Thermal Stability and Chemistry of Fluorescent Nanocrystals for use as a Novel Geothermal Tracer

Abstract

Fluorescent nanocrystals are promising candidates for a range of applications, ranging from biomedical imaging and sensing to solar energy conversion and lighting. Recently, these nanometer-sized semiconductor crystals (also referred to as “quantum dots”) have shown potential to be used as novel geothermal reservoir tracer particles. Quantum dots have size-dependent, tunable electronic and optical properties that make them promising candidates for use as tracers in geothermal fields. In this study, organic molecules were investigated as quantum-dot-surface-stabilizing ligands in order to create water-soluble nanocrystals that behave as conservative tracers in geothermal media. More extensive modification of the surface chemistry of nanocrystals could also make them attractive materials for reactive tracers. The thermal stability of organic-ligand-stabilized core/shell quantum dots under simulated geothermal conditions was studied through autoclave experiments at temperatures exceeding 150 ºC. These tests looked for degradation, agglomeration, and solubility, all of which would alter the optical properties of the tracers. Quantum dot behavior and response was also tested in flow-through reactors packed with geothermal media using in-line fluorometers, and compared to conventional tracers.