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A facile one step synthesis of alumina monolith with bimodal pore structure from emulsion template
Materials Letters 68 (2012) 234–236
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A facile one step synthesis of alumina monolith with bimodal pore structure from emulsion template Xiang Li, Xinmei Liu ⁎, Xinlong Yan, Zhanquan Zhang, Dezhi Han, Lei Han, Zifeng Yan ⁎ State Key Laboratory for Heavy Oil Processing and Key Laboratory of CNPC, China University of Petroleum, Qingdao, 266555, China
a r t i c l e
i n f o
Article history: Received 24 April 2011 Accepted 12 October 2011 Available online 18 October 2011 Keywords: Multilayer structure Emulsion template Porous materials Alumina monolith
a b s t r a c t In this work, the macro-mesoporous alumina monolith has been achieved for the first time via copolymerization of styrene emulsion and aluminum precursor. After elimination of organic components by calcination at 800 °C, the well-crystallized η-Al2O3 phase was obtained, with SBET of 247.7 m 2/g. The spherical macropores in the micrometer range originated from a condensation reaction during drying, and the wormhole-like mesopores (ca. 3.6 nm) distributed on the macroporous walls were the result of the assembly of nanoparticles. The method can be extended to prepare other porous metal oxide monoliths. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental section
Hierarchical macro-mesoporous ceramic materials presenting multimodal or multiscale porosity has been paid much attention due to their potential application in catalysis, separation, or electrode materials [1]. In general, it can be said that a macroporous ceramic framework offers chemical and mechanical stability, as well as high convective heat transfer, high turbulence, low pressure drop, and a high external mass transfer rate due to interconnections between the macropores, while the smaller pores provide the functionality for a given application (e.g. enhanced catalytic properties or selective binding of an analyte) [2,3]. Alumina is the most widely used support of catalysts owing to its attractive mechanical properties and adjustable surface properties [4,5]. While the poor intra-diffusional properties will be the critical for its use in the coming catalytic processes. An alternative is to develop synthetic methods to prepare tough and hierarchical porous alumina monoliths. Several reports on porous alumina monolith preparation can be found [6–11]. These Macro-mesoporous alumina monoliths were generally prepared with polymer template method including the following steps: (1) to prepare organic foam monolith, (2) to fill the organic foam with precursor sol, and (3) to remove the template by calcinations or extraction [8]. In the present study, we describe a novel emulsion template method to synthesize macro-mesoporous alumina monolith. The as-synthesized alumina monolith is prepared in one step, and contains both polymer and aluminum precursor. The obtained η-Al2O3 monolith exhibits high specific surface area after calcinations at 800 °C.
Styrene (analytical reagent, AR), Divinylbenzene (DVB, AR), sodium hydroxide (AR) and aluminum nitrate (AR) were purchased from Sinopharm Chemical Reagent Co. Azobisisobutyronitrile (AIBN, AR) was purchased from Aldrich Chemical Inc. Sorbitan monooleate 80 (Span 80, chemical purity, CP) was purchased from Nanjing Chemical Reagents Co. Typically, 2.0 g of monomer (styrene), 0.5 g of cross-linker (DVB), 0.02 g of initiator (AIBN) and 0.09 g of emulsifier (Span 80) were introduced into a flask to form a homogeneous phase. Both of styrene and DVB were washed with 0.2 M NaOH and then with deionized water to remove inhibitors. Then, 7.6 ml of Al(OH)3 (2.4 M) was added dropwise into the homogeneous phase with a syringe at room temperature under vigorous stirring, thus the highly concentrated water-in-oil (W/O) emulsion (volume fraction of the dispersed phase φ = 0.75) was generated. The emulsion was put in a glass mold (i.d. 7 mm, length 100 mm) which was then sealed with a plug and maintained at 60 °C for 24 h, during which time polymerization of styrene occurred. The wet monoliths were removed from the molds by carefully breaking the glass containers, and then dried at 60 °C for 24 h, to obtain cylindric precursor of alumina monolith. The cylinder was divided into several short parts with a knife. Finally, the alumina monoliths were obtained after calcination at 800 °C for 4 h. The heating rate was 1 °C⋅min− 1. XRD measurements were carried out at a speed of 0.01° s − 1 by a Bruker Axs diffractometer (Germany) with CuK alpha radiation generated at 40 kV, 30 mA. N2 adsorption–desorption isotherms were measured on Micromeritics TRISTAR 3000 analyzer at 77 K. Specific surface area of the samples was calculated using the BET method. The pore distribution and mean pore size of the desorption branches of nitrogen adsorption isotherms were calculated using BJH method. Scanning electron microscopy (SEM) studies were carried out using
⁎ Corresponding authors. Tel.: + 86 0532 86983056; fax: + 86 0532 86981787. E-mail addresses: [email protected] (X. Liu), [email protected] (Z. Yan). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.10.040
X. Li et al. / Materials Letters 68 (2012) 234–236
235
Fig. 1. (a) Photograph of as-synthesized alumina monolith; (b) Photograph of alumina monolith after calcination at 800 °C; (c, d) SEM images of alumina monolith after calcination at 800 °C; (e) TEM image of alumina monolith after calcination at 800 °C; (e) SEAD patterns of alumina monolith after calcination at 800 °C.
