BiVO4 nanocomposite photocatalysts with highly enhanced photocatalytic activity for rhodamine B degradation under visible light irradiation

Accepted Manuscript BiFeO3/BiVO4 nanocomposite photocatalysts with highly enhanced photocatalytic activity for Rhodamine B degradation under visible light irradiation

Buagun Samran, Sumneang lunput, Siriporn Tonnonchiang, Saranyoo Chaiwichian PII:

S0921-4526(19)30138-3

DOI:

10.1016/j.physb.2019.02.049

Reference:

PHYSB 311354

To appear in:

Physica B: Physics of Condensed Matter

Received Date:

18 December 2018

Accepted Date:

23 February 2019

Please cite this article as: Buagun Samran, Sumneang lunput, Siriporn Tonnonchiang, Saranyoo Chaiwichian, BiFeO3/BiVO4 nanocomposite photocatalysts with highly enhanced photocatalytic activity for Rhodamine B degradation under visible light irradiation, Physica B: Physics of Condensed Matter (2019), doi: 10.1016/j.physb.2019.02.049

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ACCEPTED MANUSCRIPT BiFeO3/BiVO4 nanocomposite photocatalysts with highly enhanced photocatalytic activity for Rhodamine B degradation under visible light irradiation Buagun Samrana, Sumneang lunputb, Siriporn Tonnonchiangc, Saranyoo Chaiwichianb,* aDivision

of Physics, Faculty of Science, Nakhon Phanom University, Muang District, Nakhon Phanom, 48000

Thailand bDepartment

of Science and Mathematics, Faculty of Industry and Technology, Rajamangala University of

Technology Isan, Phangkon, Sakon Nakon, 47160, Thailand cDivision

of Radiological Technology, Faculty of Science, Ramkhamhaeng University 2086, Ramkhamhaeng

Road, Huamak, Bangkapi, Bangkok 10240, Thailand

*E-mail: [email protected], Tel. +66 979418005, Fax. +66 42772158

Abstract In this paper, the BiFeO3/BiVO4 nanocomposite photocatalysts were successfully synthesized by the homogeneous precipitation method followed with the hydrothermal method. The characteristics of as-prepared photocatalysts were measured by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Brunauer, Emmett and Teller (BET), Photoluminescence (PL) and UV–vis diffuse reflectance spectra (UV-vis DRS) techniques. The photocatalytic activity of rhodamine B (RhB) with the photocatalysts was estimated by the visible light irradiation. The experimental results were found that a mole ratio of 0.5:0.5 of BiFeO3:BiVO4 exhibited the highest photocatalytic performance as compared with other photocatalysts. More importantly, BiFeO3 decorated on the BiVO4 surface to form a composite, resulting in its large surface area and enhanced photoabsorption to the visible light regions. Moreover, it also was synergistic with the BiVO4 to hinder the rapid recombination of electron-hole pairs. The stability and recyclability of 0.5BiFeO3/0.5BiVO4 were also tested by five recycling runs, and the addition of the radical

ACCEPTED MANUSCRIPT scavengers in the photodegradation process of RhB under visible light irradiation was detected through trapping experiments. The results were found that hydroxyl radicals (OH•) and holes (h+) was the major active species, which had a considerable part of RhB degradation. The photocatalytic mechanism of BiFeO3/BiVO4 nanocomposite photocatalysts was also discussed. Keywords: BiFeO3; BiVO4; Rhodamine B; Trapping Experiment; Photocatalytic Activity 1. Introduction Recently, the organic and inorganic pollutants, such as dyes and/or heavy metal ions from textile, papermaking, printing, dyeing and agricultural industries are very important culprits to lead to the wastewater and harmful to human health and ecosystem [1,2]. Therefore, it is very urgent to search for the way to solve the wastewater. Semiconductor photocatalysis is a green technology, which has drawn a lot of attention from several researcher groups for organic pollutants degradation in water and environmental purification due to its quick reaction and environmentally friendly [3]. More recently, various semiconductors are employed for organic pollutants degradation, such as Bi2WO6, TiO2, CeO2, Bi2O3, BiOBr, BiVO4 and so on [4-9]. Among these semiconductors reported, BiVO4 has gained the most popularity for water splitting and organic pollutants degradation as well as environmental treatment [10,11]. BiVO4 can be categorized into three major crystalline structures, such as tetragonal zircon, tetragonal scheelite, and monoclinic scheelite [12,13]. From reports of researchers, monoclinic-BiVO4 shows excellent photocatalytic performance in comparison with tetragonal-BiVO4 due to its narrow band gap energy (2.4 eV) and distortions of the BiO6 octahedron and VO4-3 tetrahedron, which causes better photocatalytic efficiency than tetragonal-BiVO4 (3.1 eV) [14,15]. However, pure BiVO4 is still having low photocatalytic activity owing to its narrow band gap energy of pure BiVO4 causes inefficient separation and rapid recombination of photogenerated electron and hole pairs that makes it

