Hydrotalcite and hydrotalcite compounds_industrial additives

Hydrotalcite

[Overview]
Hydrotalcite was first discovered in Sweden in 1842. It is a carbonated magnesium-aluminum double hydroxide that exists in the form of leaves and rotating plates or fibrous masses in its natural state. Hydrotalcite and hydrotalcite-like compounds have special layered structures and physical and chemical properties, and have the catalytic performance of shape-selective adsorption with adjustable pore size, and occupy an important position in the fields of adsorption and catalysis. LDHs anionic layer pillar materials have been widely used in catalysis, ion exchange and adsorption, medicine, functional polymer materials, additives and papermaking.

[Structure]
A typical hydrotalcite compound is hydrotalcite, whose molecular formula is Mg6A12(OH)16CO3·4H2O, its main laminate structure is very similar to brucite Mg(OH)2, the structural center is Mg2+, the six vertices are OH-, and the adjacent MgO6 octahedrons share edges to form a unit layer (laminar thickness About 0.47nm), the layers are stacked on top of each other, and the layers are associated through hydrogen bonds. The Mg2+ located on the layer can be replaced by Al3+ isomorphs with similar radii within a certain range, so that the main layer plate has a permanent positive charge; there is an exchangeable anion CO32- between the middle layers, and the negative charge it carries is the same as the positive charge on the layer. balance, making the structure electrically neutral. In addition, there is some crystal water in the remaining space between the layers, and these water molecules can be removed without destroying the layered structure.
Mg2+ and A13+ in LDHs are replaced by other M2+ and M3+ isomorphously to obtain hydrotalcite compounds with similar structures, which have the following general chemical composition formula: [M2+1-xM3+x(OH)2]z+[An-]z /n&mibromopyridineddot;mH2O, the structure is the same as that of hydrotalcite , only the number of anion and cation species is different. The structure of LDHs is shown in Figure 1-1.

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