Can hematite nanoparticles be an environmental indicator?

Environmental indicators play an important role in assessing the state of the environment and understanding the trend of environmental changes. Iron oxide nanostructures are widespread in multiple ecosystems, and are therefore suitable for providing environmental indicators with measurable physical or chemical properties that are sensitive to the environmental conditions. It has been found that the morphologies of natural hematite (α-Fe ₂O₃) nanocrystals have large variations depending on thermodynamic and chemical conditions of their formation environments. To assess the applicability of nanomorphology as an environmental indicator, we construct a morphology map of hematite nanocrystals in hydrous environments, characterized with different temperatures, humidity and supersaturation of oxygen. Our model indicates that the fractional surface areas of morphologically significant facets change with humidity and temperature, and can be used to track the variation of these environmental conditions.