Preparation, Modification And Application Of A Sort Of Anions Clay Materials

Hydrotalcite-like compounds is a sort of anionic clays with double-layer structure. It is a layered mixed hydroxides containing exchangeable anioris. The anionic clays was found application in agriculture, industry, medicine and other field. The characters and effects on using of hydrotalcite are closely related to its composition, crystal structure and synthesis methods. The study of the hydrotalcite synthesis conditions can guide the applications of HTLCs. The cations on the layers could be changed in wide range. The anionic surfactant SDS can be introduced into the interlayer in order to a significant organic solubilization. Many elements (Cu, Fe) with potential catalytic activity can be introduced into the brucite layer in order to get HTLCs and Mixed Oxides with high dispersion active metal cations.Mg₃Al-CO₃^2--HTLCs, CuMgAl-CO₃^2--HTLCs, CuMgFe-CO₃^2--HTLCs, and CuMgAlFe-CO₃^2--HTLCs were synthysized by the constant co-precipitation method and the hydrothermal method. The HTLCs and synthesized compounds were characterized by XRD, TEM, TG-DSC, FT-IR, BET and TPD. Crystallization of Mg-Al hydrotalcite carbonate, the relative intensity of crystal diffraction, state of CO₃^2- interlayer anion and the reconstruction of the layered double oxides (LDO), were studied to evaluate the impact of hydrothermal conditions. The adsorbability of the hydrotalcite surface modified by SDS was evaluated by its adsorption of p-nitrophenol in aqueous solution. The catalytic activity of the materials was evaluated by catalytic catalytic wet air oxidation of p-nitrophenol.The effect of hydrothermal conditions on the crystallization of Mg₃Al-CO₃^2- hydrotalcite showed that, when the hydrothemal temperature lower than 270 ℃, with the rising of hydrothermal temprature, crystallinity of the samples increased, and 003, 006 faces grown preferentially. But when the temperature were above 270℃, the crystallinity became weakener. The analysis of d110 and crystal unit cell parameter showed that the samples have the same or similar crystal composite in a suitable temperature range. Specific surface, total pore volume and mean average pore size of the samples decreased with higher hydrothermal temperature. The capacity of micro-pore and small-pore increased with higher hydrothermal temperature. The HT decomposed to LDO between 300 ℃ and 380 ℃. On the higher hydrothemal temperature, decarbonization process migrated to higher temperature, and the decomposition temperature interval narrowed down. LDO was easy to reconstruct to hydrotalcite at hydrothermal conditions. MgO in LDO recovering into HT was easier than AlO(OH) and MgAl₂O₄.The adsorption of p-nitrophenol on HT surface modified by SDS showed that, the HT crystal composite did not changed when its surface modified by SDS. SDS was accreted to the HT and LDO samples stably in virtue of surface adsorption effect. The saturation adsorption time of p-nitrophenol on LDO was 4 hour, and the saturation adsorption capacity was 0.74 g/g which was affected by temperature. The p-nitrophenol saturation adsorption capacity on HT and on LDO surface modified by SDS was more than the one on HT, but less than the one on LDO. The results showed that it can be achieved by surface modification to increase the saturation adsorption capacity of organic compounds.The application of catalytic wet air oxidation for the treatment of p-nitrophenol wastewater showed that, CuMgAlCO₃-HTLCs, CuMgFeCO₃-HTLCs and CuMgAlFeCO₃-HTLCs can be synthesized when the content of Cu was less than 15% and the content of Fe was less than 8%. The addition of transition metals decreased the crystallinity of samples. The optimal dosage of catalyst was 0.5g/L . All of the materials synthysized from HTLCs have high catalytic activity while the one calcined at 500℃ had the highest activity. The p-nitrophenol was first oxidized to normal alkanes under high temperature and pressure with the transition metals oxides catalyst, and the final product was water and carbon dioxide.