【摘要】 采用均匀沉淀法(尿素水解法)合成了高结晶度的CO32-型MgAl-LDH,探索了温度和时间对产物的影响.研究发现,n(Mg)/n(Al)进料比为2时,较低反应温度(如100℃)下很难得到n(Mg)/n(Al)=2的LDH.这可能与Mg(OH)2溶解度较高,Mg2+难以与Al3+一同沉淀有关.为提高产物n(Mg)/n(Al),我们采用提高n(Mg)/n(Al)投料比(如3∶1,4∶1,5∶1)的方法.研究发现,反应时间较短时,可得较纯的LDH相,但产物的n(Mg)/n(Al)远低于进料比;若反应时间延长,会出现水菱镁矿(hydromagnesite)和菱镁矿(magnesite,MgCO3)的杂相.由此推断,为得到高n(Mg)/n(Al)的LDH,不能单纯增加n(Mg)/n(Al)进料比,其他条件如尿素浓度,尤其是反应温度等也需改变.更多还原

【Abstract】 CO2-3 type LDH was synthesized by the homogeneous precipitation method(urea hydrolysis) with varied temperature and reaction time.Compositions and structure of LDH obtained revealed that at the temperature of 100℃,n(Mg)/n(Al) molar ratio was less than the starting ratio of 2.Under acidic conditions,Mg(OH)2 solubility was larger than Al(OH)3,LDH with lower n(Mg)/n(Al) ratios was obtained.To obtain LDH with higher n(Mg)/n(Al) ratios,the starting n(Mg)/n(Al) ratios were increased to 3∶1,4∶1 and 5∶1,but the final LDH product always showed a n(Mg)/n(Al) ratio lower than the initial solution ratio.At an initial ratio of 5∶1,pure LDH phases were formed at short reaction time,but some mixed phases such as hydromagnesite and magnesite appeared with increasing time.Thus increasing the n(Mg)/n(Al) starting ratio only is not a good way,and other conditions such as urea concentration and especially reaction temperature may be important factors influencing the final n(Mg)/n(Al) ratios of the resulting LDH products.更多还原