Surface and Interface Chemistry of Clay Minerals

Chapter 5

Surface and Interface Chemistry of Clay Minerals R.A. Schoonheydta and C.T. Johnstonb a b

Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium Department of Soil and Environmental Sciences, Purdue University, West Lafayette, Indiana, USA

Chapter Outline 5.1. Introduction 139 5.2. Surface Atoms 140 5.3. Surface Structures and Properties 142 5.3.1. Siloxane Surface with Permanent Charge 142 5.3.2. Neutral Siloxane Surface 144 5.3.3. Hydroxyl Surface 145 5.4. Clay–Water Interactions 148 5.5. Clay Mineral–Dye Complexes in Aqueous Clay Mineral Dispersion 150 5.5.1. Monomers 151 5.5.2. Aggregates 152

5.1

5.6. TMI Complexes at Clay Mineral Surfaces 154 5.6.1. Planar Surfaces Prefer Planar Complexes 154 5.6.2. Chiral Clay Minerals 155 5.7. Proteins on Clay Mineral Surfaces 157 5.8. Clay Mineral Films 159 5.8.1. LbL Films 160 5.8.2. LB Films 160 5.9. Perspectives 164 References 165

INTRODUCTION

The surface properties of clay minerals depend on many factors including chemical composition, nature of the surface atoms (mainly oxygen and hydrogen), extent and type of charge, and the type of exchangeable cations. One distinguishes between the edge surface and the planar surface, edges usually being associated with defect sites and pH-dependent charges. It is convenient to start the discussion on surface and interface chemistry of clay minerals with the electronegativity of the atoms in the clay mineral structures. They give qualitative information on the hydrophilic or hydrophobic character of the Developments in Clay Science, Vol. 5A. http://dx.doi.org/10.1016/B978-0-08-098258-8.00005-5 © 2013 Elsevier Ltd. All rights reserved.

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oxygen atoms at the surface of clay mineral layers. Three types of surfaces are discussed: charged surfaces, neutral surfaces, and hydroxylated surfaces. Then, adsorption of (i) water molecules, (ii) cationic dyes, (iii) transition-metal ion (TMI) complexes, and (iv) cationic proteins are reviewed. Amphiphilic adsorbed cations can be used to organize clay mineral layers in nanosized films. This is a convenient end point for a reflection on the perspectives of the surface and interface chemistry of clay minerals.

5.2 SURFACE ATOMS The basal surface atoms of a 2:1 clay mineral are the oxygen atoms of the Si tetrahedron. For 1:1 clay minerals, the surface is constituted by oxygen atoms on the Si side of the layer and by OH groups from Al octahedra (kaolinite) and Mg octahedra (serpentine) on the Al or Mg side of the layer. These basal surface oxygen atoms and hydrogen atoms are chemically similar but crystallographically different. Permanent charge is introduced in the siloxane surface of clay minerals as a result of isomorphous substitution. Common examples are Al for Si in the tetrahedral sheet and Mg for Al in the octahedral sheet. When Al substitutes for Si in the tetrahedral sheet, local distorsions occur because of the difference between the Si–O and Al–O bond lengths, respectively, 0.162 and 0.177 nm (Nemecz, 1981). The bridging oxygen, Si–O–Al, also occurs in zeolites (Sauer, 1989). The most important structural–chemical information about the surface oxygens can be obtained from simple considerations of the Pauling electronegativity of the atoms of the crystallographic unit cell (Table 5.1). As the ionicity of a bond is proportional to the difference in electronegativities of the atoms involved in the bond, it follows that the ionicity of the bonds in clay minerals follows the order H
O < Si
O < Al
O < Mg
O < Li
O:

TABLE 5.1 Pauling Electronegativity of the Most Common Atoms in Clay Minerals Atom

w (Pauling)

w (Sanderson)

O

3.44

3.46

Si

1.90

1.74

Al

1.61

1.54

Mg

1.31

1.42

Li

0.98

0.86

H

2.2

2.31

Data from Huheey (1978)

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As a consequence, the charge on the oxygen atom is expected to increase in the same order: O(H) < O(Si) < O(Al) < O(Mg) < O(Li). Although these considerations are oversimplified, because they do not take into account the structure and chemical composition of the clay minerals, they provide the correct qualitative differences between these structural oxygens. Sanderson’s electronegativity equalization principle states that the electron flow in a molecule or solid is such that, at equilibrium, the electronegativities of all the atoms in the molecule or solid are equal (Sanderson, 1976). The electronegativity of molecules and solids is then calculated as the geometric mean of the electronegativities of the constituent atoms (Table 5.1). The calculated electronegativity values of selected clay minerals are given in Table 5.2. Using the semi-empirical electronegativity equalization method (EEM) (Mortier, 1987), the structure type can also be taken into account. This has been done for kaolinite and Kþ-montmorillonite (Nulens et al., 1998). These numbers are also given in Table 5.2. The data show that beidellite and montmorillonite (Mt) are the most electronegative 2:1 clay minerals. Both have tetrahedral Al in the structure. They are predicted to have the most reactive surfaces. Besides these overall chemical properties of clay minerals, special attention must be given to the surface atoms of oxygen and hydrogen. When one compares the charges on the atoms calculated with the EEM (Nulens et al., 1998), the charge on the surface hydrogens of kaolinite is higher than on the inner hydrogens. The charge on the oxygen atoms in contact with an exchangeable cation is higher than in the absence of exchangeable cations. In other words, the cations (represented as point charges) polarize the oxygens with which they are in contact (Table 5.3). One comes then to the following general conclusions about the surface properties of clay minerals: In the absence of isomorphous substitution and defect sites, the clay mineral surface is composed of oxygen atoms involved in Si–O bonds. The latter have considerable covalent character and the surface is hydrophobic. Hydrophilicity is introduced by isomorphous substitution, inducing the presence of the exchangeable cations, which are hydrophilic and which polarize the surface oxygen atoms (Nulens et al., 1998).

TABLE 5.2 Sanderson’s Electronegativity Values of Typical Clay Minerals Clay

Idealized chemical formula

w (Sanderson)

w (EEM)

Hectorite

Si8Mg5.25Li0.75O20(OH)4

2.760

Beidellite

Si7.25Al0.75Al4O20(OH)4

2.928

Montmorillonite

Si87.75Al0.25Al3.5Mg0.5O20(OH)4

2.927

5.11

Kaolinite

Si4Al4Si4O10(OH)8

2.895

3.27

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TABLE 5.3 Charges on Surface Atoms Obtained by EEM Structure

Atom

Kaolinite

H (inner)

0.152

H (surface)

0.219

Montmorillonite

Charge (in electron charge)

O (no cation)


0.522 to
0.741a

O (Kþ)


0.800 to
0.867a

a

The charge depends on the crystallographic position.

Hydrophilicity may also arise from the presence of hydroxyl groups at the surface, such as in kaolinite, and from defect sites.

5.3 SURFACE STRUCTURES AND PROPERTIES 5.3.1 Siloxane Surface with Permanent Charge In order to better understand the surface structure and properties of clay minerals, consider the physical and conceptual model of smectite, a representative clay mineral (Fig. 5.1). The atomic force microscopy (AFM) image of a Langmuir–Blodgett (LB) film of smectite particles (SWy-2 Mt) deposited on a ZnSe substrate is shown in Fig. 5.1A. The irregularly shaped particles are approximately 500 nm in diameter and 1 nm in thickness (Ras et al., 2003). A small portion (52 nm  52 nm) of an idealized cross section of one of these particles is shown in Fig. 5.1B. Each individual rectangular box is a ‘supercell’ made of four unit cells with dimensions of 1.04 nm  1.8 nm. In nature, multiple smectite particles are often stacked on top of each other and this is illustrated in Fig. 5.1C, where five fundamental particles are stacked one on top of the other. The molecular structure of the clay mineral is shown in Fig. 5.1D, where two fundamental particles are shown separated by three layers of H2O molecules. The structural formula of SWy-2 Mt is Na0.74(Si7.76Al0.24)IV(Al3.08Fe3þ0.42Mg0.48)O20(OH)4 (S´rodon and McCarty, 2008). This structural formula reveals the presence of three types of isomorphous substitution. Some Al3þ ions have substituted for Si4þ ions in the tetrahedral sheet. In the octahedral sheet, Mg2þ has substituted for Al3þ and Fe3þ has substituted for Al3þ. The first two types of isomorphous substitution result in the development of a negative charge (also known as a ‘permanent charge’) due to the charge imbalance of the cations. Under oxidizing conditions,

Chapter

5

D

˜0.96 nm thick Interlayer water

Interlayer cation d-spacing 1–5 nm

O

O

Si

Si

Å 800 600 400

52

52 nm

nm

˜0–4 nm

O, H Al, Mg, Fe(II, III), Li O, H

1000 nm

A

B

C

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A B

200 00

C

0

1

2 mm

FIGURE 5.1 (A) AFM image of Wyoming montmorillonite, (B) idealized crystal structure of a smectite particle, (C) A smectite particle with five layers, and (D) a three-layer hydrate.

structural Fe3þ does not contribute to development of the charge. However, structural Fe3þ can be reduced under anoxic conditions, leading to an increase in the cation exchange capacity (CEC). Depending on the extent of substitution, the distance between the negatively charged sites ranges from 0.9 to 1.35 nm (1.2–1.8 mmol/m2) (S´rodon and McCarty, 2008). However, because smectite layers are stacked on top of each other, the effective surface charge density is increased by a factor of 2, and the separation between negative charge sites is further reduced to 0.65–0.84 nm (Johnston and Tomba´cz, 2002; Schoonheydt and Johnston, 2007). Octahedral substitution (e.g. Mg2þ ! Al3þ) results in a charge deficit, which is delocalized over about eight surface oxygen atoms on each side of the fundamental particle (Fig. 5.2A), whereas substitution in the tetrahedral layer (e.g. Al3þ ! Si4þ) results in a more localized charge only on one side of the particle; this is illustrated in Fig. 5.2B. The negative charge that results from isomorphous substitution is balanced by the presence of exchangeable cations of which Ca2þ, Mg2þ, Kþ, and Naþ ions are the most common. The charge of the ion, ionic radius, enthalpy of hydration, and hydrolysis constant are the most important properties of the exchangeable cation. A common feature to these cations is that they all have appreciable enthalpies of hydration, with values ranging from
300 to

144

Handbook of Clay Science Isomorphous substitution of Mg ® Al in the octahedral layer (montmorillonite)

0.7 nm Isomorphous substitution of AI ® Si in the tetrahedral layer (saponite)

0.3 nm FIGURE 5.2 Isomorphous substitution in octahedral (upper part) and tetrahedral (lower part) sheets.


2000 kJ mol–1 (Burgess, 1978). As a result, these cations are capable of organizing hydration, or partial hydration, shells and they impart an overall hydrophilic nature to the clay mineral. This is reflected by the presence of H2O molecules clustered around the exchangeable cations in the clay mineral interlayer space shown in Fig. 5.1D.

