Formation and Aggregation of ZrO2 Nanoparticles on Muscovite (001)

The aggregation of nanoparticles is a key step in the formation of solid phases and a controlling factor for the behavior of suspended nanoparticles in solution. Using a charged mineral surface [muscovite (001)] we apply the surface X-ray diffraction techniques Crystal Truncation Rod (CTR) measurements and Resonant Anomalous X-ray reflectivity (RAXR) to investigate the aggregation process of Zr nanoparticles at the sub-nm scale. The aggregation process was studied as a function of ionic strength (0, 1, 10, and 100 mM NaCl), and the interfacial particles were characterized by CTR/RAXR and AFM. The observations are consistent with an aggregation process that follows a multi-step mechanism, which starts with the 3D aggregation of primary building units to form nanosheets. These sheets continue to grow through addition of building units to their reactive edges at higher ionic strength. Once the size and concentration of aggregates is sufficient, “face-to-face” stacking of nanosheets becomes the preferred aggregation mechanism as this minimizes the electrostatic repulsion of the charge that accumulates along nanosheet edges.