Removals of Polyethylene Terephthalate (PET) Nanoplastics from an
Activated Sludge: Improvement of Yields by Ni-Cu-C Nanocomposite
RUKİYE ÖZTEKİN a , DELİA TERESA SPONZA a , *
a Department of Environmental Engineering
Dokuz Eylül University
Tınaztepe Campus, 35160 Buca/Izmir,
TURKEY
* Corresponding Author
Abstract: - In this study, the maximum polyethylene terephthalate (PET) nanoplastics (NPs) removal efficiency
was investigated under optimum conditions by using various experimental parameters to improve the removal
efficiency by using Ni-Cu-C NCs in an activated sludge solution. The effect of increasing pH values (4.0, 5.0,
6.0, 7.0 and 8.0), increasing adsorption times (30 min, 60 min, 90 min and 120 min), different Ni-Cu-C NCs
adsorbent concentrations (100 mg/l, 200 mg/l, 300 mg/l and 400 mg/l) and different PET NPs concentrations (1
mg/l, 5 mg/l, 10 mg/l and 15 mg/l) on the adsorption yields of PET NPs was investigated in an activated sludge
process during adsorption process. The characteristics of the synthesized Ni-Cu-C NCs were assessed using
XRD, FTIR, FESEM, EDX and HRTEM analyses. ANOVA statistical analysis was used for all experimental
samples. In order to remove 10 mg/l PET NPs with yields as high 99.20% and 99.42% in an activated sludge
process via adsorption; the Ni-Cu-C NCs adsorbent concentration, adsorption time, pH and temperature should
be 300 mg/l, 120 min, 7.0 and at 25oC, respectively. Adsorption process; it is an easily applicable,
environmentally friendly and economical method.
Key-Words: - Activated sludge; Adsorption; Adsorption isotherm; Adsorption kinetic; Adsorption mechanism;
ANOVA statistical analysis; Nanoplastics; Nikel-copper-carbon nanocomposite (Ni-Cu-C NCs); Polyethylene
Terephthalate (PET).
Received: March 24, 2024. Revised: August 16, 2024. Accepted: September 21, 2024. Published: November 29, 2024.
1 Introduction
Plastics are petrochemical-based organic polymers
that can be converted into different shapes and sizes.
The demand for plastics has been continuously
increasing due to low cost, inertness, flexibility,
resistance to oxidation and high durability among
others and they have been used since a hundred years,
[1-3], and will continue to increase in the future.
Studies performed to detect the plastic enumeration
showed that they will double in 20 years and almost
quadruple by 2050, [4]. Approximately 76% of the
total plastic production is treated as waste: 12% is
burned, 79% is buried or released into the
environment, and only 9% is recycled, [5]. The
incineration of plastics causes the release of carbon
monoxide, dioxins and dioxin-related intermediates,
as well as nitrogen oxides, into the atmosphere. This
situation causes air pollution and makes it very
difficult to completely remove plastic waste from the
ecosystem. Plastics are synthetic materials made up
of polymers, which are long molecules around chains
of carbons atoms, especially hydrogen, nitrogen,
oxygen, and sulfur, [6]. Plastics can be categorized
based on their size, i.e., microplastics ( > 25 mm),
mesoplastics (5–25 mm), microplastics (MPs) (0.1–5
mm), and nanoplastics (NPs) ( < 100 nm), [7].
Nanoplastics (NPs) are caused by plastic
contamination, which is a global environmental
problem due to their persistence in the environment.
Moreover, due to the poor degradability of NPs, they
tend to exist for a long time in the environment. The
widespread presence of NPs in environmental
matrices is due to their undesirable effects on
biodiversity of both terrestrial and aquatic
ecosystems; are studied as the main vectors of toxic
pollutants and their common causes. NPs also be
associated with dangerous substances/agents, leading
to potential risks. NPs can lead to a risk to the water
environment by transporting pathogens and the
desorption of toxic chemicals. Because NPs have a
huge surface area and hydrophobicity, they can
adsorb on their surfaces with various contaminated
toxic/dangerous substances such as antibiotics agent,
persistent organic pollutants (POPs), polycyclic
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aromatic hydrocarbons (PAHs), heavy/toxic metals,
polychlorinated biphenyls (PCBs) and become a new
contaminant in wastewater. Several emerging
contaminants, such as Bisphenol A, atrazine,
perfluoro alkylates, etc., can impose harmful effects
on biodiversity through their adsorption and
desorption on NPs. If the emerging contaminant-
loaded NPs invade the food chain through ingestion
by biota, it will lead to potential hazards to human
health and the ecosystem, [8]. The ingestion of NPs
obstructs the digestive tract, inhibit growth, cause
reproductive disorders, increase mortality of aquatic
life forms like marine bivalves, microalgae,
amphipods, etc., [9, 10]. So, it is necessary to set
strict discharge standards for NPs and emphasize the
development of advanced treatment technologies to
minimize the quantity of NPs entering into different
environmental components.
Plastics are used in a wide variety of sectors for
example; packaging, building, transportation,
renewable energy, medical devices or sport
equipment. The most common plastic materials in
commercial products found in effluents are
polypropylene (PP), polyethylene (PE), polystyrene
(PS), polyvinyl-chloride (PVC), polycarbonate (PC),
polyamides (PA), polyester (PES) and polyethylene
terephthalate (PET), depending on the type of
products produced by the plant, [11, 12]. These are
reversible thermoplastic polymers, highly recyclable
materials that can be heated, cooled and shaped
repeatedly, [11, 12]. These represent approximately
90% of world production, [11-14].
Polyethylene terephthalate (PET) is widely used
in packaging materials for its excellent abrasive
resistance, dimensional stability, and insulation, [15].
PET, like other thermoplastic polymers, such as
Polyethylene (PE), Polypropylene (PP), Polystyrene
(PS) and Polycarbonates (PC), can be recycled by
melting through high temperature processes, and
reintegrated into new products, [16, 17]. This
recycling technology, however, consumes sizable
amounts of energy and, upon melting, lower grade
polymers are produced, with reduced thermal and
mechanical stability, which limit the applicability of
this technique to a reduced number of cycles, [18].
The chemical degradation of PET and other plastics
into their constituents represents another industrial
viable approach, [19]. Focusing on PET, 70 million
tons of this plastic are annually produced worldwide,
[20], underlining the necessity of developing
effective recycling approaches for this polymer. PET
is made up of building block monomers, such as
terephthalic acid (or benzene-1,4-dicarboxylic acid,
H2BDC) and ethylene glycol, and it can be
conveniently exploited as a source of organic ligands,
[21, 22]. The use of PET has made our lives more
convenient, but improper handling of PET has caused
serious damage to the environment. Despite the
existence of PET recycling processes, a considerable
amount of PET inevitably enters the wastewater
treatment plants (WWTPs), [23]. As a non–volatile
solid, PET may adversely affect the rheological
properties of sludge in WWTPs, and new industrial
discharge processes in WWTPs have been proposed,
[24, 25].