5.3.2 Neutral Siloxane Surface The least reactive surface found on clay minerals is the neutral siloxane surface that occurs on 2:1 phyllosilicates where no isomorphous substitution has occurred (e.g. talc and pyrophyllite) and on the silica tetrahedral side of 1:1 kaolin group minerals (Yariv, 1992; Giese and van Oss, 1993; Michot et al., 1994; Charnay et al., 2001). In addition, this type of surface is also present in clay minerals with permanent charge as ‘neutral siloxane surface’ sites which are regions on the siloxane surface not in the near vicinity of exchangeable cations, waters of hydration surrounding exchangeable cations, or the isomorphous substitution sites themselves (Johnston, 1996; Johnston and Tomba´cz, 2002; Liu et al., 2009; Rana et al., 2009; Boyd et al., 2011). These portions of the clay mineral surface are less hydrated and are considered to provide favourable adsorption domains for non-polar and semi-polar organic solutes.

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145

The external oxygen atoms on the siloxane surface are relatively weak electron donors (Lewis bases) and are not capable of having strong interactions with water molecules. Clay minerals dominated by the neutral siloxane surface (e.g. talc and pyrophyllite) are hydrophobic as evidenced by contact angle and flotation measurements (Giese et al., 1990; Schrader and Yariv, 1990; Michot et al., 1994; Malandrini et al., 1997). These surfaces are nonpolar and are not capable of forming hydrogen bonds with water molecules. Recent theoretical studies have shown that the neutral siloxane surface interacts only weakly with water molecules (Nulens et al., 1998; Croteau et al., 2009). With this type of surface, the water molecules interact predominantly with each other and not with the surface. Additional support comes from recent ab initio molecular dynamics studies of the water–siloxane surface interactions (Tunega et al., 2002; Cygan et al., 2009; Croteau et al., 2010) where very weak hydrogen bonds are spontaneously broken and created by the movement of water molecules. These types of surfaces can play an important role in the attenuation of neutral organic contaminants (NOC) and were the subject of a recent review (Boyd et al., 2011). Earlier studies demonstrated that smectites with lower charge densities were more effective adsorbents for NOC compared to clay minerals with higher charge densities (Jaynes and Boyd, 1990; Lee et al., 1990). Recently, clay minerals with more exposed neutral siloxane surfaces were shown to have an unexpectedly high affinity for the highly non-polar class of solutes known as dioxins (Liu et al., 2009; Rana et al., 2009; Li et al., 2012). Among the smectites, the tetrahedrally substituted trioctahedral saponite has a higher affinity for dibenzo-p-dioxin (DD) than SWy-2 Mt. The approximate charge distribution of saponite is shown by the small purple circles on the left side of Fig. 5.3A. For this clay mineral, most of the siloxane surface is not influenced by isomorphous substitution. This type of surface interacts favourably with molecules such as DD. This explains, in part, the high affinity of DD for saponite. For comparison, the charge distribution of a clay mineral with the same charge density but isomorphous substitution exclusively in the octahedral sheet is shown by the green circles on the right side of Fig. 5.3B. Almost the entire surface is influenced by isomorphous substitution in the octahedral sheet because it is distributed over more surface oxygen atoms (eight vs. three) and this charge is manifest on both sides of the smectite particle. SWy-2 Mt has more isomorphous substitution in the octahedral sheet and thus reflects the surface character depicted in Fig. 5.3 and thereby has a lower affinity for the hydrophobic solute DD.

5.3.3

Hydroxyl Surface

Another type of surface that clay minerals and related hydroxides possess is the hydroxyl surface. An example is the aluminium octahedral surface of kaolinite (Fig. 5.4). This surface is found on 1:1 clay minerals (kaolin group

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B 3.9 nm

0.8

nm

1.2 nm

1.6 nm

3.9 nm

4.1 nm

A

0.8 nm

1.2

nm

0.8 nm

0.4 nm

FIGURE 5.3 Schematic diagram of charge distribution in smectitic clay minerals with isomorphous substitution in the tetrahedral layer (A) and octahedral layer (B). Charge distribution was calculated using a total surface area of 750 m2 g–1 and cation exchange capacity of 94 cmol kg–1.

Hydroxyl surface H O Al (oct) OH Si (tet) O

Siloxane surface FIGURE 5.4 Hydroxyl and siloxane surface of kaolinite.

minerals, halloysite, serpentine) and 2:1 clay minerals, and also on hydroxides such as gibbsite and brucite. In the case of kaolinite, the two surfaces (hydroxyl and siloxane) have different structures and corresponding surface chemistries. This was shown recently in an ab initio molecular dynamics study of water interacting with both types of surfaces (Tunega et al., 2002, 2004; Croteau et al., 2009, 2010). Unlike the siloxane surface, which interacts very weakly with interfacial water molecules, the hydroxyl surface interacts more strongly with water molecules. This is shown in Fig. 5.5, where the closest Osurface to Owater distances are plotted over the time course of the molecular dynamics study. The average O  O distances for two different surface oxygen atoms in the tetrahedral sheet are 0.445 and 0.427 nm, respectively.

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7 Ow in D(T)–H2O (4.452 Å)

O3

Distance (Å)

6

Ow in D(T)–H2O (4.271 Å)

O6

5 4 3 2

Ow in D(O)–H2O (2.632 Å)

O1

1 500

0

1000

1500

2000

Time (fs) FIGURE 5.5 The time evolution of the distances between the water oxygen atom and two basal surface atoms (O3 and O6) in the D(T)–H2O system (two upper curves). The bottom curve represents the time evolution of the O1  Ow distance in the D(O)–H2O system. Horizontal lines indicate mean values and correspond to the numbers given in the figure.

Gibbsite—edge view Charge neutral OH groups A

B Edge site C

Edge OH groups Charge = -0.5

Al3+ in octahedral coordination FIGURE 5.6 Edge sites of kaolinite.

In contrast, the corresponding Osurface to Owater distances for the oxygen atoms in the hydroxyl plane are 0.263 nm. The considerably shorter distance for the octahedral oxygen atoms reflects the fact that water molecules are hydrogenbonded to the hydroxyl surface. Hydroxyl groups located at edges, steps, and related defects of clay mineral particles are different and are called terminal OH groups. Theses OH groups are under-coordinated and carry either a positive or negative charge depending on the type of metal ion and the pH of the ambient aqueous solution (Fig. 5.6; see Chapter 8). These terminal OH groups also have the

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potential to chemisorb (also referred to as specific adsorption) certain types of ions, regardless of the pH value. An example is the high affinity of both terminal Al–OH and Fe–OH groups for the phosphate ion. Because the terminal OH groups have either a partial positive or partial negative charge, these sites are more reactive than the charge-neutral OH groups found on basal surfaces.

5.4 CLAY–WATER INTERACTIONS The interaction of H2O with smectites was the subject of continuous study over the past 75 years (Buswell et al., 1937; Henniker, 1949; Low, 1961; Graham, 1964; Sposito and Prost, 1982; Newman, 1987; Schoonheydt and Johnston, 2007; Marry et al., 2008; Anderson et al., 2010; Johnston, 2010). The chemical mechanisms that contribute to clay mineral–water interactions include H-bonding, charge–dipole attraction, ligand–ligand repulsion, and van der Waals interactions. In addition, contributions can also occur through hydrolysis and redox reactions depending on the nature of the exchangeable cation. Although most of these forces operate at distances <3 nm, some extend over larger spatial scales including diffuse-layer swelling (McBride, 1997; McBride and Baveye, 2002; Quirk, 2003; Laird, 2006). The discussion here will be limited to the group of expandable 2:1 (TOT) clay minerals in the smectite group, as they are among the most interesting and important clay minerals related to clay mineral–water interactions. The chemical mechanisms of hydration of interlayer cations for these types of clay minerals are mainly through electrostatic interactions that maximize charge–dipole attraction and minimize water–water repulsion (Feller et al., 1995; Glendening and Feller, 1995, 1996). In the interlayer region of the clay mineral, the overall hydration energy of the cation is attenuated to some extent by the negative charge of the clay mineral surface which satisfies a portion of the charge of the cation. The height of the interlayer space is limited, and in this sense water molecules in the interlayer space are ‘nanoconfined’. As the extent of isomorphous substitution increases in the clay mineral, the interlayer spaces become more nanoconfined. It is useful to consider the interaction of water with smectites as a function of water activity. Water uptake by Naþ- and Caþþ-smectite obtained using two different adsorption methods (Prost et al., 1998) is shown in Fig. 5.7. Using vapour phase adsorption, the activity of water ranges from 0 to 0.98 (Prost et al., 1998). Under these conditions, smectites generally adsorb up to 0.6 g H2O/g
1, depending on the type of clay mineral and nature of the interlayer cation (Mering, 1946; Mooney et al., 1952a,b; Newman, 1987; Prost et al., 1998; Xu et al., 2000). This type of data is illustrated on the left side of Fig. 5.7A and is termed ‘crystalline swelling’. Higher water activities (aw > 0.98) were obtained through pressure membrane studies (Sposito, 1972; Low, 1980; Prost et al., 1998). In order to express the high water activity values obtained in pressure plate studies, the x-axis units can be expressed

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5

16 000 400

Capillary condensation

Na Ca

4

300

12 000

250

log(mg H2O/g clay)

Water content (mg H2O/g clay)

350

200 150

8000

100 50 0

4000

0

3

2

0.2 0.4 0.6 0.8 Crystalline swelling

1 Crystalline swelling

0 0

0.25

0.5

aw

0.75

1

0 -6

-4

-2

0

log(log(1/aw))

FIGURE 5.7 Water sorption isotherms of Naþ (D) and Ca2þ (♦) montmorillonite.

as ‘log(log(1/aw))’ (right side of Fig. 5.7B). Capillary condensation occurs for aw values >0.8, and this is represented by the dashed boxes in both Fig. 5.7A and B. For water activities (aw) <0.8, the water molecules are strongly polarized by their close proximity to the exchangeable cations in the interlayer space, based on spectroscopic evidence from Fourier transform infrared (FTIR) studies (Russell and Farmer, 1964; Poinsignon et al., 1978; Sposito et al., 1983; Johnston et al., 1992; Bishop et al., 1994; Xu et al., 2000; Rinnert et al., 2005) and quasi inelastic neutron scattering (QENS) studies (Cebula et al., 1981; Swenson et al., 2000; Malikova et al., 2005, 2007, 2010; Sobolev et al., 2010). Vibrational studies have shown that they are less hydrogen-bonded to each other and that the water molecules are strongly polarized by the interlayer cation extending to about 12 H2O molecules per interlayer cation. These findings are in good agreement with QENS studies which reveal that water diffusion in the interlayer space is about an order of magnitude slower relative to bulk water (Malikova et al., 2007). Water molecules in the interlayer space can also be studied indirectly, either by studying their effect on the exchangeable cations or on the clay mineral structure. The effect of water on the exchangeable cations was mainly studied by the NMR of 7Liþ (Alvero et al., 1994; Alba et al., 1998; Porion et al., 2009), 23Naþ (Laperche et al., 1990; Hanaya and Harris, 1998; Gevers and Grandjean, 2001; Porion et al., 2005), 39Kþ (Bowers et al., 2008), 111Cd2þ and 113Cd2þ (Bank et al., 1989), and 133Csþ (Weiss et al., 1990; Kim and Kirkpatrick, 1997; Earl and Johnston, 1998). At high water

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contents, the NMR signals of these cations in the interlayer space resemble those in aqueous solution. As the water content decreases, the NMR signals broaden, as the cations are interacting simultaneously with water molecules and with surface oxygen atoms. Changes in clay mineral hydration were shown to influence the clay mineral structure (Sposito et al., 1983; Xu et al., 2000). Upon heating smectites, small cations such as Liþ irreversibly migrate into the clay mineral structure, resulting in an overall decrease of the layer charge. This is the Hofmann–Klemen effect (Hofmann and Klemen, 1950).

