Solid-state NMR studies of 1H spin diffusion in adsorbed organic molecules

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Surface Science
• Materials Chemistry

Background:

• Understanding molecular dynamics on porous materials is crucial for catalysis and adsorption.
• Proton (1H) spin diffusion is a key NMR technique for probing molecular motion and interactions.
• Previous studies have explored spin diffusion in adsorbed systems, but detailed analysis of multiple diffusion pathways is ongoing.

Purpose of the Study:

• To investigate the 1H spin diffusion times of toluene (MB) and tetrahydrofuran (THF) adsorbed on various porous solids.
• To differentiate between intermolecular and intramolecular spin diffusion mechanisms.
• To elucidate the role of surface interactions, such as hydrogen bonding, in influencing spin diffusion.

Main Methods:

• Selective inversion recovery technique in 1H NMR spectroscopy.
• Measurement of spin diffusion times across a range of milliseconds to hundreds of milliseconds.
• Analysis of magnetization recovery curves to identify tri-exponential decay behavior.

Main Results:

• Observed tri-exponential magnetization recovery, indicating multiple relaxation and diffusion processes.
• Identified two distinct spin diffusion processes: intermolecular (adsorbent-adsorbate) and intramolecular (within adsorbate).
• Demonstrated more effective intermolecular spin diffusion for THF compared to MB due to hydrogen bonding with surface hydroxyl groups.

Conclusions:

• 1H spin diffusion is influenced by both molecular structure and surface interactions.
• Hydrogen bonding plays a significant role in enhancing intermolecular spin diffusion for adsorbates like THF.
• The findings provide insights into the dynamics of molecules adsorbed on porous materials, relevant for surface chemistry and materials science.