Title


Science and Technology Indonesia
e-ISSN:2580-4391 p-ISSN:2580-4405
Vol. 6, No. 3, July 2021

Research Paper

Modification of Cu/Cr Layered Double Hydroxide by Keggin Type Polyoxometalate as
Adsorbent of Malachite Green from Aqueous Solution
Neza Rahayu Palapa1, Tarmizi Taher2, Alfan Wijaya3, Aldes Lesbani1,3*
1Graduate School of Faculty of Mathematics and Natural Sciences, Sriwijaya University, Palembang, South Sumatra, Indonesia2Department of Environmental Engineering, Institut Teknologi Sumatera, Lampung Selatan, Indonesia3Research Center of Inorganic Materials and Complexes, Faculty of Mathematics and Natural Sciences, Sriwijaya University, Indralaya, Indonesia
*Corresponding author: aldeslesbani@pps.unsri.ac.id

AbstractModification of Cu/Cr layered double hydroxides (LDHs) has been conducted by intercalation using Keggin type polyoxometalate[𝛼-SiW12O40]4− to form CuCr-[𝛼-SiW12O40]. The materials were analyzed by XRD, FTIR, and surface area analyses. Furthermore,materialswereusedasselectivityadsorbentsofcationicdyessuchasmalachitegreen, rhodamine-Bandmethyleneblue. Themala-chite green is more selective than others from an aqueous solution. The adsorption of malachite green showed that the adsorptioncapacity of CuCr-[𝛼-SiW12O40] was higher than pristine LDHs. The adsorption process was followed pseudo second order kineticmodel and Langmuir isotherm adsorption. The Qmax value of CuCr-[𝛼-SiW12O40] reached 55.322 mg/g at 323 K after 100 min-utes adsorption time. Thermodynamic parameters such as ΔG, ΔH and ΔS confirm that the adsorption process was endothermic,spontaneous, and more favorable at high temperatures. The intercalated material was higher structural stability toward reusabilityadsorbent than pristine LDHs.
KeywordsMalachite Green, Polyoxometalate, Intercalation, Layered Double Hydroxides, Adsorption

Received: 7 April 2021, Accepted: 20 July 2021
https://doi.org/10.26554/sti.2021.6.3.209-217

1. INTRODUCTION

The existence of chemical substances in the environment is
a vital topic to discuss until this decade due to toxic prop-
erties and caused pollution in the land and aquatic systems.
These chemicals including heavy metals, organic pollutants,
and also dyes. Dyes substances were produced from industrial
activities including textile, plastic, printing, leather, and so on
(Abdelkader et al., 2011). These dyes are usually released to
the environment directly without gradually further treatment
thus can impact humans, ora, and fauna (Dahri et al., 2014).
The removal of dyes from wastewater is an important way
to minimize the serious eect. Various physicochemical and
biological methods have been applied to remove dyes from
wastewater such as adsorption, coagulation, ltration, precipita-
tion, light decomposition, and also using bacterial process (Dai
et al., 2018; Gholami et al., 2020; Srinivasan and Sadasivam,
2018; Xu et al., 2018b). Among these methods, adsorption
is a suitable method for the removal of dyes from wastewater
due to fast process, simple way, easy procedure, and also no
contamination eect before and after the process (Nazir et al.,
2020; Jarrah et al., 2020; Naseeruteen et al., 2018). The eec-

tiveness of the adsorption process is depending on the ability
of the adsorbent. Various kinds of adsorbents have been used
for removing dyes from wastewater such as zeolites (Oliveira
et al., 2019), activated carbon (Mall et al., 2005), natural layer
structure materials such as bentonite and kaolinite (Bulut et al.,
2008), and also synthetic materials such as layered double hy-
droxides (Das et al., 2018; Lesbani et al., 2020c; Parida and
Mohapatra, 2012).

