One-dimensional Bi₂O₃ QD-decorated BiVO₄ nanofibers: electrospinning synthesis, phase separation mechanism and enhanced photocatalytic performance

Abstract

In this work, we design and successfully fabricate novel Bi₂O₃ quantum dot (QD)-decorated BiVO₄ nanofibers by a direct heat treatment of as-spun fibers. The Bi₂O₃ QDs with a size of 5–15 nm are well dispersed on the surface of the BiVO₄ nanofibers with a diameter of 400–700 nm to form a Bi₂O₃ QD-decorated BiVO₄ nanofiber photocatalyst. Based on the phase separation mechanism and the properties of solvents, a possible formation process of the Bi₂O₃ QD-decorated BiVO₄ nanofibers has been proposed. The BiVO₄ nanofibers decorated with Bi₂O₃ QDs exhibit much better photocatalytic performance than pure BiVO₄ nanofibers. Photocurrent responses and electrochemical impedance spectra prove that decorating BiVO₄ nanofibers with very small Bi₂O₃ QDs can effectively promote the separation of photoinduced carriers, which is beneficial for photocatalytic properties. More significantly, this work is relevant to environmental purification and photoelectrochemistry.

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1 Introduction

In modern society, the application of semiconductor photocatalysts to solar energy conversion and environment purification has attracted extensive attention.^1,2 Nowadays, owing to their specific crystalline structure, a lot of progress in bismuth-based photocatalysts has been achieved, such as BiOX (X = Cl, Br, I),^3,4 BiVO₄,⁵ Bi₂MoO₆,⁶ Bi₂O₃,^7,8 Bi₄Ti₃O₁₂ (ref. 9) and Bi₂WO₆.^10,11

Among them, BiVO₄ (E_g ≈ 2.40 eV) has been found to be an outstanding visible-light-response photocatalyst for pollutant degradation and oxygen evolution owing to its particular structure of the valence band (formed by Bi 6s or a hybrid orbital of Bi 6s and O 2p) and the conduction band (formed by V 3d).^12–16 However, the practical application of BiVO₄ in environment decontamination is impeded in that there exists a shortcoming in the form of effectively separating photoactivated electrons and holes.^15,16 As a result, great effort has been made to improve its photocatalytic properties via building heterojunctions,¹⁷ morphological control,¹⁸ ion doping,¹⁹ facet selective deposition,²⁰ and so on. In addition, surface modification or decoration has also been widely used to enhance the photocatalytic performance because surface modification and decoration may have a significant influence on the photocatalytic process by altering the charge-transfer pathways occurring at the water–photocatalyst interface and the light absorption property of photocatalysts.^21,22 For instance, gold particles have been used to decorate the surface of BiVO₄ nanotubes and nanosheets forming Au/BiVO₄ heterogeneous nanostructures, and thus the photocatalytic activity is markedly enhanced due to the surface plasmon resonance effect.²³ Besides, surface fluorination not only affects surface or bulk incorporation of fluorine as the post-fluorination (exposure of pre-crystallized photocatalyst to fluorine-containing atmosphere), but also is highly flexible in controlling the crystal modification in terms of phase, size, crystallinity, shape and exposed crystal facets which are responsible for photocatalytic activity.²⁴

Recently, as a novel method among many surface modification techniques, semiconductor quantum dots have been widely used to decorate photocatalysts by surface loading or embedding, such as CdS QDs/TiO₂, CdTe QDs/ZnO and Bi₂S₃ QDs/TiO₂.^25–27 Constructing a surface decoration system which contains semiconductor quantum dots and substrate photocatalysts can effectively improve the photocatalytic properties due to the high surface-to-volume ratio of quantum dots and the promotion of charge carrier separation.²⁸ However, the quantum dots aggregate easily to minimize the specific area caused by the high surface energy, which will have an adverse effect on photocatalysis. Until now, to overcome this problem, only a few methods have been used to fabricate quantum dot-decorated photocatalysts, including hydrothermal method, refluxing, pyrolysis of organometallic precursors, ultrasonic method, and so on.^28–31 Nevertheless, electrospinning can solve the problem more perfectly because electrospinning is a facile preparation method to fabricate photocatalysts with stable structure and large specific area for preventing quantum dots from aggregation. The quantum dots can well disperse on/into the one-dimensional (1D) photocatalysts to form composite photocatalysts.^32–34 In addition, electrospinning is an ideal technique to yield abundant amounts of continuous nanofibers with 1D structure. The fibers are porous and the diameter can be controlled in the range of nanometers to a few micrometers.^35,36 Therefore, electrospun quantum dots/nanofibers composite photocatalysts have been fabricated with excellent photocatalytic activity.²¹ However, to the best of our knowledge, quantum dot-decorated BiVO₄ nanofibers fabricated by electrospinning have not been reported.

