Ionic liquid-assisted synthesis of Pt nano thin films at toluene–water interface: Enhanced CO tolerance in methanol fuel cells and adsorptive removal of p-nitrophenol from water

Article abstract of DOI:10.1016/j.poly.2018.06.020

In this investigation, we report a one-pot method for the synthesis of Pt/ionic liquid nano thin films at organic-aqueous media at room temperature without using any harsh conditions. Synthesized Pt/ionic liquid thin films were characterized with common analytical techniques. Transmission electron microscope images confirmed the formation of spherical particles having a size distribution in the range of 4–12 nm. Ionic liquids have a key role in the control of better size distribution and prevent from agglomeration of nanostructures by preparing a shell around particles. These catalysts were applied for the reduction of toxic p-nitrophenol into non-toxic p-aminophenol and exhibited good catalytic activity. Also, they exhibit excellent CO tolerance in methanol oxidation process of fuel cells. This method provides a novel, rapid, low cost and economical alternative for the reduction of toxic organic pollutants in water and also to prepare high quality catalysts with low metal loading for methanol fuel cells. Pt/1-aminoethyl-3-methylimidazolium bromide exhibits better CO tolerance than Pt/1-methyl-3-octylimidazolium chloride and Pt/1-methyl-3-octylimidazolium tetrafluoroborate thin films.

Full text of DOI:10.1016/j.poly.2018.06.020

Polyhedron 151 (2018) 483–497
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Ionic liquid-assisted synthesis of Pt nano thin films at toluene–water
interface: Enhanced CO tolerance in methanol fuel cells and adsorptive
removal of p-nitrophenol from water
a,b
Saba Hamzepour Sharfand a, S. Jafar Hoseini a,b, , Mehrangiz Bahrami
⇑
a Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj 7591874831, Iran
b Prof. Rashidi Laboratory of Organometallic Chemistry, Department of Chemistry, College of Sciences, Shiraz University, Shiraz 7194684795, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In this investigation, we report a one-pot method for the synthesis of Pt/ionic liquid nano thin films at
organic-aqueous media at room temperature without using any harsh conditions. Synthesized Pt/ionic
liquid thin films were characterized with common analytical techniques. Transmission electron micro-
scope images confirmed the formation of spherical particles having a size distribution in the range of
4–12 nm. Ionic liquids have a key role in the control of better size distribution and prevent from agglom-
eration of nanostructures by preparing a shell around particles. These catalysts were applied for the
reduction of toxic p-nitrophenol into non-toxic p-aminophenol and exhibited good catalytic activity.
Also, they exhibit excellent CO tolerance in methanol oxidation process of fuel cells. This method pro-
vides a novel, rapid, low cost and economical alternative for the reduction of toxic organic pollutants
in water and also to prepare high quality catalysts with low metal loading for methanol fuel cells.
Pt/1-aminoethyl-3-methylimidazolium bromide exhibits better CO tolerance than Pt/1-methyl-3-
octylimidazolium chloride and Pt/1-methyl-3-octylimidazolium tetrafluoroborate thin films.
Ó 2018 Elsevier Ltd. All rights reserved.
Received 2 March 2018
Accepted 5 June 2018
Available online 14 June 2018
Keywords:
Platinum/ionic liquid nanostructure
Thin film
p-Nitrophenol reduction
Methanol oxidation
Fuel cell
1. Introduction
oxidation process. So it is important to find new ways to decrease
the cost of Pt catalyst and increase the durability against CO poi-
Direct methanol fuel cell (DMFC) is one of the new promising
alternative power sources for future energy generation due to its
low emissions, high energy densities and low operating tempera-
ture [1,2]. Platinum nanoparticles (NPs) are the best catalysts used
in DMFCs. The success of DMFC depends on these three facts: (i)
cost, (ii) durability and (iii) performance of the electrocatalysts
applied in fuel cells to increase the rate of methanol oxidation in
anode [3]. In order to decrease the electrocatalysts cost and
increase the durability and performance, and also decrease the
CO poisoning of catalysts, some strategies are applied such as using
alloyed nanostructures [4,5], nanostructured thin films [4–7] and
ionic liquids as stabilizer [8]. In the case of alloying strategy, some
co-catalysts were added to metallic platinum such as Mo [9], Ru
[10], Ni [11] and Sn [12]. Furthermore, some metal oxides such
as CeO2 [13] was used to promote the electrooxidation of methanol
and increase the CO tolerance. Despite the synthesis of these cata-
lysts, Pt electrocatalyst is remain a common catalyst for methanol
soning and catalyst deactivation. Applying the nanocatalyst thin
films and also using ionic liquids as stabilizer are the other ways.
The best strategy to prepare high quality thin films of nanostruc-
tures with lower cost, lower processing time and available equip-
ment is liquid- liquid interface self-assembly which attracts more
attention now a days [14–16]. The important fact in this strategy
is (i) a contact angle of 90° of the particles for the interfacial
entrapment of NPs and (ii) using two immiscible solvents [14]. A
thin layer is prepared after the addition of reducing agent at inter-
faces which contains self-assembled nanostructures. These thin
films have low metal loading, but all the metal atoms are on the
surface of a film. So a better catalytic activity is considered in com-
parison with other nanostructures. Unfortunately, by passing time,
these nanostructures may aggregate which leads to decrease the
catalytic activity. In order to encounter this challenge, using ionic
liquids as stabilizer is useful. Some advantages of ionic liquids sup-
ported metal NPs are (i) prevent from agglomeration by preparing
a protective layer, (ii) dissolving metal precursors due to the high
polarity of ionic liquids, (iii) their low surface tension leads to pref-
erentially adsorb onto other surfaces, contribute to weakening the
particle coarsening in the growth state of metallic particles leading
to the generation of very small particles and (iv) applying a reac-
⇑
Corresponding author at: Prof. Rashidi Laboratory of Organometallic Chemistry,
Department of Chemistry, College of Sciences, Shiraz University, Shiraz
7194684795, Iran. Fax: +98 7136460788.
E-mail address: sj.hoseini@shirazu.ac.ir (S.J. Hoseini).
https://doi.org/10.1016/j.poly.2018.06.020
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

