Fabrication of Heterogeneous-Phase Solid-Solution Promoting Band Structure and Charge Separation for Enhancing Photocatalytic CO₂ Reduction: A Case of Zn_XCa_1–XIn₂S₄

Photocatalytic CO2 reduction into solar fuels illustrates huge charm for simultaneously settling energy and environmental issues. The photoreduction ability of a semiconductor is closely correlated to its conduction band (CB) position. A homogeneous-phase solid-solution with the same crystal system always has a monotonously changed CB position, and the high CB level has to be sacrificed to achieve a benign photoabsorption. Herein, we report the fabrication of heterogeneous-phase solid-solution ZnXCa1-XIn2S4 between trigonal ZnIn2S4 and cubic CaIn2S4. The ZnXCa1-XIn2S4 solid solutions with orderly tuned photoresponsive range from 540 to 640 nm present a more negative CB level and highly enhanced charge-separation efficiency. Profiting from these merits, all of these ZnXCa1-XIn2S4 solid solutions exhibit remarkably strengthened photocatalytic CO2 reduction performance under visible light (λ > 420 nm) irradiation. Zn0.4Ca0.6In2S4, bearing the most negative CB position and highest charge-separation efficiency, casts the optimal photocatalytic CH4 and CO evolution rates, which reach 16.7 and 6.8 times higher than that of ZnIn2S4 and 7.2 and 3.9 times higher than that of CaIn2S4, respectively. To verify the crucial role of the heterogeneous-phase solid solution in promoting the band structure and photocatalytic performance, another heterogeneous-phase solid-solution ZnXCd1-XIn2S4 has been synthesized. It also displays an upshifted CB level and promoted charge separation. This work may provide a new perspective into the development of an efficient visible-light driven photocatalyst for CO2 reduction and other photoreduction reactions.