Some treatment technologies for the removal of
nano/microplastics in water have been developed,
including flocculation [26], ingestion by microbes
[27], biofilter technology [28], chlorination [29], UV
oxidation [30] and membrane filtration [31].
Different removal technologies based on adsorption
mechanisms have been proven to be effective
approaches to remove NPs in aquatic environments.
The chemically synthesized sponge materials, [32-
35], graphene materials, [36], and biochar materials,
[37], can be used to remove NPs and NPs in natural
waters. Filtration could also be applied to NPs
removal in aquatic environments. The biofilter
prepared by Kuoppamaki et al. not only removes
nutrients and heavy metals in rainwater, but also
remove NPs, [38]. In addition to adsorption and
filtration, some other technologies also show
excellent application prospects in the removal of NPs
in the aquatic environment. Electrocoagulation (EC)
removes NPs through a series of physical-chemical
reactions, [39, 40]. In flocculation process,
Lysozymeamyloid fibrils servesas a novel
natural bio-flocculant for removing dispersed
NPs from water, [41]. Enriched NPs can be
combined with recycling technology to achieve
harmless treatment of NPs. Also, Noncovalent
interactions removal mechanism with pressure-
sensitive adhesive removal technology, [42],
collect and fuse NPs into large bulks in the
microbubble with solar energy removal
technology, [43], were applied for the removal of
NPs from aquatic environments.
In WWTPs, the most frequently engaged
secondary treatment technologies are biological
processes, notably activated sludge processes (ASP),
which rely on the activated microorganisms in the
sludge to degrade/transform the NPs, [44-46]. At Fig.
1, was determined to the mechanism of sorption of
NPs removal during ASP in WWTPs. Currently, the
reported MPs removal methods in sludge are mostly
based on the degradation of MPs by bacteria in
activated sludge, but cannot be used as the
mainstream technology because of the lower
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efficiency. For example, the bacteria strain isolated
from activated sludge degraded 17% of PET NPs of
2.63 g/l, which was incubated at 30oC under a
pH=7.0-7.5 with a reactor residence time of 168 days,
[47]. Hyper-thermophilic composting (hTC)
technology was used for in situ degradation of MPs
in sludge, hTC significantly enhanced biodegradation
of sludge-based MPs and after 45 days of hTC
treatment, 43.7% of the MPs were removed from the
sewage sludge, which was the highest ever reported
for MPs biodegradation, [48].
* Fig. 1 can be found in the Appendix section.
Adsorption is mainly classified into two types:
physical adsorption and chemisorption (described as
activated adsorption as well). Physical adsorption is
the adhesion of an adsorbent to the surface of an
adsorbate because of the nonspecific (such as
independent of the nature of the material) van der
Waals force, whereas chemisorption occurs while
chemical bonding creates strong attractive forces, for
example chemical adsorption constructs ionic or
covalent bonds through chemical reactions.
Nevertheless, physical adsorption is a reversible
process but less specific, whereas chemisorption is
irreversible but more specific, [49]. When adsorption
occurs over biological systems, the process is
referred to as biosorption. Biosorption is a process
that combines metal removal and recovery.
Biosorption is effective due to the adsorbents’ low
cost and ease of regeneration. Bacteria, fungi, algae,
industrial waste, agricultural waste, natural residues,
and other biological materials have all been widely
used to adsorb heavy metals from wastewater, [50].
Physical adsorption, chemisorption, electrostatic
interactions, simple diffusion, intra-particle
diffusion, hydrogen bonding, redox interactions,
complexation, ion exchange, precipitation, and pore
adsorption are all possible mechanisms to adsorb
heavy metal ions onto bio-adsorbents, [51, 52].
Different removal technologies based on
adsorption mechanisms have been proven to be
effective approaches to remove NPs in aquatic
environments. The chemically synthesized sponge
materials, [53-56], graphene materials, [57], and
biochar materials, [58], can be used to remove NPs in
natural waters. Many factors can also affect the NPs
removal efficiency including pH, temperature,
adsorbents types, dissolved organic matter (DOM),
and ions, but pH and temperature are the two most
important factors. pH affects the adsorption
efficiency mainly by influencing the charge on the
surface of NPs and the adsorbent. Temperature can
affect the adsorbate diffusion rate and equilibrium
capacity, and higher temperatures achieve more NPs
adsorption, [56]. Different adsorbents types have
different electrostatic and hydrogen bonding
interactions with NPs, thereby altering the adsorption
capacity. DOM changes the interaction of absorbents
with NPs, [59]. On top of this, ions can influence the
electrostatic attraction between NPs and the
adsorbent, which in turn alters the NPs adsorption by
adsorbent, [60, 61]. In other words, the adsorption
removal of NPs has the advantages of high adsorption
capacity, high removal efficiency, low energy
consumption and reusability. However, the
adsorbents need to be eluted from the adsorbed NPs
after use, which allows for the potential risk that the
NPs would re-enter the environment.
Adsorbent is a pollutant remover widely used in
water treatment plants with the advantages of high
efficiency, simple operation and environmental
friendliness. Carbon-based adsorbents such as
modified activated carbon (AC) and other carbonic
materials (graphene oxide and carbon nanotubes)
have received a lot of attention recently because of
their high thermal and chemical stability, [62]. AC is
the most commonly used adsorbent which is
characterized by low cost, a large surface area, high
thermal and chemical stability, high porosity, and a
controllable pore size distribution, [63]. However, an
AC adsorbent lacks functional groups, so its use in
heavy-metal ion adsorption has been limited due to
its low uptake and slow kinetics, [64]. Metal-organic
framework carbon materials have been increasingly
proposed in recent years as adsorbents for a wide
range of applications. Metal-organic framework
carbon materials have a large specific surface area
and a large number of pores, which can effectively
adsorb various pollutants, [65], and is also a very
promising water purification material. Metal-organic
framework carbon materials show excellent
adsorption removal performance in the removal of
heavy metals, [66, 67], the removal of pesticides,
[68], and the removal of cesium and strontium, [69].
The studies performed with the removal of PET is
limited with few recent studies: n some studies it was
shown that the PET was converted to new shape
nanocomposites. Soni et al., [70], prepared PET-
based carbonaceous compounds using hydrothermal
processes to investigate of PET waste conversion to
carbonaceous materials. Sharifian et al., [71],
prepared PET-based AC (PET-AC) to reuse the PET
with homogeneous and heterogeneous porosity
textures to separate some pollutants. Pasanen et al.,
[72], generated magnetic ZIF-8 nanoparticles (Nano-
Fe@ZIF-8) for magnetic extraction and
depolymerization of PET nanoplastics. The Zn(II)
present in Nano-Fe@ZIF-8 subsequently acted as a
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catalyst for the depolymerization of the PET
nanoplastics using ethylene glycol. Zheng et al., [73],
prepared carbon-based adsorbents, such as graphene,
graphene oxide (GO), activated carbon/biochar
(AC/BC), carbon nanotubes (CNTs) to detect their
potential effectiveness in removing microplastics and
nano-plastics like PET and vinyl alcohol from
aqueous solutions. Kang et al., [74], developed a
MoS2/g-C3N4 photocatalyst that can cenvert the PET
into valuable organic chemicals. Kang et al., [74],
upcycled the PET plastic wastes into value-added
chemicals by using a nickel (Ni)-based catalyst
prepared via electrochemically depositing copper
(Cu) species on Ni foam (NiCu/NF).
