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La difusión del huésped en las redes de interpenetración de micro y mesoporos
Filipe Furtado1, Petrik Galvosas, Maraisa Gonçalves
1Department of Environmental Engineering, UFZ-Helmholtz Centre for Environmental Research, Leipzig, Germany.
Journal of the American Chemical Society
|February 9, 2011
Resumen
La RMN con gradiente de campo pulsado revela que la difusión de moléculas invitadas en poros jerárquicos depende del historial de la muestra. La difusividad es mayor después de la disminución de la presión (desorción) que después del aumento de la presión (adsorción).
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Química Física es la química física.
- Ingeniería Química Ingeniería Química.
Sus antecedentes:
- Los materiales porosos jerárquicos combinan microporos y mesoporos, lo que influye en la difusión de las moléculas invitadas.
- Comprender la difusión en estos sistemas complejos es crucial para las aplicaciones en catálisis, separación y almacenamiento.
- Los estudios anteriores se centraron en sólidos puramente mesoporosos, dejando la difusión en sistemas mixtos menos explorados.
Objetivo del estudio:
- Para investigar las propiedades de difusión de las moléculas invitadas en materiales porosos jerárquicos (carbón activado MA2) bajo presión externa variable.
- Para determinar la influencia de la historia de adsorción-desorción en la difusividad molecular.
- Para comparar el comportamiento de difusión en sistemas mixtos micro/mesoporosos con los puramente mesoporosos.
Principales métodos:
- Utilizando la resonancia magnética nuclear de gradiente de campo pulsado (PFG-NMR) para monitorear la difusión.
- Aplicando variaciones de presión controladas en la atmósfera externa.
- Empleando ciclohexano como la molécula invitada y carbón activado MA2 como el material poroso.
Principales resultados:
- La difusividad del ciclohexano en el carbón activado MA2 está significativamente influenciada por el historial de presión de la muestra.
- Se observaron consistentemente difusividades más altas en la rama de desorción (después de la disminución de la presión) en comparación con la rama de adsorción (después del aumento de la presión) a presiones equivalentes.
- Un modelo simple reprodujo cualitativamente las difusividades observadas y su dependencia de concentración.
Conclusiones:
- El "efecto historia" juega un papel dominante en la determinación de la difusión de moléculas invitadas en materiales porosos jerárquicos.
- PFG-NMR es una herramienta poderosa para elucidar los mecanismos de difusión en arquitecturas complejas de poros.
- Los hallazgos proporcionan información sobre el transporte molecular en carbones activados relevantes para las tecnologías de almacenamiento y separación de gases.
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