Task-Specific Synthesis of 3D Porous Carbon Nitrides from the Cycloaddition Reaction and Sequential Self-Assembly Strategy toward Photocatalytic Hydrogen Evolution

Abstract

Carbon nitride has drawn widespread attention as a low-cost alternative to metal-based materials in the field of photocatalysis. However, the traditionally synthesized carbon nitrides always suffer a bulky architecture, which limits their intrinsic activities. Here, a cycloaddition reaction is proposed to synthesize a triazine-based precursor with implanted sodium and cyano groups, which are mostly retained in the resulting carbon nitride after the following polymerization. Incorporated sodium and cyano defects can not only tune the band structure of the carbon nitride but also provide more additive active sites. The optimized properties enable it an adorable photocatalytic hydrogen evolution rate of 1070 μmol h–1 g–1, varying by almost an order of magnitude from the pristine carbon nitride (79 μmol h–1 g–1). Moreover, a sequential self-assembly strategy has been adopted to further improve its architecture. As a consequence, a three-dimensional (3D) porous carbon nitride microtube cluster is constructed, indicating abundant exposed active sites and the faster separation of charge carriers. The corresponding photocatalytic hydrogen evolution rate is 1681 μmol h–1 g–1, which is very competitive compared with the reported pure carbon nitride photocatalysts. Briefly, this new approach may offer opportunities to fabricate task-specific carbon- and nitrogen-based materials from the molecular level.

Porous Carbon Nitride Thin Strip: Precise Carbon Doping Regulating Delocalized π‐Electron Induces Elevated Photocatalytic Hydrogen Evolution

“…[31,32] For instance, polymerization of melamine and in situ generated cyanuric acid induced a hexagonal cylinder supramolecular self-assembly precursor and subsequently hexagonal tubular C 3 N 4 was obtained after thermal treatment of supramolecular. [33][34][35] Enlightened by this, molecule self-assembly strategy could bring specially shaped micro-nanomaterials. [36,37] 1D length-diameter ratio and quantum confinement effect are conducive to exposure of active sites, mass diffusion, directional charge transport, and inhibition of charge recombination, which endow carbon nitride materials with elevated catalyst efficiency.…”

Overall Regulation of Exciton Dynamics by Defect Engineering in Polymeric Photocatalysts for Hydrogen Evolution

“…Some strategies have been applied to regulate the exciton dynamics; for instance, nanostructuring such as forming nanocrystals or quantum dots enhances the multiple exciton generation because of the quantum confinement effect, , and surface plasmon resonance promotes the exciton generation by near-field enhancement and the exciton dissociation via exciton-plasmon coupling . Among them, engineering defects (four main categories according to the dimensions, e.g., the point, line, planar, and volume) has been considered as an effective, comprehensive, and facile way to enhance the performance of photocatalysts, − such as increasing light absorption by narrowing the band gap, improving charge transfer and separation via temporarily trapping photogenerated electrons and holes, or maneuvering surface reactions through adsorption and activation of reactant molecules. , In addition, the effect of defects on regulating the exciton dynamics is also explored. , On the positive side, a proper amount of defects in photocatalysts can promote exciton dissociation. ,− For example, the formation of ordered–disordered chains in the heptazine-based melon (HM) [which is also called polymeric carbon nitride (CN)], which has suitable band structures with the built-in electric field at the abundant ordered–disordered interfaces, can accelerate the exciton dissociation into free electrons and holes and thus effectively enhance the PC performance . Another study shows that the incorporation of oxygen vacancies in the low-dimensional bismuth oxybromide (BiOBr) can promote exciton dissociation because the oxygen vacancies significantly distort the surrounding localization of band-edge states, leading to the instability of excitons .…”

Heterogeneous Photocatalytic Organic Transformation Reactions Using Conjugated Polymers-Based Materials

“…Zou’s group reported a facile hydrogen-bond-induced supramolecular assembly strategy for fabrication of oxygen-doped porous g-C 3 N 4 . , Experiment and DFT calculation demonstrated that O atom preferentially doped on two-coordinated N position, and the porous network and O-doping synergistically enhanced the light harvesting, charge separation, and wettability. Zhu’s group synthesized a triazine-based precursor with implanted sodium and cyano groups, which were mostly retained in the resulting carbon nitride after the following polymerization . Transport, transfer, and separation efficiency of charge carriers are facilitated by the strong coordination effect between sodium cations and nitrogen pots, established through the ion–dipole interaction.…”

“…Zhu's group synthesized a triazine-based precursor with implanted sodium and cyano groups, which were mostly retained in the resulting carbon nitride after the following polymerization. 59 Transport, transfer, and separation efficiency of charge carriers are facilitated by the strong coordination effect between sodium cations and nitrogen pots, established through the ion−dipole interaction. Meanwhile, Dontsova's group constructed morphology-controlled carbon nitrides by the heat treatment of 3amino-1,2,4-triazole tetramer OATA.…”