Solvent Choice to a Phase-Controllable Shift of Covellite-CuS Nanoparticles for Cation Exchange Reactions and Plasmonic Photodetectors

Abstract Among the copper-deficient Cu2−xS nanoparticles (NPs), the unique disulfide (S−S) covalent bonds in covellite-CuS NPs provide an ideal template for a phase-controllable shift into other Cu2−xS NPs. In this regard, a rational choice of a reducing solvent to break the S−S bonds is highly desirable. Herein, two solvents of R−NH2 and R−SH, where R = linear dodecyl, were selected to trigger a phase shift of the covellite-CuS NPs before cation exchange (CE) reactions. The CuS NPs were reduced into cubic-phase digenite-Cu1.8S NPs by the R−NH2 solvent under thermal heating. In contrast, they were converted into hexagonal-phase djurleite-Cu1.94S NPs by the R−SH. The above three-phase Cu2−xS NPs are suitable for plasmonic photodetectors. Thereafter, these two phase Cu2−xS NPs with a plate-like morphology were exchanged with Zn2+, In3+, and Ga3+, and ZnS, CuInS2, and CuGaS2 NPs with a cubic zinc blende phase and a hexagonal wurtzite phase were produced. For djurleite-Cu1.94S NPs exchanged with Ga3+, a dissolution/reprecipitation mechanism was proposed to interpret the unusual reaction behaviors. These polymorphic metal sulfide NPs exhibit distinct optical responses. Therefore, our research achievements provide a facile approach for a phase shift of the CuS NPs, holding great promise in the CE reaction-enabled polymorphic synthesis of binary/ternary/multinary metal sulfides with phase-related physicochemical properties.