Jan 20, 2016 – NMR Topical Group Meeting

The North Jersey ACS NMR Topical Group proudly presents its January monthly meeting at Princeton University, Frick Chemistry Laboratory Atrium, Wednesday, January 20, 2016. [ register ]

Featured Presentation

Prof. Rob Messinger

Department of Chemical Engineering, The City College of New York

“Measuring and Understanding Local (Dis)order: Crystallization of Zeolite Nanosheets & Defects in Li-ion Battery Electrodes”

Abstract:

Measuring and understanding how order develops in crystallizing materials is a challenging problem, especially during the syntheses of self-assembled materials that exhibit both crystalline and mesoscopic order. Surfactant-directed zeolite MFI nanosheets exhibit improved transport and catalytic properties compared to their bulk zeolite counterparts, particularly with respect to large molecules. During their hydrothermal syntheses, coupled framework crystallization and surfactant self-assembly processes occur that are poorly understood and difficult to control. Local compositions, atomic and mesoscale structures, and surfactant-framework interactions were monitored throughout their syntheses by multi-dimensional solid-state ¹H and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), and electron microscopy measurements. The analyses establish how the atomic and mesoscale framework structures evolve during hydrothermal synthesis, revealing that the zeolite MFI nanosheets form via intermediate nano-layered frameworks with 2D crystal-like structures.

Similarly, identifying and characterizing atomic-scale disorder in crystalline solids can be challenging experimentally, particularly for lithium-ion intercalation electrodes that can exhibit multiple oxidation and spin states. LiVPO₄F is one of the most energy-dense polyanionic electrode materials currently known for lithium-ion batteries, but recent solid-state NMR measurements have revealed unusual extents of local disorder. Highly crystalline LiVPO₄F samples were synthesized, as determined by XRD and scanning transmission electron microscopy (STEM) measurements. Solid-state ⁷Li NMR spectra reveal unexpected paramagnetic lithium environments that can account for up to 20% of the total lithium content. Multi-dimensional and site-selective solid-state ⁷Li-⁷Li dipolar recoupling NMR experiments establish unambiguously that the unexpected lithium environments are defects within the LiVPO₄F crystal structure, further revealing the sub-nanometer-scale proximities between them. The lithium defects are shown to exhibit altered electronic environments that result from changed oxidation states of nearby paramagnetic vanadium atoms. The results provide a general strategy for characterizing sub-nanometer-scale disorder in lithium-containing crystalline solids, including highly paramagnetic materials with short NMR relaxation times on the order of ms.

Program

6:00 pm   Dinner
7:00 pm  Seminar

Meeting Venue

A57, Frick Chemistry Laboratory Atrium, Princeton University [ directions ]

Dinner Cost:

$15 employed / $5 students, postdoc, retired, unemployed.
No charge for seminar only.

Questions:

Frank.Rinaldi@bms.com or Anuji.Abraham@bms.com

Register:

Please register online below or via e-mail to Frank Rinaldi   frank.rinaldi@bms.com    Anuji Abraham Anuji.Abraham@bms.com