adsorption of alcohols by smectites: iii. nature of the bonds

Clay Minerals (1980) 15, 225-237.

A D S O R P T I O N OF A L C O H O L S BY SMECTITES: III. N A T U R E OF THE BONDS

F. A N N A B I - B E R G A Y A , M. I. C R U Z , L. GATINEAU AND J. J. FRIPIAT

Centre de Recherche sur les Solides ~i Organisation Cris'talline lmparJitite, 1B, rue de la F~rollerie, 45045 Orleans, France

(Received 30 January 1980)

A B S T R A C T : In previous papers of this series it was shown that it is possible to determine both the amount of methanol adsorbed in the interlamellar space of charge-deficient Ca-montmori l- lonite or of homoionic clays and the amount of methanol occluded in a system of micropores between clay particles. This paper deals with the distinction between methanol molecules in the cation coordination shell within the interlamellar space from those not directly influenced by the cation. An OH stretching band at about 3520 cm-1 or an OD stretching band in the 2600 2650 cm - J region permits this distinction. At 35~ and at relative methanol vapoar pressures between 0.1 and 0.9, one molecule of CH3OD is influenced directly by Na +, 2 molecules are influenced b y Ba 2+, 1.31-8 molecules by Li and 4 molecules by Ca 2+. Thus , only 20-50~o of the adsorbed alcohol molecules may be within the coordination shell of the cation in the interlamellar space.

I N T R O D U C T I O N

In the first two papers of this series (Annabi-Bergaya et al., 1979; preceeding paper, this issue), desorption isotherms of methanol and isopropanol from montmorillonites have been analysed, the basal spacing being measured during the desorption process. The montmorillonite used for these studies was pretreated in such a way as to reduce its CEC, this reduction being achieved by the so-called Hofmann-Klemen effect. The residual lattice charge was neutralized by Ca 2+ and each sample was characterized by the ratio R of the residual to the initial charge.

It was shown that the total experimental isotherm (obtained gravimetrically) was the sum of two contributions, namely that of the internal isotherm corresponding to the molecules inside the interlamellar space, and that of the external isotherm, corresponding to the molecules inside micropores and between the clay microcrystals. These micropores fill at low relative pressure and their volume was estimated to be about 0-12 cm3/g. With such a microporosity the contribution of the 'external' isotherm to the total experimental isotherm was about as large as the contribution of the 'internal' isotherm. The present paper deals with the study of the type of bonds at the origin of the adsorption of methanol using IR spectroscopy and takes into account the results of the two first papers. In particular, the unexpected large contribution of micropores to the total adsorption complicates the interpretation of the IR data. The molecules in these pores constitute a kind of 'balast', smearing spectral features of molecules in a quasi-liquid state onto the spectrum characteristics of species adsorbed within the interlamellar space.

Within the interlamellar space it may also be anticipated that those molecules interact- ing directly with the exchangeable cations will present spectral features different from

0009-8558/80/0900-0225502.00 1980 The Mineralogical Society

226 F. Annabi-Bergaya et al.

those than can be assigned to molecules hydrogen-bonded to each other. By progressively reducing the relative pressure, these particular features will show up more clearly since molecules in the first coordination shell are more strongly retained.

Although numerous papers have treated the subject of adsorption of alcohols by clays, the results are not always concordant. Initially a CH--O interaction between the alcohol and the oxygen of the surface of the clay was proposed (Bradley, 1945; MacEwan, 1948). However, Dowdy & Mortland (1967) found that the frequencies of the CH stretching band of the adsorbed ethanol are similar to that observed for ethanol in the liquid and even in the vapour state. These findings contradicted the idea of an important CH O contribution. The most obvious bond is between the alcoholic OH and oxygen of the surface of the clay. Emerson (1957) calculated a theoretical model suggesting this configu- ration. Brindley & Ray (1964) supported this idea of the OH--O bond in a study of the adsorption of alcohols with various chain lengths by Ca-montmorillonite.