5.5 CLAY MINERAL–DYE COMPLEXES IN AQUEOUS CLAY MINERAL DISPERSION In aqueous dispersion, clay minerals may be present as single layers, particles, and aggregates. The ideal dispersion consists of individual clay mineral layers that are randomly diffusing in the aqueous medium. This ideal dispersion is probably never attained, but dilute aqueous dispersion of Liþ- and Naþexchanged smectites come close to it. To probe the surface of these clay mineral layers in aqueous dispersion, the probe molecule must be very selectively adsorbed, with the amount remaining in the equilibrium solution being below the detection limit. The aqueous dispersion cannot be perturbed by the adsorption of the probe, and a very sensitive detection technique of the adsorbed probe is necessary. The molecules that fulfil these criteria almost ideally are cationic dyes. The most frequently used dyes are shown in Fig. 5.8. They

N Cl H3C

N

S

N+

CH3

O

-

CH3 • H 2O

CH3

H3C

CH3

N

N +

O

Cl -

O

H3C

CH3

CO2-

• HCl

O

N H

N CH3

Methylene blue: MB+

Rhodamine 6G

C8H17

O

CH3

N N

CH3 CH3CH2

Rhodamine B: RhB

O

C10H20

N

+

CH3

CH3

C8AzoC10N

Cyanine dye

+

+

+

N Me3

Me3 N

O

O CH

N N

-

H3C

N

N H

O

ClO4

M

N+

N

C18H35

N H3C

CH3

N

+ N

+

N H

Oxazine perchlorate

CH3

+

+N C15H37

+

Me3 N

N Me3

M-TMAP

(M = H2, Zn )

Oxacyanine

FIGURE 5.8 Typical dye molecules used for the preparation of clay mineral–dye composites.

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are strongly and selectively adsorbed by ion exchange. They have high molar extinction coefficients and can therefore be detected spectroscopically at such extremely small loadings as 0.1% of the CEC in dilute aqueous smectite dispersion. At these low loadings, the aqueous clay mineral dispersion is hardly perturbed by the adsorbed dye molecules.

5.5.1

Monomers

The position of the band maxima of molecules in solution is determined by the energy difference of the ground state S0 and the first excited state S1 as well as by the interaction of the molecules with the solvent molecules. This is schematically shown in Fig. 5.9. When the solvent interacts more strongly with the excited state than with the ground state, the absorption band maximum shifts to a longer wavelength, or lower frequency and wavenumber, than in vacuum. This is called a red shift. If the ground state interacts more strongly with the solvent than the excited state, the absorption band maximum shifts to a shorter wavelength or higher frequency and wavenumber than in vacuum. This is a blue shift. A red shift of 5–10 nm is commonly observed for dye cations adsorbed on smectite surfaces in aqueous dispersion (Yariv and Cross, 2002; Bujda´k, 2006). In the case of methylene blue (MBþ) on hectorite at extremely small loadings of 0.1% of the CEC, a monomer band at 652 nm was observed, which was blue-shifted with respect to its position in aqueous solution (664 nm) (Cenens and Schoonheydt, 1988). This means that at these small loadings some MBþ molecules are not interacting directly with the hectorite surface but remain in an aqueous environment near the hectorite layers. The 652-nm band was much weaker in an aqueous dispersion of saponite and Mt. Thus, hectorite with isomorphous substitution in the octahedral sheets and more diffuse negative charge interacted less strongly with MBþ molecules than saponite and Mt with isomorphous substitution in the tetrahedral sheets and more localized negative charge (Jacobs and Schoonheydt, 2001).

Excited state S1

na

nb > na a

nc < na c

Ground state S0

b FIGURE 5.9 Ground state and excited state of a dye molecule (A) in vacuo; (B) the solvent interacting more strongly with the ground state than with the excited state; and (C) the solvent interacting more strongly with the excited state than with the ground state.

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5.5.2 Aggregates The distribution of cationic dyes over the smectite surfaces in dilute aqueous dispersion is governed by dye–dye interactions and dye–clay mineral surface interactions. If the former are stronger, dye aggregation is observed. If the latter are dominant, dye molecules are distributed over the surface so as to maximize the dye–surface interactions, and monomers are dominant. In dilute aqueous dispersions, dye–dye interactions are dominant and aggregates are observed even at loadings below 1% of the CEC. In air–dry clay and mineral–dye composites, the dye–surface interactions are dominant, and monomers are dominant at low loadings (Fig. 5.10). Thus, when a solution of MBþ containing dimers with a band maximum around 600 nm and monomers with a band maximum around 660 nm was contacted with a dilute aqueous dispersion of hectorite, aggregates were instantaneously formed with a characteristic absorption band at 570 nm, together with monomers on the surface with a characteristic band at 670 nm. As the adsorption process continued, the 570-nm band decreased and the monomer band increased, indicating the break-up of aggregates and the adsorption of monomers on the hectorite surface (Jacobs and Schoonheydt, 2001). In an aqueous dispersion equilibrated for 24 h, four bands of MBþ were observed in the spectrum (Fig. 5.10): monomers at 670 nm; H dimers and aggregates at 600 nm with a shoulder around 570 nm; J dimers at 723 nm; and protonated MBH2þ with a band at 760 nm. When this MBþ-hectorite dispersion was cast into a film, the bands of the H and J dimers and aggregates

0.40 Film Dispersion

Original Mb solution 0.35

Mb–Hec:

0 min 8 min

660, 674 nm

670

0.30

Absorbance

Absorbance

664

0.25 590

0.20 670

0.15 0.10 0.05 0.00 550

600

650

l

700

750

400 450 500 550 600 650 700 750 800 850

l

FIGURE 5.10 Right: Spectra of a methylene blue–hectorite dispersion (blue) and that of the corresponding cast film. Left: Spectrum of a methylene blue solution (dotted line) and of the methylene blue–hectorite dispersions, immediately after preparation (red) and 8 min after preparation (blue). From Jacobs and Schoonheydt (2001).

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disappeared, and only those of monomers remained. The removal of water by evaporation during film formation allowed the MBþ molecules to interact more strongly with the hectorite surface. Thus, aggregates were broken up and monomers were located on the surface of the hectorite layers in the film. The difference between H and J dimers and aggregates is in the orientation of the transition dipole moment of the individual molecules in the aggregate, as illustrated for dimers in Fig. 5.11. If the electronic overlap of the two molecules in the dimer is negligible, the spectral properties of the dimer can be obtained with perturbation theory (Kasha et al., 1965). In the dimer, the energy level of the excited state of the monomer is split into two energy levels, one at higher and one at lower energy. When the monomers have parallel transition dipole moments and are inclined with an angle between 54.7 and 90 , the transition to the highest energy level is allowed (see Fig. 5.11). The absorption band of the monomer shifts to shorter wavelengths. The dimers with such a blue shift of the band maximum are called H dimers. When the two transition dipole moments are parallel but inclined by an angle smaller than 54.7 , or when they are oblique with an angle smaller than 54.7 , the transition to the lowest energy level is allowed and one observes a shift of the band maximum to longer wavelengths. These dimers are called J dimers (Del Monte et al., 2001). H dimers and H aggregates are commonly observed in aqueous clay mineral–dye dispersions (Cenens and Schoonheydt, 1988; Bujda´k, 2006). Their amount depends on the CEC, the loading, the particle size, and the

a

Fluorescent oblique J dimer

S1 q < 54.7°

R

Fluorescent coplanar J dimer

Non-fluorescent coplanar H dimer

S0

Monomer levels

Dimer levels

q < 54.7° S1

q > 54.7° S0 Monomer levels

q = 0°

q = 54.7°

q = 90°

Dimer levels

FIGURE 5.11 Orientation of transition dipole moments of individual molecules in H and J dimers (left). The corresponding energy diagram (right).

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location of the isomorphous substitution. J dimer and aggregates have been described for MBþ, rhodamine, and cyanine dyes on clay mineral surfaces. In an aqueous dispersion of hectorite, a band at 723 nm was assigned to the J dimer of MBþ (Cenens and Schoonheydt, 1988). The spectra of the J dimers of rhodamine B on Mt and saponite were characterized by two bands, one blue-shifted (537.5 nm) and the other red-shifted (584.5 nm) with respect to the position of the monomer band (567 nm). This typical spectrum was interpreted as arising from head-to-tail dimers, with the aromatic planes of the molecules tilted with respect to each other (Lopez Arbeloa et al., 2002). J aggregates of cyanine dyes on Laponite contained two to three molecules, much fewer than in aqueous solution (Lu et al., 2002).