ACCEPTED MANUSCRIPT hard for useful applications. To resolve this problem, numerous researchers have been focused on the improvement of BiVO4 by the coupling with metal oxide semiconductors to reduce quick recombination of photoinduced charge carriers and to increase photocatalytic efficiency. In recent years, a perovskite-type BiFeO3 has been considered as one of the significant oxide semiconductor with ferroelectricity and antiferromagnetic properties, which have received much attention for its potential applications as a photocatalyst in wastewater treatment under visible light irradiation because of its narrow band gap energy (2.2 eV) and high physical and chemical stabilities [16-19]. The use of BiFeO3/BiVO4 nanocomposite photocatalysts is a way of choice for resolving an inefficient separation and rapid recombination of electron-hole pairs, resulting in its increased photocatalytic performance. However, to the best of our knowledge, there are few reports on the properties of BiFeO3/BiVO4. Recently, several methods have been employed for fabricating heterojunction photocatalysts, such as hydrothermal, co-precipitation, sol-gel, solvothermal and microwave processes [20-24]. In this study, the BiFeO3/BiVO4 nanocomposite photocatalysts were synthesized via a simple hydrothermal method, in which BiFeO3 was decorated on the surface of BiVO4 particles to form visible-light-active nanocomposite photocatalysts. Photocatalytic activity of all photocatalysts was obtained by the RhB dye degradation under visible light irradiation. 2. Experimental details 2.1. Synthesis of the photocatalysts Pure BiFeO3 particles were prepared by a homogeneous precipitation method. In a typical procedure, 0.1 M of Bi(NO3)3•5H2O and Fe(NO3)3•9H2O were dissolved in 50 ml of nitric acid (HNO3) solution (2.5 M) and 50 ml of deionized water, respectively. Then, both solutions were mixed together in a 1:1 molar ratio and the pH was slowly adjusted to 10 by adding sodium hydroxide (NaOH) solution (6 M) under continually magnetic stirrer for 24 h.

ACCEPTED MANUSCRIPT to ensure the ferritization process. The obtained precipitates were filtered and washed with deionized water several times till pH was neutral and then dried at a temperature of 80 °C for 24 h. Finally, the BiFeO3 particles were calcined at 600 °C for 3 h. The hydrothermal method was used to synthesize BiFeO3/BiVO4 nanocomposite photocatalysts. Firstly, the concentration amount of 0.1 M of Bi(NO3)3•5H2O and NH4VO3 was dissolved in 50 ml of nitric acid (HNO3) solution (2.5 M). Both solutions were mixed together in a molar ratio of 1:1 and continually stirred with a magnetic stirrer. After that, ammonium hydroxide (NH4OH) solution (6 M) was slowly added dropwise to the solution mixture until pH was reached to 7. The previously as-prepared BiFeO3 particles were then added into the solution in different mole ratios together with a continuous stirrer for 30 h. The obtained solutions were poured into a 100 ml Teflon-lined stainless steel autoclave and heated at a temperature of 180 °C for 6 h. Finally, the precipitates of BiFeO3/BiVO4 were collected by centrifugation at 5,000 rpm for 10 min and washed with deionized water several times and then dried in air at 80 °C for 24 h. 2.2.

