective membranes were allowed to be in contact
and stirred (400 rpm) for 2 hours. In that duration of time (2 hours), 15 mL aliquot of the solution from
each beaker was obtained for every 24 minutes interval starting from time equals zero. Each 15 mL
aliquot was diluted to 140 mL using ultrapure water, and then filtered using size 42 Whatman filter
paper. After filtration, each solution was digested and the pH of each resulting solution was adjusted to
5.5 using 0.1 M HCl and 0.1 M NaOH and the pH was verified using a pH meter. Three 10 mL
samples (triplicates) were obtained from the 35 mL digested solution and subjected to Perkin Elmer
Optima 8000 Inductively Coupled Plasma – Optical Emission Spectrometer (ICP-OES) to determine
the concentration of the solution after each adsorption time.
The concentration obtained from the ICP-OES were adjusted considering the dilution factor used
and the adsorption capacities for each adsorption time were calculated and a graph was generated by
plotting the adsorption capacity versus time for each heavy metal, for each membrane blend. From the
graph generated, the equilibrium adsorption capacities were determined and were fitted to Langmuir
and Freundlich adsorption isotherms, and Pseudo-first-order and pseudo-second-order kinetic models.
3. Results and discussion
3.1. CA/Fe-MNZ nanostuctured membrane characterization
3.1.1. Fourier-transform infrared spectroscopy (FTIR). Different CA membrane blends (e.g., M1,
M2, M3 and M4) were electrospun with varying concentrations of Fe-MNZ. FTIR analysis for each
membrane blend was conducted to determine the effect of the addition of Fe-MNZ on CA. Changes in
band peaks from the FTIR result signifies the interaction between CA and Fe-MNZ. Figure 1 shows
the FTIR result for the different blends of the electrospun nanofiber membranes. Based on the results
of FTIR, considering the diagnostic region of the IR spectra presented, a broad signal can be observed
between 3200 cm-1 and 3600 cm-1. This is the characteristic signal for the O–H (hydroxyl group)
present in pure CA. The changes in the broadness in the said range of frequency for O–H correspond
to the weakening of the bond between O and H of O–H due to hydrogen bonding present. This can be
observed for all the membrane blends upon the addition of Fe-MNZ. Increasing the concentration of
Fe-MNZ made the signal broader since the iron (Fe) in Fe-MNZ is present as akageneite/ferric
oxyhydroxide (β-FeOOH) [10]. The presence of O–H from β-FeOOH increases the species
participating in hydrogen bonding which made broader signals in the range being considered. In
reference to pure CA (M1), it is evident that the signal became weaker for M2 and M3. This is because
of the low dipole moment present. The amount of O–H from pure CA was compensated by the amount
of O–H from β-FeOOH, wherein hydrogen bonding governs preventing the oscillation of the dipole
moment. Thus, producing a weak signal. For M4, it can be seen that it has the strongest signal for O–
H. Broad signal can also be observed but its strong signal can be attributed to the presence of more O–
H which does not participate in hydrogen bonding due the increase in concentration of the Fe-MNZ.
Moreover, a distinct change in band peak between 1700 cm-1 and 1750 cm-1 can be seen. At this range
of frequency, it is expected to be an ester group from pure CA (M1). Slight weakening of the signal
can be observed for M2, M3 and M4 due to hydrogen bonding between the O–H of β-FeOOH and O
from the C=O of the ester group of pure CA (M1), which further resulted to a low dipole moment for
The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
4
the ester group. Hence, resulting to a weaker signal. This is also the reason for the decrease in the
signal between 1250 cm-1 and 1350 cm-1 for the C–O in the ester group. For the band peak changes
between 1000 cm-1 to 1100 cm-1, this refers to the interaction in the C–O bond present in between the
repeating units of pure CA.
Figure 1. FTIR result for electrospun CA nanofibers with varying concentrations of Fe-MNZ.
3.1.2. Scanning electron microscopy (SEM). Morphological structure is very important for
electrospun nanofibers since it greatly affects the properties of the said nanofibers. In this study, each
membrane blend was subjected to SEM analysis to determine the effect of the addition of Fe-MNZ on
the pure CA, specifically with regards to the fiber diameters of the nanofibers that were produced.