The role of the exchangeable cations in bonding alcohols was emphasized by Glaeser (1953), Gutierrez-Rios & Rodriguez (1961), Gutierrez-Rios et al. (1962) and Bissada & Johns (1969). Dowdy & Mortland (1967), investigating ethanol adsorbed by AI-, Cu-, Ca- and NHa-montmorillonites, observed a broad band in the OH stretching region at 3300 3400 cm-1 corresponding to the frequency of liquid ethanol. Molecular association, involving hydrogen bonding, thus plays a role in the adsorbed state. Dowdy (1966) showed that when the relative pressure of ethanol was decreased a band at 3500 cm -~ appeared, whilst the OH bending vibration shifted from 1242 to 1265 cm -~.

In summary there are thus at least three types of bonds: (i) The H bond between the molecules of alcohols in the microporous space. (ii)The H bond between the molecules of alcohols in the interlamellar space. (iii) The dipole-cation bond between the alcohol molecules and the cation in the

interlamellar space. Tarasevich et al. (1968), and Tarasevich & Oveharenko (1969) in an IR study of the

adsorption ofpropanol and of CH3OD by montmorillonite confirmed that these are two modes of interaction: the dipole-cation bond and the H bond between the alcohols and the oxygen of the surface of the clay, with the latter predominating with increase in alcohol content. This paper aims to show that from IR study of the methanol adsorption by charge deficient Ca-montmorillonites and by homoionic clays (Na +, Li + and Ba2+), it is possible to distinguish in a quantitative manner between molecules directly coordinated to the cations from those hydrogen-bonded to each other.

A P P A R A T U S AND M E T H O D S

The adsorption instrument has been described by Annabi-Bergaya et al. (1979). The cell used for IR measurements was fitted with NaCI windows. The cell could be heated at about 200~ for degassing and was connected to the adsorption instrument.

Oriented clay films (2 mg/cm 2) were deposited by sedimentation on a fluorite disk which limits the useful spectral range above 1200 cm-1. The films were 'washed' several times with alcohol vapour to remove the initial water and the desorption started from a relative pressure of ~ 90~. The IR spectra were recorded at each step of the desorption isotherm. IR spectra, the number of molecules in the interlamellar space and in the microporous volume were monitored simultaneously.

Alcohol bonds on smectites 227

R E S U L T S A N D D I S C U S S I O N

IR spectra obtained for CH30H adsorbed by charge-deficient Ca-montmorillonites

In the adsorbed methanol the CH stretching vibrations appear between 3000 and 2800 cm-1 and the CH bending vibrations between 1500 and 1400 cm ]. The observed vibrational bands are in good agreement with those observed by Noether (1942) in the liquid state.

Three spectral regions are important in the present study: (i) OH stretching vibrations between 3000 and 3700 cm- ~ for the alcohol and for the

residual water, and at 3620 cm-] for the hydroxyls of the clay octahedral layer (Farmer & Russell, 1964).

(ii) OH bending vibrations of the residual water about 1630 cm- 1. After the clay surface is 'washed' several times with alcohol vapour the intensity of this band is very weak, indicating that preadsorbed water has been almost completely removed.

(iii) OH bending vibration of methanol between 1300 and 1400 cm ]. Numerous spectra recorded at decreasing methanol contents and at decreasing R (i.e.

at decreasing lattice charge) permit the following observations to be made: (i) A broad band is observed at 3330 _+ 10 cm-l at high values of P/Po. As the relative

vapour pressure decreases, the intensity of this band also decreases and its minimum is shifted slightly to a lower frequency ( ~ 3290 cm-J). This is observed irrespective of the value of R. These modifications are shown in Figs 1, 2 and 3. This broad band contains the OH stretching vibration of methanol molecules in the interlamellar space as well as in the micropores. The corresponding OH bending has its transmittance minimum at 1370 cm- 1.

(ii) The residual H20 bending at about 1650 cm-] is practically constant in intensity

2.5

I 0 0 1 '

80 ~

~ 6o

o 40

2O

0 4000

Wavelength (microns)

3 4 ~ 5 6 7 8 9 , , ~ . . . . . . . . . ~ , , , , ~ . ~ I I I I I I I I I I ] I I I I I I I l l l l l l [ I T I I I I i l l

/

2

P/Po: 0.57 = O. 16 -2 : 0.007 - 3 = 0 - 4 = 0 a 170~

I I I [ I i I I 5500 3000 2500 2000 1800 1600 1400 1200

Wovenumber (cm -~)

FIG. 1. IR spectra observed for CH3OH adsorbed by Ca-montmorillonite (R= 1).

