The discovery that nanoscale minerals are participants in many geochemical and biogeochemical processes was an important advance in geochemistry. However, this discovery has brought additional complexity to our conceptual models of the natural world, and numerous challenges to the experimental and computational tools used to test them. In this talk I will summarize the challenges to mineralogy, primarily structure determination, and to geochemistry, particularly in understanding kinetic controls on effective reactivity.

Determining accurate models of nanoparticle structure is a pressing task, because knowledge of mineral structure is a prerequisite for understanding stability and intrinsic reactivity. For most nanoparticles formed at low temperature, the crystal unit cell is an incomplete description of structure, and there is a need for better ways to identify defects, disorder and strain. Moreover, nanoparticle surfaces remain uncharted territory, limiting our understanding of interfacial processes including ion adsorption, as well as the surface hydration and protonation reactions that greatly affect nanoparticle structure and stability. Addressing these challenges is feasible, however, because we are far from exhausting the structural information that experimental scattering and imaging approaches provide.

It is very difficult to predict how nanomaterials react under changing environmental redox conditions. Insight into structure­—at both the molecular and aggregate scales—is crucial for understanding the kinetic factors that can constrain the ways in which reactions proceed. In addition, recently developed time-resolved methods can probe nanoparticle transformations and surface reactions at the relevant timescales, from picoseconds to microseconds. The observation of reactions as they occur will be a powerful approach for understanding the mechanisms controlling nanoparticle reactivity.