Accepted Manuscript
Methyl orange adsorption comparison on nanoparticles: Isotherm, kinetics, and
thermodynamic studies
A.A.A. Darwish, M. Rashad, Hatem A. AL-Aoh
PII:
S0143-7208(18)30989-6
DOI:
10.1016/j.dyepig.2018.08.045
Reference:
DYPI 6959
To appear in:
Dyes and Pigments
Received Date: 30 April 2018
Revised Date:
20 July 2018
Accepted Date: 23 August 2018
Please cite this article as: Darwish AAA, Rashad M, AL-Aoh HA, Methyl orange adsorption comparison
on nanoparticles: Isotherm, kinetics, and thermodynamic studies, Dyes and Pigments (2018), doi:
10.1016/j.dyepig.2018.08.045.
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ACCEPTED MANUSCRIPT
Methyl orange adsorption comparison on nanoparticles: isotherm, kinetics,
A.A.A. Darwish1,2, M. Rashad1,3,*, Hatem. A. AL-Aoh4
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and thermodynamic studies
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(1) Nanotechnology Research Laboratory, Department of Physics, Faculty of Science, University of Tabuk, Tabuk,
Saudi Arabia
(2) Department of Physics, Faculty of Education at Al-Mahweet, Sana'a University, Al-Mahweet, Yemen.
(3) Department of Physics, Faculty of Science, Assiut University, Assiut, Egypt.
(4) Department of chemistry, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia
*Corresponding author. Tel: +966556061705, E-mail address: mohamed.ahmed24@science.au.edu.eg
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Abstract
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A batch equilibrium system has been used to investigate the adsorption of methyl orange
(MO) on NiO or CuO nanoparticles (NPs). The effects of experimental conditions such as
initial concentration, agitation time, solution pH and temperature were examined. Langmuir
and Freundlich's models were used for determining the adsorption parameters at three different
temperatures. It was observed that the Langmuir model fits well with the experimental
adsorption data. The pseudo first-order, second-order and intra-particle diffusion models were
applied to investigate the kinetic data. The obtained results indicate that experimental kinetics
data of NiO and CuO NPs were only well explained by the second-order model. It was found
that the adsorption capacities of NiO NPs are higher than that of CuO NPs for each
temperature. However, CuO NPs has higher adsorption rate than that of NiO NPs. The
thermodynamic parameters (∆H⁰, ∆S⁰, and ∆G⁰) were determined and their values indicate
that the adsorptions of MO on NiO and CuO NPs are endothermic and spontaneous processes.
Thermodynamics parameters also confirm that the adsorption of MO is chemical and physical
adsorption on the surfaces of NiO and CuO NPs, respectively.
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Keywords: Methyl orange, Nanoparticles, Isotherm, kinetics, thermodynamics
1. Introduction
Methyl orange (MO) is an acidic anionic mono-azo dye [1-3] commonly and continuously
used in textiles, laboratory experiments and other commercial products [4]. This dye is toxic to
aquatic life [5]. Increasing heart rate, vomiting, shock, cyanosis, jaundice, quadriplegia, and
tissue necrosis in humans can be obtained due to acute exposure to this hazard dye [6, 7].
Therefore, it is essential to remove this dye from wastewaters is generated by industries related
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to the use and synthesis of MO before its discharge to the environment. Thus, various techniques
such as photocatalytic degradation via metal oxide [8-16], degradation by the combined
electrochemical process [17], membrane filtration, solvent extraction, adsorption and others have
been applied for industrial wastewaters purification before their disposal to the environment [18].
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Adsorption is the best and the most comprehensive technique has been used for the
removal of azo dyes from water and industrial wastewaters because of its ability to remove like
these dyes at any concentration, easy to design and a relatively lower cost [18, 19]. Granulated,
powdered and fibers activated carbons (GAC, PAC, ACF) represent an intersecting adsorbents.
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On the other hand, using of these types of activated carbons is limited due to their higher cost
[20, 21]. Other low-cost materials like chitosan [22], peat [23], chitin [24], silica [25], goethite,
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chitosan beads and goethite impregnated with chitosan beads [26] ,slag [27], peach nut shells
[28] and fly ash [29] have been used for adsorption of azo dyes such as MO from aqueous
solution. It was found that these low-cost adsorbents have no sufficient adsorption performance
towards MO. Therefore, more work is required in this filed to used other types of adsorbents for
the elimination of this hazard contaminant from industrial wastewaters.
Currently, nanoparticles (NPs) such as ferric oxide–biochar nanocomposites derived from
loaded
on
activated
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pulp and paper sludge [4], nanostructured proton-containing δ-MnO2 [30], silicon carbide (NPs)
carbon
[31],
synthesized
functionalized
CNTs
with
3-
aminopropyltriethoxysilane loaded TiO2 nanocomposites [32], ZnO NPs [33] and NiO NPs [34]
have been proposed as efficient adsorbents for removing MO from industrial wastewaters.