Layered double hydroxide (LDHs) is a class of synthetic
layer materials with positively charged and consists of inter-
layer anions (Lesbani et al., 2020a). Interlayer anions can
be exchanged with various anions to increase interlayer dis-
tance or gallery of LDHs. The general formula of LDHs is
[M2+1−xM3+x (OH)2]x+(An−)x/n].nH2O, where M is divalent
and trivalent metal ions and An− is interlayer anions with va-
lence n (Palapa et al., 2020b). The interlayerof LDHs contains
anions such as nitrate, chloride, sulfate, and other ions due
to synthetic conditions (Doungmo et al., 2016; Lesbani et al.,
2020b; Parida and Mohapatra, 2012). The unique properties
of interlayer LDHs is the ion exchange properties. Interlayer
anions can be exchanged with other anions to obtain a high
interlayer distance of LDHs (Ma et al., 2013; Oktriyanti et al.,

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https://doi.org/10.26554/sti.2021.6.3.209-217


Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

Figure 1. Chemical structure of Malachite Green

2020; Zhu et al., 2017). These novel properties are useful for
various applications of LDHs such as adsorbents (Shan et al.,
2015), catalysts (Sun et al., 2019), biomedical materials (Liao
and Chen, 2016), and other industrial applications (Zubair
et al., 2017).

Adsorption of dyes using LDHs has been tested for various
dyes such as methylene blue (Lesbani et al., 2020a), indigo
carmine (Starukh and Levytska, 2019), methyl orange (El-
moubarki et al., 2017), and malachite green (Lesbani et al.,
2020c). That dyes are classied as cationic and anionic dyes
depending on the structures of dyes. One of the toxic dyes is
malachite green. This dye is classied as a cationic dye with
the chemical structure shown in Figure 1.

LDHs are almost treated with physical or chemical tech-
niques before being applied as an adsorbent in the adsorption
process (Silaen, 2020). This step aims to increase the surface
area and interlayer distance of LDHs for active sites of adsorp-
tion. On the other hand, intercalation using a large anion is
eective to increase the interlayer distance of LDHs and sur-
face area properties (Palapa et al., 2020a). Large anions such as
polyoxometalate ions are frequently used as an anion for the in-
tercalation process onto LDHs (Legagneux et al., 2009). Then
materials after intercalation were applied as adsorbents of dyes
(Lesbani et al., 2020b). Polyoxometalates are metal-oxygen
clustercompoundswithvarious structures suchasKeggin, Daw-
son, Anderson, and also Lacunary form (Carriazo et al., 2007;
Yang et al., 2012; Yun and Pinnavaia, 1996). Among these
structures, Keggin is well known used not only as a catalyst
(Lesbani et al., 2015) and building blocks (Long et al., 2010)
but also for intercalation anion of LDHs (Bi et al., 2011). Ac-
cording to Nijs et al. (1999) MgAl LDH was intercalated using
[H2W12O40]6− to form pillared compounds with various mass
ratios of polyoxometalate. The others type of polyoxometa-
late K3[𝛼-PW12O40] and K4[𝛼-SiW12O40] have been carried
out as intercalants on ZnAl and CaAl LDH as reported by
Lesbani et al. (2018); Taher et al. (2019). According to pre-
vious research, the LDH intercalated using polyoxometalate
has been reported to enhance adsorptive capacity. Xu et al.
(2018a) reported that ZnAlFe-polyoxometalate was applied
as an adsorbent to remove methylene blue in an aqueous so-
lution and obtained an adsorptive capacity is 67.47 mg/g. Bi

et al. (2011), also reported that ZnAl-[PW10Mo2O40]5− was
conducted to remove cationic dyes. The adsorption capacity
of ZnAl-[PW10Mo2O40]5− slightly enhanced compared ZnAl
pristine (from 12 mg/g to 30 mg/g).

