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INELASTIC NEUTRON SCATTERING OF WATER AND ICE IN POROUS SOLIDS
J. Ramsay, H. Lauter, J. Tompkinson
To cite this version:
J. Ramsay, H. Lauter, J. Tompkinson. INELASTIC NEUTRON SCATTERING OF WATER AND ICE IN POROUS SOLIDS. Journal de Physique Colloques, 1984, 45 (C7), pp.C7-73-C7-79.
�10.1051/jphyscol:1984707�. �jpa-00224268�
J O U R N A L D E PHYSIQUE
Colloque C7, supplément au nQ9, Tome 45, septembre 1984 page C7-73
INELASTIC NEUTRON SCATTERING OF WATER AND ICE IN POROUS SOLIDS
J.D.F. Ramsay, H.J.
au ter*
and J. ~om~kinson*Chenristry Division, AERE, Harwell, Oxfordshire 0x11 ORA, U.K.
* ~ n s t i t u t Max von Laue-Paul Langevin, 38042 Grenoble, France
Résumé
-
L'arrangement intermoléculaire de l'eau à 80 K dans les gels de titane, les zéolites et le chlorhydrate d'alumine a été étudié par la diffusion inélas- tique des neutrons. Les mesures effectuées de 35 jusqu'à 250 meV, comprennentles fréquences des libration et déformation des molécules. Les spectres ont mis en évidence des différences avec la glace qui augmentent quand la taille des pores de l'adsorbat diminue. Ces effets sont attribués à une structure de l'eau moins organisée que celle de la glace et dans laquelle les liaisons hydrogène sont moins nombreuses.Abstract
-
The intermolecular structure of sorbed water and its dependence on the surface and porous properties of the adsorbent has been studied byincoherent inelastic neutron scattering measurements of water at 80K in titania gels, Zeolite-A and aluminium chlorohydrate. An energy transfer range from -35 to-250 meV was covered which included the frequences of molecular librations and deformation mode. Spectra showed an increasing departure from that of bulk ice as the pore size and water uptake was reduced. These changes can be tentatively ascribed to a less ordered water structure where hydrogen bonding is restricted compared to that in bulk ice.
1
-
INTRODUCTIONThere is considerable evidence which suggests that the properties of water close to solid interfaces are significantly different from those in the bulk /1,2/. However the range of influence of interfaces on water structure still remains controversial.
Structural studies of water within porous materials may provide an important insight into this problem, as has been demonstrated by recent neutron diffraction
measurements of D20 within porous silicas
1 3 1 .
From these it was concluded that there was no appreciable structural modification in the liquid but at low temperature there was evidence of structural disorder and the formation of cubic ice, rather than the normal hexagonal ice. Changes in the structure of water are also reflected in the intermolecular vibrational spectra, particularly thelibrational bands which are very sensitive to variations in hydrogen bonding. This has been demonstrated by several investigations /4,5,6/ of bulk ice and water, using mainly infra red and Raman spectroscopy, which have been related to structural predictions based on computer simulation / 7 , 8 / . For the study of water in porous materials however, inelastic neutron scattering (INS) has a particular advantage, because apart from the absence of selection rules, the incoherent cross-section of the H-atom is considerably larger than that of other atoms. This feature is demonstrated in the present INS investigation of ice and water adsorbed at low temperature in well characterised porous titania gels and zeolites.
2
-
VIBRATIONAL SPECTRA OF LIQUID WATER AND ICEVibrational spectra of water and ice have been determined extensively by infra red /4,9/ and Raman spectroscopy /6,10,11/, although neutron scattering measurements
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984707
JOURNAL
DE
PHYSIQUEhave been much l e s s n m e r o u s . The f r e q u e n c i e s of t h e t h r e e i n t r a m o l e c u l a r modes c o r r e s p o n d i n g t o t h e vl symmetric v i b r a t i o n - a c t i v e i n t h e Raman and i n a c t i v e i n t h e i n f r a r e d , t h e d e f o r m a t i o n mode ( s c i s s o r s v i b r a t i o n ) , v2, and t h e v3 a n t i s y m m e t r i c v i b r a t i o n
-
a c t i v e i n t h e i n f r a r e d and i n a c t i v e i n t h e Raman a r e shown i n Table 1.Only one of t h e s e , t h e v2 v i b r a t i o n , f a l l s w i t h i n t h e r a n g e of energy t r a n s f e r covered i n t h e p r e s e n t study. Bands of l o u e r f r e q u e n c y a r i s e from i n t e r m o l e c u l a r v i b r a t i o n s c o r r e s p o n d i n g t o l i b r a t i o n a l and t r a n s l a t i o n a l motions. The f r e q u e n c i e s of t h e s e , which a r e s e n s i t i v e t o hydrogen bonding and t h e s t r u c t u r e of i c e and l i q u i d w a t e r ( t h e y a r e a b s e n t i n t h e v a p o u r ) , a r e l e s s w e l l d e f i n e d and t h e
approximate r a n g e s a s determined by Raman s p e c t r o s c o p y /6,11/ a r e shown i n Table 1.
