Aqueous Controlled Synthesis And Self-assembly Of Copper Sulfide Colloidal Nanomaterials

In order to obtain materials with particular compositions, sizes and shapes, it is essential to develop simple, controllable, general, and environment friendly synthetic methods, and study the growth mechanism of nanocrystals. Assembling the nanocrystals into advanced functional structures also paves the way for the practical applications. The aqueous colloidal synthesis of colloidal semiconductor nanocrystals is an advantageous alternative to the widely used organometallic route. Copper chalcogenide nanoparticles (NPs) represent a promising material for solar energy conversion, electrical charge storage, and plasmonic devices. However, it is difficult to achieve high-quality NP dispersions in experimentally convenient and technologically preferred aqueous media. Also problematic is the transition from NP dispersion to continuously crystalline nanoscale materials, for instance nanowires or similar high aspect ratio nano/micro structures capable of charge transport necessary for such applications. In this dissertation, valuable explorations have been carried out on the novel aqueous synthetic method for Cu2S nanocrystals as well as their self-assembly.(1) Aqueous Controlled Synthesis of TGA-caped Copper Sulfide Colloidal nanocrystals. We show that aqueous synthesis of high-quality monodispersed high-chalcocite Cu2S NPs, with sizes from2to10nm, is possible. When reaction time increased, the NP shape evolved from nearly spherical particles into disks with predominantly hexagonal shape. We also demonstrate that the concentration of the Cu/S ratio, the pH of the sovent, the reaction temperature and the reaction time can impact of the size, shape, composition of the nanocrystals.(2) Self-assembly of TGA-caped Copper Sulflde Colloidal Nanocrystals. The monodispersed Cu2S NPs were found to spontaneously self-assemble into nanochains and subsequently to nanoribbons. The width and length of the nanoribbons were4-20nm and50-950nm, respectively, depending on the assembly conditions. We observed the formation of nanoribbons with continuous crystal lattice and charge transport pathways making possible the utilization of self-assembly processes in the manufacturing of photovoltaic and charge storage devices. The Cu2S nanocrystals can also assemble into supercrystal with tetrahedral and fusiform profile, respectively.(3) Aqueous Controlled Synthesis of Copper Sulfide nanorod arrays and chiral Cu2S nanocrystals. We introduced the L-cysteine stabilizers in the same synthesis system in aqueous solution. The superstructure of the Cu2S nanorod arrays on the flexible microsheet were synthesized. The optical properties and the growth of (D, L)-cysteine and (D, L)-penicillamine stabilized Cu2S nanocrystals were investigated. The monodispersity of Cu2S NPs were successfully synthesized, and the nanoparticles with size-dependent circular dichroism absorption in visible light region were observed. The NIR spectra of these Cu2S show a plasmonic absorption, and the superior NIR absorptions have made copper chalcogenide nanocrystals promising candidates for photothermal applications including therapies.