Tailoring of Crystal Phase Distinct Cu_2–<i>x</i>S Templates for Polymorphic Synthesis of Binary Metal Sulfide Nanoparticles

Cation exchange (CE) reaction utilizing the Cu_2-<i>x</i>S nanoparticles (NPs) as the template is an attractive approach to address the limitations in the current polymorphic synthesis of metal sulfide NPs. As such, preformation of the Cu_2-<i>x</i>S NPs with the hexagonal phase and cubic phase is highly desired. Here, we report a facile crystal phase tailoring of Cu_2-<i>x</i>S NPs by tuning the amount of the sulfur precursor thiourea. Hexagonal phase roxbyite Cu_1.8S NPs with a disk-like shape were preferentially synthesized at a low amount of thiourea, and it progressively shifted to cubic phase digenite Cu_1.8S as the amount of thiourea increased. Pure digenite Cu_1.8S NPs with a polyhedral shape were synthesized at a large amount of thiourea. An excess of thiourea is essential to the generation of reactive H₂S and thus the formation of digenite Cu_1.8S. By means of CE reactions of roxbyite Cu_1.8S and digenite Cu_1.8S NPs with Cd²⁺, Zn²⁺, and Mn²⁺, binary wurtzite and zinc blende CdS, ZnS, and MnS NPs were produced. The morphology of the two-phase Cu_1.8S templates was generally preserved, except for the wurtzite MnS NPs. The resulting CdS and ZnS NPs exhibit fine chemical stabilities, while the MnS NPs exhibit poor chemical stability. Both of the wurtzite and zinc blende MnS NPs were evolved into small Mn₃O₄ NPs by air oxidation. Therefore, our research achievements suggest the significance of phase tailoring of the Cu_2-<i>x</i>S templates, holding great promise in the synthesis of other polymorphic metal sulfides with novel physicochemical properties and functionalities.