484
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Scheme 3. p-nitrophenol reduction reaction progressed by UV–Vis spectrometer.
Scheme 1. Schematic illustration for the formation of Pt/ionic liquid nanostruc-
tured thin films and applying as electrocatalysts in DMFCs and p-nitrophenol
reduction reaction.
Fig. 1. Different stabilization modes of ionic liquids with Pt NPs.
phenol reduction was reported by using iron-acid reducing agent
[23]. Furthermore, catalysts that contain Zn, Al and Sn have been
reported which leads to the formation of large amounts of undesir-
able metal oxide wastes [24]. So, applying an alternative method is
important. According to our investigation, Pt/1-aminoethyl-3-
methylimidazolium bromide exhibits higher CO tolerance than
Pt/1-methyl-3-octylimidazolium chloride and Pt/1-methyl-3-
octylimidazolium tetrafluoroborate thin films in methanol oxida-
tion process due to the larger size of halogen atom (Br) (larger area
of protective layer which leads to the formation of particles).
Scheme 2. Working electrode preparation and thin film transfer to the surface of
glassy carbon electrode.
tion even in high temperatures due to their high thermal stability
[17]. Applying stabilizers such as surfactants, quaternary ammo-
nium salts and polymers is general for the stabilization of transi-
tion metal NPs. The catalytic activity of nanostructures depends
on the abundance of metal active sites and also concentration
and type of stabilizers (nature of the anion) [18]. According to
DLVO theory of stabilization, high charge of imidazolium salt pro-
vides the protective layer for metallic NPs [18]. Imidazolium ionic
liquids have preorganized structures due to their hydrogen bond
2. Experimental
2.1. Materials and methods
and
p
–
p
stacking which is an entropic driver for the synthesis of
Chemical compounds and solvents were purchased from
Aldrich and Merck companies. Organometallic complex of [PtCl2 (-
cod)] (cod = cis,cis-1,5-cyclooctadiene), was prepared according to
the literature [25]. Chemicals and solvents used are of the highest
commercially available quality and are used as received. The crys-
tal structure of thin film NPs were characterized by X-ray diffrac-
tion (XRD) patterns using a Bruker AXS (D8 Advance) instrument
well-ordered nanostructures [19]. In this study, we are synthesized
Pt thin films stabilized by different ionic liquids and investigated
their catalytic activity and stability in methanol oxidation process
of fuel cell. Also, they were applied as catalyst for the reduction of
p-nitrophenol (toxic) in water. p-Aminophenol is a compound with
a wide range of applications such as synthesis of some precursors
for pharmaceutical companies, applied as a corrosion inhibitor and
lubricating agent [20]. Bhaumik et al. investigated the catalytic
reduction of p-nitrophenol using NaBH4 as reducing reagent and
copper NPs (2–15 nm) as catalyst which exhibited better result
than commercial Cu nanopowder. NPs small size and great BET
surface area is the reason for better catalytic activity [21]. Also,
they used porous organic–inorganic hybrid nickel phosphonate
that exhibit a very good catalytic activity for the nitroarenes reduc-
tion in the presence of NaBH4. Nickel(II) sites at the surface of this
catalyst made it effective for the reduction process [22]. p-nitro-
employing the reflection Bragg–Brentano geometry with Cu K
a
radiation. The energy dispersive analysis of X-ray (EDAX) and
field-emission scanning electron microscopy (FE-SEM) images
were performed using a Philips XL30 instrument with an accelerat-
ing voltage of 20 kV. Transmission electron microscopy (TEM)
images were obtained using a Philips CM-10 TEM microscope
operated at 100 kV. Fourier-transform infrared spectra were
obtained with a FT-IR8600 spectrometer (JASCO Co., Japan). The
loading amounts of metal NPs were determined by inductively
coupled plasma (ICP) analyzer (Varian, Vista-Pro). The UV–Vis

