Application of palladium nanoparticle-decorated Artemisia abrotanum extract-modified graphene oxide for highly active catalytic reduction of methylene blue, methyl orange and rhodamine B

Article abstract of DOI:10.1002/aoc.5123

A green palladium-based catalyst supported on Artemisia abrotanum extract-modified graphene oxide (Pd NPs/RGO-A. abrotanum) hybrid material has been used as a recoverable and heterogeneous nanocatalyst for the catalytic reduction of various dyes, includin

Full text of DOI:10.1002/aoc.5123

Received: 2 May 2019
DOI: 10.1002/aoc.5123
Revised: 21 June 2019
Accepted: 27 June 2019
F U L L P A P E R
Application of palladium nanoparticle‐decorated Artemisia
abrotanum extract‐modified graphene oxide for highly
active catalytic reduction of methylene blue, methyl orange
and rhodamine B
Mirmehdi Hashemi Salehi1 | Mohammad Yousefi2
Ebrahim Balali1
| Malak Hekmati1
|
1 Department of Organic Chemistry,
A green palladium‐based catalyst supported on Artemisia abrotanum extract‐
modified graphene oxide (Pd NPs/RGO‐A. abrotanum) hybrid material has
been used as a recoverable and heterogeneous nanocatalyst for the catalytic
reduction of various dyes, including methylene blue, methyl orange and rhoda-
mine B, in the presence of NaBH4 as reducing agent in aqueous medium at
room temperature. With the help of UV–visible spectroscopy, the catalytic
reactions were investigated. According to the results, these reactions followed
the pseudo‐first‐order rate equation.
Faculty of Pharmaceutical Chemistry,
Tehran Medical Sciences, Islamic Azad
University, Tehran, Iran
2 Department of Chemistry, Yadegar‐e‐
Imam Khomeini (RAH) Shahr‐e‐Rey
Branch, Islamic Azad University, Tehran,
Iran
Correspondence
Mohammad Yousefi, Department of
Chemistry, Yadegar‐e‐Imam Khomeini
(RAH) Shahr‐e‐Rey Branch, Islamic Azad
University, Tehran, Iran.
KEYWORDS
Artemisia abrotanum, dyes, graphene, palladium nanoparticles, reduction
Email: myousefi50@hotmail.com
1 | INTRODUCTION
properties such as thermal and chemical stability, large
specific surface area, high mechanical strength, water sol-
In recent years, the utilization of supports in the process
of producing nanoparticles (NPs) has attracted much
attention. The supports prevent agglomeration of NPs
and increase their stability and efficiency. The resulting
heterogeneous catalysts have many advantages over
homogeneous metal catalysts, such as ease of handling,
simple work‐up and recyclability.[1,2] Therefore, many
researchers are trying to develop a simple and green
method to produce heterogeneous nanocatalysts.
Graphene oxide (GO) and reduced graphene oxide
(RGO) are a new class of promising and efficient supports
and catalysts, which have been considered by many sci-
entists.[3–7] GO is a two‐dimensional material derived
from graphene sheets with a large number of oxygen‐
containing functional groups such as epoxy, hydroxyl
and carboxylic groups (Figure 1).[8] GO has useful
ubility and electron conductivity.[9–11]
The presence of organic dyes in wastewaters provides
more chemical oxidation and therefore leads to severe
rancidity.[12] Azo dyes are able to show colour in waste-
waters even at small concentrations.[13] They contain
N═N double bonds and belong to the synthetic organic
dyes and due to their weak dissociation, high toxicity
and long durability are considered as the main pollutants
of effluent of the textile, leather, wood, paper and cos-
metic industries.[14] Therefore, degradation of these dyes
from wastewater is very important. Adsorption,[14–18]
coagulation[18–20] and membrane filtration[21] are some
conventional methods for treatment of wastewaters con-
taining azo dyes. The main drawback of these methods
is that the nature of the pollutant is maintained after
treatment. The prominent point of the method used in
Appl Organometal Chem. 2019;e5123.
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https://doi.org/10.1002/aoc.5123

