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Facile preparation of porous flower-like ZnO microspheres with excellent photocatalytic performance
Materials Letters 139 (2015) 393–396
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile preparation of porous flower-like ZnO microspheres with excellent photocatalytic performance Huayi Wu a, Qingshui Xie b, Li An a, Peng Jin a, Dong-Liang Peng b, Chuanjing Huang a,n, Huilin Wan a,n a State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, PR China b Department of Materials Science and Engineering, College of Materials, Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen 361005, China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 July 2014 Accepted 18 October 2014 Available online 28 October 2014
Porous flower-like ZnO microspheres were successfully fabricated by a facile, green and cost efficient method. In this method, the flower-like precursor was first synthesized and subsequently annealed at 450 1C for 30 min. The SEM and TEM results reveal that the obtained microspheres well inherit the morphology of the precursor and possess numerous mesopores which originated from the release of carbon dioxide and water during annealing process. Noteworthily, porous flower-like ZnO microspheres display significantly enhanced photocatalytic activity for the degradation of methylene blue (MB) compared to hexagonal ZnO disks. The improved photocatalytic activity of flower-like ZnO microspheres can be ascribed to their higher specific surface areas. & 2014 Elsevier B.V. All rights reserved.
Keywords: Zinc oxide Porous materials Photocatalysis Semiconductors
1. Introduction Zinc oxide (ZnO) has been widely applied in many fields such as solar cells [1], piezoelectric devices [2], chemical sensors [3] and photocatalysts [4]. Particularly, due to its high photosensitivity and long-term stability, ZnO has become one of the most researched photocatalysts [5]. The structures have a significant impact on properties. Consequently, it is important to design and prepare ZnO with desired structures [6]. Till now, numerous distinct ZnO structures have been synthesized, including plates [7], nanosheets [8], flowers [9] and spheroids [10]. Hierarchical porous ZnO materials have attracted enormous attention owing to their large surface area and high surface-tovolume ratio which can facilitate the adsorption and diffusion of reactant molecules and thus enhance the catalytic performance [11,12]. Generally, the synthesis methods for hierarchical porous ZnO architectures requires the assistant of templates, complicated controlling process, or the use of organic solution [13–15], which are not conductive to economic and environmental-friendly production. Therefore, it is significant to develop a green and cost efficient method to produce hierarchical porous ZnO structures.
n
Corresponding authors. Tel.: þ 86 592 2186569; fax: þ86 592 2183047. E-mail addresses: [email protected] (C. Huang), [email protected] (H. Wan). http://dx.doi.org/10.1016/j.matlet.2014.10.101 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Herein, a simple, green and template-free approach was introduced to prepare porous flower-like ZnO microspheres. The phase structures and morphologies of the samples were measured by various instruments. Meanwhile, the photocatalytic efficiencies of the products were also investigated for the degradation of MB under UV irradiation.
2. Experimental Typically, an aqueous solution (50 mL) containing 0.48 mmol of Zn(NO3)2 6H2O, 0.26 mmol of (CH2)6N4 and 0.03 mmol of K3C6H5O7 H2O was heated at 90 1C for 2 h and then aged at ambient temperature for 10 h. After that, the precursor was obtained by centrifugation, washed with DI water and dried at 60 1C for 12 h. Subsequently, the precursor was calcined at 450 1C in air for 30 min and the flower-like ZnO microspheres could be harvested. For comparison, hexagonal ZnO disks were also fabricated. The aqueous solution (100 mL) comprised 1.26 mmol of (CH2)6N4 and 0.48 mmol of K3C6H5O7 H2O was prepared at room temperature. The obtained precursor (0.1 g) was added to the above solution and the resulting mixture was transferred into a 200 mL Teflon-lined autoclave. The autoclave was kept at 120 1C for 10 h. After cooled to room temperature, hexagonal ZnO disks could be collected.
