Ca(II) doped β-In2S3 hierarchical structures for photocatalytic hydrogen generation and organic dye degradation under visible light irradiation

Accepted Manuscript Ca(II) doped β-In2S3 hierarchical structures for photocatalytic hydrogen generation and organic dye degradation under visible light irradiation Shuang Yang, Cheng-Yan Xu, Bao-You Zhang, Li Yang, Sheng-Peng Hu, Liang Zhen PII: DOI: Reference:

S0021-9797(16)31029-3 http://dx.doi.org/10.1016/j.jcis.2016.12.028 YJCIS 21862

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

24 October 2016 14 December 2016 14 December 2016

Please cite this article as: S. Yang, C-Y. Xu, B-Y. Zhang, L. Yang, S-P. Hu, L. Zhen, Ca(II) doped β-In2S3 hierarchical structures for photocatalytic hydrogen generation and organic dye degradation under visible light irradiation, Journal of Colloid and Interface Science (2016), doi: http://dx.doi.org/10.1016/j.jcis.2016.12.028

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Ca(II) doped β-In2S3 hierarchical structures for photocatalytic hydrogen generation and organic dye degradation under visible light irradiation Shuang Yang a, b, Cheng-Yan Xu a, b*, Bao-You Zhang a, b, Li Yang a, Sheng-Peng Hu a, b, c, Liang Zhen a, b* a

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001,

China b

MOE Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Harbin Institute of

Technology, Harbin 150080, China c

School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai

264209, China. *

Corresponding authors. Tel: 86-451-86412133; Fax: 86-451-86413921;

E-mail: [email protected] (C.Y. Xu); [email protected] (L. Zhen)

Abstract: Hierarchical structures assembled by two-dimensional (2D) nanosheets could inherit the characteristics of nanosheets and acquire additional advantages from the unique secondary architectures, which would have important influences on the photocatalytic properties of semiconductor nanomaterials. In this work, we successfully synthesized Ca(II) doped β-In2S3 hierarchical structures stacked by thin nanosheets by a simple solution chemical process. The effects of reaction temperature and Ca2+ concentration on the size and morphology of the products were systematically investigated. The photocatalytic applications of the β-In2S3 hierarchical structures were evaluated for hydrogen production and degradation of Rhodamine B 1

(RhB) under visible light irradiation (λ > 420 nm). The β-In2S3 hierarchical structures showed promising activity towards photocatalytic hydrogen production (145.0 μmol g−1 h−1) and RhB solution (1 × 10-5 M) was completely degraded within 100 min under visible light irradiation. Keywords: Chemical synthesis, β-In2S3 hierarchical structures, Hydrogen production, Photocatalysis.

1. Introduction In recent years, energy and environmental issues have been considered as the biggest global problems. Photocatalysis brings a new way to exploit renewable energy resource and environment remediation using abundant sunlight, which has attracted the attention of many researchers.[1-4] Until now, many photocatalysts have been extensively studied for hydrogen production and degradation of organic pollutants. As a traditional photocatalyst, TiO2 have been widely applied in water splitting and environment treatment, but it has practical limitations due to their intrinsic band gaps, which is mainly photosensitive in the UV range.[5, 6] Recently, several narrow bandgap semiconductors, which are sensitive to visible light, were developed for solving energy and environmental issues. For example, Fu et al.[7] successfully developed a simple solvothermal method for the synthesis of Pt modified CdS nanorods. The photocatalytic H2 evolution rate of CdS nanorods could be remarkably improved by varying the loading amount of Pt under visible light irradiation. Zhang et al.[8] found that flower-like CdSe architectures composed of ultrathin nanosheets

