Synthesis and Characterization of Carbonate Intercalated Layered Double Hydroxides and Their Structure Recovery Properties
|School||Harbin Engineering University|
|Keywords||Hydrothermal method Precipitator Memory effect|
Research on environmental-friendly catalytic materials has become an important link in Green Chemistry. LDHs’s calcined products (LDOs) have bigger relative surface and stronger alkalinity compared to hydrotalcite precursors. This kind of novel function material demonstrated broad application prospects in the fields of environment, catalysis, adsorption, etc.A series of nickel aluminum and cobalt aluminum hydrotalcites were synthesized by co-precipitation and hydrothermal methods, as well as a further exploration on the synthesis conditions was carried into execution. Calcine-recovering experiments were also carried on. The presented samples were characterized in detail by XRD, TG-DSC, FT-IR, TEM, SEM, BET techniques.The results indicated that the best pH condition for the synthesis of Ni-Al hydrotalcite is 10. LDHs has a better Layered structure ordering when the cation ratio Ni2+/Al3+ is 3 for Ni-Al hydrotalcite but Co2+/Al3+ is 2 for Co-Al hydrotalcite. LDHs synthesized by hydrothermal method possessed a better crystallinity than that synthesized by co-precipitation method. Besides LDHs synthesized using urea as precipitator possessed higher structure integrality compared to that using alkali as precipitator, but poorer thermal stability.The thermal stability of Co-Al hydrotalcites is much worse than the Ni-Al hydrotalcite.The calcination temperature is a main aspect that affected the structure of layered double hydroxide. As the increase of the calcination temperature, the structure of NA-3-HTL gradually collapsed; meanwhile, the NiO crystal phase began to appear. Furthermore, the NiO crystalling phase grew older with the calcination temperature increasing. At 450℃, the hydrotalcite completely collapsed, and at 1100℃, the spinel phase appeared. For NA-3-HTL its structure collapsed at 250～300℃, and the Co3O4 crystal phase also appeared at this temperature range. Spinel phase formed at 700℃.For the Ni-Al LDO sample, its structure recovery effect has direct relation with the calcination temperature. The LDO sample obtained at 200- 350℃can be recovered completely.The crystallinity and structural integrity of recovered HTL are better than the original. For Co-Al LDO, the structure recovery effect is more excellent in the structural integrity. By increasing the calcination temperature, the obtained LDO sample can not completely reconstrued its layed structure, due to the existence of the oxide The structure recovery ability of layered materials HTlCs depends not only on the reconstruction of the original performance and calcination temperature, but also largely on the recovery conditions. Therefore, by controlling the recovery temperature, recovery time and recovery of media, the recovery effect will be better.Under the very condition of the experiment, Ni-Al LDO samples calcined ranged 200℃to 350℃can recover completely. Whereas the Co-Al LDO calcined at 200℃has the best recovery effect. For both of these two terms, LDOs samples’structure can not be completely restored if calcination temperature rise further to structural collapse temperature.