228

I00

8O

60

g 40 Fe

20

F. Annabi-Bergaya et al.

Wavelength (m~crons)

2.5 3 4 5 6 7 8 9

2

\ / / P, P7 ~ 2 - I - A / : 0 . 1 2 - 2

o _

0 I I I 1 I I I i 4000 3500 3000 2500 2000 1800 1600 1400 1200

Wovenumber (cm -I)

FIG. 2. IR spectra observed for CH3OH adsorbed by Ca- montmorillonite (R=0.59).

2.5 I00

80

6 0

o

E

o 4 0 F--

20


3 4 5 6 7 8 9 I ~ I I I I I I I I I I I I I I I I I I I I I I I I I I I I ~ l l l l l l l l l l l l l l l l l l l ] I I I 1 [ 11

I p/p~ Z~

1 I I I I I I 3500 3 0 0 0 2500 2 0 0 0 1800 1600 1400

Wavenumber (cm -I )

FIG. 3. IR spectra observed for CH3OH adsorbed by Ca- montmorillonite (R = 0.26).

0 -

4000 1200


except for the sample heated under vacuum at 170~ This means that lowering the vapour pressure of methanol does not remove the residual water which, as might have been anticipated, resists the 'washing' procedure. Its width and some modulation suggest the superimposition of several contributions. The observation that the sample with R=0.26 has no visible H20 bending band implies that at least a fraction of the residual water is in the interlamellar space. For this sample there is no interlamellar space available for adsorption (Annabi-Bergaya et al., 1979).

(iii) As the methanol content decreases a band appears at 3520 cm -1. Its intensity decreases with R and the methanol OH bending vibration shifts to 1360 cm - 1. In order to facilitate the band assignment, similar spectra were recorded in identical systems but by using CH3OD instead of CH3OH. One example only is shown in Fig. 4 for the Ca-clay with R = I . The OD vibration appears between 2700 and 2100 cm -1. Assuming an isotopic OH/OD ratio of 1.35, the correlations between the OH and OD stretching are as follows. To the OH band between 3330 and 3290 cm-] corresponds an OD band between 2470 and 2435 cm ~ whereas the stretching at 3520 cm 1 should appear at 2607 cm -1. Again as P / P o l O , the relative intensity of the 2607 cm- 1 band increases and it is the only contribution to the OD stretching that remains in spectrum 3, Fig. 4.

After heating for 24 h at 160 ~ under vacuum (spectrum 4, Fig. 4) an isotopic O H - O D exchange occurs with the octahedral lattice OH. The resulting octahedral OH is at 2680 cm-] and a shoulder at 3520 cm-1 is again observed.

From these observations and from point (iii) above, it may be proposed that the 3520 cm- ~ OH stretching, or the 2607 cm- ~ OD stretching, belongs to CH3OH, or CH3OD, in strong interaction with the exchangeable cation, in this case Ca 2+. In other words this band would be characteristic of methanol belonging to the first cationic coordination shell. Another possibility could be that these bands belong to either residual H20 or D20,

WovelencJ?h (microns)

2 .5 3 4 5 6 7 8 9 i i i i / i i J i i i i i i i i i i i i i i T I 1 I I I I I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I I I I

4 0 0 0

R = I CH30D P / P o : 0 . 7 0 - I = 0 . 0 0 7 - 2

= 0 - 3

= 0 ~ 160~ - 4

~ 4 I I I I I I I I

5 5 0 0 5 0 0 0 2 5 0 0 2 0 0 0 1 8 0 0 1 6 0 0 1400 1200

Wavenumber ( cm - I )

FIG. 4. IR spect ra observed for C H 3 O D adsorbed by Ca- mon tmor i l l on i t e (R = 1).


2,5

o ~3

4 0 0 0


5

Li CH30D

6 7 8 9

P/Po = 0 . 9 0 - I = 0 , 4 0 - 2

= 0 . 0 4 - 5

= 0 - 4

= O h 1 6 0 ~

I I I ~ 3 5 0 0 3 0 0 0 2 5 0 0 2 0 0 0 1800 1600 1400

Wovenumber (cm - I )

FIG. 5. IR spectra observed for CH3OD adsorbed by Li- montmorillonite.

