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Novel Bi2O3 loaded sepiolite photocatalyst: Preparation and characterization
Materials Letters 168 (2016) 143–145
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Novel Bi2O3 loaded sepiolite photocatalyst: Preparation and characterization Li Guishui, Cheng Lijun n, Zhang Bing, Li Yi Tianjin Key Laboratory of Integrated Design and On-line Monitoring for Light Industry & Food Machinery and Equipment, College of Mechanical Engineering, Tianjin University of Science & Technology, 300222, China
art ic l e i nf o
a b s t r a c t
Article history: Received 22 November 2015 Received in revised form 10 January 2016 Accepted 11 January 2016 Available online 13 January 2016
Novel Bi2O3 loaded sepiolite photocatalysts were first prepared to overcome the problem that the Bi2O3 powder particles are easily agglomerated. The crystalline phases, morphologies, specific surface areas and light absorption abilities were characterized by XRD, SEM, BET and UV–vis diffuse methods, respectively. And malachite green (MG) was used as the model pollutant to investigate their photocatalytic activities. Bi2O3 particles were scattered on the surface of the sepiolite from the XRD analysis and the SEM observation. The 25% Bi2O3/sepiolite had the largest specific surface area and the smallest band gap energy, which contributed to its strongest adsorption ability and efficient photocatalytic degradation ability for MG. & 2016 Elsevier B.V. All rights reserved.
Keywords: Bi2O3 Sepiolite Photocatalyst Malachite green Composite materials Semiconductors
1. Introduction Organic substances, such as organic dyes, have caused considerably damage to the environment and human beings because of their high toxicity character. Bi2O3, a semiconductor with band gap of 2.8 eV, has been widely used to decompose organic dyes, such as Rhodamine B [1–4], methyl orange [1,3], methyl blue [3], malachite green [5] and demonstrated to be an effective visible light-driven photocatalyst. However, ultra fine Bi2O3 powders easily agglomerate into larger particles, resulting in weakening of photocatalytic performance. Dispersing Bi2O3 particles onto clay minerals is a promising method to resolve the agglomeration problem of Bi2O3 powders. Sepiolite is a fibrous, hydrated Mg–Al silicate clay mineral. Its each structural block consists of two tetrahedral silica sheets and a central octahedral sheet containing magnesium, resulting in zeolite-like channels. The unique pore structure with interior channels contributes for its strong adsorption ability [6]. Recently, sepiolite has been employed as the support to prepare TiO2 loaded sepiolite photocatalyst and the results showed that loading TiO2 onto sepiolite indeed improved the dispersion situation of TiO2 particles and ultilized the adsorption ability of sepiolite sufficiently [6–10]. n
Corresponding author. E-mail address: [email protected] (C. Lijun).
http://dx.doi.org/10.1016/j.matlet.2016.01.051 0167-577X/& 2016 Elsevier B.V. All rights reserved.
To our best knowledge, there is no report about loading Bi2O3 on sepiolite. In order to overcome the disadvantage that Bi2O3 powder particles are easily agglomerated and improve the photocatalytic activity of Bi2O3 powder, Bi2O3/sepiolite photocatalysts were explored to be fabricated and their performances relating to photocatalytic activity were characterized.
