Elsevier

Journal of Solid State Chemistry

Volume 258, February 2018, Pages 526-535
Journal of Solid State Chemistry

1D Bi2S3 nanorod/2D e-WS2 nanosheet heterojunction photocatalyst for enhanced photocatalytic activity

https://doi.org/10.1016/j.jssc.2017.11.017Get rights and content

Highlights

  • An efficient 1DBi2S3/2D e-WS2 photocatalyst was synthesized.

  • Photocatalytic efficiency of 1DBi2S3/2D e-WS2 on MO was higher than pristine ones.

  • Possible photocatalytic degradation mechanism for the MO was proposed.

  • Fast charge transfer observed over 1DBi2S3/2D e-WS2 hybrid.

  • 2D e-WS2 nanosheets play a key role in photodegradation.

Abstract

The development of high-activity, long-life, precious-metal-free photocatalysts for redox reactions in photoelectrochemical cells and fuel cells remains challenging. The synthesis of high-activity heterostructured photocatalysts is crucial for efficient energy conversion strategies. Herein, a novel photocatalyst based on 1D Bi2S3 nanorods self-assembled on 2D exfoliated tungsten disulfide (e-WS2) nanosheets has been developed for the degradation of methyl orange (MO) dye in aqueous solution. We demonstrate a novel and facile hydrothermal method for the synthesis of a Bi2S3 nanorod/e-WS2 nanosheet heterostructure. The photocatalytic properties of the heterostructure under visible light were investigated. Enhanced photocatalytic activity was attributed to the presence of strong surface active sites, as well as the specific morphology of the composite. We also observed the fast transfer of electron-hole pairs at the material interface. This work demonstrates a non-noble semiconductor photocatalyst for the degradation of pollutants and evolution of H2.

Introduction

With the recently increased emphasis on the environmental effects of contaminated water from industries such as leather and textiles production, the degradation of pollutants in contaminated water has gained increasing attention from researchers [1], [2], [3]. Because it offers high resistance to photocorrosion, TiO2 is widely considered in the exploration of semiconductor photocatalysts for the degradation of pollutants in aqueous solutions [4], [5]. However, TiO2 is limited in use in photocatalytic applications because it is intrinsically hindered by properties including a wide band gap, low electron mobility, and short hole diffusion length (10–100 nm). Various strategies including doping, co-catalysis, and heterostructure formation have been investigated to address these issues. One of the key research targets for photocatalysts is the development of high-specific-surface-area and high-structural-stability semiconductor heterojunctions. To date, 1D and 2D transition-metal sulfides including FeS2 [6], Bi2S3 [7], [8], MoS2 [9], [10], [11], WS2 [12], [13], WSe2 [14], and MoSe2 [15] have been widely used in photocatalytic applications because they have suitable band gap energies that yield low recombination rates for electron-hole pairs. Compared to 1D metal sulfides, 2D materials exhibit unique characteristics in photocatalytic applications. Bi2S3, a visible-light active material with a band gap of 1.25–1.61 eV, has attracted great attention because of its visible-light active photocatalytic performance [16], [17]. For example, Sarkar et al. [18] reported that a solvothermally synthesized Bi2S3 nanoparticle photocatalyst demonstrated visible irradiation-driven photoactivity towards the degradation of methylene blue, and ascribed this activity to the material's remarkable specific surface area. However, the application of pure Bi2S3 in pollutant photodegradation remains limited because the material is relatively low in efficiency and stability, showing rapid recombination of photogenerated electron-hole pairs. The loading of earth-abundant elements as co-catalysts has been an ongoing research subject for the fabrication of low-cost and noble metal-free photocatalysts. Pei et al. [19] reported a heterojunction of Bi2S3 and Bi2MoO6, which showed enhanced photocatalytic activity with improved charge transfer and separation, as well as diminished charge-carrier recombination. In another study, Wang et al. [20] synthesized a Bi2MoO6/Bi2S3 photoelectrochemical sensor that has been successfully applied in the selective gallic acid analysis to supervise drug quality. In addition, Bi2S3 decorated on Bi2MoO6 nanobelts as a platform has exhibited excellent selectivity, reproducibility, and light-harvesting capability. Similarly, Bi2WO6/Bi2S3 [21], [22], [23], [24], Bi2S3/Bi2Sn2O7 [25], Bi2S3/TiO2 [26], Bi2S3/CdS [27], Bi2S3/WO3 [28], Bi2S3/Fe2O3 [29], Bi2S3/BiPO4 [30], Bi2S3/g-C3N4 [31], Bi2S3/Bi2SiO5 [32], Bi2S3/rGO [33], and various Bi-based [34] heterojunctions have demonstrated excellent photocatalytic activity under visible-light irradiation.

2D transition metal dichalcogenides (TMDs) with layered structures have received extensive research attention in the last decade because they have unique structures analogous to graphene and good properties for relevant applications [35], [36]. WS2, an inorganic graphene analog, is a chemically stable layered semiconductor with the band gap of ~1.3 eV, with WS2 monolayers connected by van der Waals forces. WS2 is used in various applications including solar cells, gas sensors, Li ion batteries, and the photodegradation of pollutants in aqueous solutions [37]. Thus, WS2 is considered a suitable candidate for next-generation substitution of noble metals. To fully incorporate the above-mentioned benefits in a single system, the concept of 1D/2D metal sulfide heterojunctions was proposed. To date, little effort has been attempted to grow 1D nanorods on 2D nanosheets, which may be caused by the difficulties in the growth of 1D and 2D nanomaterials in a single synthetic system. For instance, we previously reported that a hydrothermally synthesized CdS/WS2 hybrid exhibited very high photocatalytic degradation of crystal violet dye under UV and visible-light irradiation [38].