an S-4800 high resolution analytical field emission scanning electron microscope with an operating voltage of 5.0 kV. Transmission electron microscopy (TEM) images were collected on a JEOL JEM 2100 electron microscope operated at 200 kV. The mechanical compressive strength was evaluated using a universal tensile testing machine (SHIMADZU Universal Testing Machine AGS-X 5kN) at RT.
3. Results and discussions The alumina monolith with diameter of 7.0 mm was prepared, examples of which are shown in Fig. 1 (a) and (b). The size and shape of the monolith are determined by the size and shape of the vessel used. After the calcination, the resulting alumina monoliths maintained their original shapes, and there is no crack or breakage except reduced sized somewhat. Fig.1 (c) is a representative picture of alumina monolith, in which the macropores are in spherical shape with a diameter range of 8–20 μm. The spherical macropores are interconnected via windows with the diameters approximately 2–4 μm (Fig. 1 (d)). The wall thickness is about 200 nm. The macropores were occupied by aqueous solution drops during polymerization. After drying, the water vaporized, followed by condensation of aluminum precursor on the surface of polystyrene. The removal of organic components by high-temperature calcination, leaded to the formation of the interconnected macroporous structure. The TEM image of alumina monolith (Fig. 1 (e)) indicates that the crystallite sizes are in the 8–12 nm size range. The wide-angle XRD pattern of alumina monolith shows that all the peaks could be attributed to the η-Al2O3 (Fig. 2). According to the η-Al2O3 (440) diffraction peak based on Scherrer's formula, the average crystallite size of alumina monolith was estimated to be about 10.5 nm. The smallangle XRD patterns (the inset in Fig. 2) indicate that the sample contained disordered mesopores without a long-range order in the pore arrangement. The TEM image of alumina monolith reveals that the wormhole-like mesopores in the macroporous frameworks were the result of the assembly of the η-Al2O3 nanoparticles. The selected area electron diffraction (SAED) from the same part of the sample is shown in the inset in Fig. 1 (f). It presents concentric diffraction ring patterns, corresponding to the strongest (440), (400) and (311) diffraction of η-Al2O3. The clearly resolved spots on the diffraction rings of the SAED pattern combined with the high intensity of XRD
peaks, verify that the mesostructures of alumina monolith are composed of crystalline η-Al2O3 nanoparticles [12]. Fig. 3(a) depicts the nitrogen adsorption–desorption isotherm of alumina monolith. The adsorption isotherm is in agreement with type IV in the IUPAC classification with a hysteresis loop, which is characteristic of a disorderedly mesoporous material [13]. The pore size distribution curve (Fig. 3(b)) was calculated from the desorption branch of a nitrogen isotherm using the BJH method. A narrow pore size distribution with a maximum diameter of around 3.6 nm is observed; the pore volume (single point adsorption total pore volume of pores less than 170.7 nm) and the BET specific surface area are 0.33 cm 3/g and 247.7 m 2/g, respectively. In addition, the average compressive strength for the alumina monolith is 0.48 MPa. 4. Conclusion We have described a facile synthetic method to prepare alumina monoliths using highly concentrated W/O emulsion template. The
Fig. 2. XRD patterns of alumina monolith after calcination at 800 C.