2. Experimental 2.1. Materials Raw sepiolite was purchased from Shijiazhuang Xinlei Mining. All reagents such as Bi(NO3)3 5H2O, HNO3, NaOH were of analytical grade and were used without further purification. 2.2. Preparation of photocatalyst Refinery of sepiolite: the raw sepiolite powder was added into deionized water (the ratio of sepiolite mass and deionized water volume was 1:20) and stirred for 120 min, then the suspension was centrifuged and the solid was dried at 120 °C. The Bi2O3/sepiolite photocatalysts with 5%, 25% and 50% mass percent of Bi2O3 were prepared by chemical precipitation method. Firstly, 0.97 g Bi(NO3)3 5H2O was dissolved in 100 mL HNO3 solution, which was obtained by diluting 5 mL HNO3 to 100 mL. Then, 8.854 g, 1.398 g and 0.466 g sepiolite were added, respectively. Under rigorous stirring, 500 mL NaOH solution with
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L. Guishui et al. / Materials Letters 168 (2016) 143–145
concentration of 10 g/L was dropped into the above solution. After reacting for 120 min, the precipitate was centrifuged, washed by deionized water for several times, dried at 120 °C and sintered at 400 °C for 4 h. 2.3. Characterization The crystalline phases of the samples were determined by powder X-ray diffraction (XRD) analysis on a XD-3 unit using Cu Kα radiation. The morphologies of the samples were observed by scanning electronic microscopy (SEM, SU1510). The specific surface areas of the samples were measured by nitrogen adsorptiondesorption method on a Quantachrome QuadraSorb SI apparatus. UV–vis diffuse reflectance spectra were recorded on a Lambda 750S UV/vis spectrometer and BaSO4 powders were used as a reflectance standard. And the absorbance of MG aqueous solution was tested with a 722 Vis spectrophotometer. 2.4. Photocatalytic degradation of MG The photocatalytic activity of the as-prepared photocatalyst was evaluated by degradation of MG aqueous solution, which was performed in a 250 mL beaker under continuous stirring. 0.05 g of the photocatalyst was dispersed in 100 mL MG solution with concentration of 50 mg/L. Before irradiation, the suspension was stirred in the dark for 30 min to reach adsorption equilibrium. Then the suspension was irradiated under 200 W incandescent lamp which was positioned about 5 cm away from the beaker. At given time interval, certain amount of suspension was sampled, centrifuged and analyzed by the spectrophotometer. The initial concentration and absorbance of MG solution were denoted by C0 and A0 respectively, while the concentration and absorbance of MG solution at any time were denoted by C and A respectively. According to the linear relationship between concentration and absorbance (C/C0 ¼A/A0), C/C0 could be calculated. To verify the role of the photocatalyst, blank experiment with no photocatalyst added was also conducted. Fig. 2. SEM images of sepiolite (a) and Bi2O3 loaded sepiolite (b).
3. Results and discussion 3.1. XRD Fig. 1 shows the XRD patterns of the samples. It can be seen that all the samples were well crystallized. 5% Bi2O3/sepiolite almost had the same pattern as sepiolite for the very low content of Bi2O3. When the content of Bi2O3 reached 25% and 50%, some
characteristic diffraction peaks labeled by circle were observed, which could be indexed as Bi2O3 (JCPDS file no. 27-0050), indicating that Bi2O3 particles were loaded onto the sepiolite. 3.2. SEM and specific surface area The morphologies of sepiolite and 25% Bi2O3/sepiolite are shown in Fig. 2. It can be seen from Fig. 2(a) that the sepiolite had a fibrous morphology with smooth surface. While after loading, Bi2O3 particles were scattered on the surface of sepiolite, resulting in course surface, as shown in Fig. 2(b). The specific surface area of sepiolite and Bi2O3 loaded sepiolite were measured by N2 adsorption-desorption method. The results showed that the specific surface area of sepiolite was 3.179 m2/g. After being loaded with Bi2O3 particles, the specific surface area increased up to 5.220, 7.640, 5.129 m2/g for 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and 50% Bi2O3/sepiolite, respectively. Obviously, 25% Bi2O3/sepiolite demonstrated the largest specific surface area, which contributed for its strongest adsorption ability, as seen in photocatalytic activity section. 3.3. UV–vis diffuse reflectance spectra
Fig. 1. XRD patterns of sepiolite and Bi2O3 loaded sepiolite.