Among many quantum dot candidates to decorate BiVO₄ fibers, a bismuth-based photocatalyst, Bi₂O₃, which possesses a feasible bandgap (E_g ≈ 2.8 eV), is an ideal choice to construct heterojunctions with BiVO₄.^37,38 Up to now, Bi₂O₃ quantum dots have been prepared to enhance the photocatalytic performance of TiO₂ and Bi₃NbO₇ semiconductor photocatalysts by fabricating composite photocatalysts.^39,40

Herein, we demonstrate the in situ synthesis of Bi₂O₃ quantum dot-decorated BiVO₄ nanofibers via a facile electrospinning method. As a comparison, BiVO₄ nanofibers were prepared under similar conditions, where the solvent proportion is the only variable. A reasonable formation process is put forward based on the solvent properties and phase separation mechanism. The as-prepared Bi₂O₃ quantum dot-decorated BiVO₄ nanofibers exhibit a much higher visible-light-driven photocatalytic activity than BiVO₄ nanofibers. Besides, the method could point the way to the industrial production of efficient photocatalysts by electrospinning in the future.

2 Experimental

2.1 Preparation of catalysts

All reagents were of analytical purity, received from Aladdin Reagents (Shanghai), and used without further purification. In a typical synthesis, 0.84 g of citric acid was dissolved in 6 mL of ethanol with magnetic stirring at room temperature, and then 0.6468 g of Bi(NO₃)₃·5H₂O was added into the mixture. After the Bi(NO₃)₃·5H₂O had dissolved, 0.1560 g NH₄VO₃ was added slowly into the Bi(NO₃)₃ solution. Afterward, the above mixture was added into a certain concentration of a solution of PVP (polyvinylpyrrolidone, K-90) in DMF (N,N-dimethylformamide) (2.0 g of PVP was dissolved in 20 mL of DMF) with continuous stirring for 12 h. Thus the spinnable precursor sols were obtained. Then, the precursor sols were transferred into a 10 mL syringe which was attached to a stainless steel needle with inner diameter of 0.510 mm (21 G) and then were ejected from the needle with a voltage of 14 kV. The distance between the needle and collector was 12 cm. The feeding rate of the suspension in the syringe was controlled at 1.0 mL h⁻¹ by using a syringe pump. The sols were spun at about 25 °C in air by electricity. The humidity was controlled below 30%. The as-spun fibers in the form of nonwoven mats were collected from a collector plate (Al foil). The as-spun fibers were annealed at 500 °C for 2 h with a ramp rate of 1 °C min⁻¹ using a chamber furnace. The electrospinning process is shown in Scheme 1. The calcination samples were Bi₂O₃ quantum dot-decorated BiVO₄ nanofibers (denoted as BQDs–BVNFs). For comparison, BiVO₄ nanofibers were fabricated by a similar route. The only change of the synthesis conditions was the solvent proportion which was adjusted to 16 mL DMF and 10 mL ethanol. The as-calcinated samples were pure BiVO4 nanofibers (denoted as BVNFs).

Scheme 1 Fabrication of BQDs–BVNFs.

2.2 Characterization

The structure of the obtained monoclinic scheelite BiVO₄ was confirmed by X-ray diffraction (XRD) using a Rigaku D/max-2000 diffractometer with Cu Kα radiation (λ = 0.15406 nm). Diffraction patterns were collected from 10° to 90° at a rate of 4° min⁻¹ with a scan width of 0.02°. The morphology of the products was observed by a Camscan MX2600FE field emission scanning electron microscope (FE-SEM). The operating voltage was set to 20 kV and the sample was prepared by dropping pre-ultrasonic-dispersed (10 min) ethanol turbid liquid onto a chip of silicon. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) of the hierarchical structures were carried out with an FEI Tecnai G2 S-Twin operating at 300 kV. UV-visible diffuse reflectance spectra were acquired with a spectrophotometer (TU-1900) and BaSO₄ was used as the reflectance standard. Raman spectra were recorded using a HORIBA Xplore instrument with an Ar⁺ laser source of 488 nm wavelength in a macroscopic configuration (532 nm). X-ray photoelectron spectroscopy (XPS) analysis was carried out using an American electronics physical HI5700ESCA system with X-ray photoelectron spectroscope using Al Kα (1486.6 eV) monochromatic X-ray radiation. The peak positions were corrected against the C 1s peak (284.6 eV) of contaminated carbon.