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H. Wu et al. / Materials Letters 139 (2015) 393–396
The crystal structures of the samples were tested on a Rigaku Ultima IV X-ray diffractometer. The morphologies of the products were investigated by Hitachi S-4800 field-emission scanning electron microscope and JEM-2100 transmission electron microscope. A Nicolet 330 spectrometer was used to collect the Fourier transform infrared (FT-IR) spectrum. A TriStar 3020 system was applied to measure the Brunauer Emmett Teller (BET) surface area of the products. The thermogravimetric (TG-DTA) analysis was conducted on a SDTQ600 thermal analyzer. The photocatalytic measurements were performed by transferring 100 mg of the achieved ZnO samples to 150 mL of methylene blue (MB) solution (10 mg L 1) under UV irradiation. At regular intervals, 5 mL of suspension was taken out from the solution and centrifuged to remove the photocatalysts. Subsequently, the absorption spectrum of MB solution was tested by a UV-visible spectrophotometer.
3. Results and discussions As shown in Fig. 1A, the XRD pattern of the precursor reveals that the sample contains two phases. One is wurtzite structured ZnO and the other may be the crystalline zinc citrate phase [16]. For a better understanding of the sample, the FT-IR spectrum was performed. In Fig. 1B, the strong and sharp absorption peaks at 1572 and 1397 cm 1 can be assigned to the stretching vibrations of COO- for the coordinated citrates [17]. The strong absorption band centered at 3445 cm 1 is originated from the vibration of the hydroxyl group. The FT-IR results corroborate the presence of zinc citrate. Some of zinc citrate converted to crystal ZnO during aging
process. The thermal process of the precursor was measured by TG-DTA (Fig. 1C). The weight loss occurring below 300 1C can be ascribed to the departure of adsorbed water. The weight loss from 300 to 400 1C can be attributed to the transformation from the precursor to ZnO, relating to the strong exothermic peak at 365 1C in the relevant thermal gravimetric curve. Fig. 1D shows the SEM micrograph of the precursor, wherein a large amount of uniform and disperse flower-like microspheres with an average diameter of 3 μm can be observed. The high-magnification SEM micrograph (Fig. 1D, inset) shows that the flower-like microsphere is assembled by irregular nanosheets with the thickness ranging from 10 to15 nm. The XRD pattern of the obtained sample after annealing is manifested in Fig. 2A. All the diffraction peaks can be attributed to wurtzite structured ZnO (JCPDS no. 36-1451). The sharp and strong peaks indicate the high crystalline of the products. As shown in Fig. 2B, the flower-like ZnO microspheres can be seen, indicating that the sample well inherits the morphology of the precursor after calcination. The microsphere is composed of numerous aggregated nanoparticles (the inset in Fig. 2B and Fig. 2C). Moreover, a great deal of nanopores can be carefully discerned from the TEM image (Fig. 2C), which resulted from the release of carbon dioxide and water during annealing process. The selected-area electron diffraction (SAED) pattern reveals the polycrystalline nature of the flower-like ZnO microspheres (Fig. 2C, inset). The HRTEM image exhibits the lattice fringes spacing of 0.24 nm, corresponding to distance of the (101) lattice planes (Fig. 2D). In Fig. 2E, the N2 adsorption-desorption profiles of the flower-like ZnO microspheres present typical type IV isotherm, further evidencing the porous structure. The specific surface area of the product is about 27.0 m2 g 1. According to the pore size
Fig. 1. The XRD pattern (A), FT-IR spectrum (B), TG-DTA curves (C), SEM image (D) of the obtained precursor.
H. Wu et al. / Materials Letters 139 (2015) 393–396
395
Fig. 2. The XRD patterns of the different ZnO products (A), SEM image of flower-like ZnO microspheres (B), TEM images of flower-like ZnO microspheres (C, D), N2 adsorption-desorption isotherms of the different ZnO products (E), SEM image of hexagonal ZnO disks (F).
