- Email: [email protected]
Parameter control in the synthesis of ordered porous zirconium oxide
November 2001
Materials Letters 51 Ž2001. 187–193 www.elsevier.comrlocatermatlet
Parameter control in the synthesis of ordered porous zirconium oxide Hang-Rong Chen, Jian-Lin Shi ) , Zi-Le Hua, Mei-Ling Ruan, Dong-Sheng Yan State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, People’s Republic of China Received 28 November 2000; accepted 5 January 2001
Abstract The ordered porous zirconium oxide with thermal stability up to 6008C has been synthesized by a surfactant-assisted route and a post-synthetic treatment with phosphoric acid. XRD, N2 adsorption, HRTEM and UV–VIS spectroscopy were adopted for the characterization of the synthesized sample. It was shown that the parameter control, including the lower molar ratio of surfactant to zirconium resource Ž0.2–0.3., higher hydrothermal temperature Ž1108C., and the suitable H 3 PO4 concentration Ž0.2–0.3 M., is important for the synthesis of high-quality zirconium oxide material with ordered pore structure. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Ordered porous zirconium oxide; Parameter control; Phosphoric acid Žpost-treatment.
1. Introduction The synthesis of silica-based mesoporous materials, designated as M41s w1x, has fueled considerable interest in this new class w2–4x. Shortly after, a number of nonsilicate MCM-41-type mesostructured materials were prepared, such as oxides of antimony, tungsten, iron, tin, etc., through a generalized electrostatic approach w5–7x. However, a major problem of these nonsoliceous materials is their thermal stability upon removal of the template. So far, only a minority of mesostructured oxides besides silica have
)
Corresponding author. Fax: q86-21-62513903. E-mail address: [email protected] ŽJ.-L. Shi..
been synthesized, in which the hexagonal pore structure exists even after calcination w8–10x. Of the nonsilicate mesoporous materials, zirconium oxide has received great interest for both weakly acidic and basic surface sites, providing high activity as bifunctional catalysts. Several routes have been attempted in the synthesis of mesoporous zirconia, mainly based on two synthesis mechanisms. A scaffolding mechanism was first proposed by Knowels and Hudson w11x, in which mesoporous zirconia has been prepared with cationic surfactants w12x. Fripiat used the same mechanism to synthesize the mesoporous zirconia with anionic surfactants w13x. However, one of the major problems of the scaffolding mechanism is the disordered pore structure in the synthesized samples. Templating
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 2 8 6 - 5
188
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
mechanism has been widely used in the synthesis of MCM-41-type of materials w14x. Surfactant-templating synthesis of mesoporous zirconia with anionic surfactant w15x, nonionic surfactant w16x, as well as amphoteric surfactant w17x, have been reported. However, the mesostructure, in most cases, will collapse under high thermal treatment. Ciesla et al. w18,19x have synthesized for the first time the highly ordered mesoporous zirconium oxide with thermal stability up to 5008C, using the post-treatment of phosphoric acid solution Ž0.5 M.. Wong and Ying w20x also indicated that phosphate head groups remaining on the inorganic wall appeared necessary for thermal stability. In this paper, we focus on the synthesis of thermally stable mesostructure zirconium oxide with suitable parameter control by the templating mechanism. The suitable treatment concentration of phosphoric acid seems much important for the ordered pore structure.
2. Experimental 2.1. Materials synthesis An aqueous solution of analytically pure ZrSO4 P 4H 2 O was dropped into the pure C 16TMABr solution under certain temperatures with continuous stirring. The molar ratio of surfactant to zirconium was controlled to be 0.6, 0.4, 0.3 and 0.2, respectively designated as SrZr-0.6, SrZr-0.4, SrZr-0.3, and SrZr-0.2. After stirring for 3 h, the mixtures were loaded in PTFE-lined stainless steel autoclaves and heated at different temperatures, from 908C to 1208C for 24 h. The precipitated products were filtered, washed and dried at 1008C. The dried precipitate was afterwards treated with phosphoric acid solution Ž y s 1.5, 0.75, 0.25 and 0.05 M.. The as-synthesized sample was calcined in flowing air at 5008C for 6 h to remove the surfactant. The calcined samples were designated as P1.5, P0.75, P0.25 and P0.05, respec-
Fig. 1. X-ray powder diffraction patterns of the as-synthesized samples with different molar ratios of surfactant to zirconium Žabbr. SrZr.: Ža. 0.6, Žb. 0.4, Žc. 0.3, and Žd. 0.2.
