Synthesis and characterization of New CoCuZnAl-Hydrotalcite-Like Anionic Clays

摘要

Hydrotalcites (HT), also known as anionic clay with a molecular formula Mg6Ah(OH)16CO3 .4H20 possess positively charged brucite [Mg(OH)2]- like octahedral layers in which a part of Mg2+ cations are isomorphously substituted by A13+ cation. The excess positive charge of the octahedral layers resulting from this substitution is compensated by interstitial layers built up of CO32- anions and crystal water. Both Mg2+ as well as A13+ cations can be isomorphously substituted by divalent cations such as Cu, Ni, Co, Zn etc., trivalent cations like AI, Fe, Cr, Ga, Ru, Rh or tetravalent cations, for example, Ti, Zr, and Sn. The resulting synthetic materials are described with a general formula [M(lI)1-xM(III)x(OH)2]x+ [(An-)x n.H20]x- and are commonly re- ferred to as hydrotalcite-like compounds (HTlc) or layered double hydrox- ides (LDHs) because of their structural similarity with that of HT. HTlcs are receiving increasing interest in recent years due to their potential applica- tions in various technologies as ion exchangers, adsorbents, ionic conduc- tors, catalysts and catalyst supports. The copper containing HTlcs are always accompanied by other phases, such as malachite (MT) [CU(OH)2CUCO3] and gheradite (GT) [CU(OH)2NO3] due to the operation of Jahn-Teller effect in Cu2+ ion. However, it can be stabilized in the octahedral layer if another divalent cation is present in the brucite-Iike layer.