Phase-Selective Chemical Extraction of Selenium and Sulfur from Nanoscale Metal Chalcogenides: A General Strategy for Synthesis, Purification, and Phase Targeting
journal contributionposted on 09.02.2011, 00:00 by Ian T. Sines, Raymond E. Schaak
Controlling the composition and phase formation of bulk and nanoscale solids underpins efforts to control physical properties. Here, we introduce a powerful new chemical pathway that facilitates composition-tunable synthesis, post-synthesis purification, and precise phase targeting in metal chalcogenide systems. When metal selenides and sulfides react with trioctylphosphine (TOP) at temperatures that range from 65 to 270 °C, selenium and sulfur are selectively extracted to produce the most metal-rich chalcogenide that is stable in a particular binary system. This general approach is demonstrated for SnSe2, FeS2, NiSe2, and CoSe2, which convert to SnSe, FeS, Ni3Se2, and Co9Se8, respectively. In-depth studies of the Fe−Se system highlight the precise phase targeting and purification that is achievable, with PbO-type FeSe (the most metal-rich stable Fe−Se phase) forming exclusively when other Fe−Se phases, including mixtures, react with TOP. This chemistry also represents a new template-based nanoparticle “conversion chemistry” reaction, transforming hollow NiSe2 nanospheres into hollow NiSe nanospheres with morphological retention.