2.3 Photocatalytic test

The photocatalytic activities of the samples were evaluated by the degradation of RhB under simulated sunlight irradiation by using a 300 W Xe lamp (Trusttech PLS-SXE 300, Beijing) with a cutoff filter (λ ≥ 400 nm). The RhB initial concentration was 10 mg L⁻¹. An amount of 0.05 g of photocatalyst was put into 100 mL of RhB solution. Before the photodegradation experiment was initiated, the suspension was magnetically stirred in the dark for 55 min to reach adsorption–desorption equilibrium and sonicated for 5 min. The final preparation was the addition of 0.1 mL H₂O₂ into the above solution. Once the photodegradation experiment started, at given time intervals, 4 mL aliquots of solution were sampled and centrifuged to remove the photocatalysts. The filtrates were analyzed by the variations of the absorption band maximum (554 nm). The efficiency of RhB photodegradation was estimated according to the following formula: η = [(A₀ − A_t)/A₀] × 100%, where A₀ and A_t are the absorbance of the pre- and post-irradiation RhB solution, respectively. For photocatalytic activity comparison, BiVO₄ nanofibers with a glossy surface were synthesized using the same conditions except the proportion of solvents (DMF: 16 mL; ethanol: 10 mL).

2.4 Photoelectrochemical measurements

The photoelectrochemical characteristics were measured with a CHI604C electrochemical workstation using a standard three-compartment cell. Catalyst-coated FTO glass served as working electrode and a piece of Pt sheet, a Ag/AgCl electrode and 0.5 M sodium sulfate were used as the counter electrode, reference electrode and electrolyte, respectively. The photocurrent and electrochemical impedance spectroscopy (EIS) measurements were carried out at the open circuit potential. The light source employed was a 300 W xenon lamp.

3 Results and discussion

Fig. 1 shows the XRD patterns of BQDs–BVNFs and BVNFs synthesized by electrospinning and subsequent annealing treatment at 500 °C for 2 h. The XRD patterns of these two samples are assigned to monoclinic scheelite BiVO₄ which is in good agreement with the standard card no. 14-0688. From observation of the XRD patterns, with the decoration of Bi₂O₃ quantum dots on the BiVO₄, there is no obvious shift of main peaks of BiVO₄, demonstrating that the Bi species are present in a separate phase rather than incorporated into the BiVO₄ lattice, which is similar to previous results.^39,41 However, no characteristic peaks belonging to Bi₂O₃ quantum dots are found in the BQDs–BVNFs pattern. The absence of XRD peaks of Bi₂O₃ quantum dots is ascribed to their very small size and low content in BVNFs.^31,42,43

Fig. 1 The XRD patterns of the BQDs–BVNFs and BVNFs.

SEM and TEM images of as-spun fibers and BQDs–BVNFs are shown in Fig. 2. As Fig. 2a shows, the as-spun fibers have a one-dimensional uniform texture structure with a glossy surface and are randomly oriented under the synthesis conditions used (DMF : ethanol = 20 mL : 6 mL). The diameter of these as-spun fibers is about 100–300 nm, and the length of individual fibers is up to tens of micrometers. After calcination at 500 °C, the surface of the BQDs–BVNFs is much coarser due to decomposition of organic ingredient and redundant ions, but the fibers still retain a one-dimensional structure. Meanwhile, the diameter of BQDs–BVNFs (300–600 nm) is larger than that of as-spun fibers. The unique phenomenon may result from the surface element gathering of as-spun fibers, which is proved from XPS spectra discussed below. Further information about the BQDs–BNFs one-dimensional structure is obtained from TEM images (Fig. 2c–f). It is confirmed that nanofibers have diameters of about 300–600 nm, which agrees well with that revealed by SEM images. The quantum dots of 5–15 nm are well dispersed on the surface of the BiVO₄ nanofibers as shown in Fig. 2d. The HRTEM investigation demonstrates the nanofibers are composed of BiVO₄ nanoparticles and the interplanar spacing is 0.475 nm, which corresponds well to the (110) plane of monoclinic BiVO₄. Besides, the Bi₂O₃ quantum dots with a diameter of 5–15 nm can be observed on the surface of the BiVO₄ nanofibers and the interplanar spacings of 0.331 nm and 0.409 nm correspond to the (111) and (020) plane of α-Bi₂O₃, respectively. The discernible diffraction spots of the corresponding SAED pattern can be indexed as the (020) and (121) reflections (Fig. 2f), demonstrating the centers of BiVO₄ nanofibers consist of BiVO₄ nanocrystals. As shown in Fig. S1,† SAED pattern of the fibers' surface could confirm the existence of α-Bi₂O₃ on the surface. Furthermore, the SAED patterns selected from different regions (center or surface) exhibit different diffraction patterns, indicating the Bi₂O₃ quantum dots are attached to the surface of BiVO₄ nanofibers.