5.6 TMI COMPLEXES AT CLAY MINERAL SURFACES 5.6.1 Planar Surfaces Prefer Planar Complexes Cationic TMI complexes are strongly adsorbed in the interlayer space of smectites by ion exchange. This strong adsorption is visible in (i) the shape of the exchange isotherms and (ii) in the formation constants of the complexes, which are larger than in aqueous solution. Over-exchange is frequently observed. Thus, more TMI complexes are adsorbed than needed for neutralization of the ion exchange sites. This strong adsorption is especially evident for complexes with aliphatic and aromatic amines and with heterocyclic molecules with nitrogen in the ring. Examples are ethylenediamine (en), 2,20 bipyridine (bipy), and 1,10-phenanthroline (phen). The complexes can be synthesized in solution and ion exchanged. They can also be prepared in the interlayer space by adsorption of the ligands on a smectite previously exchanged with the TMI. In the case of the complexes of en and Cu2þ, it was found that the thermodynamic formation constant Kf of the bis-complex, [Cu(en)2]2þ, was three orders of magnitude larger in the interlamellar space of Mt than in aqueous solution:  2þ  2þ þ 2en $ CuðenÞ2 þ 6H2 O: CuðH2 OÞ6 Log Kf is 23.1 as compared to 20 for complexation in aqueous solution (Maes et al., 1977, 1978; Maes and Cremers, 1978, 1979). This extrastabilization is attributed to the removal of the two axial water molecules and their replacement by the clay mineral surface in the interlayer space (Maes et al., 1980). For the complexes of Ni2þ with eight d electrons and Co2þ with seven d electrons, the transfer of the complexes from aqueous solution to the interlamellar space is accompanied by a change of spin state. [Ni(en)2]2þ turns from paramagnetic with two unpaired electrons to diamagnetic with all d electrons paired, and [Co(en)2]2þ from a high-spin complex with three unpaired electrons to a low-spin complex with one unpaired

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4

Clay mineral surface N

5  103

N

3

Co

0.02 T H

N

2

N

Clay mineral surface 1

5  103

FIGURE 5.12 Electron spin resonance spectra of Co(en)22þ in hectorite films: Experimental (1) and simulated (2) spectrum in the gII region and experimental (3) and simulated spectrum (4) in the gI region. From Schoonheydt and Pelgrims (1983).

electron. The latter is easily visible with electron paramagnetic resonance (EPR) spectrum (Schoonheydt et al., 1979; Schoonheydt and Pelgrims, 1983). Figure 5.12 shows the EPR spectrum of this low-spin [Co(en)2]2þ complex in an oriented clay mineral film. The clear separation of the parallel and perpendicular parts of the spectrum shows unambiguously that the complex is oriented with its CoN4 plane parallel to the surface of the clay mineral layers, as schematically shown in the right-hand side of Fig. 5.12. The general conclusion is that the replacement of the two axially coordinating water molecules by the clay mineral surface increases the in-plane ligand field strength and decreases the axial ligand field strength. This leads to an overall stabilization of the complexes. In other words, planar clay mineral surfaces like planar complexes.

5.6.2

Chiral Clay Minerals

Tris(2,20 -bipyridyl) and tris(1,10-phenanthroline) complexes are chiral with a D and a L configuration, as schematically shown in Fig. 5.13 for M ¼ Ru2þ. Solutions containing equal amounts of both configurations are racemic solutions. Solutions containing either the D configuration or the L configuration are enantiomeric solutions. The exchange isotherms reflect the strong preference of these complexes for the clay mineral surfaces. Exchange in excess of the CEC is often observed (Schoonheydt et al., 1978). There is, however, a significant difference in exchange behaviour of the bipyridyl and phenanthroline complexes. At low ionic strength, racemic [Ru(bipy)3]2þ is exchanged up to the CEC and the enantiomers up to 1.5–2.5 times the CEC. At high ionic strength,

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Ru

Ru

L–Ru(bipy)32+

D–Ru(bipy)32+

A

B

C

D

FIGURE 5.13 Top: Configuration of the chiral tris(bipyridyl)Ru(II) complexes. Bottom: Arrangement of racemic pairs (A) and enantiomers (B) of tris(phenanthroline)Ru(II) and (C) and (D) the same for tris(bipyridyl)Ru(II) on smectite surfaces. From Sato et al. (1992), reproduced with permission of ACS.

adsorption in excess of the CEC is obtained both for racemic and enantiomeric solutions (Yamagishi, 1987, 1993; Villemure, 1990; Sato et al., 1992). [Ru(phen)3]2þ, on the other hand, adsorbs as a racemic pair when offered from a racemic solution. It adsorbs as individual molecules from enantiomeric solutions. In the former case, the amount adsorbed reaches twice the CEC; in the case of adsorption of enantiomers, exchange occurs up to the CEC (Yamagishi, 1987, 1993). This difference in exchange behaviour can be traced back to subtle differences in interaction between the complexes on the clay mineral surfaces (Sato et al., 1992). The phenanthroline complexes in a racemic solution and on the clay mineral surfaces form stable (D, L) pairs with an intermolecular distance of 0.92 nm. The intermolecular distances of the enantiomers, L–L and D–D, on the smectite surface are 1.34 nm. The bipyridyl complexes do not form (D,L) pairs and the intermolecular distances, L–D, L–L, and D–D, on the clay mineral surfaces are almost the same: 0.93 nm for a racemic pair and 0.95 nm for the enantiomers. The corresponding configurations of the bipyridyl and phenanthroline complexes are shown in Fig. 5.13. Each complex covers three hexagonal holes of the tetrahedral sheets. In the case of adsorption from racemic solutions of [M(phen)3]2þ, all the hexagonal holes are occupied. Adsorption takes place in a second layer on top of the complexes. In the case of adsorption of D– and

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L–[M(phen)3]2þ complexes from enantiomeric solutions only, half of the hexagonal holes are occupied. The surface is chiral and there is room for adsorption of molecules on the clay mineral surface in between the enantiomers. This is exactly what was observed. With L–[M(phen)3]2þ complexes on the Mt surface, D-type enantiomers were preferentially adsorbed, and vice versa (Yamagishi, 1987, 1993). This leads to two practical applications for smectites loaded with one of the enantiomers of the bipyridyl and phenanthroline complexes: (i) improvement of the optical purity of a solution by selective adsorption of one enantiomer and (ii) asymmetric synthesis or the conversion of a prochiral molecule into an optically active molecule. The first application means that a smectite loaded with D– or L–[M(II)(phen)3]2þ complexes can be used as packing material in a chromatographic column for separation of enantiomers in a racemic solution. Examples are the resolution of the L and D isomers of Co(acac)3 (acac, acetylacetonate) and of the optical isomers of amino acids, such as glycine, alanine, valine, leucine, proline, and serine (Yamagishi, 1987). The second application is in the area of chiral catalysis. Oxidation of alkylphenylsulphides to the corresponding sulphoxides over D–[Ni(phen)3]2þ–Mt in water with selectivities of 90% or more and enantiomeric excesses up to 78% has been reported (Yamagishi, 1987, 1993; Nakamura et al., 1988). Organization and compactness of the bipyridyl and phenanthroline complexes can be influenced by alkyl chains on one of the bipyridyl and phenanthroline ligands, such as in [Ru(bipy)2Li] (i ¼ 1–3) (L1 ¼ 2,20 -bipyridyl; L2 ¼ 4,40 -diundecyl-2,20 -bipyridyl; L3 ¼ 5,50 -diundecyl-2,20 -bipyridyl) (Sato et al., 2005). Such complexes with two alkyl chains on one of the bipyridyl and phenanthroline ligands are amphiphilic. Oriented films with alternating clay mineral layers and amphiphilic complexes can be prepared with the LB technique. Possible areas of application of these films are in nonlinear optics and in electron transfer processes (Tamura et al., 1999; Okamoto et al., 2000, 2001; Umemura, 2002; Umemura et al., 2002; He et al., 2004).

5.7

PROTEINS ON CLAY MINERAL SURFACES

The adsorption of positively charged proteins is an ion-exchange process, nicely illustrated with lysozyme, a protein with a molar mass of 12,500, in Fig. 5.14 (Johnston et al., 2011). These exchange isotherms have three major characteristics. i. The amount adsorbed depends on the analytic method used to determine it. With the BCA assay method, the amount of lysozyme in the equilibrium solution is determined. The amount adsorbed is calculated as the difference between the amount of lysozyme in solution before exchange and the amount in the equilibrium solution. With the three other methods, namely, thermogravimetric analysis (TGA) and determination of N and C contents, the adsorbed amount of lysozyme is determined after

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Na

BCA assay

1250

Cs

TGA

Lysozyme sorbed (mg/g clay)

Carbon content Nitrogen content

1000

750

500

250

0 0

20

40

60

0

200

400

600

800

Equilibrium concentration (mg/L) FIGURE 5.14 Adsorption isotherms of lysozyme on Naþ (left) and Csþ (right) saponite.

washing the lysozyme–saponite complex and drying it at room temperature. The main difference between these three methods and the BCA assay is the washing of the lysozyme–saponite complex before analysis. The data of Fig. 5.14 show that a fraction of weakly adsorbed lysozyme is washed away both on Naþ-saponite and on Csþ-saponite. This weakly adsorbed fraction is measured with the BCA assay method but not with TGA or analysis of C and N contents. ii. The average positive charge of a lysozyme molecule can be deduced from the ratio of the number of moles of Naþ going into solution to the number of moles of lysozyme adsorbed after washing. A Naþ/lysozyme value of þ9 was obtained. iii. The third characteristic of the isotherms seen in Fig. 5.14 is that far less lysozyme is adsorbed on Csþ-saponite than on Naþ-lysozyme. In the case of Csþ-saponite, lysozyme adsorption is not accompanied by interlayer expansion, while for Naþ-saponite a d001 spacing of 4.2 nm was observed. This 4.2 nm corresponds exactly to a monolayer of lysozyme molecules in the interlayer space. iv. The fourth characteristic of the isotherms of Fig. 5.14 is the vertical part in the beginning of the lysozyme adsorption process. For Naþ-saponite, this amounts to about 100 mg/g and for Csþ-saponite to 150 mg/g. As there is no interlayer expansion in Csþ-saponite, these adsorbed amounts correspond to the adsorption of lysozyme at the edges of the saponite layers. For protamine, a protein with a molar mass of 4500, an average charge of þ13 was obtained from the ion exchange on Naþ- and Csþ-saponites

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(Szabo et al., 2008). Complete ion exchange and intercalation was observed for Naþ-saponite. However, only one-third of the Csþ ions were exchangeable, leading to partial intercalation of protamine molecules. The interesting conclusion is that adsorption of cationic proteins in the interlayer space of smectites is dependent both on the molar mass of the proteins and on the swelling behaviour of the smectites in dilute aqueous dispersion. The adsorption of negatively charged proteins is possible only by dispersive interactions between the siloxane surface of the clay minerals and the surface atoms and functional groups of the proteins. These dispersive interactions must overcome the electrostatic repulsions of clay mineral–protein and protein– protein. Adsorption is pH-dependent and increases with decreasing negative charge of the protein molecules. Thus, one expects maximum adsorption of negatively charged proteins when the experiments can be performed as closely as possible to the point of zero charge of the protein (Quiquampoix et al., 1993). In the case of adsorbed enzymes, one often observes a shift of the pH of optimal enzymatic activity to higher values with respect to the solution pH (Quiquampoix et al., 1993). Several reasons can be invoked to explain this behaviour: (i) conformational changes of the enzyme in the adsorbed state; (ii) pH-dependent orientation of the active site of the enzyme in the adsorbed state; and (iii) exchange of inorganic cations, such as Naþ and Ca2þ, by positively charged enzymes. As a consequence, the clay mineral surface becomes hydrophobic and the enzyme will be preferentially adsorbed with its hydrophobic parts oriented towards the hydrophobic siloxane surface. Finally, the nature and amount of enzymes or proteins adsorbed determine the amount of water that can be adsorbed by the hybrid clay mineral–protein composites. In view of the importance of extra-cellular enzymes in soils and of the development of heterogeneous biocatalysts and hybrid biomaterials, knowledge of all these parameters is important and detailed investigations are needed to understand them (Quiquampoix and Burns, 2007; Ruiz-Hitzky et al., 2008).

