Atomic‐ and Molecular‐Level Functionalizations of Polymeric Carbon Nitride for Solar Fuel Production

Abstract

Polymeric carbon nitride (PCN) is a metal‐free semiconductor that has received extensive research attention due to its unique advantages such as low cost, high stability, and visible‐light response. However, pristine PCN is not an ideal photocatalyst because of fast electron–hole recombination and its inert surface for molecular adsorption. Nevertheless, benefiting from the N‐linked tri‐s‐triazine structure, PCN can be readily functionalized through chemical modifications. As such, researchers have made enormous efforts to develop various strategies for modifying PCN to achieve enhanced photocatalytic activities. Herein, recent advances in PCN functionalizations with different atomic or molecular units, including metal and nonmetal elements, small functional groups, organic functional fragments, and metal complex motifs, are summarized. Moreover, the effect of different PCN functionalization strategies on the molecular structure, optical properties, electronic behaviors, and photocatalytic activities particularly for water splitting and CO2 reduction is discussed. In the end, the remaining challenges in the structural modification of PCN and future opportunities of functional PCN‐based photocatalysts for efficient solar fuel production are elaborated on.

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 .…”

Nitrogen-rich porous polymeric carbon nitride with enhanced photocatalytic activity for synergistic removal of organic and heavy metal pollutants

“…These results indicate that the structure of DCCN-S becomes disordered and the crystallinity is reduced, probably due to the formation of defect sites. The structure of the samples was also demonstrated by the solid-state 13 C CPMAS-NMR spectra (Fig. S4 †) and FT-IR spectra (Fig.…”

“…All binding energies were calibrated using the C 1s peak at 284.8 eV as a reference. The solid-state 13 C cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectra were recorded on an Agilent DD2-500 MHz NMR spectrometer at room temperature. The elemental analysis was performed on a UNICUBE/ OXYCUBE elemental analyzer.…”

“…Photocatalysis is a promising technology to remove pollutants owing to its low-cost, environmental friendliness, simple operating conditions and reusability. [11][12][13] Yang et al prepared a white fungus-like mesoporous Bi 2 S 3 /TiO 2 hybrid photocatalyst by a pulsed electrodeposition technique, which showed excellent photocatalytic performance in the synergistic removal of 2,4dichlorophenoxyacetic acid and CrIJVI). 14 Zhao et al prepared a novel flower-like AgI/BiVO 4 heterojunction by a facile in situ deposition method, and it exhibited high photocatalytic activity towards simultaneous removal of tetracycline and CrIJVI).…”

Well-defined surface catalytic sites for solar CO2reduction: heterogenized molecular catalysts and single atom catalysts

“…An inorganic polymeric semiconductor, C 3 N 4 has attracted enormous interest due to its low cost, high thermal and chemical stability, nitrogen-rich structure, and suitable bandgap (2.7 eV). [92][93][94] In CO 2 reduction, C 3 N 4 -based materials have been employed as photocatalysts [95][96][97] or coupled with metalligand complexes [76][77][78][79][98][99][100][101][102][103][104] to achieve enhanced catalysis. For example, Roy and co-workers 76 deposited cobalt phthalocyanine cyanine on mesoporous C 3 N 4 via a weak p-p stacking interaction for visible-light CO 2 reduction.…”