Hydrothermal synthesis of Mn-doped CdS hollow sphere nanocomposites as efficient visible-light driven photocatalysts

Article abstract of DOI:10.1039/c4ra16995f

A series of Mn-doped CdS hollow sphere photocatalysts has been directly synthesized by a simple and facile hydrothermal route for the first time. It was demonstrated that GSH acts as the S source and a gas bubble-template in this process. The products were characterized by XRD, SEM, TEM, HRTEM, XPS, and UV-vis spectroscopy. The as-prepared CdS and Mn-doped CdS hollow spheres all showed much higher activity than P25 under visible light (λ > 420 nm) irradiation. Among them, the 2.0 mol% Mn-doped CdS sample exhibited the highest photoactivity for the removal of organic pollutant RhB, and about 99.2% MO was decomposed after 50 min of visible light irradiation. Moreover, this catalyst also showed good stability, and after four cycles, the degradation efficiency still remained at 85%. The excellent photoactivity of the as-prepared Mn-doped CdS hollow spheres could be attributed to the synergistic effects of its appropriate band-gap structure and the special porous spherical morphology. The unique hollow sphere structure may favor the harvesting of excited light due to its special multiple scattering effect within the interior space, and the doping of Mn²⁺ may facilitate the generation of photoinduced electrons and hole pairs, and inhibit their recombination rate by acting as temporary trapping sites. This material may have great application potentials in environmental remediation and energy harvesting.

Full text of DOI:10.1039/c4ra16995f

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Graphical abstract

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Hydrothermal Synthesis of Mn-Doped CdS Hollow Spheres
Nanocomposite as Efficient Visible-Light Driven Photocatalysts
Chunyan Zhanga,b, Jiasheng Laic, Juncheng Hua*
aKey Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission &
Ministry of Education, SouthꢀCentral University for Nationalities, Wuhan 430074, PR China
Email: junchenghuhu@hotmail.com
bDepartment of Chemistry and Life Science, Liuzhou Teachers College, Liuzhou 545004, PR China
cDepartment of Physics and Information Science, Liuzhou Teachers College, Liuzhou 545004, PR China
ABSTRACT
A series of Mnꢀdoped CdS hollow spheres photocatalysts have been directly synthesized by a simple
and facile hydrothermal route for the first time. It was demonstrated that GSH act as the S source and a
gas bubbleꢀtemplate in this progress. The products were characterized by XRD, SEM, TEM, HRTEM,
XPS, and UVꢀvis. The asꢀprepared CdS and Mnꢀdoped CdS hollow spheres all showed much higher
activity than P25 under visible light (λ>420 nm) irradiation. Among them, the 2.0 mol% Mnꢀdoped
CdS sample exhibited the highest photoactivity for the remove of organic pollutants RhB, and about
99.2 % MO was decomposed after 50 min visible light irradiation. Moreover, this catalyst also showed
good stability, and after four recycles, the degradation efficiency still remained at 85 %. The excellent
photoactivity of the asꢀprepared Mnꢀdoped CdS hollow spheres could be attributed to a synergistic
effect of its appropriate bandꢀgap structure and the special porous spherical morphology. The unique
hollow spheres structure may be favor of harvesting the exciting light due to its special multiple
scattering effect within the interior space, and the doping of Mn2+ may facilitate the generation of
photoinduced electrons and holes pairs and inhibit their recombination rate by acting as temporary
trapping sites. This material may have great application potential in environmental remediation and
energy harvest.
KEYWORDS: Hollow Spheres, CdS, doping, manganese, Photocatalysis
1. Introduction
Solar energy, due to its distinct advantages of clean, accessible and inexhaustible,1 is being intensively
pursued, especially the visible light portion which accounts for 43 % of the solar is attracting
increasing attention.2 Recently, the development of photocatalysts with high visibleꢀlight activities has