Table 1
S p e c t r a l f r e q u e n c i e s (meV) of i c e and w a t e r determined from i . r . and Raman Spectroscopy
*
Values from Raman measurements a t 269K / 6 / ; a t 123K 2vL and vL i n c r e a s e d by -8 and 4 meV r e s p e c t i v e l y . N.B. 100 meV J 806 cm-'B O
Oxygen9
1 Hydrogenw a t e r i c e I
Fig. 1
-
L i b r a t i o n a l modes o f w a t e r a b o u t t h e t h r e e p r i n c i p a l a x e s o f t h e molecule.The l i b r a t i o n a l motions of w a t e r a b o u t t h e t h r e e p r i n c i p a l a x e s of a n i s o l a t e d molecule a r e shown i n Fig. 1. These a r e r e f e r r e d t o a s t h e wagging, t w i s t i n g and r o c k i n g v i b r a t i o n s r e s p e c t i v e l y , and o n l y two of t h e s e (about t h e A and C a x e s ) a r e a c t i v e i n t h e i.r. and Raman. A l 1 t h r e e l i b r a t i o n s s h o u l d be observed by n e u t r o n s c a t t e r i n g and s h o u l d i n c r e a s e i n f r e q u e n c y i n t h e same o r d e r a s t h e r e c i p r o c a l of t h e r e s p e c t i v e moments of i n e r t i a a b o u t t h e axes: 1-l <
lil
< - l I n b u l k w a t e r and i c e t h e r e i s s t r o n g m o l e c u l a r c o u p l i n g due t o H-boniing forces)and t h e 3 l i b r a t i o n s of one uncoupled molecule w i l l t e n d t o g i v e a broad band o f f r e q u e n c i e s . These w i l l have a h i g h e r f r e q u e n c y i n i c e compared t o w a t e r because of t h e more e x t e n s i v e hydrogen bonding, a s h a s been observed ( T a b l e 1 ) . Moreover i n i c e , which has a s t r u c t u r e w i t h f o u r H-bonds p e r molecule ( c . f . i c e I h ) , compared t o t h e d i s o r d e d H- bonded s t r u c t u r e of l i q u i d w a t e r , t h e r e w i l l be more p o s s i b i l i t y t h a t t h ef r e q u e n c i e s o f t h e s e p a r a t e l i b r a t i o n s w i l l b e r e s o l v a b l e . v 3
433 399
v 2 204 205
"1 407 384
2%
1 7 9 , 1 3 6 , 1 2 8 *
VL
92-89, 6 8 , 56-53 1 1 3 , 9 3 , 7 5 *
"T 22-7 -35
-
53
-
MPERIMENTAL 3.1 M a t e r i a l sT i t a n i a s h a v i n g d i f f e r e n t s u r f a c e and porous p r o p e r t i e s (Table 2) were p r e p a r e d a s f o l l o w s : hydrous t i t a n i u m o x i d e (HTO) was p r e c i p i t a t e d from a s o l u t i o n of t i t a n i u m c h l o r i d e w i t h sodium hydroxide. The wet sample was f i l t e r e d a s a p a s t e ( c o n t a i n i n g exchangeable ~ a + i o n s ; t h i s was d r i e d s l o w l y ( a t
-
295K and e v e n t u a l l y a t 350K) samples c o n t a i n i n g d i f f e r e n t water c o n t e n t s b e i n g removed p r o g r e s s i v e l y . A s i m i l a r procedure was used t o p r e p a r e d e u t e r a t e d samples and a l s o t h o s e c o n t a i n i n g CS+ and Li+ a s exchangeable c a t i o n s . Mesoporous t i t a n i a s 1 and II were prepared 1121 by d r y i n g two d i f f e r e n t s o l s ( c o n t a i n i n g primary p a r t i c l e s of a n a t a s e having d i f f e r e n t s i z e s ) t o g i v e h a r d g l a s s y g e l s . P r o p e r t i e s-
