Graphitic carbon nitride (g−C3N4) is a metal-free semiconductor of great promise for sustainable photocatalysis,[1] whose performance can be enhanced with defect engineering, typically introducing nitrogen vacancies.[2] To fill this gap, we here present a study employing advanced first-principles simulations[3] to investigate the structural and electronic properties of nitrogen vacancies in monolayer g−C3N4, explicitly accounting for out-of-plane corrugation and supercell-size effects. We show that the correct energetics of nitrogen vacancies can only be captured when long-range buckling of the g−C3N4 sheet is fully described.[4] Our analysis mainly focuses on two non-equivalent nitrogen vacancies, achieved upon removal of a N atom from either the center or the edge of the heptazine unit. Both are found to introduce localized in-gap states associated with shallow acceptor levels and deep donor levels. These are found to be related to the red-shifted absorption and weak photoluminescence observed experimentally for N-deficient g−C3N4 samples. Furthermore, energy-level alignment of the defects states at the water-semiconductor interface provides a rationale for the experimentally reported enhancement of photocatalytic reduction reactions, concomitant with a deterioration of oxidation activity. Overall, our study establishes direct correspondences between defect-induced electronic structure modifications and multiple experimental observables, offering a unified microscopic framework that connects nitrogen-vacancy physics to the photocatalytic and optoelectronic properties of g-C3N4, and provides a transferable, predictive strategy for the rational design and discovery of defect-engineered carbon nitride photocatalysts and related metal-free catalytic materials.[4]
Engineering Light with Defects: Vacancy-Driven Optical and Catalytic Functions in g-C₃N₄
Alessandro Landi
2026
Abstract
Graphitic carbon nitride (g−C3N4) is a metal-free semiconductor of great promise for sustainable photocatalysis,[1] whose performance can be enhanced with defect engineering, typically introducing nitrogen vacancies.[2] To fill this gap, we here present a study employing advanced first-principles simulations[3] to investigate the structural and electronic properties of nitrogen vacancies in monolayer g−C3N4, explicitly accounting for out-of-plane corrugation and supercell-size effects. We show that the correct energetics of nitrogen vacancies can only be captured when long-range buckling of the g−C3N4 sheet is fully described.[4] Our analysis mainly focuses on two non-equivalent nitrogen vacancies, achieved upon removal of a N atom from either the center or the edge of the heptazine unit. Both are found to introduce localized in-gap states associated with shallow acceptor levels and deep donor levels. These are found to be related to the red-shifted absorption and weak photoluminescence observed experimentally for N-deficient g−C3N4 samples. Furthermore, energy-level alignment of the defects states at the water-semiconductor interface provides a rationale for the experimentally reported enhancement of photocatalytic reduction reactions, concomitant with a deterioration of oxidation activity. Overall, our study establishes direct correspondences between defect-induced electronic structure modifications and multiple experimental observables, offering a unified microscopic framework that connects nitrogen-vacancy physics to the photocatalytic and optoelectronic properties of g-C3N4, and provides a transferable, predictive strategy for the rational design and discovery of defect-engineered carbon nitride photocatalysts and related metal-free catalytic materials.[4]I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