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
tively, while the calcined sample without treatment of phosphoric acid was named as P0. 2.2. Analysis XRD patterns were obtained using a Rigaku Drmax-RB diffractometer. Analyses were performed with Cu Target Ž40 kV, 60 mA., whose typical scan speed was 58rmin, with a step of 0.0028 and ranging from 1.88 to 108. N2 adsorption–desorption isotherms were obtained at 77.35 K on a Micromeritics Tristar 3000 analyzer. The samples were outgassed at 2508C in flowing N2 for at least 20 h before measurement. High-resolution transmission electron microscopy ŽHRTEM. was measured with JEOL 200CX electron microscope operated at 200 kV. Diffuse reflectance UV–VIS spectra were taken on a Shimadzu UV-3101PC UV–VIS–NIR scanning spectrophotometer, equipped with an integrating sphere using BaSO4 as the reference.
189
3. Results and discussion The X-ray diffraction patterns of the as-synthesized samples with different molar ratios of SrZr are shown in Fig. 1. With the decrease in the molar ratio of SrZr, the as-synthesized samples show a more narrow and sharp Ž100. peak with stronger intensity. Furthermore, the Ž110. and Ž200. reflections become visible for the SrZr-0.3 sample. This means that the hexagonal pore structure can be formed under the lower ratio of SrZr, which results from the self-assembly of surfactant under certain concentrations. The XRD patterns of as-synthesized mesophases obtained at different temperatures are shown in Fig. 2. At low temperature ŽF 1008C., both the Ž100. reflections of these two samples show broad peaks and much lower intensity. This indicates that mesoporous zirconia materials obtained at low temperature were poorly ordered and the mesostructure was very unstable. Nevertheless, the XRD pattern of the as-sample obtained at higher temperature Ž1108C.
Fig. 2. XRD patterns of as-synthesized samples obtained at different hydrothermal temperatures: Ža. 908C, Žb. 1008C, Žc. 1108C, Žd. 1208C.
190
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
Fig. 3. XRD patterns of the calcined samples treated with different concentrations of H 3 PO4 : Ža. P1.50, Žb. P0.75, Žc. P0.25, Žd. P0.05, Že. P0.
obviously shows the characteristics of ordered pore structure of zirconia w18x. With further increase of hydrothermal temperature to 1208C, the value of d100 spacing decreases, and two small peaks of Ž110. and Ž200. become undetectable. This can be due to the polymerization and condensation of zirconium resource and surfactant at different temperatures, which result in the formation of curved hexagonal phase. The concentration of phosphoric acid solution is an important factor for the stably ordered pore structure of zirconium oxide. The XRD patterns of the calcined samples treated with different concentrations of phosphoric acid are shown in Fig. 3. The values of d100 spacing increase with the increase of treatment concentration, which indicates that the group of phosphate has been incorporated into the framework of zirconium oxide, which induced the increase in wall thickness. Meanwhile, the intensity of peak Ž100. presents an interesting change. The P0.25 sample shows the strongest intensity of peak Ž100., while the P0 sample shows the lowest intensity and broad peak of Ž100. reflection. It can be concluded from the results of XRD patterns that a suitable concentration of H 3 PO4 treatment is very important for the ordering structure and thermal stability in the calcined sample. The results of XRD patterns are well consistent with the results of the N2 adsorption analysis shown in Fig. 4. The suitable treatment concentration can be helpful to the in-
Fig. 4. The BET surface areas of the calcined samples treated by different concentrations of H 3 PO4 .
