Nano-CdS by polymer-inorganic solid-state reaction: Visible light pristine photocatalyst for hydrogen generation

Article abstract of DOI:10.1016/j.materresbull.2006.04.031

We have explored the possibility of using environmentally stable nano-CdS embedded in thermally stable polymer matrix as an efficient photocatalyst for the hydrogen generation by photodecomposition of hydrogen sulphide under visible light irradiation. Initially, we restricted our attempt to the usage of nano-CdS synthesized by novel polymer-inorganic solid-state reaction between cadmium iodide and polyphenylene sulphide (PPS). The structural study revealed the formation of nanocrystallites of CdS with the particle size ranging from 6 to 28 nm entrapped in modified (cyclized) PPS matrix. A quantum yield of 19.7% for the H₂ generation was accomplished with CdS-PPS nanocomposite in pristine state, which appears to be superior in comparison to that of the conventional Pt loaded CdS. We believe that this straightforward approach can be extended to synthesise other nano-metal sulphides in polymer network for photocatalytic and allied applications.

Full text of DOI:10.1016/j.materresbull.2006.04.031

Materials Research Bulletin 41 (2006) 2219–2225
www.elsevier.com/locate/matresbu
Nano-CdS by polymer-inorganic solid-state reaction: Visible light
pristine photocatalyst for hydrogen generation
a,c
c,
b
b
K.G. Kanade , Jin-OoK Baeg , U.P. Mulik , D.P. Amalnerkar , B.B. Kale
b,**
*
a
Department of Chemistry, Mahatma Phule College, Pimpri, Pune 411 017, India
b
Centre for Materials for Electronics Technology (C-MET), Panchawati, Off Pashan Road, Pune 411 008, India
c
Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, Yuseong, Daejeon 305-600, Republic of Korea
Received 16 January 2006; received in revised form 21 April 2006; accepted 25 April 2006
Available online 15 May 2006
Abstract
We have explored the possibility of using environmentally stable nano-CdS embedded in thermally stable polymer matrix as an
efficient photocatalyst for the hydrogen generation by photodecomposition of hydrogen sulphide under visible light irradiation.
Initially, we restricted our attempt to the usage of nano-CdS synthesized by novel polymer-inorganic solid-state reaction between
cadmium iodide and polyphenylene sulphide (PPS). The structural study revealed the formation of nanocrystallites of CdS with the
2
particle size ranging from 6 to 28 nm entrapped in modified (cyclized) PPS matrix. A quantum yield of 19.7% for the H generation
was accomplished with CdS–PPS nanocomposite in pristine state, which appears to be superior in comparison to that of the
conventional Pt loaded CdS. We believe that this straightforward approach can be extended to synthesise other nano-metal sulphides
in polymer network for photocatalytic and allied applications.
#
2006 Elsevier Ltd. All rights reserved.
Keywords: A. Semiconductor; A. Polymer; D. Catalytic properties
1
. Introduction
The dream to harvest energy from sunlight for electric power generation or chemical fuels such as hydrogen is yet
to be realized at economically viable large scale. Photocatalytic production of hydrogen from water, H S and organic
2
waste using semiconductors is one of the potential strategies for converting the sunlight energy into chemical energy.
Conventionally, various metal sulphides, particularly CdS have been used as photocatalyst [1–3]. However, these
metal sulphides are prone to photocorrosion. To overcome the problem of photocorrosion, attempts are being made
to use highly stable metal oxides as visible light photocatalyst. Unfortunately, most of the oxides have wide band gap
and absorb very little of the visible light [4,5]. Therefore, the improvement in the stability of CdS based
photocatalysts utilizing visible range of the spectrum is a great challenge. Organic compounds as sacrificial
promoter [6] and mesoporous silica [7,8] have been reported to increase the stability and enhance the photocatalytic
activity of CdS. Also, many researchers have reported the use of various transition metal doping methods for the
preparation of CdS for their improved photocatalytic activity [9–11]. The uses of nanocrystalline semiconducting
*
Corresponding author.
** Corresponding author. Tel.: +91 20 25899273; fax: +91 20 25898180.
E-mail addresses: jobaeg@krict.re.kr (J.-O. Baeg), kbbb1@yahoo.com (B.B. Kale).
0025-5408/$ – see front matter # 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2006.04.031

