Synthesis And Characterization Of Anionic Pillared Magnetic Binary Hydrotalcite-like Compounds

Hydrotalcite-like compounds (HTLcs) are a sort of anionic clays with double-layer structure. Because of their special structure, they have exhibited excellent properties as a new type of catalytic materials and received much attention.Magnetic binary ZnAl HTLcs were synthesized with magnetic substrates and double layered hydrotalcite by chemical co-precipitation and hydrothermal method. The presented samples were characterized in detail by XRD, ICP, FT-IR, TG-DSC, TEM, SEM, VSM and N₂ adsorption-desorption techniques. The influence of the different method, mol ratio, crystalline temperature, calcination temperatures and amount of magnetic component on the structure, crystallinity, and magnetic properties of the materials was studied. The results showed that typical layered structures of hydrotalcite are not affected by introducing a certain amount of magnetic substrates during the synthetic process. XRD results showed that hydrotalcite synthesized by hydrothermal method possessed higher purity and better crystallinity than by co-precipitation method. The products treated by hydrothermal method possessed higher interlayer spacing (0.48 nm) and bigger grain size (9.00～16.00 nm). The results of the elementary analysis exhibited that Zn/Al molar ratios in ZnAl HTLcs and Zn/Al molar ratios in reagent are the same. Magnetic properties showed that the amount of magnetic substrates had determined the magnetic hydrotalcite saturation magnetization. The saturation magnetization increases with increasing amount of magnetic substrates and decreases with increasing calcination temperatures.Magnetic binary CoAl HTLcs were synthesized by coprecipitation and hydrothermal method. Thermal decomposition of CoAl HTLcs and effect of calcination temperature on composition and structure of the products were also researched. The results of the XRD and ICP showed that the hydrotalcites with Co/Al molar ratios of 2 to 4 have nice crystal form and high purity. TG-DSC results revealed that the decomposition of magnetic CoAl HTLcs proceeded in two stages. The first large endothermic effect below 220℃involves the loss of physically absorbed (surface) and interlayer water and the second endothermal effect, between 220℃and 402℃, corresponds to the decomposition (dehydroxylation) of the hydroxide layers and the removal of anions (carbonate) in the brucite-like layers. The S_BET and pore diameter information of magnetic CoAl HTLcs were tested by N₂ adsorption-desorption analysis.