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Mesoporous Materials Produced from Hydrothermally Synthesized Hectorites
81
Mesoporous Materials Produced from Hydrothermally Synthesized Hectorites
Torii, T. Iwasaki, Y. Onodera and K. Hatakeda Government Industrial Research Institute, Tohoku, Nigatake 4-2-1, Sendai 983, Japan K.
Miyagino-ku,
ABSTRACT Novel mesoporous materials having exceptionally large pores were produced from hydrothermally synthesized silicate-bearing hectorites. Experiments suggest that interlayer anisotropic silicates act as larger pillars. Method o f preparing such materials is described, together with their porous properties. The mesoporous material from a precursory hectorite synthesized at 15OoC has a total specific surface area of 848 m2g-’, a pore volume of 0.98 cm3g-l and an pore average diameter of 46 1, values which are significantly higher than those of conventional pillared clays. INTRODUCTION Smectite minerals, which consist of two-dimensional silicate layers separated by hydrated exchangeable cations, swell with a variety of molecules and form intercalated complexes. Metal-oxide pillared clays, prepared from smectites and polynuclear metal complex cations, have attracted considerable attention as new types o f molecular sieves, which are structurally different from zeolites. These materials offer new possibilities as catalysts and adsorbents [ I ] . Recently a new hydrothermal method of producing silicate-bearing hectorites was proposed [2.3]. On dehydration of interlayer water these synthetic hectorites converted to porous materials with mesopores and micropores [4].Organophil ic hectorites prepared from silicate-bearing hectorites and a dialkyl dimethyl quaternary ammonium chloride showed attractive rheological properties in organic solvents [5]. Upon removal of organic materials by heating, they transformed into novel mesoporous materials characterized by extremely large specific surface areas and high thermal stability. The present paper is concerned with these mesoporous materials produced from hydrothermally synthesized silicate-bearing hectorites. EXPERIMENTAL
82 K. Torii. T. Iwasaki, Y. Onodera and K. Hatakeda
Preparation
of
mesoporous m a t e r i a l s
S i l i c a t e - b e a r i n g h e c t o r i t e s having d i f f e r e n t l a y e r charge and i n t e r l a y e r s i 1 i c a t e content were synthesized hydrothermal l y a t 1 25-300°C under autogeneous water vapor pressure f o r 2 h from a s l u r r y o f Si:Mg:Li:Na=4.00:2.70:0.30:0.35. O r g a n o p h i l i c h e c t o r i t e s were prepared from t h e s y n t h e t i c s i l i c a t e - b e a r i n g h e c t o r i t e s and a d i a l k y l dimethyl quaternary amnonium (ANK1A) c h l o r i d e c o n t a i n i n g 75% octadecyl,
24% hexadecyl, and 1 % octadecenyl groups as a l k y l groups ( t r a d e
name: Arquad 2HT-75,
L i o n Akzo C o . , L t d . ) .
Both h e c t o r i t e s and quaternary ammonium
were d i s s o l v e d i n hot water (8OoC) s e p a r a t e l y t o g i v e a c o n c e n t r a t i o n o f 2%. and then mixed, s t i r r e d , and b o i l e d f o r 30-60 min. A f t e r f i l t r a t i o n and washing w i t h warm water,
the o r g a n o p h i l i c h e c t o r i t e s were d r i e d and powdered. The amounts o f
quaternary ammonium e q u i v a l e n t t o t h e amount o f methylene b l u e adsorbed were used f o r r e s p e c t i v e h e c t o r i t e s except the value o f 0.96 meq g-l f o r samples H-01 and H-02. Mesoporous m a t e r i a l s were prepared from o r g a n o p h i l i c h e c t o r i t e s by h e a t i n g a t 300-900°C
i n the atmosphere f o r 1 h.
A n a l y t i c a l procedures S p e c i f i c surface areas, pore volumes, pore diameters and pore s i z e d i s t r i b u t i o n s were c a l c u l a t e d from the n i t r o g e n adsorption-desorption isotherms f o r 1 h using Micromeritics
a t -196OC on t h e samples heated a t 300'-900°C
a c c e l e r a t e d s u r f a c e area and porosimetry ASAP 2400. The micropore volume and mesopore surface area o f samples were obtained by T-plot method [6]. The diameter o f mesopores i s designated more than -20
8.