2

could be formed by a facile solvothermal method, which possess the superior visible-light-responsive photocatalytic H2 evolution activities. Sun et al.[9] demonstrated the synthesis of visible-light active Zn-Cd-S solid solutions with surface defects for photocatalytic H2 evolution. As the most popular visible-light-driven photocatalysts, the practical applications of cadmium chalcogenide semiconductors are also limited because of toxic and not environmentally friendly. Therefore, the exploration of efficient and environmental photocatalysts with visible-light-driven is the highly challenge in the photocatalytic fields. As a typical III-VI group sulfide, In2S3 is known to crystallize in three polymorphic forms: defective cubic structure (α-In2S3), defective spinel structure (β-In2S3), and layered hexagonal structure (γ-In2S3).[10, 11] Of these, β-In2S3 is the stable form with tetragonal or cubic crystal structure at room temperature, and it is an n-type semiconductor with desired band gap energy (2.0–2.3 eV) corresponding to visible light region[12-14]. Various kinds of β-In2S3 micro/nanostructures, such as nanoparticles, nanoflakes, nanosheets, nanorods, nanotubes, microspheres, urchin-like structures, and hollow nanostructures, have been prepared by different synthetic methods.[14-22] However, there are only a few reports regarding metal ions doping β-In2S3 micro/nanostructures. Wang et al.[23] investigated the introduction of Zr4+ ions into β-In2S3 ultrathin nanoflakes via a facile solvothermal method. These Zr-doped β-In2S3 nanoflakes, with a red shift of 0.22 eV in the UV-visible spectrum, possessed

better

photoelectrochemical

water

splitting

activity.

Maha

and

co-workers[24] prepared Sn-doped β-In2S3 thin films by spray pyrolysis technique.

3

The photoconductive properties of these β-In2S3 thin films can be modified by Sn doping, which makes it more suitable for optoelectronic applications. Choe et al.[25] synthesized Co2+ doped β-In2S3 single crystals with defective structures by the chemical transport reaction method. The size and morphology of semiconductor materials have important influences on the photocatalytic properties, such as the separation or transport of electrons and holes and the transportation related to active species.[26] In particular, hierarchical structures with nanoscale building blocks have shown high specific areas effective for photocatalysis application, which is considered to enhance light harvesting capacity.[22, 27] Metal ions doping has been shown to be efficient way to control hierarchical structures of semiconductor materials. For example, Jiang et al.[28] successfully prepared hierarchical structures based on Fe-doped BiOBr hollow microspheres, which exhibit excellent photocatalytic activity for degradation of Rhodamine B. The Fe ions play a vital role in the self-assembly process of hierarchical structures. Zhang et al.[29] developed Mn doped flower-like ZnO hierarchical structures by a facile ion-exchange process. The inner structures of ZnO hierarchical structure were nanosheets or nanorods with the doped different amount of Mn ion. More importantly, the introduction of Mn ion into ZnO hierarchical structure could enhance photocatalytic performance. Until now, there are no reports on the synthesis of β-In2S3 hierarchical structures controlled by metal ions doping. In this work, Ca(II) doped β-In2S3 hierarchical structures stacked by 2D nanosheets were successfully fabricated via a simple solution chemical process. The phase,

4

morphologies and microstructures of the products were carefully examined. We systematically investigated the effects of the reaction temperature and Ca2+ concentration on the size and morphology of the products. A possible formation process of Ca(II) doped β-In2S3 hierarchical structures was proposed. Furthermore, the photocatalytic applications of the β-In2S3 hierarchical structures were evaluated for hydrogen production and degradation of RhB under visible light irradiation. 2. Experimental sections 2.1 Synthesis All the reagents were of analytical grade and were used as received without further purification. In a typical hot-injection route, 5.0 mmol of indium chloride tetrahydrate (InCl3 •4H2O) was added into 10 mL of triethylene glycol (C6H14O4, TEG) in a beaker under magnetic stirring until the formation of a clear indium precursor. 0.2 mmol of anhydrous calcium chloride (CaCl2) and 0.75 mmol of sulfur powder (S) were dissolved into 30 mL of TEG in a 50 mL three-necked round-bottom flask. The flask was quickly heated from room temperature to 220°C under magnetic stirring. Subsequently, 1 mL of indium precursor solution was swiftly injected into the flask with vigorous stirring. The reaction solution was maintained at 220°C for 30 min. Finally, the reaction solution was cooled to room temperature naturally. The products were precipitated by high speed centrifugation. The obtained products were washed several times with absolute ethanol, and dried at 60°C in air. In order to investigate the effect of reaction temperature and Ca2+ concentration, comparative experiments were carried out by changing single experimental parameter. 2.2 Characterization Powder X-ray diffraction (XRD) was recorded by Rigaku D/max 2500 diffractometer with Cu Kα irradiation (λ = 1.54178 Å). Field-emission scanning 5

