Platinum nanoparticles supported on polymeric ionic liquid functionalized magnetic silica: effective and reusable heterogeneous catalysts for the selective oxidation of alcohols in water

Article abstract of DOI:10.1039/c6ra16851e

In this research, the syntheses of core-shell magnetic silica nanostructures, functionalized by a polymeric ionic liquid and immobilization of platinum nanoparticles, are described. Firstly, the magnetic silica nanoparticles were synthesized and modified using an amine-containing organosilane through a single-step process. The synthesized nanostructures were functionalized by the synthesis and polymerization of a pyridinium ionic liquid and a methyl methacrylate monomer, respectively, onto their surfaces. The platinum nanoparticles were immobilized on the functionalized nanoparticles. The obtained functionalized nanostructures have been used in the selective aerobic oxidation, in an aqueous medium, of primary and encumbered secondary aliphatic alcohols, and exhibit high activity at mild temperatures.

Full text of DOI:10.1039/c6ra16851e

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ghasemisarabbadeih, Z. Ekhtiari, R. Hosseinzadeh khanmiri, E. Ghorbani-Kalhor and L. Edjlali, RSC Adv.,
2016, DOI: 10.1039/C6RA16851E.
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Supported Platinum Nanoparticles onto the Polymeric Ionic Liquid
Functionalized Magnetic Silica: As an Effective and Reusable Heterogeneous
Catalyst for Selective Oxidation of Alcohols in Water
Esmail Vessallya, Mostafa Ghasemisarabbadeihb, Zeynab Ekhteyaric, Rahim Hosseinzadeh-
Khanmirid, Ebrahim Ghorbani-Kalhor*d and ladan Ejlalid
aDepartment of Chemistry, Payame Noor University, Tehran, Iran
bDepartment of Chemistry, Faculty of Science, Imam Hossein University, Tehran, Iran
cDepartment of Chemistry, Kurdistan University, Sanandaj, Iran
dDepartment of Chemistry, Tabriz Branch, Islamic Azad University, Tabriz, Iran
Eꢀmail: ekalhor@iaut.ac.ir
Abstract
In this research, the synthesis of coreꢀshell nanostructure of magnetic silica, functionalization by
polymeric ionic liquid and immobilization of platinum nanoparticles, are described. Firstly, the
magnetic silica nanoparticles was synthesized and modified by amineꢀcontaining organosilane
through the singleꢀstep process. The nanostructures were functionalized by synthesis and
polymerization of pyridinium ionic liquid and methyl methacrylate monomer onto their surfaces,
respectively. The platinum nanoparticles were immobilized on the functionalized nanoparticles.
The obtained functionalized nanostructures have been used in selective aerobic oxidation of
primary and encumbered secondary aliphatic alcohols in the aqueous medium with high activity
at mild temperature.
Keywords: Magnetic silica, Pyridinium ionic liquid, Platinum nanoparticle, Aerobic oxidation,
Alcohol
Introduction
The selective oxidation of hydrocarbons and of other organic compounds has become of
considerable importance as a means for the direct synthesis of valuable oxygenꢀcontaining
compounds such as aldehydes, ketones and carboxylic acids.1ꢀ4 The selective oxidation of
alcohols is one of the most effective approaches to produce this compound that was abundantly
used in the recent decades.5ꢀ7 The conventional methods for oxidation of alcohols are consisted
of using stoichiometric amount of hazardous reagent such as nitric acid, potassium dichromate,

