Enhanced photocatalytic carbon dioxide reduction over iron tungstate/covalent organic framework heterojunctions by the induced unified adsorption and reduction sites.

Inorganic-organic S-scheme heterostructure photocatalysts have demonstrated exceptional potential in boosting charge separation for CO2 reduction. However, the reduction typically occurs at the inorganic site, resulting in underutilization of high CO2 adsorption capacity of organic material. To resolve this mismatch, we combined a low conduction band iron tungstate (FeWO4) with a dioxin-linked covalent organic framework (COF) to construct S-scheme heterojunction, where the COF serve as the reduction photocatalysts and FeWO4 act as the oxidation photocatalysts, for photocatalytic CO2 reduction. Density functional theory (DFT) calculations and in-situ spectroscopic analyses confirm that the FeWO4/COF hybrids steer an S-scheme charge transfer pathway driven by an enhanced internal electric field. Benefiting from the synergy between the strong CO2 adsorption at the COF cyano site, which aligns with its role as the reduction site, and the unique S-scheme electron transfer, the composites achieve a significantly higher CO yield (55.9 μmol·g-1·h-1) than COF (5.5 μmol·g-1·h-1) with 100 % selectivity and no sacrificial agents or sensitizers. Isotope tracer experiments verify that the CO was from CO2. In-situ Fourier transform infrared spectroscopy (FT-IR) coupled with two-dimensional correlation spectroscopy (2D-COS) unveils the sequential reduction process of CO2. This study envisions a harmoniously aligned inorganic/organic S-scheme heterojunction for boosting CO2 photoreduction.