- Email: [email protected]
g-C3N4 composites
Author’s Accepted Manuscript Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites Song Xue, Xiaoyi Hou, Wenhe Xie, Xiucheng Wei, Deyan He www.elsevier.com
PII: DOI: Reference:
S0167-577X(15)30580-2 http://dx.doi.org/10.1016/j.matlet.2015.09.067 MLBLUE19583
To appear in: Materials Letters Received date: 7 July 2015 Revised date: 29 August 2015 Accepted date: 14 September 2015 Cite this article as: Song Xue, Xiaoyi Hou, Wenhe Xie, Xiucheng Wei and Deyan He, Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.09.067 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites Song Xue, Xiaoyi Hou, Wenhe Xie, Xiucheng Wei and Deyan He
School of Physical Science and Technology, Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000, China. Fax: +86-931-8913554; Tel: +86-931-8912546;
ABSTRACT N-doped Bi2O3/g-C3N4 composite photocatalysts were prepared via a cost-effective and eco-friendly ultrasonic dispersion method. It was shown that N-doped Bi2O3 nanoparticles have been perfectly coated by thin g-C3N4 layers. Under visible-light irradiation, the optimum photocatalytic activity of the composite with 66.7 wt.% of g-C3N4 is almost 4.6 times as high as that of pure g-C3N4 and 8.2 times of Bi2O3, and the RhB degradation efficiency can reach 94.4 % in 15 min. The dramatically improved performance of the composite can be attributed to an enhancement of visible-light absorption and a synergistic effect of N-doped Bi2O3 nanoparticles and g-C3N4 coatings.
Keywords: Semiconductors; Composite materials; Ultrasonic dispersion; photocatalysis; Visible light.
Corresponding author. E-mail: [email protected] 1
1.
Introduction
Semiconductor photocatalysis technology has attracted considerable interest for its environmental remediation and clean energy production. [1] To date, a number of semiconductor photocatalysts have been developed. Among them, bismuth oxide is an attractive candidate due to its unique properties such as proper band gap (~2.8 eV), high refractive index and dielectric permittivity, marked photoconductivity and photoluminescence. [2] However, as a visible-light photocatalyst, pure Bi2O3 has a poor decomposition efficiency of organic pollutants for its low absorption rate of incident photons and low separation rate of photogenerated electron-hole pairs. [3] Many efforts have been made to improve the photocatalytic activity of Bi2O3, including energy band modulation by doping with metal and non-metal ions [4], construction of proper electron and hole transport structures by compositing with metals or other semiconductors [5]. Recent work has shown that, as a p-type dopant of Bi2O3, nitrogen is the most suitable. [6] Nitrogen is closest to oxygen in atomic size and electronic structure. As a result, nitrogen doping leads to the minimum strain in Bi2O3 and significantly improves the photocatalytic efficiency of Bi2O3 by increasing the absorption rate of incident photons. On the other hand, graphitic carbon nitride (g-C3N4) as a typical metal-free polymeric semiconductor has been extensively investigated in the fields of photocatalytic water splitting and environmental pollutant degradation under visible-light irradiation. It can be easily fabricated [7] and compounded with other semiconductors [8]. More importantly, it is conducive to the charge transfer. [9, 10] The composite of coating layered g-C3N4 on N-doped Bi2O3 is expected to be a promising material for visible-light driven photocatalysis. In this paper, N-doped Bi2O3/g-C3N4 composite photocatalysts were synthesized through a cost-effective and eco-friendly ultrasonic dispersion method. To the best of our knowledge, there are few reports on the preparation of N-doped Bi2O3/g-C3N4 composite photocatalysts. It was found that the synthesized composite with 66.7 wt.% of g-C3N4 shows remarkable photocatalytic activity under visible-light irradiation, its RhB degradation efficiency reaches 94.4 % in 15 min. 2.