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became a challenging and interesting topic. These photocatalysts can utilize abundant solar energy and
water resources in nature to solve many related problems, such as organic pollutants degradation and
H2 production from water splitting.3ꢀ5 the development of photocatalysts has become a challenging and
interesting topic of research. Various approaches have been developed to enhance the activity and
extend the response of photocatalysts to the visible light region, such as controlling the size and shape
of nanocrystals. Because of the high lightꢀharvesting efficiency, fast mobility of charge carriers, and
superior catalytic activity,6,7 hollow structured materials have been recognized as one type of promising
material for applications in the field of photocatalytic processes. Man Luo et. al.8 have prepared the
general strategy for oneꢀpot synthesis of metal sulfide hollow spheres. On the other hand, doping
metallic (Pt, Au and Ag et. al.) and nonmetallic (C, N and F et. al.) elements into conventional
photocatalysts to decrease the band gap is a very good choice .9ꢀ15
CdS, as an important IIꢀVI group semiconductor material and a wellꢀknown visibleꢀlightꢀsensitive
material,16 with a bandꢀgap of 2.42 eV, has attracted considerable attention for the conversion of solar
energy into chemical energy in recent years. Lee and Shen17 have reported kinds of CdS with various
structures such as flowerlike nanostructures, tetrapodꢀlike nanoorods and long branched NPs. However,
the low separation efficiency of photogenerated electrons and holes and the fact that easily corroded
making it not favorable for the wide applications in environmental remediation and solar
conversion.18,19 Recently, many studies that attempting to improve CdS photocatalytic performance
focus on structure design or surface modification,20ꢀ25 Such as nanowires, nanobelts, nanorods, and
nanospheres. But it was not satisfying the achievement for increasing both the photoactivity and
stability.26ꢀ29 Metal ions doping (such as Mn, Co, Fe, Ni, etc.) is demonstrated to been an effective
means in controlling the band gap and absorption properties. Man Luo et. al.30 have prepared oneꢀpot
synthesis of CdS and Niꢀdoped CdS hollow spheres. The optical properties of bulk IIꢀVI
semiconductors containing manganese are essentially modified by electronic transitions within the
halfꢀfilled 3d shell of the Mn2+ ions.31 Doping Mn2+ can alter the charge separation and recombination
dynamics by creating electronic states in the midgap region, which is in favor of the improvement of
power conversion efficiency.32 Min Yan et. al. have prepared triangular Mn doped CdS nanowires33 and
Chuanwei Cheng et. al. have prepared singleꢀcrystal Mn2+ꢀdoped CdS nanowires.34 Mn2+ has been the
most extensively studied luminescence activator in II–VI semiconductor. Mn doped CdS NPs are
interesting because of the fact that Mn2+ ions provide good traps for the excited electrons, which gives
rise to their potential use in nonlinear optics, electronic and optoelectronic devices. These exciting

