Preparation, surface and crystal structure, band energetics, optoelectronic, and photocatalytic properties of AuxCd1-xS nanorods

Article abstract of DOI:10.1002/cplu.201402388

A series of novel Au_xCd_1-xS materials (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) were prepared and their optical properties, structural-surface morphology, and photocatalytic activity for oxidation and reduction reactions under visible-light irradiation were studied. X-ray diffraction confirmed the shrinkage of the hexagonal crystal structure of CdS; the lattice parameters decreased as a=4.190→4.072 ? and b=c=6.790→6.635 ? with increased loading (1-10 mol%) of the Au³⁺ dopant. Optical spectra of Au_xCd_1-xS revealed a significant red-shift (485→538 nm) of the absorption onset and band edge emission (506→530 nm) with notable quenching in photoluminescence. The bandgap energy decreases (2.71→2.41 eV) with increasing Au³⁺ doping of the CdS nanorods along with considerable shifting of valence band (+1.13→+1.04 eV) and conduction band positions (-1.58→-1.36 eV) versus NHE. The surface area of bare CdS (90.56 m² g^-1) is gradually reduced to 12.32 m² g^-1 with increasing Au³⁺ doping content. The photocatalytic activity considerably improves with doping, where the Au_0.1Cd_0.9S composite displays the highest levels of photooxidation (95%) of 0.5 mM salicyldehyde and reduction of 5 mM m-dinitrobenzene to m-nitroaniline (44 %) and m-phenylenediamine (52 %) relative to bare CdS (50 %) probably due to the homogeneous dispersion of Au³⁺ ions throughout CdS crystal, their superior band-energetics for facile charge-separation and better photostability.

Full text of DOI:10.1002/cplu.201402388

DOI: 10.1002/cplu.201402388
Full Papers
Preparation, Surface and Crystal Structure, Band
Energetics, Optoelectronic, and Photocatalytic Properties
of AuxCd1ÀxS Nanorods
Rohit Singh and Bonamali Pal*[a]
A series of novel AuxCd1ÀxS materials (x=0, 0.01, 0.02, 0.03,
0.05, 0.07, 0.1) were prepared and their optical properties,
structural-surface morphology, and photocatalytic activity for
oxidation and reduction reactions under visible-light irradiation
were studied. X-ray diffraction confirmed the shrinkage of the
hexagonal crystal structure of CdS; the lattice parameters de-
creased as a=4.190!4.072 Š and b=c=6.790!6.635 Š with
increased loading (1–10 mol%) of the Au3+ dopant. Optical
spectra of AuxCd1ÀxS revealed a significant red-shift (485!
538 nm) of the absorption onset and band edge emission
(506!530 nm) with notable quenching in photoluminescence.
The bandgap energy decreases (2.71!2.41 eV) with increasing
Au3+ doping of the CdS nanorods along with considerable
shifting of valence band (+1.13!+1.04 eV) and conduction
band positions (À1.58!À1.36 eV) versus NHE. The surface
area of bare CdS (90.56 m2 gÀ1) is gradually reduced to
12.32 m2 gÀ1 with increasing Au3+ doping content. The photo-
catalytic activity considerably improves with doping, where the
Au0.1Cd0.9S composite displays the highest levels of photooxi-
dation (95%) of 0.5 mm salicyldehyde and reduction of 5 mm
m-dinitrobenzene to m-nitroaniline (44%) and m-phenylenedi-
amine (52%) relative to bare CdS (50%) probably due to the
homogeneous dispersion of Au3+ ions throughout CdS crystal,
their superior band-energetics for facile charge-separation and
better photostability.