Experimental
Sample synthesis: In this work, g-C3N4 was prepared by heating melamine at 550 °C for 2 h in N2 atmosphere, and undoped Bi2O3 was synthesized by a hydrothermal process and subsequent calcination. All the used chemicals were analytical grade without further purification. In a typical process of synthesizing undoped Bi2O3, 4 mmol Bi(NO3)3.5H2O and 4 mmol NH4OH were added into 75 mL deionized water and stirred with a magnetic stirrer until completely dissolved. The obtained suspension was poured into a 100 mL Teflon-lined stainless steel autoclave, and kept at 160 °C for 12 h. The autoclave was then cooled down to room temperature naturally. The product was collected, washed with deionized water and dried at 60 °C in air. Finally, it was annealed at 500 °C for 12 h in a muffle furnace. For the preparation of N-doped Bi2O3, the same experimental conditions were used except that the forementioned synthesis reagents were well mixed and grinded with urea. N-doped Bi2O3/g-C3N4 composite photocatalysts were prepared via an 2
ultrasonic dispersion method. In brief, 50 mg g-C3N4 was ultrasonicated in 50 mL deionized water for 1 h, and then 100 mg N-doped Bi2O3 was added and subsequently stirred for 48 h. N-doped Bi2O3/g-C3N4 composite was obtained after the solution having been dried at 60 °C. Structural characterization: The structure and morphology of the samples were characterized by X-ray diffraction (XRD, Philips X’ Pert Pro diffractometer, Cu Kα radiation, λ = 0.15418 nm), UV-Vis spectrophotometer (Shimadzu UV-3600), micro-Raman spectrometry (Raman, Jobin-Yvon LabRAM HR800 UV with a radiation of 532 nm), and high-resolution transmission electron microscope (HR-TEM, FEI Tecnai F30). Photocatalytic test: The photocatalytic activity of the samples was evaluated by adding 50 mg as-prepared material into 50 mL rhodamine B (RhB) aqueous solution with a concentration of 10-5 mol/L and examining the photodegradation of RhB. The formed suspension was stirred in dark for 60 min to establish an adsorption/desorption equilibrium. The photodegradation was performed under visible-light irradiation using a 150 W Xe lamp with an air mass 1.5 filter and a 420 nm cut-off filter. The degradation efficiency is defined as C/C0, where C0 is the concentration of the RhB solution after the adsorption/desorption equilibrium being established and C is the concentration after various intervals of the irradiation time. 3.
Results and discussion XRD patterns of the as-prepared samples are shown in Fig. 1a. It can be seen that, for N-doped Bi2O3 (NBIO), the
diffraction peaks are wider than those of undoped Bi2O3 (BIO), indicating a reduced crystallinity due to nitrogen doping. On closer inspection we found that all the diffraction peaks of BIO can be indexed as those of Bi2O2.33 (JCPDS 27-0051). It has been proved that the occurrence of oxygen defects in Bi2O3 is due to the extended calcining time (Fig. 1b), which is beneficial to the substitutional doping of nitrogen atoms. For graphitic carbon nitride (CN), a strong peak is observed at 2 = 27.5°, which corresponds to the characteristic interplanar staking peak (002) of aromatic system. It is also seen that the nitrogen doping does not change the crystal phase structure of BIO, while the intensity ratio of some main diffraction peaks (2 = 29.2°, 30.5°, 32.9°) for NBIO has been changed after being composited with CN, suggesting that there is a strong interaction between the NBIO nanoparticals and the coated CN layers.
Fig. 1 3
Fig. 2a-c show TEM images of the prepared CN/NBIO composite. It can be seen that the NBIO nanoparticles are coated by CN sheets. The fringes with interplanar spacing of 0.32 and 0.29 nm are observed in the HR-TEM image shown in Fig. 2d, which correspond to the (002) plane of CN and (211) plane of BIO, respectively. The morphology, structure and composition of the NBIO nanoparticles were characterized by TEM and energy dispersive X-ray (EDX)
spectrum (Fig. S1). HR-TEM image again reveals that the phase structure of BIO does not change after nitrogen doping. The EDX spectrum indicates the presence of Bi, O, and N elements in NBIO.
Fig. 2 Fig. 3a shows diffuse reflectance spectra (DRS) of the prepared samples. As expected, a sharp absorption edge appears at 560 nm for BIO, indicating that BIO has intensive absorption to the visible light. After nitrogen atoms were incorporated into BIO, the absorbance of the formed NBIO increases further, implying that nitrogen doping significantly enhances the absorption to visible light. The absorption edge is close to 500 nm for pure NBIO while it is around 450 nm for pure CN. The CN/NBIO composite shows a similar light absorbance to that of the pure NBIO, both have a secondary absorption edge due to the additional valence states from doped N atoms. Fig. 3b shows Raman spectra measured at room temperature for pure BIO and NBIO samples. Almost the same spectra are obtained for both samples, indicating that the crystal structure and phase composition of the BIO sample do not change after nitrogen doping.