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achievements motivated us to investigate Mn2+ doped CdS hollow spheres. Herein, we report a simple
templateꢀfree hydrothermal method to prepare Mnꢀdoped CdS hollow spheres using biomolecule
LꢀGlutathione reduced (GSH) as sulfur source and bubble source. A largeꢀscale of uniformed and well
dispersed Mnꢀdoped CdS hollow spheres were obtained without traditional tedious and intricate
template removal procedures. This oneꢀstep route provides both the expected hollow structure and the
Mn2+ doping. In addition, we experimentally demonstrate the asꢀprepared Mnꢀdoped CdS hollow
spheres have an enhanced photocatalytic activity and improved durability for organic pollutants
removal. The possible effect factors for the activity and stability are also discussed in detail.
2. Experiment details
2.1 Materials
Manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O) was purchased from Sinopharm Chemical
Reagent Co, Ltd (Shanghai, China), GSH(C6H12N2O4S2) and cadmium nitrate tetrahydrate
(Cd(NO3)2·4H2O) were purchased from Aladdin. All chemicals used in the experiments are of
analytical grade and were used without further purification.
2.2 Synthesis of Mnꢀdoped CdS
In a typical preparation, 0.825 mmol of GSH, appropriate molar ratios of Cd(NO3)2· 4H2O and
Mn(CH3COO)2·4H2O with the total mole number of Cd2+ and Mn2+ being 0.825 mmol were dissolved
into a mixed solution of 80.0 mL of deionized water. The Mnꢀdoping concentration was designed as
1.0, 2.0, 3.5, and 5.0 mol% (denoted as X mol% Mnꢀdoped CdS), which was the mole ratio of the
theoretical yield. After being continuously stirred for 1 h, the clear solution was transferred into a
stainless steel vessel (Teflon cups with an inner volume of 100 mL), which was heated and maintained
at 180 for 5 h and then cooled to room temperature naturally. The products were obtained by suction
filtration, washed with deꢀionized water and anhydrous ethanol alternately, and then dried at 60 ℃
overnight in an oven. Through varying the molar percentage of Mn2+ in the solutions, a series of
Mnꢀdoped CdS hollow spheres with different compositions were obtained.
2.3 Characterization
The structure and phase of the samples were characterized by power Xꢀray diffraction (XRD)
employing a scanning rate of 0.05°/S in the 2θ range from 10° to 80°, in a Bruker D8 Advance using
monochromatized Cu Kα=1.5404Å. The microstructure and composition size were observed using a

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transmission electron microscope (TEM) and highꢀresolution transmission electron microscopy
(HRTEM) using a Tecnai G20 microscope operated at an accelerating voltage of 200 kV with an
energyꢀdispersive Xꢀray spectrometer (EDS) performed at 300 kV, respectively. The specimens of
TEM and HRTEM measurements were prepared by spreading a droplet of ethanol suspension onto
copper grids coated with perforated carbon films, and allowed to dry in air. Scanning electron
micrographs (SEM) were performed with a SU8000 fieldꢀemission scanning electron microscope
(FESEM, Hitachi, Japan) at an accelerating voltage of 15 KV. The surface composition of the catalysts
was analyzed by Xꢀray photoelectron spectroscopy (XPS) which was equipped with a VG Multilab
2000 (VG Inc.) photoelectron spectrometer using monochromatic Al Kα radiation under vacuum at
2×10−6 Pa. All the binding energies were referenced to the C1s peak at 284.8 eV of the surface
adventitious carbon. The UVꢀvis DRS were collected using a Shimadzu UVꢀ2450 spectrophotometer
from 200 to 800 nm using BaSO4 as background. Reactive brilliant rhodamineꢀB (RhB) and methyl
orange (MO) were chosen as the simulated pollutants to evaluate the photocatalysis activities of the
asꢀprepared Mnꢀdoped CdS hollow spheres. The catalytic mechanism and durability of the
photocatalyst were also discussed.
2.4 Photocatalytic Activities and Durability Measurements
The photocatalytic activity of the sample was evaluated by the degradation of dye RhB (50 mL, 1×10−5
mol L−1) and MO (50 mL, 10mg L−1 ) under simulated visibleꢀlight (equipped with a 420 nm cutoff
filter) irradiation by a 350 W Xe lamp with 32.86 lm/W luminous efficiency. In each experiment, 50
mg of the photocatalyst and 50 mL of aqueous solution of RhB or MO were added into a flask, the
suspension was ultrasonic treatment for 10 min and stirred for 1h in the dark in order to reach the
adsorptionꢀdesorption equilibrium at room temperature. The reaction was ensured at room temperature
and reduce the interference of the infrared radiation by passing into condensate water. At given time
intervals, 3 mL liquid were sampled and then filtered to remove the catalyst particles for analysis. The
filtrates were finally analyzed using a UVꢀvis spectrophotometer (UVꢀ2450).
In order to test Mnꢀdoped CdS hollow spheres durability, four cycles of photocatalytic
measurements were employed by using 2.0 mol% Mnꢀdoped CdS hollow spheres as a representative
sample. The photocatalyst was separated from aqueous solution after each run of reactions. The filtered
catalyst was washed by anhydrous ethanol and reused in the subsequent recycling experiment. After
the experiment, the XRD spectrum of the final catalyst was also detected.