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potassium permanganate, sodium hypochlorite and organic peroxides.8ꢀ10 These methods have
any environmental issue include producing abundant wastes using mentioned oxidant.11, 12
Aerobic oxidation of alcohols in presences of transition metals or organic freeꢀradical initiator is
attractive choice that was reported more than other methods in recent years.13ꢀ15
Heterogeneous catalyst systems, as a significant goal of green chemistry to maximize the
efficiency of the reactants and minimize the production of wastes, are highly regarded in organic
process, especially in the oxidation of alcohols.13, 16 Heterogeneous catalyst systems have many
advantage in compare to homogeneous systems such as more recyclability, simple workup
process, low toxicity and more selectivity to produce the controllable approaches in the
reactions.17 Recently, numerous methods have been developed for design and preparation of
heterogeneous catalysts based on synthetic and natural nanomaterials such as nanoparticles,
polymeric nanostructures and carbon allotropes.18ꢀ21 Among them, silica nanoparticles (NPs) due
to theirs high specific surface area, extraordinary thermal and mechanical properties, and high
stability to different conditions has been thought to be an ideal support in heterogeneous
catalysis.22, 23 The silica NPs have potential to produce the advance catalysts because these
particles can be easily functionalized by wide range of organic and inorganic active species via
physical and chemical interactions.24 The organic functionalization of the silica NPs was carried
out by initial modification of particles surface using organosilane agents that were provided the
ability to make covalent bonds with any organic or polymeric groups.25 The metal cations (or
nanoparticles) can be effectively loaded onto the more suitable sites of organic functionalized
silica NPs via electrostatic interactions and coordination with negative potential of porous silica
structure and surface active species, respectively.26 Recently, abundant papers were reported the
synthesis of multiꢀfunctional silica NPs by various methods using large scope of organic and
inorganic reagent that was used in the organic reactions as a heterogeneous catalyst.27ꢀ31
Herein, we have focused on the design and preparation of a novel magnetic silica NPs with
highly disperse properties and good affinity for immobilization of platinum NPs as an efficient
heterogeneous catalyst for oxidation of alcohols in aqueous medium. For this reason, the
magnetic silica nanoparticles was prepared and modified using amineꢀcontaining organosilane
(APTES). The resultant particles were functionalized by sequential reaction with 4ꢀ
(Bromomethyl)pyridine, 2ꢀbromoethanol and 2ꢀbromoꢀ2ꢀmethylpropanoyl bromide to produce
pyridinium ionic liquid onto their surfaces as an initiator in the copperꢀmediated atom transfer

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radical polymerization (ATRP) of methyl methacrylate (MMA) to afford wellꢀdefined polymer
with pyridinium ionic functionality situated between the chain and particle surfaces. Due to the
existence of the ionic center, ability of ester functions of polymeric chain to interaction with
water and hydrophilic nature of silica, these NPs have good dispersity in aqueous mediums. Next
the platinum NPs successfully immobilized on these NPs, and the final catalyst (Pt@MSꢀILꢀ
PMMA) was characterized by FTIR, TGA, ICPꢀOES, EDX, SEM, TEM and XRD techniques
(Scheme 1).

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NH2
O
O
O
Si
Si
HO
O
O
Si
O
O
O
O
O
O
Si
H2N
O
O
Si
NH2
O
TEOS, APTES
Fe3O4
Si
O
Si
O
Si
O
NH4OH,
isopropanol
OH
O
4-(Bromomethyl)pyridine
H2O, ultrasonic irradiation
O
O
O
O
Si
Si
O
H
HO
OH
Si
NH2
OH
N
PF6
O
N
Br
N
N
Br
2-bromoethanol
O
H2O, ultrasonic irradiation
NaPF6
H2O/CH3CN, NaPF6
reflux
Si
O
Si
O
O
O
N
O
N
PF6
OH
O
Br
O
Br
n
N
PF6
O
O
N
PF6
O
O
N
O
N
O
O
Si
O
Si
CuBr/bpy, DMF
O
O
N
O
O
N
PF6
PF6
O
O
Br
Pt NPs
Br
n
O
O
O
O
Na2PtCl4 (aq.)
NaBH4
Scheme 1. Preparation of Platinum NPs supported on ionic liquid based poly(methyl methacrylate)ꢀ
functionalized magnetic silica NPs (Pt@MSꢀILꢀPMMA).

