Influence of temperature, pressure, and fluid salinity on the distribution of chlorine into serpentine minerals

Accepted Manuscript Full length Article Influence of temperature, pressure, and fluid salinity on the distribution of chlorine into serpentine minerals Ruifang Huang, Weidong Sun, Wenhuan Zhan, Xing Ding, Jihao Zhu, Jiqiang Liu PII: DOI: Reference:

S1367-9120(17)30124-4 http://dx.doi.org/10.1016/j.jseaes.2017.03.015 JAES 3012

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

15 September 2016 16 March 2017 17 March 2017

Please cite this article as: Huang, R., Sun, W., Zhan, W., Ding, X., Zhu, J., Liu, J., Influence of temperature, pressure, and fluid salinity on the distribution of chlorine into serpentine minerals, Journal of Asian Earth Sciences (2017), doi: http://dx.doi.org/10.1016/j.jseaes.2017.03.015

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Design of a solar light-responsive metal oxide/CdS/SrTiO3 catalyst with enhanced charge separation for hydrogen evolution

En-Chin Su1, Jia-Min Yeh1, Bing-Shun Huang2, Ju-Ting Lee1, Ming-Yen Wey1,* 1

Department of Environmental Engineering, National Chung Hsing University,

Taichung 402, Taiwan, R.O.C. 2

Taiwan Research Institute, Taipei, 251, Taiwan, R.O.C.

*Corresponding author. Tel.: +886-4-22840441 ext533; fax: +886-4-22862587 E-mail address: [email protected] (M.-Y. Wey)

1

Abstract A cadmium sulfide/strontium titanate (CdS/SrTiO3) composite with excellent charge separation efficiency was successfully developed by a simple precipitation process. The small band gap of CdS and the redox potential difference between CdS and SrTiO3 extended the solar light absorption range and improved the photo-generated charge separation, resulting in enhanced photocatalytic hydrogen evolution efficiency under solar irradiation. The ultraviolet–visible and photoluminescence analysis results indicated that the CdS/SrTiO3 composite possessed optimal synergistic effect for charge separation and solar light absorption when the coupling ratio of SrTiO3 was controlled at 3 wt%. Based on the improved charge separation of the CdS/SrTiO3(3), the CdS/SrTiO3(3) could exhibit significantly increased hydrogen evolution efficiency after coating with a small amount of PtO or CuO. The optimal photocatalytic hydrogen evolution efficiency was achieved when the surface of CdS/SrTiO3(3) was coated with 0.2 wt% of PtO; the hydrogen evolution rate of 0.2PtO/CdS/SrTiO3(3) was about 6 times higher than that of CdS, 4 times higher than that of CdS/SrTiO3(3), and 2.5 times higher than that of 0.3CuO/CdS/SrTiO3(3). Keywords: CdS/SrTiO3; charge separation; solar light-response; hydrogen evolution

2

1. Introduction Alternative fuel development has emerged as a necessary strategy to relieve the seriousness of the global energy crisis and environmental pollution caused by abundant consumption of fossil fuels (Nabgan et al., 2016; Yavor et al., 2015). Solar energy – which can provide the highest power per unit area – is not only the source for the evolution of fossil fuels (e.g., oil, coal, and natural gas) but also the source for renewable alternative energy (e.g., wind energy and hydro energy) formation (Hosseini and Wahid, 2016; Marone et al., 2014; Parthasarathy and Narayanan, 2014). The photocatalytic evolution of hydrogen using semiconductors is a promising and clean process to convert solar energy into a green alternative fuel (Abanades and Flamant, 2006; Fujishima and Honda, 1972). To date, strontium titanate (SrTiO3) – which possesses superior physicochemical stability, photocorrosion resistibility, and a conduction band (–0.5 eV vs. normal hydrogen electrode (NHE)) which is more negative than that of titanium dioxide (TiO2) (–0.29 eV vs. NHE) (Sharma et al., 2014; Bera et al., 2014) – has been regarded as a preferred material for photocatalytic hydrogen evolution reaction, the efficiency of which has been widely studied

