18
S. Verma et al. / Applied Catalysis A: General 489 (2015) 17–23
Scheme 1. Synthesis of magnetically separable palladium(II) complex immobilized to graphene oxide 1.
2. Experimental
was allowed for continue stirring at room temperature for 24 h.
Subsequently, 80 ml water was slowly added and temperature of
reaction mixture was raised to 98 ◦C using an oil bath. After another
24 h, 200 ml of water was added, followed by another addition of
30% H2O2 (20 ml). Finally, oxidation product was filtered and puri-
fied by rinsing with 50 ml of 5% HCl solution. The filtrate cake was
repeatedly washed with copious amount of HPLC grade water until
the pH was about 6. This processed dark brown oxidized material
was dried in oven at 90 ◦C. The dried product was grounded with a
mortar and pestle to the fine powder.
2.1. Materials
Graphite powder and PdCl2 was purchased from Sigma–Aldrich
and used as received. KMnO4, H2SO4, NaNO3, HCl, NaOH, FeCl3,
ethylene glycol, and sodium acetate were obtained from Merck
(India). All the chemicals were of analytical grade and used without
further purification.
2.2. Techniques used
2.4. Synthesis of iron nanoparticles containing
graphene–magnetite nanocomposite
Fourier transform infrared spectroscopy (FT-IR) was conducted
by Perkin–Elmer spectrum RX-1 IR spectrophotometer. High res-
olution transmission electron microscopy (HR-TEM) and energy
dispersive X-ray spectroscopy (EDAX) of the nanocomposites was
executed using Phillips CM 200 operating at an acceleration volt-
age of 200 kV. Scanning electron microscopy (SEM) was performed
by Jeol Model JSM-6340F. For FE-SEM analysis aqueous dispersions
of GO and graphene–metal nanocomposites were deposited on the
glass slides, while very dilute aqueous suspensions were deposited
on carbon coated copper grids for HR-TEM analysis. The phase char-
acterization was carried out by X-ray diffractometer (XRD; model
No. PW1710). Sample for XRD was prepared by the deposition of
well dispersed graphene–metal nanocomposite on glass slide fol-
lowed by drying; the analysis was performed by using cobalt as
the target material. The conversions and selectivity of the products
were determined by high resolution GCMSD, EI, quadrapole mass
analyzer, EM detector. 1H NMR and 13C NMR spectra of the products
were performed at 500 MHz by using Bruker Avance-II 500 MHz
instrument. ICP-AES analysis was carried out by inductively cou-
pled plasma atomic emission spectrometer (ICP-AES, PS-3000UV)
by Leeman.
In the typical synthesis, graphene oxide (200 mg) was dispersed
in water (80 ml) through sonication for 30 min. The mixture of
ferrous sulphate (0.5 g, 1.7 mmol), PEG 4000 (1.0 g) and double dis-
tilled water (5 ml) was added slowly in to the GO solution with
vigorous stirring for 24 h. Total volume of solution was made up to
approx. 1 l by adding water. After 1 h, NaBH4 (1 g, 26 mmol) added
to this reaction mixture at 80 ◦C and kept it for next 2 h. The black
colored iron nanoparticles supported graphene oxide 2 was sepa-
rated by external magnet and washed with water and dried at 65 ◦C
under vacuum.
2.5. Synthesis of magnetically separable Pd(II) complex
immobilized to GO 1
A
solution of homogeneous palladium complex, i.e.
PdCl2(CH3CN)2 (0.25 g, 1 mmol) in dichloroethane (10 ml) was
mixed with magnetite–graphene nanocomposite (1 g) and the
resulting suspension was heated at 80 ◦C under stirring for 4 h. The
yellowish colored heterogeneous Pd+2/Fe/FeO/graphene nanocom-
posite was collected by magnetic separation and washed several
times with water, ethanol, and acetone, respectively. Finally the
sample was dried at 80 ◦C for 2 h under vacuum. The catalyst
was stored at room temperature without taking any precaution.
The weight percentage of palladium in the final catalyst was
found to be 10.23 wt% (0.96 mmol/g) as determined by induc-
tively coupled plasma-atomic emission spectroscopy (ICP-AES)
analysis.
2.3. Preparation of graphene oxide (GO)
Graphene oxide (GO) was prepared by harsh oxidation of
graphite powder. In a typical procedure, graphite powder (1.0 g),
NaNO3 (1.0 g) and H2SO4 (45 ml) were mixed in a reaction vessel
on an ice bath. This is followed by gradually addition of KMnO4
(6.0 g) under maintained temperature and then reaction mixture