Chen Kai Loon, Mylon Steven E, Elimelech Menachem
Department of Chemical Engineering, Environmental Engineering Program, Yale University, New Haven, Connecticut 06520-8286, USA.
Langmuir. 2007 May 22;23(11):5920-8. doi: 10.1021/la063744k. Epub 2007 May 1.
Early-stage aggregation kinetics studies of alginate-coated hematite nanoparticles in solutions containing alkaline-earth metal cations revealed enhanced aggregation rates in the presence of Ca2+, Sr2+, and Ba2+, but not with Mg2+. Transmission electron microscopy (TEM) imaging of the aggregates provided evidence that alginate gel formation was essential for enhanced aggregation to occur. Dynamic light scattering (DLS) aggregation results clearly indicated that a much lower concentration of Ba2+ compared to Ca2+ and Sr2+ was required to achieve a similar degree of enhanced aggregation in each system. To elucidate the relationship between the alginate's affinities for divalent cations and the enhanced aggregation of the alginate-coated hematite nanoparticles, atomic force microscopy (AFM) was employed to probe the interaction forces between alginate-coated hematite surfaces under the solution chemistries used for the aggregation study. Maximum adhesion forces, maximum pull-off distances, and the work of adhesion were used as indicators to gauge the alginate's affinity for the divalent cations and the resulting attractive interactions between alginate-coated hematite nanoparticles. The results showed that alginate had higher affinity for Ba2+ than either Sr2+ or Ca2+. This same trend was consistent with the cation concentrations required for comparable enhanced aggregation kinetics, suggesting that the rate of alginate gel formation controls the enhanced aggregation kinetics. An aggregation mechanism incorporating the gelation of alginate is proposed to explain the accelerated aggregate growth in the presence of Ca2+, Sr2+, and Ba2+.
对包裹藻酸盐的赤铁矿纳米颗粒在含有碱土金属阳离子的溶液中的早期聚集动力学研究表明，在Ca2+、Sr2+和Ba2+存在的情况下聚集速率增强，但在Mg2+存在时并非如此。对聚集体的透射电子显微镜（TEM）成像提供了证据，表明藻酸盐凝胶形成对于增强聚集的发生至关重要。动态光散射（DLS）聚集结果清楚地表明，与Ca2+和Sr2+相比，在每个体系中实现相似程度的增强聚集所需的Ba2+浓度要低得多。为了阐明藻酸盐对二价阳离子的亲和力与包裹藻酸盐的赤铁矿纳米颗粒增强聚集之间的关系，采用原子力显微镜（AFM）来探测在用于聚集研究的溶液化学条件下包裹藻酸盐的赤铁矿表面之间的相互作用力。最大粘附力、最大拉脱距离和粘附功被用作指标，以衡量藻酸盐对二价阳离子的亲和力以及包裹藻酸盐的赤铁矿纳米颗粒之间由此产生的吸引相互作用。结果表明，藻酸盐对Ba2+的亲和力高于Sr2+或Ca2+。这一相同趋势与可比的增强聚集动力学所需的阳离子浓度一致，表明藻酸盐凝胶形成速率控制着增强聚集动力学。提出了一种包含藻酸盐凝胶化的聚集机制，以解释在Ca2+、Sr2+和Ba2+存在下聚集体生长加速的现象。
