Reports: DNI1051804-DNI10: Hybrid Inorganic-Organic Nanoscale Arrays: Structural Control and Mechanisms of Formation

Gordana Dukovic, University of Colorado Boulder

This PRF award has supported two projects in my group. The first deals with the structural characterization of periodic hybrid inorganic-organic nanostructures, and the identification of the role they play in the synthesis of anisotropic ZnO nanoparticles. In the second project, we are investigating the fundamental photochemical properties of oxynitride nanoparticles.

We discovered that Zn(OAc)2 readily reacts with phosphonic acids (PAs) to produce highly periodic hybrid organic-inorganic nanostructures. The first phase of this project involved extensive characterization by TEM, STEM-EELS, low-angle XRD, FTIR, and solid-state 31P NMR to determine the chemical structure of these materials. These efforts revealed that Zn(OAc)2 reacts with PAs to form insoluble layered Zn-phosphonates. Such materials are known in the literature, but have not been previously synthesized by similar methods. Furthermore, we found that layered Zn-phosphonates can react with 1-undecanol to produce isotropic, soluble ZnO nanocrystals. However, to obtain anisotropic rod-shaped nanocrystals, both the molecular Zn(OAc)2 and the heterogeneous Zn-phosphonate precursors are required. The dimensions of the anisotropic ZnO nanocrystals are relatively insensitive to the length of the aliphatic chain of the PA in the C10-C18 length range.  The presence of an insoluble source of precursor in the reaction mixture presents a contrast to the homogeneous nucleation and growth mechanisms commonly invoked to describe formation of nanocrystals (e.g., CdSe). Since many metals are known to form layered phosphonates, these materials may have a broader application in synthesis of nanoscale materials. This work has been submitted for publication describing both the structural characterization of layered phosphonates and their role in the nanoparticle synthesis.

We are now investigating the fundamental photochemical properties of nanoparticles of a mixed-metal oxynitride (Ga1-xZnx)(N1-xOx). (Ga1-xZnx)(N1-xOx) is a fascinating recently discovered semiconductor because it absorbs visible light, with the absorption onset dependent on the value of x, even though the constituent semiconductors GaN and ZnO absorb in the UV. My group has developed a method to synthesize (Ga1-xZnx)(N1-xOx) nanoparticles with a wide range of x values (0.2 < x < 0.99) and band gaps ranging from 2.7 to 2.2. eV, using ZnO nanoparticles as one of the precursors. In the PRF-supported work, we are investigating how the composition impacts the ability of this material to perform photochemical reactions, such as reduction of methyl viologen, driven by visible light. Photochemical reactivity is a complicated function of valence and conduction band energies, surface chemistry, and other factors. Our goal is to unravel this complexity and elucidate the underlying mechanisms of light-driven reactivity.

In its first 1+ years, this funding from PRF has allowed my research group to follow up on an interesting discovery made in my laboratory (formation of periodic organic-inorganic hybrid structures) and reach interesting conclusions about the chemical structure and reactivity of the material. The funding is also allowing us to investigate the photochemical properties of a new and poorly understood material. Two graduate students have been trained in the course of the work supported by PRF. In a broader context of my career, this funding has helped launch my young research group in new exploratory directions.