Introduction
Recently, anisotropic nanocrystals (NC) such as nanorods (NR)
and nanowires (NW) have attracted widespread attention.[1–5]
In contrast to conventional spherical nanoparticles, in these
materials many beneficial physicochemical properties[6–11] can
be improved owing to the availability of different atomic
planes on crystal facets, the two-dimensional quantum con-
finement effect, their larger per-particle surface area, high dif-
fusion of charge carriers, length to diameter controlled absorp-
tion and emission, and extended lifetime of photogenerated
charge carriers. In this context, metallic or semiconducting
nanostructures with different anisotropies have been broadly
studied[12–14] for photovoltaic applications and for the photoca-
talytic production of hydrogen and degradation of toxic pollu-
tants. It is well proven that the activity of a semiconductor (SC)
can be further improved by modifying its surface with metal
nanoparticles (NPs). The free electrons will transfer from the
semiconductor to the metal (M) side (if fm >fs) until their
Fermi levels are aligned by generation of a Schottky barrier
through the M–SC interface.[15–17] As a result, various nanocom-
posites such as Cu/ZnO, Au/CeO2, Pt/CdS, Au/ZnO, and sulfur/
graphene (S/GR) have been studied[16–21] to improve charge
separation for facile photophysical and chemical properties. It
has been well-accepted that photoactivity is highly dependent
upon the size distribution of the deposited metal particles, and
the interfacial contact area and nature of metal–support inter-
actions. Conventional metal deposition techniques lead to un-
controlled and irregular size distribution of metal particles
onto the SC surface[13,22,23] that have a poor electrical contact,
that is, M-NPs are present only on the surface and not at all
uniformly throughout the crystal. Moreover, the higher amount
of metal ions present would act as recombination centers for
eÀ/h+ pairs[24] through the process described by Equation (1).
eÀ
ð1Þ
M
nþ þ n ! M0þ
CB
Before recombination, eÀ/h+ pairs are well separated by
a large electric field within the space charge region. But when
the metal concentration increases, this region becomes nar-
rower and the depth of light that can penetrate the SC ex-
tends beyond the space charge region. As a result, the recom-
bination of photogenerated eÀ/h+ pairs in the SC increases as
there is no driving force to separate them. This means that im-
provement in photoactivity is always governed by the number
of metal particles deposited in the semiconductor and not by
their loading. In contrast, metal ion doping is believed to im-
prove the physicochemical properties because it can lead to
a shift of band edge levels that drive oxidation and reduction
reactions. The creation of doping levels results in the narrow-
[a] R. Singh, Dr. B. Pal
School of Chemistry and Biochemistry
Thapar University
Patiala, Punjab 147 004 (India)
Fax: (+91)175-2364498
E-mail: bpal@thapar.edu
Supporting information for this article (including preparation of Au3+
-
doped CdS/TiO2 solar cells, EDS and MP-AES analysis, absorption spectra,
summary of various physical properties of AuxCd1ÀxS sample, and GC-MS
traces) is available on the WWW under http://dx.doi.org/10.1002/
cplu.201402388.
ChemPlusChem 2015, 80, 851 – 858
851
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
ing of the band gap for higher visible spectral response, suita-
ble stable structures, homogeneous distribution of charge, and
more importantly the improvement of ionic bond formation.
Cadmium sulfide (CdS), a visible-light-driven photocatalyst
having band gap of roughly 2.4 eV and suitable negative flat-
band potential, is a promising material. However, some short-
comings, such as quick recombination of photogenerated
charge carriers and photodissolution during the photocatalytic
reaction in aqueous medium, have restricted its practical appli-
cation. Literature reports[25–27] revealed that the intentional in-
corporation of Mn+ ions into crystal lattices by replacing some
extra charge and creates more defects sites in the CdS crystal,
which may help in effective separation and migration of the
photoexcited charge species for improved photocatalytic prop-
erties.
Thus, in the present study, AuxCd1ÀxS (x=0, 0.01, 0.02, 0.03,
0.05, 0.07, 0.1) nanorod composites were prepared in order to
study the modified optoelectronic properties, band gap
energy, band positions, surface and structural changes, cur-
rent–voltage characteristics, and photocatalytic activity for the
model oxidation and reduction reactions under sunlight irradi-
ation.
Cd2+ ions led to a homogeneous dispersion of Mn+xCd1Àx
S
junctions throughout the crystal, which is believed to result in
better ohmic contact relative to that of M-CdS composites
made by deposition (see Scheme 1). To address this, various
Mn2+-, Cu2+-, Ni2+-, and In3+-doped CdS nanoparticles were
studied[28–31] in order to improve visible response and enhance
photocatalytic activity, durability, and efficiency in solar cells.
However, the doping of Au3+ into CdS-NR has not been inves-
tigated despite their comparable dimensions (Au3+ =0.85 Š,
Cd2+ =0.97 Š),
Well-matched bands energetics,[32,33] quick Fermi level equili-
bration, and the homogeneous dispersion of Au3+ ions into
the elongated CdS-NR crystal were expected due to the better
diffusion of charge carriers along the crystallographic c-axis.
