Donor–Acceptor Modification of Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

Abstract

charge carriers, such as morphological control, [10][11][12] elemental doping, [13,14] molecular engineering, [15,16] and heterostructure construction. [17][18][19] In particular, molecular engineering is a rather effective method to regulate the chemical composition and electronic structure of CN.Efforts have been devoted to building organic conjugated copolymers with donor-acceptor system to improve the charge mobility in organic photovoltaic field. [20,21] As such, it is supposed that the construction of intramolecular D-A conjugated copolymers could be a helpful strategy to increase the photocatalytic performance of polymeric photocatalysts. Generally, the D-A conjugated copolymers could be synthesized through the copolymerization between electron donor and acceptor units. The introduction of donor or acceptor units could extend π-conjugated system and induce the intramolecular charge transfer of D-A conjugated copolymers under internal electric field, which help to facilitate the dissociation of photogenerated electrons and holes. [22][23][24][25] Moreover, the construction of D-A structure could flexibly regulate the band structure of conjugated copolymers through the pushpull effect on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), [22,26,27] narrowing the bandgap of copolymers toward extended visiblelight absorption. For instance, Fan et al. fabricated a range of aromatics-incorporation g-C 3 N 4 -based D-A copolymer via nucleophilic substitution reactions and proposed the concept of intramolecular charge transfer transition to clarify the photo catalytic mechanism upon long-wavelength-light illumination. [24] Creatinine-derived moiety as donor unit was also incorporated into melem by copolymerization of creatinine and urea to broaden the absorption range and promote the charge spatial separation. [28] Chen et al. integrated π-deficient pyridine group with carbon nitride skeleton to modulate the electron structure, enabling tunable bandgap and boosted carrier migration. [29] Herein, modified CN-based conjugated copolymers with D-A structure were obtained by thermal copolymerization of 2-aminobenzimidazole (abIM) and urea (Figure 1a). [30,31] abIM was chosen as the reactant and serves as electron acceptor unit due to its high electron affinity. As expected, the as-prepared D-A polymeric photocatalysts with adjustable bandgap exhibit larger surface area, stronger visible-light absorption and faster charge carrier separation as compared to pristine CN. The photocatalytic hydrogen evolution rate of the optimal sample is 2566 µmol g −1 h −1 , which is ≈2.7 times that of pristine CN.The construction of conjugated copolymers with a donor-acceptor (D-A) system has emerged as a promising strategy for improving photocatalytic activity. Herein, a donor-acceptor modified carbon nitride (CN) conjugated copolymer is fabricated via facile thermal copolymerization of 2-aminobenzimidazole (abIM) and urea. The experimental results demonstrate that the abIM units are successful...

Facile one‐pot pyrolysis preparation of SnO2/g‐C3N4 composites for improved photocatalytic H2 production

“…The peaks at around 398.4, 399.4, 400.8 and 404.4 eV corresponded to the CNC bond, the N(C) 3 bond, the NH bond and delocalized π electrons, respectively, 26 which confirmed that all three samples contained all the typical groups of g‐C 3 N 4 . It could be clearly observed that the CNC and N(C) 3 peaks of both CN‐1.0SnO 2 and CN‐2.0SnO 2 shifted to higher binding energies compared with those of CN‐0.0SnO 2 , respectively, indicating that the electron densities around the N atom decreased in CN‐1.0SnO 2 and CN‐2.0SnO 2 70 . The two peaks at around 486.8 and 495.3 eV in Fig.…”

“…It could be clearly observed that the C N C and N (C) 3 peaks of both CN-1.0SnO 2 and CN-2.0SnO 2 shifted to higher binding energies compared with those of CN-0.0SnO 2 , respectively, indicating that the electron densities around the N atom decreased in CN-1.0SnO 2 and CN-2.0SnO 2 . 70 The two peaks at around 486.8 and 495.3 eV in Fig. 2(c) corresponded to Sn 3d levels.…”

Construction of a heterojunction with fast charge transport channels for photocatalytic hydrogen evolutionviaa synergistic strategy of Co-doping and crystal plane modulation

“…The PL intensity of Co-C 3 N 4 is significantly reduced, which means that the recombination of photoexcited carriers is effectively suppressed. 54 The formation of heterojunctions promotes a further reduction of the PL intensity for CdS(111)/Co-C 3 N 4 and CdS(002)/Co-C 3 N 4 , indicating that the construction of heterojunctions provides a fast transport path for excited state electrons. 55 TR-PL tests were performed to obtain more detailed information on the decay behavior of photogenerated carriers.…”

Electron-rich pyrimidine rings enabling crystalline carbon nitride for high-efficiency photocatalytic hydrogen evolution coupled with benzyl alcohol selective oxidation

“…42 This observation could be explained by the introduction of electron-rich pyrimidine rings that could induce the internal electric field to accelerate the exciton dissociation by the charge density redistribution over the PCN networks. 43 Moreover, the electron-rich pyrimidine rings would serve as the donor units to improve the charge separation and transfer by rapidly collecting photoexcited holes without recombination through the strong donor–acceptor interaction. 39 To further support the above deduction, the charge transfer property was then systematically investigated by surface photovoltage (SPV), photoluminescence (PL), and electron paramagnetic resonance (EPR) spectra.…”