MESOGEOCHEMISTRY: NANOPOROUS STRUCTURES IN GEOLOGICAL ENVIRONMENT

The emergence of nanotechnology has made it possible to manipulate material structures at nanometer scales and has greatly advanced our understanding of how these nano-scale structures give rise to novel physical and chemical properties of materials. This new technology will shape the landscape for many other disciplines of science and engineering including geochemistry. Scientifically, the discovery that matters in a nano-scale confinement could exhibit novel behaviors not seen in bulk systems. Our preliminary studies indeed indicate that chemical reactions in mesopores can be significantly modified, both thermodynamically and kinetically, due to the nano-scale confinement.

Mesoporous structures are ubiquitous in geologic materials and they constitute an integral part of overall porosity of rocks. The following are some mesostructures in geologic materials and their possible effect on geochemical processes: 1. Diatomaceous materials. Our transmission electron microscopic (TEM) observation reveals that diatomaceous materials display both micron-scale and nano-scale pore structures. The mesopores are regularly distributed with a pore size of ~ 3 nm. Unlike non-mesoporous silica materials, the dissolution kinetics of diatomaceous materials usually displays a nonlinear dependence on saturation degree which may indicate, as we suspect, the control of mesopores on mineral dissolution kinetics. 2. Nano-scale copper inclusions in partially weathered illite, pointing to the control of nanostructures on geochemical reactions. We suspect that the preferential enrichment of trace metals in mesopores may be responsible, to a large extent, for the generally observed irreversibility of metal uptake or release by natural materials. 3. Mesoporous Fe-oxyhydroxide in paleosol sample, which will play important role in sorption of metals and reaction with organic molecules. 4. Nanometer scale pores at grain boundaries of minerals.