Bimetallic organic framework carbon materials
are preferred because they have the ability to improve
the stability and activity of the original materials,
[75]. Copper (Cu) and nickel (Ni) have often been
used to develop inefficient composite catalysts due to
their good synergy, low cost, and high removal
efficiencies, [75, 76]. Cu and Ni-based bimetallic
organic framework carbon materials have been
applied to catalytic hydrogenation, [77], solar cells,
[78], advanced oxidation processes (AOPs), [79-81],
and excellent performance efficiencies have been
recorded. Only a few studies have been conducted on
the technology of Cu and Ni-based bimetallic organic
framework carbon materials, which have great
potential in removing NPs in aqueous systems. Apart
from that, Cu-C NCs and Ni-C NCs were reported for
supercapacitor electrode application and
electrocatalytic oxidation of phenol, respectively,
[82, 83]. In the light of all this information, the
development of non-noble Cu-Ni carbon materials
(CuNi@C) that can effectively remove NPs from
water; It is a new approach that is effective and
important in preventing the pollution caused by NPs
in the ecosystem.
Based on data given above inn this study, the
maximum PET NPs removal efficiency was
investigated under optimum conditions by using
various experimental parameters to improve the
efficiency using Ni-Cu-C NCs in an activated sludge
solution. The effect of increasing pH values (4.0, 5.0,
6.0, 7.0 and 8.0), increasing adsorption times (30
min, 60 min, 90 min and 120 min), different Ni-Cu-
C NCs adsorbent concentrations (100 mg/l, 200 mg/l,
300 mg/l and 400 mg/l) and different PET NPs
concentrations (1 mg/l, 5 mg/l, 10 mg/l and 15 mg/l)
in an activated sludge process on PET removal during
adsorption process was investigated. The
characteristics of the synthesized NCs were assessed
using XRD, FTIR, FESEM, EDX and HRTEM
analyses, respectively. In addition to, experimental
results were evaluated with ANOVA statistical
analysis.
2 Materials and Methods
2.1 Chemicals
As a pure powder activated carbon (PAC) source,
powder activated charcoal was purchased from
Sigma-Aldrich, German. Nickel (II) nitrate
hexahydrate [Ni(NO3)2.6H2O] (98%), copper (II)
nitrate hexahydrate [Cu(NO3)2.6H2O] (98%), sodium
hydroxide [NaOH] (98%), potassium hydroxide
[KOH] (99%) and hydrochloric acid [HCl] (37%)
were provided from Sigma-Aldrich, Germany. PET
(granular) was purchased from Sigma-Aldrich,
Germany.
2.2 Synthesis of Ni-Cu-C NCs Adsorbents
Pure powder activated charcoal as a PAC were
synthesized using a 2.2 N KOH solution and heated
at 500°C for 5 h. The washed and dried 70 g PAC was
soaked in 2.4 N/600 ml KOH overnight. The filtered
blackish-wet carbonic solid was washed several
times with 0.15 M HCl and with deionized water until
obtaining a neutral pH=7.0 level of the wet carbonic
solid. The dried and washed black-carbonic solid was
then heated for 5 h at 500°C. The Ni-Cu-C NCs were
prepared at increasing concentrations (100 mg/l, 200
mg/l, 300 mg/l and 400 mg/l) of Ni−Cu loaded on
PAC. 2.2 g of PAC was dispersed in 85 ml of
deionized water under ultrasonication for 25 min. An
appropriate amount of Cu(NO3)2.6H2O and
Ni(NO3)2.6H2O was dissolved separately in 25 ml of
deionized water and then added to the PAC/H2O
suspension with stirring for 25 min. 2.2 M NaOH
solution was added dropwise to the metal ions’ PAC
suspension until the pH level was 11.0, with stirring
for 35 min, and then heated at 155°C in an autoclave
for 3 h. The dried mass washed and filtered. Then,
Ni-Cu-C NCs were separately calcined at 450°C for
5 h.
2.3 Activated Sludge Solution
Activated sludge was obtained from a municipal
wastewater treatment plant in İzmir, Turkey.
Activated sludge was used for experimental studies
in the laboratory conditions.
2.4 Characterizations
2.4.1 X-Ray Diffraction (XRD) Analysis
Powder XRD patterns were recorded on a Shimadzu
XRD-7000, Japan diffractometer using Cu Kα
radiation (λ=1.5418 Å, 40 kV, 40 mA) at a scanning
speed of 1o min-1 in the 10-80o 2θ range.
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2.4.2 Raman Spectrum Analysis
Raman spectrum data was collected with a Horiba
Jobin Yvon-Labram HR UV-Visible NIR (200-1600
nm) Raman microscope spectrometer, using a laser
with λ=512 nm. The spectrum was collected from 10
scans at a resolution of 2 cm-1. The zeta potential was
measured with a SurPASS Electrokinetic Analyzer
(Austria) with a clamping cell at 300 mbar.
2.4.3 Fourier Transform Infrared Spectroscopy
(FTIR) Analysis
The FTIR spectra of samples was recorded using the
FT-NIR spectroscope (RAYLEIGH, WQF-510).
Experimental samples were scanned using infrared
light and their chemical properties were observed in
FTIR spectra.
2.4.4 Field Emission Scanning Electron
Microscopy (FESEM) Analysis
The morphological features and structure of the
synthesized catalyst were investigated by FESEM
(FESEM, Hitachi S-4700). FESEM images were
used to investigate the composition of the elements
present in the synthesized nanocomposite.
2.4.5 Energy Dispersive X-Ray (EDX)
Spectroscopy Analysis
The morphological features and structure of the
synthesized catalyst were investigated by an EDX
spectrometry device (TESCAN Co., Model III
MIRA) to investigate the composition of the
elements present in the synthesized catalyst.
2.4.6 High Resolution Transmission Electron
Microscopy (HRTEM) Analysis
The structure of the samples was analyzed by
HRTEM analysis. HRTEM analysis was recorded in
a Technai G2 F20 S-TWIN TEM/HR(S)TEM (FEI,
USA) under 200 kV accelerating voltage. Samples
were prepared by applying one drop of the suspended
material in ethanol onto a carbon-coated copper
HRTEM grid and allowing them to dry at 25oC.
2.4.7 N2 Adsorption Desorption and Pore Size
Measurement
Adsorption and desorption isotherms were measured
with nitrogen gas. Pore volume and pore area
distributions were attained using the Barrett, Joyner,
and Halenda (BJH) method and the reference curve
of Harkins-Jura was used.
2.4.8 Raman Spectroscopy
Raman spectroscopy is based on Raman scattering,
an inelastic scattering process that is only observed in
a tiny proportion (~1 in 106) of the photons scattered
by a molecule.