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
485
Fig. 2. FT-IR spectra of (a1) Pt/[C2NH2mim][Br] thin film, (a2) [C2NH2mim][Br] ionic liquid, (b1) Pt/[C8mim][Cl] thin film, (b2) [C8mim][Cl] ionic liquid, (c1) Pt/[C8mim][BF4]
thin film and (c2) [C8mim][BF4] ionic liquid.
spectra were carried out using a Lambda 25 spectrophotometer
(Perkin–Elmer).
noethyl-3-methylimidazolium bromide hydrobromide. After that,
1-aminoethyl-3-methylimidazolium bromide hydrobromide
(24.2 g, 1 equiv.), potassium hydroxide (4.7 g, 1 equiv.) and anhy-
drous methanol (250 mL) were added to a round bottom flask
and stirred for 5 h at room temperature. KBr was separated by
using filtration. Methanol and water were removed from mixture
under reduced pressure at 70 °C [26].
2.2. 1-Aminoethyl-3-methylimidazolium bromide [C2NH2mim][Br]
ionic liquid synthesis
In the first step, N-methylimidazolium (30.4 g, 0.37 mol) and
acetonitrile (250 mL) were added to a three-necked round bottom
flask refluxed in a 75 °C oil bath under argon atmosphere. Then, 2-
bromoethylamine hydrobromide (38.9 g, 0.19 mol) was added.
After 24 h, the flask was cooled to room temperature. The obtained
solid phase at the bottom of the flask was washed with ethanol for
three times and dried at 70 °C vacuum for a night to obtain 1-ami-
2.3. 1-Methyl-3-octylimidazolium chloride [C8mim][Cl] ionic liquid
synthesis
Equal molar amounts of chlorooctane and 1-methylimidazole
were added to a round bottom flask and stirred for 24–72 h (until

486
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Fig. 3. XRD pattern of the as-synthesized catalysts (a) Pt/[C2NH2mim][Br], (b) Pt/[C8mim][Cl] and (c) Pt/[C8mim][BF4] thin films.
Fig. 4. (a,b) FE-SEM images of the Pt/[C2NH2mim][Br] nano thin film.
Fig. 5. (a) TEM image of Pt/[C2NH2mim][Br] nano thin film and (b) histogram of particles size distribution.

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
487
Fig. 6. (a,b) FE-SEM images of the Pt/[C8mim][Cl] nano thin film.
Fig. 7. (a,b) TEM images of Pt/[C8mim][Cl] nano thin film and (c) histogram of particles size distribution.
two phases formed) under reflux condition at 70 °C. The unreacted
2.4. 1-Methyl-3-octylimidazolium tetrafluoroborate [C8mim][BF4]
ionic liquid synthesis
starting material which was in the upper phase was decanted and
ethyl acetate was added and decanted again to remove the unre-
acted materials. The remained ethyl acetate was removed by heat-
ing the bottom phase under vacuum up to 70 °C [27].
The product of Section. 2.3 ([C8mim]Cl) was transferred to a
plastic container followed by the addition of aqueous HBF4 (40%)

488
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Fig. 8. (a,b) FE-SEM images of the Pt/[C8mim][ BF4] nano thin film.
Fig. 9. (a) TEM image of Pt/[C8mim][BF4] nano thin film and (b) histogram of particles size distribution.
Fig. 10. EDAX spectra of (a) Pt/[C2NH2mim][Br], (b) Pt/[C8mim][Cl] and (c) Pt/[C8mim][BF4] thin films.

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
489
Fig. 11. EDAX elemental mapping analysis of Pt/[C2NH2mim][Br] thin film (b) C, (c) N, (d) Br, (e) Pt and (f) C, N, Br, Pt.
Fig. 12. EDAX elemental mapping analysis of Pt/[C8mim][Cl] thin film (b) C, (c) N, (d) Cl, (e) Pt and (f) C, N, Cl, Pt.
at a 1.1:1 molar ratio. Methylene chloride was used to separate
[C8mim]BF4 from HCl (equal volume to the initial amount of
[C8mim]Cl). This extraction is followed by using separatory funnel.
The remained methylene chloride in the [C8mim]Cl/methylene
chloride mixture was removed by rotary evaporator at 95 °C tem-
perature. Activated carbon and alumina were used to remove
impurities [27].
2.5. Formation of Pt/ionic liquid thin films at toluene–water interface
[PtCl2(cod)] organometallic complex (1 mM, 25 mL) was dis-
solved in toluene using ultrasonic bath (Scheme 1, top phase). Aqu-
eous solution (25 mL) of ionic liquids ([C2NH2mim][Br], [C8mim]
[Cl] or [C8mim][BF4], 0.01 g, 200 and 200
lL, respectively) was also
prepared (Scheme 1, bottom phase). Then, the as-prepared solu-