distribution (the inset in Fig. 2E), the flower-like ZnO microspheres have two kinds of pores located at 2 and 30 nm, indicating the presence of mesopores. The photodegradation of MB was used to investigate the photocatalytic activity of as-synthesized flower-like ZnO microspheres. For comparison, photodegradation of MB over hexagonal ZnO disks (Figs. 2A and 2F) was also performed under identical conditions. Fig. 3 shows the degradation rate of MB over the flower-like porous ZnO microspheres and hexagonal ZnO disks. Without any catalyst, the degradation rate of MB under UV irradiation is extremely slow and can be negligible (Fig. 3c). Strikingly, approximately 99% of MB can be decomposed in the
presence of the ZnO microspheres within 40 min, whereas only 40% of MB is removed for hexagonal ZnO disks during the same irradiation. This is because the surface area of ZnO microspheres (27.0 m2 g 1) is larger than that of hexagonal ZnO disks (1.6 m2g 1, Fig. 2E). The large surface area of flower-like ZnO microspheres can effectively improve dye-adsorption and lightharvesting, giving rise to the greatly strengthened photodegradation activity of MB [18]. In addition, a rough comparison of the photocatalytic properties among different ZnO catalysts is also summarized and listed in Table 1. Compared with other ZnO catalysts, the flower-like ZnO microspheres prepared in our work exhibit enhanced photodegradation activity of MB.
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H. Wu et al. / Materials Letters 139 (2015) 393–396
that of hexagonal ZnO disks. The greatly improved photocatalytic activity can be ascribed to the larger specific surface area of porous flower-like ZnO microspheres. The present work further implies that this method may be extended to fabricate other metal oxides with porous flower-like structures.
Acknowledgments This work was supported by the Ministry of Science and Technology of China (2010CB732303, 2013CB933102), the National Natural Science Foundation of China (21073148, 21033006), PCSIRT (No. IRT1036), NFFTBS (No. J11030415).
References Fig. 3. The degradation rate of MB over different ZnO structures: (a) flower-like ZnO microspheres, (b) hexagonal ZnO disks, (c) without any catalyst.
Table 1 A rough comparison of photodegradation efficiencies of MB for various ZnO catalysts. Samples
Total decomposition time (min)
Ref
Porous ZnO microspheres Dandelion-like ZnO Ce-doped ZnO nanostructures our work
80 60 75 40
[4] [10] [19] -
4. Conclusions In conclusion, porous flower-like ZnO microspheres are synthesized for the first time through a facile, economic and green method. Under UV-irradiation, the flower-like ZnO microspheres can decompose 99% of MB within 40 min, three times faster than
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Li Z, Zhou Y, Xue G, Yu T, Liu J, Zou Z. J Mater Chem 2012;22:14341–5. Könenkamp R, Word RC, Schlegel C. Appl Phys Lett 2004;85:6004–6. Su YK, Peng SM, Ji LW, Wu CZ, Cheng WB, Liu CH. Langmuir 2010;26:603–6. Lei AH, Qu BH, Zhao WC, Wang YG, Zhang QL, Zou BS. Mater Lett 2012;66:72–5. Ding Q, Miao YE, Liu T. ACS Appl Mater Interfaces 2013;5:5617–22. Zhang J, Sun L, Yin J, Su H, Liao C, Yan C. Chem Mater 2002;14:4172–7. Wan LJ, Wang XY, Yan SC, Yu H, Li ZS, Zou ZG. Cryst Eng Comm 2012;14:154–9. Yan Y, Liu P, Wen JG, To B, Al-Jassim MM. J Phys Chem B 2003;107:9701–4. Gu CY, Huang JR, Wu YJ, Zhai MH, Sun YF, Liu JH. J Alloys Compd 2010;501 (4499-04). Song LX, Jiang QX, Du PF, Xiong Y YF. J. Mater Lett 2014;123:214–6. Liu Z, Bai H, Sun D. Appl Catal, B 2011;104:234–8. Shi J, Ye J, Li Q, Zhou Z, Tong H, Xi G, et al. Chem Eur J 2012;18:3157–62. Zhang HJ, Wu RF, Chen ZW, Liu G, Zhang ZN, Jiao Z. CrystEngComm 2012;14:1775–82. Bhattacharyya S, Gedanken A. Micro Meso Mater 2008;110:553–9. Li JF, Lu GZ, Wang YQ, Guo Y, Guo YL. J Colloid Interface Sci 2012;377:191–6. Xie QS, Li JG, Tian Q, Shi RR. J Mater Chem 2012;22:13541–7. Che P, Fang D, Zhang D, Feng J, Wang J, Hu N, Meng J. J Coord Chem 2005;58:1581–8. Liu B, Xu J, Ran SH, Wang ZR, Chen D, Shen GZ. Cryst Eng Comm 2012;14:4582–8. Rezaei M, Habibi-Yangjeh A. Mater Lett 2013;110:53–6.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile preparation of porous flower-like ZnO microspheres with excellent photocatalytic performance Huayi Wu a, Qingshui Xie b, Li An a, Peng Jin a, Dong-Liang Peng b, Chuanjing Huang a,n, Huilin Wan a,n a State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, PR China b Department of Materials Science and Engineering, College of Materials, Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen 361005, China
art ic l e i nf o
a b s t r a c t
Article history: Received 28 July 2014 Accepted 18 October 2014 Available online 28 October 2014
Porous flower-like ZnO microspheres were successfully fabricated by a facile, green and cost efficient method. In this method, the flower-like precursor was first synthesized and subsequently annealed at 450 1C for 30 min. The SEM and TEM results reveal that the obtained microspheres well inherit the morphology of the precursor and possess numerous mesopores which originated from the release of carbon dioxide and water during annealing process. Noteworthily, porous flower-like ZnO microspheres display significantly enhanced photocatalytic activity for the degradation of methylene blue (MB) compared to hexagonal ZnO disks. The improved photocatalytic activity of flower-like ZnO microspheres can be ascribed to their higher specific surface areas. & 2014 Elsevier B.V. All rights reserved.
