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(Montanari et al., 1997). Calcined Co–Mg–Al LDH are equally active in both NO

and SO

removal but doping with cerium oxide is required (Palomares et al., 1999).

Calcined LDH are superior to zeolites, spinels, perovskite-type oxides, and sup-

ported metals as catalysts for the decomposition of N

O(Kapteijn et al., 1996). N

is a greenhouse gas, contributing to the destruction of stratospheric ozone. The main

anthropogenic sources of N

O emission are cultivated soils, biomass burning, com-

bustion processes, and the chemical industry, especially plants manufacturing adipic

acid or nitric acid. A wide range of LDH, including Co–Al, Ni–Al, Cu–Al,

Co–Pd–Al, Co–Rh–Al, Co–Mg–Al, Co–La–Al, and Co(II)–Co(III) LDH, are pre-

cursors of catalysts for N

O decomposition (Kannan and Swamy, 1994; Armor et

al., 1996; Xu and Zeng, 1998; Pe

rez-Ramı

rez et al., 1999). The removal of NO

and

O by LDH derivatives was reviewed by Serwicka (2001).

Pillaring of LDH is a new trend in catal yst synthesis. Various bulky POMs and

FeðCNÞ

3

ions were intercalated into LDH to obtain microporous materials. Like

zeolites, such pillared LDH can serve as shape-selective catalysts (see Section

13.1.4.H).

Incorporation of tetr avalent metal cations such as Zr

and Sn

into the LDH

structure results in unusual acid–base properties after calcinati on, or yields novel

materials having catalytic properties similar to those of zeolites containing Zr

(Velu et al., 1997a, 1999a; Tichit et al., 2002a).

B. Medical Applications

Since LDH have a prolonged buffering effect and bile- binding activity, they can act

as antacids for the treatment of gastric or duodenal ulcers. In experimental studies

with rats and dogs, Mg–Al–CO

LDH inhibit signiﬁcantly gastric lesions induced by

stress and aspirin (Ishihara and Okabe, 1981). The effectiveness of LDH was con-

ﬁrmed in patients having gastric or duodenal ulcers. Unlike sodium bicarbonate,

LDH are effective in treating ulcerative gastritis (Barlattani et al., 1982). The effec-

tiveness of LDH in healing gastric ulcers is comparable to that of ranitidine; the

respective healing rates are 81% for LDH and 79% for ranitidine (Holtermu

ller

et al., 1993). As to duodenal ulcers, endoscopy performed at the end of 4 weeks of

treatment shows healing in 68.2% of patients. Side effects associated with aluminium

and magnesium hydroxides are well known. These are constipation, phosphate de-

pletion, malaise, and anorexia for aluminium hydroxide; and diarrhea and hyp e-

rmagnesemia, leading to renal malfunction for magnesium hydroxide. On the other

hand, no side effects were observed during treatment with LDH (Bhanumathi et al.,

1993).

Apart from their use as antacids, LD H were evaluated as phosphate binders.

Hyperphosphataemia in patients with end-stage renal failure may lead to secondary

hyperparathyroidism and renal osteodystrophy. Absorption of inorganic phosphate

may be prevented by administering compounds that form insoluble phosphate com-

plexes in the gastrointestinal tract. Rankin et al. (2001) studied phosphate

13.1.8. Industrial and Environmental Applications: Conventional and Novel 1061

precipitation at different pH values in aqueous solution and in various food mixtures

in the presence of LDH, Al(OH)

, CaCO

, and Mg(OH)

, with LDH showing con-

siderable promise as phosphate binders.

C. Additives for Polymers

Synthetic LDH are commercially used as acid neutralizers or HCl scavengers in

stabilizer packages for poly(vinyl chloride) (PVC). PVC undergoes autocatalytic

dehydrochlorination when exposed to heat or UV light, becoming brittle and

changing colour. Mori et al. (1981) reported that add ing LDH to PVC in the pres-

ence of 6-anilino-1,3,5-triazine-2, 4-dithiol and zinc stearate, jointly used as a sta-

bilizer, reduces the rate of PVC discolouration. Van der Ven et al. (2000) investigated

the mechanism of stabilization by LDH by measuring the thermal stability and HCl

adsorption capacity. Thermal stability is determined by monitoring the time required

to effect a change in colour of PVC/LDH compounds on heating at 200 1C. There is

a linear relationship between thermal stability and HCl adsorption capacity. The

reaction between HCl and LDH occurs in two steps: (i) interlayer anions react with

HCl; and (ii) the LDH decompose, giving rise to metal chlorides.

