Elsevier

Applied Surface Science

Volume 471, 31 March 2019, Pages 813-821
Applied Surface Science

Full Length Article
Systematic optimization of promoters in trace SnS2 coating SnO2 nano-heterostructure for high performance Cr(VI) photoreduction

https://doi.org/10.1016/j.apsusc.2018.12.042Get rights and content

Highlights

  • Series of SnS2 coated on SnO2 nanospheres are prepared by in-situ trace vulcanization.

  • The obtained SnS2/SnO2 catalysts exhibit an enhanced surface photovoltage signals.

  • Strong interface interaction of SnS2 and SnO2 promotes the separation of carriers.

  • 19.5% SnS2 containing catalysts shows the best photodegradation activity of Cr(VI).

Abstract

Constructing heterojunction semiconductor materials with a strong interfacial interaction are emerging as a forefront strategy for promoting excellent photocatalytic performance. Herein, we report a novel SnS2/SnO2 heterojunction material via in-situ trace vulcanization strategy to coat SnS2 on the SnO2. The thickness of the coating layer can be regulated by controlling the content of SnS2. Moreover, molar ratio of S to Sn, particle size of SnO2 precursor, and vulcanization time that governs the SnS2 content of heterojunction catalyst were controlled to optimize photocatalytic performance. SnS2/SnO2 heterojunction catalyst with 19.5% SnS2 content delivered a ultrahigh visible-light activity in Cr(VI) degradation, remarkably superior to the inert SnO2 precursors and full-vulcanized SnS2 under identical testing conditions. The enhanced interfacial interaction can remarkably enhance the separation and transfer of photogenerated charges. The systematic methodology of interface regulation in SnS2/SnO2 system reported in this work would promote the understanding of nano-heterojunction material for high-performance water treatment application.

Graphical abstract

SnS2 is obtained from SnO2 in-situ transformed in the process of trace vulcanization. Strong interfacial interaction between SnO2 and SnS2 has promoted the separation of photoinduced electrons and holes effectively and provided more electrons to reduce the Cr(VI) to Cr(III).

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Introduction

Growing concern about the seriousness of water pollution urgently demands the development of a eco-friendly technology for the removal of hazardous materials, especially Cr(VI), from contaminated water [1], [2], [3], [4]. Among numerous approaches to removal of Cr(VI), photocatalytic Cr(VI) reduction, especially under visible light radiation, may be the most economical, clean, recyclable and effective mean for the future water treatment [5], [6], [7], [8]. However, in most cases, photocatalysis is not active for Cr(VI) reduction owing to the sluggish photoreduction kinetics. As a remedy, the nano-heterojunction photocatalytic materials were developed for their remarkable superiorities in accelerating photoreduction kinetics. Nano-heterojunction formed by chemically distinct semiconductors in a single nanostructure has created a revolution for unique optical properties and diverse functionalities [9], [10], [11], [12], [13]. The strong interfacial interaction at the nanoscale could prodcue novel properties nonexistent in the individual component and show great potential for enhancing the performance [14], [15]. Therefore, tremendous efforts have been devoted to construct the heterojunction in recent years. However, heterogeneous structure is easily detached during the photoreaction progress, resulting in degenerative catalytic activity and cycling performance. In-situ synthesis technology is a breakthrough method to form the heterostructure with strong interfacial interaction [16]. The sturdy interface can dominate the transfer direction of photoinduced charges and effectively separate photogenerated electrons and holes for promoting photocatalytic activity [17].

As a superior photocatalyst with excellent physicochemical properties, SnO2 displays many significant merits, such as chemical stability, non-toxicity, low-cost, etc [15], [18]. SnO2 possesses a low valence-band edge potential which endows the holes in the band with high oxidation ability [13]. Furthermore, SnO2 also act as an electron acceptor owe to its high electron mobility and more positive conduction band [19]. Unfortunately, due to its wide bandgap (Eg = 3.5–3.8 eV), SnO2 could only harvest ultraviolet light (λ < 420 nm) which accounts for less than 4% of the whole solar energy, thus greatly restricting the utilization of solar energy in practical application [19], [20], [21], [22], [23], [24]. Developing a novel photocatalyst which can efficiently harvest more solar light is urgently desired. Till now, multiple SnO2-based heterojunction photocatalyst have been studied to broaden the scope of optical absorption, such as SnO2/g-C3N4, Ag3PO4/SnO2, SnO2/Cu2O, and SnO2/Co3O4 [25], [26], [27], [28], [29], [30]. In-situ growth of a semiconductor component with narrow band gap on the surface of SnO2 nanocrystals achieves a wide photochemical response in visible region. Among various photocatalysts, SnS2 can be a promising candidate for the in-situ formation of Sn-based heterojunction catalysts due to its narrow band gap (2.25 eV) and easily coating on the adjacent SnO2 by vulcanization reaction [31].

Herein, we prepared a heterojunction catalyst with SnS2-shell coating on the SnO2 porous nanosphere by trace vulcanization process. The photocatalytic properties were improved by deliberately introducing strong interfacial interaction, which was investigated in detail below. Combining our kinetic analyses and the literature data ever reported, we conclude that interfacial interaction associated with the content of SnS2 is the key that enhances the separation and transfer of photogenerated charge carriers. The method of systematically regulating the interface to achieve effective separation and transfer of photogenerated charge carriers in SnS2/SnO2 system is first reported in this work, which may be extended to other heterojunction material systems for important environmental applications.

