Disclosing Interfaces of ZnO Nanocrystals Using Dynamic Nuclear Polarization: Sol‐Gel versus Organometallic Approach

Abstract

The unambiguous characterization of the coordination chemistry of nanocrystal surfaces produced by wet‐chemical synthesis presently remains highly challenging. Here, zinc oxide nanocrystals (ZnO NCs) coated by monoanionic diphenyl phosphate (DPP) ligands were derived by a sol‐gel process and a one‐pot self‐supporting organometallic (OSSOM) procedure. Atomic‐scale characterization through dynamic nuclear polarization (DNP‐)enhanced solid‐state NMR (ssNMR) spectroscopy has notably enabled resolving their vastly different surface‐ligand interfaces. For the OSSOM‐derived NCs, DPP moieties form stable and strongly‐anchored μ2‐ and μ3‐bridging‐ligand pairs that are resistant to competitive ligand exchange. The sol‐gel‐derived NCs contain a wide variety of coordination modes of DPP ligands and a ligand exchange process takes place between DPP and glycerol molecules. This highlights the power of DNP‐enhanced ssNMR for detailed NC surface analysis and of the OSSOM approach for the preparation of ZnO NCs.

Unveiling the Surface Structure of ZnO Nanorods and H2 Activation Mechanisms with 17O NMR Spectroscopy

“…This work demonstrates an 17 O NMR-based general approach for unraveling surface reaction mechanisms on oxide nanomaterials in detail, especially for following the fate of surface oxygen species, and thus the catalyst at the atomic scale. In addition, recent signal enhancement techniques such as dynamic nuclear polarization can be conveniently combined in order to further increase the sensitivity of the method (e.g., studying micron-sized oxides, which are often the case for many industrial catalysts). − Such results should be able to assist the rational design of catalytic oxides with improved performances.…”

Evidence of Graphene-like ZnO Nanostructures via Zinc Dimethoxide Hydrolysis–Condensation Under Ambient Conditions on a Au(111) Surface Using SERS: Simulation and Experiment

“…A large variety of zinc oxide (ZnO) nanostructures, mainly in the Wurtzite polymorph, has been reported to exhibit excellent electrical, optical, and electrochemical properties in a wide range of applications. − However, recent experimental and theoretical studies have been focused on the study of atomic-scale layered ZnO nanostructures with graphene-like structures, usually abbreviated as g-ZnO. − The most common synthetic route toward g-ZnO is based on a chemical vapor deposition (CVD) process under ultrahigh vacuum conditions not only over Cu(111), Pd(111), Ag(111), − Pt(111), and Au(111) − but also over defectuous and nondefectuous graphene. − Moreover, the preparation of layered zinc oxide using zinc nitrate as a precursor in hydrothermal conditions, as well as the preparation of layered zinc hydroxide materials by the hydrolysis of diethyl zinc and zinc carboxylate at room temperature has also been explored recently. , The study of organozinc compounds such as dialkyl zinc or alkyl zinc alkoxides and their corresponding transformation toward zinc oxo–hydroxide clusters and nanostructures have been extensively studied. − More recently, Terlecki et al has shown that various reactions involving hydrolysis of organozinc precursors can provide completely different ZnO- or even Zn­(OH) 2 -based nanostructures . However, although zinc dialkoxides exhibit easier handling in air moisture conditions compared to dialkyl zinc or alkyl zinc alkoxides, only a few reports on the hydrolysis and condensation of zinc dialkoxides are reported in the literature. , We have recently reported, both theoretically and experimentally, that the formation of small hydroxyl-terminated (ZnO) n planar clusters with n < 6 is possible via the hydrolysis–condensation of zinc dimethoxide. , However, regardless of the preparation methodology, characterizing these g-ZnO structures has so far been a hard task.…”

In Situ Preparation of Amphibious ZnO Quantum Dots with Blue Fluorescence Based on Hyperbranched Polymers and their Application in Bio-Imaging

“…They are of great interest in various applications, such as optoelectronics [8,9], biophotonics [10][11][12][13][14][15], and nanomedicine [14][15][16]. Among these QDs, cadmium series QDs (such as CdSe [17], CdSe/CdS [18]) and zinc series QDs (such as ZnSe [19], ZnO [20][21][22]) often have excellent fluorescence. However, cadmium series QDs are actually toxic under certain conditions and free Cd 2+ ions can be liberated from QDs, resulting in the cytotoxicity of QDs [23].…”