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Fig. 3 Fig. 4 shows the visible-light photocatalytic activity evaluated by measuring the RhB degradation and the degradation kinetics calculated by fitting the measured data. It can be seen from Fig. 4a and b that, for CN, BIO, NBIO, and CN/NBIO photocatalysts, the efficiencies of the photocatalytic activities respectively reach 22.5%, 22.6%, 75.3%, and 94.4% within 15 min, and the corresponding apparent rate constants of the RhB photodegradation are about 0.0231, 0.0129, 0.0331, and 0.1063 min-1. Obviously, nitrogen doping in BIO greatly enhances its visible-light photocatalysis. Moreover, CN/NBIO composite photocatalyst exhibits significantly higher photocatalytic activity for the photodegradation of RhB than those of CN and NBIO. Fig. 4c and d show the photocatalytic performance of the as-prepared CN/NBIO composites with different weight percents. The composite with 66.7 wt.% of CN shows the optimum photocatalytic performance, maybe it is just an applicable loading amount of CN, leading to the CN coating thickness being optimal for the visible-light absorption and the separation and transfer of photogenerated electron-hole pairs. The recycling experiments showed that the composite still have a good photodegradation activity after five cycles (Fig. S2).
Fig. 4 5
The superior photocatalytic activity of the obtained CN/NBIO composite photocatalysts could be ascribed to the enhancement of the visible-light absorption, and the high separation and easy transfer of photogenerated electron-hole pairs. Nitrogen doping in BIO enhances its wide-spectrum light absorption, which could produce extra photogenerated electrons and holes and lead to the better visible-light photocatalytic activity. The composite structure is supposed to favor the electron and hole transport across individual BIO particle, driven by strong dipolar fields arising from charged surface domains, as demonstrated in other covering structures such as C3N4/BiPO4 [8] and TiO2@TiO2-x [11]. These charged surface domains of BIO would, in effect, electrostatically drive the photogenerated electrons or holes from BIO into the conduction or valence bands of CN (Fig. S3). 4.
Conclusions In summary, N-doped Bi2O3/g-C3N4 composite photocatalysts with superior photocatalytic activity were prepared
via a facile ultrasonic dispersion method. For the sample with 66.7 wt% of g-C3N4, the RhB degradation efficiency can reach 94.4% in 15 min. The improved photocatalytic activity could be ascribed to the enhancement of the visible-light absorption, and the high separation and easy transfer of the photogenerated electron-hole pairs. Acknowledgments This project was financially supported by the National Natural Science Foundation of China with grant nos. 11179038 and the Specialized Research Fund for the Doctoral Program of Higher Education with grant no. 20120211130005. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version. References [1] Li R, Han H, Zhang F, Wang D, Li C. Energ Environ Sci 2014;7:1369-76. [2] Leontie L, Caraman M, Alexe M, Harnagea C. Surf Sci 2002;507:480 - 5. [3] Xiao X, Hu R, Liu C, Xing C, Qian C, Zuo X, et al. Appl Catal B-Environ 2013;140-141:433-43. [4] Li JZ, Zhong JB, Zeng J, Feng FM, He JJ. Mat Sci Semicon Proc 2013;16:379-84. [5] Liu X, Cao H, Yin J. Nano Res 2011;4:470-82. [6] Kumar S, Baruah A, Tonda S, Kumar B, Shanker V, Sreedhar B. C. Nanoscale 2014;6:4830-42. [7] Liu J, Zhang Y, Lu L, Wu G, Chen W. Chem Commun 2012;48:8826-8. [8] Pan C, Xu J, Wang Y, Li D, Zhu YF. Adv Funct Mater 2012;22:1518-24. [9] Shi L, Liang L, Ma J, Wang F, Sun J. Dalton Trans 2014;43:7236-44. [10] Shi L, Liang L, Wang F, Ma J, Sun J. Cataly Sci Technol 2014;4:3235. [11] Lin T, Yang C, Wang Z, Yin H, Lü X, Huang F, et al. Energ Environ Sci 2014;7:967-72. 6
List of Figure Captions： Fig. 1. XRD patterns of the as-prepared samples. Fig. 2. TEM and HR-TEM images of the CN/NBIO composites. Fig. 3. (a) UV-Vis diffuse reflectance spectra and (b) Raman spectra of the as-prepared samples. Fig. 4. Visible-light photocatalytic activity evaluated by degradation of RhB (a, c) and the corresponding degradation kinetics calculated by fitting the curves (b, d).
HIGHLIGHTS A cost-effective and eco-friendly ultrasonic dispersion method was used to prepare N-doped Bi2O3/g-C3N4 composite photocatalysts. A dramatic improvement of photocatalytic activity for the composite photocatalysts was observed. A proper mechanism for the improvement photocatalytic activity was demonstrated.