(Saito

et al., 2015; Jain et al., 2013; Su et al., 2016). However, due to the large band gap (3.2 eV) of SrTiO3, the 45% of solar energy present as visible light (García-López et al., 2015) cannot be utilized by SrTiO3, resulting in limited hydrogen evolution efficiency 3

under solar irradiation. Cadmium sulfide (CdS) – a semiconductor with a small band gap (2.4 eV) and a conduction band that is more negative than that of SrTiO3 (Majeed et al., 2016; Shahzad et al., 2015; Soltani et al., 2013) – was developed and applied in the photocatalytic hydrogen evolution system for improving the utilization of visible light energy. However, because of the rapid recombination rate of photo-generated electron-hole pairs in CdS, the intrinsic activity of CdS cannot be seen very well (Khan et al., 2016; Vu et al., 2014). It has been reported that combining CdS with other semiconductors (e.g., zinc oxide (ZnO) or TiO2) can effectively retard the charge recombination rate. The photo-generated electron migration from the conduction band of CdS to that of ZnO or TiO2 will be induced leading to inhibited charge recombination and improved photocatalytic redox ability. Besides, it has been proven that modifying the surface of photocatalyst with metal oxides (e.g., platinum oxide (PtO), gold oxide (AuO), and copper oxide (CuO)) can further improve the charge separation efficiency (Yu et al., 2016; Li et al., 2011; Xu and Sun, 2009). The work function of metal ions is higher than that of CdS; hence, the metal oxide exhibits a better electron attraction than CdS. At the same time, a Schottky barrier is formed in the heterojunction between CdS and the metal oxide, and the Schottky barrier will hinder the photo-generated electron from returning to the 4

conduction band of CdS, effectively quenching the charge recombination and improving the photocatalytic activity (Escobedo Salas et al., 2013). Inspired by the properties of SrTiO3 and CdS mentioned above, we found that there is potential to enhance the photocatalytic activity under solar irradiation by combining CdS and SrTiO3. Besides one photocatalytic oxidation study (Wu et al., 2016), the efficiency of CdS/SrTiO3 composite for photocatalytic reduction has been rarely studied to date. Thus, we designed CuO/CdS/SrTiO3 and PtO/CdS/SrTiO3 triple-junctions to increase the hydrogen evolution efficiency. The CdS/SrTiO3 design was for improved visible light response and charge separation enhancement, and the CuO or PtO modification was for further improving the charge separation. The effects of the SrTiO3 coupling ratio, metal oxide decoration, and metal oxide coating amount on the optical properties, charge separation efficiency, and hydrogen evolution activity were investigated in detail. 2. Materials and methods 2.1 Catalyst preparation CdS/SrTiO3 A modified precipitation method was used to synthesize the CdS/SrTiO3 composite

(Jang et al., 2007; Shen et al.; Liu et al., 2010; Jang et al., 2007). Cadmium acetate (Cd(OAc)2
2H2O, purity = 98 %, Alfa Aesar) was dissolved in ethanol, and 5

SrTiO3 powder (purity = 99.5 %, Aldrich) was added to the mixture. After mixing for 30 min, sodium sulfide (Na2S, purity = 98 %, Aldrich) was slowly added into the solution, and stirred for 24 h. The mixture was washed with distilled water until neutral and then dried at 80 °C. The orange precipitate was ground to a fine powder with an agate mortar and then calcined at 600 °C for 2 h to form CdS/SrTiO3). The obtained composite is named CdS/SrTiO3(x), where x is the weight ratio of SrTiO3. CuO/CdS/SrTiO3 The CuO/CdS/SrTiO3 composite was synthesized by impregnation. An appropriate amount of copper acetate (Cu2(CH3COO)·2H2O, purity = 98 %, J.T Baker) was dissolved in distilled water after which CdS/SrTiO3 was mixed into the solution under vigorous stirring for 24 h. The mixture was heated at 80 °C until the solvent evaporated completely. The powder was calcined at 250 °C for 2 h, and the CuO/CdS/SrTiO3 composite was formed. The photocatalyst obtained was named (y)CuO/CdS/SrTiO3(x), where y was the CuO loading weight percentage. PtO/CdS/SrTiO3 The PtO/CdS/SrTiO3 composite was synthesized by impregnation. An appropriate amount of chloroplatinic acid hydrate (H2PtCl6·xH2O, purity = 99.95%, UR) was dissolved in ethanol (CH3CH2OH, purity = 99.5 %, Shimakyu Chemical) solution, and CdS/SrTiO3 was mixed into the solution under vigorous stirring. After stirring for 6