The doping of Au3+ at different concentration levels into CdS-
NR was presumed to result in a change in the conduction
band and valence band edge positions, which facilitates the
transfer of eÀ and h+ for corresponding reduction and oxida-
tion processes. Moreover, Au3+ doping into CdS-NR imparts
Results and Discussion
Structural and morphological analysis
Figure 1 shows X-ray diffraction peaks of AuxCd1ÀxS (x=0, 0.01,
0.02, 0.03, 0.05, 0.07, 0.1) composites having characteristics of
the hexagonal phase of the wurtzite crystal structure (JCPDS
No. 41-1049). No peaks of any other segregated phases (Au3+
or AuS) or impurities were detected even at 10 mol% loading,
indicated the effective doping of Au3+ into the CdS hexagonal
crystal. The relatively intense (002) diffraction peak indicates
that the CdS-NR have grown along the crystallographic c-axis.
Figure 1b (enlarged view; 2q=22–328) shows that the peak
positions of the (100), (002), and (101) planes are slightly red-
shifted with the increase in Cd2+/Au3+ molar ratio. The 2q
value along the (002) diffraction plane exhibits a red-shift from
26.2178 to 26.8448 with increasing loading of Au3+ (0!
Scheme 1. Schematic representation of structural and morphological difference in CdS nanorods after Au3+ doping and deposition.
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
852
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
and doped samples. As shown
in Figure 3, CdS particles are
found to have a rodlike shape
with a diameter of about 5–
10 nm and a length of 100–
200 nm. These nanorods are
well dispersed and do not dis-
play morphological changes
even after the doping of 2 and
5 mol% Au3+ into CdS lattices.
The interplaner distance notably
increases 0.34<0.39<0.45 nm
for the bare, 2 mol% and
5 mol% Au3+-doped CdS-NR,
respectively, which completely
agrees with their profile of
frame at different portions of
the image and might be due to
differences in their ionic radii.
EDS analysis also confirms the
presence of Cd, S, and Au in the
Figure 1. a) XRD patterns of AuxCd1ÀxS samples (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) and b) an enlarged view of
the peaks corresponding to the (100), (002), and (101) crystal planes.
AuxCd1Àx
S
nanostructure. Au
10 mol%), which is quite reasonable because the ionic radius
of Cd2+ (0.97 Š) is larger than that of Au3+ (0.85 Š).
was found to be present in reasonable loadings: 0.70, 2.88,
6.40, and 8.88 atom% for the 1, 3, 7, and 10 mol% Au3+
-doped CdS samples (SI-Figure 1). Furthermore, the microwave
plasma atomic emission spectrometry (MP-AES) analysis re-
vealed 0.28, 2.54, 5.29, and 6.69% of Au in 1, 2, 5 and 7 mol%
Au3+-doped CdS samples, respectively (SI-Figure 2).
The surface area (Table S1) of bare CdS-NR (90.56 m2 gÀ1) sig-
nificantly decreased to 12.32 m2 gÀ1 after increasing levels of
Au3+ incorporation, which might be attributed to the partial
filling of pores in the CdS nanocrystals and surface morpholog-
ical changes.
The lattice constants (a=4.190!4.072 Š and b=c=6.790!
6.635 Š) were found to decrease with increasing Au3+ loading,
indicating the replacement of Cd2+ ions with Au3+. The expo-
nential behavior of the lattice constants of CdS-NR with in-
creasing Au3+ loading is shown in Figure 2. These results are
not in line with Vegard’s law,[34] which indicates a linear rela-
tionship between the lattice constants and the dopant concen-
tration for a homogeneous solid solution. Therefore, it is pre-
sumed that there is an optimum level of Au3+ doping into CdS
crystal, above which it will no longer behave as a solid solu-
tion.
Optical study
High-resolution transmission electron microscopy (HRTEM)
and energy-dispersive X-ray spectroscopy (EDS) analysis have
been carried out to elucidate the size, shape, crystallinity, lat-
tice interplaner distance, and elemental composition of bare
The absorbance of CdS-NR (SI-Figure 3) is significant red-shift-
ed (485!538 nm) with an increase upon Au3+ doping. Clearly,
CdS-NR formed in the absence of thiol groups exhibited ab-
sorbance around 510–515 nm (not shown here), which indi-
cates the role of a stabilizing agent in providing less agglomer-
ated nanoparticles. Interestingly, AuxCd1ÀxS samples do not ex-
hibit any characteristic surface plasmon band (SPR) despite
having a high loading of Au3+ probably due to the mixing of
electronic states at the Au3+–CdS interface. This is consistent
with previous reports[25,35] which explain that in this type of
strong composites the boundary effect of Au is significantly re-
duced due to the delocalization of plasma electrons into the
CdS portion and therefore the exciton as well as the plasmon
band is suppressed. The above results show that the absorp-
tion spectrum is broadened by the doping of Au3+; this indi-
cates that doped samples have greater carrier concentration.