5.8

CLAY MINERAL FILMS

There are several ways of organizing clay mineral particles: casting, spincoating, self-assembling, also called fuzzy assembling or layer-by-layer (LbL) deposition, and application of the LB technique. With all these techniques, the goal is to obtain films consisting of continuous layers of nonoverlapping elementary clay mineral layers. This ultimate goal can be attained to a large extent by self-assembling and by the LB technique, so the discussion will be limited here to these techniques. These nanofilms are ideal samples for crystal-chemical studies of the clay minerals, for studies of the adsorbed molecules, and their organization at the clay mineral surfaces and for development of electrochemical and optical devices. A review of the preparation of films containing clay mineral particles has been published recently (Zhou et al., 2011).

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5.8.1 LbL Films Self-assembling, fuzzy assembling, or LbL deposition refers to the alternate deposition of layers of positively charged molecules and layers of smectite on a suitable substrate such as glass or mica. The deposition is done from dilute aqueous solutions of cationic polymers and from dilute aqueous clay mineral dispersions. After each deposition, the excess material is washed away, and the films are gently dried before a new deposition is made. The film formation process was studied by van Duffel et al. (1999) and Kotov (2001). AFM studies show that the substrate on which the film was deposited was not fully covered with clay mineral layers and particles. Although a linear increase of film thickness with number of depositions was observed, the partial overlap of randomly oriented clay mineral layers led to film roughness (measured as the standard deviation of the film height from the average along a straight line over the film). The roughness increased with the number of layers and was proportional to the concentration of cationic polymer in the solution used for deposition. For film thicknesses of approximately 80 nm, the roughness attained values of 4–5 nm in the case of Laponite and 10–12 nm in the case of hectorite. If the cationic polymer was deposited in large amounts, it induced aggregation of clay mineral layers in the film and roughness was increased. Since Laponite has very small layer sizes, overlap of layers was minimal. Surface coverages of 90% or more could be attained, leading to relatively smooth films. Hectorite, which is composed of layers with different sizes and shapes, gave surface coverages of 60–65%, leading to a much larger roughness than for Laponite (van Duffel et al., 1999). The LbL growth of these films can be followed with spectroscopy. In the case of clay mineral–protein films, the deposition of protein layers is seen in the growth of the amide I band at 1658 cm–1 with the number of layers. The deposition of clay mineral layers is followed with the intensity of the Si–O stretching vibration around 1000 cm–1. In both cases, a stepwise increase of the intensities of these bands is detected (Fig. 5.15; Szabo et al., 2007). When a layer of protein molecules was deposited, the amide I band increased in intensity and the Si–O band intensity remained constant. Conversely, when a layer of clay mineral layers was deposited, the Si–O band intensity increased and the amide I band intensity remained constant. Anyhow, films were prepared with magnetic properties (Mamedov and Kotov, 2000; Mamedov et al., 2000), with nonlinear optical properties (van Duffel et al., 2001), and for sensing applications (Kleinfeld and Ferguson, 1994; de Melo et al., 2002; Qian et al., 2002; Zhou et al., 2002).

5.8.2 LB Films An elegant method to prepare films of clay minerals is the LB technique. A solution of amphiphilic molecules in a volatile solvent is spread on the water

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A

B 0.20

-1

A (1000 cm )

0.20

0.8

1.6 0.15

1.4

0.10

pH 8 0.00 0

0.15

1

2

3

4

5

7

6

0.6 pH 4

0.4

pH 4

0.05

Absorbance at 1000 cm-1

Absorbance at 1658 cm-1

-1

A (1658 cm )

0.25

8

Layer number

0.10

Lysozyme 0.05

Papain

1.2

pH 8

0.2

1.0

0 0

1

2

3

4

5

6

7

8

Layer number

0.8 0.6 0.4

Lysozyme Papain

0.2

Protamine

Protamine 0.00

0.0 0

1

2

3

4

5

Layer number

6

7

8

0

1

2

3

4

5

6

7

8

Layer number

FIGURE 5.15 IR absorbance of (A) amide I band (at 1658 cm–1) and (B) in-plane Si–O band (at 1000 cm–1) of the protein/saponite assemblies deposited on ZnSe crystal at pH 4 as a function of the number of individual layers. Insets: Build-up functions of papain films deposited at pH 4 and 8.

surface of dilute aqueous clay mineral dispersion in an LB trough. The dispersion is prepared at least 24 h before use and subjected to an ultrasonic treatment to ensure complete swelling and delamination of the clay mineral particles. An instantaneous ion-exchange reaction between the clay mineral particles and the amphiphilic cations takes place at the air–water interface, giving a monolayer of delaminated clay mineral particles covered with amphiphilic cations. The monolayer is then compressed and transferred to a substrate by vertical upstroke or horizontal deposition. If the substrate is hydrophilic, vertical deposition is preferred; if it is hydrophobic, one can perform the horizontal deposition. In the first case, the sequence is substrate/clay mineral/amphiphilic cation; in the second case, it is substrate/amphiphilic cation/clay mineral. Multilayers are constructed by repetition of the procedure. The film thickness and the amount of amphiphiles are checked in the case of horizontal deposition. Both are found to increase linearly with the number of layers deposited, thus indicating that, on the average, the overall composition of the layers is identical (Umemura et al., 2001a,b). AFM study reveals beyond any doubt that the LB films contain elementary clay mineral layers with typical shapes: laths of hectorite, laths and irregularly shaped plates in the case of saponite, irregular plate-like shapes for Wyoming bentonite, and aggregates of very small layers in the case of Laponite (Szabo et al., 2009). All clay mineral layers are horizontally deposited, and this calls for a spectroscopic study with polarized light. Polarized FTIR spectra of the Si–O vibrations and the structural O–H vibrations of saponite are shown in Fig. 5.16. The band positions and dichroic ratios are given in Table 5.4 (Ras et al., 2003). Highly resolved spectra of the in-plane and out-of-plane Si–O vibrations have been obtained. It is confirmed that the structural OH groups of the trioctahedral

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A

B

996

3680 In-plane n(Si–O) n(OH)

0.05 au

0.002 au

Out-of-plane n(Si–O)

Ap

1063

Ap

As

As

3800

3600

3400

3200

1200

1100

1000

900

800

Wavenumber (cm-1)

Wavenumber (cm-1)

FIGURE 5.16 Polarized ATR-FTIR spectra of a hybrid Langmuir–Blodgett monolayer of SapCa-1 saponite clay and dioctadecyl thiacyanine surfactant prepared on a 50 mg dm–3 clay dispersion, deposited on ZnSe at a surface pressure of 5 mN m–1: (A) n(OH) region and (B) n(Si–O) region.

TABLE 5.4 Band Positions (cm–1) and Dichroic Ratios R (As/Ap)a of Si–O and O–H Vibrations Si–O vibration

Saponite

Dichroic ratio

Wyoming bentonite

Dichroic ratio

In-plane Si–O

996

1.11

1024

1.11

Out-of-plane Si–O

1063

0.23

1085

0.12

Stretching O–H

3680

0.33

3628

1.08

Bending O–H

b

919

1.18

885

1.13

846

1.31

a

As and Ap are, respectively, the absorption of the in-plane and out-of-plane polarized light. Not detectable with ZnSe as substrate.

b

saponite are vibrating almost perpendicularly to the planar surface while those of the dioctahedral Wyoming bentonite almost horizontally in the plane to the surface of the clay minerals layers. The OH bending vibrations of Wyoming bentonite had slightly different dichroic ratios, suggesting that the orientation of these OH groups depends on the cationic composition of the octahedral sheet: AlAlOH (919 cm–1), AlFeOH (885 cm–1), and AlMgOH (846 cm–1).

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There are several spectroscopic techniques available to study the amphiphilic molecules adsorbed in the mono and multilayers, the most popular being FTIR, fluorescence, and UV–Vis spectroscopies. With the octadecylammonium (ODA) cation as the amphiphilic cation, the most prominent observations are the following: – The organization of the alkyl chains is dependent on the amount of the clay mineral particles in the dispersion of the LB trough. At low clay mineral concentration (<10 ppm), the alkyl chains are highly ordered, similar to a crystalline ordering. This is reflected in the position of the CH2 stretching vibration at 2925 cm–1. At higher clay mineral concentration (>10 ppm), the alkyl chains are disordered, as evidenced from the 2917 cm–1 position of the CH2 stretch (Ras et al., 2005). This difference in ordering was also observed by Umemura et al. (2003). It indicated that, at low clay mineral concentration, the ODA cations are organized at the air–water interface of the LB trough in two-dimensional crystalline aggregates to which the clay mineral particles are attached. At higher clay concentrations, the clay mineral layers are attached to the ODA cations at the air–water interface before the formation of the two-dimensional crystalline aggregates. In both cases, the alkyl chains are oriented largely perpendicular to the surface (Umemura et al., 2003). – The monolayer films of clay mineral layers and ODA cations deposited on ZnSe by upstroke vertical deposition did not contain water (Ras et al., 2003). This means that, in the configuration of ZnSe/clay mineral/ODA, there is no water at both the ZnSe/clay mineral and clay mineral/ODA interfaces, thus indicating that there are no residual Naþ cations and that the dense ODA layer is completely hydrophobic. Two remarks end this discussion of the ODA–clay mineral films: i. The ammonium group of the molecule is oxidized to the corresponding carbamate in the presence of dissolved CO2 and methanol. The latter is present in the chloroform solution used to spread ODA cations on the surface of water (Ras et al., 2005); ii. Short-chain, water-soluble alkylammonium cations can also be used for construction of hybrid clay mineral/alkylammonium films (Umemura et al., 2001a,b). This means that, under suitable conditions, the alkylammonium cations are captured by the clay mineral layers at the air–water interface before they are solubilized in the water of the sub-phase. Hybrid clay mineral–dye systems can be converted into optical materials if the organization of both the clay mineral layers and the molecules can be controlled. Thus, films (i) with nonlinear optical properties (Ogata et al., 2002, 2003a,b; Umemura et al., 2002; Higashi et al., 2006; Kawamata et al., 2006, 2008), (ii) with two-photon absorption (Kawamata et al., 2010), and (iii) with fluorescence resonance energy transfer properties were prepared and reported (Takagi et al., 2006; Hussain and Schoonheydt, 2010; Hussain et al., 2010).

