Suppressed Cation Exchange Reactions in Covellite CuS Nanoparticles: A Surface Capping Effect by Metal-Amine Complexes.

Utilization of copper-deficient Cu2-xS nanoparticles (NPs) as the cation exchange (CE) template has attracted a great deal of attention to yield complicated and metastable nanomaterials. However, the surface chemistry of the Cu2-xS NPs during the CE reactions is somewhat overlooked. Herein, we report a surface capping on the (0 0 6) planes of the covellite CuS NPs by Zn2+-oleylamine complexes. Despite the presence of a strong reducing agent trioctylphosphine (TOP), the splitting of the S-S bonds within the CuS NPs─which act as diffusion barriers for guest cation incorporation─was completely inhibited, leading to suppressed CE reaction kinetics with Zn2+. To circumvent this surface capping effect, the CuS-TOP dispersion was preheated to split the S-S bonds and thus trigger a pseudomorphic phase transformation into djurleite Cu1.94S. The high-quality wurtzite ZnS NPs were facilely generated after the injection of the preheated CuS-TOP dispersion into the CE reaction solution. Analogous to Zn2+, wurtzite CdS NPs with high crystallinity were generated by preheating of the CuS-TOP dispersion. Therefore, our research achievements highlight the significance of surface chemistry of the Cu2-xS template during the CE reactions, providing an effective strategy to control the reaction kinetics and/or thermodynamics.