Fig. 3 shows the UV–vis diffuse reflectance spectra of Bi2O3 loaded sepiolite photocatalysts. From the extrapolation principle, the absorption edges of 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and
L. Guishui et al. / Materials Letters 168 (2016) 143–145
145
50% Bi2O3/sepiolite were estimated to be 510, 555 and 551 nm, respectively, which corresponded to the band gap energies of 2.43, 2.23 and 2.25 eV. Apparently, 25% Bi2O3/sepiolite had the smallest band gap energy. 3.4. Photocatalytic activity
Fig. 3. UV–vis diffuse reflectance spectra of Bi2O3 loaded sepiolite.
The photocatalytic activities of Bi2O3 loaded sepiolite photocatalysts were evaluated by degrading MG solution, as shown in Fig. 4. According to the results, 74.44%, 90.27% and 61.69% MG were respectively adsorbed by 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and 50% Bi2O3/sepiolite after the suspension was placed in the dark for 30 min. Once the suspension was irradiated, the adsorbed MG was quickly degraded, resulting in remarkable decrease of MG concentration. It can be seen that when the irradiation time exceeded 90 min, the MG concentration for three samples became very closed. After irradiating for 180 min, approximately 97.38%, 98.15% and 96.46% MG were removed, respectively. However, there was almost no change for MG concentration when the solution was subjected to the irradiation with no photocatalyst added, which confirmed the high photocatalytic efficiency of the Bi2O3 loaded sepiolite. To test the stability of 25% Bi2O3/sepiolite, it was reused for three times. As shown in Fig. 4(b), there was no significant decrease for MG degradation after irradiating for 180 min (97.38% for the first cycle, 96.98% for the second cycle, 96.78% for the third cycle), which indicated that the photocatalyst was stable and not photocorroded.
4. Conclusion Bi2O3 loaded sepiolite photocatalysts were synthesized successfully. The Bi2O3 particles were well dispersed on the surface of the sepiolite, which resolved the agglomeration problem of Bi2O3 powders. The absorption edge of 25% Bi2O3/sepiolite reached 555 nm. Besides, its specific surface area was increased to 7.640 m2/g, which was confirmed by the very low concentration of MG after being placed in the dark. After irradiation for 180 min, approximately 98.15% of MG was degraded by 25% Bi2O3/sepiolite.
Acknowledgments This work is financially supported by the Youth Innovation Foundation of Tianjin University of Science & Technology (No. 2015LG11).
References
Fig. 4. (a) MG concentration changes with irradiation time (b) MG degradation percentages in three cycle runs.
[1] X.C. Luo, G.Q. Zhu, J.H. Peng, X.M. Wei, Hojamberdiev Mirabbos, L. Jin, P. Liu, Appl. Surf. Sci. 351 (2015) 260–269. [2] Swati Sood, Ahmad Umar, Surinder Kumar Mehta, Sushil Kumar Kansal, Ceram. Int. 41 (2015) 3355–3364. [3] W.J. Wang, X.Q. Chen, G. Liu, Z.R. Shen, D.H. Xia, Wong Po Keung, C. Yu Jimmy, Appl. Catal. B – Environ. 176–177 (2015) 444–453. [4] J. Zhang, Q.F. Han, X. Wang, J.W. Zhu, G.R. Duan, Mater. Lett. 〈http://dx.doi.org/ 10.1016/j.matlet.2015.10.024〉. [5] L.J. Cheng, Y. Kang, J. Alloy. Compd. 585 (2014) 85–93. [6] Y.L. Zhang, D.J. Wang, G.K. Zhang, Chem. Eng. J. 173 (2011) 1–10. [7] D. Karamanis, A.N. Ökte, E. Vardoulakis, T. Vaimakis, Appl. Clay Sci. 53 (2011) 181–187. [8] F.F. Li, Y.Z. Dai, M. Gong, T.P. Yu, X.J. Chen, J. Alloy. Compd. 