t a b l e 2 were determined frommeasurements of N2 a d s o r p t i o n i s o t h e r m s a t 77K made on samples o u t g a s s e d a t
-
295K.T a b l e 2
P r o p e r t i e s of porous t i t a n i a s
T i t a n i a Hydrous t i t a n i u m
o x i d e (HTO)
-
microporous
p o o r l y c r y s t a l l i n e a n a t a s e Mesoporous
t i t a n i a 1
Mesoporous
t i t a n i a II a n a t a s e
1
S p e c i f i c s u r f a c e
*
a r e a , SBET/m2g-1
+
262
*
p e r g of h y d r a t e d t i t a n i a-
a f t e r slow d r y i n g i n a i r a t-
295K221
5 4
+ R e s u l t s f o r t y p i c a l sample washed f r e e of Na+ i o n s and d r i e d i n a i r . T o t a l p o r e
*
volume, V p , cm3g-1
+
0.15
Samples of Z e o l i t e 5A ( c o n t a i n i n g exchangeable ca2+) were o b t a i n e d from t h e Linde Corp; t h e s e were s a t u r a t e d w i t h w a t e r (-0.3g g-l) by exposing a t t h e SVP i n a d e s s i c a t o r . ca2+ was enchanged f o r ~ i + and CS+ by immersing t h e z e o l i t e s e v e r a l times i n s o l u t i o n s of LINO3 and CsN03 ( 2 mol dm-3).
0.33
0.43
Aluminium c h l o r o h y d r a t e (ACH) was p r e p a r e d a s a t r a n s p a r e n t g l a s s y s o l i d by p a r t i a l l y d r y i n g a commercial (Hoechst) ACH s o l u t i o n which h a s been s t u d i e d
r e v i o u s l y /13/. The amorphous g l a s s y h y d r a t e h a s t h e p r o b a b l e c o n s t i t u t i o n
-
fail, 04 ( 0 ~ ) 2 4
( 5
0)121 "7 'Mean p o r e
*
d i a m e t e r , d /nm P
<
26.5
34
3.2 Neutron s c a t t e r i n g
S t r u c t u r e (XRD)
amorphous
I n e l a s t i c n e u t r o n s c a t t e r i n g measurements were made w i t h t h e INlB b e r y l l i u m f i l t e r s p e c t r o m e t e r 1141 i n s t a l l e d on t h e h o t s o u r c e of t h e HFR a t ILL, Grenoble.
D i f f e r e n t i a l i n c o h e r e n t c r o s s s e c t i o n s were determined by s c a n n i n g t h e i n c i d e n t n e u t r o n energy; a range from 35 t o -250 meV was covered u s i n g s u c c e s s i v e l y t h e
( I l l ) , (002) and (220) Bragg r e f l e c t i o n s of t h e copper monochromator. The
r e s o l u t i o n f u n c t i o n (FWHM) i n c r e a s e d f r o m - 3 t o 10 and 8 t o 35 m e V over t h e ranges covered by t h e (002) and (220) p l a n e s r e s p e c t i v e l y /15/. Samples, c o n t a i n e d i n t h i n r e c t a n g u l a r aluminium s a c h e t s , had a t h i c k n e s s which was c a l c u l a t e d t o g i v e a t o t a l s c a t t e r i n g c r o s s s e c t i o n of a p p r o x i m a t e l y 10%. The s c a t t e r i n g a n g l e a t t h e sample was 40'. Measurements were made a t - 8 0 K ( l i q u i d n i t r o g e n c r y o s t a t ) , a l t h o u g h - i n one experiment t h e sample was v a r i e d between 10K and 300K u s i n g a D i s p l e x c r y o s t a t .