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CdS powders with uniform particle size and large surface area for the photocatalytic decomposition of H S have also
2
been reported [12–14]. Synthesis of nano-CdS in hetero-matrices has been a subject matter of immense interest
owing to their distinctive optical, electrical and opto-electronic properties [15]. The use of organic material in the
synthesis of hetero-matrices also provides an interface for the charge transfer resulting in the increase of
photocatalytic efficiency [16–19]. Recently, we have demonstrated the synthesis of nano-CdS in hetero-matrices by
a polymer-inorganic solid-state reaction where the polymer served a dual-purpose of a reactant (sulphur source) and
a stabilizing agent [20].
In this communication, we report the photocatalytic performance of such nano-CdS–PPS composites in the
photodecomposition of hydrogen sulphide for hydrogen generation under visible light irradiation. This is a unique
attempt in which nano-CdS in hetero-matrices (where one of the matrices also acts as a reactant) has been used in order
to study the photocatalytic activity.
2
. Experimental
2
.1. Synthesis and characterization of CdS photocatalyst
Polyphenylene Sulphide (PPS) having an average molecular weight of 10,000 and cadmium iodide were obtained
from Aldrich (99% purity) and used as received. The nanocrystalline CdS in polymer matrix was prepared as per the
procedure reported in our recent paper [20]. The admixture of PPS and CdI (1:1 or 10:1 molar ratio) was heated at the
2
melting temperature of PPS (285 8C) for 48 h in a platinum crucible. The CdS-polymer powder thus obtained was
characterized by powder X-ray diffractions pattern recorded on Philips PW-1729 X-ray Diffractometer using Cu Ka
radiation with Ni filter. Transmission electron microscopy (TEM) was performed using Jeol-2100X TEM. The surface
morphology and particle size were determined using a Field Emission Scanning Electron Microscope (FESEM, JEOL-
JSM6700F). Spectroscopicstudyofthe productwascarriedoutusingUV–vis(SHIMADZUUV-2450diffusereflectance
mode) spectrophotometer. In the present study, the CdS–PPS nanocomposite prepared using the admixture of PPS and
CdI with mole ratio 1:1 is denoted as CdS-NC-1:1 and that with mole ratio 10:1 is denoted as CdS-NC-10:1.
2
2
.2. Photocatalytic measurement
About 0.5 g nano-CdS-polymer powder (CdS-NC-1:1/CdS-NC-10:1) dispersed in an aqueous solution of KOH
0.5 M, 250 ml) was introduced into cylindrical pyrex photochemical reactor with quartz window having a thermostatic
(
water-jacket. This dispersion was purged with argon for 1 h followed by bubbling of hydrogen sulfide (2.5 ml/min) for
about 1 h at 25 8C. The undercomposed hydrogen sulphide was trapped in NaOH solution and the amount of evolved
hydrogen was measured using a graduated gas burette. It was subsequently characterized by using a gas chromatograph
˚
(Shimadzu GC-14B, MS-5 A column, TCD, Ar as a carrier gas). A Xe lamp (Oriel) of intensity 450 W with cut-off filter
(>420 nm) was used as a light source. Photocatalytic activity of all samples was measured for 4 h.
3
. Results and discussion
3
.1. Crystal structure and particle morphology
Two different concentrations of precursors were used in this novel solid-state reaction for the synthesis of CdS
nanocrystallites in the polymer network. Fig. 1(a–c) represents the X-ray diffractograms corresponding to PPS, CdS-
NC-1:1 and CdS-NC-10:1, respectively. X-ray diffractogram corresponding to CdS-NC-1:1 (Fig. 1b) reveals mainly
occurrence of mixture of cubic and hexagonal phases of CdS [21]. The presence of hexagonal phase of CdI can also be
2
noticed [22]. In case of CdS-NC-1:1 (Fig. 1b), although mixed phases of CdS were formed, hexagonal phase was found
to be more dominant than cubic phase in this product The peaks pertaining to PPS were absent in this system implying
that the PPS has been completely utilized to incorporate CdS in its matrix. X-ray diffractogram corresponding to CdS-
NC-10:1 (Fig. 1c) reveals the presence of PPS, cubic CdS and hexagonal CdI2.
The average particle size of the resultant CdS nanocrystallites as derived from Scherrer’s formula was found to be
5 nm for CdS-NC-1:1 and 12 nm for CdS-NC-10:1.
1