The amounts o f organic m a t e r i a l
present i n the h e c t o r i t e s were measured by thermal g r a v i m e t r i c a n a l y s i s u s i n g a Rigaku Thermof l e x thermal balance. X-ray powder d i f f r a c t i o n (XRD) analyses were c a r r i e d o u t w i t h a Rigaku d i f f r a c t o m e t e r
(RAD-I1 B) u s i n g monochromatized CuKa
r a d i a t i o n . Methylene b l u e (ME) a d s o r p t i o n c a p a c i t i e s were measured t o e v a l u a t e c a t i o n exchange c a p a c i t i e s o f h e c t o r i t e s . RESULTS AND DISCUSSION Properties
silicate-bearing hectorites
and
organophilic hectorites
The e f f e c t o f hydrothermal s y n t h e s i s temperature on MB adsorbed,
interlayer
s i l i c a t e content and 001 spacing o f s i l i c a t e - b e a r i n g h e c t o r i t e i s shown i n Table -1 . 1. The MB a d s o r p t i o n increased from 0.28 t o 1.16 meq g w i t h increasing temperature i n the range 125°-3000C. whereas the i n t e r l a y e r s i l i c a t e content decreased from 64 t o 16 wt%. The change i n i n t e r l a y e r s i l i c a t e content
appeared
t o harmonize w i t h t h a t o f Langmuir s p e c i f i c surface area o f the s y n t h e t i c h e c t o r i t e s shown i n Table 3. As expected f o r a smectite, samples H-01-H-15
the layers o f s i x
expanded r e a d i l y on ethylene g l y c o l a t i o n ; however, abnormally
l a r g e 001 spacings f o r f o u r samples H-01-H-10
were observed i n c o n t r a s t t o
Mesoporous Materials Produced from Hectorites 83
Table 1. Effect of hydrothermal temperature on the methylene blue (MB) adsorbed, interlayer silicate content and 001 spacing of silicate-bearing hectorites Synthesis temp. OC
Samp I e H-01 H-02 H-05 H-10 H-12 H-15
MB adsorbed meq g-1
125 150 180 200 225 300
0.28 0.70 0.84 0.96 1. 08 1. 16
d (001)
Interlayer si I icatea wt. %
/a EG~
Air dried
64 48 34 29 18 16
18.8 17.4 17.3 14.3 13.2 13.6
23.9 20.0 18.5 17.4 17. 1 17. 1
acalculated from the dehydration amount of low temperature structural water between 300-650°C, bEthylene glycolated.
the spacing of 17 for the Na-smectites [71. Both 001 spacings of air dried and of ethylene glycolated hectorites decreased with increasing synthesis temperature, fitting well with the change in interlayer silicate content. These results suggest that hydrothermal products revealed smectite-like properties gradually and lost porous property as the synthesis temperature increased. The silicate-bearing hectorite is probably a kind of unstable smectite mineral. Sample yield, 001 spacings and content of intercalated AMQA cation of organophilic hectorites are shown in Table 2. The sample yield based on the precursory synthetic hectorite was 86-93%; thus the amount of AMQA cation in the organophilic hectorites showed slightly larger values compared with the expected amount. I n the samples OH-05-OH-15, the amount o f intercalated AMQA cation corresponded to the layer charge. Basal spacings of organophilic hectorites expanded by intercalation of AMQA cations, although those of three samples OH01-OH-05 were obscure. Table 2. Yield, 001 spacings, layer charge and dialkyl dimethyl quaternary ammonium (AMQA) cation content for the organophilic hectorites ~~
d (001)
Sample
Yielda 96
R
Air dried
Layer chargeb eq/Olo (OH) 2 A
AMQA cat ion eq/Ol (OH) Used Contentc C B
C/B
C/A
0.45 0.44 0.38 0.43 0.46 0.49
118 118 I11 107 104 106
408 163
Rate %
~~
OH-01 OH-02 OH-05
91
OH-I2 OH-I5
90 93 93
OH-I0
86 92
uc uc uc
38 27.8 31.3
0.13 0.32 0.38 0.43 0.46 0.49
0.53 0.52 0.42 0.46 0.48 0.52
111
107 104 106
aCalculate$ based on the precursory synthetic hectorite, bCalculated from MB adsorbed, Calculated from thermogravimetric data.
84 K. Torii.
T.Iwasaki. Y . Onodera and K. Hatakeda
Porous characteristics of the mesoporous material OH-02-600 Typical nitrogen adsorption-desorption isotherms at liquid nitrogen temperature for the mesoporous material OH-02-600 and its precursory hectorite H-02-300 are shown in Fig. 1. The isotherm of H-02-300 is of type I in the classification of Brunauer, Deming and Teller [8]and possesses a small hysteresis loop indicating that H-02-300 has both micropores and mesopores. Meanwhile the isotherm of OH-02-600 is of type IV and the hysteresis loop is of type H2 according to the manual of International Union of Pure and Applied Chemistry [9]. Some corpuscular systems tend to give H2 loops, but in these cases the distribution of pore size and shape is not well defined [lo]. The difference between the type IV for OH-02-600 and type I for H-02-300 reflects the larger interlayer spacing in the former materials. Type I and type I V isotherms were observed respectively for the AI2O3-pillared clay [l I] and Ti02-pillared clay [12.131. The most important difference between the mesoporous material OH-02-600 and the Ti0 -pillared clay is the considerably larger nitrogen amount adsorbed on 2 the former material. As shown in Table 3, the pore volume increased from 0.228 to 0.984 cm3g-' and the average pore diameter extended from 17. 1 to 46.4 8, by the transformation from H-02-300 to OH-02-600. The pore volume of OH-02-600 is fouror five-fold in contrast with Ti02-pillared clay (0.190-0.270 cm3g-') [12,131. These results ndicate that the mesoporous material OH-02-600 having exceptionally large pores was produced from the synthetic silicate-bearing hectorite H-02 by the intercalat on of AMQA cation and the removal of organic materials.
'1,
012
0:4
016
0:8
Relative pressure / P/PO
Fig. 1. Nitrogen adsorption-desorption isotherms at -196OC for the mesoporous material OH-02-600 and its precursory synthetic hectorite H-02-300. Open symbols: adsorption, Solid symbols: desorption.
Mesoporous Materials Produced from Hectorites 85
0
0 c X
?