Characterization of the photocatalysts The phase structures were identified via an X-ray diffraction (XRD, Philips X'Pert

MPD) with Cu Kα irradiation. Scanning electron microscopy (SEM, JEOL JSM-6335F) technique was used to study the morphologies. The actual microstructures and sizes were investigated by transmission electron microscopy (TEM, JEOL JEM-2010) technique. The specific surface area was evaluated by Brunauer-Emmett-Teller (BET) nitrogen adsorptiondesorption isotherm measurements at 80 °C (Autosorb 1 MP, Quantachrome). UV-vis diffuse reflection spectroscopy (UV-vis 3600, Shimadzu) with an integrating sphere attachment (ISR-3100, Shimadzu) was employed to measure the optical absorption. The spectral emission was detected by Photoluminescence (PL) AvaSpec-2048TEC-USB2-2

ACCEPTED MANUSCRIPT spectrophotometer and activated using LED (Oceans optics, LLS-345) as a light source with a wavelength of 345 nm. 2.3. Photocatalytic activity study In this experiment, RhB was used as a model dye in the photodegradation process under the irradiation of 50 W halogen lamp (Essential MR, Philips, Thailand) with a cutoff filter (λ < 400 nm). The dye initial concentration of 2 x 10-5 M was used. The 0.1 g photocatalyst was mixed into a 100 ml RhB solution together with a magnetic stirrer to disperse in an aqueous solution. Before irradiation, the solution was kept in dark for 30 min to ensure an adsorptiondesorption equilibrium of RhB and photocatalysts. After irradiation, the suspension of 3 mL was separated out of the photocatalyst by centrifugation and taken every 15 min. The absorbance amount of RhB was measured by using an UV-vis spectrophotometer (Shimadzu UV-1800). 3. Results and discussion 3.1. XRD analysis The X-ray diffraction patterns of the photocatalyst samples are shown in Fig. 1. The diffraction peaks of BiFeO3 can be obviously indexed as rhombohedral phase matches well with a JCPDS file no. 72-2035. The main diffraction peaks of BiFeO3 locates at 2 of 22.48°, 31.89°, 32.18°, 39.02°, 39.58°, and 45.84° corresponds to (010), (110), (-110), (111), (-111), (020) and (120) planes, respectively. In the parts of the diffraction peaks of BiVO4 appears at 2 of 28.83°, 30.51°, 34.56°, 35.26°, 39.78° and 42.50°, respectively, which corresponds to (121), (040), (200), (002), (211) and (051) planes of monoclinic scheelite BiVO4 with a JCPDS file no. 14-0688. While the XRD data analysis shows that BiFeO3/BiVO4 nanocomposite photocatalysts consist of rhombohedral-BiFeO3 and monoclinic scheelite BiVO4 phases. Moreover, it also is observed that at low concentration of BiFeO3 (0.2 mole ratio), the diffraction pattern of heterojunction materials was quite similar to that of pure

ACCEPTED MANUSCRIPT BiVO4 while increasing of BiFeO3 content in the composite sample, the diffraction pattern is more similar to that of pure BiFeO3, indicating that there are BiFeO3 and BiVO4 in the composite. No other impurity peaks found in BiFeO3 and BiVO4 phases, suggesting that pure phase and high crystallinity is achieved. 3.2. Morphology and BET specific surface area analyses The morphology and microstructure of pure BiFeO3, pure BiVO4 and 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalysts were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques, as illuminated in Fig. 2. It can be seen that BiFeO3 exhibits irregular-like shape with an average size of about 50-80 nm are shown in Fig. 2a. The morphology of BiVO4 shows rod-like shape, and diameter and length of rod-like shape are approximately 80-100 nm and 100-200 nm, respectively, as shown in Fig. 2b. Meanwhile, the morphology of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst comprises of a rod-like shape of BiVO4 and an irregular-like shape of BiFeO3, as shown in Fig. 2c. To more study information with regard to the morphology and actual size of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst, TEM technique was used and shown in Fig. 2d. It can be certainly seen that TEM image of 0.5BiFeO3/0.5BiVO4 photocatalyst comprises of rod-like and rectangular-like structures with a particle size from 50-100 nm. For the TEM magnification of 0.5BiFeO3/0.5BiVO4 photocatalyst is shown in Fig. 2e, the d-spacing appears at 0.2813 nm is in good agreement with (110) plane of BiFeO3, and the d-spacing locates at 0.3084 nm is matched with (-121) plane of the monoclinic-BiVO4 structure. The obtained results can efficiently confirm that the BiFeO3 and BiVO4 exist in the composite, corresponding to the XRD result. The BET specific surface areas of BiFeO3, BiVO4, and 0.5BiFeO3/0.5BiVO4 photocatalysts are 11.84, 9.23 and 31.91 m2/g, respectively, indicating that BiVO4 particles are composited with BiFeO3 particles, leading to an increment of the specific surface area which is a considerable

