Tungsten oxide quantum dots deposited onto ultrathin CdIn₂S₄ nanosheets for efficient S-scheme photocatalytic CO₂ reduction via cascade charge transfer

A novel S-scheme photocatalytic heterojunction composite nanomaterial is developed by integrating zero-dimensional WO₃ quantum dots (WQDs) on two-dimensional ultrathin CdIn₂S₄ (CIS) nanosheets with the aim of fostering carrier separation, enhancing the performance of carrier interface transport, minimizing carrier distance transport, and achieving effective photocatalytic CO₂ reduction. The composite photocatalyst WQDs/CdIn₂S₄ (WCIS) allows for the efficient photocatalytic reduction of CO₂ to CO and CH₄, as shown by product analysis and isotopic measurement. The photogenerated electrons in WQDs recombine with the holes in CIS nanosheets, and the left electrons in CIS have stronger CO₂ reduction abilities. The highest yields of CO and CH₄ achieved with the WCIS photocatalyst are 8.2 and 1.6 μmol g^-1h⁻¹ ––2.6 and 8 times higher than those for CIS, respectively. Moreover, the S-scheme WCIS possesses a stable crystal structure and recycling ability. Finally, the S-scheme charge transfer path on the WCIS composite is proposed according to theoretical calculation, in-situ irradiated X-ray photoelectron spectroscopy, and electron paramagnetic resonance (ESR) analyses.