Enhanced photocatalytic and photoelectrochemical activities of SnO2/SiC nanowire heterostructure photocatalysts
Introduction
In recent years, utilizing solar light to produce hydrogen from water using semiconductor materials is one of the promising solutions to relieve the energy crisis [1], [2], [3]. As one of the third-generation wide-band-gap semiconductor materials, silicon carbide (SiC) has been long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications. Nanostructural SiC materials have received much attention due to its high chemical stability, strong thermostability, and high photocatalytic activity. Recently, zinc blende silicon carbide (3C–SiC) with suitable band gap of 2.4 eV, has attracted great attention in photocatalytic and photoelectrocatalytic H2 evolution towards water splitting. Yang et al. [4] prepared B-doped 3C–SiC nanowires by the mixture of gangue, carbon black and boric oxide powder via a simple carbothermal reduction, and the obtained nanowires possess a high photocatalytic H2 production activity. Zhou et al. [5] reported that 2D nanosheet structural ultra-thin SiC layer covered by graphene nanosheets show improved photocatalytic H2 evolution activity in the Na2S solution. Wang et al. [6] reported that the average H2 evolution rate of platinum nanoparticle-decorated SiC nanowires (SiC NWs) photocatalyst has been up to 204 μmol g−1 h−1. Wang et al. [7] reported that a Z-scheme photocatalysis system equipped with SiC/Pt as an H2-evolving photocatalyst shows an improvement in the apparent quantum efficiency.
The composite of different semiconductor nanoparticles may facilitate the separation and transfer of the photogenerated carriers because the difference in the band edge positions creates the potential gradient at the composite interface [8]. Therefore, various heterogeneous SiC nanocomposites had been synthesized for photocatalytic hydrogen production. Mishra et al. [9] reported that a series of sulfate modified TiO2/β-SiC nanocomposite heterojunction photocatalysts show the excellent photocatalytic activity (1254 μmol in 3 h) due to the synergistic interaction of ternary species. The n-type TiO2 was deposited onto a p-type/intrinsic hydrogenated amorphous SiC to form a heterojunction, and it is promising to construct a multijunction system for highly efficient bias-free solar water splitting devices [10]. Peng et al. [11] presented that the SiC/CdS heterogeneous structure provides a feasible Z-scheme route to improve the photocatalytic activity by optimizing the intrinsic contact of the two semiconductors.
Tin dioxide (SnO2), with large band gap of 3.6 eV, possesses high stability and acid-resistance properties. Compared with TiO2/SiC heterojunction composites, SnO2 is a good electron acceptor because of its more positive conductive band edge than that of SiC [12], [13], [14]. Therefore, it is feasible to assemble a novel SnO2/SiC nanowire heterostructure photocatalyst. In this work, the unique SnO2 nanoparticles-decorated 3C–SiC NWs (SnO2/SiC NWs) were firstly prepared via a facile solvothermal synthesis method. The SnO2/SiC NWs possess effective separation of photogenerated electro-hole pairs and excellent chemical stability. The hydrogen evolution measurements reveal that SnO2/SiC NWs have the enhanced photocatalytic and photoelectrochemical (PEC) activities than that of the pristine SiC NWs.
Section snippets
Preparation of SnO2/SiC nanowires
SiC nanowires were synthesized by the sol–gel carbothermal reduction method as our earlier report described [15], [16]. The nanocomposite of SnO2/SiC nanowires were synthesized by a simple solvothermal synthesis process. In a typical synthesis process, 0.25 g of SnCl4 (≥99.0%, AR) and 15 mg of SiC NWs were dispersed homogeneously in 100 mL of isopropyl alcohol (≥99.7%, AR) under ultrasonic bath (200 W). The solution was then transferred into a Teflon-lined stainless steel autoclave (120 mL),
Results and discussion
The composition and crystalline structures of the SnO2/SiC NWs were characterized by X-ray diffraction (XRD). As shown in Fig. 1a (blue line (in the web version)), five diffraction peaks are obviously detected. The (111), (220) and (311) reflection planes can be indexed to cubic 3C–SiC (ICDD Data, JCPDS Card No. 75-0254). The small peak marked with stacking faults (SF) and the broad peak marked with SiO2 are attributed to the SF [17] and the amorphous SiO2 [18] respectively. Furthermore, Fig. 1
Conclusions
In summary, a novel SnO2/SiC nanowire heterostructure photocatalyst was fabricated by the solvothermal synthesis technique. The nanocomposite of SiC and SnO2 provides a synergistic effect by improving the light-utilization capacity and efficiently facilitating the separation of photoexcited electron-hole pairs. The hydrogen evolution rate (274 μmol g−1 h−1) of the hybrid photocatalyst with an appropriate amount of SnO2 nanoparticles is over 4 times than that of the pristine SiC nanowires. The
Acknowledgment
This work is supported by the National Natural Science Foundation of China (No. 51572243), the Zhejiang Provincial Natural Science Foundation (No. LY15E020012), 521 Talent Training Plan of Zhejiang Sci-Tech University and the Young Researchers Foundation of Zhejiang Provincial Top Key Academic Discipline of Chemical Engineering and Technology, Zhejiang Sci-Tech University (ZYG2015006).
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