Molecular diffusion and DNP enhancement in aqueous char suspensions

Area of Science:

• Physical Chemistry
• Materials Science
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Dynamic Nuclear Polarization (DNP) is a technique to enhance NMR signals.
• Carbon chars possess complex porous structures influencing molecular behavior.
• Understanding water mobility in porous media is crucial for various applications.

Purpose of the Study:

• To investigate the heterogeneous 1H dynamic nuclear polarization (DNP) effect in aqueous carbon char suspensions at low magnetic fields.
• To correlate water mobility within the porous structure with DNP enhancement.
• To explore the role of 'cage effects' and short-range interactions on DNP in porous media.

Main Methods:

• Fourier Transform pulsed-field-gradient spin-echo NMR spectroscopy to measure self-diffusion coefficients.
• Proton spin-lattice relaxation measurements.
• Application of the Torrey model to analyze diffusion in porous media.

Main Results:

• Observed multiple self-diffusion coefficients in aqueous char suspensions, indicating varying water mobility.
• Proton spin-lattice relaxation data corroborated the molecular diffusion measurements.
• The Torrey model analysis highlighted the impact of 'cage effects' on DNP in porous environments.

Conclusions:

• Short-range nuclear-electronic interactions within the pores of carbon chars play a dominant role in DNP enhancement.
• The heterogeneous nature of the porous structure significantly affects water diffusion and DNP.
• This research provides insights into DNP mechanisms in complex porous materials.