24 h, the mixture was heated at 80 °C until the solvent evaporated completely. The powder was calcined at 300 °C for 2 h, and the PtO/CdS/SrTiO3composite was formed. The photocatalyst obtained was named (z)PtO/CdS/SrTiO3(x), where z was the Pt loading weight percentage. 2.2 Photocatalytic activity tests Photocatalytic reactions were executed in a cylindrical reactor, and were evaluated under simulated sunlight irradiation (310 W/m2, XHA500). The distance between the reactor and the light source was 10 cm, and the reaction temperature was maintained at 20 °C by means of a cooling system. The photocatalysts were dispersed in methanol solution (25 % v/v), and the suspension was de-aerated by bubbling nitrogen gas for 30 min in the dark before beginning the test. The gases produced were sampled at 10 min intervals and analyzed by an online gas chromatograph (GC-TCD, Clarus 500 Perkin Elmer, Carboxen 1000 column) for hydrogen concentration evaluation. 2.3 Characterization of photocatalyst X-ray diffraction (XRD, M18XHF, Mac Science Co.) was applied to analyze the crystalline structure of the photocatalysts. Field emission scanning electron microscopy (FESEM, JSM-6700F, JEOL) was applied to study the morphologies of CdS, SrTiO3 and CdS/SrTiO3(3). The identification of elements was performed by 7

energy dispersive X-ray spectrometry (EDS). X-ray photoelectron spectroscopy (XPS, ESCALAB 250, VG Scientific) was used to determine the chemical state of photocatalysts. The microstructures of the photocatalysts were observed by field-emission transmission electron microscopy (FETEM, JEM-2100F, JEOL). The electronic transmission and the charge recombination probability of the photocatalysts were recorded by photoluminescence, LS 45, Perkin Elmer) with a xenon lamp. The optical reflection of the photocatalysts was evaluated by ultraviolet–visible spectrophotometry (UV-Vis, Lambda 35, Perkin Elmer). 3. Results and discussion 3.1 Influence of SrTiO3 coupling ratio on hydrogen evolution activity of CdS/SrTiO3 Figure 1 shows the XRD patterns of the as-prepared CdS composed with 1-10 wt% of SrTiO3. The main crystalline peaks of CdS/SrTiO3 appeared at 2Ө = 24.8°, 26.5°, 28.2°, 36.8°, 43.8°, 47.9°, 52°, 66.9°, 71.1°, and 75.6° were identified as hexagonal CdS (JCPDS Card No. 411049); the main crystalline peaks of CdS/SrTiO3 appeared at 2Ө = 33.0° and 58.4° were identified as perovskite SrTiO3 (JCPDS Card No. 840444). It was observed that the peak intensity of CdS gradually decreased with the increasing SrTiO3 coupling ratio. The results show that the SrTiO3 was successfully incorporated in CdS by precipitation. Moreover, it was found that the 8

changes in the full width at half maximum (FWHM) and position of CdS were negligible after coupling with SrTiO3, indicating that coupling CdS with SrTiO3 by precipitation method does not damage the intrinsic properties of CdS. Figure 2(a) shows that the CdS was made of particles with a size of 7 nm. In contrast, the SrTiO3 was constructed by a cubic particle with a size of 120 nm (Fig. 2(b)). Moreover, from the Fig. 2(c), it was found that the morphology of SrTiO3 could not be observed from the FESEM image of CdS/SrTiO3(3). However, the EDS analysis result confirmed that the CdS/SrTiO3(3) consisted of Sr, Ti, O, Cd, and S. According to the results, it was reasonably deduced that SrTiO3 was embedded in the CdS particle clusters. The XPS spectra of Cd 3p, S 2p, Sr 3d, Ti 2p, and O 1s for the CdS/SrTiO3(3) are presented in Fig. 3. The Cd 3p spectra in Fig. 3a exhibits peaks at 411.2 and 404.5 eV; these peaks could be assigned to the CdS nanoparticles (Cui et al., 2012; Zhang et al., 2014). As shown in Fig. 3b, the S 2p spectrum also contained two peaks at 162.2 and 160.9 eV, which are the S 2p 1/2 and S 2p3/2 spin-orbit components of S2-, respectively (Johan et al., 2016; Rengaraj et al., 2011; Abe et al., 2001). The Sr 3d spectra showed peaks at 134.5 and 132.5 eV, which corresponds to the Sr2+ ion in SrTiO3 (Yu et al., 2011; Guo and Yin, 2015) (Fig. 3c). The spectrum of the Ti 2p in Fig. 3d suggests that the characteristic peaks centered at 464.1 and 458.0 eV, 9