Herein, we report a simple single-step hydrothermally self-assembled Bi2S3/exfoliated WS2 (e-WS2) nanocomposite for photocatalytic applications. Various approaches have been developed for the synthesis of few-layer e-WS2, such as mechanical exfoliation, liquid exfoliation, and chemical vapor deposition. Considering the feasibility of operation and the subsequent synthesis of both Bi2S3 and e-WS2, direct sonication in an aqueous solution was employed to obtain few-layer e-WS2. The ultrasonicated e-WS2 with more exposed active edges was applied as a co-catalyst for Bi2S3 to improve the photocatalytic degradation of methyl orange (MO) dye. The as-synthesized nanocomposite demonstrated excellent photocatalytic efficiency under visible-light irradiation. The electrochemical properties were investigated thoroughly to determine the importance of the heterojunction. This work may facilitate new insights in the selection, design, and construction of noble metal-free photocatalysts for both the photocatalytic degradation of pollutants and sustainable energy generation.

Section snippets

Synthesis of few-layer WS2 and e-WS2

In a typical synthesis procedure (Scheme 1), 1 mol of WCl6 and 65 mmol of C2H5NS were dissolved in 50 mL of ethanol and 25 mL deionized water under constant stirring. Then, 5 mol/L HCl was used to adjust the pH of the mixed solution to 2–2.5 and the solution was stirred for 1 h at room temperature. Then the above solution was transferred into a 100-mL Teflon-lined stainless steel autoclave, sealed, and maintained at 190 °C for 24 h. After being cooled, the product was obtained by centrifuging, washed

Structure, composition, and morphological features

Fig. 1 shows the XRD patterns of the pristine Bi2S3 nanorods, e-WS2nanosheets, and Bi2S3 nanorod/e-WS2 nanosheet heterostructures. For the pristine Bi2S3 nanorods, 18 distinctive peaks at 2θ = 11.14°, 15.67°, 17.59°, 23.71°, 24.94°, 28.65°, 31.82°, 33.93°, 35.61°, 39.93°, 42.7°, 46.5°, 48.29°, 52.61°, 54.74°, 62.61°, 68.54°, and 78.78° are well matched with the standard pattern of orthorhombic Bi2S3 (JCPDS-89–8964) [39]. For the e-WS2 nanosheets, diffraction peaks at 14.32°, 28.87°, 32.57°,

Conclusions

In summary, we have rationally designed and developed a novel 1D Bi2S3 nanorod/2D e-WS2 nanosheet heterojunction as a photocatalyst for the photodegradation of MO. A dense layer of e-WS2 ultrathin nanosheets decorated on the surfaces of the Bi2S3 nanorods. Because of this heterojunction nanostructure, the photocatalyst exhibits the enhanced photodegradation of MO at a rate 1.42 and 1.19 times higher than those achieved by pristine Bi2S3 and e-WS2, respectively. EIS measurement results show that

Acknowledgments

This research was supported by the National Research Foundation of Korea (NRF) and funded by the Ministry of Science, ICT, and Future Planning (2017R1A2B1004860). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (No. NRF-2015R1A2A2A01003741) and (No. NRF-2017R1A4A1015581). This research was supported by the 2017 Research Fund (1.170013.01) of UNIST (Ulsan National Institute of Science&Technology).

References (49)

  • S.V.P. Vattikuti et al.

    Superlattic Microstruct.

    (2015)
  • A. Sarkar et al.

    J. Colloid Interface Sci.

    (2016)
  • Y. Pei et al.

    Talanta

    (2017)
  • L. Wang et al.

    Biosens. Bioelectron.

    (2017)
  • L. Yan et al.

    Appl. Surf. Sci.

    (2017)
  • X. Li et al.

    Ceram. Int.

    (2016)
  • W. Xu et al.

    Mater. Chem. Phys.

    (2015)
  • S. Kumar et al.

    Ceram. Int.

    (2016)
  • L. Hao et al.

    Int. J. Hydrog. Energy

    (2014)
  • J. Rong et al.

    J. Alloy. Compd.

    (2016)
  • A. Helal et al.

    Appl. Catal. B: Environ.

    (2017)
  • Y. Chen et al.

    Appl. Surf. Sci.

    (2016)
  • R. He et al.

    Chin. J. Catal.

    (2014)
  • W. Choi et al.

    Mater. Today

    (2017)
  • S.V.P. Vattikuti et al.

    Solid State Sci.

    (2016)
  • S.V.P. Vattikuti et al.

    Superlattice. Microstruct.

    (2016)
  • R. Wei et al.

    J. Alloy. Compd.

    (2016)
  • S.V.P. Vattikuti et al.

    Superlattice Microstruct.

    (2016)
  • L. Wei et al.

    Appl. Catal. B: Environ.

    (2014)
  • C.H. Wu et al.

    J. Hazard. Mater.

    (2006)
  • H.W. Ma et al.

    Appl. Catal. B: Environ.

    (2012)
  • J. Jin et al.

    Appl. Surf. Sci.

    (2017)
  • A. Fujishima et al.

    Nature

    (1972)
  • U.M. Sh et al.

    Science

    (2002)
  • Cited by (0)

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