Spontaneous Transformation of CdSe Nanoparticles into Nonspherical Se Crystals: Role of the Precursor Ligand

Abstract

In this report, nonspherical Se crystals were synthesized from the transformation of CdSe nanoparticles (NPs) under ambient conditions, including nanowires (—), microscale or nanoscale rods (−), crossheads, crosses (+), and other unusual highly anisotropic structures. Here, CdSe NPs are used as the starting point of synthesis; the presence of EDTA triggers the decomposition of primary CdSe NPs, and resultant gradual release of Se2– anions into solution; finally, highly pure well-crystallized nonspherical hexagonal Se (h-Se) crystals are formed via the oxidation of the released Se2– anions in air (this redox reaction will stimulate further the release of Se2– anions) and the subsequent spontaneous crystallization of Se monomers. Some key variables such as the concentrations of EDTA and CdSe NPs, and the ligand of primary NPs, were explored systematically. The experimental results show that the ligand nature of the NP precursor influences the transformation rate of CdSe NPs to Se crystals and dominates the shape and aspect ratio of Se product, while the concentrations of EDTA and CdSe NPs only influence the size of the product. Meanwhile, we also investigated intensively the transformation process of CdSe NP precursors to multiarmed Se crystals, aside from the detailed characterizations on their sizes, shapes, and crystal structures.