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2. 5 Analysis of Hydroxyl Radicals (ꢁOH)
The formation of ·OH on the surface of the UV and Vis illuminated samples was detected by a
photoluminescence (PL) method using coumarin as a probe molecule. Coumarin can readily react
with ·OH to produce the highly fluorescent product, 7ꢀhydroxycoumarin (7HC) (umbelliferone).35 The
experimental procedure was similar to the measurement of photocatalytic activity. In a typical process,
2.0 mol% Mnꢀdoped CdS (50 mg) hollow spheres and coumarins (50 mL, 5.0×10-4 mol Lꢀ1) were
ultrasonic treatment for 10 min and magnetic stirring for 1h under dark conditions. Then, the mixture
was irradiated under visibleꢀlight (λ>420 nm). At given time intervals, 3 mL liquid were sampled and
then filtered to remove the catalyst particles for measure the increase in the PL intensity around 445 nm
excited by 332 nm light.
3 Results and discussion
3.1 Microstructure characterizations
XRD measurements were employed to investigate the phase and structure of the CdS and Mnꢀdoped
CdS samples. As shown in Fig. 1, these samples show the similar line type, and all can be assigned to
the hexagonal CdS that with six characteristic diffraction peaks according to the standard JCPDS card
(NO. 77ꢀ2306). As no signals about manganese or other impurities were detected in these spectra, it
can be concluded that the doping of Mn2+ has little effect on the crystalline phase of CdS. The possible
reason may result from the low dosage of Mn2+. However, with the increasing of Mn2+ content in the
precursors, the peak intensity of these samples became stronger gradually, suggesting these samples
tend to be well crystallized.
The morphology of MnꢀDoped CdS hollow spheres microspheres was studied by SEM and TEM.
Fig. 2 is the SEM and the TEM images of 2.0 mol% Mnꢀdoped CdS hollow spheres with different
magnifications and the corresponding HRTEM Image. Fig. 2(a) shows these microspheres with
average diameter of about 300ꢀ600 nm, moreover, it is obvious that the surface of the sphere is coarse.
From the broken sphere in Fig. 2(b), we can clearly find that the spheres have typical hollow interior
structure, it can be further clearly observed that the thickness of the wall of the broken hollow sphere is
about 60 nm, indicating the thickness of hollow sphere. In Fig. 2(c), a clear contrast between the dark
edge and the pale center can be observed, which confirms that all the spheres have a hollow interior
again. The Fig. 2(a)ꢀ(c) indicated that these rough shells were constructed of loosely packed fine
nanoparticles. These nanoparticles which accumulated the spheres, as building blocks for the spheres,