2
5 . Q
ii
D
Pore diameter I Fig. 2.
i
Pore s i z e d i s t r i b u t i o n f o r t h e mesoporous m a t e r i a l OH-02-600.
F i g u r e 2 shows t h e pore s i z e d i s t r i b u t i o n s d e r i v e d from t h e d e s o r p t i o n branch o f the isotherm f o r t h e mesoporous m a t e r i a l OH-02-600.
appears t o be i n pores o f about 37
8.
Most o f t h e pore volume
The pore s i z e o f the mesoporous m a t e r i a l
OH-02-600 i s about t w i c e t h a t o f T i 0 2 - p i l l a r e d c l a y [ I l l . Pore volumes o f h e a t - t r e a t e d mesoporous m a t e r i a l OH-02 and i t s p r e c u r s o r y s y n t h e t i c h e c t o r i t e H-02 as a f u n c t i o n o f temperature a r e shown i n Fig. 3. The m a t e r i a l OH-02 was s t a b l e a f t e r being h e a t - t r e a t e d t o 6OO0C, a t which temperat u r e the volume s t a r t e d t o decrease. On t h e o t h e r hand, the pore volume o f t h e precursory h e c t o r i t e H-02 s t a r t e d t o decrease g r a d u a l l y a t 40OoC. As shown i n Fig. 3, t h e pore volume increased w i t h i n c r e a s i n g temperature i n the range of 1.0
-3
0.5
-
4
t 0
P
U
H-02
Heat-treatment temperature I @C Fig. 3. Pore volumes o f the mesoporous m a t e r i a l OH-02 and i t s precursory s y n t h e t i c h e c t o r i t e H-02 as a f u n c t i o n o f heat-treatment temperature.
86 K. Torii, T. Iwasaki, Y. Onodera and K. Hatakeda
300'-600'C.
T h i s f i n d i n g can be explained by the removal o f i n t e r l a y e r o r g a n i c
m a t e r i a l s by heat-treatment.
The sample c o l o r change from b l a c k t o w h i t e supports
t h i s explanation. The pore volume and s p e c i f i c surface area reached maximum (pore 2 -1 volume of 0.984 cm3g-l and s p e c i f i c surface area o f 848111g ) a t 600'C. The m a t e r i a l OH-02 showed decreases i n pore volume w i t h i n c r e a s i n g temperature from 600'
C t o 8OO0C, and r e t a i n e d a pore volume o f 0.345 cm3g-'
o f 255 m2g-l
-Effect
and a s u r f a c e area
a t 80OoC.
o f s y n t h e s i s temperature o f the p r e c u r s o r y h e c t o r i t e s on t h e porous
p r o p e r t i e s o f t h e mesoporous m a t e r i a l s Table 3 shows the s p e c i f i c surface areas, pore volumes and average pore diameter f o r several mesoporous m a t e r i a l s and t h e i r precursory s y n t h e t i c h e c t o r i t e s . The BET s p e c i f i c surface areas o f t h e mesoporous m a t e r i a l s d e r i v e d from t h e s i l i c a t e - b e a r i n g h e c t o r i t e s synthesized a t 150'-300°C t o 229 m2g-l
decreased from 848
w i t h i n c r e a s i n g synthesis temperature. The amount o f i n t e r l a y e r
s i l i c a t e s may r e f l e c t upon these s p e c i f i c surface areas (Fig. 4). The pore volumes a l s o decreased i n the same manner as the s p e c i f i c surface areas. The mesoporous m a t e r i a l s produced from the s i l i c a t e - b e a r i n g h e c t o r i t e s synthesized above 2OO0C possessed mesopores and micropores. This may be due t o t h e small content o f i n t e r l a y e r s i l i c a t e s . The s p e c i f i c surface area and pore volume o f t h e m a t e r i a l OH-01-600 whose precursory h e c t o r i t e was synthesized a t 125OC showed
Table 3. S p e c i f i c surface areas (SSA), pore volumes (PV) and average pore diameter (APD) f o r several mesoporous m a t e r i a l s and t h e i r precursory s y n t h e t i c hectorites
Samplea
H-01-300* OH-01 -600 H-02-300* OH-02-600 H-05-300* OH-05-600 H-lO-300* OH- 10-600 H- 1 2-300* OH-1 2-600 H-15-300* OH- 15-600
SSAb 2 -1 mg
618 738 532 848 534 560 488 410 318 261 269 229
Whole pore PV APD 3 -1 51 cm g A
0.243 0. 779 0. 228 0.984 0. 230 0. 622 0. 249 0. 598 0. 162 0. 243 0. 154 0. 255
15.7 42. 2 17. 1 46.4 17. 2 44. 4 20. 4 58. 3 20.4 37. 2 22.9 44. 5
Mesopore PV 3 -1 cm g B
0. 142 0. 776 0. 147 0.984 0..151 0. 622 0. 168 0. 584 0. 115 0. 194 0. 113 0. 231
Micropore PV cm g
-'
0.101 0. 003 0. 082 0.000 0. 078 0.000 0. 081 0. 014 0.048 0.049 0.040 0.024
Mesopore ratio B/A
0. 58 1. 00 0. 67 1.00 0. 66 1 . 00 0. 68 0. 98 0. 71 0. 80 0. 73 0. 91
Increment Pore vo 1ume ratio'
3. 21 4. 32 2. 70 2. 40
1. 50 1. 66
aLast t h r e e f i g u r e s designate the heat-treatment temperature f o r 1 h, bCalculated by BET equation f o r the samples unless o t h e y i s e s p e c i f i e d , and by Langmuir equation f o r the samples designated w i t h Pore volume r a t i o o f the mesoporous m a t e r i a l t o i t s precursory s y n t h e t i c h e c t o r i t e s .