electron microscope (FE-SEM, FEI Quanta 200F) was used to observe the morphology of the products. Transmission electron microscope and high-resolution transmission electron microscope (TEM and HRTEM, JEOL JEM 2100) was used to further characterize the microstructures of the products. Energy-dispersive spectroscopy (EDS) measurement was carried out on FEI Quanta 200F SEM. The surface chemistry and elemental valence analysis of the products were analyzed with X-ray photoelectron spectra (XPS, Thermofisher Scienticfic Company). Optical diffusion reflectance spectrum of the samples was acquired by using UV-vis spectrometer (Shimadzu UV-2550). 2.3 Photocatalytic hydrogen evolution Photocatalytic hydrogen evolution for β-In2S3 hierarchical structures under visible light irradiation was performed in CEL-SPH2N photocatalytic activity evaluation system (Beijing Au-light, China). The cylindrical reactor made of quartz vessel was 10 cm in height and 7 cm in diameter. A 300 W Xe lamp (CEL-HXF 300, Beijing Au-light, China, I = 20 A) with a cut-off filter (λ > 420 nm) was employed as visible light source. In a typical photocatalytic experiment, 20 mg photocatalyst was suspended in 100 mL 0.10 M Na2S and 0.10 M Na2SO3 mixed solution by magnetic stirring. A certain amount of H2PtCl6•6H2O aqueous solution was dripped into the system to load Pt onto the surface of the photocatalyst. Before reaction, the photocatalytic hydrogen production system was vacuumized using a mechanical pump. The concentration of H2 was analyzed by gas chromatography (GC7890 II TECHCOMP, China) equipped with a thermal conductivity detector (N 2 carrier), which was connected to the gas circulating line. According to the fitted standard curve, the amount of hydrogen production was calculated. After catalytic reaction, the suspension containing the used catalyst was centrifuged, and washed with absolute

6

ethanol for several times. The recycled catalyst was dried at 60°C in air before the next cycle of reaction. 2.4 Photodegradation activity measurements The photocatalytic activity of β-In2S3 hierarchical structures was evaluated by recording the degradation of RhB in aqueous solution under visible-light irradiation. A 300 W Xe lamp (CEL-HXF 300, Beijing Au-light, China, I =20 A) was employed as light source and a 420 nm cut-off filter was used to provide only visible-light irradiation. The photocatalytic experiments were conducted as follows: 20 mg of β-In2S3 hierarchical structures were immersed in RhB solution (1.0×10 -5 M, 200 mL) and then magnetically stirred in dark for 20 min to reach adsorption equilibrium and uniform dispersibility. The solution was then exposed to visible light irradiation for up to 100 min. During the degradation process, the suspension was magnetically stirred. About 3 mL aliquots were collected from the suspension and centrifuged immediately to remove the photocatalyst particles every 20 min. The dye concentration in the supernatant solution was acquired by measuring the absorption intensity of RhB at 554 nm using a Shimadzu UV-2550 UV–vis spectrometer. 3. Results and discussion The crystal structure and phase composition of products were examined by XRD. As shown in Fig. 1a, all the observed diffraction peaks were in good agreement with those of tetragonal β-In2S3 (JCPDS no. 25-0390). No other phases such as CaS or CaIn2S4 were observed, indicating that Ca ions were successfully incorporated in the β-In2S3 crystal structure. Fig. 1b shows the magnified XRD patterns of the products in the 20–30º range. The peaks shifted towards low angle due to crystal lattice distortion of β-In2S3 after Ca doping. The ion radius of Ca2+ (0.99 Å) was larger than that of In3+ 7