In this research, polyoxometalate Keggin ion [𝛼-SiW12
O40]4− was used as an intercalant of copper-chromium (CuCr)
LDHs to form CuCr-[𝛼-SiW12O40] LDHs. Materials were
characterized using X-Ray diraction, FTIR spectroscopy, and
nitrogen adsorption-desorption isotherm analysis. Further-
more, intercalated and pristine LDHs were applied as adsor-
bents of malachite green from an aqueous solution. Before
the adsorption process was conducted, the selectivity adsorp-
tion has been examined using a mixing solution of malachite
green (MG), rhodamine-B (Rh-B) and methylene blue (MB).
Adsorption was studied by a batch system using a small re-
actor equipped with stirring and temperature control. Based
on the above explanation, the objective of this study is to de-
termine the kinetic parameter, isotherm adsorption and ther-
modynamic studies of MG on intercalated and pristine CuCr
LDHs. Structural stability of CuCr-[𝛼-SiW12O40] toward
reusability adsorbent was also investigated systematically.

2. EXPERIMENTAL SECTION

2.1 Chemical and Instrumentation
ThechemicalswerepurchasedfromMerckr suchasCu(NO3)2
.6H2O, Cr(NO3)3.9H2O, NaOH, Na2CO3, Na2WO4, KCl,
Na2SiO3 and HCl. Water was supplied from Research Center
of Inorganic Materials and Complexes, FMIPA Universitas
Sriwijaya through ltration using Puriter water ion exchange
system under several times cycling process. The materials were
characterized by XRD Rigaku Miniex-6000. Sample was
grounded with mortar and analyzed using XRD at diraction
5-60◦ with scan speed 1◦/min. Analysis of functional group
was performed using FTIR Shimadzu Prestige-21. Sample
was mixed with KBr and was vacuumed to form KBr pellet.
Sample was analyzed in the wavenumber 400-4000 cm−1.
Analysis of nitrogen adsorption-desorption was conducted us-
ing Micrometric ASAP Quantachrome apparatus. Sample was
degassed several times prior analysis using liquid N2 to re-
move guests. Analysis of malachite green was conducted using
UV-Visible Spectrophotometer Bio-Base BK-UV 1800 PC.
Malachite green was analyzed at 617 nm.

2.2 Preparation of CuCr LDHs
Preparation of CuCr LDHs was carried out by precipitation
method as follows. As much as 7.5 M solution of Cu(NO3)2.
6H2O 0.05 L was added into 2.5 M solution of Cr(NO3)3.
9H2O 0.05 L with vigorous stirring. The mixing solution was
stirred for an hour then 4M solution of NaOH 0.025 L was
added and the solution was adjusted to pH 10 by the addition
of NaOH 4M. The mixing solution was kept for 16 hours to
form a gel. The gel was ltered and washed with water several
times and dried at 100◦C for 24 hours.

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Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

2.3 Preparation of CuCr-[𝛼-SiW12O40] LDHs
The intercalation of CuCr LDHs with [𝛼-SiW12O40]4− was
conducted by ion-exchange technique. Ion [𝛼-SiW12O40]4−

was prepared by previously reported literature (Lesbani et al.,
2015). As much as 2 g of CuCr LDH was dissolved into 0.05
L of water. Polyoxometalate K4[𝛼-SiW12O40] (15 g) was dis-
solved with 0.05 L water. The solution of CuCr LDHs was
mixed with polyoxometalate solution with mild stirring under
nitrogen ow for 24 hours to form a suspension. The suspen-
sion was ltered and washed several times usingwaterand dried
at room temperature.

2.4 Adsorption Study and Reusability Adsorbent
Before the adsorption process was conducted, the selectivity
adsorption has been tested. This study aimed to show the
materials have good selectivity for specic cationic dyes. The
mixture of cationic dyes such as MG, Rh-B and MB was pre-
pared with 10 mL and the initial concentration of each dye
is 15 mg/L. The adsorption of MG was performed by batch
system equipped with a stirring bar and temperature system
control. The adsorption process was studied by variation of
adsorption times, temperatures, and MG concentrations. The
mass of adsorbent was carried out using 25 mg. The volume of
adsorbate was 25 mL. Variation of adsorption time was studied
in the range of 5-210 minutes. Variation of initial concentra-
tion of MGwas studied at 10, 25, 50 and 75 mg/L. Variation of
adsorption temperature was studied at 303, 313, 318, and 323
K. The adsorption parameter was obtained through calculation
by kinetic model, isotherm adsorption and thermodynamic pa-
rameters. Concentration of MG after adsorption was analyzed
by UV-Visible Spectrophotometer at 617 nm.

