Ferrocenated nanocatalysts derived from the decomposition of ferrocenium in basic solution and their aerobic activities for the rapid decolorization of methylene blue and the facile oxidation of phenylboronic acid

Article abstract of DOI:10.1039/c6ra25515a

A strategic preparation of ferrocenated compounds as aerobic catalysts was successfully carried out for the decolorization of methylene blue and oxidation of phenylboronic acid without light irradiation and excess addition of hydrogen peroxide. Cyclopentadienyl radical formed by the decomposition of ferrocenium under basic conditions plays a major role in the production of reactive oxygen species (ROS) under an aerobic atmosphere.

Full text of DOI:10.1039/c6ra25515a

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Ferrocenated nanocatalysts derived from the
decomposition of ferrocenium in basic solution and
their aerobic activities for the rapid decolorization
of methylene blue and the facile oxidation of
phenylboronic acid†
Cite this: RSC Adv., 2017, 7, 5759
a
a
b
Nuttapong Kumpan, Thinnaphat Poonsawat, Laksamee Chaicharoenwimolkul,
a
a
Soraya Pornsuwan and Ekasith Somsook*
A strategic preparation of ferrocenated compounds as aerobic catalysts was successfully carried out for the
decolorization of methylene blue and oxidation of phenylboronic acid without light irradiation and excess
addition of hydrogen peroxide. Cyclopentadienyl radical formed by the decomposition of ferrocenium
under basic conditions plays a major role in the production of reactive oxygen species (ROS) under an
aerobic atmosphere.
Received 20th October 2016
Accepted 16th December 2016
DOI: 10.1039/c6ra25515a
www.rsc.org/advances
The development of a sustainable method for applications demetallation of ferrocenium. The initial degradation mecha-
related to reactive oxygen species (ROS) has attracted signicant nism of ferrocenium derivatives in the presence of a nucleo-
1
25,30,31
attention in laboratory experiments. Singlet oxygen, super- philic solvent has been previously reported.
2
oxide, hydrogen peroxide, and hydroxyl radicals are a group of
To the best of our knowledge, there are no reports that propose
ROS. In the past decade, the most extensive studies in the the generation of ROS from cyclopentadienyl radicals for the
generation of ROS were mainly focused on the well-known oxidation of phenylboronic acid. It should be emphasized that
3
Fenton reaction involving iron(II), hydrogen peroxide, photo- a radical initiator is not required for the generation of cyclo-
4
–8
9,10
catalysts, and transition metal catalysts.
Iron oxide is naturally abundant and thermally stable.
pentadienyl radicals in the ferrocenated compounds. Moreover,
the ferrocenated compounds in this study were generated from
1
1,12
2,13–16
Iron ions are widely used in the production of ROS
their potential applications include the degradation of dyes Cyclopentadienyl radicals in ferrocenated compounds were still
and advanced organic oxidation. Recently, ferrocene deriva- active even though the prepared sample had been le under
and ferrocene only without the coprecipitation with other iron ions.
1
7–20
21
22–28
tives
have gained the attention of our group. We are inter- a regular atmosphere for a period of time. Herein, we show the
ested in the properties of ferrocenated iron oxide nanocatalysts rapid activity of ferrocenated compounds on the decolorization of
prepared by the coprecipitation of Fe(II), Fe(III), redox active methylene blue with other reactivators (NaCl, NaI, water, and
5 5 2
species of ferrocene ((C H ) Fe or Fc), and ferrocenium seawater), as well as the efficient transformation of phenylboronic
+
+
29
(
(C
catalysts could completely remove methylene blue in the
absence of light and hydrogen peroxide within 2 hours and cene in concentrated sulfuric acid to yield ferrocenium (Fc )
5
H
5
)
2
FeH or Fc ) under basic conditions. The nano- acid to phenol under an aerobic atmosphere.