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NiO NPs powders with the same sizes and good dispersion have various applications such
as producing films, magnetic materials, ceramic, heterogeneous catalytic materials, alkaline
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batteries, and electrochromic [35]. NiO NPs is also used for the oxidation of a wide range of
organic compounds [36, 37]. Moreover, it was suggested by Falaki and Fakhri [34] that the NiO
NPs is nominated to be a newly suitable adsorbent due to its chemical and magnetic properties.
Therefore, it was used by the same researchers for adsorption of MO. The adsorption capacity of
MO on the NiO NPs prepared by Falaki and Fakhri [34] was found to be negligible (11.21
mg/g).
Yogesh Kumar et al. [38] synthesized CuO and NiO NPS by a hydrothermal reaction and
used these two adsorbents for adsorption of MO from aqueous solution. They found that CuO
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and NiO NPS prepared by their methodology have superior adsorption performance towards MO
comparing with other metal oxides NPS and NiO NPS obtained by Falaki and Fakhri [34]
method. Therefore, NiO and CuO NPS also have been selected in this work as promising
adsorbents for removal of MO from wastewaters.
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The higher difference between the adsorption capacity of MO onto NPS prepared by Falaki
and Fakhri method [34] and NPS synthesized by the methodology of Yogesh Kumar et al. [38]
indicates the type of materials and methods used for producing metal oxide NPS have significant
effects on their adsorption capabilities.
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Thus, the primary aim of this work is to investigate the effects of the raw material and
the type of the preparation method used for synthesis NiO and CuO NPS on their adsorption
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capacities. Moreover, the comparison between the adsorption performance of NiO NPs and CuO
NPs toward MO will also be investigated.
2. Materials and method
2.1 Preparation and characterization of the adsorbents
In a typical procedure, 0.2M Cu(NO3)2⋅6H2O was mixed with 0.2M Ni(NH2)2 in a flask.
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This flask was directly put into a microwave oven for 20 min (650 W) [39, 40]. A fine black
powder of CuO NPs is extracted. The same procedure has been repeated for NiO NCs using
Ni(NO3)2⋅6H2O as a starting material. X-ray diffraction (XRD) were used on a Shimadzu XD-3A
X-ray diffractometer at the 2?? range from 30 to 60, with monochromatized CuK?? radiation (??
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= 0.15418nm). A JEOL-JEM 200CX transmission electron microscope used for record
transmission electron microscopy (TEM) images with an 80 kV accelerating voltage. The pH of
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zero points charge (pHZPC) for both two adsorbents was determined using Theydan and Ahmed
method [41]. In this method NaNO3 solution with different concentrations (0.01 mg/L, 0.05
mg/L and 0.1 mg/L) were prepared. A series of 50 mL solutions with different initial pH values
(2, 3, 5, 7, 9, 11, and 13) for each concentration were prepared and adjusted by HNO3 or NaOH
solutions and recorded as pHi. Each of these solutions was poured into 100 mL glass bottle
containing 0.1 g of the NiO NPs and the mixtures were shaken at 150 rpm and room temperature
for 72 h. The supernatant solutions were filtered using membrane filter paper and the final pH for
each solution was measured using pH meter and recorded as pHf. The (pHi-pHf) values were
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plotted against pHi and pHZPC was determined from the crossover point of pHi and (pHi-pHf) in
the graph. These procedures were repeated with CuO NPs.
The surface area and porosity of NiO and CuO NPs were analyzed by adsorptiondesorption of N2 at 758.58 mm Hg and 77.40 deg K using BET surface analyzer (NOVA-3200
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Ver.6.09).
2.2 Adsorbate
MO with dye content 85%, molecular weight 327.33 g/mol, molecular formula
C14H14N3NaO3S, which have a maximum absorption at a wavelength of 460 nm, was supplied by
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Sigma-Aldrich. A dissolving 4 g of MO in 250 mL water and diluted to 1000 mL used for
preparing the solution of 4000 mg/L. The required concentrations of experimental solutions were
2.3 MO initial concentration effect
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prepared by diluting this stock solution using distilled water.
Experiments on the effect of MO initial concentration on its adsorption into NPs surfaces
were carried out in eleven 25 mL amber bottles have 10 mL of MO solution at different
concentrations of (50-1000 mg/L). A 0.02 g of NiO NPs was added to the bottle. Following, at
room temperature (30 ± 1⁰C), transfer to shaker incubator for 72 hours at 150 rpm. Then, these
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samples filtered through a membrane filter paper 102 (Double Rings, China) (60 × 60 cm). Using
UV-visible spectrophotometer, MO concentrations were measured before and after adsorption at
460 nm. These procedures were repeated using CuO NPs as an adsorbent. The amounts of MO
adsorbed onto the surface of NiO and CuO NPs were calculated by Eq.1.
(Co − Ce )V
W
(1)
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qe =
Co: initial concentrations, Ce: final concentrations of MO (mg/L), W (g): a mass of adsorbent, qe:
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adsorption amount per unit gram of the adsorbent at equilibrium (mg/g) and V: volume of the
solution (L).