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PII: DOI: Reference:
S0167-577X(15)30580-2 http://dx.doi.org/10.1016/j.matlet.2015.09.067 MLBLUE19583
To appear in: Materials Letters Received date: 7 July 2015 Revised date: 29 August 2015 Accepted date: 14 September 2015 Cite this article as: Song Xue, Xiaoyi Hou, Wenhe Xie, Xiucheng Wei and Deyan He, Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.09.067 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites Song Xue, Xiaoyi Hou, Wenhe Xie, Xiucheng Wei and Deyan He
School of Physical Science and Technology, Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000, China. Fax: +86-931-8913554; Tel: +86-931-8912546;
ABSTRACT N-doped Bi2O3/g-C3N4 composite photocatalysts were prepared via a cost-effective and eco-friendly ultrasonic dispersion method. It was shown that N-doped Bi2O3 nanoparticles have been perfectly coated by thin g-C3N4 layers. Under visible-light irradiation, the optimum photocatalytic activity of the composite with 66.7 wt.% of g-C3N4 is almost 4.6 times as high as that of pure g-C3N4 and 8.2 times of Bi2O3, and the RhB degradation efficiency can reach 94.4 % in 15 min. The dramatically improved performance of the composite can be attributed to an enhancement of visible-light absorption and a synergistic effect of N-doped Bi2O3 nanoparticles and g-C3N4 coatings.
Keywords: Semiconductors; Composite materials; Ultrasonic dispersion; photocatalysis; Visible light.
Corresponding author. E-mail: [email protected] 1
1.
Introduction
Semiconductor photocatalysis technology has attracted considerable interest for its environmental remediation and clean energy production. [1] To date, a number of semiconductor photocatalysts have been developed. Among them, bismuth oxide is an attractive candidate due to its unique properties such as proper band gap (~2.8 eV), high refractive index and dielectric permittivity, marked photoconductivity and photoluminescence. [2] However, as a visible-light photocatalyst, pure Bi2O3 has a poor decomposition efficiency of organic pollutants for its low absorption rate of incident photons and low separation rate of photogenerated electron-hole pairs. [3] Many efforts have been made to improve the photocatalytic activity of Bi2O3, including energy band modulation by doping with metal and non-metal ions [4], construction of proper electron and hole transport structures by compositing with metals or other semiconductors [5]. Recent work has shown that, as a p-type dopant of Bi2O3, nitrogen is the most suitable. [6] Nitrogen is closest to oxygen in atomic size and electronic structure. As a result, nitrogen doping leads to the minimum strain in Bi2O3 and significantly improves the photocatalytic efficiency of Bi2O3 by increasing the absorption rate of incident photons. On the other hand, graphitic carbon nitride (g-C3N4) as a typical metal-free polymeric semiconductor has been extensively investigated in the fields of photocatalytic water splitting and environmental pollutant degradation under visible-light irradiation. It can be easily fabricated [7] and compounded with other semiconductors [8]. More importantly, it is conducive to the charge transfer. [9, 10] The composite of coating layered g-C3N4 on N-doped Bi2O3 is expected to be a promising material for visible-light driven photocatalysis. In this paper, N-doped Bi2O3/g-C3N4 composite photocatalysts were synthesized through a cost-effective and eco-friendly ultrasonic dispersion method. To the best of our knowledge, there are few reports on the preparation of N-doped Bi2O3/g-C3N4 composite photocatalysts. It was found that the synthesized composite with 66.7 wt.% of g-C3N4 shows remarkable photocatalytic activity under visible-light irradiation, its RhB degradation efficiency reaches 94.4 % in 15 min. 2.