638 (2015) 435–442. [9] M. U˘gurlu, M.H. Karao˘glu, Chem. Eng. J. 166 (2011) 859–867. [10] G.K. Zhang, Q. Xiong, W. Xu, S. Guo, Appl. Clay Sci. 102 (2014) 231–237.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Novel Bi2O3 loaded sepiolite photocatalyst: Preparation and characterization Li Guishui, Cheng Lijun n, Zhang Bing, Li Yi Tianjin Key Laboratory of Integrated Design and On-line Monitoring for Light Industry & Food Machinery and Equipment, College of Mechanical Engineering, Tianjin University of Science & Technology, 300222, China
art ic l e i nf o
a b s t r a c t
Article history: Received 22 November 2015 Received in revised form 10 January 2016 Accepted 11 January 2016 Available online 13 January 2016
Novel Bi2O3 loaded sepiolite photocatalysts were first prepared to overcome the problem that the Bi2O3 powder particles are easily agglomerated. The crystalline phases, morphologies, specific surface areas and light absorption abilities were characterized by XRD, SEM, BET and UV–vis diffuse methods, respectively. And malachite green (MG) was used as the model pollutant to investigate their photocatalytic activities. Bi2O3 particles were scattered on the surface of the sepiolite from the XRD analysis and the SEM observation. The 25% Bi2O3/sepiolite had the largest specific surface area and the smallest band gap energy, which contributed to its strongest adsorption ability and efficient photocatalytic degradation ability for MG. & 2016 Elsevier B.V. All rights reserved.
Keywords: Bi2O3 Sepiolite Photocatalyst Malachite green Composite materials Semiconductors
1. Introduction Organic substances, such as organic dyes, have caused considerably damage to the environment and human beings because of their high toxicity character. Bi2O3, a semiconductor with band gap of 2.8 eV, has been widely used to decompose organic dyes, such as Rhodamine B [1–4], methyl orange [1,3], methyl blue [3], malachite green [5] and demonstrated to be an effective visible light-driven photocatalyst. However, ultra fine Bi2O3 powders easily agglomerate into larger particles, resulting in weakening of photocatalytic performance. Dispersing Bi2O3 particles onto clay minerals is a promising method to resolve the agglomeration problem of Bi2O3 powders. Sepiolite is a fibrous, hydrated Mg–Al silicate clay mineral. Its each structural block consists of two tetrahedral silica sheets and a central octahedral sheet containing magnesium, resulting in zeolite-like channels. The unique pore structure with interior channels contributes for its strong adsorption ability [6]. Recently, sepiolite has been employed as the support to prepare TiO2 loaded sepiolite photocatalyst and the results showed that loading TiO2 onto sepiolite indeed improved the dispersion situation of TiO2 particles and ultilized the adsorption ability of sepiolite sufficiently [6–10]. n
Corresponding author. E-mail address: [email protected] (C. Lijun).
http://dx.doi.org/10.1016/j.matlet.2016.01.051 0167-577X/& 2016 Elsevier B.V. All rights reserved.
To our best knowledge, there is no report about loading Bi2O3 on sepiolite. In order to overcome the disadvantage that Bi2O3 powder particles are easily agglomerated and improve the photocatalytic activity of Bi2O3 powder, Bi2O3/sepiolite photocatalysts were explored to be fabricated and their performances relating to photocatalytic activity were characterized.