Figure 4a shows that the band gap energies decrease
(2.71!2.41 eV) with increasing Au3+ doping in the AuxCd1Àx
S
composites. The increase in the Au3+ doping level in CdS-NR
results in the narrowing of energy band positions, which indi-
cates that the as-synthesized doped samples are adducts but
Figure 2. Variation of lattice parameters with increasing Au3+ doping into
the CdS-NR crystal structure.
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
853
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
are found to decrease from
+1.13 to 1.04 eV with increas-
ing x content in AuxCd1ÀxS sam-
ples. The band structure model
suggests that band gap posi-
tions of various doped samples
can be adjusted continuously
by changing the Au3+/Cd2+
ratio in AuxCd1ÀxS nanostruc-
tures.
The change in the photolumi-
nescence (PL) emission spectra
of CdS-NR with an increase in
Au3+ loading on excitation at
380 nm in ethanol suspension
(1 mgmLÀ1) is shown in Fig-
ure 6a. In general, PL originates
either from the band edge that
is, due to the recombination of
eÀ/h+ pairs or surface defects
i.e., the radiative recombination
of trapped charge carriers at
the defect sites. Au3+ doping at
increasing concentration levels
in CdS-NR resulted in a slight
red-shift (505!512 nm) in the
band edge emission and higher
luminescence quenching. The
introduction of Au3+ into CdS
structure by replacing some
Cd2+ ions facilitates higher sep-
aration of charge by the shut-
tling of photogenerated elec-
Figure 3. HRTEM images of pure and Au3+-doped CdS nanoparticles, their lattice interplaner distances, profile of
frame for the average fringe width, and energy-dispersive X-ray spectra.
substituted products. The was further supported by their varia-
tion in color from light yellow to golden yellow (Figure 4b) rel-
ative to the light yellow color of bare CdS-NR.
trons. The delocalization of charge carriers is extended which
prevents their recombination. It is assumed from PL spectra of
doped samples that some defect states are generated near the
highest occupied VB level prior to recombination of charge
carrier (see Figure 6b).
The band edge positions of various AuxCd1ÀxS samples were
calculated as a function of their band gap energies (Figure 5).
To determine the conduction band (CB) edge positions in rela-
tion to the normal hydrogen electrode potential (NHE), Equa-
tion (2)[34,36] was employed.
Photochemical activity
Current–voltage (I–V) characteristics
ECB ¼ X À Ee À 0:5Eg
ð2Þ
As a significant change in the band edge positions in
AuxCd1ÀxS nanostructures has been observed, it is very interest-
ing to study the I–V characteristics of bare and doped sample
to explore their plausible change upon changes in the charge
carrier concentrations. As shown in Figure 7, ruthenium-based
N719 dye sensitized CdS-NR on a TiO2 support gives a short cir-
cuit current of Jsc =0.270 mAcmÀ2, an open circuit voltage of
Voc =23.9 mW), a fill factor of 0.283, and an efficiency h of
1.82”10À3 %. This trend is somewhat improved in 10 mol%
Au3+-doped CdS-NR with Jsc=0.552 mAcmÀ2, Voc =47.4 mW,
a fill factor of 0.246, and an efficiency h of 6.46”10À3 %.
Though the efficiency of the bare and doped samples is not
Here ECB is the conduction band potential, X is the electrone-
gativity of a semiconductor, and is defined as the arithmetic
mean of the first ionization energy and electron affinity, Ee is
the energy of free electrons on the hydrogen scale and that is
equal to 4.5 eV, and Eg is band gap energy of a given semicon-
ductor. The CB positions were found to decrease from À1.58
to À1.36 eV with increasing value of x in AuxCd1ÀxS (x=0, 0.01,
0.02, 0.03, 0.05, 0.07, 0.1).The valence band (VB) edge positions
determined by using Equation (3)
satisfactory, the minute difference in the efficiency of AuxCd1Àx
nanostructure justifies the role of the metal dopant in prevent-
S
EVB ¼ ECB þ Eg
ð3Þ
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
854
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
Figure 7. a) Current density–voltage characteristics for bare and 10 mol%
Au3+-doped CdS-NR.
ing charge recombination and increasing the light absorption/
harvesting capacity.