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HASHEMI SALEHI ET AL.
2 | EXPERIMENTAL
2.1 | Preparation of Pd NPs/RGO‐A.
abrotanum nanocatalyst
In order to synthesize Pd NPs/RGO‐A. abrotanum, the A.
abrotanum extract was added to GO (100 mg) and soni-
cated for 20 min. Then, the reaction mixture was refluxed
with agitation for 2 h. The colour of the mixture changed
from light brown to black, indicating the reduction of
GO, which was stable. The RGO was separated via centri-
fugation, after cooling to ambient temperature. Following
rinsing, 30 ml of 0.3 M Na2PdCl4 under agitation was
added dropwise into the mixture at 100°C for 24 h. The
final Pd NPs/RGO‐A. abrotanum was isolated by centrifu-
gation, and washed three times with deionized water. It
was next used for assessment and catalysis research.
The amount of Pd in Pd NPs/RGO‐A. abrotanum was
0.18 mmol g−1 as measured using inductively coupled
plasma atomic emission spectrometry (ICP‐AES).
FIGURE
nanocatalyst
1
TEM image of Pd NPs/RGO‐A. abrotanum
the research reported here (catalytic reaction) is degrada-
tion of a dye during a reaction and therefore the nature of
the pollutant will change and it is converted to a com-
pound which is not harmful to the environment.
As azo dyes are difficult to degrade into non‐toxic com-
pounds, diverse treatment methods have been developed,
such as physical and chemical reduction,[22] adsorption
and oxidation. Among all solutions, catalytic reduction
has exhibited the highest efficiency. While most catalysts
have been nanosized and composed of Ag, Pt, Pd and Au
noble metals,[23] Ag NPs have attracted more attention
due to their unique characteristics and applications.
Artemisia abrotanum L. has traditionally been utilized
for pharmaceutical purposes in treating certain diseases,
like upper airway disorders.[24] The polyphenols and fla-
vonoids that are contained within A. abrotanum mean
that this herbal extract has the potential to be used in a
wide range of applications.
2.2 | Procedure of reducing organic dyes
using Pd NPs/RGO‐A. abrotanum
nanocatalyst
At first, 2.0 mg of the Pd NPs/RGO‐A. abrotanum
nanocatalyst was added into 5 ml of 10 ppm organic dye
(MB, MO or RhB) solution and stirred at room tempera-
ture. Then, 1 ml of newly prepared NaBH4 solution
(0.1 M) was added to the reaction mixture. Time‐
dependent UV–visible spectra of the organic dyes were
obtained and the change in absorption intensity was
recorded at λmax. After disappearance of the colour of
the solution, the catalyst was separated by centrifugation,
then washed with EtOH–H2O, dried and reused.
3 | RESULTS AND DISCUSSION
In terms of multiple features of graphene stated above,
we have introduced a simple green synthetic method to a
Pd NPs–graphene hybrid with A. abrotanum leaf extract
as both reductant and stabilizing agent.[25] Firstly, the
extract can effectively reduce GO and adsorb on the
RGO surface. Next, the adsorbed A. abrotanum leaf bio-
molecules can additionally reduce Pd ions in situ to Pd
NPs and cause their stabilization.
The application of the thus produced hybrid material
(Pd NPs/RGO‐A. abrotanum) as an efficient and hetero-
geneous nanocatalyst was investigated for catalytic reduc-
tion of various dyes, namely methylene blue (MB),
methyl orange (MO) and rhodamine B (RhB), in the pres-
ence of NaBH4 as reducing agent.
The Pd NPs/RGO‐A. abrotanum nanocatalyst was synthe-
sized in one step by reducing Pd(II) ions and GO with the
extract of A. abrotanum as a stabilizer and reducing agent
(Scheme 1). In this study, it is assumed that the presence
of phenols and acid compounds in the extract results in
bio‐reduction and stabilization of Pd NPs without using
toxic ingredients and toxic organic solvents.
Transmission electron microscopy (TEM) and energy‐
dispersive X‐ray (EDX) analysis were used to characterize
the nanostructure of Pd NPs/RGO‐A. abrotanum that was
prepared based on our earlier report.[25] The image corre-
sponding to the nanocatalyst (Pd NPs/RGO‐A.
abrotanum) at 200 nm indicated that the Pd NPs are well
distributed on the surface of RGO. The results showed