Fig. 2 (a and b) SEM images of the as-spun fibers and BQDs–BVNFs; the insets are at high magnification. (c and d) TEM images of the BQDs–BVNFs at low magnification; the inset in (d) is the local surface at high magnification. (e) HRTEM image of the BQDs–BVNFs. (f) The corresponding selected area electron diffraction pattern.

As Fig. 3 shows, when changing the proportion of the solvents (DMF : ethanol = 8 : 5) and keeping other conditions unchanged, the morphology of the as-prepared sample changes observably. The as-spun BVNFs are similar to BQDs–BVNFs in diameter and length as shown in Fig. 3a. However, many branch-like fibers appear due to the elongating viscoelastic thread stress balance which is caused by the variation of solvent proportion.⁴⁴ Fig. 3b shows that the BiVO₄ nanofibers still maintain the one-dimensional structure after the heat treatment, and the diameter of BVNFs is 200–500 nm. Besides, as observed in Fig. 3c, the surface of the as-prepared BiVO₄ nanofibers is smooth and no Bi₂O₃ quantum dots can be observed in the inset image. The HRTEM image in Fig. 3d indicates the interlinked nanoparticles of the smooth BiVO₄ nanofibers are single crystalline and the interplanar spacing is 0.467 nm, which corresponds well to the (011) plane of monoclinic BiVO₄.

Fig. 3 (a and b) SEM images of the as-spun fibers and BVNFs; the insets are at high magnification. (c) TEM image of the BVNFs at low magnification; the inset is at high magnification. (d) HRTEM image of the BVNFs.

To investigate the effect of the formation of Bi₂O₃ quantum dots on BiVO₄ nanofibers, the local structures of BQDs–BVNFs and BVNFs were studied by Raman spectroscopy. Fig. 4 shows the Raman spectra of BQDs–BVNFs and BVNFs excited by a green-line laser (532 nm). As Fig. 4a shows, Raman bands around 210, 324, 366, 710, and 826 cm⁻¹ are observed for both samples. These are ascribed to the typical vibrational bands of BiVO₄.^24,45,46 The band located at 210 cm⁻¹ is the external mode of BiVO₄, which offers negligible structural information. The Raman bands at 324 and 366 cm⁻¹ are attributed to the asymmetric and symmetric deformation modes of the VO₄³⁻ tetrahedron, respectively.⁴⁵ The Raman bands around 710 and 826 cm⁻¹ are assigned to the stretching modes of two different types of V–O bonds. In addition, an obvious Raman band shift of the V–O stretching vibration is observed, which is owing to the one-dimensional structure of BiVO₄ nanofibers.⁴⁷ From Fig. 4b, which is the magnified spectrum corresponding to the red dotted circle in Fig. 4a, there exists a small peak around 461 cm⁻¹ for BQDs–BVNFs, whereas there is no peak at the same position for BVNFs. This additional Raman band of BQDs–BVNFs is ascribed to the Bi₂O₃ quantum dots decorating the surface of the BiVO₄ nanofibers.⁴⁸

Fig. 4 Raman spectra of BQDs–BVNFs and BVNFs excited by a green-line laser (532 nm). (a) Characteristic peaks of BiVO₄ nanofibers lie in the region of 200–1000 cm⁻¹. (b) The magnified region of 400–600 cm⁻¹.