As shown in Figure 8A, an exponential decrease in the con-
centration (C/Co) of salicyldehyde was observed in the pres-
ence of bare and various doped AuxCd1ÀxS samples; this was
alsoevident from the change in the absorbance spectra (SI-
Figure 4) during salicyldehyde photooxidation under sunlight
irradiation. The photooxidation (%) was found to improve from
58 to 95% for the 1 and 10 mol% Au-doped samples, respec-
tively, after 3 h of light exposure. This observed trend can be
explained on the basis of the shift in VB edge positions for
facile charge separation and decrease in band gap energies
which may favor the harvesting of excitation energy and the
homogeneous dispersion of Au3+-CdS junctions for better
Fermi level equilibration in AuxCd1ÀxS samples. It seen in Fig-
ure 8B that a linear increase in CO2 evolution is noticed in the
first 2 h and a steady rate is found thereafter. The CO2 produc-
tion after 3 h exposure to sunlight was found to increase from
22% to 50% for the 10 mol% doped CdS-NR relative to pure
CdS-NR.
Figure 4. a) Band gap energy plots and b) colors of various AuxCd1ÀxS sam-
ples (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1).
Photoreduction of m-dinitrobenzene (m-DNB)
The influence of the change in CB positions of CdS-NR at in-
creasing Au3+ doping levels on its reduction ability was investi-
gated with the photoreduction of m-dinitrobenzene (5 mm)
under sunlight irradiation. The photocatalytic activity notably
improved with increasing Au3+ loading where AuxCd1ÀxS (x=
0.1) composites displayed the highest reduction
(92%) of 5 mmm-dinitrobenzene to m-nitroaniline
(yield=44%) and m-phenylenediamine (yield=
52%). Figure 9 shows a plot of mmol of m-DNB con-
sumed with time and the amount of m-NA and m-
PDA products formed. The product distribution was
studied by GC-MS analysis (SI-Figure 5), which con-
firmed the presence of m-DNB, m-NA, and m-PDA at
retention times 17.6, 16.8, and 13.5 min, respectively,
during 5 h reaction.
Figure 5. Variation of conduction and valence band edge position of various
AuxCd1ÀxS samples (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) samples.
The fact that the photoefficiencies improve with
increasing Au3+ doping content in the AuxCd1Àx
S
crystal can be well explained on the basis of a sym-
metric distribution of Au3+–CdS interfaces, which re-
sults in better separation of charge carriers. The
Figure 6. a) Change in photoluminescence (PL) spectra of CdS-NR with increasing levels
of Au3+ doping. b) Proposed diagram for luminescence in doped samples.
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
855
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
morphology of bare and
10 mol% Au3+-doped CdS-NR is
further confirmed by XRD dif-
fraction (Figure 10, bottom) pat-
tern before and after successive
cycles of salicyldehyde photo-
degradation under sunlight.
The intensity of all diffraction
peaks for bare CdS-NR (especial-
ly for the (002) plane) is notably
decreased and becomes broad
due to partial dissolution of CdS
after five successive cycles,
whereas no such changes in the
XRD pattern of 10 mol% Au3+
-doped CdS-NR are observed
after the photoreaction under
Figure 8. A) Plot of the time course of photooxidation of salicyldehyde (0.5 mm) under sunlight irradiation over
a) CdS and Au3+-doped CdS nanorods at dopant levels of b) 1 mol%, c) 2 mol%, d) 3 mol%, e) 5 mol%, f) 7 mol%,
g) 10 mol%. B) CO2 evolution (%) in the presence of various bare and Au3+-doped CdS samples.
same conditions. Thus, it revealed that the Au3+-doped CdS
sample exhibits excellent stability and does not decompose or
photocorrode during the photocatalytic reaction.