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can produce inherent porosity. Just these inherent aperture create numerous nanoscale channels for
chemical moieties travelling between the interior cavity and exterior space, which making the hollow
spheres is particularly suitable for further studies in adsorption and catalytic applications.8 Fig. 2(d)
shows the corresponding high resolution TEM image, it shows clear lattice fringes, which allowed for
the identification of crystallographic spacing. The corresponding fast Fourier transform (FFT) pattern
is shown in the inset of Fig. 2(d). As shown in Fig. 2(d), the crystallographic spacing of the 2.0 mol%
Mnꢀdoped CdS hollow spheres estimated from the HRTEM image was about 0.3582, 0.3357 and
0.3160 nm; which respectively corresponding to the (100) (002) and (101) faces. Meanwhile, the
lattice spacing of 0.3582, 0.3357 and 0.3160 nm corresponds to the (100), (002) and (101) faces of
hexagonal CdS. These results are consistent with the XRD analysis.
Fig. 3 shows the TEM image of Mnꢀdoped CdS with different Mn2+ doping concentration. In all
images of Fig. 3, the edge of these spheres is darker than their center, which clearly reveals the hollow
natural characteristic of these spheres, and indicates that the hollow structures can be generated in
different Mn2+ doping concentration. No significant difference in the size and thickness of the spheres
even the Mn2+ concentration increased to 5 mol%, but fewer nanorods appeare in the edge of the
spheres. These TEM images show the gradual develop process of the morphology following the
increase of the Mn2+ concentration.
In an effort to gain further insight into the surface information of the samples, pure CdS, 2.0 and
5.0 mol% Mnꢀdoped CdS samples were investigated by XPS. Because of the low doping concentration,
the signals of Mn 2p are very weak and it is hard to be detected. Fig. 4 provides the information of
binding energies and intensities of the surface element of S 2p of CdS and 2.0 and 5.0 mol% Mnꢀdoped
CdS. Compared with pure CdS, it can be found that the position of the peak shifts to a higher energy as
the concentration of Mn2+ increases. This may be because that some Cd2+ replaced by Mn2+ of the CdS
lattice and formed CdꢀSꢀMn bonds in the Mnꢀdoped CdS samples. The difference in electronegativity
(χ) between Cd (χp = 1.69), S (χp = 2.56) and Mn (χp = 1.55) results in a higher electron cloud density
of S atoms, thus the binding energy of S 2p (161.36 and 161.58 eV for 2.0 and 5.0 mol% Mnꢀdoped
CdS respectively) increases compared to pure CdS (161.34 eV). The asymmetric band of S 2p of
Mnꢀdoped CdS samples can be fitted into two peaks, the peaks at about 161.09 and 161.30 eV can be
assigned to the S atoms bonded to the Cd atoms. Similarly, the peaks at about 162.14 and 162.38 eV
which can be assigned to the S atoms bonded to the Mn atoms, are mainly due to the partial
substitution of Cd2+ by Mn2+ in the CdS lattice.

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UVꢀvis diffuse reflectance spectra (DRS) were measured to determine the optical properties of the
undoped and Mnꢀdoped CdS hollow spheres. As shows in Fig. 5, all the samples have strong
absorption in the visibleꢀlight region and these can be assigned to the intrinsic band gap absorption of
CdS. The direct band gap values of the undoped and Mnꢀdoped CdS hollow spheres samples were
estimated from the (Ahυ)2 versus photon energy (hυ) plot as shown in the insert of the Fig. 5, where A,
h and υ is the absorbance value, Planck constant and light frequency, respectively. After comparison, a
slight blue shift is observed in the samples doped with Mn. This slight blue shift in the absorption edge
is the outcome of the quantum confinement effect. This effect is due to the increasing of nucleation
rates with increase in doping concentrations.36 The band gap of CdS (2.30 eV) is lower than that of all
the Mnꢀdoped CdS hollow spheres (2.38, 2.36, 2.32 eV). This indicates that the introduction of Mn2+
has a significant effect on the optical property of light absorption for the asꢀprepared Mnꢀdoped CdS
hollow spheres.
3.2 Photocatalytic Properties of MnꢀDoped CdS
To demonstrate the potential applicability of Mnꢀdoped CdS hollow spheres, the photocatalytic
degradation of dye RhB under visible light irradiation (λ>420 nm) had been chosen as a model reaction
to evaluate the photocatalytic activities of the prepared samples (Fig. 6). According to the reference,
commercial product Degussa P25 and commercial CdS were also investigated under the same
experimental conditions. As can be seen from Fig. 6, only a negligible activity is detected when the
catalyst is free. Both of the CdS and Mnꢀdoped CdS hollow spheres are much superior to that of
commercial CdS, indicating the advantage of hollow structure. The unique hollow structure of
Mnꢀdoped CdS hollow spheres enables both the outer and inner surfaces of the catalyst to contact with
RhB molecules and provides more active sites to interact, and allows multiple reflections of visible
light within the interior cavities to promote the lightꢀharvesting efficiencyc.37,38
It can be found that all the Mnꢀdoped CdS hollow spheres show enhanced activities than that of
undoped CdS hollow spheres. It is possible that the Mn2+ doping can provide them with intriguing
properties inherited from the synergetic effect. While we can find that the activity of Mnꢀdoped CdS
hollow spheres is not be enhanced monotonously with the Mn2+ content increasing. This can be partly
attributed to the relatively high doping concentrations of Mn2+, which might cause a reduced
adsorption of RhB and become the recombination center of photogenerated carriers, resulting in a
decrease of photocatalytic efficiency.39
It is also found that the 2.0 mol% Mnꢀdoped CdS hollow spheres demonstrated highest activity in