2.4 Isotherm studies
The interaction between the adsorbent and adsorbate of any system can be explained by
adsorption isotherm parameters [42]. Since, these parameters give significant information on the
surface properties, the adsorption mechanisms and efficiencies of the adsorbent [42]. Langmuir
and Freundlich's equations are being the most suitable surface adsorption equations in a single
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solute system. Regarding the adsorption isotherms experiment, it was carried out as described in
Section 2.3 with the MO initial concentrations in 200-1000 mg/L range. The amounts of
adsorption at equilibrium, qe (mg/g) were calculated from Eq. 1.
2.5 Adsorption kinetics
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Adsorption of MO solutions with concentrations in the range of 50-200 mg/L on the NiO
and CuO NPs was conducted at time intervals of 10-1440 min. The same procedures as
explained in the isotherm part were applied. The amount of adsorbate adsorbed qt (mg/g) at time
t (min) was calculated from Eq. 2.
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( − )V
q = C WC
t
t
(2)
qt: MO adsorbed at time t (mg/g), Ct: solution concentrations at time t, V: volume of the liquid
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phase (L).
2.6 Solution pH effect
The effect of initial pH solution on the adsorption of MO on CuO NPs or NiO NPs was
investigated at various initial pH range of 2-11. Amber bottles containing 0.02 g of each
adsorbent were put in the incubator shaker for 3 days with a constant speed of 150 rpm and room
temperature with 10 mL of 300 mg/L of methyl orange solution. The pH was adjusted using
adsorbate solutions.
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either 0.1 M NaOH or 0.1 M HCl. Using filter paper, the adsorbents were separated from the
2.7 Adsorption thermodynamics
The effect of temperature and actual thermodynamic parameters ((∆H⁰, ∆S⁰, ∆G⁰) for
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adsorption of MO on CuO NPs or NiO NPs were investigated. In this section, 10 mL of 50, 100
and 300 mg/L of the adsorbate solutions were added to 25 amber bottles each containing 0.02 g
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of NiO or CuO NPs. The bottles were sealed and placed in the shaker incubator and shaken for 3
days at 30, 45 and 60 ⁰C. The other thermodynamic procedures were similar to that of the
isotherm studies.
Results and discussion
2.1. Adsorbents Characterizations.
Fig. 1 shows the XRD pattern for NiO and CuO NPs [40-43, 46]. A systematic study on
the XRD was performed to understand the phase symmetry of the prepared NiO and CuO NPs.
The XRD pattern obtained from the product (Fig 1a) is identical to NiO NPs. The sharp peaks
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corresponding to the planes (111), (200), (220), (311), and (222) indicate the monoclinic
structure of NiO nanocrystals which was also found to be highly crystalline. Sharp peaks were
obtained for CuO NPs (Fig 1b) at angles corresponding to the planes (110), (002), (111), (202),
and (202). This indicates the monoclinic structure of CuO NPs [47] which was found to be
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highly crystalline.
The average size of both NPs is estimated according to the following Debye-Scherer
equation [40]:
(3)
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=
??: constant is taken to be 0.94, λ: wavelength of X-ray and β: full width at half maximum
corresponding to 2 . Using Eq. 3, the calculated crystallite sizes are found to be in the range of
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14.5 ± 1.3 nm and 14 ± 1 for NiO and CuO NPs, respectively.
Fig. 2 shows the TEM image of the prepared (a) NiO and (b) CuO NPs [40-43]. The TEM
image shows that the shapes are spherical particles with a narrow size distribution in the range of
13±2 nm and 10±2 nm for NiO and CuO NPs, respectively, which is in good agreement with the
calculated results by Scherrer equation. The surface area and the porosity (total pore volume and
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average pore diameter) play an important role in the adsorption capacity and adsorption rate of
the adsorbent. Since the adsorption capacity of the adsorbent increases with increasing the
adsorbent surface area and total pore volume, whereas the average pore diameter has a positive
effect on the adsorption rate of the adsorbent. Therefore, the surface area and porosity of NiO
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and CuO NPs were investigated in this study and the results obtained are listed in Table 1. It can
be observed from this table that NiO has the surface area and pore volume higher than that of
CuO, whereas, the average pore diameter of the latter is superior to that of the former. The
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results of BET surface analyzer indicate that NiO NPs has higher adsorption capacity and lower
adsorption rate than that of CuO NPs. Moreover, to investigate the effect of solution pH on the
adsorption performance of the prepared adsorbents correctly, the pHZPC for each sample has to be
determined. This due to the adsorbate solution pH not only affects the dissociation of the
adsorbate to it ions but also have significant effects on the adsorbent surface charge. Therefore
pHZPC for both NiO and CuO NPs was determined and tabulated in Table 1.
