Edge effect-modulated exciton dissociation and charge transfer in porous ultrathin tubular graphitic carbon nitride for boosting photoredox activity

Abstract

Metal-free graphitic carbon nitride (CN) is one of the promising semiconductor candidates for photocatalytic application, but mostly only shows moderate activity, owing to the fast recombination of photoinduced electron–hole pairs due to the huge Coulomb interaction between them. The targeted relaxation of photoinduced excitons into free charge carriers is an effective strategy to enhance photocatalytic activity but still very challenging. Here, by using CN as a model, we propose that the grafting of tunable L-cysteine units in porous ultrathin tubular CN (TCN-Lc) can effectively relax photoinduced excitons into electrons and holes and then accelerate charge transfer from CN to active sites for an improved photocatalytic reaction (denoted as the edge effect), and the porous ultrathin tubular structure in CN also enlarges the specific surface area and enhances visible-light absorption ability to thus improve photocatalytic activity. The optimized TCN-Lc10 shows impressive photocatalytic performance for degrading various contaminants such as colored dye and antibiotics and for H₂ evolution (6468 μmol h⁻¹ g⁻¹) with an apparent quantum yield of up to 13.4% at 420 nm under visible light irradiation. The density functional theory (DFT) calculations also reveal that the edge effect via grafting of tunable cysteine units on the CN surface can disrupt the intrinsic electronic state distribution to form energy disordered interfaces and facilitate directional transfer of electrons to the surface. This study offers a new insight to regulate exciton dissociation and charge transfer in semiconductor photocatalysts for contaminant degradation and energy conversion.