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X. Li et al. / Materials Letters 68 (2012) 234–236
References [1] Yuan ZY, Su BL. Insights into hierarchically meso–macroporous structured materials. J Mater Chem 2006;16:663–77. [2] Colombo P, Vakifahmetoglu C, Costacurta S. Fabrication of ceramic components with hierarchical porosity. J Mater Sci 2010;45:5425–55. [3] Li X, Han D, Xu Y, Liu X, Yan Z. Bimodal mesoporous γ-Al2O3: a promising support for CoMo-based catalyst in hydrodesulfurization of 4,6-DMDBT. Mater Lett 2011;65:1765–7. [4] Misra C. Industrial alumina chemicals. Washington, DC: American Chemical Society; 1986. [5] Bagshaw SA, Pinnavaia TJ. Mesoporous alumina molecular sieves. Angew Chem Int Ed Engl 1996;35:1102–5. [6] Han YS, Li JB, Chen YJ. Fabrication of bimodal porous alumina ceramics. Mater Res Bull 2003;38:373–9. [7] Han YS, Li JB, Wei QM, Tang K. The effect of sintering temperatures on alumina foam strength. Ceram Int 2002;28:755–9. [8] Zhang Y, Liang H, Zhao CY, Liu Y. Macroporous alumina monoliths prepared by filling polymer foams with alumina hydrosols. J Mater Sci 2009;44:931–8. [9] Dacquin JP, Dhainaut J, Duprez D, Royer S, Lee AF, Wilson K. An efficient route to highly organized, tunable macroporous−mesoporous alumina. J Am Chem Soc 2009;131:12896–7. [10] Kim Y, Kim C, Yi J. Synthesis of tailored porous alumina with a bimodal pore size distribution. Mate Res Bull 2004;39:2103–12. [11] Yuan X, Xu S, Lü J, Yan X, Hu L, Xue Q. Facile synthesis of ordered mesoporous γalumina monoliths via polymerization-based gel-casting. Microporous Mesoporous Mater 2011;138:40–4. [12] Kuemmel M, Grosso D, Boissiere C, Smarsly B, Brezesinski T, Albouy PA, et al. Thermally stable nanocrystalline γ-alumina layers with highly ordered 3D mesoporosity. Angew Chem Int Ed 2005;44:4589–92. [13] Gregg SJ, Sing KSW. Adsorption, surface area and porosity. London: Academic Press; 1982. p. 304.
Fig. 3. N2 adsorption isotherms (a) and BJH pore size distributions (b) of alumina monolith after calcination at 800 C.
alumina monolith exhibits macropores in the micrometer range and mesopores concentrate on about 3.6 nm. The material with high surface area has a large range of possible applications such as catalysis and separation. Besides, this method can be extending to make other macroporous metal oxide monoliths, such as TiO2, ZnO, ZrO2 and mixed oxides.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A facile one step synthesis of alumina monolith with bimodal pore structure from emulsion template Xiang Li, Xinmei Liu ⁎, Xinlong Yan, Zhanquan Zhang, Dezhi Han, Lei Han, Zifeng Yan ⁎ State Key Laboratory for Heavy Oil Processing and Key Laboratory of CNPC, China University of Petroleum, Qingdao, 266555, China
a r t i c l e
i n f o
Article history: Received 24 April 2011 Accepted 12 October 2011 Available online 18 October 2011 Keywords: Multilayer structure Emulsion template Porous materials Alumina monolith
a b s t r a c t In this work, the macro-mesoporous alumina monolith has been achieved for the first time via copolymerization of styrene emulsion and aluminum precursor. After elimination of organic components by calcination at 800 °C, the well-crystallized η-Al2O3 phase was obtained, with SBET of 247.7 m 2/g. The spherical macropores in the micrometer range originated from a condensation reaction during drying, and the wormhole-like mesopores (ca. 3.6 nm) distributed on the macroporous walls were the result of the assembly of nanoparticles. The method can be extended to prepare other porous metal oxide monoliths. © 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental section
Hierarchical macro-mesoporous ceramic materials presenting multimodal or multiscale porosity has been paid much attention due to their potential application in catalysis, separation, or electrode materials [1]. In general, it can be said that a macroporous ceramic framework offers chemical and mechanical stability, as well as high convective heat transfer, high turbulence, low pressure drop, and a high external mass transfer rate due to interconnections between the macropores, while the smaller pores provide the functionality for a given application (e.g. enhanced catalytic properties or selective binding of an analyte) [2,3]. Alumina is the most widely used support of catalysts owing to its attractive mechanical properties and adjustable surface properties [4,5]. While the poor intra-diffusional properties will be the critical for its use in the coming catalytic processes. An alternative is to develop synthetic methods to prepare tough and hierarchical porous alumina monoliths. Several reports on porous alumina monolith preparation can be found [6–11]. These Macro-mesoporous alumina monoliths were generally prepared with polymer template method including the following steps: (1) to prepare organic foam monolith, (2) to fill the organic foam with precursor sol, and (3) to remove the template by calcinations or extraction [8]. In the present study, we describe a novel emulsion template method to synthesize macro-mesoporous alumina monolith. The as-synthesized alumina monolith is prepared in one step, and contains both polymer and aluminum precursor. The obtained η-Al2O3 monolith exhibits high specific surface area after calcinations at 800 °C.