C7-76 JOURNAL DE PHYSIQUE
4
-
RESULTS AND DISCUSSION 4.1 I c e , Z e o l i t e A and ACHThe TNS s p e c t r u m o f i c e ( F i g . 2 a ) a t -80K shows a l i b r a t i o n a l band, e x t e n d i n g from -65 meV t o - 1 3 0 meV, w i t h peaks a t 81 meV and -102 meV. There i s a l s o e v i d e n c e (220
p l a n e ) of a s h o u l d e r a t -110 meV. A broad weaker band e x t e n d s from -150 t o 240 meV w i t h a maximum-200 meV. The l i b r a t i o n a l band c a n be s y n t h e s i s e d by c o n v o l u t i n g t h r e e G a u s s i a n s ( c e n t r e d a t 7 8 , 96 and 116 meV) a s shown. The s y n t h e s i s showing bands o f low i n t e n s i t y i n t h e r a n g e 150
-
180 meV, f o l l o w e d by a maximum a t 207 meV may t e n t a t i v e l y b e a s c r i b e d t o l i b r a t i o n a l o v e r t o n e s and t h e v 2 d e f o r m a t i o nr e s p e c t i v e l y . These f r e q u e n c i e s a r e i n v e r y good a c c o r d w i t h s i m i l a r a s s i g n m e n t s d e r i v e d from r e c e n t Raman measurements ( T a b l e 1) 161.
The s p e c t r u m of s o r b e d w a t e r i n Z e o l i t e 5A a t 80K ( F i g . 2b) shows s e v e r a l d i f f e r e n t f e a t u r e s compared t o b u l k i c e : t h e l i b r a t i o n a l band now h a s no w e l l d e f i n e d maxima, and bas-broadened by s h i f t i n g t o l o w e r f r e q u e n c y , e x t e n d i n g from 45 t o -120 meV.
The b r o a d l i b r a t i o n a l o v e r t o n e band h a s now a l m o s t d i s a p p e a r e d and t h e v 2 band a t -210 meV, h a s a r e d u c e d i n t e n s i t y . Measurements made on t h e ~ i + and CS+ exchanged
forms o f Z e o l i t e A c o n t a i n i n g w a t e r s a t u r a t i n g t h e i n t r a c r y s t a l l i n e p o r e volume, showed v e r y s i m i l a r f e a t u r e s .
The changes i n t h e l i b r a t i o n band s u g g e s t t h a t t h e w a t e r i n t h e z e o l i t e c a v i t i e s h a s a more d i s o r d e r e d s t r u c t u r e compared t o t h a t o f b u l k i c e , i n which t h e number o f H- bonds may b e v a r i a b l e w i t h a n a v e r a g e somewhat l e s s t h a n t h e f o u r p e r m o l e c u l e i n hexagonal i c e . Thus, m o l e c u l a r dynamics s i m u l a t i o n s o f t h e s t r u c t u r e of l i q u i d w a t e r made by S t i l l i n g e r 1161, i n d i c a t e t h a t t h e number o f H-bonds p e r m o l e c u l e h a s a broad d i s t r i b u t i o n w i t h a mean of 2.3; t h i s would l i k e w i s e a c c o r d w i t h t h e b r o a d e r l i b r a t i o n band o b s e r v e d a t e v e n l o w e r f r e q u e n c y f o r t h e l i q u i d ( T a b l e 1). D i s o r d e r may a r i s e i n t h e z e o l i t e c a v i t i e s b e c a u s e o f t h e e f f e c t o f i n t e r a c t i o n s between t h e w a t e r m o l e c u l e s and t h e a l m i n o s i l i c a t e framework. S i n c e a t s a t u r a t i o n t h e r e a r e o n l y - 2 7 m o l e c u l e s p e r c a v i t y i n CaA, t h e development of t h e l o n g r a n g e o r d e r found i n i c e would b e p r e v e n t e d .
I n s o l i d aluminium c h l o r h y d r a t e (ACH) t h e l i b r a t i o n a l band ( F i g . 2 c ) o c c u r s a t a s l i g h t l y l o w e r f r e q u e n c y t h a n o b s e r v e d f o r CaA, b u t a g a i n shows more d i s t i n c t f e a t u r e s (maxima a t 7 0 , 76 meV and s h o u l d e r s a t 1 0 4 , 1 2 0 , 1 4 1 meV) a s o b s e r v e d i n b u l k i c e . T h i s would s u g g e s t t h a t t h e hydrogen bonding and C O - o r d i n a t i o n of w a t e r i n t h e h y d r a t e was s u f f i c i e n t l y r e g u l a r a l t h o u g h l e s s e x t e n s i v e t h a n i n i c e , t o g i v e r i s e t o d i s c r e t e l i b r a t i o n a l modes. Aïthough a d e t a i l e d i n t e r p r e t a t i o n i s n o t p o s s i b l e h e r e t h e p r e s e n t r e s u l t s a r e c o n s i s t e n t w i t h s e v e r a l s t u d i e s of l i b r a t i o n a l modes i n s i m p l e r s a l t c r y s t a l s 117,181 from which d e t a i l s of t h e environment and p o t e n t i a l f i e l d o f w a t e r m o l e c u l e s h a s been d e r i v e d .