*,
Mesoporous Materials Produced from Hectorites 87
lnteriayer silicate content / wt.%
Fig. 4. Specific surface areas for several mesoporous materials as a function of interlayer silicate content. slightly smaller values compared with the material OH-02-600. This may reflect a combination of low layer charge and high interlayer silicate content. The average pore diameter of the mesoporous materials changed from 42. 2 to 58. 3 & between the synthetic temperature range of 125°-3000C. The pore diameter of 46. 4 & for the material OH-02-600 calculated from (4 pore volume / specific surface area) is slightly greater than the 37 8 obtained from the pore-size distribution as indicated in F i g . 2. The expected layer structure change from the precursory silicate-bearing hectorites to the mesoporous materials is represented schematically in Fig. 5. In the silicate-bearing hectorites, anisotropic platy silicates exist lying flat between the silicate layers: they therefore give smectite-like basal spacings (Table 1 ) . Layers of silicate-bearing hectorites expand by the intercalation of the lengthwise AMQA cation and simultaneously the anisotropic silicates stand normally to the layer. Ultimately the mesoporous materials can be formed by the removal of organic materials. Rearranged interlayer anisotropic silicates act as
I
11
TI---
ir
I
intercalation of AMQA cation
Heat-treatme
a
0
Siilcate-bearing hectorlte
Organophilic hectorlte
Mesoporous materlai
Fig. 5. Schematic of the proposed formation of mesoporous materials from silicate-bearing hectorites.
88 K. Torii, T. Iwasaki, Y. Onodera and K. Hatakeda
long p i l l a r s i n the mesoporous m a t e r i a l s which u n t i l now had never been reported. CONCLUSION 1.
H e c t o r i t e s which include a n i s o t r o p i c p l a t y s i l i c a t e s i n the i n t e r l a y e r s c o u l d be hydrothermally synthesized. Layer charge, s i l i c a t e content, etc. c o u l d be c o n t r o l l e d by the synthesis conditions.
2. Layers o f s i l i c a t e - b e a r i n g h e c t o r i t e s were expanded by the i n t e r c a l a t i o n o f the lengthwise a l k y l quaternary ammonium c a t i o n and simultaneously t h e i n t e r l a y e r a n i s o t r o p i c s i l i c a t e s stood normally t o t h e layer. 3. Mesoporous m a t e r i a l s i n which rearranged i n t e r l a y e r a n i s o t r o p i c s i l i c a t e s a c t as long p i l l a r s were produced as the heat- t r e a t e d products o f o r g a n o p h i l i c h e c t o r i tes. 4. Porous p r o p e r t i e s o f the mesoporous m a t e r i a l s w e r e mainly c o n t r o l l e d by t h e s i l i c a t e content and h e a t - t r e a t i n g conditio n s . 5. The mesoporous m a t e r i a l s produced from a precursory h e c t o r i t e synthesized a t 15OoC had a t o t a l s p e c i f i c surface area o f 848 m2g-l, cm3g-l and an average pore diameter o f 46
8,
a pore volume o f 0.98
values which a r e s i g n i f i c a n t l y
h i g her than those o f conventional p i l l a r e d clays. ACKNOWLEDGMENT The authors wish t o express t h e i r sincere thanks t o Prof. M. Shimada o f t h e F a c u l t y o f Engineering, Tohoku U n i v e r s i t y , f o r h i s h e l p f u l suggestions. REFERENCES
1 2 3 4 5 6 7 8 9 10 11
12 13
J. Shabtai, M. Rose11 and M. Tokarz, Clays Clay Miner., 32(1984)99. T. Iwasaki and K. T o r i i , Ganko, 83(1988) 160. K. T o r i i and T. Iwasaki, Chem. L e t t . , (1988) 2045. K. T o r i i , T. Iwasaki, Y. Onodera and M. Shimada, Nippon Kagakukaishi, (1989), 345. T. Iwasaki, Y. Onodera and K. T o r i i . Clays Clay Miner., 37 (1989) 248. 6.C. Lippens and J. H. de Boer, J.Catal., 4(1965)319. G. Lagaly, Clay Miner., 16(1981) 1. S. Brunauer, L. S. Deming, W. Deming and E. T e l l e r , J. Amer.Chem. Soc., 62 ( 1 940) 1723. K. S. W. Sing e t a l . , Pure Appl. Chem., 57(1985)603. S. J. G r e w and K. S. W Sing, Adsorption, surface area and p o r o s i t y (Second E d i t i o n ) , Academic Press, London, 1982, p. 287. J. Shabtai, F. E. Massoth, M. Tokarz, G.M. Tsai and J. McCauley, i n G. E r t l (Ed), Proc. 8 t h I n t e r n a t . Congress C a t a l y s i s Vol. 4 (1984), Verlag Chemie. B e r l i n , P735. J. Sterte, Clays Clay Miner., 34 (1986) 658. S. Yamanaka, T. Nishihara and M. H a t t o r i , Mat. Chem. Phy., 1 7 (1987187.