(0.81 Å), and thus XRD peaks of the obtained product shift to lower angle region compared with the standard diffraction pattern of β-In2S3, suggesting successful doping of Ca2+ into the crystalline lattices of β-In2S3. The EDS spectrum shown in Fig. S1 demonstrates that the obtained product is composed of Ca, In, and S. The elemental mapping images reveal that In, S and Ca are homogeneously distributed (Fig. S2). The elemental mapping images show the presence of Ca in the product, which further demonstrated Ca2+ doping. The EDS result shows that the molar ratio of In:S is very close to 2:3, suggesting the formation of In2S3. The obtained Ca(II) doped β-In2S3 products were further examined by X-ray photoelectron spectroscopy (XPS). XPS spectrum in Fig. 2a confirm that the products contain In, Ca and S elements. Fig. 2b shows the XPS spectrum of In 3d peak; two bands around 444.2 and 452.1 eV are attributed to the 3d 5/2 and 3d 3/2 of the In(III) in β-In2S3[30, 31]. The binding energies of S 2p3/2 and 2p1/2 in Fig. 2c are identified at 161.1 and 162.1 eV, indicating the presence of S2-[32, 33]. As shown in Fig. 2d, the Ca 2p3/2 and 2p1/2 peaks are located at 347.5 and 351.2 eV, respectively, consistent with those reported Ca2+[34], indicating that Ca2+ partially substituted In3+ to form Ca2+ doped β-In2S3. The XPS quantitative analysis shows that Ca2+ mass ratio in the products is 4.45 %. The morphology and microstructure of the products are characterized by FE-SEM and TEM. Fig. 3a and b shows typical SEM images of as-prepared Ca2+ doped β-In2S3 hierarchical structures. The low-magnification SEM image (Fig. 3a) indicates the as-synthesized products consist of uniform flower-like spheres with diameters of 1.5

8

μm. High-magnification SEM image (Fig. 3b) clearly reveals that the flower-like spheres are assembled with numerous nanosheets, implying the formation of hierarchical structures. The detailed morphologies and structure features were further investigated by TEM and high-resolution TEM (HRTEM). As shown in Fig. 3c, TEM image confirms the highly dispersed β-In2S3 hierarchical structure. Fig. 3d shows a high-magnification TEM image of β-In2S3 hierarchical structure. It is obvious that the nanosheets are with thicknesses of about 10–20 nm. Meanwhile, these thin sheets could lead to short pathway for electron transport, which is benefit for enhancing the photocatalytic activity[35]. Selected-area electron diffraction (SAED) pattern in Fig. 3e corresponding to an individual sphere (the blue square in Fig. 3c) showed diffraction rings, which can be all indexed to the (109), (0012) and (2212) planes of β-In2S3. High-resolution transmission electron microscope (HRTEM) image (Fig. 3f) of the sheet (the red rectangle in Fig. 3d) shows three sets of clear lattice fringes with interplanar distances of 0.269, 0.277 and 0.325 nm, corresponding to (0012), (208) and (109) planes of β-In2S3, respectively. The reaction temperature of solution-phase synthesis usually is an important impact factor in adjusting the morphology and phase structure of products. Fig. 4 shows SEM images of the products obtained at lower temperatures, while keeping other reaction conditions the same as typical experiment. When the temperature was set as low as 180°C, the as-obtained products are uniform urchin-like hierarchical structures with diameters ranging from 520 to 640 nm (Fig. 4a). Upon careful examination of high-magnification SEM image, we find that these hierarchical structures are