indicating a Ti4+ oxidation state in the SrTiO3/TiO2 heterostructure (Fuentes et al., 2010); the peak of O 1s centered at 530.8 eV represented the Sr–Ti–O structure (Hu et al., 2004). The XPS analysis results imply that the CdS was successfully combined with SrTiO3, supporting the claims made above. From Fig. 4 (a), it was found that the PL intensity of CdS/SrTiO3 was lower than that of CdS. Since PL is the energy released after the recombination of the photo-generated hole and electron, the decreased PL intensity of CdS/SrTiO3 denotes retarded hole-electron recombination. Additionally, it was observed that the PL intensity decreased with the increasing SrTiO3 coupling ratio. This phenomenon was attributed to the redox potential difference between CdS and SrTiO3. It has been indicated that the reduction and oxidation potentials of CdS were -0.79 eV (NHE) and 1.61 eV (NHE), respectively (Ahmad Beigi et al., 2014; Kumar Yadav and Jeevanandam, 2015), which are more negative than the reduction potential of SrTiO3 (-0.5 eV vs. NHE) and less positive than the oxidation potential of SrTiO3 (2.7 eV vs. NHE), respectively. As shown in Fig. 4 (b), the photo-generated electron would migrate from the conduction band of CdS to that of SrTiO3, and the photo-generated hole would migrate from the oxidation band of SrTiO3 to that of CdS, leading to retarded charge recombination. Besides, the charge separation probability was increased with the increasing SrTiO3 coupling ratio, leading to a higher charge 10

separation probability. Thus, the PL intensity was inversely proportional to the SrTiO3 coupling ratio. From Fig.5, it was found that the CdS exhibited a better hydrogen evolution efficiency than SrTiO3 under irradiation by simulated sunlight, which was ascribed to the optical property of CdS. As shown in Fig.6, CdS revealed a better solar light absorption due to the smaller energy gap of CdS, resulting in better hydrogen evolution efficiency. Moreover, it was observed that the hydrogen evolution efficiency was further increased when the CdS was co-precipitated with an appropriate amount of SrTiO3, which reflected in the PL analysis result shown in Fig. 4. The hydrogen evolution activity increased when the SrTiO3 coupling ratio was increased from 0 to 3 wt%, and the highest hydrogen evolution efficiency – 169 µmol/h/g – was obtained when the SrTiO3 coupling ratio was 3 wt%. However, decreased hydrogen evolution activities were obtained when the SrTiO3 coupling ratio was increased to 5 and even 10 wt%. The excellent photocatalytic performance is usually achieved when good charge separation and good UV/visible light absorption conditions are present. The UV-Vis/DRS analysis result shown in Fig. 6 indicates that CdS exhibited the optimal visible light response. However, the light absorption edge of CdS shifted toward a shorter wavelength when the CdS was combined with SrTiO3, and the degree of blue shift was increased with the increase in SrTiO3 coupling ratio. 11

Because the SrTiO3 is intrinsically a UV light responsive material, the degree of blue shift was proportional to the SrTiO3 coupling ratio. According to the results, it was predicted that the visible light response of CdS/SrTiO3 would decrease with the increase in the SrTiO3 coupling ratio, leading to decreased hydrogen evolution efficiency. When the SrTiO3 coupling ratio was controlled at 3 wt%, the CdS/SrTiO3 exhibited an excellent synergistic effect for charge separation and solar light absorption. 3.2 Influence of metal oxide decoration on hydrogen evolution activity of CdS/SrTiO3(3) Based on the results in the previous section, it was found that CdS/SrTiO3(3) possessed the optimal solar light absorption and charge separation. In this section, small amounts of CuO and PtO were coated on the surface of CdS/SrTiO3(3) by impregnation to improve the photocatalytic hydrogen evolution efficiency, and the effects of metal oxide and loading amount on hydrogen evolution efficiency are discussed. Figure 7 shows the XRD patterns of the uncoated CdS/SrTiO3(3), the CdS/SrTiO3(3) coated with 0.3 wt% CuO, and the CdS/SrTiO3(3) coated with 0.2 wt% PtO. No obvious difference was found in the XRD patterns of these as-prepared samples, indicating that the intrinsic property of CdS/SrTiO3(3) would not be changed 12