2.4.9 Measurement of CV Curves
Electrochemical experiments (CV) were performed
on each electrode using the CHI 605E and DH-7000
electrochemical workstations for both the three-
electrode system and the two-electrode system. The
specific capacity for the nanocomposite system was
calculated using Equation (1):
(1)
In the equation: Qm : is the specific capacity (C/g); I:
is the charge/discharge current (A); ∆t: is the
discharge time (s) and m: is the mass of the active
material (g).
2.5 Adsorption Mechanism
The adsorption mechanisms of NPs by chemically
synthesized with larger sizes are based on hydrogen
bonds, electrostatic between NPs and sponge
materials are π-π interactions, [55, 59]. NPs in
aquatic environments generally have a negative
charge and can easily interact electrostatically with
positively charged substances and be adsorbed on the
surface. In comparison, the adsorption mechanisms
of NPs via micromotors with smaller sizes are
generally based on the phoretic interactions and
shoveling, noncontact shoveling, and adsorptive
bubble separation. Previous studies have reported
that the synergetic adsorption mechanisms of surface
and bubble separations also played a critical role in
NPs adsorption, [59, 84-87]. The mechanisms of
sorption of NPs removal during ASP in WWTPs was
determined in Fig. 1.
* Fig. 1 can be found in the Appendix section.
The adsorption process forms a layer of adsorbate
(metal ions) on the surface of adsorbents. Adsorption
can be reproduced for multiple applications via a
desorption method (reverse adsorption in which
adsorbate ions are transported from the adsorbent
surface) because adsorption is a reversible process in
certain circumstances, [88]. Adsorption onto a solid
adsorbent includes three major steps: transportation
of the pollutant to the adsorbent surface from aqueous
solution, adsorption onto the solid surface, and
transport within the adsorbent particle. Generally,
electrostatic attraction causes charged pollutants to
adsorb on differently charged adsorbents because
heavy metals have a vigorous affinity for hydroxyl
(OH−) or other functional group surfaces, [89].
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The critical mechanisms of NPs removal during
ASP are biodegradation or biotransformation and
sorption. The main mechanisms of NPs
biodegradation include sequential steps of
assimilation and mineralization, [90]. The NPs get
incorporated or ingested by microorganisms like
metazoan or protozoan and subsequently get
hydrolysed into simpler units via intracellular
degradation, [91]. Also, the NPs can be degraded into
simpler units by hydrolases like extracellular
enzymes secreted by microorganisms via
extracellular degradation, [61]. The simpler units,
further metabolized by the various metabolic
pathways and final end products like CO2, H2O, CH4,
are produced via the process of mineralization.
Different biodegradation mechanisms can be
observed based on the chemical structure and
polymer types of the NPs, [92]. Different enzymes
like protease, laccase, esterases, cutinase, etc., have
exhibited encouraging results in the NPs degradation,
[90, 93].
2.6 Adsorption Isotherm
Adsorption isotherms play a vital role in interpreting
the mechanism of metal ion adsorption onto different
adsorbents, [94]. Adsorption kinetic models shed
light on the surface properties of adsorbents and the
intermolecular interactions between adsorbed
molecules and the adsorbent matrix, [95]. Isotherm
and kinetic models contribute to understanding the
adsorption process, relying on various factors,
including the adsorbent’s structure and the physical
and chemical characteristics of the solute, [94]. The
Langmuir model finds application in solid–liquid
systems, elucidating that all sites on the surface of the
adsorbent have equal opportunities to be occupied by
heavy metals (such as Cu, Ni) in Equation (2):
(2)
where; qe: amount of adsorbed metal ions per unit
mass of adsorbent at equilibrium (mg/g), Ce: metal
ion concentration in solution at equilibrium (mg/l),
KL: Langmuir binding constant (l/mg), qmax:
maximum amount of metal adsorbed per unit weight
of adsorbent (mg/g).
The main properties of Langmuir model
adsorption isotherms for Ni-Cu-C NCs were
determined to homogeneous surface of bio-
adsorbents, mono layer adsorption, adsorbate amount
has no influence on the adsorption kinetic, no
interaction between the adsorbed molecules and a
dimensionless model.
Note that the best-fit R2 values calculated from
both the Langmuir model (0.995-0.999) and the
Freundlich model (0.983-0.997) are relatively close
to 1, indicating that both models can accurately
describe the adsorption process at different
temperatures (i.e., 20oC, 30oC and 40oC). However,
R2 values obtained from the Langmuir model were
slightly greater than those from the Freundlich model
for both the unary and the binary adsorptive systems,
suggesting that the former model is better in defining
these adsorption isotherm data and that both heavy
metal ions were likely to occur in a monolayer
manner based on the basic assumption of the
Langmuir model [96].
2.7 Adsorption Kinetic
Kinetic adsorption models describe the mechanism of
adsorption of Ni-Cu-C NC by biosorbents and
particularly determine the rate of biosorption during
the removal of heavy metals from wastewater on an
industrial scale to optimize the design parameters,
including the adsorbate residence time and reactor
dimension, [95]. Heavy metals (Cu, Ni) kinetics; It
conforms to the pseudo-second order adsorption
kinetics (non-linear form) in Equation (3):
(3)
where; qe (mg/g): adsorption capacity at
equilibrium, qt (mg/g): adsorption capacity at time t
(min), k2 (g/mg.min): pseudo-second-order rate
constant, respectively.
The main properties of pseudo-second order
adsorption kinetics of heavy metals were summarized
to the second-order rate equation, detected as the best
suitable model with highest R2 value, express
chemical adsorption of ions, which involve valence
forces, chemical coordination through sharing or
exchange electrons between adsorbent and heavy
metals (ion exchange), the rate of occupation of
adsorption sites is proportional to the square of the
number of unoccupied sites.
2.8 Statistical Analysis
ANOVA analysis of variance between experimental
data was performed to detect F and P values. The
ANOVA test was used to test the differences between
dependent and independent groups, [97].
Comparison between the actual variation of the
experimental data averages and standard deviation is
expressed in terms of F ratio. F is equal (found
variation of the date averages/expected variation of
the date averages). P reports the significance level,
and d.f indicates the number of degrees of freedom.
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Regression analysis was applied to the experimental
data in order to determine the regression coefficient
R2, [98]. The aforementioned test was performed
using Microsoft Excel Program.
All experiments were carried out three times and
the results are given as the means of triplicate
samplings. The data relevant to the individual
pollutant parameters are given as the mean with
standard deviation (SD) values.
3 Results and Discussions
3.1 XRD Analysis Results
The results of XRD analysis observed for Ni-Cu-C
NCs in an activated sludge solution with adsorption
process for PET NPs removal is illustrated in Fig. 2.