4.2 P o r o u s t i t a n i a s
S p e c t r a of s o r b e d w a t e r ( a t 80K) i n t i t a n i a s ( F i g . 3a,3b and 3 c ) c o n t a i n i n g p o r e s o f d i f f e r e n t s i z e s ( T a b l e 2) c l e a r l y i l l u s t r a t e t h e e f f e c t of t h e c l u s t e r s i z e on t h e i n t e r m o l e c u l a r s t r u c t u r e of w a t e r , which h a s b e e n r e f e r r e d t o w i t h Z e o l i t e A. Thus t h e s o r b e d w a t e r (0.24g g-l) w i t h i n t h e t i t a n i a h a v i n g t h e l a r g e s t p o r e s h a s a l i b r a t i o n a l s p e c t r u m ( 3 a ) which i s v e r y s i m i l a r t o b u l k i c e . The a d d i t i o n a l
s h o u l d e r a t - 5 8 meV however s u g g e s t s t h e p r e s e n c e o f some d i s o r d e r e d w a t e r which may a r i s e c l o s e t o t h e t i t a n i a s u r f a c e .
Within t h e s m a l l e r p o r e s o f t h e mesoporous t i t a n i a 1 , t h e w a t e r (0.26g g-l) h a s a l e s s o r d e r e d s t r u c t u r e , a s e v i d e n c e d by t h e b r o a d l i b r a t i o n a l band ( 3 b ) , h a v i n g s i m i l a r f e a t u r e s t o t h a t o b s e r v e d w i t h Z e o l i t e A. S i n c e t h e p o r e s i n t h e g e l a r e formed by a p a c k i n g of t h e a p p r o x i m a t e l y s p h e r i c a l p a r t i c l e s of a n a t a s e 1 1 2 1 , t h u s g i v i n g a s t r u c t u r e c o n t a i n i n g i n t e r c o n n e c t e d c a v i t i e s , i t i s p o s s i b l e t o make a c r u d e e s t i m a t e o f t h e number o f w a t e r m o l e c u l e s which would s a t u r a t e an " i n d i v i d u a l "
pore. (N.B. Fig. 3b c o r r e s p o n d s t o -75% o f t o t a l s a t u r a t i o n ) . Assuming t h e s e p o r e s a r e s p h e r o i d a l , w i t h a d i a m e t e r o f 6.5 nm, t h i s would c o r r e s p o n d t o a c l u s t e r c o n t a i n i n g -4 x 103 molecules.
I
I I I l IO
100200
Energy transferl
meVFig. 2
-
I n e l a s t i c n e u t r o n s c a t t e r i n g s p e c t r a of w a t e r a t 80K ( a ) i c e ( b ) i nz e o l i t e - A ( c ) i n aluminium c h l o r o h y d r a t e . Broken l i n e s a r e Gaussians which when s y n t h e s i s e d g i v e t h e e x p e r i m e n t a l l y determined spectrum of i c e i n ( a ) . Open and c l o s e d symbols d e n o t e measurements w i t h t h e Cu (002) and (220) monochromator p l a n e s r e s p e c t i v e l y .
