Galindo-González C, de Vicente J, Ramos-Tejada M M, López-López M T, González-Caballero F, Durán J D G
Department of Applied Physics, Faculty of Sciences, University of Granada, 18071 Granada, Spain.
Langmuir. 2005 May 10;21(10):4410-9. doi: 10.1021/la047393q.
This work is devoted to the preparation of magnetite-covered clay particles in aqueous medium. For this purpose, magnetite nanoparticles were synthesized by a coprecipitation method. These magnetic particles are adhered to sodium montmorillonite (NaMt) particles in aqueous suspensions of both materials, by appropriate control of the electrolyte concentrations. The best condition to produce such heteroaggregation corresponds to acid pH and approximately 1 mol/L ionic strength, when the electrokinetic potentials (zeta-potential) of both NaMt and Fe3O4 particles have high enough and opposite sign, as demonstrated from electrophoresis measurements. When a layer of magnetite re-covers the clay particles, the application of an external magnetic field induces a magnetic moment in clay-magnetite particles parallel to the external magnetic flux density. The sedimentation behavior of such magnetic particles is studied in the absence or presence of an external magnetic field in a vertical direction. The whole sedimentation behavior is also strongly affected by the formation of big flocculi in the suspensions under the action of internal colloidal interactions. van der Waals and dipole-dipole magnetic attractions between magnetite-covered clay particles dominate the flocculation processes. The different relative orientation of the clay-magnetite particles (edge-to-edge, face-to-edge, and face-to-face) are discussed in order to predict the most favored flocculi configuration.
这项工作致力于在水介质中制备磁铁矿包覆的粘土颗粒。为此，采用共沉淀法合成了磁铁矿纳米颗粒。通过适当控制电解质浓度，使这些磁性颗粒在两种材料的水悬浮液中附着于钠蒙脱石（NaMt）颗粒上。产生这种异质凝聚的最佳条件是酸性pH值和约1 mol/L的离子强度，此时NaMt和Fe3O4颗粒的电动电势（zeta电位）具有足够高的绝对值且符号相反，这已通过电泳测量得到证明。当一层磁铁矿重新覆盖粘土颗粒时，施加外部磁场会在粘土 - 磁铁矿颗粒中感应出一个与外部磁通密度平行的磁矩。在垂直方向上有无外部磁场的情况下，研究了此类磁性颗粒的沉降行为。悬浮液中在内部胶体相互作用的作用下形成大絮凝物，这也对整个沉降行为产生强烈影响。磁铁矿包覆的粘土颗粒之间的范德华力和偶极 - 偶极磁吸引力主导了絮凝过程。讨论了粘土 - 磁铁矿颗粒的不同相对取向（边对边、面 - 边和面 - 面），以便预测最有利的絮凝物构型。