The characterization peaks were measured at 2θ
values of 24.70o, 35.65o, 38.11o and 43.82o,
respectively, corresponding to the (100), (120), (302)
and (002) planes of implying Ni-Cu-C NCs (red
spectrum) in an activated sludge solution for PET
NPs removal via adsorption after 30 min adsorption
time (Fig. 2a). The characterization peaks were
obtained at 2θ values of 25.08o, 36.22o, 37.75o,
42.31o, 47.16o, 57.24o, 64.11o and 66.33o,
respectively, corresponding to the (010), (110), (111),
(021), (121), (211), (220) and (311) plans,
respectively, implying Ni-Cu-C NCs (green
spectrum) in an activated sludge solution for PET
NPs removal after 60 min adsorption time (Fig. 2b).
The characterization peaks were found at 2θ values
of 24.27o, 32.36o, 38.11o, 39.42o, 42.10o, 47.25o,
58.34o, 65.28o and 67.34o, respectively,
corresponding to (100), (011), (110), (111), (021),
(200), (121), (202) and (032), respectively, implying
Ni-Cu-C NCs (blue spectrum) in an activated sludge
solution for PET NPs removal after 90 min
adsorption time (Fig. 2c). The characterization peaks
were observed at 2θ values of 24.29o, 35.17o, 38.83o,
39.21o, 42.33o, 47.20o, 58.24o, 64.60o, and 67.78o,
respectively, corresponding to (002), (111), (021),
(121), (202), (033), (210), (302), and (104)
respectively, implying Ni-Cu-C NCs (pink spectrum)
in an activated sludge solution for PET NPs removal
after 120 min adsorption time (Fig. 2d).
* Fig. 2 can be found in the Appendix section.
Note the detailed XRD spectrum of similar Ni-Cu
samples was reported previously [99]. Based on XRD
data, the adsorption process of the Ni-Cu-C NCs
premix for 3 min does not result in the alloy
formation. It is represented by a mixture of metals.
The formation of an alloy occurs during the heating
of this sample in an inert atmosphere to the reaction
temperature (at 25oC).
3.2 FTIR Analysis Results
The FTIR spectrum of Ni-Cu-C NCs were
determined in an activated sludge solution during
PET NPs removal via adsorption (Fig. 3). The main
peaks of FTIR spectrum for Ni-Cu-C NCs (red
spectrum) was observed at 542 cm-1, 706 cm-1, 1005
cm-1, 1478 cm-1, 1758 cm-1 and 3751 cm-1
wavenumber, respectively, after 30 min adsorption
time during PET removal (Fig. 3a). The main peaks
of FTIR spectrum for Ni-Cu-C NCs (green spectrum)
was obtained at 618 cm-1, 645 cm-1, 1010 cm-1, 1434
cm-1, 1751 cm-1 and 3758 cm-1 wavenumber,
respectively, after 60 min adsorption time during PET
NPs removal (Fig. 3b). The main peaks of FTIR
spectrum for Ni-Cu-C NCs (blue spectrum) was
determined at 551 cm-1, 744 cm-1, 1018 cm-1, 1539
cm-1, 1701 cm-1 and 3715 cm-1 wavenumbers,
respectively, after 90 min adsorption time for PET
NPs removal (Fig. 3c). The main peaks of FTIR
spectrum for Ni-Cu-C NCs (pink spectrum) was
obtained at 516 cm-1, 638 cm-1, 1074 cm-1, 1479 cm-
1, 1724 cm-1 and 3729 cm-1 wavenumber,
respectively, after 120 min adsorption time during
PET NPs removal (Fig. 3d).
* Fig. 3 can be found in the Appendix section.
Minteniget al., [100], used FPA-based
transmission micro-FTIR to identify NPs in
wastewater and sludge samples, limiting fibre size
(10–20 lm) and lateral resolution. Xu et al., [101],
collected 68 influent and 72 effluent samples from
WWTPs and found 112 plastics of 14 different types,
which includes polyethylene (PE), polyamide (PA),
polypropylene (PP), polystyr ene (PS), PET, rayon,
polyvinyl chloride (PVC), poly methylmethacrylate
(PMMA), rubber, polyethylene and polyether
urethane (PU), polypropylene copolymer (PE-PP),
acrylonitrile styrene copolymer (AS) and poly
acrylate (PA).
3.3 FESEM Analysis Results
The morphological features of Ni-Cu-C NCs were
characterized through FESEM images (Fig. 4). The
FESEM images of Ni-Cu-C NCs were obtained in an
activated sludge solution with adsorption process for
PET NPs removal (Fig. 4).
* Fig. 4 can be found in the Appendix section.
As is seen, the material is represented by rather
short carbon filaments (nanofibers) grown on the
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particles of the Ni-Cu alloy (Fig. 4). It is worth noting
that the formed active metal particles are mainly of
biconical shape (Fig. 4). The carbon filaments grow
predominantly in two opposite directions. As follows
from the microscopic data, 1 min of exposure to the
reaction mixture is enough for the almost complete
destruction of the bulk alloy and the formation of
active particles catalyzing the growth of carbon
naofibers (Fig. 4).
Similar tangles of thin carbon nanofibers were
obtained previously when decomposing the mixture
of C2–C4 hydrocarbons on the Ni-Cr alloy [102].
The composite material is represented by carbon
filaments with catalytic particles embedded in their
structure. Such carbon composite materials with
embedded metal particles were reported to exhibit
high catalytic activity in electrocatalytic reactions
[103].
3.4 EDX Analysis Results
The EDX analysis was also performed to investigate
the composition of Ni-Cu-C NCs (Fig. 5). The EDX
analysis exhibited the composition of Ni-Cu-C NCs
in an activated sludge during adsorption process for
PET NPs removal after 120 min adsorption time (Fig.
5).
* Fig. 5 can be found in the Appendix section.
According to EDX analysis Ni and Cu atoms are
predominantly found in the active particles. EDX
data it also suggests that the formation of Ni-Cu-C
NCs particles does not occur during spontaneous
events due to redistribution of Ni and Cu atoms.
In addition to the EDX mapping, the Ni and Cu
atoms are predominantly located in the same areas
related to the active particles. The EDX data also
suggest that no redistribution of the Ni and Cu atoms
occurs during the spontaneous formation of catalytic
particles.
3.5 HRTEM Analysis Results
The HRTEM images of Ni-Cu-C NCs exhibited a
micromorphological structure in the activated sludge
solution process during PET NPs removal after 120
min adsorption time (Fig. 6).
* Fig. 6 can be found in the Appendix section.
Since the Ni-CuC alloy was formed during the
heating of the Ni-Cu-C sample to the reaction
temperature, the elemental composition of the
obtained particles was analyzed in detail by HRTEM
(Fig. 6). Therefore, the high-resolution HRTEM
images of the filament suggest that the carbon layers
are quite tightly stacked together.
3.6 Nitrogen Adsorption/Desorption Study
Analysis
Nitrogen adsorption/desorption curves and the
corresponding Barrett-Joyner-Halenda (BJH) pore
diameter distribution diagram is used to analyze the
samples of Ni-Cu-C NCs in Fig. 7a shows that the
curves of the aforementioned nanocomposite are all
of type-ⅳ isotherms and have obvious hysteresis
loops, indicating abundant pore structures. More
details on the porosity of material were obtained by
BET and BJH analyses, as shown in Fig. 7b.