HASHEMI SALEHI ET AL.
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SCHEME 1 Fabrication pathway of Pd
NPs/RGO‐A. abrotanum nanocatalyst
that the A. abrotanum extract plays a key role in enhanc-
ing the dispersibility of Pd NPs (Figure 1). Most of the
particles are in the range 10–20 nm. Furthermore, the
presence of biomolecules of the extract on the surface of
graphene and Pd NPs was proved using EDX analysis,
which confirmed the existence of C (88.3%), N (1.1%, O
(9.4%) and Pd (1.2%) as shown in Figure 2.
decrease of absorbance at λmax was observed due to decol-
orization of the dyes. This indicates that functional
groups of ─N═N─ (azo) as the chromophoric group in
the organic dyes were reduced to ─NH─NH─. The reduc-
tion reaction times for the organic dyes were completed at
40, 90 and 140 s for MB, RhB and MO, respectively. The
initial concentration of NaBH4 was high (more than 103
times) and it remained constant during the reaction.
Therefore, pseudo‐first‐order kinetics can be used for
the rate constants the decolorization of these azo dyes
and were followed from the kinetic equation: ln(Ct/
C0) = −kt (or ln(At/A0)), where Ct is the concentration
at time t, C0 is the initial concentration and k is the appar-
ent rate constant (kapp) that was obtained as 0.049, 0.022
and 0.02 s−1 for MB, RhB and MO, respectively.
After characterizing the prepared Pd NPs/RGO‐A.
abrotanum nanocatalyst, its catalytic efficiency was inves-
tigated in the reduction reactions of MB, MO and RhB in
the presence of NaBH4 as reducing agent. To investigate
the catalytic reduction reactions, a UV–visible spectro-
photometer was used. It is known that organic dye pollut-
ants, for example MB, MO and RhB, are released from
various industries and are toxic and dangerous environ-
mental pollutants. Therefore, nowadays the development
of efficient and reliable methods for catalytic reduction of
these organic dye pollutants is an important requirement.
The Pd NPs/RGO‐A. abrotanum nanocatalyst was used
to catalyse the degradation of organic dyes. The colour of
the solution disappeared quickly, indicating the success
of the degradation process. The reduction reaction pro-
cess was monitored using UV–visible spectroscopy.
Figure 3 displays the time‐dependent UV–visible absorp-
tion measurements of azo dye reduction reactions. Deter-
mination of the reaction progress was done through
recording the reduction of the absorption intensity at λmax
of 465 nm (MO), 550 nm (RhB) and 660 nm (MB). The
The effect of temperature on the catalytic performance
was investigated for the reduction of MB, MO and RhB at
25, 40 and 50°C, for which kapp was obtained (MB: 0.049,
0.058 and 0.072 s−1; MO: 0.022, 0.03 and 0.042 s−1; RhB:
0.02, 0.27 and 0.039 s−1, respectively).
The possible mechanism of organic dye reduction
using the Pd NPs/RGO‐A. abrotanum nanocatalyst is
described with an electron relay system. The Pd NPs start
the catalytic reduction by relaying electrons from the
−
donor BH4 to the organic dye molecules, where the
nanocatalyst accepts electrons from BH4− ions and trans-
ports them to the dye molecules. In fact, when NaBH4 is
added to the reaction mixture, the hydride (H−) from
−
BH4 may be surrounded by Pd NPs and adsorbed on
their surface and it then transfers its electron to the Pd
−
NPs. The hydrogen atom (H•) formed from BH4 after
electron transfer to the Pd NPs subsequently attacks a
nearby dye molecule, and then electron transfer induced
hydrogenation of the dye occurs spontaneously
(Scheme 2).
Experiments to test the catalyst recyclability of the Pd
NPs/RGO‐A. abrotanum nanocatalyst were conducted to
investigate its stability. So, the catalyst was separated by
centrifuging from the reaction mixture. It showed no
appreciable loss of catalytic performance during six cycles
of the degradation of dyes. The yield of reaction after six
uses was MB, 99 to 98%; MO, 99 to 97%; RhB, 99 to
97%. The amount of Pd in the reused Pd NPs/RGO‐A.
FIGURE
nanocatalyst
2
EDX analysis of Pd NPs/RGO‐A. abrotanum

