Construction of In‐Plane ZnIn2S4/In(OH)3 Heterojunction with Boosted CO2 Photoreduction Performance by a Three‐Phase Etching‐Hydrolysis Strategy

Abstract In this work, an in‐plane ZnIn 2 S 4 /In(OH) 3 (ZIS/IOH) heterojunction was fabricated with a gas–solid–liquid three‐phase etching‐hydrolysis strategy utilizing single‐unit‐cell ZnIn 2 S 4 nanosheets as the precursor. A portion of ZnIn 2 S 4 , which was dispersed in water, was in situ converted to crystalline and amorphous In(OH) 3 under hydrothermal condition, while the sulfur escaped in the gas phase was captured by Cu foam placed on a free‐standing porous rack above water. This unique approach enabled all In elements to retain in the lattice and prevented the incorporation of Cu impurity into the heterojunction. ZIS/IOH heterojunction exhibited remarkably boosted photocatalytic CO 2 reduction performance. The CO generation rate and selectivity reached 1807 µmol g −1 h −1 and 82%, respectively, significantly surpassing those of pure ZnIn 2 S 4 (842 µmol g −1 h −1 and 65%). The resulting heterojunction inherited ultrathin nanosheet morphology coupled with a chemically bonded interface. Moreover, In(OH) 3 functions as both electron‐accepting platform and reactant adsorption sites, greatly enhancing charge separation efficiency as well as the reaction between CO 2 and H 2 O. The synergy of improved charge separation and increased active sites lead to the remarkably boosted photocatalytic CO 2 reduction performance. This work provides a new strategy for the fabrication of 2D in‐plane heterojunctions for photocatalytic applications.