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Experimental
General
Tetraethoxysilane (TEOS, 99%), aminopropyltriethoxysilane (APTES, 99%) and all material and
solvent were purchased from Merck and Aldrich companies and used without further purification.
Characterization techniques
FTIR spectra were recorded on a Bomem MBꢀSeries FTꢀIR spectrophotometer. Transmission
electron microscopy (TEM) analysis was performed using a ZEISS EMꢀ900 at an acceleration
voltage of 80 kV. Scanning electron microscopy (SEM) and EDX were performed on a Philips
XLꢀ300 instrument. The sample was sputtered by gold to avoid undesirable electron charging.
Catalysis products were analyzed using a Varian 3900 GC by the undecane internal standard.
Ultrasonication was performed in a EUROSONIC 4D ultrasound cleaner with a frequency of 50
kHz and an output power of 350 W. Thermogravimetric analysis (TGA) was carried out using an
o
STA 1500 instrument at a heating rate of 10 C minꢀ1 in air. Xꢀray powder diffraction (XRD)
data were collected on an XDꢀ3A diffractometer using Cu Karadiation. The concentration of
Platinum was estimated using inductively coupled plasma optical emission spectrometer (ICPꢀ
1
OES) Varian Vista PRO Radial. H NMR spectra were acquired using 300 MHz NMR and 400
MHz Bruker spectrometers.
General procedure for preparation of the amineꢀmodified magnetic silica
The Fe3O4 NPs were synthesized using previously report by coꢀprecipitation method. In the first,
FeCl2.4H2O and FeCl3.6H2O with molar ratio of 1: 2 (2 mmol: 4 mmol) were dissolved in the
deionized water (250 mL) and temperature of the solution was increased to 60 oC under stirring. After
30 min ammonia solution (20 mL, 25 %) was added to the reaction (pH raised to 11), and the reaction
mixture was cooled to ambient temperature. The magnetic NPs was collected using external magnet
o
and after washing three times by water and ethanol, dried at 80 C for 6 h. Next, the Fe3O4 NPs (0.05
g) and TEOS (0.20 g, 1 mmol) were added to 2ꢀpropanol (30 mL) with ultrasonic irradiation. After 10
minute, ammonia solution (10 mL, 2 %) was added to the solution and stirred the reaction mixture for
12 h. the obtained NPs were separated via external magnet, washed by water and dried at 100 oC for 3
h. the modification of magnetic silica NPs (0.1 g) was performed in the toluene (15 mL) as solvent by
o
mixing NPs (0.1 g) and APTES (0.22 g, 1 mmol) and the reaction temperature raised 110 C under

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vigorously stirring. After completion of the reaction modified NPs was collected and washed two
times with ethanol and dried at 100 oC for 3 h.
General procedure for synthesis of pyridinium based ionic liquid onto the surface of SiO2@ Fe3O4ꢀ
NH2
The SiO2@ Fe3O4ꢀNH2 NPs (0.10 g), 4ꢀ(bromomethyl)pyridine (0.25 g, 1 mmol) and Sodium
hexafluorophosphate (0.17 g, 1 mmol) were poured in deionized water (30 mL) and sunicated
for 1 h. Then, the 2ꢀbromoethanol (0.13 g, 1 mmol) was added to reaction mixture and
refluxed for 6 h. At the end of this time, the 2ꢀbromoꢀ2ꢀmethylpropanoyl bromide (0.23 g, 1mmol)
o
solution in acetonitrile (10 mL) was injected to the reaction mixture and stirred for more 4 h at 80 C.
After completion of the reaction, the NPs were sparated using external magnet, washed two
times by ethanol and water and dried under reduced pressure at 80 oC to obtain MSꢀIL NPs
.
General procedure for synthesis of Pt@MSꢀILꢀPMMA NPs
The PMMA functionalization of MSꢀIL NPs was carried out by ATRP method.32 The MSꢀIL NPs,
CuBr (0.0067 g, 0.05 mmol) and bpy (0.0147 g, 0.1 mmol) were added to a Schlenk flask containing
DMF (10 mL) and the flask capped and sealed. The reaction flask air was removed under nitrogen
o
blowing, then MMA (1 mL) injected to the mixture and temperature was raised to 45 C. Finally, the
Pt@MSꢀILꢀPMMA NPs were separated by external magnet, washed by CHCl3 and water, and dried at
80 oC.
General procedure for selective oxidation of primary alcohols to aldehydes
The catalyst (0.03 g, 4.8 mmol %) was added to the mixture of alcohol (1 mmol) in deionized water
and stirred at 80 oC. The completion of reaction was monitored by tin layer chromatography (TLC). At
the end of reaction, the catalyst was separated by external magnet, the reaction solution was extracted
by CHCl3 analyzed by GC method.
General procedure for selective oxidation of primary alcohols to carboxylic acid and
secondary alcohols to ketones
The catalyst (0.03 g, 4.8 mmol %) was added to the mixture of alcohol (1 mmol) and K2CO3 (0.014g) in
o
deionized water and stirred at 80 C. The completion of reaction was monitored by tin layer

