Layered Double Hydroxides and the Environment: An Overview - Advanced Materials for Agriculture, Food and Environmental Safety - page 6

Brucite like layer

Water molecule

Anions

Brucite like layer

Figure 1.1 Structure of layered double hydroxide (LDHs).

1.3 Properties of Layered Double Hydroxides

Layered double hydroxides (LDHs) display unique physical and chemical
properties close to those of clay minerals. Some interesting properties of
these materials summarized by Del Hoyo [40] are:

• High specii c surface area (100±300 m 2 /g)
• Memory ef ect
• Anion exchange capacities
• Synergistic ef ects

h e LDHs exhibit anion mobility, surface basicity and anion exchange-
ability due to their positively charged layered structure. h e anions
and water, which i ll the interlayer space, are labile. h erefore a variety
of inorganic and organic anions can be intercalated in the interlayer of
LDHs through anion exchange reactions [33]. h e mixed metal oxides
obtained on calcination of LDH usually exhibit properties such as high
surface area, surface basicity and formation of homogeneous mixture with
small crystallite size when heated to higher temperature [1]. h e LDHs
as well as the oxides obtained from them exhibit excellent catalytic activ-
ity. Structure reconstruction, or so called “memory ef ect,” is another
important property of LDHs which is unique to this class of layered sol-
ids. Structure reconstruction is usually achieved by i rst decomposing the
LDH at suitable high temperature followed by treating the resultant mixed
metal oxides with a solution containing a suitable anion [41]. h ese mate-
rials have a high capacity for adsorbing anions as well as cations [38, 42].
Magnetic properties of the LDHs depend on the space between the layers.