490
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Fig. 13. EDAX elemental mapping analysis of Pt/[C8mim][BF4] thin film (a) B, (b) C, (c) N, (d) F, (e) Pt and (f) B, C, N, F, Pt.
Table 1
Effect of applying ionic liquids with different anions on the morphology and electrocatalytic activity of Pt thin films.
Entry
Thin film
Morphology
Size (nm)
Stabilizer
Jf/Jb ratio
Current density (mA cmꢀ2
)
E(V, NHE)
1
2
3
Pt/[C2NH2mim][Br]
Pt/[C8mim][Cl]
Pt/[C8mim][BF4]
Spherical NPs
Spherical NPs, agglomerated
Spherical NPs, agglomerated
7
12
4
[C2NH2mim][Br]
[C8mim][Cl]
[C8mim][BF4]
4.54
3.90
1.56
81.14
157.57
196.25
0.6
0.63
0.43
Fig. 14. Cyclic voltammograms of the Pt/[C2NH2mim][Br] thin film in (a) 0.5 M H2SO4 electrolyte and (b) 0.5 M H2SO4 electrolyte containing 0.5 M CH3OH with a scan rate of
50 mV sꢀ1
.
tions were contacted with each other in
a
100 mL beaker
2.6. Electrode preparation
(Scheme 1). When the two phases were stabilized, NaBH4 aqueous
solution (0.1 M, 5 mL) was injected as a reducing agent. Thin film
formation was completed after 24 h. These thin films were applied
as effective and excellent electrocatalysts in DMFCs. Also, they
exhibited good catalytic activity in the reduction of p-nitrophenol.
The glassy carbon electrodes should be polished with alumina
slurry (Scheme 2a) and cleaned in deionized water and ethanol
mixture using ultrasonic bath (Scheme 2b). Pt/ionic liquid thin
films were transferred from toluene–water interface to the surface

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
491
Fig. 15. Cyclic voltammograms of the Pt/[C8mim][Cl] thin film in (a) 0.5 M H2SO4 electrolyte and (b) 0.5 M H2SO4 electrolyte containing 0.5 M CH3OH with a scan rate of 50
mV sꢀ1
.
Fig. 16. Cyclic voltammograms of the Pt/[C8mim][BF4] thin film in (a) 0.5 M H2SO4 electrolyte and (b) 0.5 M H2SO4 electrolyte containing 0.5 M CH3OH with a scan rate of 50
mV sꢀ1
.
Fig. 17. Cyclic voltammograms of (a) [C2NH2mim][Br], (b) [C8mim][Cl] and (c) [C8mim][BF4] in the presence of H2SO4 (0.5 M) with a scan rate of 50 mV sꢀ1
.
of glassy carbon electrode that is used as working electrode
(Scheme 2c).
nano thin films as a working electrode was applied at room tem-
perature. However, all potentials in the manuscript were converted
to values with reference to a normal hydrogen electrode (NHE).
The area diameter of the glassy carbon electrode was 2 mm.
2.7. Electrochemical measurements
Autolab Potentiostat/Galvanostat PGSTAT12 (Eco Chemie,
Switzerland) was used to evaluate the electrocatalytic activity of
Pt/ionic liquid thin films. A standard three-electrode system con-
tains an Ag/AgCl (sat. KCl) reference electrode, a platinum wire
counter electrode and glassy carbon coated with Pt/ionic liquid
2.8. Reduction of p-nitrophenol
Reduction of p-nitrophenol to p-aminophenol was investigated
in the presence of the as- prepared Pt/ionic liquid thin films and
the apparent rate constants were obtained. After removing the cat-

492
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Fig. 18. Cyclic voltammograms of (a) [C2NH2mim][Br], (b) [C8mim][Cl] and (c) [C8mim][BF4] in the presence of H2SO4 (0.5 M) and methanol (0.5 M) with a scan rate of 50 mV
sꢀ1
.
Table 2
Comparison of different electrocatalysts.
Electrode
Jf/Jb ratio
Current density (mA cmꢀ2
)
E(V, NHE)
References
Pt thin film
1.28
1.19
1.52
1.65
1.50
1.59
0.605
1.18
3.50
0.99
0.57
4.54
3.90
1.56
–
–
–
122
–
–
–
–
0.73
0.54
0.47
0.65
–
–
–
–
0.58
–
[15]
[5]
[11]
[14]
[5]
[12]
[28b]
[28c]
[11]
[28d]
[11]
This work
This work
This work
PtPd thin film
PtNi thin film
PtSnZn thin film
PtPd/RGO thin film
Pt3Sn/RGO thin film
Pt/C
Pt/C
PtPdNiSn thin film
ETEK Pt
Commercial Pt/C
Pt/[C2NH2mim][Br]
Pt/[C8mim][Cl]
Pt/[C8mim][BF4]
–
–
–
–
81.14
157.57
196.24
0.6
0.63
0.43
liquids ([C2NH2mim][Br], [C8mim][Cl] and [C8mim][BF4]). Ionic liq-
uids can stabilize NPs in different modes. These modes are
expressed in Fig. 1. In the absence of functional groups, the stabi-
lization will occur in the way that shows in Fig. 1c.
3.1. Pt/ionic liquid thin films characterization
FT-IR analysis was used to investigate the presence of ionic liq-
uids in the as-prepared Pt thin films at the range of 4000–400
cmꢀ1. Pellets were prepared by using KBr dried at 110 °C. Compar-
ing the FT-IR spectra of Pt/[C2NH2mim][Br], Pt/[C8mim][Cl] and Pt/
[C8mim][BF4] with [C2NH2mim][Br], [C8mim][Cl] and [C8mim][BF4]
ionic liquids, confirms the presence of ionic liquid structures in the
Pt/ionic liquid thin films (Fig. 2). Presence of the peak at 1167–
1178 cmꢀ1 belongs to the ring in-plane asymmetric stretching of
the imidazolium ring [28a].
Scheme 4. Protective shell of anions in the case of (a) Pt/[C8mim][BF4], (b) Pt/
[C8mim][Cl] and (c) Pt/[C2NH2mim][Br] thin films.
XRD analysis was used for the characterization of the as-pre-
pared Pt/ionic liquid thin films. All these spectra show five diffrac-
tion peaks correspond to [(111), (200), (220), (311) and (222)]
planes of the face-centered-cubic (fcc) structure of Pt (0)
(Fig. 3a–c) [5].
FE-SEM was applied to investigate the morphology of the Pt/
ionic liquid thin films. In the case of Pt/[C2NH2mim][Br], some
spherical particles are observable on the ionic liquid support
(Fig. 4a,b). Also, TEM image exhibits the spherical structures on
the ionic liquid support (Fig. 5a). These NPs have the mean diam-
eter of 7 nm (Fig. 5b).
alyst from the reaction mixture by centrifugation, aqueous solution
of p-nitrophenol (0.2 mM, 1.7 mL) was added to a quartz cuvette
(3 ml) (Scheme 3a) followed by the addition of aqueous solution
of NaBH4 (15 mM, 0.7 mL). After the color change of this solution
from light yellow to deep yellow (Scheme 3b), the centrifuged cat-
alyst was added. The reaction progress was monitored by using
UV–Vis spectrometer (Scheme 3c). The final aqueous solution
was colorless (Scheme 2d) that contains p-aminophenol.
3. Results and discussion
In the case of Pt/[C8mim][Cl] thin film, FE-SEM shows spherical
structures (Fig. 6a,b). TEM analysis shows aggregated spherical
structures (Fig. 7a,b) with the mean diameter of 12 nm (Fig. 7c).
[PtCl2(cod)] organometallic precursor is used for the synthesis
of Pt/ionic liquid nano thin films in the presence of different ionic