The kinetic model was calculated using pseudo rst order
(P-FO) and pseudo second (P-SO) kinetic models by equation
below (Doğan and Alkan, 2003):

log (qe-qt) = log qe −
(
k1

2.303

)
t (1)

t
qt

=
1

k2qe2
+
1
qe
t (2)

Where, qe is adsorption capacity at equilibrium (mg/g); qt
is adsorption capacity at t (mg/g); t is adsorption time (minute);
k1 is adsorption kinetic rate at P-FO (/minute) and k2 is ad-
sorption kinetic rate at P-SO (g/mg.min).

Isotherm adsorption studywas conducted byLangmuirand
Freundlich equation as written as (Obike et al., 2018):

1
qe

=
1
qmax

+
1

qmaxb
.
1
Ce

(3)

ln qe = ln Kf +
(
1
n

)
ln Ce (4)

Figure 2. XRD powder Patterns of CuCr (a) and
CuCr[𝛼-SiW12O40] LDHs

Where, qmax is the maximum adsorption capacity con-
ducted in the monolayer (mg/g); b is the Langmuir adsorption
equilibrium constant (1/mg); Ce is the equilibrium concentra-
tion (mg/L); and Kf is Freundlich constant.

The reusability of adsorbent was conducted to investigate
the structural stability of adsorbent toward adsorption. Des-
orption of malachite green was performed using ultrasonic
system and adsorbent was reuse for the next adsorption pro-
cess. The dried adsorbent was reused for three cycles with a
similar procedure.

3. RESULTS AND DISCUSSION

Materials of CuCr and CuCr-[𝛼-SiW12O40] were character-
ized using XRD diraction as shown in Figure 2. The char-
acteristic diraction of CuCr LDHs appeared at 9.89◦ (003),
27.32◦ (006), 36.10◦ (015), 48.98◦ (018), 60.60◦ (110), and
62.55◦ (116) (Palapa et al., 2020b). The diraction peak at
9.89◦ with reection 003 denote the interlayer space of LDHs.
Material CuCr-[𝛼-SiW12O40] showed similar diraction as
pristine LDHs, but the interlayer of CuCr-[𝛼-SiW12O40] was
increased from 7.55 Å to 10.27 Å. However, the intercalation
of [𝛼-SiW12O40] onto CuCr LDHs can increase basal spacing
up to 2.72 Å.

The FTIR spectra of CuCr and CuCr-[𝛼-SiW12O40] were
shown in Figure 3. FTIR spectrum of CuCr LDHs showed the
intense vibration at 1381 cm−1 denotes as nitrate bending. The
broad vibration was identied at wavenumber 3448 cm−1 due
to OH stretching from water molecule. The water-associated
vibration also appeared at 1627 cm−1, which was assigned
as bending OH vibration (Daniel and Thomas, 2020). The
intercalation of CuCr LDHs with [𝛼-SiW12O40]4− ion will
replace the nitrate as anion on interlayer space. The FTIR
spectrum after intercalation showed the vibration around 1107
cm−1, which was assigned as the presence of another anion (C-
O) from carbonate. The unique vibration of [𝛼-SiW12O40]
from CuCr-[𝛼-SiW12O40] shows at wavenumber below 1000
cm−1 (W=O and Si-O).

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Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

Figure 3. FTIR Spectrum of CuCr and CuCr-[𝛼-SiW12O40]
LDHs

Analysis of adsorption-desorption nitrogen on CuCr and
CuCr-[𝛼-SiW12O40] is shown in Figure 4. The prole of
adsorption-desorption nitrogen is categorized as type IV with
H3 hysteresis loop for both LDHs. The isotherm pathway
indicated the mesopore materials, which were associated with
capillary condensation (Harizi et al., 2019). The BET calcu-
lation was obtained from data in Figure 4 as shown in Table
1.

