Cation Exchange Reactions for Varieties of Two-Dimensional Semiconductor Nanomaterials

This dissertation is focused on a general idea that cation exchange can serve as one handy method to synthesize two-dimensional (2D) nanomaterials which cannot be easily produced directly. The synthesized 2D materials have potential application values in several areas, such as nanocatalysis, and solar energy conversion field.

First, we elucidate the synthesis of thickness-controlled Cu_2–xSe nanosheets (NSs) starting from CdSe NSs via cation exchange. Ultrathin Cu_2-xSe NSs, which cannot be synthesized directly, have been made. During the cation exchange reaction, the morphology and crystal structure of CdSe NSs was reserved. Moreover, these Cu_2-xSe NSs are the thinnest NSs synthesized by cation exchange. Our demonstration indicates that cation exchange is a simple and powerful method for 2D nanomaterials synthesis.

Then, we elucidate the use of cation exchange to modify layered 2D SnS₂ NSs to non-layered Cu₂SnS₃ NSs. The resulted Cu₂SnS₃ NSs maintain the general morphology and crystallinity of starting materials, few-layer SnS₂. In specific, these Cu₂SnS₃ NSs have micrometer-sized lateral dimensions and controlled thicknesses by choosing the layer number of initial SnS₂. Our demonstration presents that layered materials can serve as templates for synthesizing non-layered 2D systems via cation exchange. Our work provides a bridge between systems of layered and non-layered materials.

Last, we demonstrate the synthesis of micrometer-sized CdSe NSs starting from micrometer-sized CuSe NSs via cation exchange. Resulting CdSe NSs remain the general 2D morphology of the staring materials. Having established the synthesis of micrometer-sized CdSe NSs, we have conducted measurements of local H₂ bubble generation on individual NS sample and determined local H₂ bubble generation rate on individual photocatalyst. Our work provides potential values for fundamental microscopic insights for photocatalysts in H₂ generation field.