First, ferrocenated compounds were generated from ferro-
+
32,33
could be reused 12 times using sodium chloride solution species appearing as a blue viscous solution,
and then an
as a reactivator. The production of active species may be orange precipitate was produced in the solution by adjusting
proposed as cyclopentadienyl radicals derived from the the pH value to 12 with sodium hydroxide (Fig. S1, ESI†). The
possible theoretical compositions of the ferrocenated
compounds consisted of iron oxide, ferrocene, and cyclo-
a
NANOCAST Laboratory, Center for Catalysis Science and Technology (CAST),
pentadienyl radical, as shown in Scheme 1.
The particle size of the prepared ferrocenated compounds
was in the range of nanoscale, as shown in the TEM images
Department of Chemistry and Center of Excellence for Innovation in Chemistry,
Faculty of Science, Mahidol University, 272 Rama VI Rd., Ratchathewi, Bangkok
1
0400, Thailand. E-mail: ekasith.som@mahidol.ac.th; Fax: +66 23547151; Tel: +66
2015123
2
(Fig. S2, ESI†). It also has the structure similar to commercial
b
Chemistry Division, Faculty of Science and Technology, Suratthani Rajabhat
University, 272 Moo 9, Surat-Nasan Rd., Khuntale, Muang, Surat Thani 84100,
Thailand
ferrocene, as illustrated in the XRD pattern (Fig. S3, ESI†). Some
residue of Fe
3
O
4
was conrmed by DSC/TGA curve (Fig. S4,
ꢀ
ESI†). The temperature at 714 C and the mass loss of about
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c6ra25515a
1
3 4
10% corresponded to the phase transition from Fe O to FeO,
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Scheme 1 The decomposition of ferrocenium species in the presence
of sodium hydroxide to yield the ferrocenated compounds.
which is thermodynamically more stable at a temperature of
ꢀ
34
5
70 C. The surface area, pore-size distribution, and pore
volume were determined by nitrogen adsorption/desorption
ꢀ
isotherm analysis (À196 C) collecting at the relative pressure
(
1
P/P ) range from 0.05 to 1.0. The average pore diameter was
1.16 nm and the pore volume was 0.14 cm g (Fig. S5, ESI†).
0
Scheme 2 The possible mechanism of decolorization of methylene
blue in the presence of ferrocenated compounds.
3
À1
The corresponding BET plot showed that the surface area of the
2
À1
ferrocenated compounds was 49.11 m g
.
X-ray photoelectron spectroscopy (XPS) was used to deter-
mine the state and composition of the ferrocenated compound
surface (Fig. S6 and Table S1, ESI†). The XPS spectra revealed
that the binding energies of C 1s were 285.0 eV (C–C in Cp),
2
5
87.0 eV (C–O), and 288.7 eV (O–C–C), and those of O 1s were
31.4 eV (Fe–O), 532.6 eV (C–O), and 533.7 eV (O–H). The
binding energies of Fe 2p at 707.2 and 708.2 eV were assigned to
2
+
35
the pattern of Fe
3 4
(ferrocene) and Fe O , respectively.
3
+
Furthermore, the binding energies of Fe 2p3/2 were 710.1,
11.6, 713.2, and 714.6 eV. The zeta potential value on the
36
7
surface of the catalyst was À24.7 mV (Fig. S7, ESI†). Note that
the surface of the catalyst was negatively charged.
Ferrocenated compounds were investigated for the produc-
37
tion of ROS in the aqueous medium. The hydroxyl and
superoxide radical intermediates were trapped with 5,5-
dimethyl-1-pyrroline-N-oxide (DMPO) in phosphate buffer
Fig. 1 FT-IR spectra of methylene blue, ferrocene, ferrocenated
st
st
solution (pH 7.4) and were observed by electron spin resonance compounds, 1 used sample, and 1 sample activated with seawater.