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the series of Mnꢀdoped CdS photocatalysts. After 25min of visible light irradiation, the RhB removal
over is as low as 0.3 % and the degradation ratio of 99.73 %, which indicates that Mnꢀdoped CdS has
more higher photocatalytic activity than Niꢀdoped CdS for RhB degradation.30 Compare with the
reaction rate constants (k), we can find that the RhB removal rate of the 2.0 mol% Mnꢀdoped CdS
hollow sphere (k= 0.1915) is about 5 times as much as that of CdS hollow sphere (k=0.0399).
Therefore, it is believed that doped right amount of Mn2+ contributed to enhanced the activity of CdS
hollow sphere. This can be attributed to more efficient light harvesting by special structure and
effective separation of photogenerated carries affected by optimal Mn2+ doping. Fig. 7 shows the
temporal evolution of absorption spectra of an RhB aqueous solution (initial concentration is 1.0 × 10−5
M, 50 mL) in the presence of 50 mg 2.0 mol% Mnꢀdoped CdS hollow spheres under visible light
(λ>420 nm) irradiation. After 25 min irradiation, the maximum absorption band of the solution
gradually shifted from 553.5 to 496 nm, which indicated that the deꢀethylation process instead of the
decomposition of the conjugated chromophore structure is the dominant process,40 and the color of
RhB aqueous solution changed from pink to colourless. Meanwhile, the absorption band gradually
decreased, which indicated that the ethyl groups of RhB were removed during irradiation41ꢀ43. For
further investigating the photodegradation of RhB, the total organic carbon (TOC) removal in
corresponding solutions at different exposure time were detected, as shown in the insert of the Fig. 7.
With the extension of irradiation time, the concentration of organic carbon decreased steadily,
indicating that RhB dye can not only be discolored but also degraded over Mnꢀdoped CdS. It can be
seen that the TOC removal efficiency increases to 52.9% for RhB after 25 min. These results further
confirmed that RhB pollutants can be removed efficiently. Cd2+ is a toxic pollutant, the content of Cd2+
is high in our Mnꢀdoped CdS. However, the release of Cd2+ to water only accounted for 0.89 wt% of
bulk Mnꢀdoped CdS.
For further testing the high activity of the 2 mol% Mnꢀdoped CdS hollow spheres, MO, a typical
chemically stable and difficultly decomposed dye, was also chosen as the goal contaminant to
photocatalytic degradation under visible light irradiation (λ>420 nm). Fig. 8 shows the change of
absorption spectra of MO aqueous solution in the presence of 50 mg catalyst. It can be seen that the
decomposition of organic pollutants MO is efficient and the degradation ratio of 99.2 % after 50 min,
which indicated that the 2.0 mol% Mnꢀdoped CdS hollow spheres shows a relatively high
photocatalytic performance. To further demonstrate the brilliant photocatalytic activity of 2 mol%
Mnꢀdoped CdS hollow spheres, salicylic acid, a typical colorless pollutant which has no light

