Session MOB. There are 6 abstracts in this session.

Session: Materials 1, time: 10:45am-11:05am

NMR Studies of Adsorption and Diffusion in New Materials for CO2 Capture

Alexander Forse
University of California, Berkeley, Berkeley, CA
Carbon capture and storage is an important technology that must be rapidly deployed to tackle the global warming crisis. Amine-functionalized metal-organic framework (MOFs) are promising adsorbents that can selectively capture CO2 at point sources, but questions remain regarding the molecular mechanisms of gas adsorption and diffusion in these materials. We have tackled this by developing in situ NMR methods to study gas-dosed adsorbents. The combination of solid-state NMR experiments on gas-dosed samples and density functional theory calculations have revealed a rich chemistry with several different CO2 capture mechanisms elucidated. Finally we show how residual chemical shift anisotropies of pore-confined CO2 can be used to study the extremely anisotropic diffusion of CO2 in MOF materials featuring 1-dimensional pores.

Session: Materials 1, time: 11:05am-11:25am

What can solid-state NMR spectroscopy tell us about mechanochemistry?

Austin Peach1; Christopher O'Keefe1; Sean Holmes1; Jacqueline Gemus1; Cameron Vojvodin1; Cristina Mottillo2; Tomislav Friscic2; Robert W. Schurko1
1University of Windsor, Windsor, Canada; 2McGill University, Montreal, Canada
Mechanochemical synthesis has emerged as an attractive alternative to conventional solvothermal synthesis, due to its adherence to many of the Twelve Principles of Green Chemistry. While much research has been conducted on accessing synthetic pathways not available via conventional solvothermal procedures, comparatively little work has been published on monitoring reaction pathways in mechanochemical reactions. In this lecture, I will demonstrate the value of modern multinuclear solid-state NMR methods for probing mechanochemical reactions, including (i) the use of 111Cd SSNMR for characterization the mechanochemical production of MOFS such as zeolitic imidazolate frameworks (ZIFs), and (ii) the application of 35Cl SSNMR for studying the formation of cocrystals of active pharmaceutical ingredients via stability and competitive milling techniques.

Session: Materials 1, time: 11:25am-11:45am

Maximizing Sensitivity in Bulk Hyperpolarization Experiments by MAS Rate Modulation

Snaedis Björgvinsdóttir; Brennan Walder; Nicolas Matthey; Lyndon Emsley
EPFL, Lausanne, Switzerland
Dynamic nuclear polarization can be used to hyperpolarize the bulk of proton-free solids, resulting in significant signal enhancements in MAS experiments. The method relies on hyperpolarization of nuclei near the surface by impregnation DNP and subsequent relay of polarization towards the bulk through slow spontaneous spin diffusion between weakly magnetic nuclei. Pulse cooling is an efficient variant of this strategy that uses a multiple contact CP sequence for bulk hyperpolarization. We show how to optimize the pulse parameters and delays in these experiments, and how spin rate modulation can be used to maximize sensitivity gains. We also extend the method to compounds with multiple chemical shifts, and show how the spin diffusion pathways can be probed with multidimensional experiments. 

Session: Materials 1, time: 11:45am-12:05pm

Natural Abundance Solid-state 33S NMR Study of NbS3: Applications for Battery Conversion Electrodes

David Halat1, 2; Sylvia Britto1, 3; Kent Griffith1, 4; Clare Grey1
1Dept of Chemistry, University of Cambridge, Cambridge, UK; 2Dept of Chemical and Biomolecular Eng, UC Berkeley, Berkeley, CA; 3Diamond Light Source, Didcot, UK; 4Dept of Mat Sci and Eng, Northwestern University, Evanston, IL
We report ultra-wideline, high-field natural abundance solid-state 33S NMR spectra of the Li‑ion battery conversion electrode NbS3, the first 33S NMR study of a compound containing disulfide (S22) units. The large quadrupolar coupling parameters (CQ ≈ 31 MHz)  are consistent with values obtained from DFT calculations, and evidence the linear Peierls distortion that doubles the number of 33S sites.

Session: Materials 1, time: 12:05pm-12:25pm

Exploring Nanocrystal Interfaces using Magic Angle Spinning Dynamic Nuclear Polarization

Daniel Lee1; Saumya Badoni1; Natalia Olejnik-Fehér1, 2; Małgorzata Wolska-Pietkiewicz3; Danielle Laurencin4; Christian Bonhomme5; Janusz Lewiński2, 3; Gaël De Paëpe1
1CEA / Univ. Grenoble Alpes, Grenoble, France; 2IPC, Polish Academy of Sciences, Warsaw, Poland; 3Chemistry, Warsaw University of Technology, Warsaw, Poland; 4CNRS - Institut Charles Gerhardt, Montpellier, France; 5Sorbonne Universite, Paris, France
The combination of magic angle spinning and high-field dynamic nuclear polarization (MAS-DNP) has revolutionized solid-state NMR spectroscopy for surface science. Here, it will be shown that MAS-DNP is not only extremely pertinent for detecting poorly-receptive calcium-43 in substituted hydroxyapatite nanocrystals (NCs) – a synthetic mimic of bone mineral – but it provides enough NMR sensitivity to be able to record 2D spectra, allowing the distinction of surface and core calcium environments. Moreover, it will be shown that MAS-DNP can be used to help extract unprecedented information concerning ligand arrangements on NC surfaces, notably providing coordination modes and inter-ligand distances. This latter analysis unveils the vast difference between the organic-inorganic interfaces resulting from two synthetic routes to zinc oxide semiconductor NCs.

Session: Materials 1, time: 12:25pm-12:45pm

Probing the Structure and Composition of Nanomaterials with Opimized DNP SENS Sample Preparations and Fast MAS DNP

Michael Hanrahan1, 2; Yunhua Chen1, 2; Rafael Bloome1; Frédéric Perras2; Takeshi Kobayashi2; Nathan Neale3; Javier Vela1, 2; Marek Pruski2; Aaron Rossini1, 2
1Iowa State University, Dept. of Chem., Ames, IA; 2US DOE Ames Laboratory, Ames, IA; 3NREL, Chemistry and Nanoscience Center, Golden, CO
The properties and functionality of nanoparticles (NPs) are controlled and modified by altering their surface structure. Thus, surface characterization is crucial for the rational design of improved NPs. DNP SENS NMR is an attractive method for surface characterization, however established sample preparations for NPs require dilution of the sample. Here we demonstrate improved sample preparation protocols for MAS DNP experiments on NPs. The NPs are deposited onto hexagonal boron nitride (h-BN) from solution or mixed as solids, then impregnated with polarizing agent solution. With this new sample preparation method 10-fold improvements in absolute sensitivity were obtained, enabling challenging 2D NMR experiments to be performed on CdS and Si NPs. These 2D NMR experiments provide detailed insight into the surface structure.