ACCEPTED MANUSCRIPT factor for enhancing photocatalytic activity. However, enhanced photocatalytic performance depends not only on the BET specific surface area alone, but also relates to many factors such as the number of photocatalysts, crystal structure, pH, intensity and so on [25-27]. 3.3. Optical property analysis The optical absorption and band gap energy of the photocatalysts were measured by using UV-vis DRS technique. The data are shown in Fig. 3. From the experimental data, the absorption of BiVO4 was estimated to be 491 nm and can be seen from Fig. 3a. The data of BiFeO3 shows the absorption of 559 nm which is presented in Fig. 3b. Meanwhile, the optical absorption of BiFeO3/BiVO4 composite clearly shifts toward the visible light region which is displayed in Fig. 3c. Moreover, the band gap energy of the photocatalysts can also be calculated from the equation: Eg  1240 /  , where Eg is the band gap energy (eV) and  is the wavelength (nm) [28-31]. The band gap energies of BiVO4, BiFeO3, and 0.5BiFeO3/0.5BiVO4 photocatalysts are evaluated to be 2.52 eV, 2.21 eV, and 2.23 eV, respectively. It is evidently seen that the BiFeO3 composited on the BiVO4 surface, there is no change of the band gap energy, indicating the optical absorption of BiFeO3 and 0.5BiFeO3/0.5BiVO4 photocatalysts is quite similar. Based on the above results, it can be confirmed that the photocatalysts can be excited under visible light irradiation, resulting in enhanced photocatalytic performance. 3.4. Photocatalytic activity The photocatalytic performance of RhB dye in an aqueous solution by the photocatalysts under visible light irradiation was carried out, as shown in Fig. 4a. The RhB photolysis experiment without any photocatalyst is 3.91%. While in the presence of photocatalysts, the photodegradation percentage of pure BiFeO3, pure BiVO4 and BiFeO3/BiVO4 nanocomposite photocatalysts with different mole ratios of 0.2:0.8, 0.4:0.6, 0.5:0.5, 0.6:0.4, and 0.8:0.2, which are 9.27%, 13.09%, 54.69%, 46.27%, 69.27%, 37.93%

ACCEPTED MANUSCRIPT and 31.93%, respectively. Moreover, it can be apparently seen that all composites show higher photodegradation rate than that of pure BiFeO3 and pure BiVO4 under identical condition. The optimum mole ratio of BiFeO3:BiVO4 is 0.5:0.5, which exhibits the best photodegradation rate of RhB dye within 120 min, indicating that the addition of BiFeO3 on the surface of BiVO4 importantly improves the photocatalytic efficiency and also reduce the rapid recombination of charge carriers effectively. In order to further confirm the photodegradation activity of RhB dye, the pseudo-firstorder kinetic model was used by the following equation [32]:

ln  C0 / Ct   kapp t where kapp is the pseudo-first order rate constant (min-1), C0 and Ct are the dyes concentration at time 0 and t [18], respectively. From the Fig. 4b, 0.5BiFeO3/0.5BiVO4 exhibits obviously higher rate constant ( kapp ) than those of other samples. Photodegradation rate constant of RhB with the 0.5BiFeO3/0.5BiVO4 is 0.00993 min-1. This might be due to the stronger visible absorption, corresponding to the enhanced photocatalytic activity. Moreover, the amount of BiFeO3 and BiVO4 affect to the separation of photogenerated charge carriers, thus increasing photocatalytic performance. Fig. 4c shows the chemical stability and reusability of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst by the five recycling runs for the degradation of RhB under visible light irradiation. From experimental results, it can be observed that after five recycling runs is slight photocatalytic activity loss, suggesting that the 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst has good stability and reusability during the photodegradation process of RhB. 3.5. Mechanism of the photocatalytic reaction process To further explain the mechanism of photocatalytic reaction of 0.5BiFeO3/0.5BiVO4, the main active species of trapping experiments in the photodegradation process were

