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Elucidación de la estructura eléctrica de doble capa dependiente del pH en la interfaz silicio/agua utilizando

Feng Wei¹, Shu-Hei Urashima¹, Satoshi Nihonyanagi^1,2

¹Molecular Spectroscopy Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.

Journal of the American Chemical Society

|April 17, 2023

Resumen

Los investigadores estudiaron la interfaz entre sílice y agua utilizando espectroscopia vibratoria. Analizaron la estructura eléctrica de doble capa, revelando especies de agua distintas en las capas difusas y compactas, cruciales para comprender las interfaces cargadas.

Área de la Ciencia:

Química de las superficies
Química Física
Ciencia de la interfaz

Sus antecedentes:

La interfaz sílice/agua es una interfaz cargada ubicua en la naturaleza.
Comprender la estructura del agua en esta interfaz es fundamental para los procesos ambientales y químicos.
Los estudios anteriores carecían de información detallada a nivel molecular sobre la capa doble eléctrica.

Objetivo del estudio:

Para elucidar la estructura del agua en la interfaz sílice/agua a través de un amplio rango de pH (2.0-12.0).
Analizar cuantitativamente las contribuciones de la capa difusa (DL) y de la capa de popa (SL) al agua interfacial.
Para determinar la densidad de carga superficial y el pKa de la interfaz sílice/agua.

Principales métodos:

Se empleó la espectroscopia de generación de frecuencia de suma vibratoria (SFG) detectada por heterodino.
Se midieron espectros de vibración selectivos de la interfaz (χ) en la región de estiramiento de OH.
Se utilizó el análisis de descomposición de valor singular (SVD) para separar los componentes espectrales DL y SL.

Principales resultados:

La parte imaginaria de los espectros SFG (Imχ2) se descompuso con éxito en contribuciones DL y SL.
La teoría modificada de Gouy-Chapman explicó la dependencia de la concentración de sal de los espectros DL.
Se determinó un pKa de 4,8 ± 0,2 para la interfaz sílice/agua.
Se identificaron y caracterizaron tres especies acuáticas distintas en el SL en función de los cambios espectrales dependientes del pH.

Conclusiones:

Este estudio proporciona una comprensión cuantitativa a nivel molecular de la capa doble eléctrica en la interfaz sílice/agua.
Los distintos componentes espectrales revelan estructuras de agua características tanto en las capas difusas como compactas.
Los hallazgos son esenciales para predecir y controlar los fenómenos interfaciales en diversos sistemas naturales y de ingeniería.

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