用液相非稳态共沉淀法合成了Zn Al类水滑石(HTlc),研究了样品中n(Al)/n(Zn+Al)(x)和层间阴离子CO2-3对Zn Al HTlc化学组成、晶体结构和粒子形貌的影响。结果表明,当0 31≤x≤0 52时可得到单一的Zn Al Cl HTlc相;x≤0 25时有ZnO杂质相出现;x>0 52时样品主要以无定形物存在。x对晶胞参数a和c影响不大;与Cl-相比,层间CO2-3对a影响不大,使c值略有降低。透射电镜(TEM)结果表明,随每摩尔HTlc样品n(Zn)增加,Zn Al ClHTlc粒子六角形片状结构规则度增加。电子衍射图谱表明,所合成的HTlc样品均为六方晶系多晶结构物质。
The aggregation and fractal structure of mixed metal hydroxides ( MMH ) agglomerates with increasing ionic strength have been studied by dynamic light scattering ( DLS ) and SEM techniques. The experiments indicate that the MMH agglomerates have two different structures in RLA regime and DLA regime, and also give the proof that the transition region between RLA and DLA may occur.
The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (st) for amphoteric solid with structural charges was established in order to investigate the effect of st on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (c) exists for amphoteric solid with structural charges. A common intersection point (CIP) should appear on the acid-base titration curves at different c, and the pH at the CIP is pHPZNC. The pK can be expressed as pK=-pHPZNC+log[(1+2aPZNC)/(1-2aPZNC)], where aPZNC≡st/eNANs, in which e is the elementary charge, NA the Avogadro抯 constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(OH)2](Cl, OH)x were evaluated. With increasing x, the pK increases, which can be explained based on the affinity of metal cations for H+ or OH- and the electrostatic interaction between charging surface and H+ or OH-.