after modifying with CuO and PtO. In addition, the characteristic peaks of CuO and PtO could not be observed from these patterns. Because the CuO and PtO coating amounts used in this study were much lower than usual and were below the detection limitation of XRD, the characteristic peak of CuO and PtO could not be detected in the patterns. XPS was used to analyze the chemical states of Cu and Pt, and the results are presented in Fig. 8. The Cu 2p spectra showed the peaks at 931.5 and 951.6 eV, and these peaks are attributed to the CuO nanostructure (Anandan et al., 2012). The Pt 4f spectra showed peaks at 71.6 eV and 74.8 eV, and these peaks are ascribed to Pt (Wang et al., 2012; Zeng et al., 2007; Xin et al., 2014). The XPS analysis results evidenced that the Cu and Pt coated on the surface of CdS/SrTiO3(3) was in the form of an oxide. Fig. 9 (a) shows the photocatalytic hydrogen evolution efficiencies of the CdS/SrTiO3(3) coated with different amounts of CuO. 0.3CuO/CdS/SrTiO3(3) showed the highest hydrogen evolution activity under simulated sunlight irradiation. However, it was observed that the hydrogen evolution efficiency was decreased with increasing CuO coating amount. This was because the excess amount of metal oxide becomes the charge recombination center on the surface of the photocatalyst (Puangpetch et al., 2009; Su et al., 2015), resulting in inhibited hydrogen evolution 13

activity.

However,

the

result

shown

in

Fig.

9(b)

indicated

that

the

0.2PtO/CdS/SrTiO3(3) revealed a better activity for hydrogen evolution, and the hydrogen evolution rate – 680 µmol/h/g – was about 2.5 times higher than that of 0.3CuO/CdS/SrTiO3(3). The result was attributable to the work functions of Pt (5.6 eV) and Cu (4.64 eV) (Tănase et al., 2016; Huang et al., 2016). It has been reported that the metal with higher work function has better electron attraction (Su et al., 2015), which results in improved electron migration and charge separation. Due to the higher work function of Pt, the 0.2PtO/CdS/SrTiO3(3) displayed a better hydrogen evolution efficiency even though the PtO coating amount (0.2 wt%) was lower than the CuO coating amount (0.3 wt%). 3.3 Influence of PtO coating amount on hydrogen evolution activity of CdS/SrTiO3(3) The effect of PtO coating amount on hydrogen evolution activity of CdS/SrTiO3(3) was further investigated to develop a PtO/CdS/SrTiO3(3) photocatalyst with the optimal synergistic effect. Figure 10 shows that the hydrogen evolution efficiency of PtO/CdS/SrTiO3(3) was increased when the PtO coating amount was increased from 0 to 0.2 wt%, and the highest hydrogen evolution efficiency – 680 µmol/h/g – was obtained when the PtO coating amount was 0.2 wt%. However, the hydrogen evolution rate dropped from 680 µmol/h/g to 180 µmol/h/g when the PtO coating 14

amount was further increased to 0.5 wt%. The FETEM images shown in Fig. 11 demonstrated that the density of PtO particle distribution was gradually increased with the increase in PtO coating amount. Besides, the PL analysis results shown in Fig. 12 indicated that the 0.2PtO/CdS/SrTiO3(3) revealed the lowest PL intensity, and the 0.5PtO/CdS/SrTiO3(3) showed a rebound PL intensity. The trend demonstrated that the excessive amount of PtO act as charge recombination centers, which was detrimental to the photocatalytic hydrogen evolution activity (Jaafar et al., 2015; Jai et al., 2016). 4. Conclusions This study provided a new perspective and a facile method for developing a photocatalyst with excellent charge separation ability and solar light-response for photocatalytic hydrogen evolution. The result showed that because of the redox potential between CdS and SrTiO3, combining SrTiO3 with CdS could effectively improve the charge separation ability. When the coupling ratio of SrTiO3 was controlled at 3 wt%, the CdS/SrTiO3 possessed the optimal synergistic effect for charge separation and solar light absorption. Based on the improved charge separation of the CdS/SrTiO3(3), the CdS/SrTiO3(3) exhibited significantly increased hydrogen evolution efficiency after coating with a small amount of metal oxide(≦ 1 wt%), which could also effectively reduce the cost 15

of photocatalytic hydrogen evolution system development. The result shows that the optimal photocatalytic hydrogen evolution efficiency was achieved when the surface of CdS/SrTiO3(3) was coated with 0.2 wt% of PtO, and the hydrogen evolution rate (680 µmol/h/g) was about 4 times higher than that of CdS/SrTiO3(3); 2.5 times higher than that of 0.3CuO/CdS/SrTiO3(3). Acknowledgments The authors would like to thank the Ministry of Science and Technology (MOST), Taiwan,

R.O.C., for providing financial support under Grant No. NSC

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Sharma, D., Upadhyay, S., Satsangi, V.R., Shrivastav, R., Waghmare, U.V., Dass, S., 2014.