Considering that the heat treatment process of BQDs–BVNFs is consistent with that of BVNFs, the formation of Bi₂O₃ quantum dot-decorated BiVO₄ nanofiber surface could be attributed to the difference in surface chemical composition between the as-spun fibers of the two samples. Therefore, XPS was used to investigate the distribution of surface elements in as-spun BQDs–BVNFs and BVNFs.⁴⁹ Fig. 5 shows the characteristic spin–orbit split peaks of the Bi 4f_5/2 and Bi 4f_7/2 signals, and V 2p_1/2 and V 2p_3/2 signals. The peak positions of both Bi and V for the two as-spun fibers are both close to those of BiVO₄ reported in another study.²⁴ However, owing to the existence of the organic components (PVP and citric acid) which possess a coordination capacity to complex with Bi³⁺ and V⁵⁺, the electron density increases and both of the spin–orbit split peaks shift towards the lower binding energy region. Furthermore, as shown in Fig. 5a, the Bi 4f_5/2 and Bi 4f_7/2 signal peaks of the as-spun BQDs–BVNFs are much stronger than those of as-spun BVNFs. On the contrary, the V 2p_1/2 and V 2p_3/2 signal peaks of the two samples shown in Fig. 5b exhibit nearly the same intensity. From the observations, a conclusion could be drawn that there exists surface element gathering in as-spun BQDs–BVNFs.

Fig. 5 XPS spectra of the as-spun fibers of both two samples: (a) the Bi 4f and (b) V 2p peak.

Based upon the synthesis condition and above analysis results, a possible formation mechanism of BQDs–BVNFs is described in Fig. 6. In the procedure of the precursor solution preparation, bismuth(III) nitrate pentahydrate is first dissolved in citric acid solution. The addition of citric acid to the solution not only provides an acidic condition which can effectively inhibit the hydrolysis of Bi³⁺ ions, but also leads to a complexing reaction with Bi³⁺ ions. Ammonium metavanadate powder is added slowly into the above solution and a blue-green homogeneous liquid forms because of the valence change of the vanadium. In the precursor solution, each ingredient is well distributed under vigorous stirring. However, there is a difference in the surface tension and conductivity between DMF and ethanol which can influence the formation of the fibers.^50,51 The surface tension of DMF is smaller than that of ethanol, nevertheless the conductivity is much larger, so the Taylor cone which contains more DMF will take shape easily.⁵² In addition, Bi³⁺ ions are most likely dissolved in DMF. On the contrary, vanadate ions are more likely to be in ethanol. Given that there is a greater volume of DMF in this system (DMF : ethanol = 10 : 3), a concentration gradient of solvents could come into being naturally, as Fig. 6 shows. Therefore, the Bi³⁺ ions diffuse to the shell level while the vanadate ions diffuse to the core level. Afterwards, the Bi³⁺ ions in the shell level could contribute to the evolution of the Bi₂O₃ quantum dots because they are easily exposed to air in the atmosphere and react with O₂ instead of reacting with vanadate ions in the process of calcination. However, the characteristic peaks of BQDs–BVNFs do not shift in the XRD pattern, indicating that extra V ions could not lead to the formation of non-stoichiometric BiVO₄. Nevertheless, when changing the proportion of the solvents (DMF : ethanol = 8 : 5), the concentration gradient of solvents is no longer so obvious. As a result, each component is well dispersed in the as-spun fibers, which leads to the formation of smooth BiVO₄ nanofibers without BQD decoration.

Fig. 6 Possible formation process of Bi₂O₃ quantum dots decorated BiVO₄ nanofibers.

UV-visible diffuse reflectance spectroscopy is used to characterize the light absorption property of the as-prepared samples. Fig. 7 shows the UV-visible absorption spectra of BQDs–BVNFs and BVNFs samples. Both of the samples possess the ability to utilize visible light for photocatalysis due to their absorption edge located at ca. 550 nm as shown in the spectra. Besides, as observed from the plot, there is no shoulder peak, which indicates that impurities are not generated with the decoration of Bi₂O₃ quantum dots. This is in agreement with the XRD analysis above. However, BQDs–BVNFs exhibit an obvious blue shift because of the existence of the Bi₂O₃ quantum dots, the bandgap of which is wider than that of BiVO₄.

Fig. 7 The UV-visible diffuse reflectance spectra of the BQDs–BVNFs and BVNFs samples.