* Fig. 7 can be found in the Appendix section.
The specific surface area of Ni-Cu-C and Cu-C N
Cs are 27.3 m2/g and 12.1 m2/g, respectively.
However, the specific surface area of Ni-Cu-C NC is
52.7 m2/g. The 3D skeleton of porous nanosheets
composed of many nanoparticles provides a larger
specific surface area as analyzed in Fig. 7(a-d). In
addition, the pore sizes of Ni-Cu-C NC is
concentrated at 4 nm, respectively, while Cu-C and
Ni-Cu NCs show a smaller and richer pore size
distribution at 2 nm. It is conducive to the infiltration
of electrolyte ions, so as to obtain more reaction sites,
which is conducive to the rapid transfer of charge,
and improve the specific adsorption capacity of
nanocomposite.
3.7 Raman Spectroscopy
To further check the graphitic character of the
composites, the materials were characterized by
Raman spectroscopy. The Raman spectra were
recorded in the range of 100–3500 cm−1, which is the
most informative for carbon materials (Fig. 8).
Raman spectroscopy is a non-destructive and
powerful technique used to identify and characterize
all the members of the carbon family. Raman spectra
measured at the lowest laser powers of 0.1÷1mW are
dominated by one-phonon peaks attributed to the G-
(~1590 cm−1) and D-bands (~1350cm−1) of
disordered sp2 carbon. Less intense second-order
peaks are attributed to 2D (~2710 cm−1), D+G (~2940
cm−1) and 2G (~3200 cm−1) bands.
* Fig. 8 can be found in the Appendix section.
In detail, the G-band refers to sp2 carbon atoms
scattering due to vibrations of the E2g mode, while
the D-band represents internal defect-induced
scattering. The shape of the Raman spectra indicates
crystallization of graphitic structures with a low
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graphitization degree typical for nanographite as
evidenced both by the rather high full-width of the G-
band and the ID/IG ratio (data not shown). The ID/IG
intensity ratio gives a measure of the structural
disorder and makes it possible to estimate the average
in-plane crystallite size (La) of the sp2 domains
according to the relation I I D G / 0 = .0055La 245.46.
The Cu/C nanocomposite shows the most disordered
nanographite phase as evidenced by having both the
highest full width of the G and D bands and the
lowest estimated crystallite size La. Therefore,
Raman analysis demonstrated that nickel, in
comparison to cobalt and copper, promotes the
formation of a more ordered sp2 carbon structure.
Enhanced formation of the more ordered
nanographite phase leading to a higher thickness of
carbon shell around the metal nanoparticles,
therefore, appears to be the reason for the increased
carbon content in the composites obtained
particularly using Co and Ni.
3.8 CV Curves of Ni-Cu-C NCs
The CV curves of all samples and pure nickel foam
(NF) at scanning rates of 5 mV/s are compared in Fig
9. They all showed obvious redox peaks, which are
caused by Ni2+/N3+, Co2+/Co3+ and Cu2+/Cu+ electron
pairs in the redox reactions. It can be clearly seen that
the CV curve of Ni-Cu-C NCs covers a higher area
than Ni-Cu and Ni-C NCs which means that Ni-Cu-
C NCs has a higher energy storage capacity. It is due
to the large specific surface area of Ni-Cu-C NCs,
which can increase the number of reactive sites and
thus improve the specific capacity.
* Fig. 9 can be found in the Appendix section.
To investigate the charge/discharge mechanism of
the electrode, the relationship between anodic peak
current and the square root of scan rate of different
samples. The correlation coefficients obtained after
linear fitting are all greater than 0.99, indicating that
there is a linear relationship between the anodic peak
current and the square root of the scanning rate, that
is, the electrochemical energy storage kinetics is
mainly controlled by the diffusion of OH- (data not
shown). Moreover, it is obvious that the slope of the
fitting line of Ni-Cu-C NCs is the larger, indicating
that the two have higher diffusion rates. Furthermore,
the relationship between the current and the scan
rates of each redox peak of Ni-Cu-C NCs/ Ni-Cu NCs
is calculated by the following formula in Eq. (4):
(4)
where; i (A): is the current, v: is the scanning rate
(mV/s). The b: is the slope value of the curve between
the logarithmic peak current and the logarithmic
scanning rate. The value of b ranges from 0.5 to 1.0.
When the value of b is close to 1, the electrochemical
reaction of the nanocomposite is capacitive behavior,
while when the value of b is close to 0.5, the reaction
is battery behavior, which is controlled by ion
diffusion. The values of b of the redox peaks of Ni-
Cu-C NCs/Ni-Cu NCs are 0.87 and 0.84 respectively,
both within the range of 0.5–1.0. It shows that the
reaction process of nanocomposite is controlled by
capacitor behavior and battery behavior
simultaneously.
3.9 Effect of Some Operational and
Environmental Conditions on PET NPs Yields
3.9.1 Effect of pH Values
The impacts of increasing pH values (4.0, 5.0, 6.0,
7.0 and 8.0) on removals of PET NPs were examined
in an activated sludge solution during adsorption
process at 25oC (Fig. 10). 43.21%, 68.93%, 75.11%,
99.31% and 40.09% PET NPs removals were
measured at pH=4.0, at pH=5.0, at pH=6.0, at pH=7.0
and at pH=8.0, respectively, in an activated sludge
solution during adsorption process, at 25oC (Fig. 10).
The maximum 99.31% PET NPs removal was
obtained at pH=7.0 in an activated sludge solution
during adsorption process, at 25oC (Fig. 10).
* Fig. 10 can be found in the Appendix section.
In adsorption studies, pH of solution plays pivotal
role in the electrostatic interactions between
adsorbates and adsorbents. In basic conditions,
formation precipitation of metal ions as their
respective hydroxide can infuence the adsorption
results, therefore we have selected the maximum
adsorption under acidic environment. As pH
increases the surface of NPs become more negatively
charged. This causes increased repulsion between
PET and Ni-Cu-C NCs. Hence the removal efficiency
decreases with increase in pH. Also change in PET
uptake with pH is shown graphically. The ANOVA
test indicated no significant differences between pH
value and NPs yields up to a pH value of pH=7.0 (p
= 0.06, F = 0.25, d.f. = 2). The ANOVA test indicated
significant differences between pH values and NPs
yields for adsorption times > pH=7.0 and < 5.0 (p =
0.74, F = 3.21, d.f. = 2).
The pH value can change the zeta potential of NPs
or heavy metal precipitation, thereby increasing or
decreasing the adsorption of certain metals.
Generally, pH value increases with the decreasing
zeta potential of NPs. However, if the NP’s zero-
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charge point is below the pH of the water, the NP
charge will be negative. Thus, the electrostatic
attraction between the metals and the polymer
increases. In contrast, precipitation of some metals
may occur in environments with a pH around 7.0. A
recent study reported that pH increases with
increasing the adsorption of Cu, zinc (Zn), Ni,
cadmium (Cd), lead (Pb), and cobalt (Co) by NPs
[104, 105-111].
