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120 Preparation of macroporous metal oxide by casting method
Science and Technology in Catalysis 2002 Copyright 9 2003 by Kodansha Ltd.
497
120 Preparation of Macroporous Metal Oxide by Casting Method
Min-Woong RYOO', Moo Sung LEE, Wan-Jin LEE, Kap Seung YANG, Jong-Ho KIM and Gon SEO Department of Applied Chemistry & The Research Institute for Catalysis, Chonnam National University, Gwangju, 500-757, Korea "Center for Development of Fine Chemicals, Abstract
Macroporous titania, zirconia, silica and alumina were prepared by casting metal alkoxide on activated carbon cloth, followed by controlled calcination treatments. The physical properties of macroporous metal oxide were investigated using TG/DTA, FE-SEM, XRD and UV-VIS spectrometer. The feasibility of macroporous titania as a photocatalyst in the decomposition of toluene was also discussed. 1. INTRODUCTION
Mesoporous materials are generally prepared using templates [ 1]. Silica sources accumulate on the surface of detergent micelle and react with each other, producing skeletal of mesoporous materials. Detergent removal by calcination or extraction brings about the formation of mesopores. Casting methods using templates have been extended their application to prepare mesoporous materials composed of carbon and metal oxides [2]. Macroporous metal oxides as well as mesoporous materials can be prepared by the casting method using activated carbon cloth (ACC) or fiber as a template. Careful calcination induces removal of carbon and conversion of incorporated metal alkoxides to metal oxides, retaining their porous structure. Since micron-order macroporous metal oxides provide controlled atmosphere for reactants, their application as microreactors and minideviees have been pursued. In this study we prepared macroporous metal oxides and investigated the photoeatalytic activity ofmacroporous titania in the decomposition of toluene. 2. EXPERIMENTAL
Dehydrated ACC reacted with metal alkoxide in anhydrous ethanol at room temperature. Titanium, zirconium, silicon and aluminum atoms incorporated on ACC were converted to their metal oxides through careful calcination treatments, producing macroporous metal oxides. TG/DTA, FE-SEM, XRD, XPS, laser Raman and UV-VIS spectrophotometer were employed to investigate physical properties of prepared macroporous metal oxides. Photocatalytic decomposition of toluene over macroporous titania was carried out using a circulating reactor.
498 M.W. Ryoo et
al.
3. RESULTS and DISCUSION
Metal atoms incorporated on ACC with a tetrahedral coordination produce macroporous metal oxides by calcination. The shape and physical properties of macroporous metal oxide are varied with the an~unt of incorporated metal alkoxides and calcination conditions. During a mild calcinations about 600 *(2,as shown in Fig. 1(A) and (B), incorporated metal atoms convert to metal oxides. Increasing calcination temperature to 800 *(2,however, they become a micro rod as shown in (C). As shown in Fig. 2, the onset wavelength of the absorption of tatania cloth is considerably shifted to visible region (red-shiR) compared to that of the commercial photocatalyst (P25). Although this shift may enhances its photocatalytic activity at visible light even without any additives. The photocatalytic decomposition of toluene over titania cloth under visible light was not examined yet. The photocatalytic decomposition rate of toluene under black UV light, however, was high at 1.2x10 -5 mol/h, per m: oftatania cloth.
P25
1.5
Titania tube o A~ 0.5
0 250
300
350
400
450
500
Wavelength (rim)
Fig. 1. FE-SEM images of marcoporous titania. Fig. 2. Reflectance UV-VIS spectra of micro(A) from Ti(8.4)/ACC and (B) and (C) from porous titania and a commercial photocatalyst Ti(18.6)/ACC.
(D) is overall view of (B).
(P25).
4. SUMMARY
Metal oxide cloths and rods were prepared by a casting method using activated carbon cloth as a template. The metal oxide cloths showed different physical properties from those of commercial titania oxides. Acknowledgment: This research was supported by the KOSEF (2000-2-31800-002-3). References 1. F. Schtith, Chem. Mater. 13 (2001) 3184. 2. R. Ryoo and S.H. Joo, 3~dIntern. Mesostructured Materials Syrup. Jeju, Korea 2002, p. 16.
