Layered Double Hydroxides and the Environment: An Overview - Advanced Materials for Agriculture, Food and Environmental Safety - page 3

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Layered Double Hydroxides and the
Environment: An Overview
Amita Jaiswal*, Ravindra Kumar Gautam and
Mahesh Chandra Chattopadhyaya*
Environmental Chemistry Research Laboratory, Department of Chemistry,
University of Allahabad, Allahabad, India
Abstract
Due to their versatility, hundreds of millions of tons of clay minerals currently
i nd applications not only in ceramics, building materials, paper coating and i ll-
ings, drilling muds, foundry molds, pharmaceuticals, etc., but also as adsorbents,
catalysts or catalyst supports, ion exchangers, etc., depending on their specii c
properties. h ere are two broad classes of clays: Cationic clays (or clay miner-
als), widespread in nature, and Anionic clays (or layered double hydroxides), more
rare in nature but relatively simple and inexpensive to synthesize on a laboratory
or industrial scale. Cationic clays have negatively charged alumina-silicate layers
with small cations in the interlayer space to balance the charge, while anionic clays
have positively charged brucite type metal hydroxide layers with balancing anions
and water molecules located interstitially. h e layered double hydroxides (LDHs)
belonging to the general class of anionic clay minerals can be of both synthetic
and natural origin. Also known as hydrotalcite-like compounds (HTLCs), these
materials are interesting because their layer cations can be changed among a wide
selection, and the interlayer anion can also be freely chosen. Like cationic clays,
they can be pillared and can exchange interlayer species, thus increasing applica-
tions and making new routes to synthesize the derivatives.
h is chapter deals with the brief history of layered double hydroxides, their
structure, properties, synthesis by dif erent methods and characterization, along
with their applications mainly in the environmental i eld.
Keywords: Layered double hydroxides, anionic clays, cationic clays, brucite,
interlayer species, heavy metals, dyes, greenhouse gases, surfactants