Spatial charge separation and high-index facet dependence in polyhedral Cu2O type-II surface heterojunctions for photocatalytic activity enhancement

Abstract

Surface heterojunction engineering has been demonstrated to be an efficient strategy for the spatial charge separation of photocatalysts. As a consequence, the improved photocatalytic activity is highly determined by the atom arrangement and coordination state of a crystallographic plane. A high-index facet exposed with a high density of low-coordination atoms generally displays better catalytic performance than the low-index one because of its high surface energy. Inspired by the above viewpoints, it is proposed that the construction of a surface heterojunction enclosed by different high-index facets or a mixed form of high-index and low-index facets is a promising avenue to further promote the photocatalytic activity. However, the synthesis of high-index facet based photocatalysts is highly challenging for surface heterojunctions. Herein, we prepare a polyhedral 30-faceted Cu₂O microcrystal type-II surface heterojunction co-exposed with 24 high-index {332} facets and 6 low-index {001} facets using a capping agent-assisted liquid-phase reduction method. Compared to the common truncated octahedral (14-facet) Cu₂O microcrystal co-exposed with 8 {111} and 6 {001} facets, the 30-faceted Cu₂O possesses a highly improved photodegradation activity in the case of normalized specific surface area. Density functional theory (DFT) calculations and in situ photodeposition of metal and metal oxide nanoparticle results indicate that the 30-faceted Cu₂O microcrystal is a well-matched {332}–{001} type-II surface heterojunction, which presents a beneficial pathway for efficient charge separation and more high-activity sites for photo-redox reaction than the truncated octahedral surface heterojunction. This work confirms the spatial charge separation and high-index facet dependence in polyhedral Cu₂O surface heterojunctions, which provides theoretical guidance for surface heterojunction engineering to enhance photocatalytic activity.