497
120 Preparation of Macroporous Metal Oxide by Casting Method
Min-Woong RYOO', Moo Sung LEE, Wan-Jin LEE, Kap Seung YANG, Jong-Ho KIM and Gon SEO Department of Applied Chemistry & The Research Institute for Catalysis, Chonnam National University, Gwangju, 500-757, Korea "Center for Development of Fine Chemicals, Abstract
Macroporous titania, zirconia, silica and alumina were prepared by casting metal alkoxide on activated carbon cloth, followed by controlled calcination treatments. The physical properties of macroporous metal oxide were investigated using TG/DTA, FE-SEM, XRD and UV-VIS spectrometer. The feasibility of macroporous titania as a photocatalyst in the decomposition of toluene was also discussed. 1. INTRODUCTION
Mesoporous materials are generally prepared using templates [ 1]. Silica sources accumulate on the surface of detergent micelle and react with each other, producing skeletal of mesoporous materials. Detergent removal by calcination or extraction brings about the formation of mesopores. Casting methods using templates have been extended their application to prepare mesoporous materials composed of carbon and metal oxides [2]. Macroporous metal oxides as well as mesoporous materials can be prepared by the casting method using activated carbon cloth (ACC) or fiber as a template. Careful calcination induces removal of carbon and conversion of incorporated metal alkoxides to metal oxides, retaining their porous structure. Since micron-order macroporous metal oxides provide controlled atmosphere for reactants, their application as microreactors and minideviees have been pursued. In this study we prepared macroporous metal oxides and investigated the photoeatalytic activity ofmacroporous titania in the decomposition of toluene. 2. EXPERIMENTAL
Dehydrated ACC reacted with metal alkoxide in anhydrous ethanol at room temperature. Titanium, zirconium, silicon and aluminum atoms incorporated on ACC were converted to their metal oxides through careful calcination treatments, producing macroporous metal oxides. TG/DTA, FE-SEM, XRD, XPS, laser Raman and UV-VIS spectrophotometer were employed to investigate physical properties of prepared macroporous metal oxides. Photocatalytic decomposition of toluene over macroporous titania was carried out using a circulating reactor.
498 M.W. Ryoo et
al.
3. RESULTS and DISCUSION
Metal atoms incorporated on ACC with a tetrahedral coordination produce macroporous metal oxides by calcination. The shape and physical properties of macroporous metal oxide are varied with the an~unt of incorporated metal alkoxides and calcination conditions. During a mild calcinations about 600 *(2,as shown in Fig. 1(A) and (B), incorporated metal atoms convert to metal oxides. Increasing calcination temperature to 800 *(2,however, they become a micro rod as shown in (C). As shown in Fig. 2, the onset wavelength of the absorption of tatania cloth is considerably shifted to visible region (red-shiR) compared to that of the commercial photocatalyst (P25). Although this shift may enhances its photocatalytic activity at visible light even without any additives. The photocatalytic decomposition of toluene over titania cloth under visible light was not examined yet. The photocatalytic decomposition rate of toluene under black UV light, however, was high at 1.2x10 -5 mol/h, per m: oftatania cloth.
P25
1.5
Titania tube o A~ 0.5
0 250
300
350
400
450
500
Wavelength (rim)
Fig. 1. FE-SEM images of marcoporous titania. Fig. 2. Reflectance UV-VIS spectra of micro(A) from Ti(8.4)/ACC and (B) and (C) from porous titania and a commercial photocatalyst Ti(18.6)/ACC.
(D) is overall view of (B).
(P25).
4. SUMMARY
Metal oxide cloths and rods were prepared by a casting method using activated carbon cloth as a template. The metal oxide cloths showed different physical properties from those of commercial titania oxides. Acknowledgment: This research was supported by the KOSEF (2000-2-31800-002-3). References 1. F. Schtith, Chem. Mater. 13 (2001) 3184. 2. R. Ryoo and S.H. Joo, 3~dIntern. Mesostructured Materials Syrup. Jeju, Korea 2002, p. 16.