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
493
Scheme 5. Poisoning the Pt surface with CO species.
Fig. 19. (a) Cyclic voltammograms of the Pt/[C2NH2mim][Br] thin film at different scan rates in 0.5 M H2SO4 + 0.5 M CH3OH, (b) Dependence of the peak currents on the
square root of the scan rates.
Fig. 20. (a) Cyclic voltammograms of the Pt/[C8mim][Cl] thin film at different scan rates in 0.5 M H2SO4 + 0.5 M CH3OH, (b) Dependence of the peak currents on the square
root of the scan rates.
Fine aggregated NPs is observable in the case of Pt/[C8mim][BF4]
thin films from FE-SEM (Fig. 8a,b) and TEM (Fig. 9a) images. The
particles mean diameter is 4 nm (Fig. 9b).
EDAX analysis shows the presence of C, N, Br, Pt elements for Pt/
[C2NH2mim][Br] (Fig. 10a), C, N, Cl, Pt elements for Pt/[C8mim][Cl]
(Fig. 10b) and B, C, N, F, Pt elements for Pt/[C8mim][BF4] (Fig. 10c)

494
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Fig. 21. (a) Cyclic voltammograms of the Pt/[C8mim][BF4] thin film at different scan rates in 0.5 M H2SO4 + 0.5 M CH3OH, (b) Dependence of the peak currents on the square
root of the scan rates.
3.2. Investigating the electrocatalytic activity
3.2.1. Methanol oxidation process in fuel cell
To investigate the electrocatalytic activity of the as-synthesized
Pt/ionic liquid thin films in methanol oxidation, the anodic half-cell
is prepared. The electrocatalysts were put on the surface of glassy
carbon electrode. Cyclic voltammograms of the thin films in 0.5 M
H2SO4 medium at a scan rate of 50 mV sꢀ1 (Fig. 14a–16a) were
recorded. Fig. 17(a–c) exhibits the voltammograms of ionic liquids
in the absence of Pt. The electrocatalytic activity of the Pt/[C2NH2-
mim][Br], Pt/[C8mim][Cl] and Pt/[C8mim][BF4] thin films was char-
acterized by cyclic voltammetry in an electrolyte of 0.5 M
methanol and 0.5 M H2SO4 medium at a scan rate of 50 mV sꢀ1
.
The resulting voltammograms are shown in Figs. 14–16b. Also,
Fig. 18(a–c) exhibits the voltammograms related to ionic liquids
in the presence of 0.5 M H2SO4 and methanol. In the presence of
methanol, some of the electrocatalysts show higher or comparable
current density and confirm that they have a potential of being the
electrocatalyst for methanol oxidation.
Table 1 exhibits the details of Figs. 14–18. Also, the effect of dif-
ferent ionic liquids with different anions on the morphology, size
and catalytic activity of Pt NPs is investigated. Furthermore, the
electrocatalytic activity of the as-synthesized thin films is com-
pared with Pt thin film and some other common electrocatalysts
in methanol oxidation process (Table 2).
Fig. 22. UV–Vis. spectra of (a) p-nitrophenol in water, (b) p-nitrophenolate
formation in the presence of NaBH4.
thin films and confirms the presence of ionic liquids in Pt thin
films.
Figs. 11–13 show the EDAX-elemental mapping for Pt/[C2NH2-
mim][Br], Pt/[C8mim][Cl] and Pt/[C8mim][BF4], respectively.
From Tables 1 and 2, and also Figs. 14–18, these results can be
concluded:
Fig. 23. (a) UV–Vis absorption spectra for the reduction of p-nitrophenol (0.2 mM) by NaBH4 (15 mM) in the presence of Pt/[C2NH2mim][Br] at 25 °C and (b) Plot of ꢀLn A
versus time for the kinetic study of the reaction of p-nitrophenol.