9

composed of numerous nanorods (Fig. 4b). As shown in Fig. S3, the lower intensity and broader peak width in the XRD patterns displayed the lower crystalline of these urchin-like hierarchical structures. When the temperature was increased to 200°C, the morphology of the as-synthesized products consists of monodisperse flower-like nanospheres with diameters in range of 680–800 nm (Fig. 4c). Higher-magnification SEM image clearly reveals that these flower-like nanospheres are built from lots of nanosheets and tiny bit of nanorods (Fig. 4d). The existence of nanorods differs from the as-synthesized products at 220°C (Fig. 3b). In addition, XRD pattern in Fig. S3 showed that the crystallinity of the products increased as the temperatures rise. As the temperature was further increased to 220°C, the as-synthesized products were β-In2S3 hierarchical structures which consist of numerous nanosheets (Fig. 3a-d). Base on the above results, we can find that the building units of the products have changed from nanorods to nanosheets with increased reaction temperatures. We further investigated the effect of Ca2+ concentration on the products (Fig. 5). Without Ca ions, the obtained products were porous network of In2S3 platelets (Fig. 5a,b and Fig. S4). When the concentration of CaCl2 was doubled, the as-synthesized products remain flower-like In2S3 spheres and the diameters of these spheres increased to 3.0 μm (Fig. 5c and Fig. S5). High-magnification SEM image (Fig. 5d) clearly reveals that flower-like structures were decorated with nanosheets, implying the formation of hierarchical structures. Compared with the samples obtained at 220°C (Fig. 3a-d), the flower-like spheres diameters increase obviously, the assembled units (nanosheets) become thicker, and the close-packed spheres have more

10

tight structures. From these experimental results, it is clear that the moderate Ca ions had a strong influence on the β-In2S3 hierarchical structure, which is beneficial to the improvement of photocatalytic performance. On the basis of the above experimental results, we propose the possible formation process of β-In2S3 hierarchical structures. First of all, the melting point of sulfur powders is relatively low (120 °C)[36-38]. During the heating process of hot-injection reaction, spherical sulfur liquid droplets could be obtained from the sulfur powders[36-38]. When the indium precursor solution was injected into the spherical sulfur liquid droplets rapidly, the spherical sulfur liquid droplets will be broken readily. Simultaneously, the chemical reactions shown in equation (1) could occur: 3HO(CH2CH2O)2CH2CH2OH + 3S + 2InCl3   3HO(CH2CH2O)2CH2CHO + In2S3 + 6HCl

(1)

(Figs. 5a,b)

and homogeneous β-In2S3 hierarchical structures. The optical absorption of β-In2S3 hierarchical structures was first determined by UV-vis diffuse reflectance spectrometer. As shown in Fig. 6a, β-In2S3 hierarchical structures have a steep absorption edge in the visible light region. By the Tauc's

11

equation[39, 40], the indirect and direct band gap of β-In2S3 hierarchical structures are estimated to be about 2.19 and 2.34 eV, respectively (Fig. 6b, c), which is close to the value of β-In2S3 reported in other literatures (1.98–2.24 eV for the indirect energy band gap and 2.28–2.64 for the direct energy band gap)[25, 41]. The band-edge potentials of the valence band (EVB) and conduction band (ECB) can be defined as[42, 43]: EVB=X–EC+0.5 Eg and ECB=X–EC–0.5 Eg (where X and EC are the geometric mean of the electronegativity of the constituent atoms (4.71 eV for In2S3), and the energy of free electrons on the hydrogen scale (about 4.5 eV), respectively. The indirect band gap of β-In2S3 hierarchical structures is selected as Eg in the above formula (about 2.19 eV).) Thus, EVB and ECB of In2S3 can be estimated to be 1.30 and –0.89 eV, respectively. This indicated that the as-prepared β-In2S3 hierarchical structures have the appropriate ECB for photocatalytic hydrogen evolution under visible light irradiation. The photocatalytic activities of β-In2S3 hierarchical structures were investigated by photocatalytic production of hydrogen from an aqueous solution containing both Na2SO3 and Na2S under visible light irradiation. As a co-catalyst, the noble metal Pt could offer low activation potentials for hydrogen generation and promote the separation of photoexcited electrons/holes as reduction/oxidation sites[44]. As shown in Fig. S6 and Fig. S7, the optimum amount of Pt loading for β-In2S3 hierarchical structures was first investigated. When no Pt loading, β-In2S3 hierarchical structures show no activity for photocatalytic hydrogen evolution. With the increase of Pt loading amounts from 0.5 to 1.0 wt%, the H2 evolution rate increases from 57.1 to