Improved

Cu2O/SrTiO3

photoelectrochemical

heterojunction

water

photoelectrode.

splitting J

Phys.

performance Chem.

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Figure captions Fig. 1 XRD patterns of CdS, SrTiO3, CdS/SrTiO3(1), CdS/SrTiO3(3), CdS/SrTiO3(5), and CdS/SrTiO3(10). Fig. 2 FESEM images of (a) CdS, (b) SrTiO3, (c) CdS/SrTiO3(3); (d) EDS analysis of CdS/SrTiO3(3). Fig. 3 Chemical states of CdS/SrTiO3(3). (a)Cd 3p, (b)S 2p, (c)Sr 3d, (d)Ti 2p, and (e)O 1s Fig. 4 PL spectra of (a) CdS, SrTiO3, and (b) CdS/SrTiO3; The mechanism of photo-generated charge separation between CdS and SrTiO3 of (b). Fig. 5 Influence of SrTiO3 coupling ratio on hydrogen evolution. Fig. 6 UV-Vis/DRS spectra of (a) CdS, SrTiO3, and CdS/SrTiO3. Fig.

7

XRD

patterns

of

CdS/SrTiO3(3),

0.3CuO/CdS/SrTiO3(3),

and

0.2PtO/CdS/SrTiO3(3). Fig. 8 XPS Cu2p spectra of (a) 0.3CuO/CdS/SrTiO3(3) and XPS Pt4f spectra of (b) 0.2PtO/CdS/SrTiO3(3). Fig. 9 Comparison of the photocatalytic hydrogen evolution. (a) Influence of CuO coating amount; (b) influence of metal oxide decoration. Fig. 10 Influence of PtO coating amount on CdS/SrTiO3(3) activity on hydrogen evolution. 25

Fig. 11 FETEM images of (a) CdS/SrTiO3(3), (b) 0.1PtO/CdS/SrTiO3(3), (c) 0.2PtO/CdS/SrTiO3(3); (d) 0.5PtO/CdS/SrTiO3(3). Fig. 12 PL spectra of CdS/SrTiO3(3) and PtO/CdS/SrTiO3(3).

26

SrTiO3 CdS

SrTiO3

Intensity (a.u.)

CdS

CdS/SrTiO3(1)

CdS/SrTiO3(3)

CdS/SrTiO3(5)

CdS/SrTiO3(10) 20

30

40

50

60

2 Theta (degree)

27

70

80

28

(a)

Cd 3p5/2 404.5 eV

Intensity (a.u.)

Intensity (a.u.)

Cd 3p3/2 411.2 eV

414

412

S 2p3/2 404.5 eV

(b)

Cd 3p

410

408

406

404

402

S 2p1/2 162.2 eV

166

400

164

Binding Energy (eV)

Sr 3d

136

Intensity (a.u.) 134

132

130

470

465

Binding Energy (eV)

156

Ti 2p

460

455

Binding Energy (eV) O 1s 530.8 eV

(e)

536

158

Ti 2p3/2 464.1 eV

O 1s

Intensity (a.u.)

Intensity (a.u.)

138

160

Ti 2p1/2 458.0 eV

(d)

Sr 3d5/2 134.5 eV

140

162

Binding Energy (eV)

Sr 3d3/2 132.5 eV

(c)

S 2p

534

532

530

Binding Energy (eV)

29

528

450

30

31

32

Intensity (a.u.)

CdS/SrTiO3(3)

0.3CuO/CdS/SrTiO3(3)

0.2PtO/CdS/SrTiO3(3)

20

30

40

50

60

2 Theta (degree)

33

70

80

34

35

36

37

38

HIGHLIGHTS




CdS/SrTiO3 was successfully developed by a simple precipitation process.




CdS/SrTiO3 showed synergistic effect for charge separation.




The charge separation was proportional to the SrTiO3 coupling ratio.




PtO/CdS/SrTiO3 revealed a better activity than CuO/CdS/SrTiO3.




The optimal H2 evolution rate was achieved when the PtO coating amount was 0.2 wt%.

39