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3.2. Adsorbate initial concentration effect on the adsorption uptake
The results of the impact of MO initial concentrations on its adsorption capability at three
different temperatures and equilibrium were presented in Fig. 3 for NiO and CuO NPs. It can be
observed from this figure that the adsorption ability of MO on both adsorbents (NiO and CuO
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NPs) increased with increment the initial concentrations of MO from 50 to 1000 mg/L. Similar
results have been observed earlier for different types of adsorbents and adsorbates [48, 49].
It can be noted that the higher initial concentration of MO has the greater adsorption rate.
This is could be due to that the initial MO concentrations providing a significant force to
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overcome all mass transfer resistance of the dye between the aqueous phase and solid phase.
However, the amounts of MO uptake (qe mg/g) are approximately constant at initial MO
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concentrations of 800 and 700 mg/L on the surface of NiO and CuO NPs, correspondingly. This
can be confirmed by the fact of all the active adsorption sites became saturated after these MO
concentrations. Furthermore, this figure indicates that NiO NPs has adsorption efficiency
towards MO higher than that of CuO NPs because the surface area and pore volume of the
former are higher than that of the latter.
3.3 Adsorption isotherms
Ce
C
1
=
+ e
qe qmax K L qmax
(4)
(5)
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1
ln qe = ln K F + ln Ce
n
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The adsorption performance in this study was investigated using the following models.
qmax: maximum adsorption capacity (mg/g), KL and KF: Langmuir and Freundlich constants,
respectively and 1/n: A Freundlich constant related to the adsorption. It can be noted that the
adsorption is favorable if 1/n value is between 0 and 1 [50].
An equilibrium parameter, RL is defined by Eq. 6 [51] was applied to investigate the
essential characteristics of the Langmuir isotherm.
RL =
1
1 + K L C0
(6)
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If RL >1, the isotherm nature is unfavourable, (RL=1, linear) and (0< RL < 1, favorable) or (RL=0,
irreversible).
Fig. 4 represents the plots of Langmuir isotherm model (Ce/qe against Ce) for adsorption of
MO onto NiO and CuO NPs. Whereas, the plots of Freundlich isotherm model (Lnqe versus
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LnCe), for adsorption of this dye on these two adsorbents, are demonstrated in Fig. 5. The
Langmuir (qmax and KL) and Freundlich (KF and n) isotherms parameters corresponding to the
correlation coefficients (R2) and RL were listed in Table 2. According to values of RL and 1/n
(Table2) that are between 0 and 1, it can be suggested that the adsorption of MO by these two
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adsorbents is approving under experimental conditions of this work. The values of Langmuir
value (R2) are higher than that of the Freundlich value illustrated that the adsorption data can be
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described by the former model. This value confirms that the surfaces of the used adsorbents are
suitable and the adsorption sites have the same adsorption ability towards MO. The results
obtained in this work agree well with the results of the adsorption selective dyes on ZnO NPs
[33]. It was found that the adsorption capacities of MO on the surface of NiO and CuO NPs are
higher than that obtained in other works, confirming the advantages of NiO and CuO NPs.
Moreover, Table 2 shows qmax and KF values for NiO NPs are higher than that of CuO NPs
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which illustrates that the former has higher adsorption efficiency for MO. This could be due to
higher surface area and pore volume of NiO NPs.
3.4 Contact time effect
The amount of MO adsorbed against the adsorption agitation time are demonstrated in Fig.
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6 at four initial MO concentrations (50,100, 150 and 200 mg/L) for NiO and CuO NPs. One can
observe from this figure that the adsorption uptake of MO on these two adsorbents increased
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with increasing contact time and then reached an area of stability. The equilibrium times are 720
and 540 min for NiO and CuO NPs, respectively. This indicates that the adsorption rate of MO
on CuO NPs is higher than that of NiO NPs. This is due to the average pore diameter of CuO
NPs is higher than that of NiO NPs (Table 1). Moreover, it can be seen from Fig.6 that the
adsorption equilibrium spend more than 10 h for the NiO or CuO NPs and it is known that the
nonmaterial have adsorption rate higher than that of observed in this study. These results indicate
that the overall adsorption process may be jointly controlled by intra-particle diffusion; hence,
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the adsorption kinetic data was further analyzed by the linear form of the Weber−Morris
equation.
3.5 Kinetic studies
The pseudo first and second-order, and intra-particle diffusion kinetic models have been
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applied to investigate adsorption mechanism of MO with initial dye concentrations in the range
of 50-200 mg/L on the surface of NiO and CuO NPs. The linearized-integral form of the pseudo-
log(qe − qt ) = log qe − K1
t
2.303
K1: the rate constant of adsorption (min-1).
(7)
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first-order model is:
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The K1 and qe values are demonstrated in Fig. 7 for NiO and CuO NPs. The parameters of
this kinetic model along with the correlation coefficients are summarized in Table 3.