Keywords: Zinc oxide Porous materials Photocatalysis Semiconductors
1. Introduction Zinc oxide (ZnO) has been widely applied in many fields such as solar cells [1], piezoelectric devices [2], chemical sensors [3] and photocatalysts [4]. Particularly, due to its high photosensitivity and long-term stability, ZnO has become one of the most researched photocatalysts [5]. The structures have a significant impact on properties. Consequently, it is important to design and prepare ZnO with desired structures [6]. Till now, numerous distinct ZnO structures have been synthesized, including plates [7], nanosheets [8], flowers [9] and spheroids [10]. Hierarchical porous ZnO materials have attracted enormous attention owing to their large surface area and high surface-tovolume ratio which can facilitate the adsorption and diffusion of reactant molecules and thus enhance the catalytic performance [11,12]. Generally, the synthesis methods for hierarchical porous ZnO architectures requires the assistant of templates, complicated controlling process, or the use of organic solution [13–15], which are not conductive to economic and environmental-friendly production. Therefore, it is significant to develop a green and cost efficient method to produce hierarchical porous ZnO structures.
n
Corresponding authors. Tel.: þ 86 592 2186569; fax: þ86 592 2183047. E-mail addresses: [email protected] (C. Huang), [email protected] (H. Wan). http://dx.doi.org/10.1016/j.matlet.2014.10.101 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Herein, a simple, green and template-free approach was introduced to prepare porous flower-like ZnO microspheres. The phase structures and morphologies of the samples were measured by various instruments. Meanwhile, the photocatalytic efficiencies of the products were also investigated for the degradation of MB under UV irradiation.
2. Experimental Typically, an aqueous solution (50 mL) containing 0.48 mmol of Zn(NO3)2 6H2O, 0.26 mmol of (CH2)6N4 and 0.03 mmol of K3C6H5O7 H2O was heated at 90 1C for 2 h and then aged at ambient temperature for 10 h. After that, the precursor was obtained by centrifugation, washed with DI water and dried at 60 1C for 12 h. Subsequently, the precursor was calcined at 450 1C in air for 30 min and the flower-like ZnO microspheres could be harvested. For comparison, hexagonal ZnO disks were also fabricated. The aqueous solution (100 mL) comprised 1.26 mmol of (CH2)6N4 and 0.48 mmol of K3C6H5O7 H2O was prepared at room temperature. The obtained precursor (0.1 g) was added to the above solution and the resulting mixture was transferred into a 200 mL Teflon-lined autoclave. The autoclave was kept at 120 1C for 10 h. After cooled to room temperature, hexagonal ZnO disks could be collected.