Figure 4. Nitrogen Adsorption-Desorption of CuCr and
CuCr-[𝛼-SiW12O40] LDHs

The data in Table 1. showed the BET analysis of CuCr
and CuCr-[𝛼-SiW12O40] LDHs. The increase of the surface
area of LDHs after intercalation by [𝛼-SiW12O40] was found
with the decreases in the pore size. Thus, the decreases in
pore size indicated the swelling and the covering of interlayer
space by macroanion [𝛼-SiW12O40]4−. These phenomena are
related to the opening of interlayer space, which was conrmed
by XRD analysis (Ouassif et al., 2020). The surface area of
CuCr-[𝛼-SiW12O40] was increased up to vefold than CuCr
LDHs. LDHs intercalated by polyoxometalate are potential
material as an adsorbent to remove pollutants from wastewater.
Furthermore, to determine the adsorption ability of CuCr-[𝛼-
SiW12O40], the adsorption selectivity of cationic dyes (MG,

Figure 5. Wavelength Scan of Selectivity Adsorption by
CuCr-[𝛼-SiW12O40] (a) and CuCr (b) LDHs onto Mixing
MG, Rh-B and MB

Figure 6. Eect of Adsorption Time (A) and Kinetic Model (B)

Rh-B and MB) has been studied as shown in Figure 5. Figure
5(A) showed that CuCr-[𝛼-SiW12O40] adsorbed MG higher
than other cationic dyes. The decrease in absorbance value
indicates a decrease in initial concentration. However, the
decrease dramatically of initial concentration of MG indicated
that the small structure of MG than Rh-B and MB (Mohadi
et al., 2021). Figure 5(B) also showed a similar nding that
MG more selectivity than others. The nal concentration of
MG after 150 min of CuCr and CuCr-[𝛼-SiW12O40] are 8.1
and 5.4 mg/L, respectively. Thus, the CuCr-[𝛼-SiW12O40]
was used as an adsorbent to remove MG from the aqueous
solution. Theadsorptionprocesswascarriedoutbytheeectof
adsorption time, theeectofMGconcentrationandadsorption
temperature. The eect of adsorption time for MG removal
using CuCr and CuCr-[𝛼-SiW12O40] was shown in Figure 6.

Figure 6(A) showed MG was higher adsorbed using CuCr-
[𝛼-SiW12O40] than pristine LDHs. This nding assumed that
the higher surface area of CuCr-[𝛼-SiW12O40] after intercala-
tion. The equilibrium amount of MG on CuCr-[𝛼-SiW12O40]
was reached after 100 minutes with MG removal up to 90%
from the initial concentration 50 mg/L. The results showed
that MG uptake on CuCr-[𝛼-SiW12O40] were higher twice
thanCuCrLDHs. Thus, theadsorptionkineticwasdetermined
by pseudo kinetic model. Figure 6(B) showed the tted of two
kinetic models. The calculated parameters were listed in Table
2. Based on Figure 6(B) and Table 2, kinetic adsorption of
MG on CuCr and CuCr-[𝛼-SiW12O40] were followed PS-O
model with coecient correlation >0.963.

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Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

Table 1. BET Surface Area Analysis of CuCr and CuCr-[𝛼-SiW12O40] LDHs

Materials Surface Area (m2/g) Pore Size (nm)

CuCr LDH 4.58 14.39
CuCr[𝛼-SiW12O40] 26.58 2.023

Table 2. Kinetic Parameter of Adsorption on CuCr and CuCr[𝛼-SiW12O40]

Adsorbent
Qeexp P-FO P-SO
(mg/g) qeCalc (mg/g) R

2 k1 qeCalc (mg/g) R
2 k2

CuCr 27.985 23.051 0.948 0.017 31.24 0.977 0.001
CuCr[𝛼-SiW12O40] 18.354 45.651 0.924 0.023 52.619 0.963 0.0007

