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.

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

“…Solid state NMR spectroscopy is nowadays a well‐established tool for studying inorganic nanoparticles [42–46] . Whether these latter are metallic, metal oxides or semiconducting, NMR allow to disclose information of prime importance regarding the structural and dynamic characterization of the SAs on their surface as well as the nanoparticles themselves [47–51] . For example, identification of facet‐dependent coordination mode of SAs on nanocrystals, [51] description of the chemical environment of the metallic site at the surface or in the core of the nanoparticles, [43] and the impact of anchored anionic SAs on the chemical stability of nanoparticles have been recently deciphered [49] .…”

Improved Magnetization Transfers among Quadrupolar Nuclei in Two-Dimensional Homonuclear Correlation NMR Experiments Applied to Inorganic Network Structures

“…The recoupling schemes have been exploited for probing proximities among homonuclear 11 B, 23 Na, and 27 Al sites in a multitude of structurally well-ordered, as well as disordered, network-based materials [8,9,38,41,[49][50][51][52][53][54][55][56]. Moreover, they have also been employed in several structural studies of both organic and inorganic systems where spin-1/2 nuclei were used as probes, e.g., 13 C [57-60], 1 H [61,62], and 31 P [63][64][65]. The spatial proximity information offered by MAS NMR that incorporates dipolar recoupling is particularly valuable for structurally disordered systems, such as glasses, for which essentially no other experimental techniques may readily provide detailed structural insight into the sub-nanometer scale.…”

ZnO nanocrystals derived from organometallic approach: Delineating the role of organic ligand shell on physicochemical properties and nano-specific toxicity

“…Most of published toxicological studies concern ZnO nanostructured materials derived from inorganic sol-gel procedures 11,12,17 , which provide ZnO NCs with highly corrugated surface structure and coated with ‘swollen’ organic ligand shell (Fig. 1) 34,35 . This type of superficies is often associated with the instability and permeability of the organic coating towards both chemical 35,36 and biological environment 17 , which induce the higher core accessibility as well as the faster core dissolution.…”

“…1) 34,35 . This type of superficies is often associated with the instability and permeability of the organic coating towards both chemical 35,36 and biological environment 17 , which induce the higher core accessibility as well as the faster core dissolution. Therefore, the lack of high-quality NCs may be identified as one of the limiting factors for development of ZnO NCs-based devices and bio-applications.…”

“…In order to avoid such unfavorable effects associated with ZnO NCs derived from the classical sol-gel synthesis or the aforementioned organometallic approach (e.g. the highly active and unstable surface or permeability of the organic shell), only very recently, we have elaborated a general and convenient o ne-pot s elf- s upporting o rgano m etallic (OSSOM) approach based on the controlled exposition of a [RZn(X)]-type precursor (X = monoanionic organic ligand) to air leading to an exquisite variety of colloidal quantum-sized ZnO crystals coated with an strongly anchored X-type organic ligand shell 35,36,41–45 . In this case, strongly bonded organic ligands provide stability and effective surface passivation to the resulting NCs (Fig.…”