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Transferencia de carga desde nanocristales n-dopados: imitación de eventos intermedios en la fotocatálisis de
Junhui Wang1, Tao Ding1, Kaifeng Wu1
1State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM) , Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023 , China.
Journal of the American Chemical Society
|June 10, 2018
Resumen
En la fotocatálisis, los electrones adicionales en los puntos cuánticos crean excitones cargados, lo que dificulta la transferencia de carga y reduce la eficiencia. Este estudio revela cómo los excitones cargados limitan el rendimiento fotocatalítico.
Área de la Ciencia:
- Fotocatálisis
- Química de los puntos cuánticos
- Dinámica de carga
Sus antecedentes:
- Las reacciones fotocatalíticas multielectrónicas implican la transferencia de carga de los cosechadores de luz a los catalizadores.
- Las cargas no excavadas en los recolectores de luz pueden formar excitones cargados, lo que complica la extracción de cargas.
- Los excitones cargados son un cuello de botella potencial para la eficiencia fotocatalítica.
Objetivo del estudio:
- Investigar la dinámica de carga en los excitones cargados dentro de los sistemas fotocatalíticos.
- Cuantificar el impacto de las cargas preexistentes en la separación y transferencia de cargas.
- Comprender las limitaciones de eficiencia en la fotocatálisis multielectrónica.
Principales métodos:
- Dopaje de sulfuro de cadmio (CdS) con puntos cuánticos de nanocristales (QD) con un electrón adicional.
- Medición de la transferencia de agujero de los QD no dopados a los aceptores conectados.
- Comparando los rendimientos de separación de carga y las tasas de transferencia para los excitones neutros frente a los cargados.
Principales resultados:
- La desintegración de los excitones cargados reduce significativamente el rendimiento de separación de carga (68,6%) en comparación con los excitones neutros (98,4%).
- La velocidad de transferencia de agujero es más lenta en presencia de dos electrones (1290 ps) frente a un electrón (776 ps).
- La tasa de recombinación de los estados separados de carga es aproximadamente el doble de rápida para los excitones cargados.
Conclusiones:
- Los excitones cargados, formados por cargas no eliminadas, son un evento intermedio clave que limita la eficiencia fotocatalítica.
- La presencia de electrones en exceso impide la transferencia de carga y acelera la recombinación de carga.
- Esta investigación proporciona información crítica sobre la optimización de los procesos fotocatalíticos mediante la gestión de los estados de excitación.
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