2. Experimental 2.1. Materials Raw sepiolite was purchased from Shijiazhuang Xinlei Mining. All reagents such as Bi(NO3)3 5H2O, HNO3, NaOH were of analytical grade and were used without further purification. 2.2. Preparation of photocatalyst Refinery of sepiolite: the raw sepiolite powder was added into deionized water (the ratio of sepiolite mass and deionized water volume was 1:20) and stirred for 120 min, then the suspension was centrifuged and the solid was dried at 120 °C. The Bi2O3/sepiolite photocatalysts with 5%, 25% and 50% mass percent of Bi2O3 were prepared by chemical precipitation method. Firstly, 0.97 g Bi(NO3)3 5H2O was dissolved in 100 mL HNO3 solution, which was obtained by diluting 5 mL HNO3 to 100 mL. Then, 8.854 g, 1.398 g and 0.466 g sepiolite were added, respectively. Under rigorous stirring, 500 mL NaOH solution with
144
L. Guishui et al. / Materials Letters 168 (2016) 143–145
concentration of 10 g/L was dropped into the above solution. After reacting for 120 min, the precipitate was centrifuged, washed by deionized water for several times, dried at 120 °C and sintered at 400 °C for 4 h. 2.3. Characterization The crystalline phases of the samples were determined by powder X-ray diffraction (XRD) analysis on a XD-3 unit using Cu Kα radiation. The morphologies of the samples were observed by scanning electronic microscopy (SEM, SU1510). The specific surface areas of the samples were measured by nitrogen adsorptiondesorption method on a Quantachrome QuadraSorb SI apparatus. UV–vis diffuse reflectance spectra were recorded on a Lambda 750S UV/vis spectrometer and BaSO4 powders were used as a reflectance standard. And the absorbance of MG aqueous solution was tested with a 722 Vis spectrophotometer. 2.4. Photocatalytic degradation of MG The photocatalytic activity of the as-prepared photocatalyst was evaluated by degradation of MG aqueous solution, which was performed in a 250 mL beaker under continuous stirring. 0.05 g of the photocatalyst was dispersed in 100 mL MG solution with concentration of 50 mg/L. Before irradiation, the suspension was stirred in the dark for 30 min to reach adsorption equilibrium. Then the suspension was irradiated under 200 W incandescent lamp which was positioned about 5 cm away from the beaker. At given time interval, certain amount of suspension was sampled, centrifuged and analyzed by the spectrophotometer. The initial concentration and absorbance of MG solution were denoted by C0 and A0 respectively, while the concentration and absorbance of MG solution at any time were denoted by C and A respectively. According to the linear relationship between concentration and absorbance (C/C0 ¼A/A0), C/C0 could be calculated. To verify the role of the photocatalyst, blank experiment with no photocatalyst added was also conducted. Fig. 2. SEM images of sepiolite (a) and Bi2O3 loaded sepiolite (b).
3. Results and discussion 3.1. XRD Fig. 1 shows the XRD patterns of the samples. It can be seen that all the samples were well crystallized. 5% Bi2O3/sepiolite almost had the same pattern as sepiolite for the very low content of Bi2O3. When the content of Bi2O3 reached 25% and 50%, some
characteristic diffraction peaks labeled by circle were observed, which could be indexed as Bi2O3 (JCPDS file no. 27-0050), indicating that Bi2O3 particles were loaded onto the sepiolite. 3.2. SEM and specific surface area The morphologies of sepiolite and 25% Bi2O3/sepiolite are shown in Fig. 2. It can be seen from Fig. 2(a) that the sepiolite had a fibrous morphology with smooth surface. While after loading, Bi2O3 particles were scattered on the surface of sepiolite, resulting in course surface, as shown in Fig. 2(b). The specific surface area of sepiolite and Bi2O3 loaded sepiolite were measured by N2 adsorption-desorption method. The results showed that the specific surface area of sepiolite was 3.179 m2/g. After being loaded with Bi2O3 particles, the specific surface area increased up to 5.220, 7.640, 5.129 m2/g for 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and 50% Bi2O3/sepiolite, respectively. Obviously, 25% Bi2O3/sepiolite demonstrated the largest specific surface area, which contributed for its strongest adsorption ability, as seen in photocatalytic activity section. 3.3. UV–vis diffuse reflectance spectra
Fig. 1. XRD patterns of sepiolite and Bi2O3 loaded sepiolite.
Fig. 3 shows the UV–vis diffuse reflectance spectra of Bi2O3 loaded sepiolite photocatalysts. From the extrapolation principle, the absorption edges of 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and
L. Guishui et al. / Materials Letters 168 (2016) 143–145
145
50% Bi2O3/sepiolite were estimated to be 510, 555 and 551 nm, respectively, which corresponded to the band gap energies of 2.43, 2.23 and 2.25 eV. Apparently, 25% Bi2O3/sepiolite had the smallest band gap energy. 3.4. Photocatalytic activity
Fig. 3. UV–vis diffuse reflectance spectra of Bi2O3 loaded sepiolite.