12

145.0 μmol g−1 h−1. However, when the amount of Pt loading to 2.0 wt %, it was surprising to note that the hydrogen evolution rate was reduced (67.2 μmol g−1 h−1). As the literature reported[45], the more active sites of β-In2S3 hierarchical structure were covered with the higher loading amount of Pt. In addition, the loading Pt could act as electron–hole recombination centers, which will result in lower photocatalytic activity. Hence, the optimum activity of β-In2 S3 hierarchical structures can be achieved with 1.0 wt% Pt loading. Based on the above results, we further compared the hydrogen evolution rate of the samples obtained with different temperatures by loading 1.0 wt% Pt as co-catalyst under visible light irradiation. As shown in Fig. 7A, the hydrogen evolution rate of β-In2S3 hierarchical structures synthesized at 220°C is much higher than that of the products synthesized at reaction temperatures of 200 and 180°C (42.6 and 27.6 μmol h−1 g−1). For comparison, the photocatalytic hydrogen production activity of commercial TiO2 (P25) was also evaluated. P25-TiO2 shows no activity for photocatalytic H2 evolution under visible light irradiation. The highly efficient photocatalytic H2 production activity of β-In2S3 hierarchical structure could be mainly ascribed to the following reasons. First, the flower-like β-In2S3 hierarchical structure could allow multiple reflections of visible light for the increased light absorption[46]. Then, the thin nanosheets could allow photoexcited charge carriers to move from the interior to the surface rapidly in order to participate in the photocatalytic reaction[47]. Eventually, compared with the products synthesized at reaction temperatures of 200 and 180°C, the β-In2S3 hierarchical structures synthesized at 220°C have the best

13

crystallinity, which would be helpful to improve the photocatalytic activity. To demonstrate the applicability of these materials in photocatalysis, the stability of β-In2S3 hierarchical structures was further investigated. As shown in Fig. 7B, the activity can be maintained over three cycles. Moreover, the catalytic activity of β-In2S3 hierarchical structures did not present any significant loss in the second and third cycles. The above results indicate that the stability of β-In2S3 hierarchical structures is satisfying, which is important for its further practical applications. In addition, the as-prepared β-In2S3 hierarchical structures were also utilized for the degradation of RhB under visible light irradiation. Fig. 8a displays the change of RhB concentration (C/C0) as a function of time over the process of photocatalytic degradation. Prior to irradiation, the adsorption behaviour was initially examined under dark condition. As shown in Fig. 8a, β-In2S3 hierarchical structures showed much stronger adsorption capability than P25-TiO2 towards degradation of RhB, proving the anionic surface characteristic of β-In2S3 hierarchical structures. (Rhodamine B (RhB), a cationic dye, is considered as pollutant in water resources[48].) During photodegradation process, blank tests exhibit little degradation, indicating the stable property of RhB under visible light irradiation. When β-In2S3 hierarchical structures were used as the photocatalysts, the concentration of RhB could be completely decreased after irradiated for 100 min. In the presence of P25-TiO2 under the same experimental conditions, 29.4 % of RhB was degraded within 100 min under visible light irradiation. Therefore, β-In2S3 hierarchical structures exhibit excellent photocatalytic activity for the degradation of organic dye