I 2

3

4

5

I 1200

in the cation hydration shell. Note that residual H 2 0 can be transformed into D20 by isotopic exchange with excess CH3OD.

This second hypothesis is, however, less probable since, as shown in Fig. 1, heating under vacuum removes most of the residual water but reinforces the 3520 cm-1 band.

In order to decide between these two hypotheses, tlie IR spectra of CH3OD adsorbed by homoionic Li, Na and Ba montmorillonites with full lattice charge ( R = 1) have been recorded.

IR spectra obtained for CH3OD adsorbed by homoionic montmorillonites

Results are shown in Figs 5, 6 and 7. In all cases a component appears between 2600 and 2650 cm- 1 in the OD stretching. Its relative intensity increases with decreasing P/Po but its absolute intensity decreases with decreasing CH3OD content. This is another argument in favour of assigning this band to CH3OD in the cation coordination shell since the absolute content in residual water is constant unless the sample is heated under vacuum.

In addition, there is no relationship between the intensity of the residual water deformation band and the intensity of the band between 2600 and 2650 cm- 1. The other spectral features do not differ noticeably from those observed for the Ca-clays.

Quantitative analysis of the CH30D stretching band

Since it may reasonably be concluded that the high frequency component of the OD stretching of adsorbed CH3OD is attributable to CH3OD in the cation coordination shell, resolution of the OD stretching band into two contributions may be attempted. In order to do this, the high frequency side of the peak assigned to the adsorbed species in this



2,5 5 4 5 6 7 8 9 I I I ~ I I I I I I I I I I IIIIIIIII I I I I I I I I lllllllllllllllllllll] iiii]ii

No CH30D P/Po: 0.90 - I ~ - - - - : 0 . 4 0 - 2

Ill : 0 .04 - 5

= 0 a 160~

0

4000 5500 5000 2500 2000 1800 1600 1400 1200

Wavenumber (cm -I)

FIG. 6. IR spectra observed for CH3OD adsorbed by Na- montmorillonite.


2.5 5 4 5 6 7 '8 9

g

<~

Ba CH30D P/Po = 0.65 - I = 0.04 - 2 = 0.004 - 5 : 0 - 4 = O~ 160~C-5

, I

I I I I I I I I 4000 5500 5000 2500 2000 1800 1600 1400

Wovenumber (cm -I)

FIG. 7. IR spectra observed for CH3OD adsorbed by Ba- montmorillonite.

1200


TABLE 1. Integrated intensity (arbitrary units) of the 2607 crn- 1 band (A l) and corresponding nl population (10 -3 mol/g clacined clay). A2 and n2

are obtained by difference (see text).

CEC Ca content R P/Po A1 n i A2 n2 (mEq/g) mitliatomeg/g

1 71% 0.290 2.55 0-813 7.00 40% 0.31l 2-80 0-610 5.25 1.20 0.600

7% 0-276 2.40 0-221 1.90 0~ 0.133 (1.20) 0-064 (0-60)

0.59 92~ 0.135 1-70 0.430 7.60 0.70 0.350 0~ 0-104 (1.40) 0.047 (0.50)

0.26 71~ - - ~0 0-141 4.70 40~ - - ~ 0 0-126 3.60 0.31 0.155

1~ 0.024 ~(0.50) 0-033 (1.70)

N.B. Values in parentheses are uncertain because of low intensity.

particular location was reproduced by symmetry on the low frequency side. Then the integrated area of this peak, say A1, was measured and deducted from the total integrated intensity (A) of the OD stretching band to obtain the contribution (A2) of the adsorbed molecules which do not belong to the coordination shell, i.e.

A =A1 +A2=klnl +k2n2

where nl and n2 are the corresponding numbers of molecules in these two situations and k~ and k2 the corresponding adsorption coefficients.

I fA is plotted with respect to n = n~ + n~ (n being given by the desorption isotherm), two cases are possible. A is either a single straight line, in which case k~ - k s , or the variation of A with respect to n is not linear, in which case, k~ 5~k2.

