2D/2D/0D TiO2/C3N4/Ti3C2 MXene composite S-scheme photocatalyst with enhanced CO2 reduction activity

• TiO 2 /C 3 N 4 forms 2D/2D core–shell van der Waals heterojunction. • 0D Ti 3 C 2 MXene quantum dots deposited on van der Waals heterojunction. • TiO 2 /C 3 N 4 /Ti 3 C 2 composite photocatalyst with enhanced CO 2 reduction activity. • S-scheme charge transfer mechanism observed between TiO 2 and C 3 N 4 . • 0D Ti 3 C 2 quantum dots extract and trap electrons from C 3 N 4 . Herein, two-dimensional (2D) TiO 2 mesoporous nanosheets with three to four C 3 N 4 layers grown in situ are employed to design a core–shell 2D/2D van der Waals heterojunction (TiO 2 /C 3 N 4 ). Edge-terminated zero-dimensional (0D) Ti 3 C 2 MXene quantum dots (TCQD) are subsequently integrated in the C 3 N 4 surface via electrostatic interactions. The constructed 2D/2D/0D TiO 2 /C 3 N 4 /Ti 3 C 2 composite heterojunction photocatalyst exhibits enhanced CO 2 reduction activity compared to TiO 2 , C 3 N 4 , TiO 2 /C 3 N 4 , C 3 N 4 /Ti 3 C 2 for CO and CH 4 production. A step-scheme (S-scheme) charge transfer mechanism operates for the prepared samples during CO 2 reduction, as authenticated by in situ X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis. This study provides a paradigm of a rational structural design for regulating the number and type of heterointerfaces and further insights into the mechanism of multijunction photocatalysts.