LDH are also used as ﬂame retardants in polymers. From an environm ental

standpoint, LDH-based ﬂame retardants are preferable to their halogen-based

counterparts. In ﬂame-retardancy tests, LDH are superior to other inorganic hy-

droxides, such as magnesium and aluminium hydroxides (Camino et al., 2001). In

mass-loss calorimetric analyses, an ethylene vinyl acetate (EVA) polymer, ﬁlled with

50 wt% of Mg–Al–CO

LDH, shows the lowest rate of heat release and the lowest

temperature for gas evolut ion. The modiﬁed EVA polymer has the longest ignition

time. The high performance of LDH is ascribed to heat absorption due to loss of

water over a wide temperature range (200–500 1C).

The composites of polymers and additives are not homogeneously mixed at the

microscopic level. In order to achieve intimate mixing, the majority of LDH/p olymer

nanocomposite materials are synthesized either by templating or in situ polymer-

ization. Template synthesis is carried out by coprecipitating LDH in solution in the

presence of soluble polymers, such as poly(styrene sulphonate), poly(a,b-aspartate),

poly(vinyl sulphonate), poly(vinyl alcohol), an d polyacrylate (Messersmith and

Stupp, 1995; Ori akhi et al., 1996, 1997; Whilton et al., 1997; Wilson et al., 1999).

Formation of LDH and the incorporation of the polymer occur sim ultaneously.

LDH are ideal materials for templating because they can be synthesized at room

temperature or under mild conditions that do not cause polymer decomposition. In

situ polymerization consists of intercalating monomer anions or polar monomer

molecules, and subsequent or concomitant polymerization (Tanaka et al., 1989;

Challier and Slade, 1994; Whilton et al., 1997; Rey et al., 1999; Isupov et al., 2001;

O’Leary et al., 2002). This method requires appropriate monomers. To date, inter-

calation of polyacrylate, polyaniline, poly(aminobenzoate) and poly(a,b-aspartate)

Chapter 13.1: Layered Double Hydroxides1062

was reported. LDH–polymer nanocomposites were also obtained by intercalating

the polymer through the delamination state (Leroux and Besse, 2001).

The above-mentioned LDH–polymer nanocomposites and their basal spacings

are summarized in Table 13.1.9. Although the properties of LDH–polymer nano-

composites were not fully investigated, LDH–polymer and smectite-polymer nano-

composites are expected to have similar properties. That is, LDH-polymer

nanocomposites containing small amounts of LDH would be expected to show

improved mechanical strength, reduced permeability toward gases and liquids, and

self-extinguishing characteristics (Giannelis, 1996) (see Chapter 10.3).

D. Environmental Applications

Adsorption of Pollutants

LDH can take up a variety of contaminants and toxic substances directly from the

environment through anion-exchange, reconstruction, and ad sorption (Fig. 13.1.12).

Capturing target anions can be attained by simple anion exchange in solution or by

reconstruction of calcined LDH. Hermosı

n et al. (1996) demonstrated that

Mg–Al–CO

LDH adsorbs 2,4,6-trinitrophenol (TNP ) by anion exchange up to

20% of its AEC when the initial pH was 2. For Mg–Al–C O

LDH calcined at

500 1C, the amount of TNP adsorbed was 40% of the AEC. Similarly, calcined LDH

can adsorb dodecyl benzenesulpho nate (Ulibarri et al., 2001), and Zn–Al–Cl LDH

can remove the pesticide 2,4-dichlorophenoxyacet ic acid from aqueous so lution by

anion exchange (Lakraimi et al., 1999).

Phosphate, a causative factor in surface water eutrophication, can be captured by

the chloride or nitrate forms of LDH through anion exchange (Shin et al., 1996;

Legrouri et al., 1999). Competing anions affect phosphate uptake. For example,

nitrate causes only a slight decrease in phosphate removal whereas sulphate causes a

12–13%, and carbonate a 33%, reduction. Toxic inorganic anions such as

Table 13.1.9. Polymer-intercalated LDH

Polymer Basal spacing (nm) References

Polyacrylate 1.20–1.34 Tanaka et al. (1989), Oriakhi et al.

(1996), Rey et al. (1999), Oleary et al.

