"Nanoparticles at Environmental Interfaces"Young-Shin Jun, Washington University Environmental nanoparticles are often poorly-crystalline or metastable structures, whose kinetics of formation and growth are poorly understood. Further, the sorption or growth of nanoparticles on mineral surfaces may control the mineral surface’s reactivity and modify its ability to influence contaminant transport. Due to the characteristic length scale, a holistic understanding of the nucleation mechanisms and kinetics of nanoparticle formation on mineral surfaces is difficult to achieve with conventional methodology. In this workshop, three new synchrotron-based techniques (CTR, GIXAS, and GISAXS) will be introduced to determine the molecular nature of nucleation on surfaces, the kinetics of surface nucleation and growth, and the effect of crystal surface topology. Two representative cases of nanoparticle or nanoscale coating formation at mineral-water interfaces will be addressed: the molecular-scale sorption geometry of silicate on iron oxide surfaces and the kinetics of iron-oxide-nanoparticle nucleation and growth on quartz. These two reactions have opposing effects with respect to the sorption of arsenate, heavy metal, and radioactive elements. Silicate sorption passivates the iron oxide surface, while iron oxide nanoparticle formation enhances the reactivity of quartz surfaces. First experimental evidences (from CTR and Si K-edge GIXAS) of well-structured sorption of silicates at the iron oxides will be presented. For study of the iron oxide growth, a new approach with time-resolved grazing incidence small angle x-ray scattering technique for in situ time-resolved investigations of nanoparticle reactions at environmental aqueous interfaces will be described. This study also includes complementary techniques such as atomic force microscopy (AFM), dynamic light scattering (DLS), and transmission electron microscopy (TEM). CTR: crystal-truncation rod diffraction |