Based on the result of SEM (Figure 2), it can be visibly observed that the fiber diameter increases with
Fe-MNZ concentration. This means that the incorporation of Fe-MNZ nanozeolite could greatly affect
the fiber diameter of the nanofibers produced. With regards to the solution preparation before
electrospinning, it was observed that the viscosity of the solution increases and Fe-MNZ are not easily
dispersed evenly in the solution at higher amounts of Fe-MNZ. The more viscous the solution is, the
larger the fiber that will be produced upon electrospinning. Similarly, this was also observed in the
study of Ji et al, wherein the membrane produced via wet spinning method exhibited a decrease in
pore size upon the incorporation of nanozeolite [11]. Relating their result in this study, the pore size
could be regarded as the spaces between the intertwined nanofibers, since there is the addition of Fe-
MNZ, the fiber diameters increases. Thus, resulting in the decrease in the spaces in between the
nanofibers or the pore size of the fabricated membrane.
In addition, statistical analysis using one-way ANOVA, considering the increasing fiber diameter
with increasing Fe-MNZ concentration, was performed. The p-value (3.59x10-5) was less than the
significance level (0.05) meaning the null hypothesis, which was the fiber diameters for all the
membrane blends were equal or insignificantly different with respect to the Fe-MNZ concentration,
was rejected. In this case, the differences in the fiber diameters obtained can be considered to be
statistically significant. Hence, the concentration of Fe-MNZ on the nanofibers has a significant effect
on the fiber diameters.
The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
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Figure 2. SEM images of the electrospun nanofibers of CA with varying amounts of Fe-MNZ at
5000x, 10000x and 20000x magnifications.
3.2. Adsorption isotherm and kinetics
Since this study was about the development of a new combination of materials, CA and Fe-MNZ, for
the adsorption of Ni2+ heavy metals, adsorption isotherm and kinetic modelling are of great
importance. The adsorption isotherm is needed to determine the governing interaction between the
adsorbate and the adsorbent. The adsorption capacities of the different membrane blends were
calculated using the results from the ICP-OES. It can be observed from Figure 3(a) that for all the
blends, equilibrium was attained after 95 minutes. But it was distinct that starting from time equals
zero, the adsorption capacities abruptly increased for M3 and M4 having more amounts of Fe-MNZ
compared to M1 and M2. The presence of Fe-MNZ affected the adsorption of Ni2+ ions on the
nanofibers produced. CA was further functionalized by the addition of Fe-MNZ resulting to the abrupt
increase in the adsorption capacity as seen for M3 and M4.
Furthermore, M3 had exhibited the best fit for the isotherm and kinetics of Ni2+ adsorption among
the other blends. Figures 3(b) and 3(c) show that Freundlich isotherm and pseudo-first order kinetics
describe the adsorption of Ni2+ ions on the said membrane blend. In this regard, multilayer adsorption
of Ni2+ occurred on the heterogeneous surface of the electrospun nanofibers with Fe-MNZ. Also,
pseudo-first order kinetics suggests that there was only physical adsorption involved wherein, mainly
the adsorption was due to the intermolecular forces present between the heavy metal and the
electrospun nanofiber.
The 5th International Conference on Water Resource and Environment (WRE 2019)
IOP Conf. Series: Earth and Environmental Science 344 (2019) 012044
IOP Publishing
doi:10.1088/1755-1315/344/1/012044
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Figure 3. Adsorption isotherm and kinetic fitting showing the best fit data, a.) adsorption capacities of
the different membrane blends, b.) Freundlich isotherm, and c.) pseudo-first order kinetics.
4. Conclusion
Upon the performance of the study, it can be said that the objectives are well met and satisfied.
Electrospun CA/Fe-MNZ nanofibers were successfully produced under optimized conditions.
Characterizations of the nanofibers were done to determine the effect of the Fe-MNZ addition to the
pure CA. FTIR results showed the interaction between CA and Fe-MNZ through the changes in the
strength of the signals at different frequencies. SEM images showed that incorporating Fe-MNZ in CA
could result to the increase in the fiber diameter of the electrospun nanofibers. This was further
supported by statistical analysis wherein the increasing fiber diameters with increasing Fe-MNZ
concentration were found to be statistically significant. Moreover, Freundlich isotherms also governed
the adsorption process of the Ni2+ under pseudo-first order kinetics.
Acknowledgment
The researchers would like to extend their gratitude to Engineering Research and Development for
Technology (ERDT) consortium of the Department of Science and Technology - Science Education
Institute (DOST-SEI), Philippines for the funds and support given through the execution of this study.
Also, the researchers are grateful for the assistance provided by Nanotech Analytical Services and
Training Corporation (NASAT Labs), Philippines for the characterization of the nanofiber samples.
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doi:10.1088/1755-1315/344/1/012044
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