Theoretical Study on Photocatalytic Reduction of CO 2 on Anatase/Rutile Mixed-Phase TiO 2 .

The construction of anatase/rutile heterojunctions in TiO 2 is an effective way of improving the CO 2 photoreduction activity. Yet, the origin of the superior photocatalytic performance is still unclear. To solve this issue, the band edges between anatase and rutile phases were theoretically determined based on the three-phase atomic model of (112) A /II/(101) R , and simultaneously the CO 2 reduction processes were meticulously investigated. Our calculations show that photogenerated holes can move readily from anatase to rutile via the thin intermediated II phase, while photoelectrons flowing in the opposite direction may be impeded due to the electron trapping sites at the II phase. However, the large potential drop across the anatase/rutile interface and the strong built-in electric field can provide an effective driving force for photoelectrons' migration to anatase. In addition, the II phase can better enhance the solar light utilization of (112) A /(100) II , including a wide light response range and an intensive optical absorption coefficient. Meanwhile, the mixed-phase TiO 2 possesses negligible hydrogenation energy (CO 2 to COOH*) and lower rate-limiting energy (HCOOH* to HCO*), which greatly facilitate CH 3 OH generation. The efficient charge separation, strengthened light absorption, and facile CO 2 reduction successfully demonstrate that the anatase/rutile mixed-phase TiO 2 is an efficient photocatalyst utilized for CO 2 conversion.