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5.9 PERSPECTIVES Swelling clay minerals have the remarkable ability to accommodate molecules in their interlayer spaces. i. Weakly coordinated axial water molecules are stripped off from polyamine complexes and the remaining planar complexes are strongly stabilized in the interlayer space. ii. The organization of chiral tris(bipyridyl) and tris(phenanthroline) complexes depends on the size-matching of these complexes with the ditrigonal holes on the surface of the tetrahedral sheets of the clay mineral layers and on subtle interactions between the adsorbed molecules. An extension of this research to chiral complexes and chiral molecules of different sizes and shapes would allow a generalization of these principles of size-matching and molecular interactions. iii. Aggregation of cationic dyes is favoured in aqueous clay mineral dispersions. Upon removal of water molecules, dye–surface interactions dominate, leading to the break-up of the aggregates and adsorbed monomers. Clearly, water molecules attenuate the dye molecule–surface interactions. As a consequence, dye molecule–molecule interactions prevail. It would be interesting to repeat these experiments in less polar solvents such as methanol to see how the balance between molecule–molecule interactions and molecule–surface interactions shifts. iv. Interlayer adsorption of cationic proteins depends on their molar mass and on the swelling of the clay minerals in the aqueous dispersion. Thus a monolayer of proteins was adsorbed on Naþ-saponite. There was no or only partial interlayer adsorption on Csþ-saponite. The research field is still wide open. The shape of adsorbed protein molecules generally is different from that in solution. The distributions of the charge and hydrophobic and hydrophilic parts over the protein surface are all factors that influence adsorption but have not been investigated systematically. The insights gained so far form the basis for the construction of clay mineral-based functional materials, of which clay mineral (bio)polymer nanocomposites are the best known (see Chapter 13). A higher level of organization is obtained in films, especially those obtained with the LB technique. The mechanism of film formation at the air–water interface is not fully understood. An ion-exchange reaction occurs in which the Naþ ions are replaced by the amphiphilic cations at the air–water interface. It requires the migration of delaminated clay mineral particles towards the air–water interface (against gravitational forces) and the diffusion of anions, associated with the amphiphilic cations, into the aqueous dispersion. There must be a huge difference in diffusion coefficients of the anions and the clay mineral layers. Up to now, functional films have been prepared, in which the functionality is associated with the adsorbed amphiphilic

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molecules and their organization at the clay mineral surface. It might be relevant to synthesize clay mineral layers with functionality in the layer itself. One can think of transition-metal ions with variable oxidation states in the lattice, Fe3þ/Fe2þbeing the best known example. Synthetic organoclays with functionality in the organic moiety is also possible. Such research efforts are very desirable and highly necessary if one wants to put clay minerals on the scene of materials science research at the place that they deserve.

REFERENCES Alba, M.D., Alvero, R., Becerro, A.I., Castro, M.A., Trillo, J.M., 1998. Chemical behavior of lithium ions in reexpanded Li-montmorillonites. J. Phys. Chem. B 102, 2207–2213. Alvero, R., Alba, M.D., Castro, M.A., Trillo, J.M., 1994. Reversible migration of lithium in montmorillonites. J. Phys. Chem. 98, 7848–7853. Anderson, R.L., Ratcliffe, I., Greenwell, H.C., Williams, P.A., Cliffe, S., Coveney, P.V., 2010. Clay swelling—a challenge in the oilfield. Earth Sci. Rev. 98, 201–216. Bank, S., Bank, J.F., Ellis, P.D., 1989. Solid-state 113Cd nuclear magnetic resonance study of exchanged montmorillonites. J. Phys. Chem. 93, 4847–4855. Bishop, J.L., Pieters, C.M., Edwards, J.O., 1994. Infrared spectroscopic analyses on the nature of water in montmorillonite. Clays Clay Miner. 42, 702–716. Bowers, G.M., Bish, D.L., Kirkpatrick, R.J., 2008. H2O and cation structure and dynamics in expandable clays: H-2 and K-39 NMR investigations of hectorite. J. Phys. Chem. C 112, 6430–6438. Boyd, S.A., Johnston, C.T., Laird, D.A., Teppen, B.J., Li, H., 2011. Comprehensive study of organic contaminant adsorption by clays: methodologies, mechanisms, and environmental implications. In: Biophysico-Chemical Processes of Anthropogenic Organic Compounds in Environmental Systems. John Wiley & Sons, New York, pp. 51–71. Bujda´k, J., 2006. Effect of the layer charge of clay minerals on optical properties of organic dyes. Appl. Clay Sci. 34, 58–73. Burgess, J., 1978. Metal Ions in Solution. Ellis Horwood Ltd. Publisher, Chichester, 481 pp. Buswell, A.M., Krebs, K., Rodebush, W.H., 1937. Infrared studies. III. Absorption bands of hydrogels between 2.5 and 3.5 micrometers. J. Am. Chem. Soc. 59, 2603–2605. Cebula, D.J., Thomas, R.K., White, J.W., 1981. Diffusion of water in Li-montmorillonite studied by quasielastic neutron scattering. Clays Clay Miner. 29, 241–248. Cenens, J., Schoonheydt, R.A., 1988. Visible spectroscopy of methylene blue on hectorite, Laponite B and barasym. Clays Clay Miner. 36, 214–224. Charnay, C., Lagerge, S., Partyka, S., 2001. Assessment of the surface heterogeneity of talc materials. J. Colloid Interface Sci. 233, 250–258. Croteau, T., Bertram, A.K., Patey, G.N., 2009. Simulation of water adsorption on kaolinite under atmospheric conditions. J. Phys. Chem. A 113, 7826–7833. Croteau, T., Bertram, A.K., Patey, G.N., 2010. Water adsorption on kaolinite surfaces containing trenches. J. Phys. Chem. A 114, 2171–2178. Cygan, R.T., Greathouse, J.A., Heinz, H., Kalinichev, A.G., 2009. Molecular models and simulations of layered materials. J. Mater. Chem. 19, 2470–2481. De Melo, P.M., Cosnier, S., Mousty, C., Martelet, C., Jaffrezic-Renault, N., 2002. Urea biosensors based on immobilization of urease into two oppositely charged clays (Laponite and Zn-Al layered double hydroxide). Anal. Chem. 74, 4037–4043.

166

Handbook of Clay Science

Del Monte, F., Ferrer, M.L., Levy, D., 2001. Preferred formation of coplanar inclined fluorescent J-dimers in rhodamine 101 doped silica gels. Langmuir 17, 4812–4817. Earl, W.L., Johnston, C.T., 1998. Applications of NMR spectroscopy to the study of the chemistry of environmental interfaces. In: Huang, P.M., Senesi, N., Buffle, J. (Eds.), Structure and Surface Reactions of Soil Particles. John Wiley, New York, pp. 251–280 Chapter 7. Feller, D., Glendening, E.D., Woon, D.E., Feyereisen, M.W., 1995. An extended basis-set abinitio study of alkali-metal cation-water clusters. J. Chem. Phys. 103, 3526–3542. Gevers, C., Grandjean, J., 2001. A multinuclear magnetic resonance study of synthetic clays suspended in water and in dodecyldimethylamine oxide solutions. J. Colloid Interface Sci. 236, 290–294. Giese, R.F., van Oss, C.J., 1993. The surface thermodynamic properties of silicates and their interactions with biological materials. In: Guthrie, G.D., Mossman, B.T. (Eds.), Health Effects of Mineral Dusts, Reviews in Mineralogy 28, pp. 327–346. Chapter 10. Giese, R.F., van Oss, C.J., Norris, J., Costanzo, P.M., 1990. Surface energies of some smectite clay minerals. In: Farmer, C.V., Tarento, R.J. (Eds.), Proc. of the 9th Int. Clay Conf. (Strasbourg, France, 1989), vol. 2, 33–41. Glendening, E.D., Feller, D., 1995. Cation-water interactions: the Mþ(H2O)n clusters for alkali metals, M ¼ Li, Na, K, Rb, and Cs. J. Phys. Chem. 99, 3060–3067. Glendening, E.D., Feller, D., 1996. Dication-water interactions: M2þ(H2O)n clusters for alkaline earth metals M¼Mg, Ca, Sr, Ba, and Ra. J. Phys. Chem. 100, 4790–4797. Graham, J., 1964. Adsorbed water on clays. Rev. Pure Appl. Chem. 14, 81–91. Hanaya, M., Harris, R.K., 1998. Two-dimensional Na-23 MQ MAS NMR study of layered silicates. J. Mater. Chem. 8, 1073–1079. He, J.-X., Yamagishi, A., Iwao, M., Abe, Y., Umemura, Y., 2004. Creation of a novel solid surface as a model photosynthetic system. II. Application of the LB and self-assembly methods to fixation of a light driven polypyridyl Ru(II) complex. Electrochem. Commun. 6, 61–65. Henniker, J.C., 1949. The depth of the surface zone of a liquid. Rev. Mod. Phys. 21, 322–341. Higashi, T., Miyazaki, S., Nakamura, S., Seike, R., Tani, S., Hayami, S., Kawamata, J., 2006. Nonlinear optical properties of Langmuir-Blodgett films consisting of metal complexes. Colloids Surf. A Physicochem. Eng. Asp. 284–285, 161–165. Hofmann, U., Klemen, R., 1950. Verlust der Austauschfa¨higkeit von Lithiumionen an Bentonit durch Erhitzung. Z. Allg. Anorg. Chem. 262, 95–99. Huheey, J.E., 1978. Inorganic Chemistry: Principles of Structure and Reactivity, second ed. Harper and Rox, New York, p. 737. Hussain, S.A., Schoonheydt, R.A., 2010. Langmuir-Blodgett monolayers of cationic dyes in the presence and absence of clay minerals: N, N’-dioctadecyl thiacyanine, octadecyl rhodamine B and Laponite. Langmuir 26, 11870–11877. Hussain, S.A., Chakraborty, S., Bhattarcharjee, D., Schoonheydt, R.A., 2010. Fluorescence resonance energy transfer between organic dyes adsorbed onto nano-clays and Langmuir-Blodgett films. Spectrochim. Acta A Mol. Biomol. Spectrosc. 75, 664–670. Jacobs, K.Y., Schoonheydt, R.A., 2001. Time dependence of the spectra of methylene blue-clay mineral suspensions. Langmuir 17, 5150–5155. Jaynes, W.F., Boyd, S.A., 1990. Trimethylphenylammonium-smectite as an effective adsorbent of water soluble aromatic-hydrocarbons. J. Air Waste Manag. Assoc. 40, 1649–1653. Johnston, C.T., 1996. Sorption of organic compounds on clay minerals: a surface functional group approach. In: Sawhney, B. (Ed.), Organic Pollutants in the Environment. Clay Minerals Society, Boulder, CO, pp. 1–44. Chapter 1.