(ESR), as shown in Fig. S8 and Table S2, ESI.† Cyclopentadienyl
radical is proposed as a major candidate to initiate the forma-
tion of ROS under aerobic atmosphere. Unfortunately, cyclo- compounds was achieved by reactivating with 0.1 mol dm
pentadienyl was not observed in ESI-MS. Instead, the m/z of 130 NaCl, 0.1 mol dm NaI, and seawater and washing with DI
for dihydrofulvalene was obtained (Fig. S9, ESI†). The decolor- water, as shown in Fig. 2. Moreover, the concentration of
ization of methylene blue was performed using 100 mg of methylene blue aer reactivation by ion sources is shown in
À3
À3
catalyst. The kinetic study was performed by collecting a sample Fig. S12, ESI.† The reusability of the catalyst was studied for 12
3
(
3 cm ) every 10 minutes for 2 hours. It was found that the C/C
0
cycles. Aer the end of each cycle, the catalyst was reactivated
quickly decreased to 0.019 in 10 minutes (Fig. S11, ESI†). The for 10 minutes before using it in the next cycle. The adsorption
possible mechanism was proposed through decolorization from was quite consistent (95–98%) for 8 cycles (reactivated with
the reaction of ROS with methylene blue and the adsorption on NaCl, and NaI and washed with DI water) and an exponential
th
the surface of the negatively charged catalyst, as shown in drop in the catalyst performance started from 8 cycle onwards
Scheme 2. Moreover, the pH measurements of the reaction were (20–55%). In the case of reactivation by seawater, the activity of
carried out. The color change of methylene blue was due to the catalyst directly decreased from 97% to 77%. The used fer-
activity of the catalyst and not due to the pH change of the rocenated compounds were reactivated by salt solutions and
solution (Fig. S11, ESI†).
seawater via an ion-exchange mechanism.
As shown in Fig. 1, the adsorption of methylene blue was
To further illustrate the catalytic activity of the ferrocenated
observed by FT-IR during the rst cycle of the catalysis reaction compounds in the oxidation of phenylboronic acid towards the
and the reactivated ferrocenated compounds exhibited the cyclopentadienyl radical as active species, a reaction composed
dominant peak corresponding to the C]C stretching of meth- of 20 mg of catalyst obtained a phenol with 14% conversion at
À1
ꢀ
ylene blue at 1600 cm . Interestingly, the adsorbed methylene 80 C for 24 hours (entry 1). K CO was used as a base to
2
3
blue on the surface of ferrocenated compounds was removed by enhance the solubility of phenylboronic acid in the phenyl
washing with salt solutions. The reusability of the ferrocenated boronate. Furthermore, different amounts of ferrocenated
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Table 2 The oxidation of phenyl boronic acid in the presence of
a
cyclopentadiene and azobisisobutyronitrile (AIBN)
b
Entry
Catalyst
Yield (%)
1
2
3
Cyclopentadiene (0.25 mmol)
1
4
98
Azobisisobutyronitrile (0.125 mmol)
Cyclopentadiene (0.25 mmol) and
azobisisobutyronitrile (0.125 mmol)
a
2
Reaction conditions: phenylboronic acid (0.25 mmol), THF : H O
b
3
ꢀ
(1 : 1) 5 cm , for 24 hours under an aerobic atmosphere at 80 C.
%
yield of phenylboronic acid to phenol analyzed by GC-MS with
hexadecane as the internal standard.
Fig. 2 Reusability of the ferrocenated catalyst with and without
reactivation by NaCl, NaI, and seawater and washing by DI water.
respectively (entry 1 and 2 in Table 2). The results indicated high
performance of the cyclopentadienyl radicals with 98%
yield under atmospheric oxygen at 80 C, as shown in Table 2
ꢀ
compounds were added as catalysts in the oxidation of phe-
nylboronic acid (entry 2, 3, 5, and 6). The results showed that
the reaction conversion was increased on increasing the
amount of the catalyst. The amount of ferrocenated compounds
at 200 mg exhibited the best conversion yield (94%), as shown in
entry 6 of Table 1. To study the effect of temperature, we
(
entry 3). This conrms that cyclopentadienyl radicals play
a major role as the active species in the oxidation of phenyl-
boronic acid.