As evident from the comparative graph of surface area, lat-
tice constant c, and photoactivity (Figure 11) an increase in the
doping level (or mol%) of Au3+ in CdS (up to 10 mol%) result-
ed in a decrease in its surface area and lattice constant and an
increases in its photooxidation and -reduction ability(%). This
inverse surface area/photoactivity relationship leads us to con-
Figure 9. Photocatalytic efficiency for m-DNB (5 mm) reduction by various
AuxCd1ÀxS samples (x=0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) after 5 h of sunlight
irradiation.
doping of Au3+ ions into the CdS matrix imparts extra negative
charge to the crystal, which results in its higher reduction abili-
ty. More importantly, the change in CB edge positions from
À1.58!À1.36 eV results in facile charge transfer to reaction
species (ÀNO2), whose reduction potential (À0.8 eV) lies much
closer to that of the 10 mol% Au3+-doped CdS sample. Also,
the conduction band minimum of CdS at À1.36 eV is more
negative than the Fermi level of Au (À1.3 eV on NHE
scale).[37,38] Therefore, in the Au/CdS system, better Fermi level
equilibration takes place, which results in suppression of the
recombination of charge carriers and makes them available for
corresponding reduction and oxidation processes.
It is well known that CdS often decomposes during a photo-
chemical reaction, which deteriorates its activity.[39] As shown
in Figure 10 for the salicyldehyde photo-oxidation in the pres-
ence of bare CdS-NR, catalyst degradation on the order of
21% was recorded after five repeated cycles due to its photo-
chemical dissolution upon light irradiation. In contrast, the
10 mol% Au3- doped CdS-NR effectively photodegraded the
salicyldehyde without any significant deactivation even after
a similar recycling process, which indicates its higher stability
and activity; only a slight decrease (4%) in photoefficiency is
noticed after five cycles. Any change in the surface structural
Figure 10. Photocatalytic activity and stability during reaction cycles with
bare and 10 mol% Au3+-doped CdS-NR for degradation of salicyldehyde
(0.5 mm, 100 mL, 0.2 g) under 3 h of sunlight irradiation and the relative
change in XRD patterns.
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
856
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
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 Š) and an X-ray diffractometer (PANalytical X’Pert PRO
with Cu-Ka (k=1.54060 Š). 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 m”0.25 mm”0.25 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
www.chempluschem.org
857
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
[21] W. Peng, X. Li, Nano Res. 2013, 6, 286–292.
tional Fellowship (Sanction order no. F-16–1886(SC)/2010(SA-III))
by Ministry of Social Justice and Empowerment, India. We would
like to acknowledge Sophisticated Analytical Instruments Labora-
tories (SAI), Thapar University for access to analytical facilities.
[22] R. Singh, B. Pal, J. Mol. Catal. A: Chem. 2013, 378, 246–254.
[23] Z. Mei, S. Ouyang, D. M. Tang, T. Kako, D. Golbergc, J. Ye, Dalton Trans.
2013, 42, 2687–2690.
[24] S. Liu, E. Guo, L. Yin, J. Mater. Chem. 2012, 22, 5031–5041.
[25] F. Yang, N. N. Yan, S. Huang, Q. Sun, L. Z. Zhang, Y. Yu, J. Phys. Chem. C
2012, 116, 9078–9084.
Keywords: CdS nanostructures · band energetics · crystal
phase distortion · doping · photocatalysis
[26] L. Ren, F. Yang, Y. R. Deng, N. N. Yan, S. Huang, D. Lei, Q. Sun, Y. Yu, Int.
J. Hydrogen Energy 2010, 35, 3297–3305.
[27] Y. F. Li, D. Xu, J. I. Oh, W. Z. Shen, X. Li, Y. Yu, ACS Catal. 2012, 2, 391–
398.
[28] T. Zuo, Z. Sun, Y. Zhao, X. Jiang, X. Gao, J. Am. Chem. Soc. 2010, 132,
6618–6619.
[1] C. J. Murphy, N. R. Jana, Adv. Mater. 2002, 14, 80–82.
[2] S. H. Kang, S. H. Choi, M. S. Kang, J. Y. Kim, H. S. Kim, T. Hyeon, Y. E.
Sung, Adv. Mater. 2008, 20, 54–58.
[29] M. Luo, Y. Liu, J. Hu, H. Liu, J. Li, ACS Appl. Mater. Interfaces 2012, 4,
1813–1821.
[3] D. Katz, T. Wizansky, O. Millo, E. Rothenberg, T. Mokari, U. Banin, Phys.
Rev. Lett. 2002, 89, 086801.
[30] R. Sasikala, A. R. Shirole, V. Sudarsan, K. G. Girija, R. Rao, C. Sudakarc,
S. R. Bharadwaj, J. Mater. Chem. 2011, 21, 16566–16573.
[31] F. Zhang, X. W. He, W. Y. Li, W. K. Zhang, J. Mater. Chem. 2012, 22,
22250–22257.