There is no reason why nl and n2 should be proport ional to each other since, obviously, as P/Po decreases nl In2 increases (the coordination shell content (n~) increases relative to n as P/Po decreases). In all cases one single straight line has been observed and thus it may be concluded that kl ~-k2 =k. It is now possible to calculate n~ and n2 since A~ and A2 are known separately: n l = A 1/k and n2 = A2/k. The results of these calculations are shown in Tables 1 and 2. All of these results were obtained at about 35~ Taking into account the approximate character of these calculations it is clear from Table 2 that for values of P/Po between 4 and 90~, nl is approximately constant for the Ba-clay.

I f we consider the results for the charge deficient Ca-montmorillonites (Table 1) the same observation is true for a large range of relative pressures. In this case a plot of n~ averaged for each value of R with respect to the number of Ca 2+ per weight unit must yield a straight line and it does, as shown in Fig. 8. The slope of this curve gives an average number of 4 methanol molecules in the first coordination shell.

Thus, f rom Table 2 and from the cation contents we can calculate the variation of the number of methanol molecules associated with Li, Na and Ba with respect to P/Po. This is represented in Fig. 9. For Ba 2+ this number is close to 2; for Na + it is close to 1 but it increases slightly for P/Po>0.8. For Li +, it is about 1.3 for P/Po<0.5 and 1.8 for


TABLE 2. Integrated intensity (arbitrary units) of the band observed between 2600 and 2650 can- 1 (A l) and corresponding CH3OD population nl (10 -3 mol/g calcined clay). A2 is the difference between the total

integrated intensity of the OD stretching band and A I. n2 is the corresponding population.

Li Na Ba

P/Po AI A2 nl n2 AI A2 nl n2 AI A2 nl n2

0'4~o 4.4~.

16.2~ 39.7~ 63.3~o 90%

0.126 0-148 (0.7) (0.9) 0.173 0.390 1.0 2.3 0.183 0-590 1.1 3.5 0.188 0.880 1.1 5.2 0-233 1-200 1.3 6.6 0-291 1.330 1.7 7.9 0.316 1.710 1-9 10.15

0.070 0.090 (0.4) (0.6) 0.108 0-174 0-7 1.1 0-131 0.322 0.9 2.1 0.132 0-503 0.9 3.3 0.190 0.607 1.2 4.0 0.156 0.723 1.0 4.75 0.260 1.100 1-7 7.2

0.134 0.288 (0.3) (0.7) 0.343 1.135 0.9 2-85 0.410 1.326 1.0 3.3 0.460 1.820 1.2 4-6 0.480 2.278 1-2 5.45 0.406 2-530 1.05 6-35 0.486 2.566 1.2 6.45

N.B. Values in parentheses are uncertain because of the low intensity.

4

~3

o

|

I IO -3 cation 0/g

F1G. 8. Variation in amount of CH3OD molecules in the coordination shell o f the cation for Ca-montmorillonite. The weight unit refers to lg of calcined clay.

5 I

4, / ( D '

g 3 I

o

c

0 0

t5 ID ID

o12 6:4 0"6 0"8 P/P0

FIG. 9. Variation of cationic coordination shell content (molecule per cation) of CH3OD with respect to P/Po: o Ca; * Li; | Ba; a Na.


P/Po>0.5. In all cases, as P / P o l O the coordination shell content decreases as the interlamellar space collapses.

We shall see later what kind of structural information can be extracted from these results, but since most of the interpretation that has been presented in this paper is based on the possibility of distinguishing in the complex OH or OD stretching band the contribution of molecules in the cation coordination shell, it is appropriate to present some theoretical justification.

When a methanol molecule approaches a cation, neglecting all other types of interaction, the vibrational energy levels of the OH vibrator are perturbed by the electrical field. This type of perturbation has been studied recently for adsorbed water by Poinsig- non et al. (1978). Starting from an isolated OH vibrator, the frequency shift towards lower values is more pronounced, the higher the polarizing field. Ab initio calculations by Alml6f et al. (in Janoschek (1977)) predict such a shift in this direction.