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
191
Fig. 5. The N2 adsorption–desorption isothermals of the samples: Ža. P0.25, Žb. P0.75.
crease of the surface area as well as the thermal stability. The direct calcination of the unphosphated sample results in a collapse of the structure, showing much lower surface area Ž- 10 m2rg.. The reason lies in that the phosphate groups act through the substitution of the thermally unstable sulfate groups
and also through the bridging of uncondensed Zr–OH groups w21x, thus resulting in a stability of the inorganic framework of zirconium oxide. However, in our study, the BET surface area makes a remarkable decrease with the further increase of treatment concentration. This indicates that certain kinds of zirco-
Fig. 6. The UV–VIS spectra for the calcined samples treated with different H 3 PO4 concentrations: Ža. P0.05, Žb. P0.25, Žc. P0.75, Žd. P1.50, and a referent sample Že. pure Zr3 ŽPO4 .4 .
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
192
Table 1 The pore structure parameters of the P0.25 sample calcined at different temperatures Calcining temperature Ž8C. d100 spacing Žnm. BET surface area Žm2rg. Pore volume Žcm3rg.
100 4.08 – –
450 3.20 406 0.194
500 3.14 388 0.168
nium phosphate may form in the zirconium framework, inducing an increase of the wall thickness and the destruction of pore structure. The distinctive difference in N2 adsorption–desorption isothermal between the samples P0.25 and P0.75 shown in Fig. 5 can be attributed to the destruction of the pore structure, which induces the nonsuperposition of the adsorption and the desorption isothermal for the sample P0.75. Fig. 6 shows the UV–VIS spectra for the calcined samples treated with different H 3 PO4 concentrations and the referent sample of pure Zr3 ŽPO4 .4 . As illustrated, when treated with a low concentration of H 3 PO4 Žcurves a, b., the adsorption peaks present around 210 nm, due to the Zr–O–Zr coordination w22x. However, with the increase of treatment concentration, the adsorption band makes clearly red shift, and both of the two adsorption peaks Žcurves c, d. present neither the ZrO 2 nor the Zr3 ŽPO4 .4 adsorption. Most probably, these two peaks can further
550 3.06 348 0.160
600 3.03 293 0.131
650 2.96 149 0.072
700 2.86 71 0.048
be confirmed in the same way as those which resulted from the certain kinds of zirconium phosphate formed in the framework of zirconia. The phosphate groups are believed to complex the metal oxopolymers and to interact with the positively charged headgroup of the surfactant, leading to complete cross-linking. However, the formation of certain zirconium phosphates will certainly be harmful to the ordering of the framework. Therefore, it is believed that the suitable H 3 PO4 concentration is very important to support the pore structure and to enhance the BET surface area. The pore structure parameters of the P0.25 sample calcined at different temperatures are summarized in Table 1. The highest thermal stability can be obtained at 6008C, which is the highest temperature reported for the ordered porous zirconium oxide. The HRTEM images of this sample are shown in Fig. 7. In conclusion, the parameter control is very important in the synthesis of thermally stable zirconium
Fig. 7. Representative HRTEM image of the calcined sample P0.25.
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
oxide with highly ordered Žand thermally stable. pore structure.
Acknowledgements This work was supported by the National Natural Science Foundation of China with Contract No. 59882007.
References w1x C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 Ž1992. 710. w2x Q. Huo, D. Margolese, U. Ciesla, P. Feng, T.E. Gier, P. Sierger, R. Leao, P.M. Petroff, F. Schuth, G.D. Stucky, Nature 368 Ž1994. 317. w3x A. Steel, S.W. Carr, M.W. Anderson, J. Chem. Soc., Chem. Commun. Ž1994. 1571. w4x A. Firouzi, D. Kumar, L.M. Bull, P. Besier, Q. Huo, S.A. Walker, J.A. Zasadzinski, G. Glikka, J. Nicol, D. Margolese, G.D. Stucky, Science 267 Ž1995. 1138. w5x Q. Hou, D.L. Margolese, U. Ciesla, D.G. Demuth, P. Feng, T.E. Cier, P. Sierger, A. Firouzi, B.F. Chmelka, F. Schuth, G.D. Stucky, Chem. Mater. 6 Ž1994. 1176.