Chapter

5

Surface and Interface Chemistry of Clay Minerals

167

Johnston, C.T., 2010. Probing the nanoscale architecture of clay minerals. Clay Miner. 45, 245–279. Johnston, C.T., Tomba´cz, E., 2002. Surface chemistry of soil minerals. In: Dixon, J.B., Schulze, D.G. (Eds.), Soil Mineralogy with Environmental Applications. Soil Science Society of America, Madison, pp. 37–67. Chapter 2. Johnston, C.T., Sposito, G., Erickson, C., 1992. Vibrational probe studies of water interactions with montmorillonite. Clays Clay Miner. 40, 722–730. Johnston, C.T., Premachandra, G.S., Szabo, T., Lok, J., Schoonheydt, R.A., 2011. Interaction of biological molecules with clay minerals: a combined spectroscopic and sorption study of lysozyme on saponite. Langmuir 28, 611–619. Kasha, M., Rawls, H.R., Ashraf El-Bayoumi, M., 1965. The exciton model in molecular spectroscopy. Pure Appl. Chem. 11, 371–392. Kawamata, J., Seike, R., Higashi, T., Inada, Y., Sasaki, J., Ogata, Y., Tani, S., Yamagishi, A., 2006. Clay templating Langmuir-Blodgett films of non-amphiphilic ruthenium(II) complexes. Colloids Surf. A Physicochem. Eng. Asp. 284–285, 135–139. Kawamata, J., Yamaki, H., Ohshiye, R., Seike, R., Tani, S., Ogata, Y., Yamagishi, A., 2008. Fabrication of hybrid LB films consisting of a smectite clay and a nonamphiphilic chiral ruthenium complex. Colloids Surf. A Physicochem. Eng. Asp. 321, 65–69. Kawamata, J., Suzuki, Y., Tenma, Y., 2010. Fabrication of clay mineral–dye composites as nonlinear optical materials. Philos. Mag. 90, 2519–2527. Kim, Y., Kirkpatrick, R.J., 1997. Na-23 and Cs-133 NMR study of cation adsorption on mineral surfaces: local environments, dynamics, and effects of mixed cations. Geochim. Cosmochim. Acta 61, 5199–5208. Kleinfeld, E.R., Ferguson, G.S., 1994. Stepwise formation of multilayered nanostructural films from macromoleular precursors. Science 265, 370–373. Kotov, N.A., 2001. Ordered layered assemblies of nanoparticles. Mater. Res. Bull 26, 992–997. Laird, D.A., 2006. Influence of layer charge on swelling of smectites. Appl. Clay Sci. 34, 74–87. Laperche, V., Lambert, J.F., Prost, R., Fripiat, J.J., 1990. High-resolution solid-state NMR of exchangeable cations in the interlayer surface of a swelling mica: 23Na, 111Cd, And 133Cs vermiculites. J. Phys. Chem. 94, 8821–8831. Lee, J.F., Mortland, M.M., Chiou, C.T., Kile, D.E., Boyd, S.A., 1990. Adsorption of benzene, toluene, and xylene by two tetramethylammonium-smectites having different charge densities. Clays Clay Miner. 38, 113–120. Li, H., Johnston, C.T., Boyd, S.A., Teppen, B.J., 2012. Relating clay structural factors to dioxin adsorption by smectites: molecular dynamics simulations. Soil Sci. Soc. Am. J. 76, 110–120. Liu, C., Li, H., Teppen, B.J., Johnston, C.T., Boyd, S.A., 2009. Mechanisms associated with the high adsorption of dibenzo-p-dioxin from water by smectite clays. Environ. Sci. Technol. 43, 2777–2783. Lopez Arbeloa, F., Martinez Martinez, V., Ban˜uelos Prieto, J., Lopez Arbeloa, I., 2002. Adsorption of rhodamine 3B dye on saponite colloidal particle in aqueous suspension. Langmuir 18, 2658–2664. Low, P.F., 1961. Physical chemistry of clay-water interactions. Adv. Agron. 13, 269–327. Low, P.F., 1980. The swelling of clay: II. Montmorillonites. Soil Sci. Soc. Am. Proc. 44, 667–676. Lu, L., Jones, R.M., McBranch, D., Whitten, D., 2002. Surface enhanced superquenching of cyanine dyes as J aggregate on Laponite nanoparticles. Langmuir 18, 7706–7713.

168

Handbook of Clay Science

Maes, A., Cremers, A., 1978. Stability of metal uncharged ligand complexes in ion exchangers. Part 3. Complex ion selectivity and stepwise stability constants. J. Chem. Soc. Faraday Trans. 1 74, 2470–2480. Maes, A., Cremers, A., 1979. Stability of metal uncharged ligand complexes in ion exchangers. Part 4. Hydration effects and stability changes of copper-ethylenediamine complexes in montmorillonite. J. Chem. Soc. Faraday Trans. 1 75, 513–524. Maes, A., Marynen, P., Cremers, A., 1977. Stability of metal uncharged ligand complexes in ion exchangers. Part 1. Quantitative characterization and thermodynamic basis. J. Chem. Soc. Faraday Trans. 1 73, 1297–1301. Maes, A., Peigneur, P., Cremers, A., 1978. Stability of metal uncharged ligand complexes in ion exchangers. Part 2. The copper þ ethylenediamine complex in montmorillonite and sulphonic acid resin. J. Chem. Soc. Faraday Trans. 1 74, 182–189. Maes, A., Schoonheydt, R.A., Cremers, A., Uytterhoeven, J.B., 1980. Spectroscopy of Cu(en)22þ on clay surfaces. Surface and charge density effects. J. Phys. Chem. 84, 2795–2799. Malandrini, H., Clauss, F., Partyka, S., Douillard, J.M., 1997. Interactions between talc particles and water and organic solvents. J. Colloid Interface Sci. 194, 183–193. Malikova, N., Cadene, A., Marry, V., Dubois, E., Turq, P., Zanotti, J.M., Longeville, S., 2005. Diffusion of water in clays—microscopic simulation and neutron scattering. Chem. Phys. 317, 226–235. Malikova, N., Cadene, A., Dubois, E., Marry, V., Durand-Vidal, S., Turq, P., Breu, J., Longeville, S., Zanotti, J.M., 2007. Water diffusion in a synthetic hectorite clay studied by quasi-elastic neutron scattering. J. Phys. Chem. C 111, 17603–17611. Malikova, N., Dubois, E., Marry, V., Rotenberg, B., Turq, P., 2010. Dynamics in clays—combining neutron scattering and microscopic simulation. Int. J. Res. Phys. Chem. Chem. Phys. 224, 153–181. Mamedov, A.A., Kotov, N.A., 2000. Free standing layer-by-layer assembled films of magnetite nanoparticles. Langmuir 16, 5530–5533. Mamedov, A.A., Ostrander, J., Aliev, F., Kotov, N.A., 2000. Stratified assemblies of magnetite nanoparticles and montmorillonite prepared by the layer-by-layer assembly. Langmuir 16, 3941–3949. Marry, V., Rotenberg, B., Turq, P., 2008. Structure and dynamics of water at a clay surface from molecular dynamics simulation. Phys. Chem. Chem. Phys. 10, 4802–4813. McBride, M.B., 1997. A critique of diffuse double layer models applied to colloid and surface chemistry. Clays Clay Miner. 45, 598–608. McBride, M.B., Baveye, P., 2002. Diffuse double-layer models, long-range forces, and ordering in clay colloids. Soil Sci. Soc. Am. J. 66, 1207–1217. Mering, J., 1946. On the hydration of montmorillonite. Trans. Faraday Soc. 42, 205–219. Michot, L.J., Villieras, F., Francois, M., Yvon, J., LeDred, R., Cases, J.M., 1994. The structural microscopic hydrophilicity of talc. Langmuir 10, 3765–3773. Mooney, R.W., Keenan, A.G., Wood, L.A., 1952a. Adsorption of water vapor by montmorillonite. I. Heat of desorption and application of BET theory. J. Am. Chem. Soc. 74, 1367–1374. Mooney, R.W., Keenan, A.G., Wood, L.A., 1952b. Adsorption of water vapor by montmorillonite. II. Effect of exchangeable ions and lattice swelling as measured by X-ray diffraction. J. Am. Chem. Soc. 74, 1371–1374. Mortier, W.J., 1987. Electronegativity equalization and its applications. Struct. Bond. 66, 125–143. Nakamura, Y., Yamagishi, A., Iwamoto, T., Koga, M., 1988. Adsorption properties of montmorillonite and synthetic saponite as probing materials in liquid column chromatography. Clays Clay Miner. 36, 530–536.

Chapter

5

Surface and Interface Chemistry of Clay Minerals

169

Nemecz, E., 1981. Clay Minerals. Akademiai Kiado, Budapest. Newman, A.C.D., 1987. The interaction of water with clay mineral surfaces. In: Newman, A.C.D. (Ed.), Chemistry of Clays and Clay Minerals. The Mineralogical Society, London, pp. 1–480. Monograph No. 6. Nulens, K.H.L., Toufar, H., Janssens, G.O.A., Schoonheydt, R.A., Johnston, C.T., 1998. Clay minerals and clay mineral-water interactions: a combined EEM-Monte Carlo Study. In: Yamagishi, A., Aramata, A., Taniguchi, M. (Eds.), The Latest Frontiers of Clay Chemistry. Proceedings of the Sapporo Conference on the Chemistry of Clays and Clay Minerals (Sapporo, Japan, 1996). The Smectite Forum of Japan, Sendai, pp. 116–133. Ogata, Y., Kawamata, J., Chong, C.-C., Mahikara, M., Yamagishi, A., Saito, G., 2002. Optical second harmonic generation of zwitterionic molecules aligned on clays. Mol. Cryst. Mol. Liq. 376, 345–350. Ogata, Y., Kawamata, J., Chong, C.-C., Yamagishi, A., Saito, G., 2003a. Structural features of a clay film hybridized with a zwitterionic molecule as analyzed by second harmonic generation behavior. Clays Clay Miner. 51, 181–185. Ogata, Y., Kawamata, J., Yamagishi, A., Chong, C.-C., Saito, G., 2003b. A novel film with noncentrosymmetric molecular alignment of D-p-A zwitterionic molecules fabricated at an airwater interface. Synth. Met. 133–134, 671–672. Okamoto, K., Tamura, K., Takahashi, M., Yamagishi, A., 2000. Preparation of a clay-complex hybrid film by the Langmuir-Blodgett method and its application as an electrode modifier. Colloids Surf. A Physicochem. Eng. Asp. 169, 241–249. Okamoto, K., Taniguchi, M., Takahashi, M., Yamagishi, A., 2001. Studies on energy transfer from chiral polypyridyl Ru(II) to Os(II) complexes in cast and Langmuir-Blodgett films. Langmuir 17, 195–201. 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. Porion, P., Faugere, A.M., Delville, A., 2005. Analysis of the degree of nematic ordering within dense aqueous dispersions of charged anisotropic colloids by Na-23 NMR spectroscopy. J. Phys. Chem. B 109, 20145–20154. Porion, P., Faugere, A.M., Delville, A., 2009. Long-time scale ionic dynamics in dense clay sediments measured by the frequency variation of the Li-7 multiple-quantum NMR relaxation rates in relation with a multiscale modeling. J. Phys. Chem. C 113, 10580–10597. Prost, R., Koutit, T., Benchara, A., Huard, E., 1998. State and location of water adsorbed on clay minerals: consequences of the hydration and swelling-shrinkage phenomena. Clays Clay Miner. 46, 117–131. Qian, D.-J., Nakamura, C., Wenk, S.-O., Ishikawa, H., Zorin, N., Miyake, J., 2002. A hydrogen biosensor made of clays, poly(butylviologen) and hydrogenase sandwiched on a glass carbon electrode. Biosens. Bioelectron. 17, 789–796. Quiquampoix, H., Burns, R.G., 2007. Interactions between proteins and soil mineral surfaces: environmental and health consequences. Elements 3, 401–406. Quiquampoix, H., Staunton, S., Baron, M.H., Ratcliffe, R.G., 1993. Interpretation of the pH dependence of protein adsorption on clay mineral surfaces and its relevance to the understanding of extra-cellular enzyme activity in soils. Colloids Surf. A Physicochem. Eng. Asp. 75, 85–93. Quirk, J.P., 2003. Comments on “Diffuse double-layer models, long-range forces, and ordering of clay colloids” Soil Sci. Soc. Am. J. 67, 1960–1961. Rana, K., Boyd, S.A., Teppen, B.J., Li, H., Liu, C., Johnston, C.T., 2009. Probing the microscopic hydrophobicity of smectite surfaces. A vibrational spectroscopic study of dibenzo-p-dioxin sorption to smectite. Phys. Chem. Chem. Phys. 11, 2976–2985.

