Oral Presentation 23rd International Society of Magnetic Resonance Conference 2023

DNP-SENS of Metal Oxides and Sulfides by D-RINEPT sequences (#119)

Hiroki Nagashima 1 , Julien Trebosc 2 , Olivier Lafon 3 , Jean-Paul Amoureux 3 4
  1. National Institute of Advanced Industrial Science And Technology, Tsukuba, IBARAKI, Japan
  2. IMEC, University of Lille, CNRS, Lille, France
  3. UCCS, University of Lille, CNRS, Lille, France
  4. Bruker Biospin, Wissembourg

Dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP-SENS) is a powerful technique to analyze the atomic-level structure of the surface of inorganic nanomaterials. Nevertheless, these materials often contain quadrupolar nuclei, such as 17O, 27Al, 33S, 43Ca, 49Ti, 67Zn, etc. Recently, we have shown that through-space INEPT (D-RINEPT) using symmetry-based dipolar recoupling built from adiabatic pulses can efficiently transfer polarization from protons to quadrupolar nuclei, including those with low gyromagnetic ratio, such as 49Ti, 95Mo and 67Zn [1].

Here, we report recent development and applications of this NMR experiment to characterize nanomaterials. We notably observed 33S and 67Zn near the surface of ZnS nanoplatelets, which are promising quantum dots [2]. This study represents the first experimental demonstration of DNP-enhanced 33S NMR experiments. The DNP-enhanced broad 33S spectra were acquired in a piecewise manner using variable offset cumulative spectroscopy (VOCS) approach. DNP data were combined with ultra-high field NMR experiment and DFT calculation to understand the structure of ZnS nanoplatelets.

The DNP-enhanced D-RINEPT experiment was also applied to detect the NMR signals of enable 43Ca nuclei of calcium silicate hydrate (C-S-H) which is a primary constituent of cements. Furthermore, this polarization transfer was combined with homonuclear dipolar decoupling to acquire 2D 1H-43Ca heteronuclear correlation spectra, which allows the identification of Ca sites corresponding to Ca-O layers and Ca2+ ion.

We also improved the resolution of DNP-SENS NMR spectra of half-integer spin quadrupolar nuclei by combining D-RINEPT and MQMAS sequences. To maximize the efficiency, we developed D-RINEPT-split-t1-MQMAS-QCPMG sequence with FAMN or Coslp [3] excitation and reconversion pulses and limited number of phase cycle step. This novel technique has been applied to identify 27Al, 17O and 11B sites near the surface of γ-alumina, ZnO nanocrystals, (ZnO-ZrO2)/SiO2 catalysts and BN/SiO2 catalysts.

 H.N. acknowledges JSPS Grant-in-Aid for Early-Career Scientists (JP20K15319) and JST, PRESTO Grant Number JPMJPR2276. 

 

64394ece49470-%E7%94%BB%E5%83%8F1.jpg

  1. [1] H. Nagashima, J Trébosc, Y Kon, K Sato, O Lafon, and J-P Amoureux J. Am. Chem. Soc., 2020, 142, 10659–10672.
  2. [2] E. Bellan et al submitted.
  3. [3] I. Hung, Z. Gan, J. Magn. Reson. 2021, 328, 106994.