According to Barnes & Hallam (1970), the OD stretching of a CH3OD monomer is at 2715 cm-1 (OH at 3679 cm-1). The OD stretching of CH3OD in the Ca 2+ coordination shell (4 molecules/cation) is at about 2605 cm- 1 whereas it is observed at 2630 cm- 1 for Ba 2+ (2 molecules/cation), 2640 cm-1 for Li + ( ~ 1-3 molecules/cation) and 2650 cm-1 for Na + (l molecule/cation). These shifts are of the same order of magnitude but weaker than those observed for water exposed to a similar polarizing field. Therefore both theory and experimental data support the assignment of the band observed between 2600 and 2650 cm- 1 to CH3OD in the coordination shell.

The methanol molecules outside the coordination shell (n2).

From the adsorption study, we know that n2 is a composite population. It contains molecular species inside the interlamellar space and in the micropores, but it is impossible to separate their respective contributions on the basis of their IR spectral features. These molecules are hydrogen bonded to each other and the frequency at which their OH (or OD) stretching is observed provides information on the size of the molecular aggregate, often called the degree of polymerization. Using a matrix isolation technique, Van Thiel et al. (1957) have observed that the frequency of the OH stretching decreases when the degree of polymerization increases. Barnes & Hallam (1970) have shown that a cyclic tetramer has an OH frequency at 3379 cm- 1 (2508 cm- 1 for OD). For the pentamer these frequencies would be 3359 cm- 1 (OH) and 2476 cm- 1 (OD) respectively, whereas what is called the 'high polymer' is characterized by a frequency between 3297 and 3254 cm-1 (OH) or between 2439 and 2414 cm- 1 (OD).

According to Luck (1976), the value of the angle which measures the lack of linearity of the O H - - O bond rules the OH frequency in these polymeric structures. This angle would be zero (ideal linearity) in the high polymer and 20 ~ in the cyclic tetramer.

The broad band corresponding to the n2 population covers the range of frequencies observed for tetramer, pentamer and high polymer but the lack of resolution does not allow any distinction between these situations. The only distinction that can be made is the following. In parts I and II of this investigation we were able to differentiate the number of molecules within the interlamellar space from the total content in adsorbed species. Knowing nl we can then calculate the proportion of molecules which are in the cation coordination shell with respect to the interlamellar content. This is shown in Fig. 10.

~176 t

Alcohol bonds on smectites

0 o O@ 0

Q

235

o~ 2 o :4 0:6 o:8 P/Po

FIG. 10. Ratio of the cation coordination shell content of methanol to the interlamellar content with respect to P/Po: o Ca; * Li; | Ba; ~ Na.

The striking result is that in all cases studied here, for P/Po > 0-15 this ratio is between 25 and 50~.

C O N C L U S I O N S

1, Using IR spectroscopy and knowing the methanol desorption isotherm, it has been possible to calculate the number of methanol molecules in the cation coordination shell for Li, Na, Ca and Ba montmorillonites. These values are summarized in Table 3.

2. Using results from the previous adsorption study and the present IR data it is possible to separate, in the interlamellar space, molecules belonging to the coordination shell from those outside this shell.

3. The coordination shell content represents only 25-50~o of the interlamellar space content.

Since we know from the previous two papers of this series that the amount within the micropores is of the same order of magnitude as the interlamellar content, the number of adsorbed species under the direct influence of the exchangeable cation is much smaller

TABLE 3. Cation coordination

shell content (molecule/cation) in the interlamellar space.

Cations Molecules/cation

Na + 1 Ba 2+ 2

Li + (1-3-1.8)* Ca 2+ 4.0+0-5

* According to the relative vapour pressure.

236 F. A n n a b i - B e r g a y a et al.

t h a n is u s u a l l y c l a i m e d . S u b t r a c t i n g f r o m t he t o t a l n u m b e r o f m o l e c u l e s r e t a i n e d b y t h e

clay, t he n u m b e r w h i c h a re a s s u m e d to be o n t he e x t e r n a l su r face , a n d d i v i d i n g t h e

d i f f e rence ( t he n u m b e r o f m o l e c u l e s in i n t e r l a m e l l a r p o s i t i o n ) b y t h e n u m b e r o f i n t e r -

l a m e l l a r c a t i o n s l e a d s to a v e r y e r r o n e o u s e s t i m a t e o f t he c o o r d i n a t i o n she l l c o n t e n t .