One can observe that the calculated qe values are not agreed well with the experimental qe
values for both adsorbents and each concentration. Moreover, the values of the correlation
coefficients (R2) are smaller than that will be observed in the case of the pseudo-second-order
kinetic model. This behavior indicates that the adsorptions kinetic data obtained in this work
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cannot be predicted well by the pseudo-first-order kinetic model. Similar results were observed
in other works [33, 51]. The following equation represents the linearized-integral form of the
pseudo-second-order kinetic model:
(8)
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t
1
t
=
+
2
qt
qe
K 2q e
K2: the rate constant of pseudo-second-order kinetic model (g/mg.min).
The kinetic parameters (qe and K2) of this model were established in Fig. 8 for NiO and
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CuO NPs. The values of (R2) are listed in Table 3 and they are higher than that observed in the
case of a pseudo-first-order kinetic model for both tow adsorbents used in this work.
Furthermore, there is a good agreement between the calculated and experimental qe values
(Table 3) for both kinds of adsorbents. This agreement confirms that the pseudo-second-order
kinetic model is well describing the obtained kinetic results and the adsorption of MO by NiO
and CuO NPs is chemisorption process in nature. Similar results were reported by Ghaedi et al.
[52].
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The kinetic data were also analyzed by the intra-particle model in the linear form (Eq. 8) to
investigate the diffusion of MO into adsorbents pores.
q =K
t
dif
t +C
(9)
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Kdif: rate constant of the intraparticle diffusion (mg/g.min)1/2, t0.5: square root of the time and C:
constant (gives information about the thickness of the boundary-layer [53]).
The calculated parameters of Kdif and C were listed in Table 4. The values of the regression
coefficients (R2) for the plots are higher than 0.9 and the C values are larger than zero. These
values indicate the contribution of surface adsorption. It can be seen from Fig. 9 that the plots
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were not linear over the whole time range and separated into two linear regions. This separation
indicates that the adsorption process of MO on NiO and CuO NPs has been carried out by
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multiple steps. Moreover, these lines don’t start from the origin, which indicates intra-particle
diffusion is not the controlling step of sole rate. These obtained results are agreed with those
reported by Lafi and Hafiane [54]. Moreover, Table 3 illustrates that the MO adsorption rates
using CuO NPs are higher than of NiO NPs. This is because the pore diameter in the case of CuO
NPs is higher than that of NiO NPs.
The kinetic data obtained in this study illustrate that the adsorption of MO on these two
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prepared adsorbents NPs is a chemical process that involves the intraparticle diffusion step.
3.6 pH effect on adsorption
Fig. 10 represents the effect of pH on MO adsorption onto NiO and CuO NPs. As shown in
this figure, a sharply increasing in the amounts of MO adsorbed at equilibrium on the surface of
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the adsorbent as pH is expanded within the ranges of 2 to 8 and 2 to 6.5 for NiO and CuO NPs,
respectively. On the other hand, a further increase in the pH value leads to stridently decreasing
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in quantity adsorbed. A pHZPC is 8.1 and 7.6 for NiO and CuO NPs, respectively. The adsorption
sites are positively and negatively charged when pH< pHZPC and pH > pHZPC, correspondingly.
In the acidic medium, MO present in the cationic form due to banding of H+ with –SO3 – to form
of –SO3H and in the anionic form in the basic medium [54]. Therefore, increasing the adsorption
of MO in the above mention pH ranges (2-8, 2-6.5) could be explained concerning decreasing
the electrostatic repulsion force between the cationic form of MO and the positive charge of the
adsorption site which are decreased with increasing pH of MO solution. Whereas, adsorption of
MO is sharply decreased over these pH ranges due to raising the electrostatic repulsion force
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between the anionic form of MO and negatively adsorption site of the adsorbents used in this
work. Similar behavior was observed previously for the adsorption of MO onto aluminum-based
MOF/graphite oxide composite [55]. One can see from Fig. 10 that the maximum MO
adsorptions values are at pH 8 and 6.5 in the case of NiO and CuO NPs, in that order.
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3.7 Temperature effect on adsorption
The temperature dependence of the adsorption capacity of MO onto NiO and CuO NPs
was investigated at 30, 45 and 60⁰C for initial concentrations of MO solutions (50, 100 and 300
mg/L). The results obtained in this work are demonstrated for NiO and CuO NPs in Fig. 11. As
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shown in this figure, the amounts of MO adsorbed on the surface of the two adsorbents increased
with increasing solution temperature, which indicates an endothermic process. This behavior can
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be explained by increases in the MO mobility [50], and also, the adequate energy could be
required for more molecules to affect the interaction of surface active site [56].
Moreover, the increase of temperature causes internal structure swelling of these
adsorbents enabling a more number of molecules of dye to penetrate [57]. The obtained results
are well agreed with the results reported in the literature [58].
3.8 Adsorption thermodynamics studies
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A change of standard enthalpy (∆H⁰), entropy (∆S⁰) and free energy (∆G⁰) as
thermodynamic parameters were determined using the following:
o
=
∆Η
+
o
∆
− T∆S
o
(10)
(11)
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∆G
∆
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=−
R: universal gas constant and T: adsorption temperature. Fig. 12 represents the plots of lnKC
against 1/T for NiO NPs and CuO NPs, respectively. The values of (∆H⁰, ∆S⁰) were computed
and listed in Table 5.