Figure 7. Eect of Initial Concentration of MG and Adsorption

The eect of initial concentration and adsorption tempera-
ture of MG were presented in Figure 7. The amount of MG
adsorbed on CuCr-[𝛼-SiW12O40] was increased by increasing
adsorption temperature, which was conducted on a batch ad-
sorption system. The adsorption patterns for both materials
have equilibrium after 20 mg/L and higher MG was adsorbed
at 323 K. Furthermore, the data of initial concentration and ad-
sorption temperature for both materials were calculated using
Langmuir and Freundlich isotherm model to obtain isotherm
adsorption.

The data in Table 3 showed that adsorption of MG by
CuCr and CuCr-[𝛼-SiW12O40] follow Langmuir isotherm ad-
sorption model rather than Freundlich model. The coecient
correlation for Langmuir isotherm is almost close to one than
Freundlich isotherm. The qmax for CuCr-[𝛼-SiW12O40] is
higher than pristine LDHs. As expected of increasing surface
area properties thus this higher of qmax value is matched re-
sults. Thus, Table 4. Showed MG adsorption using several
adsorbents.

Table 4 showed the comparison of malachite green adsorp-
tion using several adsorbents. Based on results, the adsorption

Figure 8. Reusability of Adsorbents

capacity of CuCr-[𝛼-SiW12O40] showed in slightly high as
compared other materials assumed that CuCr-[𝛼-SiW12O40]
is eective sorbent to remove malachite green in the aqueous
phase. The increasing adsorption capacity of malachite green
on CuCr-[𝛼-SiW12O40] is equal with increasing of interlayer
space after intercalation, thus the adsorption process probably
occurs mainly on the interlayer of CuCr-[𝛼-SiW12O40] than
the surface of the adsorbent (Siregar et al., 2021).

The thermodynamic data as shown in Table 5 was also cal-
culated from data in Figure 7. The thermodynamic parameter
results were described for a higher concentration of MG, which
was conducted at various temperatures. The ΔG of adsorption
has a negative value means adsorption of MG on CuCr and
CuCr-[𝛼-SiW12O40] spontaneously occurred in a batch sys-
tem. The ΔH value is less than 40 kJ/mol and conrms the
adsorption process was endothermic (Taher et al., 2017). The
value of ΔS is positive forboth CuCrand CuCr-[𝛼-SiW12O40]
forMGadsorptionprocess. Thus, thisndingindicatedthat the
increased degree of freedom of interaction between solid and
solution from adsorbate and adsorbent molecules (Jaśkaniec
et al., 2018; Qu et al., 2019).

LDHs are unstable materials toward acid thus the ultra-
sonic system was applied for a reusability test of CuCr-[𝛼-
SiW12O40] todesorbmalachitegreenontheadsorbent. Figure
8 showed that the adsorption capacity of CuCr LDH largely

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Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

Table 3. Isotherm Model Parameters of MG Adsorption Process on CuCr and CuCr-[𝛼-SiW12O40]

LDH
Adsorption Adsorption T (K)
Isotherm Constant 303 313 318 323

CuCr Langmuir qmax 6.016 22.008 23.198 27.585
kL 0.098 0.05 0.176 0.771
R2 0.989 0.973 0.985 0.994

Freundlich n 6.518 1.963 3.273 2.826
kF 2.725 2.227 6.555 6.991
R2 0.785 0.9 0.964 0.868

CuCr-[𝛼-SiW12O40] Langmuir qmax 12.127 35.372 46.035 55.322
kL 0.094 0.233 0.297 0.564
R2 0.929 0.998 0.993 0.998

Freundlich n 1.972 3.178 3.479 4.048
kF 1.301 6.586 17.676 10.664
R2 0.755 0.855 0.861 0.645

Table 4. Comparison of Malachite Green Adsorption by Several Adsorbents

Adsorbents qmax Ref.