Mesoporous Materials Produced from Hydrothermally Synthesized Hectorites
Torii, T. Iwasaki, Y. Onodera and K. Hatakeda Government Industrial Research Institute, Tohoku, Nigatake 4-2-1, Sendai 983, Japan K.
Miyagino-ku,
ABSTRACT Novel mesoporous materials having exceptionally large pores were produced from hydrothermally synthesized silicate-bearing hectorites. Experiments suggest that interlayer anisotropic silicates act as larger pillars. Method o f preparing such materials is described, together with their porous properties. The mesoporous material from a precursory hectorite synthesized at 15OoC has a total specific surface area of 848 m2g-’, a pore volume of 0.98 cm3g-l and an pore average diameter of 46 1, values which are significantly higher than those of conventional pillared clays. INTRODUCTION Smectite minerals, which consist of two-dimensional silicate layers separated by hydrated exchangeable cations, swell with a variety of molecules and form intercalated complexes. Metal-oxide pillared clays, prepared from smectites and polynuclear metal complex cations, have attracted considerable attention as new types o f molecular sieves, which are structurally different from zeolites. These materials offer new possibilities as catalysts and adsorbents [ I ] . Recently a new hydrothermal method of producing silicate-bearing hectorites was proposed [2.3]. On dehydration of interlayer water these synthetic hectorites converted to porous materials with mesopores and micropores [4].Organophil ic hectorites prepared from silicate-bearing hectorites and a dialkyl dimethyl quaternary ammonium chloride showed attractive rheological properties in organic solvents [5]. Upon removal of organic materials by heating, they transformed into novel mesoporous materials characterized by extremely large specific surface areas and high thermal stability. The present paper is concerned with these mesoporous materials produced from hydrothermally synthesized silicate-bearing hectorites. EXPERIMENTAL
82 K. Torii. T. Iwasaki, Y. Onodera and K. Hatakeda
Preparation
of
mesoporous m a t e r i a l s
S i l i c a t e - b e a r i n g h e c t o r i t e s having d i f f e r e n t l a y e r charge and i n t e r l a y e r s i 1 i c a t e content were synthesized hydrothermal l y a t 1 25-300°C under autogeneous water vapor pressure f o r 2 h from a s l u r r y o f Si:Mg:Li:Na=4.00:2.70:0.30:0.35. O r g a n o p h i l i c h e c t o r i t e s were prepared from t h e s y n t h e t i c s i l i c a t e - b e a r i n g h e c t o r i t e s and a d i a l k y l dimethyl quaternary amnonium (ANK1A) c h l o r i d e c o n t a i n i n g 75% octadecyl,
24% hexadecyl, and 1 % octadecenyl groups as a l k y l groups ( t r a d e
name: Arquad 2HT-75,
L i o n Akzo C o . , L t d . ) .
Both h e c t o r i t e s and quaternary ammonium
were d i s s o l v e d i n hot water (8OoC) s e p a r a t e l y t o g i v e a c o n c e n t r a t i o n o f 2%. and then mixed, s t i r r e d , and b o i l e d f o r 30-60 min. A f t e r f i l t r a t i o n and washing w i t h warm water,
the o r g a n o p h i l i c h e c t o r i t e s were d r i e d and powdered. The amounts o f
quaternary ammonium e q u i v a l e n t t o t h e amount o f methylene b l u e adsorbed were used f o r r e s p e c t i v e h e c t o r i t e s except the value o f 0.96 meq g-l f o r samples H-01 and H-02. Mesoporous m a t e r i a l s were prepared from o r g a n o p h i l i c h e c t o r i t e s by h e a t i n g a t 300-900°C
i n the atmosphere f o r 1 h.
A n a l y t i c a l procedures S p e c i f i c surface areas, pore volumes, pore diameters and pore s i z e d i s t r i b u t i o n s were c a l c u l a t e d from the n i t r o g e n adsorption-desorption isotherms f o r 1 h using Micromeritics
a t -196OC on t h e samples heated a t 300'-900°C
a c c e l e r a t e d s u r f a c e area and porosimetry ASAP 2400. The micropore volume and mesopore surface area o f samples were obtained by T-plot method [6]. The diameter o f mesopores i s designated more than -20
8.