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HASHEMI SALEHI ET AL.
FIGURE 3 UV–visible absorption spectral changes for the reduction process of (a) MB, (b) RhB and (c) MO by NaBH4 in the presence of
Pd NPs/RGO‐A. abrotanum nanocatalyst and corresponding plots of rate constant
SCHEME 2 Possible mechanism of organic dye reduction catalysed by Pd NPs/RGO‐A. abrotanum nanocatalyst in the presence of NaBH4
abrotanum catalyst was 0.175 mmol g−1 (for fresh catalyst
it was 0.175 mmol g−1), which was measured using ICP‐
AES. These results show that the synthesized hybrid cat-
alyst is a stable, effective and recoverable catalyst.
For an evaluation of the performance of the prepared
catalyst, we have compared the apparent rate constant
(kapp) for Pd NPs/RGO‐A. abrotanum with those of some
literature reports for the reduction of organic dyes MB,

HASHEMI SALEHI ET AL.
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TABLE 1 Comparison of catalytic efficiency of Pd NPs/RGO‐A. abrotanum catalyst with previous literature for the reduction of MB, RhB
and MO
Organic dye
Catalyst
kapp (s−1
)
Ref.
[26]
MB
Ni/CPM‐1 (0.5 wt% Ni, r.t.)
9.51 × 10−3
7.16 × 10−3
3.7 × 10−4
4.9 × 10−2
1.6 × 10−3
7 × 10−3
[27]
[28]
MB
Fe3O4@polydopamine (1 wt% Ag, r.t.)
NiNTAs (33 mg l−1, r.t.)
MB
MB
Pd NPs/RGO‐A. abrotanum (0.18 mmol g−1 Pd, r.t.)
PVP‐Au/PVPPANI/Fe2O3 (0.13 mg ml−1, r.t.)
Ag‐Fe3O4 (0.74 mg ml−1, r.t.)
This work
[29]
RhB
RhB
RhB
RhB
MO
MO
MO
MO
[30]
[26]
Ni/CPM‐1 (0.5 wt% Ni, r.t.)
7.85 × 10−3
2.2 × 10−3
4 × 10−2
Pd NPs/RGO‐A. abrotanum (0.18 mmol g−1 Pd, r.t.)
MnFe2O4@SiO2@Ag (0.24 mg ml−1, r.t.)
Fe3O4@His@Ag (0.24 mg ml−1, r.t.)
Ag‐γ‐Fe2O3@CS (0.67 wt% Ag, r.t.)
Pd NPs/RGO‐A. abrotanum (0.18 mmol g−1 Pd, r.t.)
This work
[31]
[32]
[33]
4.2 × 10−3
0.6 × 10−3
2 × 10−2
This work
Mater. Sci. Eng. C 2018, 90, 57; d) H. Veisi, S. Razeghi, P.
Mohammadi, S. Hemmati, Mater. Sci. Eng. C 2019, 97, 624; e)
H. Veisi, S. B. Moradi, A. Saljooqi, P. Safarimehr, Mater. Sci.
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RhB and MO (Table 1). It can be seen that the Pd
NPs/RGO‐A. abrotanum catalyst leads to a rapid reduc-
tion reaction compared to the other catalysts considered.
4 | CONCLUSIONS
Pd NPs/RGO‐A. abrotanum can be applied as an effective
and heterogeneous nanocatalyst for reduction of various
dyes, namely MB, MO and RhB, in the presence of
NaBH4 as reducing agent.
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How to cite this article: Hashemi Salehi M,
Yousefi M, Hekmati M, Balali E. Application of
palladium nanoparticle‐decorated Artemisia
abrotanum extract‐modified graphene oxide for
highly active catalytic reduction of methylene blue,
methyl orange and rhodamine B. Appl Organometal
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