The p o r e s w i t h i n t h e microporous t i t a n i a a r e c o n s i d e r a b l y s m a l l e r and a r e of t h e o r d e r of m o l e c u l a r s i z e a s i s e v i d e n t from t h e t y p e 1 a d s o r p t i o n i s o t h e r m o b t a i n e d w i t h N2 a t 77K. Although f u r t h e r d i s c u s s i o n i s n o t a p p r o p r i a t e h e r e , i t i s p r o b a b l e t h a t N2 i s o n l y p a r t i a l l y a c c e s s i b l e t o t h e s t r u c t u r e due t o t h e s m a l l s i z e of t h e p o r e s , and s t r o n g r e t e n t i o n of water even a f t e r pumping. For t h i s r e a s o n t h e v a l u e s of SBET and V quoted i n Table 2 a r e l i k e l y t o be u n d e r e s t i m a t e s ; f u r t h e r m o r e t h e v a l u e of d g l t h o u g h s m a l l , cannot be determined p r e c i s e l y £rom a t y p e 1 i s o t h e r m 1191. ~ i g P ' 3 c shows t h e l i b r a t i o n a l band of a g e l sample c o n t a i n i n g a t y p i c a l l y h i g h w a t e r c o n t e n t (35% weight l o s s on i g n i t i o n ) . Although i t i s e v i d e n t t h a t t h e l i b r a t i o n a l band i s broadened and s h i f t e d t o lower frequency (-45 meV), t h e r e i s a d i s t i n c t maximum a t 70 meV (lower t h a n i n i c e ) . The l a t t e r may i n d i c a t e t h a t t h e w a t e r molecules a r e l e s s hydrogen bonded, b u t n e v e r t h e l e s s have a more o r d e r e d s t r u c t u r e t h a n i n mesoporous t i t a n i a 1 and z e o l i t e A, which i s perhaps more a k i n t o t h e CO-ordinated w a t e r i n ACH. Such a s t r u c t u r e might a r i s e from t h e e x t e n s i v e co- o r d i n a t i o n of w a t e r m o l e c u l e s w i t h t h e hydroxylated t i t a n i a s u r f a c e , which c o u l d o c c u r i n micropores.
The p o s s i b l e i n f l u e n c e of t h e t i t a n i a s u r f a c e on t h e w a t e r s t r u c t u r e can a l s o b e s e e n i n Fig. 4 , which shows l i b r a t i o n a l bands of HTO a t p r o g r e s s i v e s t a g e s of d e h y d r a t i o n . For a t h i c k p a s t e (26% w/w a s T i 0 2 ) t h e band ( 4 a ) i s v e r y s i m i l a r t o t h a t of i c e a l t h o u g h t h e r e i s an a d d i t i o n a l s h o u l d e r a t -65 meV
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p o s s i b l y due t o w a t e r n e a r t h e s u r f a c e of t h e s m a l l (< 4nm) amorphous p a r t i c l e s . I n t h e a l m o s tJOURNAL
DE
PHYSIQUEL t I 1 I
O 100 200
IEnergy transferlmev
Fig. 3
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INS s p e c t r a of water a t 80K i n porous t i t a n i a l g e l s ; ( a ) and ( b ) , mesoporous t i t a n i a s 1 and II, ( c ) microporous HTO.s o l i d g e l , c o n t a i n i n g a lower water c o n t e n t (55% w/w a s T i 0 2 ) , t h i s band i s much more e v i d e n t (4b) u n t i l on f u r t h e r d e h y d r a t i o n ( 7 6 % w/w a s T i 0 2 ) a broader band s h i f t e d t o lower energy, i s observed (4c).
Samp:es c o n t a i n i n g CS+ and ~ i + i o n s , had s i m i l a r l i b r a t i o n a l s p e c t r a t o t h a t
described f o r t h e HTO c o n t a i n i n g exchangeable ~ a + i o n s , which would suggest t h a t t h e pore s i z e and t i t a n i a s u r f a c e have a more dominant e f f e c t on t h e i n t e r m o l e c u l a r s t r u c t u r e of w a t e r t h a n t h e charge d e n s i t y of t h e c a t i o n . The e f f e c t s of deuterium s u b s t i t u t i o n on t h e l i b r a t i o n a l band i n one HTO p r e p a r a t i o n (65% w/w Ti02) were a l s o i n v e s t i g a t e d . The band was s h i f t e d t o lower energy, w i t h a maximum a t -55 meV, and extended d o m t o -35 meV; a small maximum, a t -154 me corresponded t o t h e v 2 v i b r a t i o n . m e s e s h i f t s have a r a t i o v e r y c l o s e t o 2$: a s i s e x p e r t e d f o r modes i n v o l v i n g mainly motions of hydrogen atoms.
I n one experiment l i b r a t i o n a l bands of water i n HTO (65% w/w TiOp) were measured a t i n c r e a s i n g temperatures (10, 45, 200 and 300K) extending above t h e m e l t i n g p o i n t of bulk i c e . Although band broadening occurred w i t h i n c r e a s e s i n temperature, t h e p o s i t i o n of t h e peak maximum remained almost unchanged, i n d i c a t i n g an absence of a d i s t i n c t phase t r a n s i t i o n . This would suggest t h a t t h e e f f e c t s of t h e f o r c e f i e l d s w i t h i n t h e HTO micropores dominate t h e s t r u c t u r e of water, and r e s u l t i n a more e x t e n s i v e H-bonded arrangement of t h e molecules above 273K, p o s s i b l y by r e s t r i c t i n g l i b r a t i o n a l and t r a n s l a t i o n motion.