Styrene (analytical reagent, AR), Divinylbenzene (DVB, AR), sodium hydroxide (AR) and aluminum nitrate (AR) were purchased from Sinopharm Chemical Reagent Co. Azobisisobutyronitrile (AIBN, AR) was purchased from Aldrich Chemical Inc. Sorbitan monooleate 80 (Span 80, chemical purity, CP) was purchased from Nanjing Chemical Reagents Co. Typically, 2.0 g of monomer (styrene), 0.5 g of cross-linker (DVB), 0.02 g of initiator (AIBN) and 0.09 g of emulsifier (Span 80) were introduced into a flask to form a homogeneous phase. Both of styrene and DVB were washed with 0.2 M NaOH and then with deionized water to remove inhibitors. Then, 7.6 ml of Al(OH)3 (2.4 M) was added dropwise into the homogeneous phase with a syringe at room temperature under vigorous stirring, thus the highly concentrated water-in-oil (W/O) emulsion (volume fraction of the dispersed phase φ = 0.75) was generated. The emulsion was put in a glass mold (i.d. 7 mm, length 100 mm) which was then sealed with a plug and maintained at 60 °C for 24 h, during which time polymerization of styrene occurred. The wet monoliths were removed from the molds by carefully breaking the glass containers, and then dried at 60 °C for 24 h, to obtain cylindric precursor of alumina monolith. The cylinder was divided into several short parts with a knife. Finally, the alumina monoliths were obtained after calcination at 800 °C for 4 h. The heating rate was 1 °C⋅min− 1. XRD measurements were carried out at a speed of 0.01° s − 1 by a Bruker Axs diffractometer (Germany) with CuK alpha radiation generated at 40 kV, 30 mA. N2 adsorption–desorption isotherms were measured on Micromeritics TRISTAR 3000 analyzer at 77 K. Specific surface area of the samples was calculated using the BET method. The pore distribution and mean pore size of the desorption branches of nitrogen adsorption isotherms were calculated using BJH method. Scanning electron microscopy (SEM) studies were carried out using
⁎ Corresponding authors. Tel.: + 86 0532 86983056; fax: + 86 0532 86981787. E-mail addresses: [email protected] (X. Liu), [email protected] (Z. Yan). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.10.040
X. Li et al. / Materials Letters 68 (2012) 234–236
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Fig. 1. (a) Photograph of as-synthesized alumina monolith; (b) Photograph of alumina monolith after calcination at 800 °C; (c, d) SEM images of alumina monolith after calcination at 800 °C; (e) TEM image of alumina monolith after calcination at 800 °C; (e) SEAD patterns of alumina monolith after calcination at 800 °C.
an S-4800 high resolution analytical field emission scanning electron microscope with an operating voltage of 5.0 kV. Transmission electron microscopy (TEM) images were collected on a JEOL JEM 2100 electron microscope operated at 200 kV. The mechanical compressive strength was evaluated using a universal tensile testing machine (SHIMADZU Universal Testing Machine AGS-X 5kN) at RT.