M o d e l s f o u n d e d o n t h e r ea l p o p u l a t i o n o f t he i n t e r l a m e l l a r s p a c e a n d o n t h e c a t i o n

c o o r d i n a t i o n she l l c o n t e n t s will be d i s c u s s e d in t he las t p a p e r o f t h i s series.

R E F E R E N C E S

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ANNABI-BERGAYA F., CRUZ M.I., GATINEAU L. • FRIPIAT J.J. (1980) Adsorption of alcohols by smectites: II. Role of the exchangeable cations. Clay Miner. 15 (previous paper, this issue).

BARNES A.J. & HALLAM H.E. (1970) Infrared cryogenic studies: Part 4. Isotopically substituted methanols in Argon matrices. Trans. Farad. Soc. 66, 1920-1931.

BISSADE K.K. & JOHNS W.D. (1969) Montmorillonite-organic complexe~gas chromatographic determina- tions of energies of interactions. Clays Clay Miner. 7, 197-204.

BRADLEY W.F. (1945) Molecular associations between montmorillonites and some polyfunctional organic liquids. J. Am. Chem. Soc. 67, 975 981.

BRINDLEY G.W. ~r RAY S. (1964) Complexes of Ca-montmorillonite with primary monohydric alcohols. Am. Miner. 49, 106-115.

DOWDY RH. (1966) Alcohol-water interactions on montmorillonite surfaces. PhD Thesis, Michigan State Univ. DowDY R.H. & MORTLAND M.M. (1968) Alcohol-water interactions on montmorillonite surfaces: II. Ethylene-

glycol. Soil Sci. 105, 36-43. EMERSON W.W. (1957)Organo-clay complexes. Nature 180, 48 49. FARMER V.C. & RUSSELL J.D. (1964) The infra-red spectra of layer silicates. Spectrochim. Acta. 20, 1149-1173. GLAESER R. (1953) Complexes organo-argileux et r~le des cations ~changeables. Th~se Sc. Phys. S6rie A. 260 l, n ~

3473 Paris. GUTIERREZ-RIos ER. & RODRIGUEZ A. (1961) Complejos interlaminares de montmorillonita con acetona.

Anales de la Real Sociedad Espanola de Fisica y Quimica LVII, 117 130. GUTIERREZ-RIos E.R., RODRIGUEZ A. & GALACHE M.I. (1962) Complejos interlaminares de montmorillonita

con sustancias organicas. Anales de la Real Sociedad Espanola de Fisica y Quimica. LVII, 53-68. JANOSCI-IEK (1976) Chapter 3 in: Recent Developments in Theory and Experiments. The Hydrogen Bond/I: Theory.

(P. Schuster, G. Zundel & C. Sandorly, editors). North Holland Publishing Company, Amsterdam. LUCH (1976) Chapter 2 in: Recent Developments in Theory and Experiments. The Hydrogen Bond/ll: Structure

and Spectroscopy. (P. Schuster, G. Zundel & C. Sandorly, editors). North Holland Publishing Company, Amsterdam.

MACEWAN D.M.C. (1948) Complexes of clay with organic Compounds: I. Complex formation between montmorillonite halloysite and certain organic liquids. Trans. Farad. Soc. 44, 349-367.

NOETHER H.D. (1942) Infrared raman spectra of polyatomic molecules: XVII. Methyl-d3-alcohol-d and methyl-d3-alcohol. J. Chem. Phys. 10, 693-699.

POINSIGNON C., CASES J.M. & FRIPIAT J.J. (1978) Electrical polarization of water molecules adsorbed by smectites. An infrared study. J. Phys. Chem. 82, 1855-1860.

TARASEVICH Y.I. & OVCHARENKO F.D. (1969) Infrared spectra of deuterated methanol adsorbed on montmorillonite. Dokladi Akademii Nauk SSSR. 187, 372-375.

TARASEVICH Y.I., RADUL N.M. & OVCHARENKO F.D. (1968) Infrared spectroscopic study of adsorption of n-propyl alcohol on montmorillonite. Kolloidnyl Zhurn. 30, 137-143.