193
w6x T. Abe, A. Taguchi, M. Iwamoto, Chem. Mater. 7 Ž1995. 1429. w7x A. Stein, M. Fendorf, T.P. Jarvie, K.T. Mueller, A.J. Benesi, T.E. Mallouk, Chem. Mater. 7 Ž1995. 304. w8x D.M. Antonelli, J.Y. Ying, Angew. Chem., Int. Ed. Engl. 34 Ž1995. 2014. w9x D.M. Antonelli, J.Y. Ying, Chem. Mater. 8 Ž1996. 874. w10x Z.R. Tian, W. Tong, J.Y. Wang, N.G. Duan, V.V. Krishnan, S.L. Suib, Science 276 Ž1997. 926. w11x J.A. Knowels, M.J. Hudson, J. Chem. Soc., Chem. Commun. Ž1995. 2083. w12x M.J. Hudson, J.A. Knowels, J. Mater. Chem. 6 Ž1996. 89. w13x G. Pacheco, E. Zhao, A. Garcia, A. Sklyarov, J.J. Fripiat, J. Mater. Chem. 8 Ž1998. 219. w14x G.S. Atard, J.C. Glyde, C.G. Goltner, Nature 378 Ž1995. 366. w15x G. Larsen, E. Lotero, M. Nabity, L.M. Petkovic, D.S. Shobe, J. Catal. 164 Ž1996. 246. w16x Neeraj, C.N.R. Rao, J. Mater. Chem. 8 Ž1998. 1631. w17x A. Kim, P. Bruinsma, Y. Chen, L.Q. Wang, J. Liu, Chem. Commun. Ž1997. 161. w18x U. Ciesla, S. Schacht, G.D. Stucky, K.K. Unger, F. Schuth, ¨ Angew. Chem., Int. Ed. Engl. 35 Ž1996. 541. w19x U. Ciesla, M. Froba, G. Stucky, F. Schuth, ¨ Chem. Mater. 11 Ž1999. 227. w20x M.S. Wong, J.Y. Ying, Chem. Mater. 10 Ž1998. 2067. w21x J. Blanchard, F. Schuth, ¨ P. Trens, M. Hudson, Microporous Mesoporous Mater. 39 Ž2000. 163. w22x H.R. Chen, J.L. Shi, J. Yu, L.Z. Wang, D.S. Yan, Microporous Mesoporous Mater. 39 Ž2000. 171.
Materials Letters 51 Ž2001. 187–193 www.elsevier.comrlocatermatlet
Parameter control in the synthesis of ordered porous zirconium oxide Hang-Rong Chen, Jian-Lin Shi ) , Zi-Le Hua, Mei-Ling Ruan, Dong-Sheng Yan State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, People’s Republic of China Received 28 November 2000; accepted 5 January 2001
Abstract The ordered porous zirconium oxide with thermal stability up to 6008C has been synthesized by a surfactant-assisted route and a post-synthetic treatment with phosphoric acid. XRD, N2 adsorption, HRTEM and UV–VIS spectroscopy were adopted for the characterization of the synthesized sample. It was shown that the parameter control, including the lower molar ratio of surfactant to zirconium resource Ž0.2–0.3., higher hydrothermal temperature Ž1108C., and the suitable H 3 PO4 concentration Ž0.2–0.3 M., is important for the synthesis of high-quality zirconium oxide material with ordered pore structure. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Ordered porous zirconium oxide; Parameter control; Phosphoric acid Žpost-treatment.
1. Introduction The synthesis of silica-based mesoporous materials, designated as M41s w1x, has fueled considerable interest in this new class w2–4x. Shortly after, a number of nonsilicate MCM-41-type mesostructured materials were prepared, such as oxides of antimony, tungsten, iron, tin, etc., through a generalized electrostatic approach w5–7x. However, a major problem of these nonsoliceous materials is their thermal stability upon removal of the template. So far, only a minority of mesostructured oxides besides silica have
)
Corresponding author. Fax: q86-21-62513903. E-mail address: [email protected] ŽJ.-L. Shi..
