Amine-Modified S-Scheme Porous g-C₃N₄/CdSe–Diethylenetriamine Composite with Enhanced Photocatalytic CO₂ Reduction Activity

Photocatalytic CO2 reduction has been known to be one of the most potential technologies for sustaining the development of human society. However, rapid recombination of photoexcited charges in semiconductors often gets in the way of photocatalytic reaction and annoyingly suppresses the photocatalytic performance. Here, amine-modified step-scheme (S-scheme) porous graphite carbon nitride (g-C3N4)/CdSe–diethylenetriamine (A-PCN/CdSe–DETA) was fabricated via a simple one-step microwave hydrothermal method. The presence of amine functional groups allows for the uniform dispersion of CdSe–DETA on PCN by acting as an organic linker to anchor CdSe–DETA onto PCN nanosheets and forming a close-contact interface. The successful formation of the S-scheme heterojunction along with the built-in electric field between PCN and CdSe–DETA was substantiated through X-ray photoelectron spectroscopy analysis, radical trapping test, and the density functional theory calculation. Taken together, the modification by amine and formation of the S-scheme heterojunction resulted in the optimized A-PCN/CdSe–DETA composite exhibiting extraordinary photocatalytic CO2 reduction performance without the use of a sacrificial agent, achieving a CO production rate of 25.87 μmol/(h g) under visible-light irradiation. This work provides insight into the functionalization of S-scheme photocatalysts using amine functional groups, providing enormous opportunities for various applications beyond photocatalysis.