Rational fabrication of cadmium-sulfide/graphitic-carbon-nitride/hematite photocatalyst with type II and Z-scheme tandem heterojunctions to promote photocatalytic carbon dioxide reduction

Artificial photosynthesis has become one of the most attractive strategies for lowering atmospheric carbon dioxide (CO2) level and achieving the carbon balance; whereas, the fast electron-hole recombination and sluggish charge transfer in photocatalysts are themain stumbling blocks to the applications. Constructing semiconductor nano-heterostructures provides a promising strategy to accelerate the separation and transfer of photoinduced charge carriers for promoting the multielectron CO2 reduction reaction. Herein, a CdS/g-C3N4/α-Fe2O3 three-component photocatalyst consisting of type II and Z-scheme tandem heterojunctions is skillfully fabricated via the solvothermal synthesis followed with photoinduced deposition. The CdS/g-C3N4/α-Fe2O3 tandem-heterojunction photocatalyst exhibits superior performance toward the conversion of CO2 to fuels (CO and CH4), compared with the single- and binary-component systems, owing to the favorable energy-level alignment, accelerated charge separation, facilitated water dissociation and sufficient reactive-hydrogen provision. The total consumed electron number of CdS/g-C3N4/α-Fe2O3 catalyst for CO2 reduction is about 10.5 times that of pure g-C3N4. The photocatalytic mechanism is elucidated according to detailed characterizations and in-situ spectroscopy analyses. This work sheds light on the rational construction of heterojunction photocatalysts to promote the conversion of CO2 to solar fuels, without using any sacrifice reagent or noble-metal cocatalysts.