A host–guest self-assembly strategy to enhance π-electron densities in ultrathin porous carbon nitride nanocages toward highly efficient hydrogen evolution

Converting solar energy into renewable clean fuels of hydrogen via photocatalytic water splitting provides the most prospective strategy for tackling the energy and environmental issues. The performance of most photocatalysts is closely related to the intrinsic activity and active edge sites; however, simultaneously regulating them to realize synergic effects remains significant scientific and technological challenge. Here, we report an elaborate design and synthesis of porous carbon nitride nanocages (CN-C) with abundant π-electron densities by a novel host–guest supramolecular self-assembly strategy, overcoming one of the major challenges of traditional copolymeration method, i.e., the required highly matched chemical structure and physical properties of the π-electron-rich monomers to nitrogen-rich monomers. This strategy primarily depends on the cooperation of the host supramolecular precursor growth and the self-regulation of guest supermolecules to compensate the inherent shortage of each component. Interestingly, the structural topology and electron densities of CN-C are found to be easily modulated by only varying the amount of urea. Benefiting from the synergic effects of hierarchically porous structures with enriched active sites and excellent accessibility, increased abundant π-electron densities and improved visible-light absorption, the CN-C nanocages exhibit remarkable photocatalytic hydrogen evolution activity under visible light exposure with H2 generation rate of 1135 μmol h−1g−1, which is 19 times higher than that of pristine CN (59.8 μmol h−1g−1). This powerful strategy provides a profound molecular-level insight into the control of morphology and π-electron densities within carbon-based materials.