been synthesized, in which the hexagonal pore structure exists even after calcination w8–10x. Of the nonsilicate mesoporous materials, zirconium oxide has received great interest for both weakly acidic and basic surface sites, providing high activity as bifunctional catalysts. Several routes have been attempted in the synthesis of mesoporous zirconia, mainly based on two synthesis mechanisms. A scaffolding mechanism was first proposed by Knowels and Hudson w11x, in which mesoporous zirconia has been prepared with cationic surfactants w12x. Fripiat used the same mechanism to synthesize the mesoporous zirconia with anionic surfactants w13x. However, one of the major problems of the scaffolding mechanism is the disordered pore structure in the synthesized samples. Templating
00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 2 8 6 - 5
188
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
mechanism has been widely used in the synthesis of MCM-41-type of materials w14x. Surfactant-templating synthesis of mesoporous zirconia with anionic surfactant w15x, nonionic surfactant w16x, as well as amphoteric surfactant w17x, have been reported. However, the mesostructure, in most cases, will collapse under high thermal treatment. Ciesla et al. w18,19x have synthesized for the first time the highly ordered mesoporous zirconium oxide with thermal stability up to 5008C, using the post-treatment of phosphoric acid solution Ž0.5 M.. Wong and Ying w20x also indicated that phosphate head groups remaining on the inorganic wall appeared necessary for thermal stability. In this paper, we focus on the synthesis of thermally stable mesostructure zirconium oxide with suitable parameter control by the templating mechanism. The suitable treatment concentration of phosphoric acid seems much important for the ordered pore structure.
2. Experimental 2.1. Materials synthesis An aqueous solution of analytically pure ZrSO4 P 4H 2 O was dropped into the pure C 16TMABr solution under certain temperatures with continuous stirring. The molar ratio of surfactant to zirconium was controlled to be 0.6, 0.4, 0.3 and 0.2, respectively designated as SrZr-0.6, SrZr-0.4, SrZr-0.3, and SrZr-0.2. After stirring for 3 h, the mixtures were loaded in PTFE-lined stainless steel autoclaves and heated at different temperatures, from 908C to 1208C for 24 h. The precipitated products were filtered, washed and dried at 1008C. The dried precipitate was afterwards treated with phosphoric acid solution Ž y s 1.5, 0.75, 0.25 and 0.05 M.. The as-synthesized sample was calcined in flowing air at 5008C for 6 h to remove the surfactant. The calcined samples were designated as P1.5, P0.75, P0.25 and P0.05, respec-
Fig. 1. X-ray powder diffraction patterns of the as-synthesized samples with different molar ratios of surfactant to zirconium Žabbr. SrZr.: Ža. 0.6, Žb. 0.4, Žc. 0.3, and Žd. 0.2.
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
tively, while the calcined sample without treatment of phosphoric acid was named as P0. 2.2. Analysis XRD patterns were obtained using a Rigaku Drmax-RB diffractometer. Analyses were performed with Cu Target Ž40 kV, 60 mA., whose typical scan speed was 58rmin, with a step of 0.0028 and ranging from 1.88 to 108. N2 adsorption–desorption isotherms were obtained at 77.35 K on a Micromeritics Tristar 3000 analyzer. The samples were outgassed at 2508C in flowing N2 for at least 20 h before measurement. High-resolution transmission electron microscopy ŽHRTEM. was measured with JEOL 200CX electron microscope operated at 200 kV. Diffuse reflectance UV–VIS spectra were taken on a Shimadzu UV-3101PC UV–VIS–NIR scanning spectrophotometer, equipped with an integrating sphere using BaSO4 as the reference.
189
3. Results and discussion The X-ray diffraction patterns of the as-synthesized samples with different molar ratios of SrZr are shown in Fig. 1. With the decrease in the molar ratio of SrZr, the as-synthesized samples show a more narrow and sharp Ž100. peak with stronger intensity. Furthermore, the Ž110. and Ž200. reflections become visible for the SrZr-0.3 sample. This means that the hexagonal pore structure can be formed under the lower ratio of SrZr, which results from the self-assembly of surfactant under certain concentrations. The XRD patterns of as-synthesized mesophases obtained at different temperatures are shown in Fig. 2. At low temperature ŽF 1008C., both the Ž100. reflections of these two samples show broad peaks and much lower intensity. This indicates that mesoporous zirconia materials obtained at low temperature were poorly ordered and the mesostructure was very unstable. Nevertheless, the XRD pattern of the as-sample obtained at higher temperature Ž1108C.
