Environmental Engineering Reference
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h is space can be adjusted by insertion of organic anions with dif erent
chain lengths. h is suggests that these hybrid materials would work as
tunable magnets [43]. h e LDHs intercalated with long-chain surfactant
molecules such as dodecyl sulphate have the ability to swell in organic
solvents. h is property of delamination is exploited in the preparation of
monolayers, which are used extensively in the synthesis of nanohybrids
and nanocomposites [44].
h e interlayer anions present in LDHs can be exchanged by other
anions. h e order of preference for some common inorganic anions is as
follows:
NO
3
-
< Br
-
< Cl
-
< F
-
< OH
-
< SO
4
2-
< CO
3
2-
NO
3
-
is an anion which can be easily replaced by a more strongly held
one like CO
3
2-
. h erefore when preparing precursor for interaction, nitrate
salts are preferred and CO
3
2-
is tried to be kept away. h e interaction
involves a guest molecule that is introduced into the host without af ect-
ing the structure of the host. Upon interaction of the guest molecule, the
existing ion is replaced. h e interlayer anions weekly bonded to hydroxide
layers (e.g., NO
3
-
, Cl
-
) can be exchanged more easily [45-47].
1.4
Synthesis of Layered Double Hydroxides
Layered double hydroxides (LDHs) can be synthesized with a wide range
of compositions and a variety of M(II)/M(III) cation combinations con-
taining dif erent anions in the interlayer spaces. A number of synthetic
techniques have been successfully employed in the preparation of LDHs.
h ere are number of methods used to synthesize LDHs which are pre-
sented below. [1].
1.4.1 Co-precipitation Method
Co-precipitation remains the most commonly used technique for the syn-
thesis of LDHs. h is technique involves the addition of aqueous solutions
of M(II), M(III) and the anion that will be incorporated into the LDH
structure. h is method allows the direct preparation of LDHs for a variety
of anions and cations. h erefore, this method is commonly used for the
formulation of organic-anion LDHs, which are dii cult to obtain by other
methods [3]. Following are the three methods of co-precipitation which
can be used for the synthesis of LDHs.
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