Oberflächenstabilisatoren und ihre Rolle bei der formkontrollierten Synthese von kolloidalen Metall‐Nanokristallen

Facile Synthesis of Platinum Right Bipyramids by Separating and Controlling the Nucleation Step in a Continuous Flow System

Colloidal synthesis of metal nanocrystals with controlled shapes and internal structures calls for a tight control over both the nucleation and growth processes. Here we report a method for the facile synthesis of Pt right bipyramids (RBPs) by separating nucleation from growth and controlling the nucleation step in a continuous flow reactor. Specifically, homogeneous nucleation was thermally triggered by introducing the reaction solution into a tubular flow reactor held at an elevated temperature to generate singly-twinned seeds. At a lower temperature, the singly-twinned seeds were protected from oxidative etching to allow their slow growth and evolution into RBPs while additional nucleation of undesired seeds could be largely suppressed to ensure RBPs as the main product. Further investigation indicated that the internal structure and growth pattern of the seeds were determined by the temperatures used for the nucleation and growth steps, respectively. The Br^- ions involved in the synthesis also played a critical role in the generation of RBPs by serving as a capping agent for the Pt{100} facets while regulating the reduction kinetics through coordination with the Pt(IV) ions.

Metal Cation Valency Dependence in Morphology Evolution of Cu2-x S Nanodisk Seeds and Their Pseudomorphic Cation Exchanges

A crucial parameter in the design of semiconductor nanoparticles (NPs) with controllable optical, magnetic, electronic, and catalytic properties is the morphology. Herein, we demonstrate the potential of additive metal cations with variable valency to direct the morphology evolution of copper-deficient Cu_2-x S nanoparticles in the process of seed-mediated growth. In particular, the djurleite Cu_1.94 S seed could evolve from disk into tetradecahedron in the presence of tin(IV) cations, whereas they merely formed sharp hexagonal nanodisks with tin(II) cations. In addition to djurleite Cu_1.94 S, the tin(IV) cations could be generalized to direct the growth of roxbyite Cu_1.8 S and covellite CuS nanodisk seeds into tetradecahedra. We further perform pseudomorphic cation exchanges of Cu_1.94 S tetradecahedra with Zn²⁺ and Cd²⁺ to produce polyhedral zinc sulfide (ZnS) and cadmium sulfide (CdS) NPs. Moreover, we achieve Cu_1.8 S/ZnS and Cu_1.94 S/CdS tetradecahedral heterostructures via partial cation exchange, which are otherwise inaccessible by traditional synthetic approaches.