According to the positive values of ∆H⁰ obtained in this work, the adsorption of MO on these
two adsorbents is the endothermic process. These results are in agreement with the results
observed in the part of the temperature effect. Since it was found in the temperature effect
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section, that adsorption of MO by NiO and CuO NPs increases with rising temperature indicating
that the adsorption of this adsorbate by these prepared two adsorbents is the endothermic
process. The values of ∆H⁰ (Table 5) are in the range of (28.999– 36.488 kJ/mol) and (15.844–
30.482 kJ/mol) for NiO NPs and CuO NPs, correspondingly. This means that the adsorption of
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MO on NiO NPs can be classified as chemical adsorption and physical adsorption in the case of
CuO NPs at lower adsorbate initial concentration and chemical adsorption at higher
concentration [20, 59]. The positive values of ∆S⁰ confirm randomness increasing at the
adsorbate-solution interface during the process of adsorption.
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On the other hand, the ∆G⁰ negative values indicate that the MO adsorption onto NiO NPs
or CuO NPs is a spontaneous process. It can also be seen from Table 5 as the adsorption
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temperature increased the values of ∆G⁰ becoming more negative, which indicates the most
favorable condition for higher adsorption efficiency is temperature. This means that the affinity
of MO molecules to uptake onto the surfaces of this two adsorbent is directly proportional to
solution temperatures. The obtained results agree well with the results for the methylene blue
adsorption on activated carbon fiber and granular activated carbon [49].
As shown in Table 5, most of the parameters of thermodynamic for the MO adsorption
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onto the NiO NPs are higher than that of CuO NPs, which confirms that the adsorption
performance of the former towards MO is higher than that of the latter.
3.9 Comparison of performance of NiO and CuO NPs with reported adsorbents
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The maximum adsorption capacities of NiO and CuO NPs used in this work along with
that of the other adsorbents have been used in the literature for removal of MO from aqueous
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solution were summarized in Table 6 to demonstrate the importance of NiO CuO NPs used in
this work compared with others. It can be seen from this table that NiO and CuO NPs have
adsorption performance superior to that of other which indicates that these adsorbents NPs will
meet a significant interest in the case of water purification activities.
4. Conclusions
Nanoparticles (NPs) adsorbent as NiO and CuO were prepared and characterized. These
NPs were used for water purification. Methyl orange (MO) was used as an impurity in water.
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The structural properties of the synthesized CuO NPs have been confirmed using XRD and
TEM. Characterization results confirmed that the adsorptive properties of NiO are better than
that of CuO NPs. Adsorption isotherms for adsorption of MO on the surfaces of these prepared
adsorbents were investigated by Langmuir and Freundlich models at three different temperatures.
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The isotherm results indicate the experimental data is described using Langmuir model.
The adsorption capacities of NiO NPs (188.68, 303.03 and 370.37 mg/g) are higher than of CuO
NPs (121.95, 166.67 and 217.39 mg/g). The pseudo-first-order, pseudo-second-order, and
intraparticle diffusion kinetic models were used to analyze the kinetic adsorption parameters.
SC
The experimental kinetic data described well by the pseudo-second-order model. It was also
found the MO adsorption rates on CuO NPs were higher than that for NiO NPs. The ∆H⁰, ∆S⁰
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and ∆G⁰ parameters were investigated as a thermodynamic study. These values of the
thermodynamic parameters obtained that the NiO NPs adsorption affinity for MO is more
effective than of CuO NPs. Finally, these presented results recommend that the nanoparticles
adsorbents have efficiency for wastewater treatment and superior to the other adsorbent (Table
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Figure caption
The XRD spectrum of as-prepared (a) NiO and (b) CuO NPs.
Figure 2
The TEM spectrum of as-prepared (a) NiO and (b) CuO NPs.
Figure 3
Effect of initial concentration and solution temperature on the adsorption
of MO on NiO and CuO NPs.
Figure 4
Langmuir isotherm models for adsorption of MO on NiO and CuO NPs at
different temperatures.
Figure 5
Freundlich isotherm model for the adsorption of MO on NiO and CuO
NPs at different temperatures.
Figure 6
Effect of the contact time on the adsorption capacity of MO on NiO and
CuO NPs.
Figure 7
Pseudo-first-order kinetics model for the adsorption of MO on NiO and
CuO NPs at 30 ± 1 °C.
Figure 8
Pseudo-second-order kinetics model for the adsorption of MO on NiO and
CuO NPs at 30 ± 1 °C.
Figure 9
Intraparticle diffusion model for the adsorption of MO on NiO and CuO
NPs at 30 ± 1 °C.
Figure 10
Effect of initial pH on the adsorption of MO on NiO and CuO NPs
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Figure 1
Figure 11
Effect of temperature on the adsorption capacity of MO on NiO and CuO
NPs
Figure 12
Plots of LnKc versus 1/T for the adsorption of MO on NiO and CuO NPs
at different dye concentrations.
