Facile synthesis of porous InNbO4 nanofibers by electrospinning and their enhanced visible-light-driven photocatalytic properties
Introduction
Ever since Fujishima and Honda reported photoelectrochemical water splitting using a TiO2 electrode in 1972 [1], semiconductor photocatalysis has attracted much attention because of the great potential in environmental remediation and hydrogen energy production [2], [3], [4], [5], [6], [7], [8]. As the largest proportion of the solar spectrum or artificial light sources is visible light, it is necessary to develop highly active photocatalysts that work efficiently under a wide range of visible-light irradiation conditions [9], [10], [11], [12], [13], [14], [15]. Considerable efforts have been contributed to the design and development of hybrid materials based on TiO2 with visible light response, such as doping with metal or nonmetal elements, coupling with carbon materials or other narrow band-gap semiconductors [16], [17], [18], [19], [20]. Although modified TiO2 makes the utilization of visible light possible, many researchers focus their efforts on the design and development of new non-TiO2 and single-phase oxide photocatalysts with visible-light response [21], [22], [23], [24], [25].
InNbO4 is considered to be a potential photocatalytic material for water splitting and dye waste treatment owing to its layered wolframite structure and photoinduced hydrophilicity [26], [27], [28], [29], [30]. Zou et al. reported that InXO4 (X = Ta, Nb) loaded with NiO could split water directly into H2 and O2 under visible-light irradiation, and these photocatalysts were synthesized through calcining pre-dried In2O3 and Nb2O5 at 1100 °C for 2 d based on a solid-state reaction [26], [27], [28], [29]. Zhang and coworkers developed a nonaqueous sol–gel route to prepare the nanocrystalline InNbO4 photocatalyst at 200 °C for 24 h [30]. Photocatalytic performances of those InNbO4 photocatalysts under visible light irradiation have been proven to be evidently improved. Moreover, InNbO4 thin films could be fabricated by a sol–gel method combined with subsequent annealing at 950 °C for 12 h [31]. Recently, a wet-chemical technique has been developed to synthesize InNbO4 photocatalysts for decomposition of organic contaminants [32]. Despites these advances, high reaction temperature or long reaction time is often unavoidable during the synthesis of crystalline InNbO4. Therefore, it is highly desirable to develop high-performance InNbO4 photocatalysts with well-defined nanostructures by a mild method.
One-dimensional (1D) nanostructured semiconductor photocatalysts have so far aroused much interest because of their novel nanoarchitectures (controlled surface or porosity) and unique physicochemical properties [33], [34], [35], [36], [37], [38]. For instance, Zhang et al. reported that hollow mesoporous 1D TiO2 nanofibers exhibited enhanced photocatalytic activity towards photodegradation of Rhodamine B (RhB) [33]. Among various methodologies, electrospinning is a most convenient and direct technique to fabricate continuous fibers with diameters down to the nanoscale. It has been extensively investigated for preparing 1D nanostructured materials due to the low cost, versatility, and ease of manufacturing [38], [39], [40], [41]. Tong and coworkers found that N, Fe and W doped TiO2 nanofibers could be fabricated by coaxial electrospinning and direct annealing [42]. The short nanofiber membrane of InNbO4 with good visible-light-driven photocatalytic function was synthesized through electrospinning followed by calcination [43]. Recently, Bi4Ti3O12 nanofibers that exhibited both enhanced visible-light-driven photocatalytic decomposition of RhB and favorable recycling capability were fabricated through electrospinning combined with subsequent calcination in our group [44]. Herein, we report a facile electrospinning route to fabricate long porous InNbO4 nanofibers with diameters of 50–100 nm on a large scale. The resulting InNbO4 nanofibers exhibit enhanced visible-light-driven photocatalytic activity for photodegradation of RhB that was as a model organic compound.
Section snippets
Material synthesis
Acetic acid, In2O3, Nb2O5 and N,N-dimethylformamide (DMF) were of analytical grade, and were supplied by Shanghai Chemical Reagent Co. Ltd. China. In(NO3)3, ethanol niobium and poly(vinylpyrrolidone) (PVP, Mw ≈ 1,300,000) were obtained from Sigma–Aldrich. All the chemicals were used as received without further purification. In a typical procedure, the precursor solution for electrospinning was prepared by dissolving In(NO3)3 (0.2 g), ethanol niobium (0.17 mL), PVP (0.5 g) and acetic acid (1 g) in DMF
Results and discussion
Fig. 1a displays the SEM images of the as-spun INO-PRE nanofibers. Obviously, the surface of these nanofibers is very smooth, and the diameters are in the range of 100–200 nm. Fig. 1b displays the SEM images for the INO-NF nanofibers which were obtained by annealing the INO-PRE nanofibers at 600 °C. Clearly, the INO-NF nanofibers exhibit shrinkage because of the decomposition of PVP during the calcination process. Fig. 1c shows the XRD pattern of the INO-NF nanofibers. All the diffraction peaks
Conclusions
The porous InNbO4 nanofibers with diameters of 50–100 nm have been successfully fabricated by electrospinning combined with subsequent annealing. These nanofibers show much higher photocatalytic activity for photodecomposition of RhB under visible-light irradiation than that of the InNbO4 crystallites synthesized by a high-temperature solid-state reaction method. This may be assigned to the porous nanofibrous architecture, high surface area and relatively narrower band gap. This work provides a
Acknowledgments
This work was supported by Natural Science Foundation of China (Grant Nos. 21271078 and 51002057), PCSIRT (Program for Changjiang Scholars and Innovative Research Team in University), and NCET (Program for New Century Excellent Talents in University, No. NECT-12-0223).
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