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
495
Fig. 24. (a) UV–Vis absorption spectra for the reduction of p-nitrophenol (0.2 mM) by NaBH4 (15 mM) in the presence of Pt/[C8mim][Cl] at 25 °C and (b) Plot of ꢀLn A versus
time for the kinetic study of the reaction of p-nitrophenol.
Fig. 25. (a) UV–Vis absorption spectra for the reduction of p-nitrophenol (0.2 mM) by NaBH4 (15 mM) in the presence of Pt/[C8mim][BF4] at 25 °C and (b) Plot of ꢀLn A versus
time for the kinetic study of the reaction of p-nitrophenol.
Scheme 6. Mechanism for the reduction of p-nitrophenol on the surface of Pt/ionic liquid thin films.

496
S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
Table 3
Comparison of apparent rate constants for p-nitrophenol reduction with different thin film nanocatalysts.
Entry
Composition
Metal loading (
l
g)a
Apparent rate constant (sꢀ1
)
References
1
2
3
4
5
6
7
8
Pt/[C2NH2mim][Br]
Pt/[C8mim][Cl]
Pt/[C8mim][BF4]
PtZnSn
1.2
1.0
1.0
–
3.2
–
2.1
2.3
–
–
–
–
4.0
–
4.47 ꢁ 10ꢀ3
5.27 ꢁ 10ꢀ3
4.44 ꢁ 10ꢀ3
4.60 ꢁ 10ꢀ3
1.98 ꢁ 10ꢀ3
3.15 ꢁ 10ꢀ3
3.84 ꢁ 10ꢀ3
2.14 ꢁ 10ꢀ3
9.50 ꢁ 10ꢀ4
2.9 ꢁ 10ꢀ3
1.0 ꢁ 10ꢀ3
9.0 ꢁ 10ꢀ5
1.29 ꢁ 10ꢀ4
5.57 ꢁ 10ꢀ3
1.59 ꢁ 10ꢀ4
This work
This work
This work
[14]
[15]
[31]
[15]
[15]
[31]
[32]
Pt thin film
PtNi/RGOb
Pt/ACc
Pt/PVPd
9
Pt/RGO
Pt/RGO
Pt/C
PtNi
Pt Pure
Pt/ZIF-8/Fe3O4
NiPt NPs
10
11
12
13
14
15
[32]
[31]
[33]
[34]
4.0
[33]
a
b
c
Obtain from ICP.
Reduced-graphene oxide.
Aminoclay.
d
Polyvinylpyrrolidone.
1. Ionic liquids with different anions applied as stabilizer for the
synthesis of Pt electrocatalysts. Larger anions can produce a lar-
ger protective layer and prevent from agglomeration. In the
case of Pt/[C2NH2mim][Br] thin film, particles are obtained
(Fig. 5) due to the larger size of (Br) anion. Also, the size of par-
ticles are smaller than Pt/[C8mim][Cl] that contains (Cl) anion.
In the case of Pt/[C8mim][BF4], four (F) anion in tetrafluorobo-
rate anion group can more stabilize Pt NPs, so the size of NPs
is reduced but they are agglomerated (Fig. 9). Scheme 4 shows
the effect of anion size on preventing from agglomeration.
2. As is reported in previous studies, the ratio of the maximum
peak current density in the forward scan (Jf) to the maximum
peak current density in the backward scan (Jb) is used to indi-
cate the tolerance of catalysts toward CO poisoning. Scheme 5
shows the poisoning of Pt surface during the methanol oxida-
tion process.
Pt-CHO ! Pt-CO þ Hþ þ eꢀ
ð4Þ
Pt-OH2 ! Pt-OH þ Hþ þ eꢀ
Pt-OH ! Pt-O þ Hþ þ eꢀ
ð5Þ
ð6Þ
ð7Þ
Pt-CO þ Pt-O ! CO2
The overall reaction is:
CH3OH þ H2O ! CO2 þ 6Hþ þ 6eꢀ
ð8Þ
Furthermore, scan rates between 20 and 100 mV sꢀ1 were
applied and the related cyclic voltammograms were recorded for
the as-prepared thin films in 0.5 M H2SO4 and 0.5 M CH3OH elec-
trolyte (Figs. 19–21a). The increase in the current density with
the scan rate is observed. Also, Figs. 19–21b show that peak current
densities are linearly proportional to the square root of the scan
rates, suggesting that the electrocatalytic oxidation of methanol