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H. Wu et al. / Materials Letters 139 (2015) 393–396
The crystal structures of the samples were tested on a Rigaku Ultima IV X-ray diffractometer. The morphologies of the products were investigated by Hitachi S-4800 field-emission scanning electron microscope and JEM-2100 transmission electron microscope. A Nicolet 330 spectrometer was used to collect the Fourier transform infrared (FT-IR) spectrum. A TriStar 3020 system was applied to measure the Brunauer Emmett Teller (BET) surface area of the products. The thermogravimetric (TG-DTA) analysis was conducted on a SDTQ600 thermal analyzer. The photocatalytic measurements were performed by transferring 100 mg of the achieved ZnO samples to 150 mL of methylene blue (MB) solution (10 mg L 1) under UV irradiation. At regular intervals, 5 mL of suspension was taken out from the solution and centrifuged to remove the photocatalysts. Subsequently, the absorption spectrum of MB solution was tested by a UV-visible spectrophotometer.
3. Results and discussions As shown in Fig. 1A, the XRD pattern of the precursor reveals that the sample contains two phases. One is wurtzite structured ZnO and the other may be the crystalline zinc citrate phase [16]. For a better understanding of the sample, the FT-IR spectrum was performed. In Fig. 1B, the strong and sharp absorption peaks at 1572 and 1397 cm 1 can be assigned to the stretching vibrations of COO- for the coordinated citrates [17]. The strong absorption band centered at 3445 cm 1 is originated from the vibration of the hydroxyl group. The FT-IR results corroborate the presence of zinc citrate. Some of zinc citrate converted to crystal ZnO during aging
process. The thermal process of the precursor was measured by TG-DTA (Fig. 1C). The weight loss occurring below 300 1C can be ascribed to the departure of adsorbed water. The weight loss from 300 to 400 1C can be attributed to the transformation from the precursor to ZnO, relating to the strong exothermic peak at 365 1C in the relevant thermal gravimetric curve. Fig. 1D shows the SEM micrograph of the precursor, wherein a large amount of uniform and disperse flower-like microspheres with an average diameter of 3 μm can be observed. The high-magnification SEM micrograph (Fig. 1D, inset) shows that the flower-like microsphere is assembled by irregular nanosheets with the thickness ranging from 10 to15 nm. The XRD pattern of the obtained sample after annealing is manifested in Fig. 2A. All the diffraction peaks can be attributed to wurtzite structured ZnO (JCPDS no. 36-1451). The sharp and strong peaks indicate the high crystalline of the products. As shown in Fig. 2B, the flower-like ZnO microspheres can be seen, indicating that the sample well inherits the morphology of the precursor after calcination. The microsphere is composed of numerous aggregated nanoparticles (the inset in Fig. 2B and Fig. 2C). Moreover, a great deal of nanopores can be carefully discerned from the TEM image (Fig. 2C), which resulted from the release of carbon dioxide and water during annealing process. The selected-area electron diffraction (SAED) pattern reveals the polycrystalline nature of the flower-like ZnO microspheres (Fig. 2C, inset). The HRTEM image exhibits the lattice fringes spacing of 0.24 nm, corresponding to distance of the (101) lattice planes (Fig. 2D). In Fig. 2E, the N2 adsorption-desorption profiles of the flower-like ZnO microspheres present typical type IV isotherm, further evidencing the porous structure. The specific surface area of the product is about 27.0 m2 g 1. According to the pore size
Fig. 1. The XRD pattern (A), FT-IR spectrum (B), TG-DTA curves (C), SEM image (D) of the obtained precursor.
H. Wu et al. / Materials Letters 139 (2015) 393–396
395
Fig. 2. The XRD patterns of the different ZnO products (A), SEM image of flower-like ZnO microspheres (B), TEM images of flower-like ZnO microspheres (C, D), N2 adsorption-desorption isotherms of the different ZnO products (E), SEM image of hexagonal ZnO disks (F).
distribution (the inset in Fig. 2E), the flower-like ZnO microspheres have two kinds of pores located at 2 and 30 nm, indicating the presence of mesopores. The photodegradation of MB was used to investigate the photocatalytic activity of as-synthesized flower-like ZnO microspheres. For comparison, photodegradation of MB over hexagonal ZnO disks (Figs. 2A and 2F) was also performed under identical conditions. Fig. 3 shows the degradation rate of MB over the flower-like porous ZnO microspheres and hexagonal ZnO disks. Without any catalyst, the degradation rate of MB under UV irradiation is extremely slow and can be negligible (Fig. 3c). Strikingly, approximately 99% of MB can be decomposed in the
presence of the ZnO microspheres within 40 min, whereas only 40% of MB is removed for hexagonal ZnO disks during the same irradiation. This is because the surface area of ZnO microspheres (27.0 m2 g 1) is larger than that of hexagonal ZnO disks (1.6 m2g 1, Fig. 2E). The large surface area of flower-like ZnO microspheres can effectively improve dye-adsorption and lightharvesting, giving rise to the greatly strengthened photodegradation activity of MB [18]. In addition, a rough comparison of the photocatalytic properties among different ZnO catalysts is also summarized and listed in Table 1. Compared with other ZnO catalysts, the flower-like ZnO microspheres prepared in our work exhibit enhanced photodegradation activity of MB.