NiAl LDH 27.32 (Lesbani et al., 2020c)
CuAl LDH 55.22 (Palapa et al., 2020a)

CuAl-LDH/BC 470.96 (Palapa et al., 2020c)
ZnAl LDH 11.1 (Palapa et al., 2018)
Apricot-AC 17.6 (Abbas, 2020)

Leucaena leucocephala 2.389 (Lee et al., 2018)
NiFe-LDH/calcined 73.68 (Elmoubarki et al., 2017)

MW-Carbon nanotubes 11.95 (Rajabi et al., 2016)
CuCr LDH 27.585 This work

CuCr-[𝛼-SiW12O40] 55.322 This work

Table 5. Thermodynamic Parameter of MG Adsorption on CuCr and CuCr-[𝛼-SiW12O40]

Adsorbents T (K) Qe (mg/g) ΔG (kJ/mol) ΔS (J/mol K) ΔH (kJ/mol)

CuCr LDH 303 27.357 -1.455 35.792 12.3
313 28.516 -1.097
318 31.807 -0.918
323 32.434 -0.739

CuCr-[𝛼-SiW12O40] 303 41.421 -0.552 39.7457 11.491
313 44.678 -0.9494
318 45.382 -1.1482
323 46.606 -1.3469

decreased after two cycles adsorption process while CuCr-[𝛼-
SiW12O40] relatively stable. The three cycles adsorption pro-
cess of malachite green showed that adsorption capacity for
both adsorbents was decreased. On the other hand, the ad-
sorption capacity of CuCr-[𝛼-SiW12O40] has almost slightly
larger than pristine LDHs. Thus, the intercalation process was
increased the structural stability of LDHs.

4. CONCLUSIONS

The intercalated CuCr LDHs using polyoxometalate Keggin
anion to form CuCr-[𝛼-SiW12O40] was successfully prepared
and analyzed by XRD, FTIR and surface area analysis. The
CuCr-[𝛼-SiW12O40] was applied as an adsorbent of MG. The
eect of adsorption time showed the optimum uptake after
100 minutes. Material CuCr-[𝛼-SiW12O40] has a higher ad-
sorption capacity than pristine LDHs due to high surface area

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Neza et. al. Science and Technology Indonesia, 6 (2021) 209-217

properties. The kinetic parameters showed that the adsorption
process follows PS-O kinetic model. Langmuir isotherm was
appropriate than Freundlich isotherm models for both adsor-
bents. Material CuCr-[𝛼-SiW12O40] has higherQmax (55.322
mg/g at 323 K) than CuCr LDHs (27.585 mg/g at 323 K).
Thermodynamic parameter results showed the negativity of
ΔG with increasing temperature indicated that the adsorption
favorable in high temperature. Enthalpy of adsorption showed
the value is less than 40 kJ/mol and the adsorption process
was endothermic. The positive value of ΔS denotes the con-
centration of adsorbate has high interaction with adsorbent
and aected the entropy to be increased. Structural stability
of CuCr LDHs was slightly increased after the intercalation
process.

5. ACKNOWLEDGEMENT

We thank Ministry of National Education and Culture, Repub-
lik Indonesia for nancial support through HIBAH DISER-
TASIDOKTOR2020-2021fromDirectorateGeneralHigher
Edication (DIKTI) Republic Indonesia with primary contract
number : 054/E4.1/AK.04.PT/2021 and derivative contract
number : 0163.02/UN9/SB3.LP2M.PT/2021. We also grate-
fully acknowledge to Research Center of Inorganic Materials
and Complexes FMIPA Universitas Sriwijaya for instrumental
analysis.

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	INTRODUCTION
	EXPERIMENTAL SECTION
	Chemical and Instrumentation
	Preparation of CuCr LDHs
	Preparation of CuCr-[-SiW12O40] LDHs
	Adsorption Study and Reusability Adsorbent

	RESULTS AND DISCUSSION
	CONCLUSIONS
	ACKNOWLEDGEMENT