on the Pt/[C2NH2mim][Br], Pt/[C8mim][Cl] and Pt/[C8mim][BF4]
thin film is a diffusion-controlled process [5].
The bigger ratio of Jf/Jb, the less poisoning with CO species via
decomposition of methanol; The Jf/Jb ratios for the Pt/[C2NH2-
mim][Br], Pt/[C8mim][Cl] and Pt/[C8mim][BF4] thin films are 4.54,
3.90 and 1.56, respectively, and all are larger than those for the
ETEK Pt (0.99), another type of commercial Pt/C (0.57), and Pt NP
thin films (1.28), respectively (Table 2). Furthermore, we con-
cluded that the catalysts (Pt/[C2NH2mim][Br]) exhibit higher Jf/Jb
ratio than agglomerated catalysts (Pt/[C8mim][Cl] and Pt/[C8mim]
[BF4]) due to their more active sites.
3.2.2. p-Nitrophenol reduction
Reduction of p-nitrophenol was investigated in the presence of
Pt/ionic liquid thin films. The reaction progress was followed by
using a UV–Vis spectrometer. By the addition of NaBH4, the
absorption peak centered at 317 nm is shifted to 400 nm due to
the formation of p-nitrophenolate ions (Fig. 22). The details of
the mechanism of the reaction are illustrated in Scheme 6. Investi-
gations show that adsorption of p-nitrophenolate on the catalyst
surface, generation of active hydrogen atoms and the rate of charge
transfer are important facts that affect the reaction rate.
In the absence of catalysts, the reduction of p-nitrophenol did
not show any remarkable progress. In the presence of Pt/ionic liq-
uid thin films as catalyst, the absorption peak at 400 nm decreased
and the absorption peak intensity at 300 nm increased due to the
formation of p-aminophenol [30]. UV–Vis absorption spectra of
the reduction of p-nitrophenol were recorded every 60 s. The
pseudo first-order kinetics can be used to evaluate the rate con-
stants for the reduction of p-nitrophenol according to the NaBH4
high concentration. Furthermore, the absorbencies at k = 400 nm
were recorded with time and the apparent rate constants were
performed in Table 3. Figs. 23–25a exhibit the UV–Vis absorption
spectra for the reduction of p-nitrophenol in the presence of Pt/[C2-
NH2mim][Br], Pt/[C8mim][Cl] and Pt/[C8mim][BF4] thin films at 25
°C. Also, the plot of ꢀLn A versus time for the kinetic study of the
reaction of p-nitrophenol is illustrated in Figs. 23–25b.
3. The onset of current attributed to methanol oxidation is at
approximately 0.6 V (vs. NHE) for the Pt/[C2NH2mim][Br] thin
film, 0.63 V for the Pt/[C8mim][Cl] thin film and 0.43 V for the
Pt/[C8mim][BF4] thin film, being more negative than that at a
pure Pt NP thin film electrode (ca. 0.73 V vs. NHE). Therefore,
Pt/ionic liquid thin films can easily do the methanol oxidation
process than Pt thin film.
Generally, methanol oxidation at Pt NPs has two main steps: (i)
dehydrogenation (inner-sphere electron transfer) that is fast and
(ii) oxidation (electrochemical oxygen transfer reaction) that is
the rate-determining step. The oxidation mechanism is as follow
[29]:
Pt þ CH3OH ! Pt-CH3O þ Hþ þ eꢀ
Pt-CH3O ! Pt-CH2O þ Hþ þ eꢀ
Pt-CH2O ! Pt-CHO þ Hþ þ eꢀ
ð1Þ
ð2Þ
ð3Þ