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chromatography (TLC). At the end of reaction, the catalyst was separated by external magnet and the
reaction solution was extracted by CHCl3 analyzed by GC method.
Results and discussion
The FTIR spectra of the each step of preparation of the Pt@MSꢀILꢀPMMA are provided and
shown in Fig. 1I. The Fe3O4 peaks are appeared at 647, 593 and 448 cmꢀ1 correspond to the
stretching vibrations of Fe–O bonds, while the absorption peak at 3248 cmꢀ1 is the OH stretching
vibration characteristic peak, indicating the existence of some amount of ferric hydroxide in
Fe3O4.33 These peaks are appeared in the all of spectra. In the spectrum of the magnetic silica
NPs and next steps, the peaks at 463, 1088 cmꢀ1 and 585 cmꢀ1 are respectively resulted by
stretching and bending vibrations of Si–O–Si and stretching vibrations Fe–O–Si, and the
absorption peaks of silanol groups (Si–OH) are observed at 3460, 1100 and 960 cmꢀ1.34 After
modification of the NPs, the peaks of aliphatic CꢀH are at 2847 and 2926 cmꢀ1, and the CꢀN
peaks are covered by the broad peaks of SiꢀOH and Si–O–Si bonds. In the case of the MSꢀIL, the
broad peak at 1486ꢀ1760 cmꢀ1 can be explained by presence of C=O, C=N and C=C, and the PꢀF
with CꢀBr peaks vibrations are appeared in 580ꢀ600 cmꢀ1 respectively.35, 36 Due to the formation
of polymeric chain in the Pt@MSꢀILꢀPMMA, the broad peak at 1440ꢀ1780 cmꢀ1 was observed
corresponding to the C=O vibrations of ester groups.37
The XRD patterns of the magnetic silica and Pt@MSꢀILꢀPMMA are shown in the Fig. 1II, that
are confirmed the retention of Fe3O4 NPs in the structure of the both cases and existence of the Pt
NPs onto the surface of the Pt@MSꢀILꢀPMMA catalyst. The characteristic diffractions of Fe3O4
and Pt NPs are noted in their patterns that are in good agreement with previously reports.38, 39
The TGA analysis of the magnetic silica, MSꢀILꢀPMMA and Pt@MSꢀILꢀPMMA NPs are used
to specify the presence of desired function and measurement the amounts of the organic content
o
and Pt NPs. As seen in the Fig. 1III, the initial weight losses before 120 C are occurred due to
the elimination of moisture and Volatiles. In the case of MSꢀILꢀPMMA and Pt@MSꢀILꢀPMMA,
o
the new step of the weight losing at 380 C are occurred due to the decomposing their organic
contents. Using comparison the remaining weights of the all of cases at 700 oC, the percentage of
the organic contents and Pt NPs was measured 3.4 % and 1.2 %, respectively.

