In Situ Growth of Amine-Rich g-C ₃ N ₄ with Carbon Defects for Boosting Visible-Light Photocatalytic CO ₂ Reduction Performance

High Resolution Image Download MS PowerPoint Slide Carbon dioxide (CO 2 ) conversion into fuels and valuable chemicals driven by sunlight is a promising method for solving global warming and the shortage of fossil-derived chemicals simultaneously. Two-dimensional graphiticcarbon nitride (g-C 3 N 4 ) has been viewed as a highly favorable material for photocatalytic CO 2 reduction. However, its overall performance is relatively low due to poor charge separation. Engineering the g-C 3 N 4 structure by introduction of a carbon (C) vacancy is an effective strategy to mitigate severe charge recombination, while amine groups (–NH 2 ) could be beneficial for CO 2 capture. Herein, we present a facile method for spontaneous growth of amine-functionalized g-C 3 N 4 with rich C vacancies by adding trace Ni 2+ ions during thermal treatment. Insightful investigation by various advanced characterizations revealed that the carbon defects could induce a microporous structure, resulting in high surface area. In addition, the resultant defects upshift the conduction band of g-C 3 N 4 and promote charge carrier separation. Both of these contribute to enhanced CO 2 reduction ability. Meanwhile, the exposed edge amino enhances the CO 2 adsorption strength, as verified by both experimental and theoretical results. When coupled with the [Co(bpy) 3 ] 2+ molecular cocatalyst, the amine-rich g-C 3 N 4 nanotubes with Ni 2+ ion-induced carbon defects (Cv-CN) exhibit a superior visible-light-induced CO 2 -to-CO conversion rate of 330 μmol g –1 h –1, which is 66-fold and 3-fold higher than those of bulk g-C 3 N 4 (bulk CN, 5 μmol g –1 h –1 ) and g-C 3 N 4 nanotubes (CN, 120 μmol g –1 h –1 ), respectively, in a liquid–gas phase reaction. Density functional theory (DFT) calculations demonstrate that carbon vacancy introduction creates edge amino groups capable of forming strong hydrogen bonds with CO 2 molecules, resulting in a 13-fold enhancement in adsorption energy from −0.01 to −0.13 eV. This work offers a facile and spontaneous strategy for synthesizing high-reactive g-C 3 N 4 for photocatalytic CO 2 reduction.