Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials

Abstract

Surface characterization is crucial for understanding how the atomic-level structure affects the chemical and photophysical properties of semiconducting nanoparticles (NPs). Solid-state nuclear magnetic resonance spectroscopy (NMR) is potentially a powerful technique for the characterization of the surface of NPs, but it is hindered by poor sensitivity. Dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) has previously been demonstrated to enhance the sensitivity of surfaceselective solid-state NMR experiments by one to two orders of magnitude. Established sample preparations for DNP SENS experiments on NPs require the dilution of the NPs on mesoporous silica. Using hexagonal boron nitride (h-BN) to disperse the NPs doubles DNP enhancements and absolute sensitivity as compared to standard protocols with mesoporous silica. Alternatively, precipitating the NPs as powders, mixing them with h-BN, then impregnating the powdered mixture with radical solution leads to further four-fold sensitivity enhancements by increasing the concentration of NPs in the final sample. This modified procedure provides a factor 9 improvement in NMR sensitivity as compared to previously established DNP SENS procedures, enabling challenging homonuclear and heteronuclear 2D NMR experiments on CdS, Si and Cd3P2 NPs. These experiments allow NMR signals from the surface, subsurface and core sites to be observed and assigned. For example, we demonstrate that the acquisition of DNP-enhanced 2D 113Cd113Cd correlation NMR experiments on CdS NPs and natural isotropic abundance 2D 13C29Si HETCOR of functionalized Si NPs. These experiments provide a critical understanding of NP surface structures.

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

“…Therefore, in order to probe the transformations taking place at the SA level, NMR appeared to be the most suitable technique. 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] .…”

“…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] . NMR spectroscopy can therefore meet challenges in nanoscience.…”

Identifying the Molecular Edge Termination of Exfoliated Hexagonal Boron Nitride Nanosheets with Solid-State NMR Spectroscopy and Plane-Wave DFT Calculations

“…Figure S8). 83,103 Eight 1D 11 B spin-diffusion SSNMR spectra were recorded for both h-BN ( Figure 3A) and h-BNNS ( Figure 3B) with varying 11 B spin-diffusion times from 100 µs to 100 ms. Nitrogen has two NMR active nuclei, 14 Therefore, we initially suggest that the two higher frequency 15 N signals correspond to bulk NB3 sites near the edge of the BN sheet (diso ~ -280 ppm and -288 ppm, blue and pink fits, respectively).…”

Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy

“…The particles were further purified by precipitation-redispersion three more times. refocused-INADEQUATE-CPMG, 62,79 heteronuclear J-resolved 81,102 and J-HMQC experiments 83 were performed using previously described pulse sequences. A schematic illustration of all pulse sequences is shown in Figure S6.…”

“…73 DNP NMR experiments were performed on the nanoplatelets and nanospheroids by adding anti-solvent to precipitate and purify the NCs, then physically mixing the precipitated NCs with h-BN, followed by impregnation with a TEKPol 1,1,2,2tetrachloroethane solution. 62 DNP-enhanced 13 C CPMAS NMR spectra were acquired to extract DNP enhancements and identify and confirm the structure of the ligands on the CdSe NCs surfaces (Figure 2C). Comparison of 13 C CPMAS spectra obtained with and without microwave irradiation to drive DNP shows that the 13 13 C solid-state NMR spectra are similar (Figure 2C).…”