3. Results and discussions The alumina monolith with diameter of 7.0 mm was prepared, examples of which are shown in Fig. 1 (a) and (b). The size and shape of the monolith are determined by the size and shape of the vessel used. After the calcination, the resulting alumina monoliths maintained their original shapes, and there is no crack or breakage except reduced sized somewhat. Fig.1 (c) is a representative picture of alumina monolith, in which the macropores are in spherical shape with a diameter range of 8–20 μm. The spherical macropores are interconnected via windows with the diameters approximately 2–4 μm (Fig. 1 (d)). The wall thickness is about 200 nm. The macropores were occupied by aqueous solution drops during polymerization. After drying, the water vaporized, followed by condensation of aluminum precursor on the surface of polystyrene. The removal of organic components by high-temperature calcination, leaded to the formation of the interconnected macroporous structure. The TEM image of alumina monolith (Fig. 1 (e)) indicates that the crystallite sizes are in the 8–12 nm size range. The wide-angle XRD pattern of alumina monolith shows that all the peaks could be attributed to the η-Al2O3 (Fig. 2). According to the η-Al2O3 (440) diffraction peak based on Scherrer's formula, the average crystallite size of alumina monolith was estimated to be about 10.5 nm. The smallangle XRD patterns (the inset in Fig. 2) indicate that the sample contained disordered mesopores without a long-range order in the pore arrangement. The TEM image of alumina monolith reveals that the wormhole-like mesopores in the macroporous frameworks were the result of the assembly of the η-Al2O3 nanoparticles. The selected area electron diffraction (SAED) from the same part of the sample is shown in the inset in Fig. 1 (f). It presents concentric diffraction ring patterns, corresponding to the strongest (440), (400) and (311) diffraction of η-Al2O3. The clearly resolved spots on the diffraction rings of the SAED pattern combined with the high intensity of XRD
peaks, verify that the mesostructures of alumina monolith are composed of crystalline η-Al2O3 nanoparticles [12]. Fig. 3(a) depicts the nitrogen adsorption–desorption isotherm of alumina monolith. The adsorption isotherm is in agreement with type IV in the IUPAC classification with a hysteresis loop, which is characteristic of a disorderedly mesoporous material [13]. The pore size distribution curve (Fig. 3(b)) was calculated from the desorption branch of a nitrogen isotherm using the BJH method. A narrow pore size distribution with a maximum diameter of around 3.6 nm is observed; the pore volume (single point adsorption total pore volume of pores less than 170.7 nm) and the BET specific surface area are 0.33 cm 3/g and 247.7 m 2/g, respectively. In addition, the average compressive strength for the alumina monolith is 0.48 MPa. 4. Conclusion We have described a facile synthetic method to prepare alumina monoliths using highly concentrated W/O emulsion template. The
Fig. 2. XRD patterns of alumina monolith after calcination at 800 C.
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X. Li et al. / Materials Letters 68 (2012) 234–236
References [1] Yuan ZY, Su BL. Insights into hierarchically meso–macroporous structured materials. J Mater Chem 2006;16:663–77. [2] Colombo P, Vakifahmetoglu C, Costacurta S. Fabrication of ceramic components with hierarchical porosity. J Mater Sci 2010;45:5425–55. [3] Li X, Han D, Xu Y, Liu X, Yan Z. Bimodal mesoporous γ-Al2O3: a promising support for CoMo-based catalyst in hydrodesulfurization of 4,6-DMDBT. Mater Lett 2011;65:1765–7. [4] Misra C. Industrial alumina chemicals. Washington, DC: American Chemical Society; 1986. [5] Bagshaw SA, Pinnavaia TJ. Mesoporous alumina molecular sieves. Angew Chem Int Ed Engl 1996;35:1102–5. [6] Han YS, Li JB, Chen YJ. Fabrication of bimodal porous alumina ceramics. Mater Res Bull 2003;38:373–9. [7] Han YS, Li JB, Wei QM, Tang K. The effect of sintering temperatures on alumina foam strength. Ceram Int 2002;28:755–9. [8] Zhang Y, Liang H, Zhao CY, Liu Y. Macroporous alumina monoliths prepared by filling polymer foams with alumina hydrosols. J Mater Sci 2009;44:931–8. [9] Dacquin JP, Dhainaut J, Duprez D, Royer S, Lee AF, Wilson K. An efficient route to highly organized, tunable macroporous−mesoporous alumina. J Am Chem Soc 2009;131:12896–7. [10] Kim Y, Kim C, Yi J. Synthesis of tailored porous alumina with a bimodal pore size distribution. Mate Res Bull 2004;39:2103–12. [11] Yuan X, Xu S, Lü J, Yan X, Hu L, Xue Q. Facile synthesis of ordered mesoporous γalumina monoliths via polymerization-based gel-casting. Microporous Mesoporous Mater 2011;138:40–4. [12] Kuemmel M, Grosso D, Boissiere C, Smarsly B, Brezesinski T, Albouy PA, et al. Thermally stable nanocrystalline γ-alumina layers with highly ordered 3D mesoporosity. Angew Chem Int Ed 2005;44:4589–92. [13] Gregg SJ, Sing KSW. Adsorption, surface area and porosity. London: Academic Press; 1982. p. 304.
Fig. 3. N2 adsorption isotherms (a) and BJH pore size distributions (b) of alumina monolith after calcination at 800 C.
alumina monolith exhibits macropores in the micrometer range and mesopores concentrate on about 3.6 nm. The material with high surface area has a large range of possible applications such as catalysis and separation. Besides, this method can be extending to make other macroporous metal oxide monoliths, such as TiO2, ZnO, ZrO2 and mixed oxides.