170

Handbook of Clay Science

Ras, R.H.A., Johnston, C.T., Franses, E.I., Ramaekers, R., Maes, G., Foubert, P., De Schryver, F. C., Schoonheydt, R.A., 2003. Polarized infrared study of hybrid Langmuir-Blodgett monolayers containing clay mineral nanoparticles. Langmuir 19, 4295–4302. Ras, R.H.A., Johnston, C.T., Schoonheydt, R.A., 2005. Chemical instability of octadecylammonium monolayers. Chem. Commun. 4095–4096. Rinnert, E., Carteret, C., Humbert, B., Fragneto-Cusani, G., Ramsay, J.D.F., Delville, A., Robert, J.L., Bihannic, I., Pelletier, M., Michot, L.J., 2005. Hydration of a synthetic clay with tetrahedral charges: a multidisciplinary experimental and numerical study. J. Phys. Chem. B 109, 23745–23759. Ruiz-Hitzky, E., Ariga, K., Lvov, Y. (Eds.), 2008. Bio-inorganic Hybrid Materials: Strategies, Syntheses, Characterization and Applications. Wiley, New York, 503 pp. Russell, J.D., Farmer, V.C., 1964. Infra-red spectroscopic study of the dehydration of montmorillonite and saponite. Clay Miner. Bull. 5, 443–464. Sanderson, R.T., 1976. Chemical Bonds and Bond Energies, second ed. Academic Press, New York. Sato, H., Yamagishi, A., Kato, S., 1992. Monte Carlo simulations for the interactions of metal complexes with silicate sheets of clay. Comparison of binding sites between tris(1,10-phenanthroline)metal(II) and tris(2,2’-bipyridine)metal(II) chelates. J. Am. Chem. Soc. 114, 10933–10940. Sato, H., Hizoue, Y., Tamura, K., Yamagishi, A., 2005. Orientational tuning of a polypyridyl Ru (II) complex immobilized on a clay surface towards chiral discrimination. J. Phys. Chem. B 109, 18935–18941. Sauer, J., 1989. Molecular models in ab initio studies of solids and surfaces: from ionic crystals and semiconductors to catalysts. Chem. Rev. 89, 199–255. Schoonheydt, R.A., Johnston, C.T., 2007. Surface and interface chemistry of clay minerals. In: Bergaya, F., Theng, B.K.G., Lagaly, G. (Eds.), Handbook of Clay Science. Elsevier, Amsterdam, pp. 87–112. Chapter 3. Schoonheydt, R.A., Pelgrims, J., 1983. Preparation, spectroscopy and reaction with O2 of Co (en)22þ on the surface of hectorite. J. Chem. Soc. Faraday Trans. 2 79, 1169–1180. Schoonheydt, R.A., Pelgrims, J., Heroes, Y., Uytterhoeven, J.B., 1978. Characterization of tris (2,2’-bipyridyl)ruthenium(II) on hectorite. Clay Miner. 13, 435–438. Schoonheydt, R.A., Velghe, F., Uytterhoeven, J.B., 1979. Characterization of [Ni(en)x]2þ (x ¼ 1,2,3; en ¼ ethylenediamine) on the surface of montmorillonite. Inorg. Chem. 18, 1842–1847. Schrader, M.E., Yariv, S., 1990. Wettability of clay minerals. J. Colloid Interface Sci. 136, 85–94. Sobolev, O., Buivin, F.F., Kemner, E., Russina, M., Beuneu, B., Cuello, G.J., Charlet, L., 2010. Water-clay surface interaction: a neutron scattering study. Chem. Phys. 374, 55–61. Sposito, G., 1972. Thermodynamics of swelling clay-water systems. Soil Sci. 114, 243–251. Sposito, G., Prost, R., 1982. Structure of water adsorbed on smectites. Chem. Rev. 82, 553–573. Sposito, G., Prost, R., Gaultier, J.P., 1983. Infrared spectroscopic study of adsorbed water on reduced-charge Na/Li montmorillonites. Clays Clay Miner. 31, 9–16. S´rodo n, J., McCarty, D.K., 2008. Surface area and layer charge of smectite from CEC and EGME/ H2O-retention measurements. Clays Clay Miner. 56, 155–174. Swenson, J., Bergman, R., Howells, W.S., 2000. Quasielastic neutron scattering of twodimensional water in a vermiculite clay. J. Chem. Phys. 113, 2873–2879. Szabo, T., Szekeres, M., Dekany, I., Jackers, C., De Feyter, S., Johnston, C.T., Schoonheydt, R.A., 2007. Layer-by-layer construction of ultrathin hybrid films with proteins and clay minerals. J. Phys. Chem. C 111, 12730–12740.

Chapter

5

Surface and Interface Chemistry of Clay Minerals

171

Szabo, T., Mitea, R., Leeman, H., Premachandra, G.S., Johnston, C.T., Szekeres, M., Dekany, I., Schoonheydt, R.A., 2008. Adsorption of protamine and papain proteins on saponite. Clays Clay Miner. 56, 494–504. Szabo, T., Wang, J., Volodin, A., Van Haesendonck, Ch., Schoonheydt, R.A., 2009. AFM study of smectites in Langmuir-Blodgett films: saponite, Wyoming bentonite, hectorite and Laponite. Clays Clay Miner. 57, 706–714. Takagi, S., Eguchi, M., Tryk, D.A., Inoue, H., 2006. Porphyrin photochemistry in inorganic/ organic hybrid materials: clays, semiconductors, nanotubes and mesoporous materials. J. Photochem. Photobiol. C 7, 104–126. Tamura, K., Setsuda, H., Tanugichi, M., Yamagishi, A., 1999. Application of the LangmuirBlodgett technique to prepare a clay-metal complex hybrid film. Langmuir 15, 6915–6920. Tunega, D., Benco, L., Haberhauer, G., Gerzabek, M.H., Lischka, H., 2002. Ab initio molecular dynamics study of adsorption sites on the (001) surfaces of 1:1 dioctahedral clay minerals. J. Phys. Chem. B 106, 11515–11525. Tunega, D., Gerzabek, M.H., Lischka, H., 2004. Ab initio molecular dynamics study of a monomolecular water layer on octahedral and tetrahedral kaolinite surfaces. J. Phys. Chem. B 108, 5930–5936. Umemura, Y., 2002. Hybrid films of a clay mineral and an iron(II) complex cation prepared by a combined method of the Langmuir-Blodgett and self-assembly techniques. J. Phys. Chem. B 106, 11168–11171. Umemura, Y., Yamagishi, A., Schoonheydt, R.A., Persoons, A., De Schryver, F.C., 2001a. Fabrication of hybrid films of alkylammonium cations (CnH2nþ1NH3þ; n¼ 4-18) and a smectite clay by the Langmuir-Blodgett method. Langmuir 17, 449–455. Umemura, Y., Yamagishi, A., Schoonheydt, R.A., Persoons, A., De Schryver, F.C., 2001b. Formation of hybrid monolayers of alkylammonium cations and a clay mineral at the air-water interface: clay as an inorganic stabilizer of soluble alkylammonium amphiphiles. Thin Solid Films 388, 5–8. Umemura, Y., Yamagishi, A., Schoonheydt, R., Persoons, A., De Schryver, F., 2002. LangmuirBlodgett films of a clay mineral and ruthenium(II) complexes with a non-centrosymmetric structure. J. Am. Chem. Soc. 124, 992–997. Umemura, Y., Onodera, Y., Yamagishi, A., 2003. Layered structure of hybrid films of an alkylammonium cation and a clay mineral as prepared by the Langmuir-Blodgett method. Thin Solid Films 426, 216–220. Van Duffel, B., Schoonheydt, R.A., Grim, C.P.M., De Schryver, F.C., 1999. Multilayered clay films: atomic force microscopy study and modeling. Langmuir 15, 7520–7529. Van Duffel, B., Verbiest, Th., Van Elshocht, T., Persoons, A., Schoonheydt, R.A., 2001. Fuzzy assembly and second harmonic generation of clay-polymer-dye monolayer films. Langmuir 17, 1243–1249. Villemure, G., 1990. Effect of negative surface charge densities of smectite clays on the adsorption isotherms of racemic and enantiomeric tris(2,2’-bipyridyl)ruthenium(II) complexes. Clays Clay Miner. 38, 622–630. Weiss Jr., C.A., Kirkpatrick, R.J., Altaner, S.P., 1990. The structural environments of cations adsorbed onto clays: cesium-133 variable-temperature MAS NMR spectroscopic study of hectorite. Geochim. Cosmochim. Acta 54, 1655–1659. Xu, W., Johnston, C.T., Parker, P., Agnew, S.F., 2000. Infrared study of water sorption on Na-, Li-, Ca- and Mg-exchanged (SWy-1 and SAz-1) montmorillonite. Clays Clay Miner. 48, 120–131.

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Yamagishi, A., 1987. Optical resolution and asymmetric syntheses by use of adsorption on clay minerals. J. Coord. Chem. 16, 131–211. Yamagishi, A., 1993. Chirality recognition by a clay surface modified with an optically active metal chelate. In: Tamaru, K. (Ed.), Dynamic Processes on Solid Surfaces. Plenum Press, New York, pp. 307–347. Yariv, S., 1992. Wettability of clay minerals. In: Schrader, M.E., Loeb, G. (Eds.), Modern Approaches to Wettability: Theory and Applications. Plenum Press, New York, pp. 279–326. Chapter 11. Yariv, S., Cross, H. (Eds.), 2002. Organo-Clay Complexes and Interactions. Marcel Dekker, New York, p. 450. Zhou, Y., Hu, N., Zeng, Y., Rusling, J.F., 2002. Heme-protein-clay films: direct electrochemistry and electrochemical catalysis. Langmuir 18, 211–219. Zhou, C.-H., Shen, Z.-F., Liu, L.-H., Liu, S.-M., 2011. Preparation and functionality of claycontaining films. J. Mater. Chem. 21, 15132–15153.