Dissolution Behavior of Isolated and Aggregated Hematite Particles Revealed by in Situ Liquid Cell Transmission Electron Microscopy

Dissolution behavior of isolated and aggregated hematite particles in 10, 36, and 103 nm, respectively, was investigated using in situ liquid cell transmission microscopy (LCTEM). The high spatial and temporal resolution of LCTEM enables us to differentiate the respective effects of primary particle size, crystal defects, and aggregation state on particle dissolution. At similar electron-beam irradiation parameters, the initial surface-area normalized dissolution rates (R-SA,R-Int) of isolated 10, 36, and 103 nm particles are 4.64 +/- 3.60, 0.91 +/- 0.44, and 0.24 +/- 0.04 mg m(-2) s(-1), respectively. Interface free energy, calculated from the measured decreases with the decreasing primary particle size. No RsA,Inu preferential etching occurs on 10 nm, defect-free nanoparticles, whereas dissolution preferentially originates from crystal defects on 103 nm particles. In dissolution of aggregated particles, dissolution occurs more rapidly on the particles that are more accessible to bulk solution than the others inside the aggregate. As dissolution proceeds, dendritic aggregates break into several smaller aggregates that respectively shrink into even smaller and more compact aggregates, followed by reaggregation together. This study directly shows microscopic dissolution behavior of isolated and aggregated particles in different primary particle sizes, which is important to understand bioavailability, transport, and fate of nanoparticles in aquatic systems.

分别使用原位液相池透射显微镜（LCTEM）研究了粒径为10、36和103纳米的孤立赤铁矿颗粒和聚集赤铁矿颗粒的溶解行为。LCTEM的高空间和时间分辨率使我们能够区分初级粒径、晶体缺陷和聚集状态对颗粒溶解的各自影响。在相似的电子束辐照参数下，孤立的10、36和103纳米颗粒的初始表面积归一化溶解速率（$R_{SA}$，$R_{Int}$）分别为4.64±3.60、0.91±0.44和0.24±0.04毫克/平方米·秒。根据测量值计算出的界面自由能随着初级粒径的减小而降低。在无缺陷的10纳米纳米颗粒上未出现$R_{SA,Int}$优先蚀刻现象，而103纳米颗粒的溶解优先源于晶体缺陷。在聚集颗粒的溶解过程中，聚集体内比其他颗粒更易接触本体溶液的颗粒溶解得更快。随着溶解的进行，树枝状聚集体分裂成几个较小的聚集体，这些聚集体分别收缩成更小且更紧密的聚集体，然后再次聚集在一起。这项研究直接展示了不同初级粒径的孤立颗粒和聚集颗粒的微观溶解行为，这对于理解水生系统中纳米颗粒的生物可利用性、迁移和归宿具有重要意义。