Construction of in‐plane ZnIn2S4/In(OH)3 heterojunction with boosted CO2 photoreduction performance by a three‐phase etching‐hydrolysis strategy

ZnIn2S4 with nanosheet structure shows great potential as photocatalyst for CO2 reduction, however, its photocatalytic performance is still restricted by the low charge separation efficiency and insufficient active sites. In this work, an in‐plane ZnIn2S4/In(OH)3 heterojunction was fabricated with a gas‐solid‐liquid three‐phase etching‐hydrolysis strategy utilizing single‐unit‐cell ZnIn2S4 nanosheets as the precursor. A portion of ZnIn2S4, 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. The CO generation rate and selectivity reached 1807 μmol g−1 h−1 and 82%, respectively, significantly surpassing those of pure ZnIn2S4 (842 μmol g−1 h−1 and 65%). 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 CO2 and H2O. The synergy of improved charge separation and increased active sites lead to the remarkably boosted photocatalytic CO2 reduction performance. This work provides a new strategy for the fabrication of 2D in‐plane heterojunctions for photocatalytic applications.