(2002)

Poly(styrenesulphonate) 1.96–2.16 Oriakhi et al. (1996, 1997), Wilson et

al. (1999), Leroux and Besse (2001a)

Poly(vinylsulphonate) 1.27–1.33 Oriakhi et al. (1996), Wilson et al.

(1999)

Polyaniline 1.33–1.35 Challier and Slade (1994)

Poly(vinyl alcohol) 18.0 Messersmith and Stupp (1995)

Poly(a,b-aspartate) 0.90–1.51 Whilton et al. (1997)

Poly(aminobenzoate) 1.55 Isupov et al. (2001)

13.1.8. Industrial and Environmental Applications: Conventional and Novel 1063

SeO

2

; SeO

2

; and Cr

2

may be removed by anion exchange or the recon-

struction process (Goswamee et al., 1 998; You et al., 2001). Again, competing anions

in solution strongly decrease the adsorption of SeO

2

and Cr

2

. Adsorbed SeO

2

or Cr

2

can be released from LDH by ion exchange with CO

2

. Kameda et al.

(2000) investigated the treatment of waste acid solution with calcined LDH. Alm ost

100% of the chloride ions in hydrochloric acid can be removed.

The hydrophobic environment induced by intercalation of surfactants permits

adsorption of nonanionic and hydrophobic organic contaminants. Organo-LDH

modiﬁed with dodecyl sulphate are as good as organo-montmorillonites in adsorbing

hydrophobic pesticides (Villa et al., 1999). Similarly, Dutta and Robins (1994)

showed that py rene can intercalate from methanol–water mixtures into Li–Al LDH-

containing interlayer myristic and hexanoic acids.

LDH a nd calcined LDH can also remove humic substances from water but it is

uncertain whether intercalation of humic substances occurs (Amin and Jayson, 1996;

Seida and Nakano, 2000; Hussein et al., 2001).

LDH can also be used to remove metal cations from aqueous solutions. In the

case of transition metal cations, such as Cu

,Ni

,Co

, and Zn

, the process is

one of substitution, mainly for Mg

in the structure (Komarneni et al., 1998). This

can be achieved by shaking a mixture of an aqueous solution of the appropriate salt

(pH 4–5) and Mg–Al–CO

LDH or Mg–Al –NO

LDH at room temperature for 1

day. A second method for removing metal cations from solutions is based on the

Organophilic

modification

[Adsorbents]

Ion exchange

(including capture through

reconstruction)

[Adsorbents]

Gas adsorption

[Adsorbents]

Conversion to mixed oxides

Support of catalysts

[Environmental catalysts]

Decomposition of NO

, SO

, N

Solid base catalysts

Support for water-soluble catalysts

Recovery of CO

Removal of ionic contaminants and ionic

hazardous substances

·Removal of hydrophobic

contaminants

Removal of toxic metals by

precipitation or substitution

Buffer effect

Diadochy

[Decontaminants]

LDHs

Fig. 13.1.12. Environmental applications of LDHs. (Environmental catalysts are described in

Sections 4.1 and 4.5)

Chapter 13.1: Layered Double Hydroxides1064

buffer effect (Lehmann et al., 1999; Seida et al., 2001). Adding Mg-based LDH to

aqueous solutions leads to an increase in pH, which causes meta l cations in the

solution to precipitate as metal hydroxides. This process was used to remove toxic

and Zn

cations. These two methods are more straightforward than using a

combination of LDH and metal ion-chelating compounds (Tsyganok et al., 2001).

Adsorption of carbon dioxide onto LDH was investigated as a possible method

for recovery of CO

from hot gas streams (Yamamoto et al., 1995; Ding and Alpay,

2001; Yong et al., 2001). The recovery of CO

from power-plant ﬂue gases is con-

sidered to be the ﬁrst step in reducing total CO

emission. The carbon dioxide

adsorption capacity of LDH, ranging from 10 to 33 cm

(STM)/g, is dependent on

the micropore volume, interlayer spacing, and layer charge density of the material.

Waste Barriers

Containers of cementitious materials and glasses are commonly used in immobili-

zation strategies for the disposal of hazardous and radioactive waste. To predict the

safety of these containers, changes in the composition and structure of the container

material during degradation, cement or glass is subjected to hydrothermal treatmen t

at 80–200 1C, or to continuous leaching in salt solutions (Abdelouas et al., 1994;

Wang and Scrivener, 1995; Faucon et al., 1996; Paul and Glasser, 2000; Scheidegger

et al., 2001). LDH were found to be one of corrosion products of cement or glass.

