Co-MgAl三元类水滑石的合成、微结构及吸附性能研究

采用水热法制备了Co-MgAl三元类水滑石层状化合物(HTLcs),利用X射线衍射(XRD)、扫描电镜(SEM)比较研究了不同Co2+比例条件下对合成产物物相、晶体微结构及晶体生长的影响,同时利用生长基元的配位体理论对其合成机理进行了初步探讨.以甲基橙(MO)模拟染料废水为吸附对象,比较研究了三元类水滑石与二元水滑石焙烧产物的吸附性能和吸附机理.研究结果表明:钴离子同层板二价镁离子存在着交换作用,钴离子掺杂量的不同,没有影响水滑石固有的层板结构,但影响了构建钴镁铝三元类水滑石过程中各晶面的生长.Co∶Mg∶Al为1∶2∶1的HTLcs经过500 ℃焙烧后,焙烧产物(LDO)仍呈现片状结构.但径向尺寸和厚度同焙烧前相比略有减小,产物的均一性、规整性相比焙烧前变差,其对甲基橙模拟染料废水的吸附脱色性能随着时间的增加,呈缓慢增加的趋势,达到吸附平衡需要时间更长为70 min,脱色率仅为60;左右,明显低于二元镁铝水滑石焙烧产物(MgAl-LDO)(90;).吸附动力学研究表明Co-MgAl-LDO焙烧产物对甲基橙的吸附过程更符合准二级动力学方程,吸附等温线符合Freundlich模型,而二元MgAl-LDO对甲基橙的吸附过程较符合准一级动力学方程,吸附等温线符合Langmuir模型.

Preparation,Microstructure and Adsorption Properties of Co-MgAl Ternary Hydrotalcite-like Compounds

Co-MgAl ternary hydrotalcite-like compounds (HTLcs) were prepared by hydrothermal method.The different Co2+ ratios on the phase composition, crystal structure and crystal growth of HTLcs were investigated by the X-ray diffraction (XRD) and scanning election microscopy (SEM).Simultaneously, the growth mechanism was discussed by the ligand field theory.The adsorption performance and mechanism of calcined Co-MgAl-HTLcs and MgAl-LDHs were comparative investigated with methyl orange (MO) as the adsorption object.The results show that there is exchange exists in Mg2+ and Co2+ at layer board.The lamellar structure of hydrotalcites are not affected at different Co2+ ratios, but the each crystal planes growth of Co-MgAl-HTLcs are affected during the crystal formation process.The calcined Co-MgAl-HTLcs of Co∶Mg∶Al=1∶2∶1 can maintain sheet structure after 500 ℃ calcining.But the crystal size and thickness slightly are decrease compared with that before calcined, the homogeneity and regularity of the product became relative poorer than before calcined.The adsorption decolorization performance of Co-MgAl-LDO is slowly increasing with the time increase on MO simulated dye wastewater.It took the longer to reach adsorption equilibrium for 70 min.The decolorization rate is only to 60%, which is the lower than the MgAl-LDO (90%).The adsorption kinetic study shows that the adsorption process of Co-MgAl-LDO on the MO is more consistent with the quasi-second-order kinetics equation, and the adsorption isotherm is in accordance with the Freundlich model.The adsorption process of MgAl-LDO is more consistent with the quasi-first order kinetic equation, its adsorption isotherm conforms to the Langmuir model.