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Interacción entre facetas y defectos durante la adsorción disociativa y molecular de agua en superficies de óxido
Nabajit Lahiri1, Duo Song1, Xin Zhang1
1Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington99352, United States.
Journal of the American Chemical Society
|January 25, 2023
Resumen
Las vacantes de oxígeno, no sólo el hierro superficial, controlan cómo el agua interactúa con la hematita. Este hallazgo aclara las interfaces óxido-agua y ayuda a diseñar mejores catalizadores.
Área de la Ciencia:
- Ciencias de los materiales
- Química de las superficies
- Nanotecnología
Sus antecedentes:
- Las terminaciones superficiales y los defectos influyen críticamente en las interacciones del agua con los óxidos metálicos.
- Comprender la interacción entre las facetas y los defectos es crucial para predecir las propiedades de la interfaz y la reactividad.
- Los modelos actuales a menudo simplifican demasiado la hidroxilación, vinculándola únicamente a la exposición de cationes superficiales.
Objetivo del estudio:
- Investigar el papel de las vacantes de oxígeno en la hidroxilación superficial de las nanopartículas de hematita (α-Fe2O3).
- Para aclarar la relación entre las facetas superficiales, los defectos y el comportamiento de adsorción / disociación del agua.
- Desafiar las nociones convencionales de control de la hidroxilación superficial.
Principales métodos:
- Se utilizó la espectroscopia de fotoelectrones de rayos X de presión ambiente basada en sincrotrones (AP-XPS) para el monitoreo in situ.
- Se estudió la adsorción de agua y la formación de grupos hidroxilo en facetas de nanopartículas de hematita diseñadas ((001), (012), (104)).
- Cálculos de la teoría funcional de la densidad (DFT) empleados para las energías de formación de vacíos de superficie y oxígeno.
Principales resultados:
- Las vacantes de oxígeno influyen significativamente en la hidroxilación, prevaleciendo sobre la exposición de cationes dependientes de la faceta.
- Las facetas de mayor energía exhiben una mayor propensión a la formación de vacíos de oxígeno.
- La hidroxilación superficial ocurre a una humedad relativa muy baja (5 × 10−5%) debido a las vacantes de oxígeno.
- La eliminación de vacantes restaura los patrones de hidroxilación esperados basados en la densidad de cationes.
Conclusiones:
- Las vacantes de oxígeno son un factor dominante en la hidroxilación superficial de la hematita, especialmente a baja humedad.
- El estudio proporciona información fundamental sobre las interfaces entre óxido metálico y agua reducibles.
- Los hallazgos allanan el camino para el diseño racional de catalizadores avanzados basados en óxidos.
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