5
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CONCLUSIONMeasurements of l i b r a t i o n a l s p e c t r a of water adsorbed a t 80K i n porous t i t a n i a s and z e o l i t e A i n d i c a t e t h e s t r u c t u r e i s more d i s o r d e r e d and l e s s e x t e n s i v e l y hydrogen bonded t h a n i n bulk i c e a t s i m i l a r temperature. These e f f e c t s become more marked a s t h e p o r e s i z e i s decreased and t h e water uptake i s reduced. T e n t a t i v e e s t i m a t e s of t h e adsorbed l a y e r t h i c k n e s s i n small mesopores show t h a t d i s o r d e r may extend o u t t o beyond-1.2 nm from t h e t i t a n i a s u r f a c e b u t such e f f e c t s a r e minimal i n l a r g e r mesopores where t h e t h i c k n e s s i s
2
4nm.O
50100
150 Energy transferlmevFig. 4
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INS s p e c t r a of w a t e r a t 80K i n HTO p r e p a r a t i o n s a t p r o g r e s s i v e s t a g e s o f d e h y d r a t i o n . P e r c e n t a g e s , w/w o f TiOg, a r e ( a ) 26 ( b ) 55 and ( c ) 76 r e s p e c t i v e l y .ACKNOWLEDGEMENTS
We a r e i n d e b t e d t o M r B.O. Booth f o r e x p e r i m e n t a l a s s i s t a n c e and t o t h e ILL, Grenoble f o r p r o v i d i n g e x p e r i m e n t a l f a c i l i t i e s and s u p p o r t a t t h e High F l u x Reactor.
REFERENCES
1. W. Drost-Hansen, Phys. Chem. Liq., 7 (1978) 243.
2. J. C l i f f o r d , i n "Water
-
A ~ o m ~ r e h e n s i v e T r e a t i s e " , Vol 5 , F. F r a n k s , Ed., p.75. Plenum P r e s s , 1975.3. D.C. S t e y t l e r , J.C. Dore and C.J. Wright, J. Phys. Chem., (1983) 2458.
4. J.E. B e r t i e and E. Whalley, J. Chem. Phys.
5
(1967) 1271.5. H. P r a s k , H. B o u t i n and S. Y i p , J. Chem. Phys., 48 (1968) 3367.
6. J.R. S c h e r e r and R.G. Snyder, J. Chem. Phys., 6 7 7 1 9 7 7 ) 4794.
7. A. Rahman and F.H. S t i l l i n g e r , J. Chem. Phys., (1971) 3336.
8. F.H. S t i l l i n g e r and A. Rahman, J. Chem. Phys.,
2
(1972) 1281.9. W.S. B e n e d i c t , N. G a i l a r and E.R. P l y l e r , J. Chem. Phys., 24 (1956) 1139.
10. P.T.T. Wong and E. Whalley, J. Chem. Phys., $?- (1975) 2 4 1 8 F 11. M. Magat and L. R e i n i s c h , Phys. Chem. L i q . ,
7
(1977) 5.12. J.D.F. Ramsay and B.O. Booth, J. Chem. Soc., Faraday Trans. 1 ,
2
(1983) 173.13. J.D.F. Ramsay and R.M. R i c h a r d s o n , I L L Workshop on "Water a t I n t e r f a c e s "
81T0555, G r e n o b l e , 1981.
14. Neutron R e s e a r c h F a c i l i t i e s a t t h e ILL High F l u x R e a c t o r . Ed. B. Maier. 1983.
15. R. Almairac, J.L. P r e f a u t , M. G a l t i e r , C. B e n o i t , A. Montaner and H.J. L a u t e r , Mol. C r y s t . L i q . C r y s t . (1981) 177.
16. F.H. S t i l l i n g e r , S c i e n c e ,
209
(1980) 451.17. J. v a n d e r E l s k e n and D.W. Robinson, S p e c t r o c h i m i c a A c t a ,
2
(1961) 1249.18. H.J. P r a s k and H. B o u t i n , J. Chem. Phys., (1966) 3284.
19. See e.g. S.J. Gregg and K.S.W. S i n g , " A d s o r p t i o n S u r f a c e Area and P o r o s i t y , Academic P r e s s , London, p. 135 e t s e q . (1967).
