Halide-Controlled Polymorphism in the Synthesis of Mercury Sulfide Nanomaterials

• Bianca Murtha, Chemistry, University of Delaware

• Emil Hernandez-Pagan, Chemistry & Biochemistry, University of Delaware

Studies on polymorphic compounds are of long-standing interest because, although these compounds share the same composition, their different crystal structures lead to distinct physicochemical properties. For example, HgS has two main polymorphs: cinnabar and zincblende. Each shows distinct optical and electromagnetic properties.  For this reason, it is crucial to develop synthetic schemes that afford polymorph control. In this work, we focus on achieving such control for HgS nanomaterials with mercury halide precursors, built on previous findings from our group. Specifically, HgCl2 and HgBr2 were utilized as precursors along with elemental sulfur, while systematically varying the reaction temperature and the sulfur concentration. The products of the reactions were characterized by powder X-ray diffraction, UV-visible and Raman spectroscopy.  Pure cinnabar could only be synthesized by using HgBr2 as a precursor under high temperature, long reaction time and high/low sulfur ratios. On the other hand, HgCl2 favored the zincblende polymorph among all of the synthesis conditions. Future directions for this project interrogating the effect of different ligands and sulfur precursors. The findings from this work will contribute to the understanding of halide-driven polymorph selectivity and synthetic routes that enable polymorph control for other material classes.