Layered Double Hydroxides and the Environment: An Overview - Advanced Materials for Agriculture, Food and Environmental Safety - page 18

are known to function as ef ective anion adsorbents in the uptake of phe-
nols, terephthalates, anionic surfactants, ionizable pesticides and herbi-
cides, humic and fulvic acids, anionic dyes, and colored organics from
aqueous solutions [132-148] .
Based on the ability of LDH to intercalate various types of anions in
interlayers, organic-inorganic composite materials could be produced
by intercalation of organic anions having functional groups in their
structures into the interlayer of LDH. h e LDHs modii ed with organic
anions are expected to take up nonionic organic compounds from aque-
ous solution depending on the functional groups in the structure of the
intercalated organic anions. For example, Mg-Al LDH intercalated with
dodecylsulfate (DS) could adsorb hydrophobic pesticides such as atra-
zine, linuron and acephate, etc., from aqueous solution. h is is due to
the modii cation of the interlayer surface of the LDH from hydrophilic
to hydrophobic.
Yo u et al. [149] examined the surfactant-enhanced adsorption of
organic compounds by Mg-Al LDHs. Organo-Mg-Al LDHs were prepared
by incorporating anionic surfactants, octylsulfate, DS, 4-octylbenzenesul-
fonate, and dodecylbenzene sulfonate, into Mg-Al LDH via ion exchange.
h e anionic surfactants were intercalated into Mg-Al LDH with the sur-
factants oriented perpendicular in the interlayer. h e octylsulfate formed
bimolecular i lms, and other surfactants resulted in monolayer structure.
Intercalation of surfactants into Mg-Al LDH decreased the surface area,
whereas surfactants dramatically enhanced the LDH ai nity for 1,2,4-tri-
chlorobenzene and 1,1,1-trichloroethane in aqueous solutions. Adsorption
potential depended on the type of surfactant as well as the coni guration of
surfactant molecules within Mg-Al LDH interlayers. h e adsorption char-
acteristics indicated that the retention of organic compounds by organo-
Mg-Al LDHs was due to a partitioning mechanism.

1.6.5.5 Removal of Dye

h e discharged el uents of industries contain a large number of dyes,
increasing the total COD of wastewaters [150]. Although most of the dyes
are nontoxic, many of them are highly toxic, like metals (Cr), with harmful
consequences to aquatic life. Moreover, the persistence of color appearance
(at concentration > 1mg/L) in treated wastewater prevents their reuse.
h e LDHs have high adsorption capacities for dye molecule and can
be very competitive with other sorbents. h ey have been demonstrated in
environmental applications due to their high ability to removed color or
dye by adsorption reaction [137-145].