It is impossible to ensure the integrity of cementitious or glass vaults over the

hundreds of years required for the decay of radioactive waste. Therefore, backﬁlls

that can absorb and retain radionuclides were investigated. Among the radionuclides

present in nuclear fuel waste,

129



is especially problematic. It has a long half-life,

and does not interact strongly with most geological materials such as clay, sand, and

rock.

129



may reach the biosphere before it decays to insigniﬁcant levels. Organic

materials are not practi cal for use as adsorbents in backﬁlls, because they are not

stable over long periods. Corrosion products of cement such as ettringite and LDH

(Altenhein-Haese et al., 1994) are potential inorganic candidates for scavenging

129



. Other inorganic materials such as imogolite, metal sulphides, copper oxides,

and coals were also invest igated. Optimal scavenging of

129



depends on environ-

mental conditions. Near-neutral pH seems optimal for LDH (Balsley et al., 1998).

However, only a small fraction of the exchange sites are occupied by I



ions, in-

dicating that anion exchange takes place only on the external surface (Olguı

n et al.,

1998; Fetter et al., 1999).

E. Future Developments

Drug Delivery and Controlled-Release Formulations

Controlled-release drug delivery is ideal for drug therapy. Ideally, the correct dosage

of drug is transported to, and absorbed by, the target, without delivery of the drug to

other tissues. Drug delivery systems are complex and difﬁcult to design. Currently,

controlled-release drugs are being used to reduce the number of doses and side

13.1.8. Industrial and Environmental Applications: Conventional and Novel 1065

effects that are associated with frequent administration. Usually, polymer-encapsu-

lated drugs are used for this purpose (Khan et al., 2001). Developing suitab le ma-

terials for the capsule is a key step in the design of a controlled-release drug delivery

system. LDH are being studied as potential reservoirs or delivery carriers of bio-

molecules. Choy et al. (2000) demonstrated that the DNA of herring tests and

methotrexate (an anticancer drug) can intercalate into Mg–Al LDH by ion exchange.

They also intercalated nucleoside mono- and triphosphate. Adsorption by LDH of

adenosine 5

-triphosphate (ATP) increases the efﬁciency of ATP transfer into cells.

This is attributed to alleviation of the electric repulsion at the cell wall when the

negative charge on the phosphate groups is neutralized by the positive hydroxide

layers (Choy et al., 2001).

A variety of pharmaceutical anionic materials were intercalated into LDH (Table

13.1.10)(Ambrogi et al., 2001; Hwang et al., 2001; Khan et al., 2001). An example is

ibuprofen [ a-methyl-4-(2-methylpropyl)benzeneacetic acid], a nonsteroidal anti-in-

ﬂammatory drug used to relieve symptoms of rheu matoid arthritis and osteoarthri-

tis. The in vitro release of this drug from ibuprofen-LDH is much slower than from a

commercial formulation in phosphate buffer at pH 7.5 (Ambrogi et al., 2001).

Biosensors, Biomimetic Catalysts, and Biological Reactions

He et al. (2001) prepared hybrid thin ﬁlms of Ni–Al–Cl LDH and an amphiphilic

anionic Ru(II) complex ([Ru(CN)

2

, where L ¼ 4,4

-di-n-dodecylaminoyl-2,2

bipyridyl), using the LB technique. Ni cations in the hydroxide layers mediates the

oxidation of [Ru(CN)

2

to [Ru(CN)



. Ru(II) cyano complexes are known to

function as a redox mediator in reactions such as the oxidation of glucose by glucose

oxidase. In this context, the LB hybrid ﬁlms are potentially useful for electrochem-

ical sensing of biomolecular materials.

Table 13.1.10. LDH intercalated with pharmaceutical materials

Guest Basal spacing (nm) Host LDH References

Ibuprofen 2.17 Mg/Al ¼ 2/1 Ambrogi et al. (2001)

Citric acid 1.21

Ascorbic acid 1.05

Retinoic acid 3.78 Zn/Al ¼ 2/1 Hwang et al. (2001)

Indoleacetic acid not given

4-Biphenylacetic acid 2.04

Diclofenac 2.23

Gemﬁbrozil 2.32

Ibuprofen 2.27 Li/Al ¼ 1/2 Khan et al. (2001)

Naproxen 2.15

2-Propylpentanoic acid 1.87

Tolfenamic acid 2.19

Chapter 13.1: Layered Double Hydroxides1066

LDH can also be used as supports for biomimetic metallomacrocyclic catalysts.