[32] E. Khon, A. Mereshchenko, A. N. Tarnovsky, K. Acharya, A. Klinkova, N. N.
Hewa-Kasakarage, I. Nemitz, M. Zamkov, Nano Lett. 2011, 11, 1792–
1799.
[4] A. Sitt, A. Salant, G. Menagen, U. Banin, Nano Lett. 2011, 11, 2054–2060.
[5] R. Singh, B. Pal, Mater. Res. Bull. 2013, 48, 1403–1410.
[6] B. Roldan Cuenya, Acc. Chem. Res. 2013, 46, 1682–1691.
[7] H. Kim, K. Yong, ACS Appl. Mater. Interfaces 2013, 5, 13258–13264.
[8] L. Li, C. Nan, Q. Peng, Y. Li, Chem. Eur. J. 2012, 18, 10491–10496.
[9] Z. Li, W. Wang, N. C. Greenhama, C. R. McNeill, Phys. Chem. Chem. Phys.
2014, 16, 25684.
[33] M. Li, X. F. Yu, S. Liang, X. N. Peng, Z. J. Yang, Y. L. Wang, Q. Q. Wang,
Adv. Funct. Mater. 2011, 21, 1788–1794.
[10] X. G. Peng, L. Manna, W. D. Yang, J. Wickham, E. Scher, A. Kadavanich,
A. P. Alivisatos, Nature 2000, 404, 59–61.
[34] M. Liu, L. Zhang, X. He, B. Zhang, H. Song, S. Lia, W. Youa, J. Mater.
Chem. A 2014, 2, 4619–4626.
[11] A. E. Saunders, A. Ghezelbash, P. Sood, B. A. Korgel, Langmuir 2008, 24,
9043–9049.
[35] M. Achermann, J. Phys. Chem. Lett. 2010, 1, 2837–2843.
[36] Q. Li, H. Meng, P. Zhou, Y. Zheng, J. Wang, J. Yu, J. Gong, ACS Catal.
2013, 3, 882–889.
[12] S. Linic, P. Christopher, D. B. Ingram, Nat. Mater. 2011, 10, 911 –921.
[13] A. Salant, M. Shalom, Z. Tachan, S. Buhbut, A. Zaban, U. Banin, Nano
Lett. 2012, 12, 2095–2100.
[37] J. Zhang, Y. Wang, J. Zhang, Z. Lin, F. Huang, J. Yu, ACS Appl. Mater. In-
terfaces 2013, 5, 1031–1037.
[38] T. T. Yang, W. T. Chen, Y. J. Hsu, K. H. Wei, T. Y. Lin, T. W. Lin, J. Phys.
Chem. C 2010, 114, 11414–11420.
[14] B. Weng, S. Liu, Z. R. Tang, Y. J. Xu, RSC Adv. 2014, 4, 12685–12700.
[15] Z. Zhang, J. T. Yates, Chem. Rev. 2012, 112, 5520–5551.
[16] M. Wang, F. Ren, G. Cai, Y. Liu, S. Shen, L. Guo, Nano Res. 2014, 7, 353–
364.
[39] N. Gupta, B. Pal, J. Colloid Interface Sci. 2012, 368, 250–256.
[40] H. Yang, Metals Mater. Int. 2006, 12, 351–355.
[17] R. Sahoo, A. Roy, C. Ray, C. Mondal, Y. Negishi, S. M. Yusuf, A. Pal, T. Pal,
J. Phys. Chem. C 2014, 118, 11485.
[18] M. M. Khan, S. A. Ansari, M. O. Ansari, B. K. Min, J. Lee, M. H. Cho, J. Phys.
Chem. C 2014, 118, 9477–9484.
[19] M. B. Boucher, N. Yi, F. Gittleson, B. Zugic, H. Saltsburg, M. F. Stephano-
poulos, J. Phys. Chem. C 2011, 115, 1261–1268.
[20] H. Zhu, N. Song, H. Lv, C. L. Hill, T. Lian, J. Am. Chem. Soc. 2012, 134,
11701–11708.
Received: November 10, 2014
Revised: January 30, 2015
Published online on February 18, 2015
ChemPlusChem 2015, 80, 851 – 858
www.chempluschem.org
858
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Copyright of ChemPlusChem is the property of Wiley-Blackwell and its content may not be
copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.