Efficient hole extraction to reactive oxidation sites over a Co3O4/Cs3Sb2Br9 p-n heterojunction for enhanced benzylic C(sp3)-H bond oxidation

Photocatalytic selective oxidation of aromatic hydrocarbons plays an important role in the production of value-added chemicals. A key step in this process is the activation of C(sp(3))-H bond by photogenerated holes. However, the inadequate hole generation and lack of surface adsorption-activation sites severely hinders the improvement in photocatalytic C-H bond oxidation. In particular, the random charge migration to the surface impedes the effective capture of holes by surface active sites to dissociate the C(sp(3))-H bond. Here, we design and fabricate a Co3O4/Cs3Sb2Br9 p-n heterojunction that effectively addresses these challenges. The p-n heterojunction forms strong built-in electric fields (BEF) facilitating spatial charge separation. Holes are accumulated on Co3O4, while electrons are accumulated on Cs3Sb2Br9, thereby offering abundant active holes and electrons. Moreover, Co3O4 shows stronger adsorption and activation capacity for the C(sp(3))-H bond, enabling the C(sp(3))-H bond dissociation with low reaction energy barrier. Consequently, the holes are directionally extracted from photoactive Cs3Sb2Br9 to catalytically active Co3O4 under visible light irradiation, thereby accelerating the toluene oxidation. The optimized 5 % Co3O4/Cs3Sb2Br9 exhibits a benzyl aldehyde (BAD) evolution rate of 5044 mu mol g(-1) h(-1) and a benzyl alcohol (BA) production rate of 1820 mu mol g(-1) h(-1), which are 12 and 17 times higher than that of blank Cs3Sb2Br9, respectively.