Due to the low activity of ferrocene and iron oxide, the aerobic
oxidation might be driven by the plausible mechanism of reactive
oxygen species generated from the cyclopentadienyl radicals in
the ferrocenated compounds with dioxygen. We, therefore,
propose that the oxidation of phenylboronic acid occurs through
the generation of perhydroxyl radical, and then generates phenol
as the product. The radical is generated from the fast dispro-
portion of superoxide radical in water, as shown in Scheme 3.
In summary, ferrocenated compounds were successfully
synthesized without coprecipitation with other iron species.
This catalyst provides a good performance in the decolorization
of methylene blue and oxidation of phenylboronic acid through
ROS. Cyclopentadienyl radical play a key role in the generation
of hydroxyl and superoxide radicals. The development of the
applications of ferrocenated compounds will be further inves-
tigated in the future.
ꢀ
attempted to lower the temperature to 31 C and it turned out
that the reaction did not proceed aer 24 hours (entry 4). It was
observed that higher temperature was required for this reac-
tion. HCl was used to quench the reaction to generate phenol
for the analysis of products. Biphenyl was not detected as
a product, indicating that the homocoupling of phenylboronic
acid did not proceed. Furthermore, the reaction was totally
incomplete in the presence of FeCl , FeCl , ferrocene, and Fe O
2 3 2 3
under the same conditions (entry 7–8). In the presence of an
extra oxidant and in the absence of light, no signicant
2 3
enhancement by ferrocene and Fe O in the oxidation of phe-
nylboronic acid was observed (Table S3†).
To determine whether cyclopentadienyl radicals were active
species for generating ROS, the reaction was proceeded by
adding distilled cyclopentadiene (0.25 mmol) and AIBN (0.125
mmol) as a radical initiator. First, the reaction in the presence
of either cyclopentadiene or AIBN showed 1% and 4% yield,
Table 1 Oxidation of phenylboronic acid catalyzed by the ferrocen-
a
ated compounds through cyclopentadienyl radical as active species
b
Entry
Catalyst
Conversion (%)
1
2
3
Ferrocenated compounds (20 mg)
Ferrocenated compounds (50 mg)
Ferrocenated compounds (100 mg)
Ferrocenated compounds (150 mg)
Ferrocenated compounds (150 mg)
Ferrocenated compounds (200 mg)
14
36
50
1
91
94
0
0
1
4
c
4
5
6
7
8
9
FeCl
FeCl
2
3
Ferrocene (100 mg)
Fe (100 mg)
1
0
2
O
3
a
Reaction conditions: phenylboronic acid (0.25 mmol), K
2
CO
3
(300
%
3
ꢀ
b
mol%), and H
2
O (10 cm ) under aerobic atmosphere at 80 C.
conversion of phenylboronic acid to phenol analyzed by GC-MS with Scheme 3 Proposed mechanism for the aerobic oxidation of phe-
c
ꢀ
hexadecane as the internal standard. Reaction at 31 C.
nylboronic acid through perhydroxyl radical.
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Decolorization of methylene blue
The ferrocenated compounds (0.10 g) were added into the
Experimental sections
Materials
À5
À3
3
methylene blue solution (1 Â 10 mol dm , 100 cm ). The
All chemicals including ferrocene (ACROS), sulfuric acid (RCI
Labscan), sodium chloride (Fisher Chemical), sodium iodide
reaction was continuously stirred and wrapped in aluminium
3
foil to maintain dark conditions. The solution (3 cm ) was
(Merck), sodium hydroxide (Merck), 5,5-dimethyl-1-pyrroline-N-
kinetically collected every 10 minutes for 2 hours and the
catalysts were separated by centrifugation at 3300 rpm for 10
minutes. The clear supernatant was analyzed by a UV-visible
spectrophotometer at lmax 664 nm. The reusability of catalyst
was studied using reactivated catalyst.
