Interfacial charge transfer in 0D/2D defect-rich heterostructures for efficient solar-driven CO2 reduction

Two-dimensional graphitic carbon nitride (g-C 3 N 4 ) has been widely explored as a promising photocatalyst for solar CO 2 conversion. However, rapid charge recombination and low visible-light utilization are severely detrimental to photocatalytic CO 2 conversion. Zero-dimensional/two-dimensional (0D/2D) heterostructures are considered the promising materials with size tunability and enhanced charge separation efficiency for photocatalysis. Herein, a 0D/2D heterostructure of oxygen vacancy-rich TiO 2 quantum dots confined in g-C 3 N 4 nanosheets (TiO 2- x /g-C 3 N 4 ) was prepared by in-situ pyrolysis of NH 2 -MIL-125 (Ti) and melamine. Charge dynamics analysis by time-resolved photoluminescence (tr-PL) and femtosecond and nanosecond pump-probed transient absorption (TA) spectra revealed that charges transfer occured from 2D-g-C 3 N 4 to 0D-TiO 2 at an ultrafast subpicosecond time scale (<1 ps) through the intimate interface. The overall fast decay of the charge carriers was attributed to interfacial charge transfer, which was accompanied by recombination relaxation mediated by shallow trapped sites. Ultrafast interfacial charge transfer greatly promoted charge separation and electrons in shallow trapped sites were easily trapped by CO 2 . In addition, combining with the synergetic advantage of strong visible light absorption, high CO 2 adsorption and large surface area, TiO 2- x /g-C 3 N 4 exhibited a superior CO evolution rate of 77.8 μmol g −1 h −1 , roughly 5 times that of pristine g-C 3 N 4 (15.1 μmol g −1 h −1 ). This work provides in-depth insights into optimizing the heterojunction for robust solar CO 2 conversion.