ACCEPTED MANUSCRIPT detected by using benzoquinone (BQ), isopropanol (IPA) and potassium iodide (KI) as superoxide radicals ( O2: )or electron ( e  ),hydroxyl radical( OH : ) and hole ( h  ), respectively. As shown in Fig. 5a, all the experiments were studied by the irradiation of visible light for 120 min. It can be observed that the 0.5BiFeO3/0.5BiVO4 in the absence of scavenger highly shows the photocatalytic performance. When BQ, IPA and KI scavengers were added into the photodegradation process of 0.5BiFeO3/0.5BiVO4, the photocatalytic performance of 0.5BiFeO3/0.5BiVO4 in the presence of KI and IPA showed lower than that of BQ. Therefore, it can be implied that h  and OH : are the major active species which have an important role in the photodegradation process of RhB under visible light irradiation. Moreover, the photodegradation process of BiFeO3/BiVO4 nanocomposite photocatalyst also depends on the corresponding valence band (VB) and conduction band (CB) potentials of BiFeO3 and BiVO4. The valence band (VB) and conduction band (CB) potentials of BiFeO3 and BiVO4 at the point of zero charges can also be calculated by the following equation [33-35]: 1 ECB    E C  Eg 2

where, ECB is the conduction band potential;  is the electronegativity of the semiconductor; E C is the energy of free electrons on the hydrogen scale ( : 4.5 eV ); and Eg is the band gap

energy of the semiconductor (for BiFeO3, Eg is 2.21 eV; for BiVO4, Eg is 2.52 eV). Consequently, according to the formula above, the calculation of CB and VB values of BiFeO3 are 0.02 and 2.23 eV, and of BiVO4 are 0.28 and 2.80 eV, respectively. Therefore, the CB edge position of BiFeO3 (0.02 eV) is more negative than that of BiVO4 (0.28 eV) and the VB edge position of BiVO4 (2.80 eV) is more positive than that of BiFeO3 (2.23 eV), and thus a difference of energy band positions exists between BiFeO3 and BiVO4 materials.

ACCEPTED MANUSCRIPT Based on the above results, the possible mechanism of the photodegradation process of RhB dye in aqueous solution over BiFeO3/BiVO4 nanocomposite photocatalyst under visible light irradiation is illustrated in Scheme 1. When the BiVO4 and BiFeO3 were irradiated by visible light simultaneously, the electrons ( e  ) on the valence band (VB) were stimulated to the conduction band (CB), and the same amount of holes ( h  ) left in VB of BiVO4 and BiFeO3. While the photogenerated electrons on the CB of BiFeO3 would conveniently be jumped to the CB of BiVO4. Simultaneously, holes on the VB of BiVO4 will transfer to the VB of BiFeO3. In such way, photogenerated electrons and holes can efficiently separate, leading to reduce the recombination of photoinduced charge carriers. Afterward, the photogenerated electrons can react with O2 to finally yield O2: , and the generated O2: may also capture with H  to form OH : . Therefore, produced OH : can further oxidize the RhB molecules to yield CO2 and H2O finally. In addition, the holes on the VB of BiFeO3 can also oxidize the RhB molecules directly, resulting in its photodegradation. At last, it can be concluded that both h  and OH : are the key oxidant in the photodegradation process of RhB molecules. 3.6. Photoluminescence To further highlight the migration, transfer, and recombination processes of photogenerated electron and hole pairs, the photoluminescence (PL) technique was used as displayed in Fig. 5b. The PL spectra of the photocatalysts were activated at 345 nm. It can be clearly seen that the PL intensity of 0.5BiFeO3/0.5BiVO4 shows lower than pure BiVO4, suggesting that the efficient separation of photogenerated electron-hole pairs. In conclusion, the composites are beneficial to obstruct rapid recombination of photogenerated charge carriers and also increase the separation of electron-hole pairs, resulting in its enhanced photocatalytic activity in the RhB degradation [36]. 4.

Conclusion

ACCEPTED MANUSCRIPT The BiFeO3/BiVO4 nanocomposite photocatalysts were successfully synthesized through a simple hydrothermal method followed by a homogeneous precipitation method. The mole ratio of 0.5:0.5 of BiFeO3:BiVO4 played the best photodegradation rate (69%) of RhB within 120 min under visible light irradiation as compared with other samples. BiFeO3 decorating in the BiVO4 was also improved the specific surface area, optical absorption, and prevented rapid recombination of photoinduced electron-hole pairs, and led to its enhanced photocatalytic performance. In addition, the 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst has also high chemical stability and recyclability, and the hydroxyl radicals and holes played the two main active species in the photocatalytic reaction process. Acknowledgments The authors would like to greatly thank the Department of Science and Mathematics, Faculty of Industry and Technology, Rajamangala University of Technology Isan and the Division of Physics, Faculty of Science, Nakhon Phanom University, Muang District, Nakhon Phanom for support. References [1]