Anionic metalloporphyrins and metallophthalocyanines were intercalated into LDH

(Ukrainczyk et al., 1995; Bonnet et al., 1996; Chibwe et al., 1996). As these inter-

calates lack microporosity, the reactants might only be able to access the metallo-

macrocycles located at the edges and external surfaces. Nevertheless, catalytic

activity for reductive dehalogenation of CCl

and for oxidation of 2,6-di-tert-

butylphenol by oxygen was conﬁrmed. Biomimetic catalysts consisting of tungstate

intercalated into LDH were also reported (Sels et al., 1999). These materials can

selectively catalyse oxidative bromination an d bromide-assisted epoxidation reac-

tions.

Lotsch et al. (2001) reported the selective intercalation of nucleoside monophos-

phates into LDH, suggesting that LDH are useful for the puriﬁcation and separation

of complex bio molecules. LDH were also investigated as supports for enzymes. The

enzyme penicillin G acylase is immobilized by LDH (Ren et al., 2001). Finally, two

biopoiesis-relevant biological reactions induced by LDH were reported: the al-

domerization of glycolaldehyde phosphates to sugar phosphates (Pitsch et al., 1995)

and the self-addition of cyanide (Boclair et al., 2001).

Electrochemical Applications

The electrochemical respon se of redox species intercalated into LDH was studied by

cyclic voltametry. Electrodes modiﬁed with LDH were prepared by casting an LDH

suspension onto an electrode or by mixing LDH with a carbon paste. Some elect-

roactive responses were observed for these modiﬁed electrodes (Itaya et al., 1987;

Mousty et al., 1994; Ballarin et al., 1998; Therias et al., 1998). A variety of elect-

roactive anions were intercalated into LDHs (Table 13.1.11). In most cases, a large

portion of the intercalated redox species are electrochemically silent. Anions in-

volved in the redox reaction at the electrodes are apparently located on particle edges

and near the electrodes (Therias et al., 1996; Dome

nech et al., 1998). Qiu and

Villemure (1995) calculated that only 3.5–6.8% of the anions in Mg–Al–[Fe(CN)

]

LDH are involved in the redox reaction. However, a way to improve electron

transfer efﬁciency was found. In Ni-based LDH, the Ni mediates the transfer of

electrons to electroactive anions. In this case, the amount of electrochemically active

anions increases in the range 17.4–27%. With Zn–Al–[Fe(CN)

] LDH, the redox

reaction proceeds by a different mechanism, and a Prussian blue-like ﬁlm forms on

the surface of the LDH (Sha w et al., 1990).

A quartz crystal microbalance (QCM) was used to investigate the mass transfer in

the redox reaction of the electroactive interlayer anions in LDH-modiﬁed electrodes

(Yao et al., 1998a). Electrochemical QCM measur ements on an electrode modiﬁed

with Mg–Al–[Fe(CN)

] LDH indicate reversible changes in mass: mass increases on

oxidation and decreases on reduction. Adsorption and desorption studies, using a

QCM and UV-visible spectroscopy, show that the excess charge generated in the ﬁlm

by reduction is compensated by the leaching out of ion-paired species; in this case

[Fe(CN)

]



or Na[Fe(CN)

]

2

. Electrochemical scanning tunneling microscopy

13.1.8. Industrial and Environmental Applications: Conventional and Novel 1067

(ECSTM) indicates that the distance between [Fe(CN)

] ions, adsorbed on the ex-

ternal surface, changes after redox reaction. This distance increases when the anions

are reduced, and decreases when the anions are oxidized (Yao et al., 1998b).

Various types of electrodes modiﬁed with LDH show electrocatalytic activity.

Phenol was oxidized at electrodes modiﬁed with Mg–Al–Cl LDH (Shaw et al., 1990),

and alcohols at electrodes modiﬁed with Ni–Al– Cl LDH ( Ballarin et al., 1999).

Electrodes modiﬁed with Mg–Al–SO

LDH are potentially useful as sulphate sensors

in the analysis of industrial and environmental water samples (Morigi et al., 2001).

