Regular ArticleControlled synthesis and exceptional photoelectrocatalytic properties of Bi2S3/MoS2/Bi2MoO6 ternary hetero-structured porous film
Graphical abstract
Introduction
In recent years, gradually increased organic contaminants demand a sustainable approach for wastewater treatment and reuse [1], [2]. Some conventional biological and chemical treatment technologies are able to degrade organic pollutants, but there still exist lots of challenges. More recently, photoelectrochemical catalysis (PEC) has been regarded as one of the promising technologies for wastewater purification because there exists synergy between photocatalysis and electrocatalysis [3], [4]. In the PEC system, photocatalyst films were immobilized on the conductive electrodes to decompose organics under certain bias potential. Such design can effectively avoid secondary contamination problems of powder photocatalysts happened in photocatalytic process [5], [6]. Meanwhile, the applied bias potential on the working electrode can further promote transfer and separation of photogenerated electron–hole pairs and increase PEC activity [7]. In the PEC system, wide band-gap semiconductors such as TiO2 were considered to be promising photocatalysts because of their nontoxicity, high stability, and strong oxidation ability [8]. However, wide band-gap semiconductors can only absorb ultraviolet (UV) light (∼5% of solar spectrum). Meanwhile the separation efficiency of photogenerated electron−hole pairs is relatively low [9], [10], [11]. Therefore, it is desirable to develop efficient visible light-responsive photocatalysts.
In the past few years, bismuth-based semiconductors (e.g. Bi6Mo2O15, BiVO4, etc.) have attracted great attention in different application fields because of their excellent physical and chemical properties [12], [13], [14]. Notably, narrow band-gap Bi2MoO6 and Bi2S3 showed acceptable photocatalytic and photoelectrochemical performance [15], [16], [17], [18]. Even so, it is necessary to further improve their performance from the application perspective. In previous research, Bi2MoO6 and Bi2S3 have been reported to couple with other semiconductors to form heterostructure composites and exhibited significantly enhanced performance [19], [20], [21]. For example, Bi2MoO6/TiO2, CdS/Bi2MoO6, Bi2MoO6/BiVO4, Bi2S3/Bi2WO6, and Bi2S3@MoS2 composites were successfully fabricated to improve photocatalytic or photoelectrochemical performance [22], [23], [24], [25]. Meanwhile, Bi2MoO6 and Bi2S3 have also coupled with each other to form Bi2S3/Bi2MoO6 heterostructure via a simple ion exchange method, and enhanced photocatalytic and photoelecrochemical performances were obtained [26], [27]. MoS2, as a narrow bandgap material with a typical layered structure, has been proved to exhibit high photoelectricity induced catalytic activities [28], [29]. Therefore, MoS2 was often used to couple with other semiconductors to improve photoelectronic properties through hydrothermal process using sulfide source and molybdenum salt as starting reactants at a relatively high temperature (≥180 °C) [30], [31], [32]. Since Bi2MoO6 can be used as starting material to prepare Bi2S3/Bi2MoO6 heterostructure through ion exchange under relatively low temperature, it is feasible to fabricate Bi2S3/MoS2/Bi2MoO6 ternary heterostructure by simultaneously producing MoS2 and Bi2S3 under a raised reaction temperature enough to produce MoS2 using Bi2MoO6 as starting material, thus enhanced photoelectrocatalytic performance can be expected. But the related work has not been mentioned until now.
Inspired by these concerns, herein, Bi2S3/MoS2/Bi2MoO6 composite films were controllably prepared via a facile hydrothermal method using the prepared Bi2MoO6 nanoflake array film as substrate material. The components of porous composite films can be tuned by changing reaction temperature and time (Scheme 1). The optimized Bi2S3/MoS2/Bi2MoO6 porous composite films have exhibited significantly higher photoelectrocatalytic performance than pure Bi2MoO6 and binary composite films (Bi2S3/Bi2MoO6 and Bi2S3/MoS2) for the degradation of organic pollutants. This high photoelectrocatalytic performance can be predominantly attributed to the synergistic effects of three components in the composite, robust visible light harvesting, and efficient transfer and separation of charge carriers.
Section snippets
Synthesis of Bi2MoO6 nanoflake array film
The Bi2MoO6 nanoflake array film was synthesized through a solvothermal method according to our previous report [33]. In brief, 0.2811 g Bi(NO3)3·5H2O and 0.0702 g Na2MoO4·2H2O were dissolved in ethylene glycol (10 mL) under magnetic stirring, respectively. Then above two solutions were slowly added to a beaker containing 20 mL ethanol. The mixed solution was stirred for 10 min and then transferred into a Tefon lined stainless steel autoclave (50 mL). The washed FTO glass (1 × 2 cm2) was then
Characterization of catalysts
The morphology and structure of the prepared films were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fig. 1A shows the SEM image of the prepared Bi2MoO6 nanoflake array film. The average thickness of Bi2MoO6 nanoflakes is ∼10 nm and the diameter is ∼80 nm. The TEM image in Fig. 1B further confirmed nanoflake structure of Bi2MoO6. The interplanar distance of 0.315 nm in HRTEM (Fig. 1C) is consistent with the (1 3 1) plane of orthorhombic phase
Conclusions
In summary, hierarchical Bi2S3/MoS2/Bi2MoO6 ternary heterostructure composite porous film has been synthesized through an in situ sulfuration reaction route using the prepared Bi2MoO6 nanoflake array film as starting substrate material. The synthetic stratagey can simultaneously produce Bi2S3 and MoS2 in sulfuration reaction process. The optimal Bi2S3/MoS2/Bi2MoO6 film exhibited significantly enhanced photoelectrocatalytic performance for the degradation of organic pollutants compared with
Acknowledgments
This work was supported by the National Natural Science Foundation of China (51772079, 21871079), and Natural Science Foundation of Heilongjiang Province of China (B2017009).
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