Full Paper
Synthesis of carboxylated GO[27]
Advance diffractometer at 40 kV and 40 mA with CuKa radiation
(l=0.15418 nm). Sample for XRD was prepared by the deposition
of well-dispersed graphene–CoPc on glass slide followed by
drying; the analysis was performed by using cobalt as the target
material. Thermogravimetric analyses (TGA) of these samples were
carried out by using a thermal analyzer TA-SDT Q-600. All samples
were analyzed in the temperature range of 40 to 9008C at a heat-
ing rate of 108Cminꢀ1 under the nitrogen flow. The porous proper-
ties of GO and GO–CoPc catalysts were examined by N2 adsorp-
tion/desorption isotherms at 77 K and the related data (surface
area, SBET; pore volume, PV; Micromeritics ASAP 2010) were calcu-
lated. XPS measurements were obtained on a KRATOS-AXIS 165 in-
strument equipped with dual aluminum–magnesium anodes by
using MgKa radiation (hn=1253.6 eV) operated at 5 kV and 15 mA
with pass energy 80 eV and an increment of 0.1 eV. To overcome
the charging problem, a charge neutralizer of 2 eV was applied
and the binding energy of C1s core level (BEffi84.6 eV) of adventi-
tious hydrocarbon was used as a standard. The XPS spectra were
fitted by using a nonlinear square method with the convolution of
Lorentzian and Gaussian functions, after a polynomial background
was subtracted from the raw spectra. The conversions and selectiv-
ity of the products were determined by high-resolution GC-FID
(Varian CP-3800). 1H NMR spectra of the products were recorded
on 500 MHz by using Bruker Avance-II 500 MHz instrument. ICP-
AES analysis was carried out by inductively coupled plasma atomic
emission spectrometer (ICP-AES, DRE, PS-3000UV, Leeman Labs
Inc., USA). Samples for ICP-AES were prepared by leaching out
0.01 g of sample with HNO3 (conc.), and then heated for 30 min
and volume to 10 mL.
In a typical experiment, GO (200 mg) was dispersed in deionized
water (100 mL) by using ultrasonicator to give a concentration of
2 mgmLꢀ1. The obtained suspension was treated with NaOH
(1.2 g) and chloroacetic acid (1.0 g) for 3 h over ultrasonicator bath
to convert the OH groups into COOH groups. The resulting GOꢀ
COOH product was neutralized by using a dilute HCl solution and
purified by repeated washing with deionized water and dried
under vacuum.
Immobilization of CoPc–tetrasulfonamide to carboxylated
GO[28,29]
Carboxylated GO (GOꢀCOOH; 200 mg) was added in DMF (1 mL)
and treated with excess thionyl chloride at 658C for 12 h to obtain
its acyl chloride derivative. Unreacted thionyl chloride was re-
moved by vacuum distillation. The product was washed with THF
(three times) and vacuum dried. The obtained GO-Cl (100 mg) was
heated at reflux with cobalt phthalocyanine tetrasulfonamide [Co-
Pc-(SO2NH2)4 complex (100 mg) in DMF under nitrogen atmos-
phere. The GO-immobilized CoPc complex was separated from the
mixture by filtration, washed with ethanol (3–4 times) by using
centrifugation and membrane filtration. The GO immobilized CoPc
complex was dried in an oven. The analytical values for the GO-
supported CoPc were found to be C 59.67, H 3.073, N 5.468, and S
4.75 %. The cobalt content in synthesized GO–CoPc was estimated
by ICP-AES analysis, and the value was found to be 1.13 wt% Co.
Based on the value of cobalt, the loading of the CoPc in GO–CoPc
After the photoreduction, the mixture was analyzed by GC. The
gaseous phase was analyzed by GC-thermal conductivity detector
(TCD) and GC-FID (Agilent 7890 A GC system) by using a column
(RGA, refinery gas analyzer) at the flow rate (H2 35, air 350, make-
up flow 27 mLminꢀ1, for TCD reference flow-45 mLminꢀ1, helium
flow 2 mLminꢀ1), injector temperature 2208C, TCD detector tem-
perature and FID detector temperature(2208C). Liquid samples
were analyzed with GC-FID model Varian CP3800 (column specifica-
tion: Stabilwax w/Integra-Guard, length 30 m, 0.25 ID) at the flow
rate 0.5 mLminꢀ1, injector temp 2508C, FID detector temperature
2758C. Autosampler (model no. Varian CP 8410) was used for in-
jecting the same amount of sample (1 mL). Calibration curve was
plotted with the help of auto sampler by injecting one microliter
sample (Figure S3 in the Supporting Information).
was found to be 2.3 mmolgꢀ1
.
Photocatalytic CO2-reduction experiment
Photocatalytic experiment was performed in borosil cylindrical
vessel (100 mL) of 5 cm diameter (Figure 1). Photoirradiation was
carried out under visible light by using 20 W white cold LED flood
light (model no. HP-FL-20W-F-Hope LED Opto-Electric Co., Ltd.). In-
tensity of the light at vessel was measured by intensity meter and
was found to be 75 Wmꢀ2. The vessel was charged initially with
water (40 mL) and triethylamine (10 mL), and then the solution
was degassed by continuous purging of nitrogen for 15 min. CO2
was bubbled through the solution for at least 30 min to saturate
the solution, then catalyst (100 mg) was added to the above-de-
scribed solution. The vessel was tightly closed during the reaction
and stirred continuously by a magnetic stirring bar to prevent sedi-
mentation of the catalyst. Samples were collected after every 2 h
by using a long needle, and the catalyst was removed with syringe
filter (2 nm PTFE, 13 mm diameter). Quantitative determination
was done by using GC-FID (flow rate 0.5 mLminꢀ1, injector temper-
ature 2508C, FID detector temperature 2758C). A calibration curve
was prepared for quantification and for confirmation of linear re-
sponse of GC-FID system.
Synthesis of graphene oxide (GO)
Graphene oxide (GO) was synthesized from graphite flakes by
using modified Hummers methods.[11] In a typical synthesis, con-
centrated H2SO4 (34 mL) was added into a flask containing graphite
flakes (1 gm) and sodium nitrate (0.75 gm) under stirring at 08C
(ice bath). Approximately 4.5 gm of KMnO4 was added gently over
20 min to the mixture and kept under stirring at RT for five days.
After that, diluted H2SO4 (50 mL, 5 wt%) was added into the mix-
ture and heated to 908C under continuous stirring for 2 h. Then,
H2O2 (30 wt%; 2.7 mL) was added into the solution and stirred for
another 2 h under ambient conditions. After completion of the re-
action, the mixture was centrifuged (6000 rpm, 15 min) and
washed with H2SO4 (3 wt%), H2O2 (0.5 wt%), and HCl (3 wt%), and
then repeatedly washed with distilled water, until the pH of the fil-
trate became neutral. Finally, the prepared GO was dispersed in
distilled water and the homogeneous GO dispersion was then cen-
trifuged and filtered.
Blank reactions were conducted to ensure that methanol produc-
tion was due to the photoreduction of CO2 and to eliminate sur-
rounding interference. One blank was Vis-illuminated without the
catalyst, and another one was kept in the dark with the catalyst
and CO2 under the same experimental conditions. An additional
blank test was Vis-illuminated with the catalyst filling N2 rather
than CO2. No product was detected in the above-described three
blank tests.
Chem. Eur. J. 2014, 20, 1 – 9
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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