Electrodes modiﬁed with Ni–Al–Cl LDH were tested as sensors for methanol, man-

nitol, and glucose (Scavetta et al., 2001). The reactants were detected through elect-

rocatalytic oxidation. SEM further shows that very few LDH particles are strictly in

Table 13.1.11. LDH intercalated with electroactive anions

Anion Basal

spacing

(nm)

Host LDH Reference

MoðCNÞ

4

1.12

FeðCNÞ

3

1.12 Mg/Al ¼ 3/1 Itaya et al. (1987)

IrCl

2

1.08

FeðCNÞ

3

1.064 Zn/Al (ratio is

not given)

Shaw et al.

(1990)1.08

m-Nitrobenzenesulphonate 1.562

2-Anthraquinonesulphonate

(AQS-2)

1.99

2,6-Anthraquinonedisulphonate

(AQDS-2,6)

1.89 Zn/Cr ¼ 2/1 Mousty et al.

(1994)

1,5-Anthraquinonedisulphonate 1.592

2,2

-Azinobis(3-

ethylbenzothiazoline-6-sulphonate)

1.95 Zn/Cr ¼ 1.8–1.9 Therias et al.

(1996)

2.08 Zn/Al ¼ 1.8–2.6

AQS-2 2.03

AQDS-2,6 1.87 Mg/Al ¼ 2.5/1 Ballarin et al.

(1998)

p-Toluenesulphonate 1.7.2–1.73

1.73 Zn/Cr ¼ 2.5/1

Bis(2-mercapto-2,2-

diphenylethanoate)

dioxomolybdate(VI) complex

not given Zn/Al ¼ 3/1 Dome

nech et al.

(1998)

Ferrocene monosulphonate 2.00 Zn/Cr ¼ 2/1

Ferrocene disulphonate 1.50 Therias et al.

(1998)

2,2,6,6-Tetramethyl-1-

oxylpiperidylidene succinate

1.67 Zn/Al ¼ 2/1

Chapter 13.1: Layered Double Hydroxides1068

contact with the electrode, that is, only a very small portion of the LDH is involved

in the electrocatalytic process. It seems, therefore, desirable to increase the contact

between the LDH and electrode (Scavetta et al., 2001).

LDH-modiﬁed electrodes were also used in applications involving alkaline sec-

ondary cells. During charge- discharge cycles, a-Ni(OH)

is preferable to b-Ni(OH)

for efﬁciency. However, a-Ni(OH)

is unstable in an alkaline medium and trans-

forms to b-Ni(OH)

. Kamath et al. (1994) synthesized a Ni–Al LDH having the same

structure as that of a-Ni(OH)

. They found that the LDH has a prolonged stability

under strongly basic conditions, and a discharge capacity value of 240 mAh/g. Ni–Al

LDH is therefore attractive for application in an alkaline secondary battery. In an

attempt at making modiﬁed electrodes, Indira and Kamath (1994) cathodically re-

duced metal salt solutions. Mg, Al, Mn, Cr, Ni, Co, La, Nd, and Pr are deposited in

the hydroxide or LDH forms, but Zn, Cd, Cu, Bi, and Pb form metallic deposits.

Finally, Moneyron et al. (1990, 1991a, 1991b, 1991c) prepared a humidity sensor

based on LDH deposited as a thick ﬁlm by screen printing. This ap plication is based

on the ability of LD H to act as protonic conductors (de Roy et al., 1985; de Roy and

Besse, 1991 ; Ducos et al., 2001).

Novel Functional Materials

The synthesis and development of novel functional materials containing LDH received

much attention. Immobilization of functional materials by intercalation into LDH is

the main route. Two ﬂuorescent anions (methyl orange and xanthene dye) and a

luminescent anion (RuðBPSÞ

4

;whereBPS¼ 4,7-diphenyl-1,10-phenanthrolinedisul-

phonate] were intercalated into LDH (Giannelis et al., 1987; Costantino et al., 1999,

2000). The photoluminescence is affected by the environment around the anions.

Especially for the xanthene dye, the absorption and emission spectra of the interlayer

dye anions are similar to those of the crystalline dye, whereas the spectra of the dye

adsorbed onto the external surface are similar to those of the dye in solution.

Intercalation of C

was accomplished by co-intercalation with toluene or hexane

into organo-LDH (Tseng et al., 1996), or by using a negatively charged C

through

reduction (Ding et al., 1996). Intercalated C

exhibits enhanced photoluminescence.

Tagaya et al. (1994) prepared a photochromic LDH complex by intercalating

sulphonated indolinespirobenzopyran in the presence of p-toluen esulphonic acid.