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List of Tables
Characteristics of NiO and CuO NPs
Table 2
Langmuir, Freundlich parameters and separation factors (RL) for the adsorption of
MO on NiO and CuO NPs at three different temperatures.
Table 3
Parameters of the pseudo-first and pseudo-second-order models for the adsorption
of MO on NiO and CuO NPs at Four initial dye concentrations and 30 ± 1 °C.
Table 4
Parameter values of an intra-particle diffusion model for the adsorption of MO on
NiO and CuO NPs at Four initial dye concentrations and 30 ± 1 °C.
Table 5
Thermodynamic parameters of MO adsorption on NiO and CuO NPs (T = 303,
318, 333K).
Table 6
Comparison of adsorption capacity of various adsorbents NPs with NiO and CuO
NPs towards MO.
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Table 1
20
30
35
40
2θ (dgree)
40
50
60
70
45
50
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(220)
SC
(311)
(222)
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(111)
Intensity (a.u)
(200)
a)
(202)
30
(111)
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(002)
b)
(202)
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20
(020)
(100)
Intensity (a.u)
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Figures
NiO NPs
80
55
90
CuO NPs
60
2θ (dgree)
Fig. 1
21
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(a)
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(b)
Fig. 2
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400
300
CuO NPs
200
RI
PT
(mg/g)
o
30 C
o
45 C
o
60 C
qe
100
0
0
200
400
600
800
400
300
NiO NPs
SC
(mg/g)
o
30 C
o
45 C
o
60 C
200
qe
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100
0
0
200
400
600
Ce
30 C
o
45 C
o
60 C
EP
3
AC
C
Ce / qe
(L/g)
4
1000
8
o
5
800
(mg/L)
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Fig. 3
6
1000
o
30 C
o
45 C
o
60 C
6
4
2
2
1
0
0
NiO NPs
200
400
600
Ce (mg/L)
CuO NPs
800
0
0
300
Ce
600
900
(mg/L)
Fig. 4
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6.0
5.5
NiO NPs
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CuO NPs
5.5
ln qe
5.0
5.0
4.5
30 C
o
45 C
o
60 C
o
30 C
o
45 C
o
60 C
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4.0
4.0
3
4
5
6
ln Ce
Fig. 5
7
50 mg/L
100 mg/L
150 mg/L
200 mg/L
40
EP
20
3
4
5
6
7
ln Ce
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60
qe (mg/g)
SC
4.5
o
CuO NPs
0
0
200
400
600
800
1000
1200
1400
1200
1400
120
qe (mg/g)
AC
C
50 mg/L
100 mg/L
150 mg/L
200 mg/L
90
60
NiO NPs
30
0
0
200
400
600
800
time
(min)
1000
Fig.6
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2.0
2.0
1.0
1.0
0.5
0.5
0.0
0.0
-0.5
-0.5
50 mg/L
100 mg/L
150 mg/L
200 mg/L
-1.0
0
200
50 mg/L
100 mg/L
150 mg/L
200 mg/L
-1.0
400
600
time (min)
800
0
TE
D
EP
AC
C
t / qt
20
600
800
50 mg/L
100 mg/L
150 mg/L
200 mg/L
30
20
10
10
CuO NPs
NiO NPs
0
0
400
40
50 mg/L
100 mg/L
150 mg/L
200 mg/L
30
200
time (min)
Fig. 7
40
SC
1.5
RI
PT
CuO NPs
1.5
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log (qe - qt)
NiO NPs
200
400
600
time (min)
0
800
0
200
400
600
800
time (min)
Fig. 8
25
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50
10
0
5
80
10
15
50 mg/L
100 mg/L
150 mg/L
200 mg/L
60
20
NiO NPs
40
20
0
0
5
10
15
(time)
100
30
20
(min)
25
30
1/2
NiO NPs
CuO NPs
EP
qe(mg/g)
80
1/2
TE
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Fig. 9
120
25
SC
(mg/g)
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20
M
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(mg/g)
qt
30
0
qt
CuO NPs
50 mg/L
100 mg/L
150 mg/L
200 mg/L
40
AC
C
60
40
20
0
2
4
6
8
10
12
pH
Fig. 10
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140
