Role of n-n Anatase-Rutile Heterojunction in the Photocatalysis of Mixed-Phase Titania

摘要

The electric field distribution in the transition region of the n-n anatase-rutile heterojunction in mixed-phase titania is provided by solving the Poisson equation. The electrons flow from anatase to rutile when rutile contacts closely with anatase, creating an accumulation of negative charges in the rutile region and a positive section in the anatase region in the vicinity of the junction. This sets up an internal electrostatic field directed from the anatase region to the rutile region, creating an energy barrier for the electron transfer from anatase to rutile. Strong electric field exists in the transition region and can exert a very efficient force for photogenerated electron hole pair separation, resulting in greater photocatalytic activity. Once a stable n-n heterojunction has formed between rutile and anatase, under illumination, the photogenerated electrons will migrate from rutile to anatase while the photogenerated holes will migrate from anatase to rutile.