3.9.2 Effect of Adsorption Time
Effects of increasing adsorption times (30 min, 60
min, 90 min and 120 mins on PET NPs removals in
an activated sludge solution during adsorption
process at pH=7.0 and at 25oC is illustrated in Fig. 11.
38.54%, 61.73%, 86.29% and 99.42% PET NPs
removals were measured after 30 min, 60 min, 90 min
and 120 min adsorption time, respectively, in an
activated sludge process during adsorption process,
at pH=7.0 and at 25oC (Fig. 11). The maximum
99.42% PET NPs removal was observed after 120
min adsorption time, in an activated sludge solution
during adsorption process, at pH=7.0 and at 25oC
(Fig. 11).
* Fig. 11 can be found in the Appendix section.
As time progresses the surface coverage of the
adsorbent is high an adsorption process takes place.
Increasing the contact time between the PET and Ni-
Cu-C NCs adsorbent would improve the percentage
removal. Increases in time are expected to enhance
sorption until saturation at equilibrium. The ANOVA
test indicated no significant differences between time
and NPs yields up to a adsorption time of 120 min (p
= 0.04, F = 0.22, d.f. = 2). The ANOVA test indicated
significant differences between adsorption times and
NPs yields for adsorption times > 120 min (p = 0.47,
F = 3.18, d.f. = 2).
3.9.3 Effect of Ni-Cu-C NCs Adsorbent
The impact of increasing Ni-Cu-C NCs adsorbent
concentrations (100 mg/l, 200 mg/l, 300 mg/l and 400
mg/l) on PET NPs removals in an activated sludge
process during adsorption process was investigated
after 120 min adsorption time, at pH=5.0 and at 25oC
(Fig. 12). 39.50%, 70.05%, 99.20% and 86.43% PET
NPs removals were observed at 100 mg/l, 200 mg/l,
300 mg/l and 400 mg/l Ni-Cu-C NCs adsorbent
concentrations, respectively, in an activated sludge
solution during adsorption process, after 120 min
adsorption time, at pH=7.0 and at 25oC (Fig. 12). The
maximum PET NPs removal was obtained as 99.20%
for 300 mg/l Ni-Cu-C NCs adsorbent concentration,
in an activated sludge solution during adsorption
process, after 120 min adsorption time, at pH=7.0 and
at 25oC (Fig. 12).
* Fig. 12 can be found in the Appendix section.
This may be due to overlapping of the adsorption
sites as a result of overcrowding of the adsorbent
particles. It is seen that percent removal increases
with the increase in the concentration of the
adsorbent. The maximum percent removal is
exhibited at a adsorbent concentration of 300 mg/l.
This is due to enhanced active sites with an optimum
increase in amount of adsorbent. As can be observed
in over trend of adsorption with the adsorbent dosage,
the adsorption increases with the increase in dosage
and reached to maximum value at 300 mg/l. These,
observations suggest that adsorption is almost
directly proportional to the amount of the dosage.
The ANOVA test indicated no significant differences
between Ni-Cu-C NCs adsorbent concentration and
NPs yields up to an adsorbent concentration of 300
mg/l (p = 0.05, F = 0.34, d.f. = 2). The ANOVA test
indicated significant differences between adsorbent
concentrations and NPs yields for adsorpbent
concentrations > 300 mg/l (p = 0.51, F = 3.06, d.f. =
2).
3.9.4 Effect of PET NPs Concentration
The impact of increasing PET NPs concentrations (1
mg/l, 5 mg/l, 10 mg/l and 15 mg/l) on the adsorption
of PET NPs were investigated in an activated sludge
solution in the present of 300 mg/l Ni-Cu-C NCs
adsorbent concentration, after 120 min adsorption
time, at pH=7.0 and at 25oC (Fig. 13). 37.83%,
74.26%, 99.31% and 88.02% PET NPs removals
were observed to 1 mg/l, 5 mg/l, 10 mg/l and 15 mg/l
PET NPs concentrations, respectively, in an activated
sludge solution during adsorption process, with 300
mg/l Ni-Cu-C NCs adsorbent concentration, after
120 min adsorption time, at pH=5.0 and at 25oC (Fig.
13). The maximum 99.31% PET NPs removal was
measured for 10 mg/l PET NPs concentration (Fig.
13).
* Fig. 13 can be found in the Appendix section.
When more adsorbate molecules bind to the active
sites of the adsorbent, diffusion accelerates the
binding of PET on the surface of the Ni-Cu-C NCs
due to the increase in driving force of concentration
gradient, resulting in higher adsorption capacities.
However, a decline of adsorption efficiency due to
higher pollutant concentration. At higher pollutant
concentrations, the number of available adsorbent
sites becomes fewer, resulting in a decrease in
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pollutant removal efficiency. The ANOVA test
indicated no significant differences between PET
NPs concentration and NPs yields up to a PET NPs
concentration of 10 mg/l (p = 0.07, F = 0.20, d.f. =
2). The ANOVA test indicated significant differences
between PET NPs concentrations and NPs yields for
PET NPs concentrations > 10 mg/l (p = 0.61, F =
3.02, d.f. = 2).
3.10 Optimization of the Experimental
Conditions in an Aerobic Activated Sludge
Treatment Plant
In this study, the high concentrations of PET NPs
were not treated effectively in a continuous flow
activated sludge process. Before aerobic activated
sludge process the biomass concentration returned by
the aeration tank was mixed with 1 liter wastewater
containing 10 mg/l PET NP concentration and 300
mg Ni-Cu-C NCs during 120 min adsorption time, at
pH=7.0 and at 25oC. After this duration the PET NPs
was removed with yields as high as around 99.20%
and 99.42%. No pH adjustement was performed for
activated sludge and during PET removal since the
pH of wastewater was 7.0.This decreased the cost of
the treatment. After this step with specific gravity
and settling ability and focculation of sludge focs
with nanocomposite the treated water was separated
from the wastewater. The COD and BOD removals
were improved in the next activated sludge process
because of the adsorption of non-biodegradable and
slowly biodegradable PET NP materials. The Ni-Cu-
C NCs nanocomposite was reused and used again in
the continuous removal of PET from wastewater.
Therefore, this process is environmentally friendly
and cost-effective, as it realizes the recycling of an
industrial waste. These experimental fndings
demonstrated a novel, reliable and efective
technology for the utilization of Ni-Cu-C NCs. Tis
process concept can be further applied in the full
scale aerobic biological treatment systems and
generally in municipal and industrial wastewater
treatment facilities.
4 Conclusion
NPs cause more serious environmental problems than
plastics and microplastics. Due to the difficult
degradation processes of NPs, difficulties in
recycling rates, large specific surface areas, and
ability to transform into more complex and toxic
structures by adsorbing other pollutants, they can
easily enter the food chain and other environments.
