SURFACE ENERGETICS AND INTERACTIONS OF CINNABAR AND METACINNABAR (HGS) NANOPARTICLES

Mercury sulfide exists as two polymorphs: the thermodynamically stable cinnabar (α-HgS) with a hexagonal structure and the metastable metacinnabar (β-HgS) with a cubic structure, both of which can form naturally via biogenic and abiogenic routes. Surface energetics studies provide insights into the thermodynamic stability differences between macroscopic and nano-sized analogues, helping to better understand the relationship between particle size and properties. At the most fundamental level, the environmental behavior of nanoparticles is primarily driven by the interaction between the inorganic surface and various molecules. Elucidating the energetics of water adsorption on nanoparticle surfaces provides essential data about their behavior in aqueous environments, while studying the energetics of surface interactions with organic molecules is crucial for understanding more complex biogeochemical systems. The thermodynamic stability and surface energy of the two polymorphs were measured using high-temperature oxidative calorimetry to assess the possibility of a phase stability reversal at the nanoscale (energy crossover) similar to other nanosized sulfides. The energetics of interactions between the surface of nano HgS and different molecules were measured using two main techniques: gas sorption of inorganic or organic vapors on the solid surface, and immersion calorimetry of the nanoparticles in an aqueous or organic solution.