Self-Supporting 3D Carbon Nitride with Tunable n → π* Electronic Transition for Enhanced Solar Hydrogen Production

Self-supporting 3D (SSD) carbon nitrides (UCN-X, X = 600-690; where X represents the pyrolytic temperature) consisting of curved layers, with plenty of wrinkles and enlarged size, are synthesized via a facile stepwise pyrolytic strategy. Such unique features of the SSD structure exhibiting dramatically improved charge mobility, extended π-conjugated aromatic system, and partial distortion of heptazine-based skeleton can not only keep the easier activation of the intrinsic π →  π* electronic transition but also awaken the n → π* electronic transition in carbon nitride. The n → π* electronic transition of UCN-X can be controllably tuned through changing the pyrolytic temperature, which can greatly extend the photoresponse range to 600 nm. More importantly, the change regularity of H₂ evolution rates is highly positive, correlated with the change tendency of n → π* electronic transition in UCN-X, suggesting the positive contribution of n → π* electronic transition to enhancing photocatalytic activity. The UCN-670, with optimal structural and optical properties, presents enhanced H₂ evolution rate up to 9230 µmol g^-1 h^-1 (Pt 1.1 wt%). This work realizes the synergistic optimization of optical absorption and exciton dissociation via fabricating an SSD structure. It offers a new strategy for the development of novel carbon nitride materials for efficient photocatalytic reactions.