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(I)
(II)
(III)
Figure 1. (I) FTIR spectra of Fe3O4, SiO2@ Fe3O4, SiO2@ Fe3O4ꢀNH2, MSꢀIL, Pt@MSꢀILꢀPMMA (a, b, c, d and e,
respectively), (II) XRD pattern of SiO2@ Fe3O4 (a) and Pt@MSꢀILꢀPMMA (b), and (III) TGA analysis of SiO2@
Fe3O4 (a), MSꢀILꢀPMMA (b) and Pt@MSꢀILꢀPMMA (c).
The SEM images of modified magnetic silica NPs and final catalyst are presented in the Fig 2, which are
shown the Semiꢀspherical of magnetic silica with average diameters of 78ꢀ95 nm. After modification and
functionalization process, due to the presence of MMA polymeric chain onto this surface, the particles
have the spongeꢀlike the morphology aggregated particles by average diameters less than 100 nm. In
addition the TEM images of the final catalyst are confirmed the coreꢀshell structure of the NPs with two
types of the dispersed small particles in their structures. The average sizes of this small particles are
measured 15ꢀ20 and low than 5 nm corresponding to Fe3O4 and Pt NPs, respectively. Also, the EDX
analysis from the Pt@MSꢀILꢀPMMA are shown the all of desired elements (Fig 2).

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(I)
(II)
(III)
(IV)

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(VI)
(V)
(VII)
Figure 2. SEM images of SiO2@ Fe3O4 (I, II), Pt@MSꢀILꢀPMMA (III, IV), TEM images of Pt@MSꢀILꢀ
PMMA (V, VI), and EDX analysis of Pt@MSꢀILꢀPMMA (VII).
The characterized catalyst have a good dispersity in the water and protic solvents such as ethanol and
methanol in compare to modified magnetic silica NPs, which are shown in the Fig. 3. All images were
captured after 2 h of dispersion of particles in the solvents.

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(I)
(II)
(III)
(IV)
Figure 3. Dispersity properties of modified magnetic silica NPs in water (I), Pt@MSꢀILꢀPMMA NPs in water
(II), ethanol (III) and in methanol (IV) after 2 h.
To evaluate the catalytic properties of this catalyst, aerobic oxidation of the primary and encumbered
secondary alcohols in the aqueous mediums is chosen. In order to optimize the reaction conditions,
oxidation of benzyl alcohol was performed as a model reaction, and the reaction was carried out in the
presence of various amounts of catalyst at different temperatures in deionized water under air blowing
(Table 1). As seen in the below, when the reaction was examined in the deionized was water without
any additives at room temperature, the low yield of benzaldehyde as the product was obtained. The
yield of reaction was increased using the higher temperature in presence of same amounts of the
catalyst (entries 1ꢀ3). Next, the reaction was examined in presence of different amounts of the catalyst
(entries 3ꢀ5). In addition this reaction was examined in the some organic solvents such as EtOH,
EtOAc and CH3CN, and the reaction was accomplished in the EtOAc and CH3CN with low and
moderate yield, respectively (entries 6ꢀ8). At the end of this step of the optimization experiments, the
4.8 mmol % of the Pt@MSꢀILꢀPMMA at 80 oC was selected as optimal amount of the catalyst and the
best temperature to obtain the highest yield of the benzaldehyde in water. It is prominent to note that
the reaction was produced the low yield of product in the presence of Pt NPs under optimized
conditions (entry 9). Similarly, the reaction was repeated using same amount of MSꢀILꢀPMMA that
was failed (entry 10). The results confirmed the synergic effect of the composite structure of the
support through the catalytic activity of Pt NPs. The main benefit of the ionic liquid polymeric shell
seems to come from increased the interaction of nanocomposites with substrates by the hydrogen
bands and dipoleꢀdipole interactions also provided the dispersed Pt NPs. Additionaly, interactions

