Excited State Dynamics in Dual-Defects Modified Graphitic Carbon Nitride

Significant efforts are focused on defect-engineering of metal-free graphitic carbon nitride (g-C3N4) to amplify its efficacy. A conceptually new multidefect-modified g-C3N4 having simultaneously two or more defects has attracted strong attention for its enhanced photocatalytic properties. We model and compare the excited state dynamics in g-C3N4 with (i) nitrogen defects (N vacancy and CN group) and (ii) dual defects (N vacancy, CN group, and O doping) and show that the nonradiative recombination of charge carriers in these systems follows the Shockley-Read-Hall mechanism. The nitrogen defects create three midgap states that trap charges and act as recombination centers. The dual-defect modified systems exhibit superior properties compared with pristine g-C3N4 because the defects facilitate rapid charge separation and extend the spectrum of absorbed light. The system doped with O shows better performance due to enhanced carrier lifetime and higher oxidation potential caused by a downshifted valence band. The study provides guidance for rational design of stable and efficient photocatalytic materials.