Fig. 2. XRD patterns of as-synthesized samples obtained at different hydrothermal temperatures: Ža. 908C, Žb. 1008C, Žc. 1108C, Žd. 1208C.
190
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
Fig. 3. XRD patterns of the calcined samples treated with different concentrations of H 3 PO4 : Ža. P1.50, Žb. P0.75, Žc. P0.25, Žd. P0.05, Že. P0.
obviously shows the characteristics of ordered pore structure of zirconia w18x. With further increase of hydrothermal temperature to 1208C, the value of d100 spacing decreases, and two small peaks of Ž110. and Ž200. become undetectable. This can be due to the polymerization and condensation of zirconium resource and surfactant at different temperatures, which result in the formation of curved hexagonal phase. The concentration of phosphoric acid solution is an important factor for the stably ordered pore structure of zirconium oxide. The XRD patterns of the calcined samples treated with different concentrations of phosphoric acid are shown in Fig. 3. The values of d100 spacing increase with the increase of treatment concentration, which indicates that the group of phosphate has been incorporated into the framework of zirconium oxide, which induced the increase in wall thickness. Meanwhile, the intensity of peak Ž100. presents an interesting change. The P0.25 sample shows the strongest intensity of peak Ž100., while the P0 sample shows the lowest intensity and broad peak of Ž100. reflection. It can be concluded from the results of XRD patterns that a suitable concentration of H 3 PO4 treatment is very important for the ordering structure and thermal stability in the calcined sample. The results of XRD patterns are well consistent with the results of the N2 adsorption analysis shown in Fig. 4. The suitable treatment concentration can be helpful to the in-
Fig. 4. The BET surface areas of the calcined samples treated by different concentrations of H 3 PO4 .
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
191
Fig. 5. The N2 adsorption–desorption isothermals of the samples: Ža. P0.25, Žb. P0.75.
crease of the surface area as well as the thermal stability. The direct calcination of the unphosphated sample results in a collapse of the structure, showing much lower surface area Ž- 10 m2rg.. The reason lies in that the phosphate groups act through the substitution of the thermally unstable sulfate groups
and also through the bridging of uncondensed Zr–OH groups w21x, thus resulting in a stability of the inorganic framework of zirconium oxide. However, in our study, the BET surface area makes a remarkable decrease with the further increase of treatment concentration. This indicates that certain kinds of zirco-
Fig. 6. The UV–VIS spectra for the calcined samples treated with different H 3 PO4 concentrations: Ža. P0.05, Žb. P0.25, Žc. P0.75, Žd. P1.50, and a referent sample Že. pure Zr3 ŽPO4 .4 .
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
192
Table 1 The pore structure parameters of the P0.25 sample calcined at different temperatures Calcining temperature Ž8C. d100 spacing Žnm. BET surface area Žm2rg. Pore volume Žcm3rg.
100 4.08 – –
450 3.20 406 0.194
500 3.14 388 0.168
nium phosphate may form in the zirconium framework, inducing an increase of the wall thickness and the destruction of pore structure. The distinctive difference in N2 adsorption–desorption isothermal between the samples P0.25 and P0.75 shown in Fig. 5 can be attributed to the destruction of the pore structure, which induces the nonsuperposition of the adsorption and the desorption isothermal for the sample P0.75. Fig. 6 shows the UV–VIS spectra for the calcined samples treated with different H 3 PO4 concentrations and the referent sample of pure Zr3 ŽPO4 .4 . As illustrated, when treated with a low concentration of H 3 PO4 Žcurves a, b., the adsorption peaks present around 210 nm, due to the Zr–O–Zr coordination w22x. However, with the increase of treatment concentration, the adsorption band makes clearly red shift, and both of the two adsorption peaks Žcurves c, d. present neither the ZrO 2 nor the Zr3 ŽPO4 .4 adsorption. Most probably, these two peaks can further
550 3.06 348 0.160
600 3.03 293 0.131
650 2.96 149 0.072
700 2.86 71 0.048
be confirmed in the same way as those which resulted from the certain kinds of zirconium phosphate formed in the framework of zirconia. The phosphate groups are believed to complex the metal oxopolymers and to interact with the positively charged headgroup of the surfactant, leading to complete cross-linking. However, the formation of certain zirconium phosphates will certainly be harmful to the ordering of the framework. Therefore, it is believed that the suitable H 3 PO4 concentration is very important to support the pore structure and to enhance the BET surface area. The pore structure parameters of the P0.25 sample calcined at different temperatures are summarized in Table 1. The highest thermal stability can be obtained at 6008C, which is the highest temperature reported for the ordered porous zirconium oxide. The HRTEM images of this sample are shown in Fig. 7. In conclusion, the parameter control is very important in the synthesis of thermally stable zirconium
Fig. 7. Representative HRTEM image of the calcined sample P0.25.