The photocatalytic activities of Bi2O3 loaded sepiolite photocatalysts were evaluated by degrading MG solution, as shown in Fig. 4. According to the results, 74.44%, 90.27% and 61.69% MG were respectively adsorbed by 5% Bi2O3/sepiolite, 25% Bi2O3/sepiolite and 50% Bi2O3/sepiolite after the suspension was placed in the dark for 30 min. Once the suspension was irradiated, the adsorbed MG was quickly degraded, resulting in remarkable decrease of MG concentration. It can be seen that when the irradiation time exceeded 90 min, the MG concentration for three samples became very closed. After irradiating for 180 min, approximately 97.38%, 98.15% and 96.46% MG were removed, respectively. However, there was almost no change for MG concentration when the solution was subjected to the irradiation with no photocatalyst added, which confirmed the high photocatalytic efficiency of the Bi2O3 loaded sepiolite. To test the stability of 25% Bi2O3/sepiolite, it was reused for three times. As shown in Fig. 4(b), there was no significant decrease for MG degradation after irradiating for 180 min (97.38% for the first cycle, 96.98% for the second cycle, 96.78% for the third cycle), which indicated that the photocatalyst was stable and not photocorroded.
4. Conclusion Bi2O3 loaded sepiolite photocatalysts were synthesized successfully. The Bi2O3 particles were well dispersed on the surface of the sepiolite, which resolved the agglomeration problem of Bi2O3 powders. The absorption edge of 25% Bi2O3/sepiolite reached 555 nm. Besides, its specific surface area was increased to 7.640 m2/g, which was confirmed by the very low concentration of MG after being placed in the dark. After irradiation for 180 min, approximately 98.15% of MG was degraded by 25% Bi2O3/sepiolite.
Acknowledgments This work is financially supported by the Youth Innovation Foundation of Tianjin University of Science & Technology (No. 2015LG11).
References
Fig. 4. (a) MG concentration changes with irradiation time (b) MG degradation percentages in three cycle runs.
[1] X.C. Luo, G.Q. Zhu, J.H. Peng, X.M. Wei, Hojamberdiev Mirabbos, L. Jin, P. Liu, Appl. Surf. Sci. 351 (2015) 260–269. [2] Swati Sood, Ahmad Umar, Surinder Kumar Mehta, Sushil Kumar Kansal, Ceram. Int. 41 (2015) 3355–3364. [3] W.J. Wang, X.Q. Chen, G. Liu, Z.R. Shen, D.H. Xia, Wong Po Keung, C. Yu Jimmy, Appl. Catal. B – Environ. 176–177 (2015) 444–453. [4] J. Zhang, Q.F. Han, X. Wang, J.W. Zhu, G.R. Duan, Mater. Lett. 〈http://dx.doi.org/ 10.1016/j.matlet.2015.10.024〉. [5] L.J. Cheng, Y. Kang, J. Alloy. Compd. 585 (2014) 85–93. [6] Y.L. Zhang, D.J. Wang, G.K. Zhang, Chem. Eng. J. 173 (2011) 1–10. [7] D. Karamanis, A.N. Ökte, E. Vardoulakis, T. Vaimakis, Appl. Clay Sci. 53 (2011) 181–187. [8] F.F. Li, Y.Z. Dai, M. Gong, T.P. Yu, X.J. Chen, J. Alloy. Compd. 638 (2015) 435–442. [9] M. U˘gurlu, M.H. Karao˘glu, Chem. Eng. J. 166 (2011) 859–867. [10] G.K. Zhang, Q. Xiong, W. Xu, S. Guo, Appl. Clay Sci. 102 (2014) 231–237.