The colour of the composite changed from red to yellow when irradiated with visible

light. Photocatalysts were also immobilized in LDH. Semiconductor particles of

TiO

, CdS, and ZnS were incorporated into the interlayer spaces, using the corre-

sponding precursors (titanium butoxide for TiO

, and anionic chelate compounds of

Cd and Zn for CdS and ZnS, respectively) (Sato et al., 1993; Robins and Dutta,

1996). A POM intercalate of LDH can decompose pesticides by a photocatalytic

reaction (Guo et al., 2001). The water-soluble POM can be recycled by immobi-

lization on the LD H.

13.1.8. Industrial and Environmental Applications: Conventional and Novel 1069

Porous carbon was obtained from LDH-containing organic anions (Putyera et al.,

1996; Xu et al., 2001). On calcination, the organic moieties in the interlayer space

convert into a carbonaceous residue, forming a microporous carbon-like material.

REFERENCES

Abdelouas, A., Crovisier, J.L., Lutze, W., Fritz, B., Mosser, A., Mu

ller, R., 1994. Formation

of hydrotalcite-like compounds during R7T7 nuclear waste glass and basaltic glass alter-

ation. Clays and Clay Minerals 42, 526–533.

Abend, S., Bonnke, N., Gutschner, U., Lagaly, G., 1998. Stabilization of emulsions by he-

terocoagulation of clay minerals and layered double hydroxides. Colloid and Polymer

Science 276, 730–737.

Adachi-Pagano, M., Forano, C., Besse, J.-P., 2000. Delamination of layered double hydrox-

ides by use of surfactants. Chemical Communications, 91–92.

Adachi-Pagano, M., Forano, C., Besse, J.P., 2003. Synthesis of Al-rich hydrotalcite-like

compounds by using urea hydrolysis reaction—control of size & morphology. Journal of

Materials Chemistry 13, 1988–1993.

Aisawa, S., Hirahara, H., Uchiyama, H., Takahashi, S., Narita, E., 2002. Synthesis and

thermal decomposition of Mn–Al layered double hydroxides. Journal of Solid State

Chemistry 167, 152–159.

Aisawa, S., Takahashi, S., Ogasawara, W., Umetsu, Y., Narita, E., 2001. Direct intercalation

of amino acids into layered double hydroxides by coprecipitation. Journal of Solid State

Chemistry 162, 52–62.

Alba, M.D., Becerro, A.I., Castro, M.A., Perdigon, A.C., 2001. Two-dimensional heteronu-

clear

H ’-

Al-correlated MAS NMR spectra of layered silicates. Chemical Commu-

nications, 249–250.

Albiston, L., Franklin, K.R., Lee, E., Smeulders, J.B.A.F., 1996. Rheology and microstruc-

ture of aqueous layered double hydroxide dispersions. Journal of Materials Chemistry 6,

871–877.

Alcaraz, J.J., Arena, B.J., Gillespie, R.D., Holmgren, J.S., 1998. Solid base catalysts for

mercaptan oxidation. Catalysis Today 43, 89–99.

Alejandre, A., Medina, F., Rodriguez, X., Salagre, P., Cesteros, Y., Sueiras, J.E., 2001. Cu/Ni/

Al layered double hydroxides as precursors of catalysts for the west air oxidation of phenol

aqueous solutions. Applied Catalysis B: Environmental 30, 195.

Alejandre, A., Medina, F., Salagre, P., Correig, X., Sueiras, J.E., 1999. Preparation and study

of Cu–Al mixed oxides via hydrotalcite-like precursors. Chemistry of Materials 11, 939–948.

Allda, R.K., Navrotsky, A., Berbeco, H.T., Casey, W.H., 2002. Thermochemistry and aque-

ous solubilities of hydrotalcite-like solids. Science 296, 721–723.

Allmann, R., 1968. The crystal structure of pyroaurite. Acta Crystallographica Section B 24,

972.

Altenhein-Haese, C., Bischoff, H., Fu, L., Mao, J., Marx, G., 1994. Adsorption of actinides on

cement compounds. Journal of Alloys and Compounds 213–214, 554–556.

Ambrogi, V., Fardella, G., Grandolini, G., Perioli, L., 2001. Intercalation compounds of

hydrotalcite-like anionic clays with antiinﬂammatory agents. I. Intercalation and in vitro

release of ibuprofen. International Journal of Pharmaceutics 220, 23–32.

Chapter 13.1: Layered Double Hydroxides1070