H.-R. Chen et al.r Materials Letters 51 (2001) 187–193
oxide with highly ordered Žand thermally stable. pore structure.
Acknowledgements This work was supported by the National Natural Science Foundation of China with Contract No. 59882007.
References w1x C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 Ž1992. 710. w2x Q. Huo, D. Margolese, U. Ciesla, P. Feng, T.E. Gier, P. Sierger, R. Leao, P.M. Petroff, F. Schuth, G.D. Stucky, Nature 368 Ž1994. 317. w3x A. Steel, S.W. Carr, M.W. Anderson, J. Chem. Soc., Chem. Commun. Ž1994. 1571. w4x A. Firouzi, D. Kumar, L.M. Bull, P. Besier, Q. Huo, S.A. Walker, J.A. Zasadzinski, G. Glikka, J. Nicol, D. Margolese, G.D. Stucky, Science 267 Ž1995. 1138. w5x Q. Hou, D.L. Margolese, U. Ciesla, D.G. Demuth, P. Feng, T.E. Cier, P. Sierger, A. Firouzi, B.F. Chmelka, F. Schuth, G.D. Stucky, Chem. Mater. 6 Ž1994. 1176.
193
w6x T. Abe, A. Taguchi, M. Iwamoto, Chem. Mater. 7 Ž1995. 1429. w7x A. Stein, M. Fendorf, T.P. Jarvie, K.T. Mueller, A.J. Benesi, T.E. Mallouk, Chem. Mater. 7 Ž1995. 304. w8x D.M. Antonelli, J.Y. Ying, Angew. Chem., Int. Ed. Engl. 34 Ž1995. 2014. w9x D.M. Antonelli, J.Y. Ying, Chem. Mater. 8 Ž1996. 874. w10x Z.R. Tian, W. Tong, J.Y. Wang, N.G. Duan, V.V. Krishnan, S.L. Suib, Science 276 Ž1997. 926. w11x J.A. Knowels, M.J. Hudson, J. Chem. Soc., Chem. Commun. Ž1995. 2083. w12x M.J. Hudson, J.A. Knowels, J. Mater. Chem. 6 Ž1996. 89. w13x G. Pacheco, E. Zhao, A. Garcia, A. Sklyarov, J.J. Fripiat, J. Mater. Chem. 8 Ž1998. 219. w14x G.S. Atard, J.C. Glyde, C.G. Goltner, Nature 378 Ž1995. 366. w15x G. Larsen, E. Lotero, M. Nabity, L.M. Petkovic, D.S. Shobe, J. Catal. 164 Ž1996. 246. w16x Neeraj, C.N.R. Rao, J. Mater. Chem. 8 Ž1998. 1631. w17x A. Kim, P. Bruinsma, Y. Chen, L.Q. Wang, J. Liu, Chem. Commun. Ž1997. 161. w18x U. Ciesla, S. Schacht, G.D. Stucky, K.K. Unger, F. Schuth, ¨ Angew. Chem., Int. Ed. Engl. 35 Ž1996. 541. w19x U. Ciesla, M. Froba, G. Stucky, F. Schuth, ¨ Chem. Mater. 11 Ž1999. 227. w20x M.S. Wong, J.Y. Ying, Chem. Mater. 10 Ž1998. 2067. w21x J. Blanchard, F. Schuth, ¨ P. Trens, M. Hudson, Microporous Mesoporous Mater. 39 Ž2000. 163. w22x H.R. Chen, J.L. Shi, J. Yu, L.Z. Wang, D.S. Yan, Microporous Mesoporous Mater. 39 Ž2000. 171.