VAN THIEL M., BECKER E.D. & PIMENTEL E.C. (1957) Infrared studies of hydrogen bonding of methanol by the matrix isolation technique. J. Chem. Phys. 17, 95 99.

RI~SUMI~: Dans des articles pr6c&tents nous avons montr6 qu'il 6tait possible d'6valuer la quantit6 de m6thanol adsorb6e dans l'espace interlamellaire d'une monmorillonite, et celle occluse dans les micropores form6s par les particules de l'argile. Ces observations ont dt6 fares sur des montmorillonites Ca de charge variable et sur des montmorillonites homoioniques satur6es par les cations Li +, Na + , Ba 2+ .

Alcohol bonds on smectites

Nous montrons maintenant, gr~tce ~ l'interpr6tation quantitative des spectres IR, que dans l'espace interlamellaire une partie seulement des mol6cules adsorb6es est en interaction directe avec le cation. Une bande de valence OH h 3520 c m - l environ ou une bande de valence OD dans le domaine 2600-2650 cm 1 permet cette distinction.

Pour des pressions relatives de m+thanol comprises entre 0.1 et 0-9,/t 35~ il y a une mol+cule d'alcool sous l'influence directe du cation pour une montmorillonite-Na +, deux mol6cules par cation pour une montmorillonite-Ba 2 +, de 1.3 h 1.8 mol6cules lorsque le cation est Li + et qua~re mol6cules pour Ca 2+ . Ces r6sultats montrent que seulement 20 ~t 50% de l'alcool adsorb+ dans l'espace interlamellaire est sous l'influence directe du cation.

KURZREFERAT: In vorausgegangenen Ver~Sffentlichungen aus dieser Serie wurde gezeigt, dal3 es m6glich ist, sowohl die Menge des in Zwischenschichten von Ca-Montmorilloniten mit Ladungsdefizit adsorbierten Methanols zu bestimmen, als auch den Anteil des Methanols, der in dem System von Mikroporen zwischen den Tonpartikeln enthalten ist. Diese Arbeit besch~iftigt sich mit tier Unterscheidung der Methanolmolekiale, die sich in der Kationenkoordinationsschale in Zwischenschichten befinden von denen, die nicht direkt yon Kationen beeinflul3t werden. Die OH-Streckschwingung bei 3520 c m - 1 oder die OD-Streckschwingung im Bereich von 2600-2650 c m - l erlaubt diese Unterscheidung. Bei 35~ und einem relativen Methanolgasdruck zwischen 0.1 und 0.9 wird ein Molekiil CH3OD direkt von Na +, 2 Molekiile werden von Ba 2+ , 1-3 bis 1.8 Molekiile von Li und 4 Molekiile yon Ca 2+ beeinflul3t. Wegen dieser Einfltisse befinden sich wahrscheinlich nur 20 50% der adsorbierten Alkoholmoleki)le innerhalb der Koordinations- schale eines Kations in Zwischenschichten.

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RESUMEN: En trabajos anteriores de esta serie se ha mostrado que es posible determinar tanto la cantidad de metanol adsorbido en el espacio interlaminar de la montmorillonita-Ca deficiente de carga o de las arcillas homoi6nicas, como la cantidad de metanol ocluido en un sistema de microporos entre les particulas de arcilla. Este articulo trate de la distinci6n entre las mol+culas de metanol en la estructura de coordinaci6n cati6nica dentro del espacio interlaminar y las que no son influidas directamente por el cati6n. Una banda de estiramiento de OH en alrededor de 3520 c m - t o una banda de estiramiento de OD en la regi6n de 2600-2650 c m - t permite esta distinci6n. A 35~ y con presiones relativas de los vapores de metanol entre 0-1 y 0-9, una mol6cula de CH3OD es influida directamente por Na +, 2 mol6culas son influidas por Ba 2 +, 1.3-1.8 mol+culas por Li y 4 mol6culas por Ca 2+. Asi pues, s61o 20-50% de las mol6culas del alcohol adsorbido pueden estar dentro de la estructura de coordinaci6n del catidn en el espacio interlaminar.

adsorption of alcohols by smectites: iii. nature of the bonds

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