The amounts o f organic m a t e r i a l
present i n the h e c t o r i t e s were measured by thermal g r a v i m e t r i c a n a l y s i s u s i n g a Rigaku Thermof l e x thermal balance. X-ray powder d i f f r a c t i o n (XRD) analyses were c a r r i e d o u t w i t h a Rigaku d i f f r a c t o m e t e r
(RAD-I1 B) u s i n g monochromatized CuKa
r a d i a t i o n . Methylene b l u e (ME) a d s o r p t i o n c a p a c i t i e s were measured t o e v a l u a t e c a t i o n exchange c a p a c i t i e s o f h e c t o r i t e s . RESULTS AND DISCUSSION Properties
silicate-bearing hectorites
and
organophilic hectorites
The e f f e c t o f hydrothermal s y n t h e s i s temperature on MB adsorbed,
interlayer
s i l i c a t e content and 001 spacing o f s i l i c a t e - b e a r i n g h e c t o r i t e i s shown i n Table -1 . 1. The MB a d s o r p t i o n increased from 0.28 t o 1.16 meq g w i t h increasing temperature i n the range 125°-3000C. whereas the i n t e r l a y e r s i l i c a t e content decreased from 64 t o 16 wt%. The change i n i n t e r l a y e r s i l i c a t e content
appeared
t o harmonize w i t h t h a t o f Langmuir s p e c i f i c surface area o f the s y n t h e t i c h e c t o r i t e s shown i n Table 3. As expected f o r a smectite, samples H-01-H-15
the layers o f s i x
expanded r e a d i l y on ethylene g l y c o l a t i o n ; however, abnormally
l a r g e 001 spacings f o r f o u r samples H-01-H-10
were observed i n c o n t r a s t t o
Mesoporous Materials Produced from Hectorites 83
Table 1. Effect of hydrothermal temperature on the methylene blue (MB) adsorbed, interlayer silicate content and 001 spacing of silicate-bearing hectorites Synthesis temp. OC
Samp I e H-01 H-02 H-05 H-10 H-12 H-15
MB adsorbed meq g-1
125 150 180 200 225 300
0.28 0.70 0.84 0.96 1. 08 1. 16
d (001)
Interlayer si I icatea wt. %
/a EG~
Air dried
64 48 34 29 18 16
18.8 17.4 17.3 14.3 13.2 13.6
23.9 20.0 18.5 17.4 17. 1 17. 1
acalculated from the dehydration amount of low temperature structural water between 300-650°C, bEthylene glycolated.
the spacing of 17 for the Na-smectites [71. Both 001 spacings of air dried and of ethylene glycolated hectorites decreased with increasing synthesis temperature, fitting well with the change in interlayer silicate content. These results suggest that hydrothermal products revealed smectite-like properties gradually and lost porous property as the synthesis temperature increased. The silicate-bearing hectorite is probably a kind of unstable smectite mineral. Sample yield, 001 spacings and content of intercalated AMQA cation of organophilic hectorites are shown in Table 2. The sample yield based on the precursory synthetic hectorite was 86-93%; thus the amount of AMQA cation in the organophilic hectorites showed slightly larger values compared with the expected amount. I n the samples OH-05-OH-15, the amount o f intercalated AMQA cation corresponded to the layer charge. Basal spacings of organophilic hectorites expanded by intercalation of AMQA cations, although those of three samples OH01-OH-05 were obscure. Table 2. Yield, 001 spacings, layer charge and dialkyl dimethyl quaternary ammonium (AMQA) cation content for the organophilic hectorites ~~
d (001)
Sample
Yielda 96
R
Air dried
Layer chargeb eq/Olo (OH) 2 A
AMQA cat ion eq/Ol (OH) Used Contentc C B
C/B
C/A
0.45 0.44 0.38 0.43 0.46 0.49
118 118 I11 107 104 106
408 163
Rate %
~~
OH-01 OH-02 OH-05
91
OH-I2 OH-I5
90 93 93
OH-I0
86 92
uc uc uc
38 27.8 31.3
0.13 0.32 0.38 0.43 0.46 0.49
0.53 0.52 0.42 0.46 0.48 0.52
111
107 104 106
aCalculate$ based on the precursory synthetic hectorite, bCalculated from MB adsorbed, Calculated from thermogravimetric data.
84 K. Torii.
T.Iwasaki. Y . Onodera and K. Hatakeda
Porous characteristics of the mesoporous material OH-02-600 Typical nitrogen adsorption-desorption isotherms at liquid nitrogen temperature for the mesoporous material OH-02-600 and its precursory hectorite H-02-300 are shown in Fig. 1. The isotherm of H-02-300 is of type I in the classification of Brunauer, Deming and Teller [8]and possesses a small hysteresis loop indicating that H-02-300 has both micropores and mesopores. Meanwhile the isotherm of OH-02-600 is of type IV and the hysteresis loop is of type H2 according to the manual of International Union of Pure and Applied Chemistry [9]. Some corpuscular systems tend to give H2 loops, but in these cases the distribution of pore size and shape is not well defined [lo]. The difference between the type IV for OH-02-600 and type I for H-02-300 reflects the larger interlayer spacing in the former materials. Type I and type I V isotherms were observed respectively for the AI2O3-pillared clay [l I] and Ti02-pillared clay [12.131. The most important difference between the mesoporous material OH-02-600 and the Ti0 -pillared clay is the considerably larger nitrogen amount adsorbed on 2 the former material. As shown in Table 3, the pore volume increased from 0.228 to 0.984 cm3g-' and the average pore diameter extended from 17. 1 to 46.4 8, by the transformation from H-02-300 to OH-02-600. The pore volume of OH-02-600 is fouror five-fold in contrast with Ti02-pillared clay (0.190-0.270 cm3g-') [12,131. These results ndicate that the mesoporous material OH-02-600 having exceptionally large pores was produced from the synthetic silicate-bearing hectorite H-02 by the intercalat on of AMQA cation and the removal of organic materials.
'1,
012
0:4
016
0:8
Relative pressure / P/PO
Fig. 1. Nitrogen adsorption-desorption isotherms at -196OC for the mesoporous material OH-02-600 and its precursory synthetic hectorite H-02-300. Open symbols: adsorption, Solid symbols: desorption.
Mesoporous Materials Produced from Hectorites 85
0
0 c X
?
