The Preparation Of Layered Double Hydroxyl Hydroxide Carrier Research

The layer double hydroxides (LDHs) such as Mg-Fe LDHs and Ni-Al LDHs with CO32-as intercalated anion and the different composition of layer board as well as Mg-Al LDHs with NO3-as intercalated anion have been prepared by coprecipitation method.The products are characterized by means of X-ray diffraction(XRD),infrared spectra(IR),spectroscopyelectronmicroscopy(SEM),transmission electron microscope(TEM) as well as laser particle size analyzer. The effects of feeding method, preparation and crystallization conditions on the phase and particle size of products were investigated.(1)The results of XRD showed that the LDHs can be prepared by both the constant-pH method and the variable-pH method, which was described as follows:For the preparation of Mg-Al-CO32-LDHs,the feeding method,the amount of intercalated anions and precipitation reaction temperature have no effect on the phase of the product, the product synthesized by the constant-pH showed perfect crystalline.The proper ratio of starting materials is n(Mg2+):n(Al3+)=3.0,n(NaOH-):n(Mg2++Al3+)=2.5, n(CO32-):n(Al3+)=1,Mg-Al-CO32-LDHs can be obtained by carrying out precipitation reaction at45℃, and then aged at65℃for18h.The Mg-Fe-CO32-LDHs were prepared by the variable-pH method, when the mater-ial ratio is n(Mg2+):n(Fe3+)=3.0,n(NaOH-):n(Mg2++Fe3+)=2.0,n(CO32-):n(Al3+)=1,Mg-Fe-CO32-LDHs can be obtained by carrying out precipitation reaction at45℃,and then aged at80℃for18h.The Ni-Al-CO32-LDHs were prepared by the variable-pH method. The proper ratio of starting materials is n(Ni2+):n(Al3+)=3.0,n(NaOH-):n(Ni2++Al3+)=2.0,n(CO32-):n(A13+)=1,Ni-Al-CO32-LDHs can be obtained by carrying out precipitation reaction at45℃, and then aged at80℃for18h.(2)EDX element analysis indicated that magnesium and aluminum elements, magnesium and iron,nickel and aluminum were contained in different composition products respectively. The mole ratio of Mg to Al is2.6, Mg to Fe is2.6and Ni to Al is2.6respectively.(3) The results of infrared spectroscopy and XRD showed that the CO32-anion has may been intercalated into the layer of the three kinds of LDHs.(4) The optimizing conditions for preparing Mg-Al-CO32-LDHs were studied by orthogonal experiments using the products particle size as the evaluation index. The optimal prepared conditions were as follows:the crystallization temperature is100℃,the crystallization time is8h,c(Mg2++Al3+)=0.5mol/L,c(OH-)=3.5rnol/L.The D50of LDHs sample synthesized in the optimal conditions is6.14μm.(5)The results of laser particle sizer analyzer showed that the particle size distribution of the LDHs with different composition of layer board was between1-20μm. The other preparation methods should be explored to obtain nano size LDHs.(6) Mg-Al-NO3-LDHs can be obtained by carrying out precipitation reaction at room temperature under N2atmosphere with n(Mg2+):n(Al3+)=3.0,n(NaOH-):n(Mg2++Al3+)=2.0,n(CO32-):n(Al3+)=1and then aged at100℃for18h. The data of XRD showed that its d003=0.8787nm implied that the intercalated anion was NO3-.(7) The results of SEM and TEM showed that the morphology of the LDHs samples is layer.