Aqueous chemistry and biochemistry of silicon

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Silicates – compounds of silicon (Si) and oxygen – are fundamentally important in both nature and industry. These two elements alone constitute 75 wt% of the Earth’s crust, while elements which fit into silicate frameworks represent another 22.5%. Erosion, migration and deposition of silicates are all controlled by aqueous chemistry. Yet it is biology that controls the overall global Si cycle. Primitive organisms such as diatoms and sponges take up the greatest share, using it to construct silicified cell walls and skeletal structures and, in so doing, sequester a major percentage of global CO2 production. Plants, including all grain crops, require a constant Si supply to defend against myriad biological and non-biological stresses. In mammals, dietary Si intake correlates with healthy connective tissue growth. Despite its appreciable biological importance, however, remarkably little is known about silicon’s interaction with organisms at the molecular level. Better knowledge of aqueous silicate chemistry is also needed in materials science to achieve sustainable production and improved properties of key industrial commodities such as concrete, zeolite catalysts, ceramics, semiconductors, coatings and paper. For example, concrete, a low-cost low-energy aggregate of silicates, is the most widely used man-made substance on Earth, with an annual production of nearly 40 billion tons (ca. 20 km3) and quickly rising. Because nearly a ton of CO2 is released during the manufacture of every ton of cement, concrete accounts for some 7-10% of man-made greenhouse gas emissions. Decreasing its environmental impact without sacrificing performance will necessitate changes being made to the chemistry of cement. The long-term goals of my research program are to unravel the fundamental chemistry of aqueous silicon and to translate that knowledge for the benefit of agriculture, human nutrition, medicine and materials science.