S.H. Sharfand et al. / Polyhedron 151 (2018) 483–497
497
[8] (a) H. Ming, X. Li, Y. Wei, L. Bu, Z. Kang, J. Zheng, RSC Adv. 3 (2013) 3655;
4. Conclusion
(b) R. Manikandan, P. Anitha, P. Viswanathamurthi, J.G. Malecki, Polyhedron
119 (2016) 300.
In this investigation, Pt thin films stabilized by different ionic
liquids were synthesized at toluene–water interface. These ionic
liquids contain different anions (F, Cl, Br) that can produce a pro-
tective layer around the Pt NPs and prevent from aggregation. Lar-
ger anion (Br) protects Pt NPs better than (Cl) and (F) anions. Due
to the fact that aggregation is not happen for Pt/[C2NH2mim][Br],
this catalyst can reuse in the catalytic processes. These catalysts
were applied in the methanol oxidation process. The considerable
fact in this study was transferring the electrocatalysts on glassy
carbon electrode surface without using any nafion which is one
of the advantages of our work. So, the conductivity and current
density is not decreased (nafion acts as insulator). Also, these cat-
alysts were applied for the reduction of p-nitrophenol (a toxic
material in water). They exhibit good catalytic activity despite
their low metal loading. This is due to the presence of all metal
atoms on the surface of the thin films.
[9] J. Gao, J. Zou, X. Zeng, W. Ding, RSC Adv. 6 (2016) 83025.
[10] R. Bavand, A. Korinek, G.A. Botton, A. Yelon, E. Sacher, J. Phys. Chem. C 121
(2017) 23104.
[11] S.J. Hoseini, M. Bahrami, M. Zanganeh, M. Roushani, M. Rashidi, RSC Adv. 6
(2016) 45753.
[12] S.J. Hoseini, Z. Barzegar, M. Bahrami, M. Roushani, M. Rashidi, J. Organomet.
Chem. 769 (2014) 1.
[13] M.A. Scibioh, S.K. Kim, E.A. Cho, T.H. Lim, S.A. Hong, H.Y. Ha, Appl. Catal. B 84
(2008) 773.
[14] (a) C.N.R. Rao, K.P. Kalyanikutty, Acc. Chem. Res. 41 (2008) 489;
(b) S. Saberi Sarmoor, S.J. Hoseini, R. Hashemi Fath, M. Roushani, M. Bahrami,
Appl. Organomet. Chem. 32 (2017) e3979.
[15] (a) S.J. Hoseini, M. Rashidi, M. Bahrami, J. Mater. Chem. 21 (2011) 16170;
(b) K.P. Kalyanikutty, U.K. Gautam, C.N.R. Rao, J. Nanosci. Nanotechnol. 7
(2007) 1916.
[16] S.G. Booth, R.A.W. Dryfe, J. Phys. Chem. C 119 (2015) 23295.
[17] M. Yang, P.S. Campbell, C.C. Santini, A.V. Mudring, Nanoscale 6 (2014) 3367.
[18] J. Kramer, E. Redel, R. Thomann, C. Janiak, Organometallics 27 (2008) 1976.
[19] R.P. Matthews, T. Welton, P.A. Hunt, Phys. Chem. Chem. Phys. 17 (2015) 14437.
[20] E. Menumerov, R.A. Hughes, S. Neretina, Catal. Sci. Technol. 7 (2017) 1460.
[21] A.K. Patra, A. Dutta, A. Bhaumik, Catal. Commun. 11 (2010) 651.
[22] A. Dutta, A.K. Patra, A. Bhaumik, Micropor. Mesopor. Mat. 155 (2012) 208.
[23] C.V. Rode, M.J. Vaidya, R. Jaganathan, R.V. Chaudhari, Chem. Eng. Sci. 56 (2001)
1299.
Acknowledgements
[24] Y. Wu, M. Wen, Q.S. Wu, H. Fang, J. Phys. Chem. C 118 (2014) 6307.
[25] R.J. Puddephatt, M.A. Thomson, J. Organomet. Chem. 238 (1982) 231.
[26] X. Zhou, T. Wu, K. Ding, B. Hu, M. Hou, B. Han, Chem. Commun. 14 (2009) 1897.
[27] M.H. Ghatee, A.R. Zolghadr, Fluid Ph. Equilb. 263 (2008) 168.
[28] (a) N.E. Heimer, R.E. Del Sesto, Z. Meng, J.S. Wilkes, W.R. Carper, J. Mol. Liq. 124
(2006) 84;
We thank Shiraz University and Yasouj University Research
Council for their support.
References
(b) H. Li, D. Kang, H. Wang, R. Wang, Int. J. Electrochem. Sci. 6 (2011) 1058;
(c) O. Lupan, L. Chow, G. Chai, H. Heinrich, Chem. Phys. Lett. 465 (2008) 249;
(d) S.J. Hoseini, N. Mousavi, M. Roushani, L. Mosadeghi, M. Bahrami, M.
Rashidi, Dalton Trans. 42 (2013) 12364.
[1] I. Do, L. Drzal, ACS Appl. Mater. Interfaces 6 (2014) 12126.
[2] S. Al-Batty, C. Dawson, S.P. Shanmukham, E.P.L. Roberts, S.M. Holmes, J. Mater.
Chem. A 4 (2016) 10850.
[3] X. Yu, F. Luo, Z. Yang, RSC Adv. 6 (2016) 98861.
[29] A. Hammnet, Catal. Today 38 (1997) 445–457.
[4] (a) S.J. Hoseini, M. Bahrami, M. Roushani, RSC Adv. 4 (2014) 46992;
(b) S. Saeed, K.S. Ahmed, N. Rashid, M. Azad Malik, P. O’Brien, M. Akhtar, R.
Hussain, W.T. Wong, Polyhedron 85 (2015) 267.
[5] S.J. Hoseini, M. Bahrami, M. Dehghani, RSC Adv. 4 (2014) 13796.
[6] S.J. Hoseini, M. Bahrami, M. Maddahfar, R. Hashemi Fath, M. Roushani, Appl.
Organomet. Chem. 32 (2018) e3894.
[30] S.J. Hoseini, M. Bahrami, N. Sadri, N. Aramesh, Z. Samadi Fard, H. Rafatbakhsh
Iran, B. Habib Agahi, M. Maddahfar, M. Dehghani, A. Zarei Baba Arabi, N.
Heidari, S.F. Hashemi Fard, Z. Moradi, J. Colloid Interface Sci. 513 (2018) 602.
[31] F. Zhao, W. Kong, Z. Hu, J. Liu, Y. Zhao, B. Zhang, RSC Adv. 6 (2016) 79028.
[32] Q. Liu, Y.R. Xu, A.J. Wang, J.J. Feng, RSC Adv. 5 (2015) 96028.
[33] S.K. Ghosh, M. Mandal, S. Kundu, S. Nath, T. Pal, Appl. Catal. A 268 (2004) 61.
[34] S. Lee, C. Yim, S. Jeon, RSC Adv. 7 (2017) 31239.
[7] (a) S.J. Hoseini, M. Dehghani, H. Nasrabadi, Catal. Sci. Technol. 4 (2014) 1078;
(b) A.L. Anderson, R. Binions, Polyhedron 118 (2016) 81.