Supercritical methanol synthesis, phase evolution and formation mechanism of Cu 1.8 S and Cu 9 S 5 /CuS complex microcrystal

Abstract The facile and fast synthesis of copper sulfide with controllable stoichiometric composition, crystal phase and shape, without using any additional surfactant and structure directing agent, is still highly attractive and remains a challenge. A supercritical methanol synthetic method was presented in this work, by which pure Cu 1.8 S and Cu 9 S 5 /CuS complexes with different particles size and phase composition could be synthesized by tuning the reaction temperature and time. It was demonstrated that higher temperature and longer time were beneficial to the formation of copper sulfides with higher Cu/S ratio and could cause obvious red shifts of band gap energies from 1.34 to 1.54 eV for copper sulfides. Furthermore, crystal phase evolution from Cu 9 S 5 to Cu 1.8 S was also observed in the preparation process. It was proposed that CuS was produced firstly by decomposing the complex Cu(CN 2 H 4 S) 2 (CH 3 COO) 2 , and then reduced to Cu 9 S 5 which was further evolved into Cu 1.8 S.