Experimental
Sample synthesis: In this work, g-C3N4 was prepared by heating melamine at 550 °C for 2 h in N2 atmosphere, and undoped Bi2O3 was synthesized by a hydrothermal process and subsequent calcination. All the used chemicals were analytical grade without further purification. In a typical process of synthesizing undoped Bi2O3, 4 mmol Bi(NO3)3.5H2O and 4 mmol NH4OH were added into 75 mL deionized water and stirred with a magnetic stirrer until completely dissolved. The obtained suspension was poured into a 100 mL Teflon-lined stainless steel autoclave, and kept at 160 °C for 12 h. The autoclave was then cooled down to room temperature naturally. The product was collected, washed with deionized water and dried at 60 °C in air. Finally, it was annealed at 500 °C for 12 h in a muffle furnace. For the preparation of N-doped Bi2O3, the same experimental conditions were used except that the forementioned synthesis reagents were well mixed and grinded with urea. N-doped Bi2O3/g-C3N4 composite photocatalysts were prepared via an 2
ultrasonic dispersion method. In brief, 50 mg g-C3N4 was ultrasonicated in 50 mL deionized water for 1 h, and then 100 mg N-doped Bi2O3 was added and subsequently stirred for 48 h. N-doped Bi2O3/g-C3N4 composite was obtained after the solution having been dried at 60 °C. Structural characterization: The structure and morphology of the samples were characterized by X-ray diffraction (XRD, Philips X’ Pert Pro diffractometer, Cu Kα radiation, λ = 0.15418 nm), UV-Vis spectrophotometer (Shimadzu UV-3600), micro-Raman spectrometry (Raman, Jobin-Yvon LabRAM HR800 UV with a radiation of 532 nm), and high-resolution transmission electron microscope (HR-TEM, FEI Tecnai F30). Photocatalytic test: The photocatalytic activity of the samples was evaluated by adding 50 mg as-prepared material into 50 mL rhodamine B (RhB) aqueous solution with a concentration of 10-5 mol/L and examining the photodegradation of RhB. The formed suspension was stirred in dark for 60 min to establish an adsorption/desorption equilibrium. The photodegradation was performed under visible-light irradiation using a 150 W Xe lamp with an air mass 1.5 filter and a 420 nm cut-off filter. The degradation efficiency is defined as C/C0, where C0 is the concentration of the RhB solution after the adsorption/desorption equilibrium being established and C is the concentration after various intervals of the irradiation time. 3.
Results and discussion XRD patterns of the as-prepared samples are shown in Fig. 1a. It can be seen that, for N-doped Bi2O3 (NBIO), the
diffraction peaks are wider than those of undoped Bi2O3 (BIO), indicating a reduced crystallinity due to nitrogen doping. On closer inspection we found that all the diffraction peaks of BIO can be indexed as those of Bi2O2.33 (JCPDS 27-0051). It has been proved that the occurrence of oxygen defects in Bi2O3 is due to the extended calcining time (Fig. 1b), which is beneficial to the substitutional doping of nitrogen atoms. For graphitic carbon nitride (CN), a strong peak is observed at 2 = 27.5°, which corresponds to the characteristic interplanar staking peak (002) of aromatic system. It is also seen that the nitrogen doping does not change the crystal phase structure of BIO, while the intensity ratio of some main diffraction peaks (2 = 29.2°, 30.5°, 32.9°) for NBIO has been changed after being composited with CN, suggesting that there is a strong interaction between the NBIO nanoparticals and the coated CN layers.
Fig. 1 3
Fig. 2a-c show TEM images of the prepared CN/NBIO composite. It can be seen that the NBIO nanoparticles are coated by CN sheets. The fringes with interplanar spacing of 0.32 and 0.29 nm are observed in the HR-TEM image shown in Fig. 2d, which correspond to the (002) plane of CN and (211) plane of BIO, respectively. The morphology, structure and composition of the NBIO nanoparticles were characterized by TEM and energy dispersive X-ray (EDX)
spectrum (Fig. S1). HR-TEM image again reveals that the phase structure of BIO does not change after nitrogen doping. The EDX spectrum indicates the presence of Bi, O, and N elements in NBIO.
Fig. 2 Fig. 3a shows diffuse reflectance spectra (DRS) of the prepared samples. As expected, a sharp absorption edge appears at 560 nm for BIO, indicating that BIO has intensive absorption to the visible light. After nitrogen atoms were incorporated into BIO, the absorbance of the formed NBIO increases further, implying that nitrogen doping significantly enhances the absorption to visible light. The absorption edge is close to 500 nm for pure NBIO while it is around 450 nm for pure CN. The CN/NBIO composite shows a similar light absorbance to that of the pure NBIO, both have a secondary absorption edge due to the additional valence states from doped N atoms. Fig. 3b shows Raman spectra measured at room temperature for pure BIO and NBIO samples. Almost the same spectra are obtained for both samples, indicating that the crystal structure and phase composition of the BIO sample do not change after nitrogen doping.