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between metal d orbital and πꢀlevel of dendrimer chains can effect on the delocalization of the electron
density over both metal and ligand. These interactions may change the electrochemical properties of
metal.40, 41 In the second step, the reaction was carried out in the same conditions as previous step in
presence of various base additive. The reaction was completed, but the obtained product is benzoic
acid. K2CO3 was selected as a mild additive in this reaction to produce the high yield of the benzoic
acid (entry 13).
Table 1. Optimization of reaction conditionsa
Entry
1
Gram of cat. (mmol %)
0.05 (8.0)
0.05 (8.0)
0.05 (8.0)
0.03 (4.8)
0.02 (3.2)
0.03 (4.8)
0.03 (4.8)
0.03 (4.8)
0.01 (4.8)e
0.03f
Solvent Additive (mmol %)
T (oC)
r.t.
50
Time (min
120
120
30
Yieldb (%)
10c
H2O
H2O
ꢀ
ꢀ
18c
90c
90c
53c
Tracec
30c
73c
2
H2O
ꢀ
80
3
H2O
ꢀ
80
30
4
H2O
ꢀ
80
30
5
EtOH
EtOAc
CH3CN
H2O
ꢀ
70
120
120
120
240
240
15
6
ꢀ
70
7
ꢀ
80
8
ꢀ
80
14c
9
H2O
ꢀ
80
0
78d
>99d
96d
24d
10
11
12
13
14
0.03 (4.8)
0.03 (4.8)
0.03 (4.8)
0.03 (4.8)
H2O
NaOH (10)
KOH (10)
K2CO3 (10)
Et3N (10)
80
H2O
80
15
H2O
80
60
H2O
80
120
abenzylalcohol (1 mmol) in solvent (5 mL) in presence of Pt@MSꢀILꢀPMMA under stirring and air blowing,
c
d
e
f
bCG measured yield, yield of benzaldehyde, yield of benzoicacid. Pt nanoparticles and MSꢀILꢀPMMAwas
used as catalyst.
In order to investigate the scope and limitations of this catalyst in the selective aerobic oxidation of
alcohols, a variety of primary alcohols were used in the two optimized reaction conditions to obtain
the corresponding aldehydes and carboxylic acids. All products were obtained in high yields. The
structure of the products are presented in the Table 2. In view of the success of the above mentioned
reactions, we decided to extend the study to secondary alcohols. In the case of secondary alcohols, the

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best results was obtained in the presence of K2CO3 as additive. As shown in Table 3, the reaction led
to the formation of products in relatively good yields. Some of selected compounds were isolated and
characterized by 1H NMR analysis.
Table 2. Aerobic oxidation of primary alcoholsa
a alcohol (1 mmol), catalyst (0.03 g, 4.8 mmol %), K2CO3 (0.014g, 10 mmol%, in the cases of carboxylic acid
preparation) water (5 mL) under air blowing at 80 oC, bCG measured yield.