140
50 mg/L
100 mg/L
300 mg/L
100
100
80
80
60
60
40
40
20
20
NiO NPs
0
50
o
2.0
EP
50 mg/L
100 mg/L
300 mg/L
1.0
30
40
50
60
o
T ( C)
2.0
50 mg/L
100 mg/L
300 mg/L
1.5
1.0
0.5
AC
C
ln Kc
1.5
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Fig. 11
60
M
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40
T ( C)
2.5
CuO NPs
0
30
RI
PT
120
SC
qe (mg/g)
120
50 mg/L
100 mg/L
300 mg/L
0.5
0.0
0.0
-0.5
NiO NPs
CuO NPs
-0.5
-1.0
0.0030 0.0031 0.0032 0.0033
1/T
-1
(K )
0.0030 0.0031 0.0032 0.0033
1/T
-1
(K )
Fig. 12
27
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Table 1
NiO NPs
78.3733
0.06842
34.920
8.1
CuO NPs
6.1881
0.0280
116.134
7.6
Table 2
C
CuO
qmax
KL
(mg/g)
(L/mg)
n
R2
12.842
0.403
2.481
0.917
KF
(mg/g)(L/mg)1/n
188.68 0.0083 0.108
45
303.03 0.0089 0.101
0.985
17.202
0.444
2.252
0.955
60
370.37 0.0088 0.102
0.997
15.992
0.502
1.992
0.958
30
121.95 0.0152 0.062
0.998
55.818
0.105
9.524
0.909
45
166.67 0.0132 0.070
0.999
23.268
0.298
3.356
0.933
60
217.39 0.0182 0.052
0.997
29.347
0.319
3.135
0.897
Adsorbent
(mg/ L)
(mg/g)
Pseudo-second-order
kinetic model
kinetic model
qe,cal
(mg/g)
20.813 11.37
AC
C
50
qe,exp
0.989
Pseudo-first-order
EP
C0
CuO
1/n
R
30
Table 3
NiO
Freundlich isotherm
2
RL
TE
D
NiO
Langmuir isotherm
SC
o
M
AN
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Adsorbent Temperature
RI
PT
Type of adsorbent
Specific surface area (m2/g)
Total pore volume (cm3/g)
Average pore diameter (Å)
pHZPC
K1
R2
-1
qe,cal
K2
R2
rate
(h )
(mg/g ) (g/mg.min)
0.0048 0.644
21.79
0.00076
0.989
0.017
100
40.107 34.76
0.0052 0.987
44.05
0.00024
0.990
0.011
150
62.326 48.58
0.0030 0.975
61.35
0.00019
0.985
0.011
200
80.005 63.18
0.0035 0.958
78.13
0.00016
0.958
0.013
50
22.259 14.655 0.0062 0.984
23.25
0.02441
0.998
0.568
100
28.976 20.483 0.0044 0.995
29.58
0.01784
0.996
0.528
150
33.419 23.206 0.0037 0.985
33.11
0.01805
0.989
0.598
200
37.065 25.474 0.0037 0.997
36.90
0.01782
0.988
0.658
28
ACCEPTED MANUSCRIPT
Table 4
CuO
qe,exp (mg/g)
Kdif (mg/h1/2g)
C
50
20.813
0.742
3.348
0.818
100
40.107
1.466
3.566
0.957
150
62.326
1.951
7.151
0.965
200
80.005
2.264
13.959
0.979
50
22.259
0.649
100
28.976
0.885
150
33.419
0.916
200
37.065
1.017
Table 5
Concentration ∆Ho
NiO
50
100
300
CuO
50
AC
C
100
(kJ/mol)
300
6.742
0.934
6.316
0.963
8.465
0.990
9.401
0.989
∆So
∆Go (KJ/mol)
(KJ/molK)
303K
TE
D
(mg/L)
318K
333K
R2
36.488
0.126
-1.690
-3.580
-5.470
0.989
33.021
0.110
-0.309
-1.959
-3.609
0.999
28.999
0.094
-0.517
-0.893
-2.303
0.993
15.844
0.058
-1.652
-2.518
-3.384
0.999
16.220
0.054
-0.256
-1.071
-1.887
0.919
30.482
0.080
-1.950
-0.855
-3.961
0.998
EP
Adsorbent
R2
RI
PT
C0 (mg/L)
M
AN
U
NiO
Intra-particle diffusion kinetic model
SC
Adsorbent
Table 6
29
ACCEPTED MANUSCRIPT
qmax (mg/g)
Sources
Ferric oxide–biochar nano-composites
derived from pulp and paper sludge
Silicon carbide nanoparticles loaded on
activated carbon
Functionalized-CNTs loaded TiO2 a
NiO NPs
NiO NPs
CuO NPs
Novel magnetic CNTs/Fe@C
NiO NPs
16.05
[4]
40.16
[31]
42.85
11.21
165.83
158.73
16.53
188.68
303.03
370.37
121.95
166.67
217.39
[32]
[34]
[38]
[38]
[60]
Present study
M
AN
U
30 oC
45 oC
60 oC
30 oC
45 oC
60 oC
SC
RI
PT
Adsorbent
Present study
AC
C
EP
TE
D
CuO NPs
30
ACCEPTED MANUSCRIPT
Highlights
Nanoparticles of Copper oxide (CuO) and Nickel oxides (NiO) NPs were produced.
RI
PT
Properties of prepared NPs were investigated using XRD, TEM and BET surface
analyzer techniques.
Adsorption of Methyl orange (MO) on this adsorbent was conducted at various
temperatures.
AC
C
EP
TE
D
M
AN
U
SC
The data of this adsorption fits greatest to the isotherm model of Langmuir.
1