Section snippets

Materials

The raw materials for the sample synthesis are K2SnO3·3H2O (from Aldrich), H2C2O4, polyvinyl pyrrolidone (PVP), CH3CSNH2 (from Aldrich) with analytical grade that were used without further purification.

Synthesis of SnO2 nanospheres

The SnO2 nanospheres with different grain size were prepared via traditional hydrothermal method. Briefly, K2SnO3·3H2O, ranging from 0.5 to 5 mmol, was firstly dissolved in 60 mL distilled water with the assistance of magnetic stirring to form clearly solution, and then 1.5 g C2H2O4 and 0.2 g PVP

Morphologies of catalysts and their heterojunction catalysts

To verify that SnS2/SnO2 heterojunction catalysts have been successfully prepared by a facile and scalable hydrothermal-assisted route via in-situ trace vulcanization, the as-prepared samples are examined by TEM measurements. TEM images in Fig. S2a and b demonstrates that the particles in sample TOS-C4 and SnO2 are nearly monodispersed porous nanospheres with diameter ranging from 25 to 40 nm. Comparatively, fully vulcanized sample SnS2 (TOS-C20) is comprised of large-size nanosheets and some

Conclusion

Monodispersed SnS2/SnO2 heterojunction catalysts were prepared by in-situ trace vulcanization using a facile and scalable hydrothermal method. The molar ratio of S to Sn, particle size of SnO2 precursor and vulcanization time were applied to adjust the SnS2 content of heterojunction catalyst for better understanding the preferred photocatalytic performance. When the SnS2 content was lower than 19.5%, the interface structure and interfacial interaction can be controllably manipulated by

Acknowledgements

This work was financially supported by National Natural Science Foundation of China (21671077, 21771075, 21871106 and 21571176). We thank the group of Tengfeng Xie from Jilin University for supporting this work.

References (58)

  • X. Chang et al.

    Probing the light harvesting and charge rectification of bismuth nanoparticles behind the promoted photoreactivity onto Bi/BiOCl catalyst by (in-situ) electron microscopy

    Appl. Catal. B.

    (2017)
  • J. Matos et al.

    Development of TiO2-C photocatalysts for solar treatment of polluted water

    Carbon

    (2017)
  • J. Yuan et al.

    TiO2/SnO2 double-shelled hollow spheres highly efficient photocatalyst for the degradation of rhodamine B

    Catal. Commun.

    (2015)
  • B. Tao et al.

    In-situ synthesis of highly efficient visible light driven stannic oxide/graphitic carbon nitride heterostructured photocatalysts

    J. Colloid Interface. Sci.

    (2016)
  • C.Q. Sun

    Size dependence of nanostructures: impact of bond order deficiency

    Prog. Solid State Chem.

    (2007)
  • M. Shim et al.

    Anisotropic nanocrystal heterostructures: synthesis and lattice strain

    Curr. Opin. Solid State Mater. Sci.

    (2010)
  • L. Carbone et al.

    Colloidal heterostructured nanocrystals: synthesis and growth mechanisms

    Nano Today

    (2010)
  • X. Yang et al.

    Graphene-spindle shaped TiO2 mesocrystal composites: facile synthesis and enhanced visible light photocatalytic performance

    J. Hazard. Mater.

    (2013)
  • J. Lang et al.

    Fabrication of the heterostructured CsTaWO6/Au/g-C3N4 hybrid photocatalyst with enhanced performance of photocatalytic hydrogen production from water

    Appl. Surf. Sci.

    (2015)
  • C. Julien et al.

    Resonant Raman scattering studies of SnS2 crystals

    Mater. Sci. Eng. B.

    (1994)
  • Zhenyi Zhang et al.

    Ultrathin hexagonal SnS2 nanosheets coupled with g-C3N4 nanosheets as 2D/2D heterojunction photocatalysts toward high photocatalytic activity

    Appl. Catal. B

    (2015)
  • C.S. Turchi et al.

    J. Catal.

    (1990)
  • J. Meichtry et al.

    heterogeneous photocatalysis of Cr(VI) in the presence of citric acid over TiO2 particles: relevance of Cr(V)–citrate complexes

    Appl. Catal. B

    (2007)
  • M. Litter

    treatment of chromium, mercury, lead, uranium, and arsenic in water by heterogeneous photocatalysis

    Adv. Chem. Eng.

    (2009)
  • L. Yang et al.

    Fast photoelectro-reduction of CrVI over MoS2@TiO2 nanotube on Ti wire

    J. Hazard. Mater.

    (2017)
  • S. Challagulla et al.

    Acrylatebased polymerizable sol-gel synthesis of magnetically recoverable TiO2 supported Fe3O4 for Cr(VI) photoreduction in aerobic atmosphere

    ACS Sustain. Chem. Eng.

    (2016)
  • L. Amirav et al.

    Modular synthesis of a dual metal–dual semiconductor nano-heterostructure

    Angew. Chem. Int. Edit.

    (2015)
  • X. Gao et al.

    Formation of mesoporous heterostructured BiVO4/Bi2S3 hollow discoids with enhanced photoactivity

    Angew. Chem. Int. Edit.

    (2014)
  • W. Wu et al.

    Controllable synthesis, magnetic properties, and enhanced photocatalytic activity of spindlelike mesoporous α-Fe2O3/ZnO core–shell heterostructures

    ACS Appl. Mater. Interf.

    (2012)
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