To ensure effective adsorption of NPs in the aquatic
environment; many studies have been conducted on
the enrichment and removal of NPs in the aquatic
environment, such as the preparation of adsorption
materials using various natural products of animals
and plants, and various studies on this subject are
continuing.
Adsorption is widely used for the removal of
contaminants from aqueous solutions, being cost-
effective and environmentally friendly treatment
process. The possible factors affecting the removal
efficiency of NPs by adsorption process include: pH,
adsorbent concentrations, adsorption time,
temperature and NP concentrations.
In this study, the maximum PET NPs removal
efficiency was investigated under optimum
conditions by using various experimental parameters
(pH, adsorption time, adsorbent concentrations and
NPs concentrations) to improve the efficiency of PET
adsorption yields using Ni-Cu-C NCs from an
activated sludge solution. The maximum 99.20-
99.42% PET NPs removal was measured at 10 mg/l
PET NPs concentration, in an activated sludge
process during adsorption process, at 300 mg/l Ni-
Cu-C NCs adsorbent concentration, after 120 min
adsorption time, at pH=7.0 and at 25oC. The
adsorption process was found to be a very effective
method in the removal of PET NPs from an activated
sludge solution with Ni-Cu-C NCs adsorbent.
Adsorption process; is an easily applicable,
environmentally friendly and economical method.
The Langmuir model finds application in solid–
liquid systems, elucidating that all sites on the surface
of the adsorbent have equal opportunities to be
occupied by heavy metals (such as Cu, Ni). Heavy
metals (Cu, Ni) kinetics; It conforms to the pseudo-
second order adsorption kinetics (non-linear form).
Based on XRD data, the adsorption process of the
Ni-Cu-C NCs premix for 3 min does not result in the
alloy formation. It is represented by a mixture of
metals. The formation of an alloy occurs during the
heating of this sample in an inert atmosphere to the
reaction temperature at 25oC. FTIR spectrum is the
most commonly used technique for detecting NPs. It
exposes plastic particles to infrared radiation,
producing spectra that correspond to the vibrations of
chemical bonds between different atoms. The FTIR
spectra were then compared with the reference
spectra stored in a library to analyze the composition
of the NPs. According to, FESEM and HRTEM
analyses, during the carbon erosion process, the
initial microdispersed Ni-Cu alloy disintegrates on
small metal particles, which catalyzes the growth of
carbon nanofibers. EDX mapping confirmed that the
distribution of metal atoms in these particles is
uniform and corresponds to the Ni/Cu weight ratio of
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Ni/Cu=88/12, which was specified during the
synthesis.
In WWTPs, the elimination of NPs is of great
importance in every aspect, as the key point
connecting urban and social water use.
One of the aspects of NPs pollution is their
carrying and transfer from one environment to
another, increasing general contamination and the
risk of ecotoxicity. To reduce NPs emissions in the
environment, it is very important and necessary to
adopt "sustainable plastic waste management"
practices, as well as to improve technologies and
processes for their removal from WWTPs. NPs
control and reduce their sources should be performed
bu using "comprehensive monitoring programs".
Most advanced purification technologies for NPs
removal are implemented at laboratory scales; For
practical applications, full-scale application
feasibility must be investigated and its applicability
must be ensured. In order to evaluate the contribution
of WWTPs to NP pollution; There is a great need for
more detailed research and evaluation of the
available data to understand the degradation
mechanism of NPs in aquatic environments.
Different international organizations and
governments around the world should urgently make
the necessary plans to create implementation
frameworks to reduce or prevent plastic pollution in
the environment by raising public awareness about
plastic pollution, switching to biodegradable
products, and discouraging the production and
consumption of plastics, and put these plans into
practice immediately. They must take the necessary
steps to an important future perspective is to better
recycle and reuse plastics; Optimizing waste
management systems and evaluating the life cycle of
NPs are also very important, and their
implementation is very necessary.
Finaly, plastics are one of the most important
materials for almost all areas of work. Plastics are
important that their correct use and, as far as possible,
their reduction, added to the good management of
waste to avoid the dangers that plastic can mean and
in our lives.
Acknowledgement:
Experimental analyzes in this study were performed
at the Laboratories of the Canada Research Center,
Ottawa, Canada. The authors would like to thank this
body for providing financial support.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
Prof. Dr. Delia Teresa Sponza and Post-Dr. Rukiye
Öztekin took an active role in every stage of the
preparation of this article.
The authors equally contributed in the present
research, at all stages from the formulation of the
problem to the final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
The experimental phases of this research study were
conducted at the National Research Council (NRC)
of Canada, Research Centres, Ontario, Canada. The
authors would like to thank this body for providing
financial support.
Conflict of Interest
The authors have no conflicts of interest to declare
that are relevant to the content of this article.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
Creative Commons Attribution License 4.0
https://creativecommons.org/licenses/by/4.0/deed.en
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APPENDIX
Fig. 1. Mechanism of sorption of NPs removal during ASP in wastewater treatment plants.
Fig. 2. XRD spectrum of Ni-Cu-C NCs (a) after 30 min (red spectra), (b) after 60 min (green spectra), (c) after
90 min (blue spectra) and (d) after 120 min (pink spectra) adsorption times, respectively, in an activated sludge
solution with adsorption process for PET NPs removal.
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Fig. 3. FTIR spectrum of Ni-Cu-C NCs (a) after 30 min (red spectra), (b) after 60 min (green spectra), (c) after
90 min (blue spectra) and (d) after 120 min (pink spectra), respectively, in an activated sludge solution with
adsorption process for PET NPs removal.
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Fig. 4. FESEM images of Ni-Cu-C NCs in an activated sludge solution with adsorption process for PET NPs
removal after 120 adsorption time (FESEM image size: 1µm).
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Fig. 5. EDX images of Ni-Cu-C NCs in an activated sludge solution with adsorption process for PET NPs
removal.
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Fig. 6. HRTEM images of Ni-Cu-C NCs in micromorphological structure level in an activated sludge solution
with adsorption process for PET NPs removal after 120 min adsorption time (HRTEM image size: 1µm).
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Fig. 7a. N2 Adsorption/Desorption of Ni-Cu-C NCs
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Fig. 7b. BJH por size distribution of Ni-Cu-C, Ni-C and Ni-C NCs
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Fig. 8. Raman Streptoscopy analysis results
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Fig. 9. CV curves of Ni-Cu-C NCs
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Fig. 10. Effect of increasing pH values in an activated sludge solution during adsorption process for PET NPs
removal, at 25oC.
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Fig. 11. Effect of increasing adsorption times in an activated sludge solution during adsorption process for PET
NPs removal, at pH=5.0 and at 25oC.
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Fig. 12. Effect of increasing Ni-Cu-C NCs adsorbent concentrations in an activated sludge solution during
adsorption process for PET NPs removal, after 120 min adsorption time, at pH=5.0 and at 25oC.
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Fig. 13. Effect of increasing PET NPs concentrations in an activated sludge solution during adsorption process
for PET NPs removal, after 120 min adsorption time, at pH=5.0 and at 25oC.
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