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adsorption in the visible light region was also chosen as the goal contaminant. Figure 9 shows the
UVꢀvis spectra of salicylic acid versus reaction time, in 4 h irradiation of visible light, salicylic acid
almost can be completely degraded, the result demonstrated again the high activity of our Mnꢀdoped
CdS.
In order to test the stability of the Mnꢀdoped CdS hollow spheres, we reused the catalyst for four
recycles by RhB degradation under visible light (λ>420 nm) irradiation. As shown in Fig. 10, the
catalyst could be reused four times without significant deactivation after 4 times recycling, the stability
of the Mnꢀdoped CdS hollow spheres is similar to Niꢀdoped CdS hollow spheres.30 The corresponding
XRD patterns (Fig. 11) have no notable peak shift before and after the photocatalytic recycles except
for a slightly enhanced intensity in diffraction peaks, indicating the high stability of the Mnꢀdoped CdS
hollow spheres.
It is well known that the hydroxyl radical (·OH) is one of the major active species responsible for
the photodegradation of organic molecules in the photcatalytic process.44 In order to further insight into
the photocatalytic mechanism and study the active species involved in the photocatalytic process, the
PL technique was employed to detect hydroxyl radicals (·OH) on the surface of visible light
illuminated MnꢀDoped CdS spheres by using coumarin as a proble molecule.35 Fig. 12 shows the
changes in the PL spectra for 5.0 × 10−4 M coumarin solution with irradiation time in the presence of
the 2.0 mol% MnꢀDoped hollow spheres. A gradual increase in the PL intensity at about 445 nm is
observed with increasing irradiation time indicating the production of ·OH radicals. However, no
increased PL intensity is observed in the absence of light irradiation or MnꢀDoped CdS hollow spheres,
which confirms that the fluorescence is caused by chemical reactions of coumarin with ·OH formed at
the Mnꢀdoped CdS hollow spheresꢀwater interface via a photocatalytic reaction.45 Therefore, Form this
results, we believe that the fast production and the highly accumulated of ·OH radicals may be the
main active oxygen species in the photocatalytic process with the Mnꢀdoped CdS hollow sphere
system.
4 Conclusions
In summary, by varying the molar ratio of different precursors, we have successfully synthesized a
series of Mnꢀdoped CdS hollow spheres with the assistance of GSH act as the S source and a gas
bubbleꢀtemplate via a simple hydrothermal method. All the catalysts showed higher photocatalytic
activity for the degradation of RhB than commercial Degussa P25 under visible light irradiation.
Among the samples, the 2.0 mol% Mnꢀdoped CdS hollow spheres show the highest photocatalytic

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activity, and PL spectra demonstrated that ·OH radicals may be the main active oxygen species in the
photocatalytic process. The high photocatalytic activity can have a close relationship with the hollow
structure as well as the Mn2+ doping. The hollow structure may favors for the harvesting of exciting
light and facilitates the transportation of reactants and products within the interior space. The doped
Mn2+ plays a key role in reducing the recombination rate of photonꢀgenerated carriers, thus promoted
the activity and stability of the catalyst. The method and idea described herein will provide a new way
to synthesize not only Mnꢀdoped CdS hollow spheres, but also for other semiconductor materials.
AUTHOR INFORMATION
Corresponding Author
*Tel: +86 27 67841302. Eꢀmail: junchenghuhu@hotmail.com.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by Natural Science Foundation of Hubei Province (2013CFA089).
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4000
3000
2000
1000
0
(e)
(d)
(c)
(b)
(a)
20
40
60
80
2 Theta / Degree
Fig. 1. XRD patterns of (a) CdS, (b) 1.0 mol % Mnꢀdoped CdS, (c) 2.0 mol % Mnꢀdoped CdS, (d) 3.5
mol % Mnꢀdoped CdS, (e)5.0 mol % Mnꢀdoped CdS.

