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In a typical procedure,[40] (0.4Àx) mmol Cd(NO3)·4H2O and x mmol
of HAuCl4·xH2O were mixed thoroughly in 10 mL of ethylenedia-
mine prior to the addition of thiourea (0.8 mmol) and refluxed at
1408C for 10 h. The products were obtained by centrifugation, and
were washed with distilled water and ethanol and then dried at
608C for 1 h.
Characterizations
The optical properties were studied with a UV/Vis absorption (Ana-
lytikjena specord-205) spectrophotometer, diffused reflectance
spectrophotometer (Avantes AvaSpec), and spectrofluorimeter
(PerkinElmer LS55). The bandgap energy of various samples was
evaluated by using the Tauc relation, which is given by ahn=
A(hnÀEg)1/2 where A is a constant, Eg is the bandgap of the materi-
al, a is the absorption coefficient of the material, h is the Planck
constant, and n is the frequency of light. The exact value of the
bandgap is estimated by extrapolating the straight-line portion of
(ahn)2 versus Eg to the x-axis. The surface and structural properties
were studied on a high-resolution transmission electron micro-
scope (HRTEM, FEI Technai G2 F20 operated at 200 keV with resolu-
tion of 0.2 ) and an X-ray diffractometer (PANalytical X’Pert PRO
with Cu-Ka (k=1.54060 ). Energy-dispersive X-ray (EDS) spectros-
copy was carried out on JEOL JSM-6510LB for elemental analysis.
Microwave plasma atomic emission spectrometry (Agilent Technol-
ogies 4100, MP-AES) was used for quantitative analysis of Au in
doped CdS samples. The Brunauer–Emmett–Teller (BET) specific
surface area was carried out on single-point smartsorb 92/93 using
N2 adsorption method after preheating 100 mg of the sample at
1508C for 1 h (N2/He 70:30, as calibration gases) at cryogenic tem-
perature. Related information on photocurrent–voltage measure-
ments of pure and doped samples is given briefly in the Support-
ing Information.
Figure 11. Correlation of lattice constant c, surface area, and photoredox
ability of various Au3+-doped CdS-NR catalysts.
clude that the role of metal as a co-catalyst in the photosepa-
ration of charge carriers helps in decreasing recombination
probability by prolonging the lifetime and the symmetric distri-
bution of charge carriers; this is attributed to the improvement
of ionic bond formation which dominates over their surface.
The substitution of Cd2+ by Au3+, that is, replacing an ion of
a lower valence state (+2) with an ion of a higher valence (+
3) state, imparts an extra charge in the process (Cd2+ =Au3+
eÀ) and is responsible for the higher number of electrons in
+
the reaction for photoreduction purposes.
Conclusion
Photocatalytic study
In summary, it is demonstrated that the manipulation of sur-
face structure, optical absorption and emission, photocatalytic
activity, and stability of CdS-NR could be controlled by the
doping content (1–10 mol%) of Au3+ ions, which might not be
possible for conventional Au/CdS nanocomposites made by
other deposition techniques. These modified physicochemical
properties were attributed to the charge separation ability
upon photoexcitation, uniform dispersion of Au3+ ions, surface
structural distortion, extra electrons imparted, and band edge
potentials suitable for ready charge transfer to reactant spe-
cies.
The photocatalytic activity was evaluated for the oxidation of 5 mL
salicyldehyde (0.5 mm) in water and reduction (under argon atmos-
phere) of m-dinitrobenzene (5 mm, 25 mmol) in a test tube contain-
ing 50 % isopropanol and 10 mg of AuxCd1ÀxS catalysts under sun-
light irradiation (40–50 mWcmÀ2). The reaction samples (after filtra-
tion through a 0.22 mm cellulose filter) were analyzed by UV/Vis
spectrophotometry and high-performance liquid chromatography
(HPLC, Agilent 1120 Compact LC) using a C-18 column and MeOH/
H2O (70:30) as a mobile phase at with detection at l=254 nm and
a flow rate of 1 mLminÀ1. Gas chromatography coupled with mass
spectroscopy (GC-MS, Shimadzu, GC-2010 and GC-MS-QP 2010
plus with RTX-5Sil-MS column (15 m0.25 mm0.25 mm) of reac-
tion samples was carried out in methanol solvent after extraction
with dichloromethane. The CO2 evolution was determined by gas
chromatography (GC, NUCON-5765 equipped with a thermal con-
ductivity detector (TCD)) by injecting a 1 mL gas sample into
a Propak-Q column with a nitrogen gas flow (30 mLminÀ1). All the
physical properties of bare and doped samples are summarized in
Table 1 in the Supporting Information.
Experimental Section
Materials and methods
Cadmium nitrate tetrahydrate (Cd(NO3)2·4H2O), ethylenediamine
(H2NCH2CH2NH2), thiourea (SC(NH2)2), hydrogen tetrachloroaura-
te(III) hydrate (HAuCl4.xH2O), m-dinitrobenzene (C6H4N2O2), m-phe-
nylenediamine (C6H8N2O2), m-nitroaniline (C6H4N2O2), 3-mercapto-
propionic acid (C3H6O2S), salicyldehyde (C7H6O2), and isopropanol
(C6H8O) were purchased from Loba Chemicals and used without
further purification. Deionized water was obtained using an ultrafil-
tration system (Milli-Q, Milipore) with a measured conductivity
35 mhocmÀ1 at 258C.
Acknowledgements
This study was supported by a grant from the Department of Sci-
ence and Technology (DST), India (Sanction order no. SR/NM/NS-
40/2008) with partial financial support from the Rajiv Gandhi Na-
ChemPlusChem 2015, 80, 851 – 858
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