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under visible light irradiation. The hydroxyl radical (·OH), photogenerated holes (h+) and superoxide anion radicals (·O2-) are three kinds of active species in photocatalytic degradation of organic pollutants.[49] To determine the main active species in the degradation of RhB, the radical-trapping experiments were studied by using three scavengers, i.e., tert-butyl alcohol (TBA), ammonium oxalate (AO) and benzoquinone (BQ), which can trap reagents for ·OH, h+ and ·O2-, respectively.[49] As shown in Fig. 8b, the addition of TBA had no effect on the photocatalytic activity of β-In2S3 hierarchical structures, while the introduction of AO and BQ obviously inhibited the activity. The above result indicates that h+ and ·O2- played important roles for the degradation of RhB over β-In2S3 hierarchical structures. Moreover, in the photocatalytic reaction, the generation of active species needs the ECB and EVB of semiconductor to meet the thermodynamic potentials.[49, 50] Therefore, the oxidizing or reducing ability of photogenerated carriers was further investigated. In the case of β-In2S3 system, the ECB of β-In2S3 (-0.89 eV) is more negative than E(O2/O2-) (-0.33 eV), which means that the photogenerated electrons in the conduction band of β-In2S3 can reduce O2 to yield ·O2-. Meanwhile, the EVB of β-In2S3 (1.30 eV) is more negative than E(OH/·OH) (2.25 eV), suggesting that the holes haven’t the capacity to oxidize OH - or H2O to ·OH. Thus, it is clear that h+ and ·O2- are the primary active species in the RhB degradation. 4. Conclusions In summary, we successfully developed a facile hot-injection synthesis strategy to

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fabricate Ca(II) doped β-In2S3 hierarchical structures stacked by 2D nanosheets. The possible formation mechanism was put forward. The reaction temperature and Ca2+concentration play key roles in the formation of β-In2S3 hierarchical structures. Ca(II) doped β-In2S3 hierarchical structures can be used for visible light photocatalytic H2 production and photodegradation of RhB. The photocatalytic hydrogen generation of Ca(II) doped β-In2S3 was strongly affected by the loose hierarchical structure and the geometry of the constituent nanosheets, which participated in the reaction quickly and increased light absorption. In addition, the excellent degradation dye activities of Ca(II) doped β-In2S3 are mainly attributed to the large amount of effectively reactive species like h+ and ·O2-. Both the facile synthetic method and the excellent photocatalytic activities make Ca(II) doped β-In2S3 hierarchical structures as potential semiconductor materials for solving the energy and environmental problems. We believe that this simple hot-injection process can be applied to synthesize other metal sulfides. Acknowledgements This work was supported by Fundamental Research Funds for the Central Universities (Grant No. HIT.BRETIII.201203). References References [1] S. Martha, D. Das, N. Biswal, K. Parida, Facile synthesis of visible light responsive

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Figures and captions

Fig. 1. (a) XRD patterns of the obtained β-In2S3 synthesized at 220 °C. (b) Magnified XRD patterns of the products in 20–30º range. The lower panels show the standard diffraction pattern of β-In2S3 (JCPDS No. 25-0390).

Fig. 2. (a) XPS survey spectrum, (b) In 3d, (c) S 2p and (d) Ca 2p XPS spectra of Ca2+ doped β-In2S3.

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Fig. 3. (a, b) SEM images, (c, d) TEM images, (e) SAED pattern, and (f) HRTEM image of Ca2+ doped β-In2S3 hierarchical structures synthesized at 220 °C.

Fig. 4. SEM images of the samples prepared at different temperatures: (a, b) 180 °C; (c, d) 200 °C.

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Fig. 5. SEM images of samples obtained without CaCl2 (a, b) and with doubled concentration of CaCl2(c, d). Typical concentration: 0.2 mmol of CaCl2, 0.5 mmol of InCl3•4H2O and 0.75 mmol of S.

Fig. 6. (a) UV-vis diffuse reflectance spectrum of β-In2S3 hierarchical structures. (b) The indirect band gap and (c) direct band gap determination of β-In2S3 hierarchical structures.

Fig. 7. (A) Comparison of H2 production rate on the samples obtained at different temperatures and P25-TiO2: (a) 220 °C, (b) 200 °C, (c) 180 °C, (d) P25-TiO2. (B) Cyclic H2 production curve of β-In2S3 hierarchical structures.

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Fig. 8. (a) Photocatalytic activity of β-In2S3 and P25-TiO2 towards RhB degradation under visible light irradiation. (b) Photocatalytic degradation of RhB over β-In2S3 in the presence of BQ, AO, and TBA.

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Graphical Abstract Ca(II) doped β-In2S3 hierarchical structures were synthesized through a facile hot-injection method. These β-In2S3 hierarchical structures exhibited enhanced hydrogen production and efficient degradation of organic dye under visible light irradiation.

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