水热体系中不同前驱物对合成镁铝水滑石微结构的影响

Effects of Different Precursors on the Microstructure of Mg-Al Hydrotalcite in the Hydrothermal System

以不同的镁源、铝源组合为前驱物,利用XRD、SEM及EDS比较研究了水热体系中不同的前驱物组合对合成镁铝水滑石(Mg-Al-LDHs)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生长机理进行了初步探讨。研究结果表明:当固定体系的p H=12,水热温度120℃、水热时间18 h的条件下,不同的前驱物组合均可以合成结晶度较好的镁铝水滑石晶体;但不同的镁源、铝源组合对产物的物相、分散性、结晶规整性、厚径比、纯度、大小及微结构有一定的影响。当镁源固定为Mg Cl2,铝源分别为Al_2O_3、Al(NO3)3、Al Cl3时,不溶性氧化铝合成的LDHs规整性、分散性及纯度较差,晶体发育不完整;当铝源分别为溶解度较好Al(NO3)3、Al Cl3时,合成产物LDHs晶体的结晶度、规整性、分散性及纯度较好,但由于溶解度和相连阴离子极性的不同,造成产物微结构的微小差异;当镁源固定为溶解度较大的Mg(NO3)2时,铝源分别为Al(NO3)3、Al Cl3时,同溶解度较小Mg Cl2相比,更有利于合成结晶度、规整度、尺寸更小的镁铝水滑石晶体。溶解度较大的镁源、铝源前驱物组合合成的镁铝水滑石有更高的结晶度和规整度。EDS分析证实,溶解度较差的Al_2O_3合成的镁铝水滑石纯度较差。溶解度较好的不同镁源、铝源前驱物组合合成的镁铝水滑石不含有任何其它阴离子杂质,平均镁铝比约为3,非常接近LDHs的理论值。

Using different Mg sources and Al sources as the precursor,Mg-Al Hydrotalcite crystals were synthesized through hydrothermal method under the different precursors.The effects of different Mg sources and Al sources precursors on the microstructure and the growth of LDHs crystals were studied by the X-ray diffraction（XRD）,scanning election microscopy（SEM） and energy dispersive spectrometer（EDS）,simultaneity,its growth mechanism was discussed using ligand theory.The results reveal that the better LDHs crystal could be synthesized at p H = 12,temperature of 120 ℃,and time of 18 h conditions using different precursor.The phase,dispersion,regularity,ratio of thickness,purity,sizeand microstructure of LDHs products are effected under the different Mg and Al sources precursors.When Mg Cl2 was fixed for Mg sources,the LDHs with poor regularity and dispersion,incomplete crystals were synthesized by using Al_2O_3 as Al sources respectively,but the LDHs with better regularity,dispersion,crystalline and purity were synthesized by using Al（NO3）3and Al Cl3 as Al sources respectively.However,the different solubility and polarity of anion resulted in the subtle differences of microstructure of the products.When Al（NO3）3and Al Cl3 was fixed for Al sources respectively,Mg（NO3）2which has better solubility than Mg Cl2 as Mg sources made for synthesizing LDHs with better crystalline,regularity,and smaller in size.When both Mg sources and Al sources have larger solubility,the LDHs with higher crystalline and regularity were synthesized.EDS analysis results confirmed that the purity of LDHs synthesized by Al_2O_3 had poor solubility.In addition,LDHs synthesized by Mg sources and Al sources which had larger solubility do not contain any impurity,and the average Mg/Al ratio is about 3,which is very close to the theoretical value.