K.G. Kanade et al. / Materials Research Bulletin 41 (2006) 2219–2225
2221
Fig. 1. X-ray diffractograms corresponding to (a) PPS, (b) CdS-NC-1:1 and (c) CdS-NC-10:1 (*: PPS, ~: hexagonal-CdI2, 5: cubic-CdS, &:
hexagonal-CdS).
The FESEM photomicrographs corresponding to PPS, CdS-NC-1:1 and CdS-NC-10:1 are presented in
Fig. 2(a–c), respectively. The clumpy and chunk-like morphological features were observed for PPS (Fig. 2a).
However, such features were absent in the photomicrograph of CdS-NC-1:1 powder (Fig. 2b), indicating the
formation of CdS in the cyclized polymer matrix. While in case of CdS-NC-10:1 nanocomposite (Fig. 2c) the
,
presence of a chunk like morphology (associated with PPS) indicates the probable retention of the polymer
network even after heating at 285 8C. This observation is in agreement with the pertinent XRD data (Fig. 1,
pattern (a) and (c)).
Fig. 3 shows TEM images recorded for samples corresponding to (a) CdS-NC-1:1 and (b) CdS-NC-10:1
nanocomposite powders. The uneven spherical shaped dark black regions (Fig. 3a) plausibly indicate the presence of
nano-CdS particles. The nearly spherical and irregular shaped dark black regions (Fig. 3b) can be associated with
nano-CdS particles as SAED pattern associated with these spots (Fig. 4) reveals occurrence of cubic CdS in close
agreement with XRD data. The SAED rings evidently indicate the polycrystalline nature of the product whereas the
spots imply the single crystalline nature of the product. Thus, it can be inferred that the as formed CdS
nanocrystallites are randomly positioned between polycrystalline and single crystalline lattices. In close agreement
with XRD results, the average size of the CdS nanocrystallites were in the range of 15–28 nm in case of CdS-NC-1:1
while it was in the range of 6–20 nm for the CdS-NC-10:1. TEM micrograph of CdS-NC-10:1 nanocomposite powder
shows that the polymer was retained in the product whereas it was missing in the case of CdS-NC-1:1 nanocomposite
powder.
3
.2. Electronic band structure by DRS
Fig. 5(a–c) shows the UV–vis diffuse reflectance spectra of the PPS, CdS-NC-1:1 and CdS-NC-10:1
nanocomposite powders. The DRS of the PPS (Fig. 5a) has absorption edge cut-off at 370 nm with corresponding band
gap of 3.35 eV, while DRS of CdS-NC-1:1 (Fig. 5b) nanocomposite powder showed the broad adsorption edge cut-off
in the visible region. The similar kind of behaviour was observed in CdS-NC-10:1 nanocomposite powder (Fig. 5c).
The broad absorption edge shoulder reveals the formation of CdS incorporated in cyclized polymer matrix. The
presence of uneven shape and size of nanocrystals (Fig. 3) of CdS in PPS matrix could also be one of the reasons for the
broad absorption peak [5].