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Table 3. Aerobic oxidation of secodary alcoholsa
OH
R2
O
R1
R1
R2
O
O
O
O
O
O
O
90 %
97 %
0.498
84 %
0.845
99 %
0.186
Yieldsb:
TOF (min-1)
99 %
1.059
99 %
0.229
0.179
O
O
O
O
O
O
Yieldsb:
TOF (min-1)
92 %
0.684
71 %
0.098
86 %
95 %
0.932
99 %
1.320
75 %
0.419
0.308
a alcohol (1 mmol), catalyst (0.03 g, 4.8 mmol %), K2CO3 (0.014g, 10 mmol%) water (5 mL) under air blowing
at 80 oC, bCG measured yield.
The kinetics of benzyl alcohol oxidation was described by a firstꢀorder rate equation for the all cases
of oxidation reactions; Equation (1).
ꢄꢈ
ꢀꢁꢂꢃꢄꢅꢆꢃꢁꢇ
=
= −ꢉꢁꢊꢋ. ꢌ
(1)
ꢄꢆ
where roxidation is the rate of oxidation reaction, the time of reaction and kobs is the rate constant.
The experiments were repeated under optimized conditions and pseudo firstꢀorder rate constants, kobs
were computed from the gradient of the graph of ln (C/Co), corresponding to ln (A/Ao) vs. reaction
time; Equation (2ꢀ4). Co was the initial concentration of benzyl alcohol, and C was the concentration at
time “t”. The activation energy for the reaction were determined from the slope of the graph of the ln
kobs vs. inverse temperature (Fig. 4).
.ꢆ
ꢌ = ꢌꢍ. ꢎꢏꢐ
(2)
(3)
ꢑꢒꢓ
ꢈ
− ln ꢈ = ꢉꢁꢊꢋ. ꢕ
ꢔ

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ꢖ = ꢗꢘꢌ
(4)
where A is benzyl alcohol UVꢀVis absorbance, ε is molar attenuation coefficient of sample and b path
length of the beam of light through the material sample.
Figure 4. Plots of ln (A/A0) vs. time (i) and Plots of ln k vs. invers temperature (ii) at optimized conditions for
oxidation of benzyl alcohol to benzaldehyde and benzoic acid, and and 1ꢀphenylethanol to acethophenone.
Table 4. Activation energy for oxidation of benzyl alcohol to benzaldehyde and benzoic acid, and and 1ꢀ
phenylethanol to acethophenone
Entry
Product
Ea (kJ.mol-1)
48.542
Benzaldehyde
Benzoic acid
Acetophenone
1
2
3
74.611
65.542
The catalyst was collect using external magnet after the completion the reaction, washed three time by
o
ethanol and water and dried at 80 C. Next, reusability of the catalyst was evaluated in the aerobic
oxidation of the primary alcohols in presence of K2CO3 for 5 times. The results show that the activity
of the catalyst was maintained after 5 time using and shown the slight decrease in yield of reaction
(Fig. 5).

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Recyclability of the catalyst
100
80
60
40
20
0
96
94
96
87
80
1
2
3
4
5
Run
Figure 5. Recyclability of the catalyst in the synthesis of benzoic acid
The proposed mechanism for oxidation of alcohols in the presence of Pt NPs was depicted below with
respect to other reports about oxidation of alcohols by transition metals.42,43
O2
Pt
B
HO
R
R
O
OH
Pt
O
BH
O O
O O
O
Pt
Pt
H
H
R
O
H
B
H
R
O
O
R
OH
R
H
2 B H2O
H2O
1/2 O2
R'
R
OH
B
O O
Pt
O
BH
H
R
1/2 O2
R'
O
R'
H2O
B
R
Figure 6. Proposed mechanism

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Conclusion
In conclusion, we demonstrated that the functionalized magnetic silica nanoparticles with poly(methylꢀ
methacrylate) using pyridinium based ionic liquid initiator by ATRP methods and immobilization of Pt
nanoparticles on this surface is an efficient and recyclable catalyst system for the selective, aerobic
oxidation of various primary and secondary alcohols. It is believed that the pyridinium groups with ester
functions of polymeric chain onto the surface of the magnetic silica are provided the paths for the
generation, stabilization, and homogeneous distribution of Pt nanoparticles and also they can
afford a means of facilitating mass transfer of the starting materials to the active sites, which
would enhance the performance of the catalyst.
Acknowledgements
The authors would like to thank Tabriz Branch, Islamic Azad University for the financial
support of this research.
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OH
OH
R1
H
R1
R2
O
Br
n
O
N
PF6
O
O
O
O
N
R1
OH
R2
R1
Pt
O
Si
O
O
N
PF6
O
Br
n
O
O
O
R1
H
O
OH
R1
H
R1, R2: alkyl, aryl