Understanding the roles of metal sources and dodecanethiols in the formation of metal sulfide nanocrystals via a two-phase approach

Abstract

We present a two-phase approach for controllable synthesis of metal sulfide nanocrystals, such as Cu_2−xS, Ag₂S and Ni₉S₈, in which the reaction takes place at the water/oil interface. This method is environmental-friendly and economical due to the use of low-toxicity and low-cost reagents. The crystal phase and composition can be manipulated by varying the amount of n-dodecanethiol (DDT) in the organic phase and the type of metal salt in the aqueous phase. For example, CuO nanocrystals can be obtained in the presence of low DDT concentration and hydroxyl ions, and Cu_2−xS nanocrystals are successfully synthesized in the presence of relatively high DDT concentration. The XPS spectra and near-infrared (NIR) absorption spectra have been collected to confirm the formation of CuO and Cu_2−xS nanocrystals. Moreover, the Cu_2−xS nanocrystals often exhibit an obvious localized surface plasmon resonance band due to their excess free holes in the valence band. A plausible formation mechanism has been proposed to study the synthesis of Cu_2−xS and CuO nanocrystals. This two-phase approach has also been extended to prepare Ag₂S and Ni₉S₈ nanocrystals, and the Ag and Ag₂S nanocrystals often coexist in the products which are closely associated with cleavage of S–C bonds or the Ag–S bond, which relies on the DDT dosage and the reactivity of the metal sources. This two-phase approach may open up a simple and environmental-friendly strategy for synthesis of metal sulfide nanocrystals with controllable crystal phase and morphology.