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K.G. Kanade et al. / Materials Research Bulletin 41 (2006) 2219–2225
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Fig. 3. TEM micrographs of (a) CdS-NC-1:1 and (b) CdS-NC-10:1.
3
.3. Photocatalytic activities of CdS embedded in PPS matrix
The photocatalytic production of hydrogen using PPS, CdS-NC-1:1 and CdS-NC-10:1 nanocomposite powders
as catalyst for the decomposition of hydrogen sulfide was carried out under the specified conditions and the relevant
data is reproduced in Table 1. An excellent photocatalytic activity was observed for CdS-NC-1:1 nanocomposite
powder. The maximum hydrogen production rate achieved was 3926 mmol/h without using any doping agent which,
in turn, implies that the nanocomposite in pristine state is an active photocatalyst for hydrogen sulfide
decomposition under visible light irradiation. Nevertheless, with CdS-NC-10:1 the hydrogen production rate
achieved was to the tune of 2838 mmol/h. The PPS matrix showed negligible photocatalytic evolution of hydrogen.
Photocatalytic activity of all samples was measured for short term (i.e.4 h) as limited by our experimental facility.
The samples were re-used for photodecomposition three times over a period of 24 h and we achieved the same
results. The CdS-NC-1:1 and CdS-NC-10:1 nanocomposite powders gave 19.7% and 11.7% quantum yields at
500 nm, respectively for the H evolution. It is worthwhile to note that CdS-NC-1:1 nanocomposite powder offers
2
higher photocatalytic activity under visible light irradiation in comparison to reported data [23–27]. It also showed
good stability under the experimental conditions used for the photodecomposition of H S. The CdS-NC-10:1
2
nanocomposite powder showed relatively less photocatalytic activity as compared to CdS-NC-1:1 because of the
Fig. 4. SAED pattern of CdS-NC-10:1 powder.

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Fig. 5. UV–vis diffuse reflectance spectra of (a) PPS, (b) CdS-NC-1:1 and (c) CdS-NC-10:1 nanocomposite powder.
Table 1
a
Photocatalytic activities of various catalysts for H
2
S splitting
Catalyst
2
H evolved (mmol/h)
CdS-NC-1:1
CdS-NC-10:1
Pt-CdS
3926
2838
1517
a
Catalyst, 0.5 g; 250 ml (0.5 M aqu.KOH); H
2
S (2.5 ml/min); 450 W Xe lamp (Oriel) with cutoff filter (l ꢀ 500 nm).
prevalence of cubic CdS in the polymer matrix. It is quite well known that the CdS particles having hexagonal
crystal structure are more efficient as photo-catalysts for hydrogen production than their counter part with cubic
crystal structure [28]. Apart from the high surface area, good degree of crystallanity is very important for better
photocatalytic activity. While material with high surface area may exhibit good photocatalytic activity initially but
is prone to fast deactivation. Therefore, for the overall efficiency of a photocatalyst, its good crystalline nature is
more important than its surface area [28,29]. To this effect, CdS-NC-1:1 nanocomposite powder showed better
activity than CdS-NC-10:1. To compare our results with well-known system, we carried out experiments using Pt-
CdS as photocatalyst for the decomposition of H S under same experimental conditions that gave hydrogen
2
evolution rate of 1517 mmol/h (Q.Y. 7.7%). This suggests that CdS–PPS nanocomposite has much higher
photocatalytic activity than the nanocrystalline Pt-CdS.
In the present case (nano-CdS in cyclized PPS matrix), PPS matrix may also be contributing in suppressing the
photocorrosion of CdS. Hence, good stability of the nanocomposite is quite explicable. Bard and co-workers [30] also
made similar observations pertaining to the polymer matrix while reporting the photocatalytic hydrogen production
using CdS particles embedded in Nafion polymer.
4
. Conclusion
We have demonstrated that a polymer-inorganic solid-state method for the synthesis of nano-CdS crystallites (size,
–28 nm) embedded in the PPS network can be advantageously used for its generic application in the
photodecomposition of H S for hydrogen generation under visible light irradiation. The photocatalytic activity
6
2
examined for such CdS–PPS nanocomposite (in the pristine state) was much higher than that of commonly used Pt-
CdS. XRD data of the nanocomposite revealed the existence of hexagonal and cubic crystal structure of the CdS. The
hexagonal nano-CdS present in the nanocomposites may be responsible for good photocatalytic activity. Our
preliminary work may open up an enormous possibility of synthesizing variety of nano-metal sulfide in polymer
network for photocatalytic and allied applications.