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(a)
(b)
d=0.3160nm
(c)
(d)
（101）
d=0.3582nm
（100）
（101）
d=0.3160nm
d=0.3357nm
（002）
5 nm
Fig. 2. (a) and (b) are SEM images of 2.0 mol % Mnꢀdoped CdS, (c) is TEM image and (d) is the
corresponding HRTEM image.

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(a)
(b)
(c)
(d)
Fig. 3. TEM image of (a) CdS, (b) 1.0 mol % Mnꢀdoped CdS, (c) 3.5 mol % Mnꢀdoped CdS and (d) 5
mol % Mnꢀdoped CdS.

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S2P
(a)
161.09
162.14
(b)
(c)
161.30
162.38
166
164
162
160
158
156
Binding energy (eV)
Fig. 4. XPS results of S 2p of (a) CdS, (b) 2.0 mol %, and (c) 5.0 mol % Mnꢀdoped CdS.

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Fig. 5. UV−vis DRS of (a) CdS, (b) 2.0 mol % Mnꢀdoped CdS, (c) 1.0 mol % Mnꢀdoped CdS, and (d)
3.5 mol % Mnꢀdoped CdS . The inset is band gap evaluation from the plots of (Ahυ)2 versus photon
energy (hυ).

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1.0
0.8
0.6
0.4
0.2
0.0
a
b
c
d
e
f
g
h
0
5
10
15
20
25
Time(min)
Fig. 6. Photocatalytic degradation curves of RhB under visible light (λ>420 nm) irradiation over (a)
CdS hollow spheres, (b) 1.0 mol % Mnꢀdoped CdS, (c) 2.0 mol % Mnꢀdoped CdS, (d) 3.5 mol %
Mnꢀdoped CdS, (e)5.0 mol % Mnꢀdoped CdS, (f) Degussa P25, (g). catalystꢀfree, (h) commercial CdS

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0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
20
18
16
14
12
10
8
0 min
5 min
10 min
15 min
20 min
25 min
0
5
10 15 20 25
Time(min)
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 7. The absorption spectra of a solution of RhB (1.0 × 10−5 M, 50 mL) in the presence of 2.0 mol % Mnꢀdoped CdS
(50mg) under visible light ( >420 nm) irradiation.
λ

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0.6
0.4
0.2
0.0
0 min
10min
20 min
30 min
40 min
50 min
200
300
400
500
600
700
Wavelength (nm)
Fig. 8. The absorption spectra of a solution of MO (10 mg / mL, 50 mL) in the presence of 2.0
mol % Mnꢀdoped CdS (50 mg) hollow spheres under visible light (λ > 420 nm) irradiation.

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0.6
0.5
0.4
0.3
0.2
0.1
0 h
0.5 h
1.0 h
2.0 h
3.0 h
4.0 h
270 280 290 300 310 320 330 340
Wavelength (nm)
Fig. 9. The absorption spectrum of a solution of salicylic acid (20 mgLꢀ1, 50 mL) in the presence of 2.0
mol% Mnꢀdoped CdS (50 mg) under visible light(>420 nm) irradiation.

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100
80
60
40
20
0
1st
2nd
3rd
4th
Recycle Times
Fig. 10. Recycled photodegradation of RhB under the visible light ( > 420 nm) irradiation over 2.0
mol % Mnꢀdoped CdS hollow spheres.
1500
No shift
Used
Fresh
1000
22
24
26
28
30
32
2 Theta/ Degree
Used
500
0
Fresh
20
40
60
80
2 Theta / Degree
Fig. 11. XRD patterns of 2.0 mol % Mnꢀdoped CdS before and after being used for fourth times.

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15
14
13
12
11
35 min
30 min
25 min
20 min
15 min
10 min
0 min
350
400
450
500
550
600
Wavelength / nm
Fig. 12. PL spectra changes observed during visible light illumination (>420 nm) of 2.0 mol %
Mnꢀdoped CdS hollow spheres in 5×10ꢀ4 M coumarin solution (excitation at 332 nm).