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ACCEPTED MANUSCRIPT [36] B. Samran, P. Krongkitsiri, S. Chaiwichian, Effect of copper dopants on visible-lightdriven photocatalytic activity of BiFeO3 photocatalysts, Modern Environ. Sci. Eng., 4 (2018) 234–243. List of figure captions Fig. 1. XRD patterns of pure BiFeO3, pure BiVO4 and BiFeO3/BiVO4 with different mole ratios. Fig. 2. SEM images of (a) pure BiFeO3, (b) pure BiVO4 and (c) 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst, (d) TEM image of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst and (e) d-spacing of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst. Fig. 3. UV-vis DRS of (a) pure BiVO4, (b) pure BiFeO3 and 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalysts. Fig. 4. (a) photodegradation efficiency of RhB dye, (b) pseudo-first order rate constant of RhB due degradation and (c) recycling runs of RhB degradation with 0.5BiFeO3/0.5BiVO4. Fig. 5. (a) trapping experiment of 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalyst and (b) PL spectra of BiVO4 and 0.5BiFeO3/0.5BiVO4 nanocomposite photocatalysts. Scheme 1. Possible mechanism of photocatalysis between BiFeO3 and BiVO4 under visible light irradiation.

ACCEPTED MANUSCRIPT Chaiwichian et al., Figure 1. 0.8BiFeO3:0.2BiVO4 0.6BiFeO3:0.4BiVO4

Intensity (a.u.)

0.5BiFeO3:0.5BiVO4 0.4BiFeO3:0.6BiVO4 0.2BiFeO3:0.8BiVO4

Pure BiVO4 Pure BiFeO3 JCPDS 14-0688(BiVO4) JCPDS 72-2035 (BiFeO3) 10

20

30

40

50

2

60

70

80

ACCEPTED MANUSCRIPT Chaiwichian et al., Figure 2.

ACCEPTED MANUSCRIPT Chaiwichian et al., Figure 3.

(b) KM-Absorbance

KM-Absorbance

(a)

BiVO4

 = 491 nm

450

500

550

600

650

400

700

450

500

550

600

Wavelength (nm)

Wavelength (nm)

(c) KM-Absorbance

400

BiFeO3  = 559 nm

0.5BiFeO3/0.5BiVO4  = 554 nm

500

550

600

Wavelength (nm)

650

700

650

700

ACCEPTED MANUSCRIPT Chaiwichian et al., Figure 4.

(b)

(a)

1.8

ln(C0/Ct)

Ct/C0

RhB photolysis Pure BiFeO3 Pure BiVO4 0.2BiFeO3:0.8BiVO4 0.4BiFeO3:0.6BiVO4 0.5BiFeO3:0.5BiVO4 0.6BiFeO3:0.4BiVO4

40

60

80

100

0.2BiFeO3:0.8BiVO4 0.4BiFeO3:0.6BiVO4

0.9

0.5BiFeO3:0.5BiVO4 0.6BiFeO3:0.4BiVO4 0.8BiFeO3:0.2BiVO4

0.6

0.0

120

0

20

Irradiation Time (min)

40

60

80

100

Irradiation Time (min)

(c)

1.0

2nd

1st

4th

3rd

5th

0.8

Ct/C0

20

1.2

0.3

0.8BiFeO3:0.2BiVO4

0

1.5

RhB photolysis BiFeO3 BiVO4

0.6 0.4 0.2 0.0

0

120

240

360

480

Irradiation Time (min)

600

120

ACCEPTED MANUSCRIPT Chaiwichian et al., Figure 5.

(a)

(b)

0.010

RhB

BiVO4

Intensity (a.u.)

kapp (min-1)

0.008 0.006 0.004

0.5BiFeO3/0.5BiVO4

0.002 0.000

No Quencher

IPA

BQ

KI

300

400

500

600

Wavelength (nm)

700

800

ACCEPTED MANUSCRIPT Chaiwichian et al., Scheme 1.

Facile 4/M performance photocatalysts WCNT in situ nanocomposites visible-light hydrothermaldriven as synthesis high

of BiVO