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 Co 3 O 4 /Cs 3 Sb 2 Br 9 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 Co 3 O 4 , while electrons are accumulated on Cs 3 Sb 2 Br 9 , thereby offering abundant active holes and electrons. Moreover, Co 3 O 4 shows stronger adsorption and activation capacity for the C(sp³)-H bond, enabling the C(sp 3 )-H bond dissociation with low reaction energy barrier. Consequently, the holes are directionally extracted from photoactive Cs 3 Sb 2 Br 9 to catalytically active Co 3 O 4 under visible light irradiation, thereby accelerating the toluene oxidation. The optimized 5 % Co 3 O 4 /Cs 3 Sb 2 Br 9 exhibits a benzyl aldehyde (BAD) evolution rate of 5044 μmol g −1 h −1 and a benzyl alcohol (BA) production rate of 1820 μmol g −1 h −1 , which are 12 and 17 times higher than that of blank Cs 3 Sb 2 Br 9 , respectively.
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