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Fig. 3 Fig. 4 shows the visible-light photocatalytic activity evaluated by measuring the RhB degradation and the degradation kinetics calculated by fitting the measured data. It can be seen from Fig. 4a and b that, for CN, BIO, NBIO, and CN/NBIO photocatalysts, the efficiencies of the photocatalytic activities respectively reach 22.5%, 22.6%, 75.3%, and 94.4% within 15 min, and the corresponding apparent rate constants of the RhB photodegradation are about 0.0231, 0.0129, 0.0331, and 0.1063 min-1. Obviously, nitrogen doping in BIO greatly enhances its visible-light photocatalysis. Moreover, CN/NBIO composite photocatalyst exhibits significantly higher photocatalytic activity for the photodegradation of RhB than those of CN and NBIO. Fig. 4c and d show the photocatalytic performance of the as-prepared CN/NBIO composites with different weight percents. The composite with 66.7 wt.% of CN shows the optimum photocatalytic performance, maybe it is just an applicable loading amount of CN, leading to the CN coating thickness being optimal for the visible-light absorption and the separation and transfer of photogenerated electron-hole pairs. The recycling experiments showed that the composite still have a good photodegradation activity after five cycles (Fig. S2).
Fig. 4 5
The superior photocatalytic activity of the obtained CN/NBIO composite photocatalysts could be ascribed to the enhancement of the visible-light absorption, and the high separation and easy transfer of photogenerated electron-hole pairs. Nitrogen doping in BIO enhances its wide-spectrum light absorption, which could produce extra photogenerated electrons and holes and lead to the better visible-light photocatalytic activity. The composite structure is supposed to favor the electron and hole transport across individual BIO particle, driven by strong dipolar fields arising from charged surface domains, as demonstrated in other covering structures such as C3N4/BiPO4 [8] and TiO2@TiO2-x [11]. These charged surface domains of BIO would, in effect, electrostatically drive the photogenerated electrons or holes from BIO into the conduction or valence bands of CN (Fig. S3). 4.
Conclusions In summary, N-doped Bi2O3/g-C3N4 composite photocatalysts with superior photocatalytic activity were prepared
via a facile ultrasonic dispersion method. For the sample with 66.7 wt% of g-C3N4, the RhB degradation efficiency can reach 94.4% in 15 min. The improved photocatalytic activity could be ascribed to the enhancement of the visible-light absorption, and the high separation and easy transfer of the photogenerated electron-hole pairs. Acknowledgments This project was financially supported by the National Natural Science Foundation of China with grant nos. 11179038 and the Specialized Research Fund for the Doctoral Program of Higher Education with grant no. 20120211130005. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version. References [1] Li R, Han H, Zhang F, Wang D, Li C. Energ Environ Sci 2014;7:1369-76. [2] Leontie L, Caraman M, Alexe M, Harnagea C. Surf Sci 2002;507:480 - 5. [3] Xiao X, Hu R, Liu C, Xing C, Qian C, Zuo X, et al. Appl Catal B-Environ 2013;140-141:433-43. [4] Li JZ, Zhong JB, Zeng J, Feng FM, He JJ. Mat Sci Semicon Proc 2013;16:379-84. [5] Liu X, Cao H, Yin J. Nano Res 2011;4:470-82. [6] Kumar S, Baruah A, Tonda S, Kumar B, Shanker V, Sreedhar B. C. Nanoscale 2014;6:4830-42. [7] Liu J, Zhang Y, Lu L, Wu G, Chen W. Chem Commun 2012;48:8826-8. [8] Pan C, Xu J, Wang Y, Li D, Zhu YF. Adv Funct Mater 2012;22:1518-24. [9] Shi L, Liang L, Ma J, Wang F, Sun J. Dalton Trans 2014;43:7236-44. [10] Shi L, Liang L, Wang F, Ma J, Sun J. Cataly Sci Technol 2014;4:3235. [11] Lin T, Yang C, Wang Z, Yin H, Lü X, Huang F, et al. Energ Environ Sci 2014;7:967-72. 6
List of Figure Captions： Fig. 1. XRD patterns of the as-prepared samples. Fig. 2. TEM and HR-TEM images of the CN/NBIO composites. Fig. 3. (a) UV-Vis diffuse reflectance spectra and (b) Raman spectra of the as-prepared samples. Fig. 4. Visible-light photocatalytic activity evaluated by degradation of RhB (a, c) and the corresponding degradation kinetics calculated by fitting the curves (b, d).
HIGHLIGHTS A cost-effective and eco-friendly ultrasonic dispersion method was used to prepare N-doped Bi2O3/g-C3N4 composite photocatalysts. A dramatic improvement of photocatalytic activity for the composite photocatalysts was observed. A proper mechanism for the improvement photocatalytic activity was demonstrated.
7