oxide (DMPO, Aldrich), monosodium phosphate (RCI Labscan),
disodium phosphate (Aldrich), methylene blue (Merck), phe-
nylboronic acid (ACROS), potassium carbonate (Carlo Erba),
cyclopentadiene (Aldrich), tetrahydrofuran (THF, RCI Labscan),
and azobisisobutyronitrile (AIBN, Aldrich) were of analytical
grade and used as received without further purication.
Deionized water (R $ 18.2 MU cm) was obtained from Nano-
Reactivation of the catalyst
pure® Analytical Deionization Water. Seawater was ltered as Aer the process was completed, the used catalyst was sepa-
nd
achieved (2 June, 2014) from Nangkham beach, Don Sak rated by centrifugation at 3300 rpm for 10 minutes and acti-
3
À3
district, Surat Thani, Thailand.
vated by stirring in 100 cm of reactivators (0.1 mol dm NaCl,
0
À3
.1 mol dm NaI, seawater and DI water) for 10 minutes. The
reactivated catalyst was separated by centrifugation at 3300 rpm
for 10 minutes and started the next run without drying.
Instruments
The ferrocenated compounds were characterized via X-ray
powder diffraction (XRD) using a Bruker D8 ADVANCE
diffractometer with Cu-Ka radiation between 10 and 80 (2
ꢀ
ꢀ
General oxidation condition of phenylboronic acid
theta). The results of TEM measurement were obtained using Phenylboronic acid (0.25 mmol) and potassium carbonate (0.75
3
a Tecnai G2 Sphera transmission electron microscope oper- mmol) were dissolved in DI water (10 cm ). The catalyst was
ated at 80 kV. Fourier transform-infrared spectroscopy (FT-IR) added into the solution and stirred at the desired temperatures
À3
was performed using Bruker Hong Kong Limited model for 24 hours. The reaction was quenched with 1 mol dm HCl
ALPHA. The UV-visible spectrophotometer was a UV-2600 and the catalyst was separated out. The product was extracted
SHIMADZU operated in range of 200–800 nm. Thermogravi- with ethylacetate and analyzed using GC-MS with hexadecane as
metric analysis (DSC/TGA) was performed using a TA instru- the internal standard.
ꢀ
ments SDT2960 simultaneous at the heating rate of 20 C per
ꢀ
minute in the range from room temperature to 800 C under
Acknowledgements
nitrogen gas. Electrospray ionization (ESI) mass spectrometry
was carried out using a microTOF and in the positive mode
The nancial support received from the Biofuel development
ion. Electron paramagnetic resonance spectroscopy (EPR) was
for Thailand fund through the Center of Excellence for Inno-
carried out using JEOL JES-RE2X operated in the X-band
vation in Chemistry (PERCH-CIC), Royal Golden Jubilee Ph.D.
microwave (8.8–9.6 GHz), magnetic eld range of 3.1 T,
Program (Grant No. PHD/0271/2550) to the PhD student
cylindrical cavity resonator (TE011 mode), and with the
3.II.MU/50/A.4 and Development and Promotion of Science and
program ES-PRIT. X-ray photoelectron spectroscopy (XPS) was
performed using a Kratos Axis Ultra. The surface area, pore
size, and pore volume were determined by Brunauer–Emmett–
Teller (BET) method using a Quantachrome Autosorb Auto-
mated Gas Sorption System with nitrogen adsorption. The zeta
potentials were determined using a Zetasizer Nano-ZS model
ZEN 3600. Gas chromatography with mass spectrometry (GC-
MS) spectra were obtained by Agilent 7890 (GC) and Agilent
Technology Talents Project (DPST) is acknowledged.
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ꢀ
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