2
5 . Q
ii
D
Pore diameter I Fig. 2.
i
Pore s i z e d i s t r i b u t i o n f o r t h e mesoporous m a t e r i a l OH-02-600.
F i g u r e 2 shows t h e pore s i z e d i s t r i b u t i o n s d e r i v e d from t h e d e s o r p t i o n branch o f the isotherm f o r t h e mesoporous m a t e r i a l OH-02-600.
appears t o be i n pores o f about 37
8.
Most o f t h e pore volume
The pore s i z e o f the mesoporous m a t e r i a l
OH-02-600 i s about t w i c e t h a t o f T i 0 2 - p i l l a r e d c l a y [ I l l . Pore volumes o f h e a t - t r e a t e d mesoporous m a t e r i a l OH-02 and i t s p r e c u r s o r y s y n t h e t i c h e c t o r i t e H-02 as a f u n c t i o n o f temperature a r e shown i n Fig. 3. The m a t e r i a l OH-02 was s t a b l e a f t e r being h e a t - t r e a t e d t o 6OO0C, a t which temperat u r e the volume s t a r t e d t o decrease. On t h e o t h e r hand, the pore volume o f t h e precursory h e c t o r i t e H-02 s t a r t e d t o decrease g r a d u a l l y a t 40OoC. As shown i n Fig. 3, t h e pore volume increased w i t h i n c r e a s i n g temperature i n the range of 1.0
-3
0.5
-
4
t 0
P
U
H-02
Heat-treatment temperature I @C Fig. 3. Pore volumes o f the mesoporous m a t e r i a l OH-02 and i t s precursory s y n t h e t i c h e c t o r i t e H-02 as a f u n c t i o n o f heat-treatment temperature.
86 K. Torii, T. Iwasaki, Y. Onodera and K. Hatakeda
300'-600'C.
T h i s f i n d i n g can be explained by the removal o f i n t e r l a y e r o r g a n i c
m a t e r i a l s by heat-treatment.
The sample c o l o r change from b l a c k t o w h i t e supports
t h i s explanation. The pore volume and s p e c i f i c surface area reached maximum (pore 2 -1 volume of 0.984 cm3g-l and s p e c i f i c surface area o f 848111g ) a t 600'C. The m a t e r i a l OH-02 showed decreases i n pore volume w i t h i n c r e a s i n g temperature from 600'
C t o 8OO0C, and r e t a i n e d a pore volume o f 0.345 cm3g-'
o f 255 m2g-l
-Effect
and a s u r f a c e area
a t 80OoC.
o f s y n t h e s i s temperature o f the p r e c u r s o r y h e c t o r i t e s on t h e porous
p r o p e r t i e s o f t h e mesoporous m a t e r i a l s Table 3 shows the s p e c i f i c surface areas, pore volumes and average pore diameter f o r several mesoporous m a t e r i a l s and t h e i r precursory s y n t h e t i c h e c t o r i t e s . The BET s p e c i f i c surface areas o f t h e mesoporous m a t e r i a l s d e r i v e d from t h e s i l i c a t e - b e a r i n g h e c t o r i t e s synthesized a t 150'-300°C t o 229 m2g-l
decreased from 848
w i t h i n c r e a s i n g synthesis temperature. The amount o f i n t e r l a y e r
s i l i c a t e s may r e f l e c t upon these s p e c i f i c surface areas (Fig. 4). The pore volumes a l s o decreased i n the same manner as the s p e c i f i c surface areas. The mesoporous m a t e r i a l s produced from the s i l i c a t e - b e a r i n g h e c t o r i t e s synthesized above 2OO0C possessed mesopores and micropores. This may be due t o t h e small content o f i n t e r l a y e r s i l i c a t e s . The s p e c i f i c surface area and pore volume o f t h e m a t e r i a l OH-01-600 whose precursory h e c t o r i t e was synthesized a t 125OC showed
Table 3. S p e c i f i c surface areas (SSA), pore volumes (PV) and average pore diameter (APD) f o r several mesoporous m a t e r i a l s and t h e i r precursory s y n t h e t i c hectorites
Samplea
H-01-300* OH-01 -600 H-02-300* OH-02-600 H-05-300* OH-05-600 H-lO-300* OH- 10-600 H- 1 2-300* OH-1 2-600 H-15-300* OH- 15-600
SSAb 2 -1 mg
618 738 532 848 534 560 488 410 318 261 269 229
Whole pore PV APD 3 -1 51 cm g A
0.243 0. 779 0. 228 0.984 0. 230 0. 622 0. 249 0. 598 0. 162 0. 243 0. 154 0. 255
15.7 42. 2 17. 1 46.4 17. 2 44. 4 20. 4 58. 3 20.4 37. 2 22.9 44. 5
Mesopore PV 3 -1 cm g B
0. 142 0. 776 0. 147 0.984 0..151 0. 622 0. 168 0. 584 0. 115 0. 194 0. 113 0. 231
Micropore PV cm g
-'
0.101 0. 003 0. 082 0.000 0. 078 0.000 0. 081 0. 014 0.048 0.049 0.040 0.024
Mesopore ratio B/A
0. 58 1. 00 0. 67 1.00 0. 66 1 . 00 0. 68 0. 98 0. 71 0. 80 0. 73 0. 91
Increment Pore vo 1ume ratio'
3. 21 4. 32 2. 70 2. 40
1. 50 1. 66
aLast t h r e e f i g u r e s designate the heat-treatment temperature f o r 1 h, bCalculated by BET equation f o r the samples unless o t h e y i s e s p e c i f i e d , and by Langmuir equation f o r the samples designated w i t h Pore volume r a t i o o f the mesoporous m a t e r i a l t o i t s precursory s y n t h e t i c h e c t o r i t e s .