The photocatalytic activities of the products are evaluated by the decomposition of RhB under visible light (λ ≥ 400 nm). Fig. 8 shows the photocatalytic degradation rate of BQDs–BVNFs and BVNFs under visible-light irradiation. Without the addition of the photocatalysts (blank), there is no obvious decrease of C (the absorption of RhB at 554 nm). However, after the addition of photocatalysts, C declined drastically, and the BQDs–BVNFs exhibit a higher photocatalytic performance than the BVNFs. According to the results of degradation test of RhB under visible light (λ ≥ 400 nm) shown in Fig. 8, photodegradation efficiency (η) of BQDs–BVNFs for RhB reaches 99.6% at 12 min. However, the photodegradation efficiency of BVNFs is only 50% under the same condition.

Fig. 8 Photocatalytic degradation of RhB under visible-light irradiation.

From the observation of the UV-visible diffuse reflectance spectra and the photocatalyic performance curve diagram, the enhanced activity of the BQDs–BVNFs is not caused by the change in luminous absorption which is blue shifted relative to that of BVNFs. Therefore, to determine the mechanism of action of the enhanced photocatalytic performance, a photocurrent transient response measurement of pure BiVO₄ nanofibers and BQDs–BVNFs heterostructure was performed. Fig. 9 shows the rapid and consistent photocurrent responses for BQDs–BVNFs and BVNFs under several on/off visible-light irradiation cycles and electrochemical impedance spectra (EIS) of the two electrodes. As shown in Fig. 9a, both electrodes are prompt in generating photocurrent with a reproducible response to on/off cycles, indicating the effective charge transfer and successful electron collection for the samples. However, it is worth noting that the BQDs–BVNFs film electrode exhibits an obvious enhanced current density, demonstrating the more efficient photoinduced charge separation and transfer in BQDs–BVNFs. In Fig. 9b, this finding is further proved by the EIS of the electrodes. The arc radius of the Nyquist plot of the BQDs–BVNFs electrode is smaller than that of the BVNFs electrode, which illustrates that the decoration of Bi₂O₃ dots on BiVO₄ nanofibers contributes to a better high-efficiency charge transfer ability. Summing up the above analysis, the enhanced separation and transfer efficiency of the photoinduced carriers may determine the high degradation activity of BQDs–BVNFs.

Fig. 9 (a) Photocurrent response of the as-prepared pure BVNFs and BQDs–BVNFs electrodes under visible-light illumination. (b) Electrochemical impedance spectra of BVNFs and BQDs–BVNFs.

Subsequently, we proposed a possible separation process of photoinduced carriers, as shown in Fig. 10. Owing to the Bi₂O₃ quantum dot surface decoration, it could be that favorable transfer of electrons from Bi₂O₃ to BiVO₄ and holes from BiVO₄ to Bi₂O₃ occurs simultaneously. As a consequence, the recombination of the photoinduced electron–hole pairs is greatly reduced. Besides, according to the equation τ = r²/π²D,⁵³ where τ is the average diffusion time from the bulk to the surface of the photogenerated carriers, r is the grain radius and D is the diffusion coefficient of the carriers, adjusting the particle size to the nanoscale can enhance the photocatalytic performance. From all the above, owing to the small size of Bi₂O₃ dots, the carriers can transfer to the photocatalyst surface more rapidly and react with the reactants. Therefore, the BQDs–BVNFs could be promising photocatalysts for photoelectrochemical energy conversion devices.

Fig. 10 Schematic of the mechanism of the photocatalytic process.

4 Conclusions

Bi₂O₃ quantum dot-decorated BiVO₄ nanofibers have been fabricated in situ by electrospinning based on the phase separation mechanism. XPS analysis demonstrates that gathering of surface elements resulting from the phase separation determines the formation of Bi₂O₃ quantum dots on the BiVO₄ nanofibers. The BQDs–BVNFs exhibit excellent photocatalytic activities, better than that of smooth BiVO₄ nanofibers, under visible light irradiation. By investigating the charge transfer property of the two samples, what could be inferred is that the formation of Bi₂O₃ quantum dots can account for the improved charge separation and rapid carrier transfer in BQDs–BVNFs. This work not only exploits a facile method for fabrication of high-efficiency quantum dot-decorated photocatalysts but also makes a significant step towards fabricating functional materials for environment decontamination and practical application.

Acknowledgements

This work was financially supported by the National Nature Science Foundation of China (21271055). We acknowledge the support by Fundamental Research Funds for the Central Universities (HIT. IBRSEM. A.201410), Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (no. QAK201304) and Program for Innovation Research of Science in Harbin Institute of Technology (B201412).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra11065j

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