396
H. Wu et al. / Materials Letters 139 (2015) 393–396
that of hexagonal ZnO disks. The greatly improved photocatalytic activity can be ascribed to the larger specific surface area of porous flower-like ZnO microspheres. The present work further implies that this method may be extended to fabricate other metal oxides with porous flower-like structures.
Acknowledgments This work was supported by the Ministry of Science and Technology of China (2010CB732303, 2013CB933102), the National Natural Science Foundation of China (21073148, 21033006), PCSIRT (No. IRT1036), NFFTBS (No. J11030415).
References Fig. 3. The degradation rate of MB over different ZnO structures: (a) flower-like ZnO microspheres, (b) hexagonal ZnO disks, (c) without any catalyst.
Table 1 A rough comparison of photodegradation efficiencies of MB for various ZnO catalysts. Samples
Total decomposition time (min)
Ref
Porous ZnO microspheres Dandelion-like ZnO Ce-doped ZnO nanostructures our work
80 60 75 40
[4] [10] [19] -
4. Conclusions In conclusion, porous flower-like ZnO microspheres are synthesized for the first time through a facile, economic and green method. Under UV-irradiation, the flower-like ZnO microspheres can decompose 99% of MB within 40 min, three times faster than
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Li Z, Zhou Y, Xue G, Yu T, Liu J, Zou Z. J Mater Chem 2012;22:14341–5. Könenkamp R, Word RC, Schlegel C. Appl Phys Lett 2004;85:6004–6. Su YK, Peng SM, Ji LW, Wu CZ, Cheng WB, Liu CH. Langmuir 2010;26:603–6. Lei AH, Qu BH, Zhao WC, Wang YG, Zhang QL, Zou BS. Mater Lett 2012;66:72–5. Ding Q, Miao YE, Liu T. ACS Appl Mater Interfaces 2013;5:5617–22. Zhang J, Sun L, Yin J, Su H, Liao C, Yan C. Chem Mater 2002;14:4172–7. Wan LJ, Wang XY, Yan SC, Yu H, Li ZS, Zou ZG. Cryst Eng Comm 2012;14:154–9. Yan Y, Liu P, Wen JG, To B, Al-Jassim MM. J Phys Chem B 2003;107:9701–4. Gu CY, Huang JR, Wu YJ, Zhai MH, Sun YF, Liu JH. J Alloys Compd 2010;501 (4499-04). Song LX, Jiang QX, Du PF, Xiong Y YF. J. Mater Lett 2014;123:214–6. Liu Z, Bai H, Sun D. Appl Catal, B 2011;104:234–8. Shi J, Ye J, Li Q, Zhou Z, Tong H, Xi G, et al. Chem Eur J 2012;18:3157–62. Zhang HJ, Wu RF, Chen ZW, Liu G, Zhang ZN, Jiao Z. CrystEngComm 2012;14:1775–82. Bhattacharyya S, Gedanken A. Micro Meso Mater 2008;110:553–9. Li JF, Lu GZ, Wang YQ, Guo Y, Guo YL. J Colloid Interface Sci 2012;377:191–6. Xie QS, Li JG, Tian Q, Shi RR. J Mater Chem 2012;22:13541–7. Che P, Fang D, Zhang D, Feng J, Wang J, Hu N, Meng J. J Coord Chem 2005;58:1581–8. Liu B, Xu J, Ran SH, Wang ZR, Chen D, Shen GZ. Cryst Eng Comm 2012;14:4582–8. Rezaei M, Habibi-Yangjeh A. Mater Lett 2013;110:53–6.