*,
Mesoporous Materials Produced from Hectorites 87
lnteriayer silicate content / wt.%
Fig. 4. Specific surface areas for several mesoporous materials as a function of interlayer silicate content. slightly smaller values compared with the material OH-02-600. This may reflect a combination of low layer charge and high interlayer silicate content. The average pore diameter of the mesoporous materials changed from 42. 2 to 58. 3 & between the synthetic temperature range of 125°-3000C. The pore diameter of 46. 4 & for the material OH-02-600 calculated from (4 pore volume / specific surface area) is slightly greater than the 37 8 obtained from the pore-size distribution as indicated in F i g . 2. The expected layer structure change from the precursory silicate-bearing hectorites to the mesoporous materials is represented schematically in Fig. 5. In the silicate-bearing hectorites, anisotropic platy silicates exist lying flat between the silicate layers: they therefore give smectite-like basal spacings (Table 1 ) . Layers of silicate-bearing hectorites expand by the intercalation of the lengthwise AMQA cation and simultaneously the anisotropic silicates stand normally to the layer. Ultimately the mesoporous materials can be formed by the removal of organic materials. Rearranged interlayer anisotropic silicates act as
I
11
TI---
ir
I
intercalation of AMQA cation
Heat-treatme
a
0
Siilcate-bearing hectorlte
Organophilic hectorlte
Mesoporous materlai
Fig. 5. Schematic of the proposed formation of mesoporous materials from silicate-bearing hectorites.
88 K. Torii, T. Iwasaki, Y. Onodera and K. Hatakeda
long p i l l a r s i n the mesoporous m a t e r i a l s which u n t i l now had never been reported. CONCLUSION 1.
H e c t o r i t e s which include a n i s o t r o p i c p l a t y s i l i c a t e s i n the i n t e r l a y e r s c o u l d be hydrothermally synthesized. Layer charge, s i l i c a t e content, etc. c o u l d be c o n t r o l l e d by the synthesis conditions.
2. Layers o f s i l i c a t e - b e a r i n g h e c t o r i t e s were expanded by the i n t e r c a l a t i o n o f the lengthwise a l k y l quaternary ammonium c a t i o n and simultaneously t h e i n t e r l a y e r a n i s o t r o p i c s i l i c a t e s stood normally t o t h e layer. 3. Mesoporous m a t e r i a l s i n which rearranged i n t e r l a y e r a n i s o t r o p i c s i l i c a t e s a c t as long p i l l a r s were produced as the heat- t r e a t e d products o f o r g a n o p h i l i c h e c t o r i tes. 4. Porous p r o p e r t i e s o f the mesoporous m a t e r i a l s w e r e mainly c o n t r o l l e d by t h e s i l i c a t e content and h e a t - t r e a t i n g conditio n s . 5. The mesoporous m a t e r i a l s produced from a precursory h e c t o r i t e synthesized a t 15OoC had a t o t a l s p e c i f i c surface area o f 848 m2g-l, cm3g-l and an average pore diameter o f 46
8,
a pore volume o f 0.98
values which a r e s i g n i f i c a n t l y
h i g her than those o f conventional p i l l a r e d clays. ACKNOWLEDGMENT The authors wish t o express t h e i r sincere thanks t o Prof. M. Shimada o f t h e F a c u l t y o f Engineering, Tohoku U n i v e r s i t y , f o r h i s h e l p f u l suggestions. REFERENCES
1 2 3 4 5 6 7 8 9 10 11
12 13
J. Shabtai, M. Rose11 and M. Tokarz, Clays Clay Miner., 32(1984)99. T. Iwasaki and K. T o r i i , Ganko, 83(1988) 160. K. T o r i i and T. Iwasaki, Chem. L e t t . , (1988) 2045. K. T o r i i , T. Iwasaki, Y. Onodera and M. Shimada, Nippon Kagakukaishi, (1989), 345. T. Iwasaki, Y. Onodera and K. T o r i i . Clays Clay Miner., 37 (1989) 248. 6.C. Lippens and J. H. de Boer, J.Catal., 4(1965)319. G. Lagaly, Clay Miner., 16(1981) 1. S. Brunauer, L. S. Deming, W. Deming and E. T e l l e r , J. Amer.Chem. Soc., 62 ( 1 940) 1723. K. S. W. Sing e t a l . , Pure Appl. Chem., 57(1985)603. S. J. G r e w and K. S. W Sing, Adsorption, surface area and p o r o s i t y (Second E d i t i o n ) , Academic Press, London, 1982, p. 287. J. Shabtai, F. E. Massoth, M. Tokarz, G.M. Tsai and J. McCauley, i n G. E r t l (Ed), Proc. 8 t h I n t e r n a t . Congress C a t a l y s i s Vol. 4 (1984), Verlag Chemie. B e r l i n , P735. J. Sterte, Clays Clay Miner., 34 (1986) 658. S. Yamanaka, T. Nishihara and M. H a t t o r i , Mat. Chem. Phy., 1 7 (1987187.