K.G. Kanade et al. / Materials Research Bulletin 41 (2006) 2219–2225
2225
Acknowledgements
This research (paper) was performed for the Hydrogen Energy R&D Center, which is one of the 21st Century
Frontier R&D Program, funded by the Ministry of Science and Technology of South Korea. One of the authors (K.G.
Kanade) sincerely acknowledges to the Principal of Mahatma Phule College, Pimpri, Pune 411017 and the staff
members of the Nanocrystalline thick film materials/glass group of C-MET Pune, for their kind support during the
synthesis.
References
[
[
[
[
[
[
[
[
[
1] T. Kida, G. Guan, N. Yamada, T. Ma, K. Kimura, A. Yoshida, Int. J. Hydrogen Energy 29 (2004) 269.
2] A. Koca, M. Sahin, Int. J. Hydrogen Energy 27 (2002) 363.
3] A.S.K. Sinha, N. Sahu, M.K. Arora, S.N. Upadhyay, Catal. Today 69 (2001) 297.
4] A. Kudo, H. Kato, I. Tsuji, Chem. Lett. 33 (2004) 1534.
5] B.B. Kale, J.O. Baeg, J.S. Yoo, S.M. Lee, S.J. Moon, H. Chang, Can. J. Chem. 83 (2005) 527.
6] S. Kambe, M. Fujii, T. Kawai, S. Kawai, F. Nakahara, Chem. Phys. Lett. 109 (1984) 105.
7] L. Nguyen, R. Kho, W. Bae, R. Mehra, Chemosphere 38 (1999) 155.
8] T. Hirai, K. Suzuki, I. Komasawa, J. Coll. Int. Sci. 244 (2001) 262.
9] T. Kida, G. Guan, A. Yoshida, Chem. Phys. Lett. 371 (2003) 563.
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
10] W.F. Shangguan, A. Yoshida, J. Phys. Chem. B 106 (2002) 12227.
11] S.A. Naman, Int. J. Hydrogen Energy 22 (1997) 783.
12] A. Eychmuller, J. Phys. Chem. B 104 (2000) 6514.
13] L.E. Brus, J. Phys. Chem. 90 (1986) 2555.
14] A.P. Alivisatos, Science 271 (1996) 933.
15] H. Chang, K. Kong, Y. Choi, E. In, Y. Choi, J.O. Baeg, S. Moon, Chem. Phys. Lett. 398 (2004) 449.
16] U. Wendy, J. Janke, J. Dittmer, A.P. Alivisatos, Science 295 (2002) 2425.
17] G. Yu, J. Gao, J.C. Hummelen, F. Wudl, A.J. Heeger, Science 270 (1995) 1789.
18] L.S. Roman, M.R. Andersson, T. Yohannes, O. Inganas, Adv. Mater. 9 (1997) 1164.
19] J.J. Dittmer, E.A. Marseglia, R.H. Friend, Adv. Mater. 12 (2000) 1270.
20] K.G. Kanade, R.R. Hawaldar, R. Pasricha, S. Radhakrishnan, T. Seth, U.P. Mulik, B.B. Kale, D.P. Amalnerkar, Mater. Lett. 59 (2005) 554.
21] ASTM card No. 06-0314 and ASTM card No. 02-0454.
22] JCPDS Card No. 33-239.
23] Z. Zou, J. Ye, K. Sayama, H. Arakawa, Nature 414 (2001) 625.
24] M. Matsumura, Y. Saho, H. Tsubomura, J. Phys. Chem. 87 (1983) 3807.
25] I.B. Rufus, B. Viswanathan, V. Ramkrishnan, J.C. Kuriacose, J. Photochem. Photobiol. A: Chem. 91 (1995) 63.
26] L. Borrell, S. Cervera-March, J. Gimenez, R. Simartto, J.M. Andjar, Solar Eng. Mater. Solar Cells 25 (1992) 25.
27] N. Serpone, E. Borgarello, M. Gratzel, J. Chem. Soc., Chem. Commun. (1984) 342.
28] M. Ashokkumar, Int. J. Hydrogen Energy 23 (1998) 427.
29] D. Beydoun, R. Amal, G. Low, S. McEvoy, J. Nanopart. Res. 1 (1999) 439.
30] A.W.H. Mau, C.B. Huang, N. Kakuta, A.J. Bard, A. Campion, M.A. Fox, J.M. White, S.E. Webber, J. Am. Chem. Soc. 106 (1984) 6537.